Clinical evaluation of the cemented Exeter Short 125 mm stem at a minimum of 3 years: A prospective cohort study

Abstract

Introduction

In 2014, Stryker introduced a modified shorter Exeter stem measuring 125 mm. Little is currently known about the functional performance of this implant in vivo. This study reports implant survival, patient reported outcome measures (PROMs), re-operation and complication rates at a minimum of 3 years for the Exeter 125 mm stem.

Methods

Prospective cohort study which followed a standardised data collection protocol. PROMs data, including the Oxford Hip Score (OHS), EQ-5D-3L and Harris Hip Score were collected at baseline (peri-operatively), 1-year post-operation and 3 years post-operation. Clinical outcomes, including revision, reoperation and rates of complications in the immediate post-operation period, and at longer term follow up were also documented.

Results

Implant survival was 100% at 3-years with no cases undergoing or planned to undergo revision surgery. At 3-years, the OHS had increased by a mean of 22.7 (S.D 10.9), the EQ-5D-3L Index by a mean of 0.467 (S.D 0.437) and the HHS by a mean of 32 (S.D 22.8) in comparison to their baseline measurements (all p < 0.001). There were no serious implant related complications such as infection, recurrent dislocation or peri-prosthetic fracture.

Conclusion

This study has demonstrated that the Exeter Short 125 mm Stem implants are a safe and effective option for total hip replacements (THR). The PROMs data obtained for the patients who received these implants were comparable to the NJR PROMs data for patients that receive a ‘standard’ THR of any size stem. With increased use of these types of implants, larger patient pools and longer periods of follow-up can further assess the longevity of the short stem implant.

1. Introduction

The Exeter polished-tapered cemented femoral stem was first introduced to clinical practice in 1970.¹ It is reported to have an overall component survivorship for aseptic loosening of 93.5% at 33 years follow up with a re-operation rate for femoral loosening of only 3.23%.² The current Exeter V40 implant has a stem length of 150 mm and neck angle of 125°. The 150 mm stem is available in a range of offsets (37.5, 44, 50 and 56 mm offset) and sizes (sizes 0 to 6).¹ In 2014, Stryker introduced a modified Exeter stem, shorter than the traditional 150 mm stem, measuring at 125 mm (Fig. 1a, Fig. 1b, Fig. 1ca,b,c). This implant intended to provide an alternative surgical solution for patient populations with a narrow femoral canal and high offsets in which standard femoral stems may be too large and risk femoral fracture.³ The Exeter Short 125 mm stem provides a surgical option with a shorter length stem while maintaining proximal component sizing across the 37.5, 44, 50 and 56 mm offset stem groups (the 30,33 and 35.5 mm stems and lower have stem lengths of <125 mm or less as standard).¹ These new Exeter short stems supplements the narrow Exeter 44 mm offset ‘00’ which has been used for cement-in-cement revisions operations and has been shown to be comparative to the performance of the standard length revision stems.⁴

Fig. 1a.

A radiographic image of a cemented Exeter Short 125 mm Stem implant with cemented Rimfit acetabular cup, 9 months post-operation.

Fig. 1b.

A radiographic image of a cemented Exeter Short 125 mm Stem implant with cemented contemporary hooded acetabular cup, 20 months post-operation.

Fig. 1c.

A radiographic image of a cemented Exeter Standard 150 mm Stem implant with cemented Rimfit acetabular cup, 13 months post-operation.

Since the Exeter Short 125 mm Stem was introduced, there have been concerns raised regarding the potential for earlier failure compared with the standard 150 mm Exeter stem implants. Short stem implants are typically used in patients with shorter and narrower femurs, so are potentially used during more difficult operations⁵ and they may be prone to implantation in a varus position.

Studies on other cemented short stem implants in Asian populations are reassuring. A 4-year post-operation analysis performed in Malaysia demonstrated no revision surgeries, no implant breakages, no peri-prosthetic fractures and excellent improvements in patients reported outcomes.⁶ A similar study performed in Hong Kong⁷ reviewed short stem implants in 42 patients with an average follow up of 9-years (range 5–12 years) and found 100% and 89% implant survival at 10 and 12-years respectively and an excellent or good Harris Hip Score (HSS) in 65% of the patients. Although a study has been performed analysing the survivorship of the short stem implant in the Australian population,¹ this study was limited by the fact that it only looked at implant survivorship and did not explore post-operative complications or patients reported outcome measures (PROMs). Our study therefore aims to analyse the outcomes of this implant further and to report implant survival as well as patient reported outcomes, re-operation and complication rates at a minimum of 3-years in a cohort of patients in whom this implant was used.

