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. 2024 Nov 7;21(11):e1004478. doi: 10.1371/journal.pmed.1004478

The association of bearing surface materials with the risk of revision following primary total hip replacement: A cohort analysis of 1,026,481 hip replacements from the National Joint Registry

Michael R Whitehouse 1,2,#, Rita Patel 1,#, Jonathan M R French 1, Andrew D Beswick 1,2, Patricia Navvuga 1, Elsa M R Marques 1, Ashley W Blom 1,2,3,‡, Erik Lenguerrand 1,2,¤,‡,*
Editor: Elisa Troiano4
PMCID: PMC11542800  PMID: 39509352

Abstract

Background

The risk of re-operation, otherwise known as revision, following primary hip replacement depends in part on the prosthesis implant materials used. Current performance evidences are based on a broad categorisation grouping together different materials with potentially varying revision risks.

We investigated the revision rate of primary total hip replacement (THR) reported in the National Joint Registry by specific types of bearing surfaces used.

Methods and findings

We analysed THR procedures across all orthopaedic units in England and Wales. All patients who received a primary THR between 2003 and 2019 in the public and private sectors were included. We investigated the all-cause and indication-specific risks of revision using flexible parametric survival analyses to estimate adjusted hazard ratios (HRs). We identified primary THRs with heads and monobloc cups or modular acetabular component THRs with head and shell/liner combinations.

A total of 1,026,481 primary THRs were analysed (Monobloc: n = 378,979 and Modular: n = 647,502) with 20,869 (2%) of these primary THRs subsequently undergoing a revision episode (Monobloc: n = 7,381 and Modular: n = 13,488).

For monobloc implants, compared to implants with a cobalt chrome head and highly crosslinked polyethylene (HCLPE) cup, the all-cause risk of revision for monobloc acetabular implant was higher for patients with cobalt chrome (hazard rate at 10 years after surgery: 1.28 95% confidence intervals [1.10, 1.48]) or stainless steel head (1.18 [1.02, 1.36]) and non-HCLPE cup. The risk of revision was lower for patients with a delta ceramic head and HCLPE cup implant, at any postoperative period (1.18 [1.02, 1.36]).

For modular implants, compared to patients with a cobalt chrome head and HCLPE liner primary THR, the all-cause risk of revision for modular acetabular implant varied non-constantly. THRs with a delta ceramic (0.79 [0.73, 0.85]) or oxidised zirconium (0.65 [0.55, 0.77]) head and HCLPE liner had a lower risk of revision throughout the entire postoperative period.

Similar results were found when investigating the indication-specific risks of revision for both the monobloc and modular acetabular implants.

While this large, nonselective analysis is the first to adjust for numerous characteristics collected in the registry, residual confounding cannot be rule out.

Conclusions

Prosthesis revision is influenced by the prosthesis materials used in the primary procedure with the lowest risk for implants with delta ceramic or oxidised zirconium head and an HCLPE liner/cup. Further work is required to determine the association of implant bearing materials with the risk of rehospitalisation, re-operation other than revision, mortality, and the cost-effectiveness of these materials.

Erik Lenguerrand and colleagues analyse data from the UK’s National Joint Registry to assess the risk of revision (i.e. re-operation following primary procedure) in patients who have under a total hip replacement according to the materials used in the joint.

Author summary

Why was this study done?

  • The classifications used to categorise hip implants in national registries are typically broad and may not allow interested parties to fully understand the risk of postoperative revision (i.e., need for further surgery) associated with different types of implant materials.

  • This research aimed to report the risk of revision by the detailed implant materials used to help the surgical community, and therefore patients, identify those with the lowest risk of further surgery or revision which will improve shared decision-making prior to surgery.

What did the researchers do and find?

  • This research analysed 1,026,481 primary total hip replacements (THRs) performed in England and Wales with information up to 15 years after these initial hip replacement operations.

  • Hip prostheses with a delta ceramic or oxidised zirconium head and highly crosslinked polyethylene liner or cup had the lowest risk of revision throughout the 15 years following surgery.

  • These findings were also found when investigating the specific reasons for revision hip replacements being performed.

What do these findings mean?

  • These results, from one of the largest registries in the world covering all public and private health care structures in England and Wales will help hospitals, surgeons and therefore patients to choose hip implants and combinations of them that can be used with the lowest risk of revision.

  • These results are not from a randomised controlled trial and therefore it is impossible to control for all factors that can influence the risk of revision.

Introduction

Total hip replacement (THR) is widely used to treat diseased and damaged joints with over 100,000 performed annually in the United Kingdom [1,2]. Although 58% to 78% of THRs last more than 25 years [3], many still fail resulting in 5,073 revisions annually in the UK in 2021 [1,4]. People experience worse pain and function after revision compared with primary THRs and often require further revision [5,6]. Each revised THR lasts about half as long as its predecessor [7]. The most common reasons for revision are aseptic loosening, dislocation, periprosthetic fracture, infection, adverse soft tissue reaction to wear debris and pain [1]. These causes are not mutually exclusive and in many cases are inextricably linked. For example: wear particles activate macrophages that have been implicated in initiating loosening; wear of the prostheses can lead to instability; and particulate debris from wear damages tissues and results in an environment prone to infection [8,9].

The role of fixation [10], instability [11], and infection [12], in implant longevity have been extensively studied from an epidemiological view point. Even though the tribological mechanisms of wear are well understood [13], large scale, representative epidemiological studies conducted across multiple settings, or whole health care system assessing the association between different bearing surfaces and failure remain sparse [14].

The materials used in the bearing surfaces are typically described by the material that makes up the articulating surface of the femoral head followed by the material that makes up the articulating surface of the cup or liner of the acetabular shell.

Studies usually use broad grouping (metal-on-polyethylene, ceramic-on-polyethylene, ceramic-on-ceramic, metal-on-metal, ceramic-on-metal) when comparing bearing materials despite these groupings consisting of aggregations of different materials. For example, metal heads are commonly either stainless steel or cobalt chrome, polyethylene has evolved over time with highly crosslinked polyethylene (HCLPE) now in widespread use and there are different types of ceramic such as alumina and delta ceramics. Some national joint replacement registries report good performance for hip implants with ceramic acetabular component [15–19] but these results are unadjusted and not underpinned by formal statistical tests. Reporting from one registry, adjusting for year of primary surgery, patient age, sex, and surgical year, have not shown statistical different results for hip implants with ceramic cup [20].

No study, using nationally representative data, has yet provided in depth evidence on the performance of each specific hip bearing surface materials, underpinned by adjusted modelling and throughout the whole post-primary operation period. It is therefore still unclear which of the materials implanted in routine orthopaedic care are the most effective options; hence, the wide variety of practice and changing patterns of practice observed.

To obtain representative evidence on the risk of revision associated with the specific type of bearing surfaces used for primary THR, we investigated the revision rates as reported in the National Joint Registry, across all orthopaedic units in England and Wales between 2003 and 2019.

Methods

Ethics statement

With support under Section 251 of the National Health Service (NHS) Act 2006, the Ethics and Confidentiality Committee (ECC) (now the Health Research Authority Confidentiality Advisory Group) allows the NJR to collect patient data where consent is indicated as “Not Recorded.”

Before Personal Data and Sensitive Personal Data are recorded, express written patient consent is provided. The NJR records patient consent as either “Yes,” “No,” or “Not Recorded.”

Data source

We assessed data from the NJR—established in 2003. It currently records all primary and revision hip replacements done in hospitals in England, Wales, Northern Ireland, the Isle of Man and the States of Guernsey. A total of 1,204,423 primary THR procedures had been recorded in England and Wales until 31 December 2019. Our analysis is based on 1,027,098 (85.3%) primary procedures, recorded in the NJR, which include patient consent and identifiers that allow revisions to be linked to primary operations with an identifiable head-cup or head-liner combination. Resurfacing procedures, stemmed MoM THR procedures, procedures with bearing implant materials that could not be resolved, with a dual-mobility bearing, implants with a monobloc acetabular component with a cup made of a single material other than HCLPE or non-HCLPE, a modular acetabular component with cobalt chrome liner or a rare combination (i.e., alumina head or liner with delta ceramic liner or head, or oxidised zirconium head and a non-HCLPE liner) were excluded (Fig A in S1 Text). Patients had given their consent for this study as part of their consent for data linkage in the NJR.

