Abstract
Background
We analysed the long-term revision rate, clinical outcomes and metal ion concentrations in blood over time in patients who had undergone metal-on-metal Articular Surface Replacement (ASR) hip arthroplasty.
Methods
A total of 38 patients (43 hips) were included: 24 patients (28 hips) underwent large-head total hip arthroplasty (XL THA), and 14 patients (15 hips) underwent hip resurfacing arthroplasty (HRA). The median follow-up time was 11 (range 7-12) years.
Results
None of 15 HRA implants were revised. Nine of 28 XL THA implants (32%) in 8 patients were revised. The Co ion levels significantly increased in the XL THA group (p=0.009) over a median time period of 84 (25-97) months.
Conclusion
The levels of Co ions in blood were higher in the patients who had undergone XL THA and increased significantly over time.
1. Introduction
Large diameter metal-on-metal (MoM) total hip arthroplasty (XL THA) and hip resurfacing arthroplasty (HRA) were introduced to provide a better range of motion, improved stability and a lower wear rate.1,2 The MoM Articular Surface Replacement (ASR) hip system (ASR XL THA and ASR HRA) was developed by DePuy Orthopedics (Leeds, UK) and introduced in 2003. Early reports from the National Registries of England and Wales and Australia showed that these implants are associated with higher-than-expected revision rates at five years.3 Therefore, the ASR hip system was recalled 2010.4
The reasons for ASR implant failure are not entirely understood. It has been generally accepted that the implant survival rate of ASR XL THA is poorer than that of ASR HRA.5,6 Furthermore, patients who undergo ASR XL THA are likely to exhibit increases in blood metal ion levels over time.6,7 In patients with ASR HRA implants, higher revision rates and a higher prevalence of adverse local tissue reactions (ALTRs) are associated the female sex, increased blood metal ion concentrations, and smaller femoral head sizes.5
In Sweden, 169 patients underwent primary hip arthroplasty with ASR XL THA and 396 underwent the same surgery with ASR HRA.8 After the implant was recalled, these patients were monitored by repeated clinical evaluations, measurements of the levels of metal ions in the blood, radiography examinations, and soft tissue imaging when needed.9,10
The aim of this study was to compare the long-term revision rate, clinical outcomes and metal ion concentrations in blood over time between patients who have undergone ASR large-head total hip arthroplasty and those who have undergone ASR hip resurfacing arthroplasty.
2. Materials and methods
2.1. Patients
A total of 40 patients (46 hips) underwent primary hip replacement with MoM ASR-prostheses (DePuy, Leeds, UK) between 2006 and 2009 in the Department of Orthopedics at Umeå University Hospital. Twenty-five patients (29 hips) underwent XL THA, 14 patients (15 hips) underwent HRA, and one patient who underwent bilateral surgery received both types of implants. In the XL THA group, a Corail stem (DePuy, Leeds, UK) was used in 28 hips, and an S-Rom stem (DePuy, Leeds, UK) was used in one hip. The type of implant was selected based on the surgeon's preference, and all patients were operated by using the posterior approach.
The indication for surgery was primary or secondary osteoarthritis in 42 cases and failed healing of a femoral neck fracture in four cases. One patient with the XL THA implant underwent early revision at two days postoperatively for anterior dislocation and a displaced cup, which was replaced with a new ASR cup. Subsequently, we included this patient in the group with primary XL THA implants because the clinical situation corresponded to the follow-up of primary arthroplasty.
Of the 40 patients, two were excluded entirely from the present study: one patient had received both types of implants, and one patient who underwent XL THA refused to undergo follow-ups. Thus, 38 patients were included in this study (24 patients/28 hips treated with XL THA and 14 patients/15 hips treated with HRA).
After the ASR hip system was recalled,4 all patients were followed up according to the national follow-up guidelines for patients who have received ASR implants,9 and data were collected prospectively. Since 2011, the follow-ups consisted of annual or biannual clinical examinations, X-ray examinations, metal ion level measurements in blood and soft tissue imaging when needed. Among the patients who received unilateral ASR implants, 5 in the XL THA group and 7 in the HRA group received an additional hip implant in the other hip during the follow-up period.