Outcomes

Our analyses estimated all-cause and cause-specific revision rates. We estimated revision rates for different head-cup or head-liner combinations. Our unit of analysis for the consideration of revision outcomes is the implant (rather than patient) so we included 260,830 primary procedures performed on contralateral sides of the same patient but on different dates.

The specific reasons for revision considered were those included as indications for revision listed on the NJR Minimum Data Set forms and categorised here as aseptic loosening, periprosthetic fracture, implant wear, malalignment, dislocation or subluxation, pain, infection, and any other reasons (lysis, implant fracture, head-socket mismatch, adverse soft tissue reaction(s), other indications).

Exposure and adjustment factors

Component data was ascertained from the implants used at the time of primary surgery and uploaded to the NJR. Materials were defined by catalogue numbers and review of implant data publicly available from manufacturers. We first identified the primary THRs with heads and monobloc cups. We modelled the modular acetabular component THRs with a head and shell/liner combination separately. Preassembled acetabular implants (e.g., a metal shell with a ceramic liner that is provided to the surgeon as a preassembled implant identified by a single catalogue number) are modelled with the modular acetabular group. A full description of the different types of head, cup, shell, and liner materials is provided in Table 1. THRs with an unclear implant construct were excluded from this report. Implants with a cobalt chrome head and an HCPLE liner or cup were used as the reference group as this was the most commonly used implant bearing surface combination over the studied period. The combination remains among the most popular across numerous national health organisations including the NHS and the care organisations in the Nordic countries [15,20].

Table 1. Description of the studied sample and all-cause revision rate.

Monobloc Modular
No. Revision(n) Rate (per 10,000) No. Revision(n) Revision (per 10,000)
Year of primary surgery <2010 111,781 2,481 222.0 111,028 4,539 408.8
2010–2014 127,413 2,939 230.7 228,155 5,378 235.7
2015–2019 139,703 1,958 140.2 309,018 3,583 115.9
Gender Female 251,218 4,410 175.5 377,914 7,375 195.1
Male 127,679 2,968 232.5 270,287 6,125 226.6
Age at primary (years) <55 14,368 446 310.4 93,190 2,452 263.1
55 to 64 48,592 1,316 270.8 165,336 3,762 227.5
65 to 74 141,877 3,086 217.5 231,077 4,420 191.3
> = 75 174,060 2,530 145.4 158,598 2,866 180.7
Body mass index <18.5 2,658 36 135.4 3,682 66 179.3
[18.5, 24.9] 51,097 734 143.6 87,542 1,393 159.1
[25, 29.9] 92,193 1,352 146.6 172,498 2,928 169.7
>29.9 84,542 1,511 178.7 177,560 3,601 202.8
Unknown BMI 148,407 3,745 252.4 206,919 5,512 266.4
ASA grade P1—Fit and healthy 40,275 952 236.4 104,981 2,322 221.2
P2—Mild disease not incapacitating 259,297 5,007 193.1 446,785 9,018 201.8
P3—Incapacitating systemic disease 76,495 1,373 179.5 93,486 2,098 224.4
P4—Life threatening disease 2,783 46 165.3 2,901 61 210.3
P5—Expected to die within 24 h with or without an operation 47 0 0.0 48 1 208.3
Fixation type Cemented 345,036 6,627 192.1 674 21 311.6
Hybrid 9 0 0.0 242,042 4,098 169.3
Reverse hybrid 30,394 638 209.9 89 8 898.9
Uncemented 35 3 857.1 395,493 9,052 228.9
Unclassified 3,423 110 321.4 9,903 321 324.1
Stem composition Stainless steel 289,364 5,219 180.4 178,564 2,785 156.0
Cobalt chrome 54,909 1,371 249.7 64,626 1,384 214.2
Titanium 30,680 656 213.8 391,672 8,865 226.3
Other or unknown 3,944 132 334.7 13,339 466 349.4
Head size (mm) 22.25 12,893 376 291.6 1,021 38 372.2
26 1,8694 506 270.7 775 27 348.4
28 241,452 4,956 205.3 144,874 4,296 296.5
30–32 93,203 1,267 135.9 268,385 4,316 160.8
> = 36 9,232 163 176.6 223,243 4,502 201.7
Unknown 3,423 110 321.4 9,903 321 324.1
Head cup Head: Alumina, Cup: HCLPE 6,621 82 123.8
Head: Alumina, Cup: non-HCLPE 12,255 273 222.8
Head: Cobalt Chrome, Cup: HCLPE 35,069 452 128.9
Head: Cobalt Chrome, Cup: non-HCLPE 69,075 1,749 253.2
Head: Delta Ceramic, Cup: HCLPE 23,279 261 112.1
Head: Delta Ceramic, Cup: non-HCLPE 14,064 285 202.6
Head: Stainless Steel, Cup: HCLPE 35,825 352 98.3
Head: Stainless Steel, Cup: non-HCLPE 182,709 3,924 214.8
Shell composition Cobalt Chrome 720 25 347.2
Stainless Steel 5,273 134 254.1
Tantalum 5,741 187 325.7
Titanium 629,205 13,011 206.8
Unknown 7,262 143 196.9
Head liner Head: Alumina, Liner: Alumina 27,602 907 328.6
Head: Alumina, Liner: HCLPE 25,191 405 160.8
Head: Alumina, Liner: non-HCLPE 3,281 157 478.5
Head: Cobalt Chrome, Liner: HCLPE 183,106 3,485 190.3
Head: Cobalt Chrome, Liner: non-HCLPE 42,389 1,791 422.5
Head: Delta Ceramic, Liner: Delta Ceramic 119,558 2,943 246.2
Head: Delta Ceramic, Liner: HCLPE 140,539 1,757 125.0
Head: Delta Ceramic, Liner: non-HCLPE 13,448 381 283.3
Head: Delta Ceramic, Pre-assembled implant 4,614 74 160.4
Head: Cobalt Chrome or Stainless Steel, Pre-assembled implant 2,648 69 260.6
Head: Oxidised, Liner: HCLPE 21,263 269 126.5
Head: Stainless Steel, Liner: HCLPE 45,672 574 125.7
Head: Stainless Steel, Liner: non-HCLPE 18,890 688 364.2
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ASA, American Society Anaesthesiologists Physical Status Classification; HCLPE, highly crossLinked polyethylene.

We also accounted for the year of the primary surgery completion, the materials used in the stem, shell, head size, implant component fixation, patient gender, age at the primary procedure, body mass index (BMI), and American Society of Anesthesiologists (ASA) grade. These variables are recorded by the surgeon or their delegate on the NJR Minimum Data Set forms [21].

Statistical analysis

We used flexible parametric survival models that estimate hazard ratios (HRs) by bearing materials assuming that they were likely to vary over time [22]. Restricted cubic splines were used to model the baseline hazard function and the time-dependent effects associated with the bearing materials combination. For each model, the best fitting model with the most parsimonious number of knots was determined using the smallest Akaike information criterion (AIC) and Bayesian information criterion (BIC) [23]. This research focussed specifically on implant-survivorship, i.e., net implant failure; therefore, non-competing rather than competing-risk modelling was used [24]. The analyses were adjusted for year of primary surgery, patient age, gender, BMI, ASA grade, implant fixation, head component size, and stem materials. We also assessed HRs for each specific reason for revision described above.

All analyses were designed prior to analysis. They were amended a posteriori to further adjust for year of surgery, to identify whether how potential changes in clinical practices over time influenced results. The adjusted results, with or without this adjustment were similar. An additional a posteriori analysis was conducted to compare modular implants with the lowest risks of revision. The same modelling strategy was used.

This study is reported as per the “Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): guidelines for reporting observational studies” statement (see S1 Strobe Checklist).

Results

A total of 1,026,481 out of 1,204,423 primary total hip replacements are included in the analysis (Monobloc: n = 378,979 and Modular: n = 647,502) (Fig A in S1 Text) with 20,869 (2%) procedures subsequently undergoing a linked first revision episode (Monobloc: n = 7,381 and Modular: n = 13,488) (Tables 1 and A–H in S1 Text).

Monobloc acetabular implants (n = 378,979)

The risks of all-cause revision by bearing surface materials used in the implant head and monobloc cup, plotted by time elapsed since the primary procedure, are reported in Fig 1 and Table 2 (with further details in Table I in S1 Text).

Fig 1. Risk of revision by head and cup materials with monobloc cups (Reference: Cobalt chrome head with highly crosslinked polyethylene cup).

Fig 1

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Flexible parametric survival model adjusted for year of primary surgery, patient gender, age, BMI, ASA grade, implant fixation, stem composition and head size. ASA, American Society of Anesthesiologists; BMI, body mass index; HCLPE, highly crosslinked polyethylene.

Table 2. Monobloc acetabular component-all-cause revision HR and 95% CI by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup.

1 year 2 years 10 years
HR 95% CI P-value* HR 95% CI P-value* HR 95% CI P-value*
Head: Stainless Steel, Cup: HCLPE 0.81 [0.70, 0.95] 0.010 0.81 [0.69, 0.95] 0.014 0.8 [0.66, 0.97] 0.030
Head: Delta Ceramic, Cup: HCLPE 0.67 [0.57, 0.79] <0.001 0.65 [0.54, 0.77] <0.001 0.61 [0.50, 0.75] <0.001
Head: Alumina, Cup: HCLPE 0.63 [0.49, 0.80] <0.001 0.67 [0.52, 0.85] 0.002 0.75 [0.55, 1.03] 0.079
Head: Stainless Steel, Cup: non-HCLPE 1.2 [1.07, 1.36] 0.005 1.19 [1.05, 1.36] 0.012 1.18 [1.02, 1.36] 0.031
Head: Cobalt Chrome, Cup: non-HCLPE 1.32 [1.17, 1.49] <0.001 1.31 [1.15, 1.48] <0.001 1.28 [1.10, 1.48] 0.002
Head: Delta Ceramic, Cup: non-HCLPE 0.88 [0.75, 1.03] 0.115 0.87 [0.74, 1.03] 0.102 0.86 [0.71, 1.05] 0.127
Head: Alumina, Cup: non-HCLPE 0.84 [0.70, 0.99] 0.05 0.87 [0.73, 1.03] 0.113 0.92 [0.76, 1.13] 0.284
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Flexible parametric survival model adjusted for year of primary surgery, patient gender, age, BMI, American Society of Anesthesiologists grade, implant fixation, stem composition and head size. HCLPE, highly crosslinked polyethylene.

* Wald test.

Compared to implants with a cobalt chrome head and HCLPE cup (reference group), the risk of revision was lower for patients with a delta ceramic head and HCLPE cup implant, at any postoperative period. Implants with a stainless steel head and HCLPE cup had also a lower risk of revision. Implants with an alumina head and HCLPE cup had a lower risk of revision for the first 5 postoperative years. The HRs adjusted for year of primary surgery, patient gender, age, BMI, ASA physical status grade, implant fixation, shell component materials, stem component materials, and head size at 10 years compared to the reference group were 0.61 (95% CI 0.50, 0.75) for delta ceramic head and HCLPE cup; 0.75 (95% CI 0.55, 1.03) for alumina ceramic head and HCLPE cup; 0.80 (95% CI 0.66, 0.97) for stainless steel head and HCLPE cup.

In contrast, the risk of revision was higher at any postoperative time for patients with cobalt chrome heads and a non-HCLPE cup and for the first 10 post-operation years for implants with stainless steel head and non-HCLPE cup.

Similar results were found when investigating indication-specific revision (Tables J–Q and Figs B, D, F, H, J, L, N, and P in S1 Text) with higher risk of revision for implant with a non-HCLPE cup. Differences were mostly observed in the first years following the primary procedure.

Modular acetabular implants (n = 647,502)

Compared to patients with a cobalt chrome head and HCLPE liner primary THR (reference group), the all-cause risk of revision varied non-constantly over time (Fig 2 and Table 3 with further details in Table R in S1 Text).

Fig 2. Risk of revision by head and liner materials with modular cups (Reference: Cobalt chrome head with highly crosslinked polyethylene liner).

Fig 2

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Flexible parametric survival model adjusted for year of primary surgery, patient gender, age, BMI, ASA grade, implant fixation, shell composition, stem composition, and head size. ASA, American Society of Anesthesiologists; BMI, body mass index; HCLPE, highly crosslinked polyethylene.

Table 3. Modular acetabular component-All-cause revision HR and 95% CI by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner.

1 year 2 years 10 years
HR 95% CI P-value* HR 95% CI P-value* HR 95% CI P-value*
Head: Alumina, Liner: Alumina 1.09 [1.00, 1.18] 0.050 1.14 [1.05, 1.24] 0.003 1.24 [1.13, 1.36] <0.001
Head: Alumina, Liner: HCLPE 0.91 [0.81, 1.01] 0.098 0.92 [0.82, 1.03] 0.143 0.94 [0.82, 1.08] 0.271
Head: Alumina, Liner: non-HCLPE 1.33 [1.11, 1.59] 0.003 1.42 [1.21, 1.68] <0.001 1.60 [1.32, 1.93] <0.001
Head: Delta Ceramic, Liner: Delta Ceramic 0.91 [0.86, 0.97] 0.004 0.93 [0.88, 0.99] 0.022 0.96 [0.90, 1.03] 0.197
Head: Delta Ceramic, Liner: HCLPE 0.78 [0.73, 0.84] <0.001 0.79 [0.73, 0.84] <0.001 0.79 [0.73, 0.85] <0.001
Head: Delta Ceramic, Liner: non-HCLPE 0.82 [0.73, 0.92] 0.001 0.84 [0.75, 0.94] 0.004 0.87 [0.77, 0.99] 0.038
Head: Oxidised Zirconium, Liner: HCLPE 0.67 [0.58, 0.77] <0.001 0.66 [0.57, 0.77] <0.001 0.65 [0.55, 0.77] <0.001
Head: Cobalt Chrome, Liner: non-HCLPE 1.30 [1.22, 1.39] <0.001 1.35 [1.26, 1.45] <0.001 1.44 [1.33, 1.55] <0.001
Head: Stainless Steel, Liner: HCLPE 0.98 [0.88, 1.09] 0.373 0.98 [0.87, 1.10] 0.377 0.98 [0.87, 1.11] 0.378
Head: Stainless Steel, Liner: non-HCLPE 1.40 [1.26, 1.55] <0.001 1.48 [1.34, 1.64] <0.001 1.62 [1.44, 1.82] <0.001
Head: Delta Ceramic, Pre-assembled implant 0.52 [0.40, 0.68] <0.001 0.53 [0.40, 0.70] <0.001 0.54 [0.39, 0.73] <0.001
Head: Cobalt Chrome or Stainless Steel, Pre-assembled implant 1.23 [0.90, 1.67] 0.169 1.20 [0.87, 1.66] 0.216 1.17 [0.83, 1.64] 0.265
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Flexible parametric survival model adjusted for year of primary surgery, patient gender, age, BMI, ASA grade, implant fixation, shell composition, stem composition and head size. HCLPE, highly crosslinked polyethylene.

* Wald test.

THRs with a delta ceramic head and HCLPE liner had a lower risk of revision throughout the entire postoperative period. The risk of revision was also constantly lower for implants with an oxidised zirconium head and HCLPE liner and THRs with a delta ceramic head and preassembled acetabular implant. This lower revision rate was limited to the first 2 years when a delta ceramic head was paired with a delta ceramic or non-HCLPE liner. The HRs adjusted for year of primary surgery, patient gender, age, BMI, ASA physical status grade, implant fixation, shell component materials, stem component materials, and head size at 10 years compared to the reference group were 0.54 (95% CI 0.39, 0.73) for delta ceramic head pre-assembled implants; 0.65 (95% CI 0.55, 0.77) for oxidised zirconia ceramic head and HCLPE cup; 0.79 (95% CI 0.73, 0.85) for delta ceramic head and HCLPE cup.

In contrast, implants with a cobalt chrome or stainless steel head and a non-HCLPE liner had a higher risk of revision from the first months post-operation onwards. From 6 months post-operation onwards, the risk of revision was higher for implants with an alumina head and alumina, or non-HCLPE liner.