The median follow-up time was 11 (range 7–12) years. At the 11-year follow-up, 30 patients (33 hips) were available. One patient (XL THA, one hip) had died 8 years after the primary hip operation, and the patient's measurements collected before death were included in the metal ion analyses. Nine hips (all treated with XL THA) in 8 patients were revised before the latest follow-up. One of these patients underwent bilateral XL THA, and after revision surgery was performed for one hip, the follow-up data corresponding to his unrevised hip were included in the study. One patient who underwent unilateral XL THA had clinical and radiological signs of cup loosening, but revision surgery was contraindicated due to the patient's medical conditions.
The present study is the part of a national multicentre study of patients with ASR implants and was conducted in accordance with the Declaration of Helsinki. Ethical permission for the study was granted by the Ethics committee of Karolinska University Hospital and Karolinska Institute (Dnr: 2014/1067–31/3), where the multicentre study is being conducted. Informed consent was obtained from all patients.
2.2. Metal ion analysis
The blood samples were analysed at ALS Scandinavia AB in Luleå, Sweden. Whole blood samples were collected, stored and the analysed in accordance with the standardized procedure described by Hailer et al.11
2.3. Clinical score-tests
The clinical outcome was measured with the EQ-5D 3L, Hip Disfunction and Osteoarthritis Outcome Score (HOOS) and the Swedish version of the Harris Hip Score (HHS), as described by Otten et al.12
2.4. Statistical analysis
The descriptive statistics of the continuous variables are expressed as medians (ranges). To analyse the differences between groups in the continuous variables, we used the Mann-Whitney U test. Differences over time were analysed with the Wilcoxon matched-pairs signed-rank test. Proportions were compared with Fisher's exact test. P-values ≤ 0.05 were considered statistically significant. Statistical analysis was performed using IBM SPSS Statistics version 25 and GraphPad Prism version 6.0 for Windows, GraphPad Software.
3. Results
Table 1 shows the clinical characteristics of the patients.
Table 1.
Clinical characteristics of the patients.a
| XL THA | HRA | p-valueb | |
|---|---|---|---|
| Number of patients | 24 | 14 | |
| Number of hips | 28 | 15 | |
| Age at the index surgery | 50 (33–63) | 44 (26–55) | 0.102 |
| Side (left/right/both) | 14/6/4 | 6/7/1 | |
| Sex (Male/female) | 19/5 | 13/1 | |
| Cup size (mm) | 58 (48–64) | 58 (52–66) | 0.197 |
| Femoral head size (mm) | 51 (43–57) | 51 (45–61) | 0.211 |
| Inclination angle (degrees) | 46 (39–54) | 44.5 (30–50) | 0.101 |
| Number of revisions | 8 patients/9 hips | 0 |
XL THA: large-head total hip arthroplasty; HRA: hip resurfacing arthroplasty.
The values are given as the median (min-max) or as absolute numbers.
Mann-Whitney U test.
As of October 2019, 9 XL THA implants (32%) in 8 patients had been revised at a median 88 (range 61–123) months after the index surgery (Table 2). All patients underwent MRI scans prior to revision. In only one patient, MRI showed a 30 ×10 × 35 mm intraarticular soft tissue reaction that histologically indicated unspecific synovitis with metal deposits. Histological analysis of extirpated intraarticular soft tissue revealed an aseptic lymphocyte-dominant vasculitis associated lesion (ALVAL) in two patients (3 hips), but preoperative MRI showed the absence of soft tissue masses in these patients. Following revision, at a median interval of 30 (range 6–53) months, both the Co and Cr ion levels statistically significantly decreased (Wilcoxon matched-pairs signed-rank test: p = 0.004 and p = 0.008, respectively).
Table 2.