Similar results were found when investigating indication-specific revisions (Tables S–Z and Figs C, E, G, I, K, M, O, and Q in S1 Text). Compared to THRs with cobalt chrome head and HCLPE liner, the risks of revision for most indications were lower for implants with a delta ceramic or oxidised zirconium head with HCLPE liner.

No difference in the risk of revision could be identified between implants with oxidised zirconium head and HCLPE liner and implants with delta ceramic head and HCLPE liner (Fig R in S1 Text).

Discussion

Compared to implants with cobalt chrome heads and HCLPE cups, the all-cause risk of revision for monobloc acetabular component primary THRs was lower for patients with a delta ceramic head and HCLPE cup implant combination. These risks were generally higher with cobalt chrome or stainless steel heads used with non-HCLPE cups. For modular acetabular components the all-cause revision risk was markedly lower when delta ceramic heads or oxidised zirconium heads were used with HCLPE. Higher risks of revision were seen with alumina heads and liners or non-HCLPE liners and for cobalt chrome and stainless steel heads with non-HCLPE liners. Similar conclusions were found when investigating indication-specific risks of revision.

The risk of revision associated with specific bearing combinations has mostly been investigated through routine reporting in registry reports without adjustment for factors that influence the risk of revision or in studies with small sample sizes that lacks the external validity of the current analysis. In a network meta-analysis of 3,177 hip replacements comparing implant survivorship by head-size, fixation and bearing, no combination had better outcomes than the reference combination of metal-on-polyethylene (not highly cross linked), small head, and cemented [25]. Due to small numbers in individual nodes the confidence intervals were very wide. As with other recent systematic reviews of RCTs considering revision outcomes with different bearing surfaces [26–30], no attempt was made to compare specific ceramic or polyethylene material combinations. From a systematic search of MEDLINE and Embase on 1 March 2023, recent registry and cohort comparative studies focusing on aspects of bearings and subsequent revision rates have not considered specific bearings surface materials including polyethylene materials or a comprehensive range of revision outcomes (Table AA in S1 Text). Consistent with our findings, in an Italian registry cohort reporting revisions due to dislocation up to 7 years after hip replacement, rates were higher with non-HCLPE liners but did not differ between different femoral head material and HCLPE combinations [31]. The low rate of revision for implant with a ceramic or oxidised zirconium head has also been reported in the Dutch Arthroplasty Register, without details by type of ceramics materials used [32].

The analysis reported here is based on an exhaustive large, nonselective data set registry, using all procedures performed by all orthopaedic units of an entire healthcare system. While several studies reported that hip implant with an alumina head had good wear properties, revision and patient reported outcomes [33–41], our results show that these implants are associated with a higher risk of revision than the most commonly used implant combinations. This had previously been reported in other studies [42,43]. The higher risk of revision for implants with a cobalt chrome head and non-HCLPE liner or cup identified in our study has also previously been reported in smaller uncontrolled studies [44–47], and in THRs using stainless steel heads [48]. Oxidised zirconium head material and HCLPE liners have also been shown to provide good results [49]. Another study could not identify any difference when compared to cobalt chrome heads [50]; our study showing good results for implant with an oxidised zirconium head provides further evidence on this bearing material combination. Two RCTs investigating oxidised zirconium heads have not reported differences in survivorship rate in comparison to cobalt chrome heads, but they were not powered to investigate revision outcomes [50,51]. The existing observational data on THRs using delta ceramic components show positive outcomes [52–59]. Our results confirm the lower risk of all-cause and indication-specific revision for primary THR with a delta ceramic head, especially with an HCLPE liner or cup. National registries report similar lower unadjusted risk of revision for implants with ceramic head and HCLPE liner/cup compared to implants with metal head and HCLPE liner/cup [15–19]; a registry showing no evidence of difference between those 2 types of implants when the risks are adjusted for year of primary surgery, patient age, gender, and surgical year, does not report continuous longitudinal postoperative risk change as done here where we also have a larger sample size [20]. The NJR does not capture squeaking or noise as a specific indication for revision (this would be captured under other indications for revision and reflected in the all-cause revision rate if bothersome enough to lead to revision) but this is a complication that has been reported with ceramic materials in THR [60].

The mechanisms by which bearing materials might influence implant longevity are multifaceted. For the acetabular component, HCLPE has been demonstrated to have significantly reduced wear compared to non-HCLPE, reducing late failure by mitigation of particle-induced periprosthetic osteolysis which can lead to implant instability and pain [61,62]. Ceramic materials have been shown in vitro to have reduced bacterial adhesion and slower biofilm development compared to metals due to their surface properties [63]. This could influence earlier revision rates both for infection and other causes as low-grade infection can masquerade as aseptic loosening and instability [8,9]. Use of a ceramic head reduces corrosion at the trunnion (the modular interface between the head and the stem), which can cause adverse reaction to metal debris requiring revision surgery [64].

In 2022, the annual NJR reported that hip implants with a metal head, mostly in cobalt chrome, and polyethylene liner/cup had been used in 47,180 procedures and were the most used implant materials over the last 5 years [1]. Our analysis, the largest of its kind to date in a comprehensive registry providing generalisable outcome data, identifies implant materials that are associated with lower risk of revision following primary THR. For monobloc acetabular component primary THRs, implants with a delta ceramic head and HCLPE cup have the lowest risk of revision and this is sustained throughout the post-operation periods. Similarly, for modular acetabular component primary THRs, implants with a delta ceramic or oxidised zirconium heads and HCLPE liner have the lowest risk of all-cause and cause-specific revision.

These results are generalisable as they were derived from all procedures performed in England and Wales since 2003. They capture the whole diversity of clinical practices across NHS and the private sector, over an extended period. This has allowed comprehensive and nonselective comparisons between implant bearing surface materials. The modelling strategy reporting the risk of revision throughout the whole postoperative period, nearly 15 years, has allowed us to depict the time-specific risk associated with each material throughout the post-operation period by specific indication for revision. This is of particular importance given that failure rates for different indications vary over time. However, these results could be influenced by residual confounding as not all factors that could influence implant selection or the risk of revision are captured in the NJR. This is not a randomised controlled trial (RCT), and it is possible that the choice of implant materials is influenced by operating unit preference. In the United Kingdom, surgeon choice is heavily constrained at unit level due to units carrying a selected range of implants imposed by hospital board regulations, mostly for economic reasons. The indication-specific revision analyses (Figs B–Q in S1 Text) is giving further insight into the role of each bearing surface materials on the considered outcome and were aligned with the overall revision analyses (Figs 1 and 2). We cannot rule out that some of the effects identified could be partially related to selection effect. Shared operative strategies, or bearing surface selection by surgeons, within the same surgical unit, may generate some clustering at unit level. Previous investigations on the same dataset accounting for unit level clustering added little value to the analyses and their modelling is currently challenging with large data set in the context of survival analysis [59]. Oxidised zirconium heads are only made by one manufacturer and hence are used with a small number of implant combinations which may restrict the generalisability but the group size is large and the NJR annual report shows similar results for this manufacturer’s implants in comparison to others [1].

The risk of revision following primary THR is influenced by the type of material used in the bearing surface. The all-cause and indication-specific risk of revision is lower for implants with a delta ceramic head and HCLPE cups or delta ceramic heads or oxidised zirconium heads and HCLPE liners. Further work is required to determine the association of implant bearing materials with the risk of rehospitalisation, re-operation other than revision, mortality, and the cost-effectiveness of these materials.

Supporting information

S1 STROBE Checklist. Checklist of items that should be included in reports of cohort studies.

(DOCX)

pmed.1004478.s001.docx (33.9KB, docx)
S1 Text

Including: Table A. Description of the studied sample and revision rate for aseptic loosening. Table B. Description of the studied sample and revision rate for peri-prosthetic fracture. Table C. Description of the studied sample and revision rate for implant wear. Table D. Description of the studied sample and revision rate for malalignment. Table E. Description of the studied sample and revision rate for dislocation or subluxation. Table F. Description of the studied sample and revision rate for pain. Table G. Description of the studied sample and revision rate for infection. Table H. Description of the studied sample and revision rate for any other reason(s). Table I. Monobloc acetabular component—all-cause revision hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table J. Monobloc acetabular component-Revision for aseptic loosening hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table K. Monobloc acetabular component-Revision for peri-prosthetic fracture hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table L. Monobloc acetabular component-Revision for implant wear hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table M. Monobloc acetabular component-Revision for malalignment hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table N. Monobloc acetabular component-Revision for dislocation or subluxation hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table O. Monobloc acetabular component-Revision for pain hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table P. Monobloc acetabular component-Revision for infection hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table Q. Monobloc acetabular component-Revision for any other reason(s) hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table R. Modular acetabular component—all-cause revision hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table S. Modular acetabular component-Revision for aseptic loosening hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table T. Modular acetabular component-Revision for peri-prosthetic fracture hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table U. Modular acetabular component-Revision for implant wear hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table V. Modular acetabular component-Revision for malalignment hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table W. Modular acetabular component-Revision for dislocation or subluxation hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table X. Modular acetabular component-Revision for pain hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table Y. Modular acetabular component-Revision for infection hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table Z. Modular acetabular component-Revision for any other reason(s) hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table AA. Registry studies identified in MEDLINE and Embase search on 1 March 2023. Fig A. PRISMA flow diagram. Fig B. Risk of revision for aseptic loosening by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig C. Risk of revision for aseptic loosening by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig D. Risk of revision for periprosthetic fracture by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig E. Risk of revision for periprosthetic fracture by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig F. Risk of revision for implant wear by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig G. Risk of revision for implant wear by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig H. Risk of revision for malignment by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig I. Risk of revision for malignment by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig J. Risk of revision for dislocation or subluxation by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig K. Risk of revision for dislocation or subluxation by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig L. Risk of revision for pain by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig M. Risk of revision for pain by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig N. Risk of revision for infection by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig O. Risk of revision for infection by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig P. Risk of revision for any other reason(s) by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig Q. Risk of revision for any other reason(s) by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig R. Modular acetabular component-all-cause risk of revision for implants with delta ceramic head and highly crosslinked polyethylenE (HCLPE) and oxidised zirconium head and HCPLE liner.

(DOCX)

pmed.1004478.s002.docx (7MB, docx)

Acknowledgments

We would like to thank Tim Wilton for his project and data oversight for this work. We thank the patients and staff of all the hospitals who have contributed data to the National Joint Registry, and the Healthcare Quality Improvement Partnership, the National Joint Registry Steering Committee, and staff at the National Joint Registry for facilitating this work.

Abbreviations

AIC

Akaike information criterion

ASA

American Society of Anesthesiologists

BIC

Bayesian information criterion

BMI

body mass index

CI

confidence interval

ECC

Ethics and Confidentiality Committee

HCLPE

highly crosslinked polyethylene

HR

hazard ratio

RCT

randomised controlled trial

THR

total hip replacement

Data Availability

The research project was reviewed and approved by the HQIP-National Joint Registry board and the data were analysed in a data safe haven approved by this data provider. The studied data and related statistical codes are archived on the University of Bristol network. The related files remains accessible to all those with due HQIP-National Joint Registry permissions that are beyond our control. Further information provided by the data controller can be accessed here:https://www.njrcentre.org.uk/research/research-requests/ contains information on research data access request to the National Joint Registry. The authors will share all codes and data with those who hold permission from the National Joint Registry, as per this data controller requirements.

Funding Statement

This article presents independent research funded by CeramTec GmbH, Plochingen (https://www.ceramtec-group.com/en/) (MRW, RP, JF, PN, EM, AWB and EL), the NIHR Bristol Biomedical Research Centre (https://www.bristolbrc.nihr.ac.uk/) (MRW, AB, AWB and EL) and the NIHR Comprehensive Clinical Research Network (https://www.nihr.ac.uk/explore-nihr/support/clinical-research-network.htm) (MRW). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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Decision Letter 0

Syba Sunny

5 Mar 2024

Dear Dr Lenguerrand,

Thank you for submitting your manuscript entitled "The association of bearing surface materials with the risk of revision following primary total hip replacement: a cohort analysis of 1,026,481 hip replacements from the National Joint Registry" for consideration by PLOS Medicine.

Your manuscript has now been evaluated by the PLOS Medicine editorial staff as well as by an academic editor with relevant expertise and I am writing to let you know that we would like to send your submission out for external peer review.

However, before we can send your manuscript to reviewers, we need you to complete your submission by providing the metadata that is required for full assessment. To this end, please login to Editorial Manager where you will find the paper in the 'Submissions Needing Revisions' folder on your homepage. Please click 'Revise Submission' from the Action Links and complete all additional questions in the submission questionnaire.

Please re-submit your manuscript by March 7th. Please let me know if you need more time.

Login to Editorial Manager here: https://www.editorialmanager.com/pmedicine

Once your full submission is complete, your paper will undergo a series of checks in preparation for peer review. Once your manuscript has passed all checks it will be sent out for review.

Feel free to email us at plosmedicine@plos.org if you have any queries relating to your submission.

Kind regards,

Syba Sunny MBBS MRes FRCPath

Associate Editor

PLOS Medicine

ssunny@plos.org

Decision Letter 1

Syba Sunny

3 Jun 2024

Dear Dr. Lenguerrand,

Many thanks for submitting your manuscript "The association of bearing surface materials with the risk of revision following primary total hip replacement: a cohort analysis of 1,026,481 hip replacements from the National Joint Registry” (PMEDICINE-D-24-00694R1) to PLOS Medicine. The paper has been reviewed by three subject experts and two statisticians; their comments are included below.

As you will see, the reviewers were positive about the paper in several regards. However, concerns were raised about the way in which the data was analysed, particularly with regard to statistical rigor, and also the role of the funder, which casts some doubt over the robustness of the conclusions presented. However, we remain potentially interested in the paper if these aspects can be addressed in a substantive way. As such, after discussing the paper with the editorial team, I’m pleased to invite you to revise the paper in response to the reviewers’ comments and our editorial requests (below). We plan to send the revised paper to some of all of the original reviewers*, and of course we cannot provide any guarantees at this stage regarding publication.

When you upload your revision, please include a point-by-point response that addresses all of the reviewer and editorial points, indicating the changes made in the manuscript and either an excerpt of the revised text or the location (eg: page and line number) where each change can be found. Please submit a clean version of the paper as the main article file and a version with changes marked should as a marked-up manuscript. Please also check the guidelines for revised papers at http://journals.plos.org/plosmedicine/s/revising-your-manuscript for any that apply to your paper.

We ask that you submit your revision by 24th June. However, if this deadline is not feasible, please contact me by email, and we can discuss a suitable alternative.

Please don’t hesitate to contact me directly with any questions (ssunny@plos.org). If you reply directly to this message, please be sure to ‘Reply All’ so your message comes directly to my inbox.

Kind regards,

Syba

Syba Sunny MBBS, MRes, FRCPath

Associate Editor

PLOS Medicine

ssunny@plos.org

*Please note: If your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.

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Editorial comments:

The editorial team all agree that this is an interesting piece of work that could be very impactful, and we are grateful that you chose to submit this to PLOS Medicine. However, we agree with the reviewers’ comments and have some concerns that will need to be addressed in full before your paper can be taken forward.

1) Thank you for stating that the study was funded by CeramTec. To ensure transparency and satisfy the team that the function of the sponsor does not preclude publication, it would be useful to add some detail on what the funding was used for, specifically, in the completion of this study.

2) Please revise your statistical analyses to address the influence of confounding variables more robustly, e.g. using rigorous sensitivity analyses. Note the comments and suggestions offered by Reviewer 3, who is a statistician.

3) Please provide a description of the formal or informal processes that might go into the decision-making process when bearing materials are chosen, with an accompanying critical discussion. This would help to address any concerns that readers might have about confounding by indication here. In your discussion, it would be useful to hear what factors specifically could have influenced decision-making – could this have been influenced by patient age or the life expectancy of the implant, for example? Our readership is global, so it would also be useful to state whether patients in the UK might have any choice over the materials used in their implants.

4) Data Availability:

The Data Availability Statement (DAS) requires some revision – please review the first sentence. Also, please describe briefly the ethical, legal, or contractual restriction that prevents you from sharing deidentified data.

5) Reporting guidance:

Thank you for including the STROBE checklist as Supporting Information. Please add the following statement, or similar, to the Methods: "This study is reported as per the ‘Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): guidelines for reporting observational studies’ Statement” and refer to the checklist’s location.