Descriptive data for the revised hips treated with XL THA.
| Hip | Sex | Age at the indexsurgery | Time to revision (months) |
Metal ion concentrations (μg/l) prerevision |
Metal ion concentrations (μg/l) postrevision time (months) |
Reason for revision | Histologically approved ALVALa |
|---|---|---|---|---|---|---|---|
| 1b |
M | 63 | 61 | Co 47 | Co 4.6 | Acetabular osteolysis | Yes |
| Cr 11.8 | Cr 22.4 | Pain | |||||
| 12 months |
Elevated ion levels |
||||||
| 2b |
M | 62 | 88 | Co 4.6 | Co 0.415 | Acetabular osteolysis | Yes |
| Cr 22.4 | Cr 1.96 | Elevated ion levels | |||||
| 12 months |
|||||||
| 3 |
M | 35 | 72 | Co 105 | Co 0.238 | Elevated ion levels | No |
| Cr 35 | Cr 3.28 | ||||||
| 53 months |
|||||||
| 4 |
M | 59 | 73 | Co 17.5 | Co 0.899 | Pain | No |
| Cr 7.47 | Cr 2.04 | Elevated ion levels | |||||
| 6 months | |||||||
| 5 |
M | 43 | 85 | Co 13.6 | Co 0.882 | Stem loosening | Yes |
| Cr 1.95 | Cr 1.06 | Pain | |||||
| 34 months | Elevated ion levels | ||||||
| 6 |
M | 43 | 88 | Co 18 | Co 0.66 | Pain | No |
| Cr 7.96 | Cr 1.81 | Elevated ion levels | |||||
| 37 months |
|||||||
| 7c |
M | 52 | 92 | Co 2.02 | Co 1.08 | Cup loosening | No |
| Cr 3 | Cr 1.15 | Pain | |||||
| 28 months |
|||||||
| 8 |
M | 52 | 108 | Co 13.9 | Co 0.697 | Stem loosening | No |
| Cr 3.05 | Cr 1.57 | Elevated ion levels | |||||
| 12 months |
|||||||
| 9 | F | 49 | 123 | Co 9.65 | Co 0.509 | Acetabular osteolysis | No |
| Cr 3.35 | Cr 1.69 | Pain | |||||
| 11 months | Elevated ion levels | ||||||
| Soft tissue mass on MRI | |||||||
XL THA: large-head total hip arthroplasty.
Aseptic Lymphocyte-Dominant Vasculitis Associated Lesions.
Same patient, bilateral XL THA - both revised.
Bilateral XL THA - one revised.
When analysing metal ion levels in patients who underwent XL THA, at initial examination at a median 45 (range 28–85) months after the index operation, the patients who eventually underwent revision surgery had significantly higher Co ion levels, whereas the difference in the Cr ion levels was not statistically significant (Table 3). There were no statistically significant differences in age at the index surgery, sex, cup size, femoral head size, taper sleeve adaptor length or cup inclination angle between the revised and unrevised groups.
Table 3.
Comparison of demographic and surgery-related variables between the revised and nonrevised XL THA groups.
| Revised XL THAa | Unrevised XL THAa | p-value | |
|---|---|---|---|
| Patients/hips (n) | 8/9 | 17/19 | |
| Age at the index surgery | 52 (35–63) | 48 (33–60) | 0.535b |
| Sex (Male/female) | 7/1 | 13/4 | 1.0c |
| Cup size (mm) | 58 (50–64) | 58 (48–62) | 0.522b |
| Femoral head size (mm) | 51 (45–57) | 51 (43–57) | 0.674b |
| Taper sleeve adaptor (n) | |||
| +2 | 2 | 2 | 0.699c |
| +5 | 3 | 8 | |
| +8 |
4 |
9 |
|
| Cup inclination (degrees) | 48 (42–54) | 46 (39–52) | 0.30b |
| Co (μg/L) at initial review | 11.3 (2.19–112) | 1.875 (0.35–14.4) | 0.009b |
| Cr (μg/L) at initial review | 4.125 (1.3–34) | 1.81 (0.399–5.42) | 0.109b |
The values are given as the median (min-max) or absolute numbers.
XL THA: large-head total hip arthroplasty.
One patient with bilateral implants, one of which was revised, was included in both groups.
Mann-Whitney U test.
Fisher's exact test.
We also analysed the association between the Co ion level and high femoral head offset (taper sleeve adaptor +8) in all patients with unilateral XL THA implants. The patients who underwent revision were included with the last follow-up before revision, one patient who died was included with the last follow-up before death, and all other patients were included with the latest follow-up. We found that the Co ion level was higher in the group with taper sleeve adapter +8 [median 13.2 μg/L (range 2.49–105)] than in the group with taper sleeve adapter +2 or +5 [median 5.1 μg/L (range 0.325–17.5)], (Mann-Whitney U test: p = 0.029).
Table 4 shows the blood metal ion levels in the patients with unrevised implants at the 11-year follow-up. Both the Co and Cr ion concentrations were higher in the patients who had undergone XL THA. The difference in the Co ion level was statistically significant (Mann-Whitney U test: p = 0.007) in patients with unilateral implants. A comparison of patients with bilateral implants was not possible due to the small sample size.
Table 4.
Descriptive data for the metal ion concentrations (μg/l) in the patients with unilateral and bilateral implants at the 11-year follow-up.
| XL THA | HRA | p-valuea | |
|---|---|---|---|
| Follow-up (months) | 125 (85–145) | 144 (120–148) | |
| Unilateral | n = 15 | n = 13 | |
| Co | 4.1 (0.325–26.4) | 0.81 (0.33–3.31) | 0.007 |
| Cr | 1.93 (0.5–5.75) | 1.51 (0.5–2.72) | 0.209 |
| Bilateral | n = 2 | n = 1 | |
| Co | 7.25 and 30.5 | 1.5 | |
| Cr | 6.6 and 16.7 | 2.11 |
The values are given as the median (min-max) or as absolute numbers.
XL THA: large-head total hip arthroplasty; HRA: hip resurfacing arthroplasty. Revised hips excluded; one patient with bilateral XL THA who underwent one revision was included with remaining unrevised hip; one patient who died was included with the latest follow-up before death.
Mann-Whitney U test.
Fig. 1 shows the differences in the metal ion levels between the initial examination and 11-year follow-up in the patients with unilateral, unrevised XL THA and HRA. Regarding the paired samples, there was a statistically significant increase in the Co ion levels in the XL THA group (Wilcoxon matched-pairs signed-rank test: p = 0.009) over a median time period of 84 (range 25–97) months, whereas the magnitude of increase in the Cr ion levels in this group was not statistically significant. In the HRA group, the differences in the Co and Cr ion levels over a median time period of 86 (range 79–89) months were not statistically significant. Fig. 2 shows metal ion concentrations over time for each individual patient with unrevised unilateral implants.
Fig. 1.
Co and Cr trends over time, showing difference between the last and the first samples (Wilcoxon matched-pairs signed-rank test; XL THA: n = 14, HRA: n = 13). Median time between the samples was 84 (25–97) months for XL THA and 86 (79–89) months for HRA. The last samples were taken on a median 124 (85–145) months for XL THA and 144 (120–148) months for HRA, after index surgery. Patients with revised (n = 8) and bilateral unrevised (n = 3) hips excluded. The mid-line represents the median, bottom and top of the box represent the first and the third quartile, and whiskers represent minimum and maximum values.
Fig. 2.
Scatter plots with the Co and Cr concentrations over time for each individual patient with unrevised unilateral implants (XL THA: large-head total hip arthroplasty; HRA: hip resurfacing arthroplasty).
We found no statistically significant differences in the clinical outcome scores between the patients with unrevised XL THA and HRA at the 11-year follow-up (Table 5).
Table 5.