When completing the checklist, please use section and paragraph numbers, rather than page numbers.

Further guidance can be found here: https://www.equator-network.org/reporting-guidelines/

6) Statistical reporting:

Please quantify the main results with 95% CIs and p values.

When reporting p values please report as <0.001 and where higher as p=0.002, for example. When reporting 95% CIs please separate upper and lower bounds with commas instead of hyphens as the latter can be confused with reporting of negative values.

Please include the actual amounts and/or absolute risk(s) of relevant outcomes (including NNT or NNH where appropriate), not just relative risks or correlation coefficients. (example for absolute risks: PMID: 28399126).

Please include any important dependent variables that are adjusted for in the analyses.

7) Prespecified analysis plan/study protocol:

Did your study have a prospective protocol or analysis plan? Please state this (either way) early in the Methods section.

a) If a prospective analysis plan (from your funding proposal, IRB or other ethics committee submission, study protocol, or other planning document written before analyzing the data) was used in designing the study, please include the relevant prospectively written document with your revised manuscript as a Supporting Information file to be published alongside your study, and cite it in the Methods section. A legend for this file should be included at the end of your manuscript.

b) If no such document exists, please make sure that the Methods section transparently describes when analyses were planned, and when/why any data-driven changes to analyses took place.

c) In either case, changes in the analysis-- including those made in response to peer review comments-- should be identified as such in the Methods section of the paper, with rationale.

For all observational studies, in the manuscript text, please indicate: (i) the specific hypotheses you intended to test, (ii) the analytical methods by which you planned to test them, (iii) the analyses you actually performed, and (iv) when reported analyses differ from those that were planned, transparent explanations for differences that affect the reliability of the study's results. If a reported analysis was performed based on an interesting but unanticipated pattern in the data, please be clear that the analysis was data-driven.

8) Author summary:

At this stage, we ask that you include a short, non-technical Author Summary of your research to make findings accessible to a wide audience that includes both scientists and non-scientists. The authors summary should consist of 2-3 succinct bullet points under each of the following headings:

• Why Was This Study Done? Authors should reflect on what was known about the topic before the research was published and why the research was needed.

• What Did the Researchers Do and Find? Authors should briefly describe the study design that was used and the study’s major findings. Do include the headline numbers from the study, such as the sample size and key findings.

• What Do These Findings Mean? Authors should reflect on the new knowledge generated by the research and the implications for practice, research, policy, or public health. Authors should also consider how the interpretation of the study’s findings may be affected by the study limitations. In the final bullet point of ‘What Do These Findings Mean?’, please describe the main limitations of the study in non-technical language.

The Author Summary should immediately follow the Abstract in your revised manuscript. This text is subject to editorial change and should be distinct from the scientific abstract. Please see our author guidelines for more information: https://journals.plos.org/plosmedicine/s/revising-your-manuscript#loc-author-summary

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Comments from the reviewers:

REVIEWER #1:

This study investigated the revision rate of primary THR reported in the National Joint Registry by specific types of bearing surfaces used.

Comments:

"We assessed data from the National Joint Registry (NJR)—established in 2003. It currently records all primary and revision hip replacements done in hospitals in England, Wales, Northern Ireland, the Isle of Man and the States of Guernsey. A total of 1,204,423 primary THR procedures had been recorded in England and Wales until 31st December 2019. Our analysis is based on 1,026,481 (85.2%) primary procedures, recorded in the NJR, which include patient consent and identifiers that allow revisions to be linked to primary operations with an identifiable head-cup or head-liner combination. "

A wealth of valuable and representative data has been used.

"unit of analysis for the consideration of revision outcomes is the implant (rather than patient) so we included 260,830 primary procedures performed on contralateral sides of the same patient but on different dates. "

Clustering by patient considered?

"used flexible parametric survival models that estimate hazard ratios (HR) by bearing materials assuming that they were likely to vary over time.(20) Restricted cubic spline function used to model the baseline function and the time-dependent effects associated with bearing materials combination only were determined using the smallest Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC).(21) The analyses were adjusted for patient age, gender, BMI, ASA grade, implant fixation, head component size, and stem materials. We also assessed HRs for each specific reason for revision described above."

Appropriate statistical models, with insightful additional analyses, have been conducted.

The Results are communicated accurately and clearly, and the figures are understandable and informative.

"However, these results could be influenced by residual confounding as not all factors that could influence implant selection or the risk of revision are captured in the NJR. This is not a randomised controlled trial (RCT), and it is possible that the choice of implant materials is influenced by surgeon preference. This choice may be constrained at the unit level due to units carrying a selected range of implants, but we cannot rule out that some of the effects identified could be partially related to selection effect. Shared operative strategies, or bearing surface selection by surgeons, within the same surgical unit, may generate some clustering at unit level. Previous investigations on the same dataset accounting for unit level clustering added little value to the analyses and their modelling is currently challenging with large dataset in the context of survival analysis.(22) Oxidised zirconium heads are only made by one manufacturer and hence are used with a small number of implant combinations which may restrict the generalisability but the group size is large and the NJR annual report shows similar results for this manufacturer's implants in comparison to others."

The main study limitations have been acknowledged in the discussion.

REVIEWER #2:

"Restricted cubic spline function used to model the baseline function" - suggest changing "baseline function" to "baseline hazard" for clarity

"the time-dependent effects associated with bearing materials combination only were determined using the smallest Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC)." - I do not completely understand what you mean here - did you investigate different forms of the restricted cubic splines (e.g., number/placement of knots) and then use AIC/BIC to determine best fit?

Did you consider adjusting for year of primary THA? It would seem that trends in implant type would have changed from 2003 - 2019, with some implant types more likely to be used in earlier years and other in later years.

How did the models account for the clustered nature of the data (potential for multiple implants per patient)?

Did the analyses for specific revision reasons include the competing risk of other revision reasons?

REVIEWER#3:

This is an interesting study on the association of bearing surface materials with the risk of revision following primary total hip replacement using data from a National Joint Registry. However, there are a few major issues needing attention.

1. The paper is difficult to follow especially for non-expert in the hip replacement field. With so many sub-categories and combinations between them (table 1), it is easy to get lost as it's not clear why the reference was chosen and why those comparisons were chosen (table 2).

2. Study design. Ideally RCTs are perferred to cohort studies for this type of study as there are many confounding factors assiciated the risk of revision following THR. Unless adjusted comprehensively for all the potential confounders, the results are subject to scrutiny. For example, year of hip replacement, ethnicity, socioeconomic status, drinking, smoking, multimorbidity, hip replacement procedures, medication and treatment in the follow-ups, all these factors could contribute to the revision but unfortunately not included in the analyses.

3. Statistical analyses. Flexible parametric survival models were used to reflect the time-dependant nature of HRs, which is mostly adequate. However, as the outcome is revision rather than all-cause mortality, there is a competing risk issue (eg. from death or not qualified for a revision due to deteriorating health) which was not addressed in the paper.

4. The abstract was poorly written. There is no HRs or P-values in the findings when higher or lower was claimed. As there were so many comparisons, it became difficult to follow what the findings are, what the conclusions are and what the interpretations are. Basically, it is difficult to find and understand key messages from the paper.

REVIEWER #4:

Thank you for letting me review this interesting paper. The authors have compared the risk of revision between different articulations in a national registry setting. Extensive statistical analyses have been carried out. The paper is well written, the aim is well described, the subject is timely and the material is substantial. Main findings were that cross-linked PE was better than non-crosslinked PE, delta ceramic and Oxinium was superior to CoCr, and so was Alumina and stainless steel. Differences were found for 'all revisions' and for 'indication-specific revisions' and were mostly observed in the first years post implantation.

The manuscript leaves me with some questions: Is a difference in dislocation, loosening, fracture or infection rate the first few years after THR caused by the articulating materials? From a clinical point of view, I would be surprised to find that the materials were responsible. In this paper no possible explanations for the findings are discussed. The reader is left with the conclusion that ceramics lower the risk of early dislocation, infection and so on. This could of course be the case, but other factors, such as time dependent factors that may or may not be adjusted for, could also affect the findings. Could poor stem or cup makes be distributed disproportionally between the groups? Differences in median follow-up could affect the risk of revision for infection, and maybe other causes also. I believe this should be explored. A critical discussion of findings that are not easily explainable from a clinical point of view would be appreciated. This is maybe particularly important because the study is sponsored by the biggest player in the ceramic industry. I suggest doing some kind of sensitivity analysis, for instance the authors may try to study a subset of patients operated in the same time period, with the same implants, in similar patients (i.e. OA, ASA 1-2, same age distribution) but with different articulating surfaces. If the findings are replicated in such sub-analyses this would certainly strengthen the results.