Clinical outcome scores at the 11-year follow-up.
| XL THA (n = 14) | HRA (n = 14) | p-valuea | |
|---|---|---|---|
| HOOS | |||
| Pain | 90.0 (25–100) | 97.5 (35–100) | 0.497 |
| Symptom | 80.0 (30–100) | 90 (20–100) | 0.388 |
| ADL | 92.7 (25–100) | 93.4 (33.8–100) | 0.761 |
| Sport/Rec | 62.6 (6.3–100) | 78.2 (0–100) | 0.322 |
| QOL | 71.9 (0–100) | 78.2 (12.5–100) | 0.210 |
| Total | 85.3 (21.3–100) | 90.1 (28.1–100) | 0.395 |
| EQ-5D index | 0.803 (0.654–1) | 1 (0.648–1) | 0.427 |
| EQ-5D VAS | 75 (10–99) | 81.5 (31–100) | 0.734 |
| HHS | 99.5 (56–100) | 97.5 (73–100) | 0.306 |
The values are given as the median (min-max).
HOOS: Hip Dysfunction and Osteoarthritis Outcome Score; HHS: Harris Hip Score.XL THA: large-head total hip arthroplasty; HRA: hip resurfacing arthroplasty. 30 patients were available at the 11-year follow up, but two patients in the XL THA group were not able to complete the scores.
Mann-Whitney U test.
4. Discussion
Our results showed a higher revision rate of XL THA implants than of HRA implants. The Co ion level increased over time in the patients with unrevised well-functioning XL THA implants. Interestingly, high Co ion levels were associated with a large femoral head offset (long taper sleeve adapter) in the XL THA implants.
Generally, the outcomes of ASR XL THA are worse than those of ASR HRA. Galea et al.6 conducted mid-to late-term follow-ups of 1721 patients with ASR implants from who were enrolled in a prospective post-recall study. The authors found that the revision rate was more than two times higher for XL THA than for HRA throughout the study period. According to the 2017 reports of Australian, UK and Finish arthroplasty registries, the 10-year revision rates for ASR XL THA were 45%, 44% and 57%, respectively, while the revision rates for ASR HRA were 30%, 27% and 35%, respectively.6 In the Swedish Hip Arthroplasty Register, the corresponding revision rates for XL THA (167 implanted, 58 revised) and HRA (396 implanted, 57 revised) were 35% and 14%, respectively.8 The XL THA revision rate in our study was 32%, which is consistent with the corresponding revision rate in the national hip arthroplasty register. In our study, in the HRA group, none of implants were revised. A possible explanation for this finding is that the majority of patients (93%) in this group were men, and there is evidence that the combination of the female sex, a small femoral head size and high blood metal ion levels seems to be corelated with increased revision rates for ASR HRA implants.5
In the published literature, higher blood metal ion levels have been associated with a higher revision rate or prevalence of ALTR.5 In asymptomatic patients, blood metal ion concentrations can be used as indicators of the risk of the development of ALTR.13 We found significantly higher Co ion levels at the 11-year follow-up in patients who had undergone XL THA than in those who had undergone HRA, which is in agreement with the findings of other studies on ASR implants.5 We also found significantly higher Co ion levels at the initial follow-up in patients who had undergone XL THA and eventually underwent revision than in those who had undergone XL THA without revision. Following revision, in our study, both the Co and Cr ion levels decreased significantly.
It has been proposed that in patients with MoM THA, elevated Co ion levels are a consequence of the release of metal debris due to corrosion on taper junctions.14 This type of corrosion has also been reported in patients with metal on polyethylene bearings.15,16 In addition, the taper may be damaged mechanically due to inadequate contact or altered stem trunnion tolerances.17 In the present study, we found that a large femoral head offset (larger taper sleeve adaptor length) was correlated with increased Co ion levels in patients who had undergone XL THA. Interestingly, Langton et al.18 showed that larger femoral head offsets may contribute to taper failure in metal-on-metal bearings. The explanation may be that the combination of a small diameter taper, such as the commonly used 14mm/12mm taper, together with a high offset taper sleeve adapter may lead to a smaller contact surface area and thereby increase the possibility for micromotion.
Galea et al.19 analysed mid-term changes in blood metal ion levels in 435 patients with unilateral ASR implants. The authors compared early (less than seven years postoperatively) with mid-term (later than seven years postoperatively) values, with a minimum of one year between visits. They found a statistically significant increase in both the Cr and Co ion levels for both types of ASR implants.19 Reito et al.7 analysed repeated metal ion measurements taken in 254 patients with ASR implants, of whom 156 had undergone XL THA and 98 had undergone HRA. The mean follow-up period was 5.2 years, and the time between measurements was 8–16 months. The authors also found that blood Co ions concentrations significantly increased over time in the patients with XL THA implants.7 Similarly, in patients who had undergone XL THA, we found a statistically significant increase in the Co ion level over a median interval of 7 years. However, during the same period, the Cr ion level in patients who had undergone XL THA as well as both the Co and Cr ion levels in the patients who had undergone HRA did not significantly change. Our results are consistent with those of a study by Kelly et al.,20 who analysed the changes in metal ion levels between a mean of 2.9 years postoperatively and a mean of 10 years postoperatively in patients who had undergone ASR XL THA and found a significant increase in the Co ion level, whereas the magnitude of increase in the Cr ion level was modest and not statistically significant. In the light of these findings, it is interesting that some promising results have been reported in management of increased blood metal ion levels in asymptomatic patients with MoM implants by using chelating agents.21
The effect of acetabular component position on the risk of ASR implant revision is still controversial. We found no statistically significant differences in the cup inclination angle between the revised and unrevised XL THA implants. Similarly, Kelly et al.,20 who reported the 10-year outcomes of a cohort of 122 patients who undergone ASR XL THA, found no significant differences in the cup inclination angle between the revised and unrevised implants. In a systematic review, Laaksonen et al.5 found 6 studies showing that cup position was not related to increased revision rate for implant failure or ALTR, while 3 studies reported that increased cup inclination was associated with early revisions and revisions for ALTR. This inconsistency may be related to the variation of definition of increased inclination angle between the studies. In addition, the explanation of clinically relevant suboptimal ASR cup position may be multifactorial, including combination of factors such are increased inclination and increased anteversion, together with smaller component sizes and female gender.
The main limitations of our study are that the sample size was small, and the type of ASR implant was selected based on the surgeon's preference rather than randomly selected. Another limitation is that only 16% (6/38) of the entire cohort were female patients, which made it difficult to analyse the potential effects of sex on the clinical outcome and evolution of metal ion concentrations over time. Finally, regular prospective measurements of metal ion concentrations were initiated after the ASR implant was recalled by the manufacturer; thus, the intervals between the primary hip arthroplasty and the initial measurement of metal ion concentrations differed between patients. The strength of the study is the relatively long follow-up period and frequent follow-ups.
In conclusion, we found that ASR XL THA led to worse outcomes than did ASR HRA at the 11-year follow-up. The levels of Co ions in blood significantly increased over time in the patients who had undergone XL THA. Based on the findings of our study, we recommend frequent long-term regular metal ion testing and clinical follow-ups, even in patients who are asymptomatic and well-functioning and have undergone ASR XL THA.
Ethics approval and consent to participate
The present study is the part of a national multicentre study of patients with ASR implants. Ethical permission for the study was granted by the Ethics committee of Karolinska University Hospital and Karolinska Institute (Dnr: 2014/1067–31/3), where the multicentre study is being conducted. All patients provided informed consent. The study was conducted in accordance with the Declaration of Helsinki.
Funding
The authors received no financial support for the research, authorship and/or publication of this article.
Authors' contributions
S.C., V.O., F.K. and P.W. designed the study; S.C., C.B. and I.M. collected, analysed and interpreted data; C.B., I.M. and S.C. wrote the first version; All authors together reviewed and finalized the manuscript.
Consent for publication
Not applicable.
Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
Declaration of competing interest
Volker Otten declared following competing interests: Speakers bureau/paid presentations for company or supplier: Johnson & Johnson DePuy, Waldemar Link GmbH & Co. KG, Smith & Nephew AB. All other authors declared that they have no competing interests, or other interests that might be perceived to influence the results and/or discussion reported in this paper.
Acknowledgement
Not applicable.
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.