Page 4, line 11. Needs a reference

Page 4, line 15. Please see NARA study. Mikkelsen RT et al, Acta Orthop 2023

Page 5, line 3-7. See Mikkelsen study

Page 7, line. I am a bit confused about the pre-assembled cups; where they grouped with the non-HCLPE liners as stated in line 3, 4?

Page 7, lines 15-17. Some factors tend to vary with time over two decades, for instance the risk of revision for infection. Did you consider adjusting for year of operation or stratified time periods? What about make of cup and stem? Poorly performing implants could skew the results, and such implants were maybe more frequent in the beginning of the study period?

Table 1. DM cups were excluded. Still some 7-800 modular cups were cemented. What were these?

Page 18, Line 23-25. Reference 31. The authors studied fractures, they did not report on dislocations.

Also I miss information on median follow-up for the study groups.

I am not familiar with all the tests that were used. It seems that the risks varied with time, and I do not know if the chosen tests handle non-proportionality properly. A statistical review will probably be called for.

REVIEWER#5:

This research study reports a cohort analysis of hip replacements reported in the UK NJR about the association of bearing surfaces materials with the risk of revision following primary total hip replacement. It is a very interesting topic of research since it contributes significantly to understanding the best option for the tribology of primary hip replacements. Moreover, this paper takes into consideration a remarkable amount of data that can be easily generalized. However, some minor changes are needed to be suitable for pubblication.

Introduction. This section can be shortened and focused more on the topic of research, that is the relationship between the tribology of the prosthesis and the risk of revision. Some lines do not give added value to the topic (ex: 3-4, 9-11, 21-23).

M&M:

- Data source, line 6: numbers given are in conflict with what is described in tables. The total amount of replacements analysed according to tables is 1.027.098, monoblocs are 378.897 and modulars are 648.201. A comprehensive check of the numbers reported should be done throughout the manuscript.

- I was not able to find eFigure 1

- How was the reference group (cobalt chrome head + HCLPE cup) determined? There is no mention of the reference group in this section

Results:

- Tables are difficult to follow. Highlighting significant positive results (lower risk of revision for "experimental groups") could be of help

- "This lower revision rate was limited to the first year when a delta ceramic head 7 was paired with a delta ceramic or non-HCLPE liner" (page 14, lines 6-7), according to sTable18, lower revision rate is seen at least up to 2 years from surgery

- Page 14, lines 16-18. Heads and cups combinations other than the reference group have been compared. However, there is no mention in the text to the reason of this choice.

Discussion. This section is difficult to follow: a revision of the structure should be done. It could be better to summarize the results at first, then compare them to previous work already available in the Literature and at the end higlight limitations and strenght of the study. Moreover, some lines (17-19) should be included in M&M section rather than in the discussion.

Any attachments provided with reviews can be seen via the following link:

[LINK]

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General editorial requests:

1. Please upload any figures associated with your paper as individual TIF or EPS files with 300dpi resolution at resubmission; please read our figure guidelines for more information on our requirements: http://journals.plos.org/plosmedicine/s/figures. While revising your submission, please upload your figure files to the PACE digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at PLOSMedicine@plos.org.

2. Please ensure that the paper adheres to the PLOS Data Availability Policy (see http://journals.plos.org/plosmedicine/s/data-availability), which requires that all data underlying the study's findings be provided in a repository or as Supporting Information. For data residing with a third party, authors are required to provide instructions with contact information for obtaining the data. PLOS journals do not allow statements supported by "data not shown" or "unpublished results." For such statements, authors must provide supporting data or cite public sources that include it.

3. We ask every co-author listed on the manuscript to fill in a contributing author statement, making sure to declare all competing interests. If any of the co-authors have not filled in the statement, we will remind them to do so when the paper is revised. If all statements are not completed in a timely fashion this could hold up the re-review process. If new competing interests are declared later in the revision process, this may also hold up the submission. Should there be a problem getting one of your co-authors to fill in a statement we will be in contact. YOU MUST NOT ADD OR REMOVE AUTHORS UNLESS YOU HAVE ALERTED THE EDITOR HANDLING THE MANUSCRIPT TO THE CHANGE AND THEY SPECIFICALLY HAVE AGREED TO IT. You can see our competing interests policy here: http://journals.plos.org/plosmedicine/s/competing-interests.

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To submit your revised manuscript please use the following link:

https://www.editorialmanager.com/pmedicine/

Your article can be found in the "Submissions Needing Revision" folder.

Decision Letter 2

Syba Sunny

16 Aug 2024

Dear Dr. Lenguerrand,

Thank you very much for re-submitting your manuscript "The association of bearing surface materials with the risk of revision following primary total hip replacement: a cohort analysis of 1,026,481 hip replacements from the National Joint Registry" (PMEDICINE-D-24-00694R2) for review by PLOS Medicine.

I have discussed the paper with my colleagues, the reviewers and a guest academic editor. I am pleased to say that, provided the remaining editorial and production issues are dealt with, we are planning to accept the paper for publication in the journal. The remaining issues that need to be addressed are listed at the end of this email.

In revising the manuscript for further consideration here, please ensure you address the specific points made by each reviewer and the editors. In your rebuttal letter you should indicate your response to the reviewers' and editors' comments and the changes you have made in the manuscript. Please submit a clean version of the paper as the main article file. A version with changes marked must also be uploaded as a marked up manuscript file.

***Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.***

We expect to receive your revised manuscript within 1 week. Of course, please do let me know directly if you need more time (ssunny@plos.org). Please email us (plosmedicine@plos.org) if you have any questions or concerns about your submission.

We ask every co-author listed on the manuscript to fill in a contributing author statement. If any of the co-authors have not filled in the statement, we will remind them to do so when the paper is revised. If all statements are not completed in a timely fashion this could hold up the re-review process. Should there be a problem getting one of your co-authors to fill in a statement we will be in contact. YOU MUST NOT ADD OR REMOVE AUTHORS UNLESS YOU HAVE ALERTED THE EDITOR HANDLING THE MANUSCRIPT TO THE CHANGE AND THEY SPECIFICALLY HAVE AGREED TO IT.

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript.

Please note, when your manuscript is accepted, an uncorrected proof of your manuscript will be published online ahead of the final version, unless you've already opted out via the online submission form. If, for any reason, you do not want an earlier version of your manuscript published online or are unsure if you have already indicated as such, please let the journal staff know immediately at plosmedicine@plos.org.

If you have any questions in the meantime, please contact me or the journal staff on plosmedicine@plos.org.

We look forward to receiving the revised manuscript by Aug 23 2024 11:59PM.

Sincerely,

Syba

Syba Sunny, MBBS, MRes, FRCPath

Associate Editor

PLOS Medicine

ssunny@plos.org

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COMMENTS FROM THE EDITORS

Firstly, thank you for your detailed and thorough responses to previous requests and comments.

We have another reviewer request that will need to be addressed (see Reviewer 5’s comments and those from the guest academic editor below). We also have a number of editorial requests, the majority of which simply pertain to journal-specific style and formatting requirements; I have put these at the very bottom of this email.

COMMENTS FROM REVIEWERS

Reviewer #2: Thank you for the comprehensive response. I have no further questions.

Reviewer #5: Authors have answered point-to-point to the comments and now the paper is more impactful.

I have a minor revision to suggest. It could be better to include in the manuscript the reasons of the choice of the reference group. In the answers given it was clearly stated, but there is no reference in the main text. It could be helpful to better understand the comparisons even for non-subspecialist readers.

Reviewer #6: For context, this review was taken on upon request by the Associate Editor, as a stand-in for the original stats reviewer (Reviewer #3). The major relevant points raised were on study design (RCTs vs. cohort study), and on the absence of competing risks models.

On the use of a cohort study (instead of RCT), my opinion is that cohort studies are valid, as explained by the authors (and also acknowledged by the original Reviewer #3, who describes RCTs as "preferred"). Given the difficulty of organizing RCTs on the subject, a (large) cohort study would provide a useful datapoint which would be of use in future meta-analyses (with risks and limitations properly acknowledged).

On the absence of addressing competing risks, the authors' rebuttal appears reasonable. It might be emphasized within the manuscript itself.

Any attachments provided with reviews can be seen via the following link:

[LINK]

COMMENTS FROM THE GUEST ACADEMIC EDITOR

Reviewer 5 was invited to act as the academic editor for your revised manuscript. She looked through all the reviewer comments as well as your revised paper. She wrote that she believed that your paper was well-written and tackled an interesting topic for the orthopaedic community. She was keen for your paper to be taken forward to publication but asked if the authors could address the point she made as Reviewer 5, namely that you include a more include a more precise explanation regarding the reference group of comparisons in the main text, as she believes this would be beneficial for non-subspecialist readers.

EDITORIAL REQUESTS

Data Availability Statement (DAS):

Thank you for your detailed DAS. I have only 1 minor amendment to suggest; the first sentence contains the phrase ‘…the data were analysed in a data safe heaven…’ – I think this is meant to read as ‘data safe haven’. Could you revise this if appropriate please?

Reporting guidance:

Thank you for amending your STROBE checklist with reference to the sections rather than page numbers.

Please include a statement in your Methods section of your main text stating ‘This study is reported as per the ‘Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): guidelines for reporting observational studies’ Statement’ and also refer to the checklist’s location.

Statistical reporting:

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Decision Letter 3

Syba Sunny

23 Sep 2024

Dear Dr Lenguerrand, 

On behalf of my colleagues and the Guest Academic Editor, I am pleased to inform you that we have agreed to publish your manuscript "The association of bearing surface materials with the risk of revision following primary total hip replacement: a cohort analysis of 1,026,481 hip replacements from the National Joint Registry" (PMEDICINE-D-24-00694R3) in PLOS Medicine.

Before your manuscript can be formally accepted you will need to address some minor editorial requests (see below) and complete some formatting changes, which you will receive in a follow up email. Please be aware that it may take several days for you to receive this email; during this time no action is required by you. Once you have received these formatting requests, please note that your manuscript will not be scheduled for publication until you have made the required changes.

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Thank you again for submitting to PLOS Medicine. We look forward to publishing your paper. 

Sincerely, 

Syba

Syba Sunny, MBBS, MRes, FRCPath 

Associate Editor 

PLOS Medicine

Editorial Requests:

- In the Abstract, first sentence, could you include:

(1) ‘otherwise known as’ before the word ‘revision’

(2) ‘in part’ after the word ‘depends’

So that it reads ‘The risk of re-operation, otherwise known as revision, following primary hip replacement depends, in part, on the prosthesis implant materials used.’

- In the Abstract, third sentence, please expand THR before introducing this abbreviation, so that it reads: ‘We investigated the revision rate of primary total hip replacement (THR) reported in the National Joint Registry by specific types of bearing surfaces used.’

- Author Summary: The first sentence is a little confusing. Suggest changing it to perhaps ‘The classifications used to categorise hip implants in national registries are typically broad and may not allow interested parties to fully understand the risk of postoperative revision (i.e. need for further surgery) associated with different types of implant materials.’

- Methods section, under ‘Statistical analysis’ – thank you for including the statement ‘This study is reported as per the ‘Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): guidelines for reporting observational studies’ Statement’ (See statement).’ Please replace the ‘(See statement)’ at the end of that sentence with the location of the file, i.e. where in the supporting information it can be found, as appropriate.

- Results section, under ‘Modular acetabular implants (n=647,502)’, the following sentence needs revision (possibly missing a word after the second ‘alumina’, and also has 2 full stops at the end of the sentence): ‘From 6 months post-operation onwards, the risk of revision was higher for implants with an alumina head and alumina, or non-HCLPE liner..’

- In the Discussion section, there is this sentence: ‘The NJR does not capture squeaking or noise as a specific indication for revision “(this would be captured under other indications for revision and reflected in the all-cause revision rate if bothersome enough to lead to revision)” but this is a complication that has been reported with ceramic materials in THR.(60)’ Is the bit in double quotation marks (“) supposed to be quoting correspondence? Can you revise accordingly, please?

Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    S1 STROBE Checklist. Checklist of items that should be included in reports of cohort studies.

    (DOCX)

    pmed.1004478.s001.docx (33.9KB, docx)
    S1 Text

    Including: Table A. Description of the studied sample and revision rate for aseptic loosening. Table B. Description of the studied sample and revision rate for peri-prosthetic fracture. Table C. Description of the studied sample and revision rate for implant wear. Table D. Description of the studied sample and revision rate for malalignment. Table E. Description of the studied sample and revision rate for dislocation or subluxation. Table F. Description of the studied sample and revision rate for pain. Table G. Description of the studied sample and revision rate for infection. Table H. Description of the studied sample and revision rate for any other reason(s). Table I. Monobloc acetabular component—all-cause revision hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table J. Monobloc acetabular component-Revision for aseptic loosening hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table K. Monobloc acetabular component-Revision for peri-prosthetic fracture hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table L. Monobloc acetabular component-Revision for implant wear hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table M. Monobloc acetabular component-Revision for malalignment hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table N. Monobloc acetabular component-Revision for dislocation or subluxation hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table O. Monobloc acetabular component-Revision for pain hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table P. Monobloc acetabular component-Revision for infection hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table Q. Monobloc acetabular component-Revision for any other reason(s) hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene cup. Table R. Modular acetabular component—all-cause revision hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table S. Modular acetabular component-Revision for aseptic loosening hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table T. Modular acetabular component-Revision for peri-prosthetic fracture hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table U. Modular acetabular component-Revision for implant wear hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table V. Modular acetabular component-Revision for malalignment hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table W. Modular acetabular component-Revision for dislocation or subluxation hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table X. Modular acetabular component-Revision for pain hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table Y. Modular acetabular component-Revision for infection hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table Z. Modular acetabular component-Revision for any other reason(s) hazard ratio (HR) and 95% confidence interval (CI) by time point from primary procedure-Reference: Implant with cobalt chrome head and highly crosslinked polyethylene liner. Table AA. Registry studies identified in MEDLINE and Embase search on 1 March 2023. Fig A. PRISMA flow diagram. Fig B. Risk of revision for aseptic loosening by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig C. Risk of revision for aseptic loosening by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig D. Risk of revision for periprosthetic fracture by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig E. Risk of revision for periprosthetic fracture by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig F. Risk of revision for implant wear by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig G. Risk of revision for implant wear by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig H. Risk of revision for malignment by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig I. Risk of revision for malignment by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig J. Risk of revision for dislocation or subluxation by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig K. Risk of revision for dislocation or subluxation by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig L. Risk of revision for pain by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig M. Risk of revision for pain by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig N. Risk of revision for infection by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig O. Risk of revision for infection by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig P. Risk of revision for any other reason(s) by head and cup types (Reference: Cobalt chrome head with highly crosslinked polyethylene cup). Fig Q. Risk of revision for any other reason(s) by head and liner types (Reference: Cobalt chrome head with highly crosslinked polyethylene liner). Fig R. Modular acetabular component-all-cause risk of revision for implants with delta ceramic head and highly crosslinked polyethylenE (HCLPE) and oxidised zirconium head and HCPLE liner.

    (DOCX)

    pmed.1004478.s002.docx (7MB, docx)
    Attachment

    Submitted filename: response to reviewers final.docx

    pmed.1004478.s003.docx (50KB, docx)
    Attachment

    Submitted filename: Responses to comments 2.docx

    pmed.1004478.s004.docx (18.6KB, docx)

    Data Availability Statement

    The research project was reviewed and approved by the HQIP-National Joint Registry board and the data were analysed in a data safe haven approved by this data provider. The studied data and related statistical codes are archived on the University of Bristol network. The related files remains accessible to all those with due HQIP-National Joint Registry permissions that are beyond our control. Further information provided by the data controller can be accessed here:https://www.njrcentre.org.uk/research/research-requests/ contains information on research data access request to the National Joint Registry. The authors will share all codes and data with those who hold permission from the National Joint Registry, as per this data controller requirements.

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