2. Methods

2.1. Design

The present study was a prospective cohort study, registered as a service evaluation with the local Research and Development department. Sixty consecutive patients who received the cemented Exeter Short 125 mm Stem implant as the femoral component during a total hip replacement (THR) were included in the study. The Exeter 125 mm stem was used alongside the 150 mm stem as part of routine care through the study period. The decision to use the stem was made intraoperatively by the treating surgeon based on the pre-operatively templating and intra-operative femoral broaching. Where it was felt the femoral canal was too narrow for a standard 150 mm stem, a 125 mm stem was used. All patients receiving the 125 m stem were included irrespective of the indication for surgery, the type of acetabular component/bearing surface used and the operating surgeon. The choice of acetabular component followed the treating surgeons standard practice and was cemented in 55 cases (92% all cemented fixation) and cementless in 5 cases (8% hybrid fixation) (Table 1). Data on implant survival, re-operation and complication rates were collected for all 60 patients at 1 and 3-years post-operation. PROMs were collected at baseline (peri-operatively), 1-year post-operation and 3-years post-operation.

Table 1.

Cup type, bearing and head (mm) used with the cemented Exeter Short 125 mm Stem.

Cup Type		Bearing		Head (mm)
	N	MoP	CoC	28	32
Hooded Contemporary (cemented)	24	24	-	-	24
Flanged Contemporary (cemented)	7	7	-	6	1
Rimfit (cemented)	24	24	-	-	24
Trident (cementless)	5	3	2	-	5
TOTAL	60	58	2	6	54

This study was conducted alongside the “Beyond Compliance”⁸ process through which the Exeter short stem was introduced into clinical practice. All surgeons within the department were already experienced users of the traditional Exeter 150 mm stem (Fig. 1c). The short 125 mm stem was available intra-operatively as an ‘option’ to use in cases in which the femoral canal was found to be narrow on pre-operative templating or tight during intra-operative femoral preparation (Fig. 1a, Fig. 1ba and b). In cases where the implant was used, the corresponding patients were informed post-operatively and counselled regarding the, “Beyond Compliance”⁸ process which included enhanced implant surveillance and follow-up as part of its monitoring processes. The service evaluation ran concurrently with the, “Beyond Compliance”⁸ process, allowing for local monitoring of implant survival, PROMs, re-operation and complication occurred. The data from this evaluation is reported in this paper.

2.2. Participants

Patients who underwent a THR procedure between September 2014 to November 2017 during which the Exeter Short 125 mm Stem was implanted were eligible to participate. All patients who received this particular implant were included without exclusion. Details of the acetabular component used, the articulation bearing, and the femoral head size were recorded for each case (Table 1). A total of 60 consecutive patients provided “Beyond Compliance”⁸ consent. Fig. 2 demonstrates the study flowchart documenting the number of patients for whom PROMs data was obtained at each stage of the study.

Fig. 2.

A CONSORT diagram of the number of patients included in the PROMs and Clinical Outcomes.

2.3. Data collection and study materials

Survival outcomes were assessed for all 60 patients using patient reports cross-referenced against clinical records and National joint registry (NJR) data. For the 3 patients that had died, the 4 patients that had withdrawn from PROMs data collection and the 5 patients that we were unable to contact at 3 years (Fig. 2) we used clinical records and National joint registry data alone. The National Joint registry collects data on all primary and revision hip procedures performed in England, Wales, Northern Ireland and the Isle on Mann. Data collection is mandatory and compliance, consent and data linkage rates for this registry are >95%. We therefore assumed that if a revision had not appeared within the NJR then the hip had not been revised.

The PROMs collected at each time-point included the Oxford Hip Score (OHS),⁹ the EQ-5D-3L,¹⁰ and the self-reported Harris Hip Score (HSS).^11,12 The number of participants providing PROMs at each time point is reported in Fig. 2. The OHS is a hip specific PROM that consists of 12 items assessing both pain and function on a 5-point Likert scale of 0–4. A score of above 41 is considered to be excellent.⁹ The EQ-5D-3L¹⁰ is a health utility measure that uses a 3-point Likert scale to assess 5 domains (mobility; self-care; usual activities; pain/discomfort; anxiety/depression). The scoring for each domain ranges from 1 to 3 (1 = no problems; 2 = some problems; 3 = extreme problems/unable). The self-reported HHS is a hip specific PROM that assesses the clinical domains of pain, function and gait/walking ability. A score of 100 is considered the best possible outcome and least level of dysfunction, whereas a score of less than 70 indicates a poor result.

Clinical outcomes (revisions, complication and re-operations) were assessed by patient reports during follow-up assessments and by cross referencing against information held in the patient's healthcare records for the 3-years post-surgery. If the patient had any subsequent complications, further surgery or diagnoses, this was also recorded.

2.4. Statistical analysis

Comparisons between the baseline PROMS to the 1 and 3 year outcomes for the OHS, EQ (5d) index and HSS were undertaken using Students t-test in SPSS (V21).¹³

3. Results

3.1. Patient population

The age of the 60 participants ranged from 37 to 88 years (Mean = 66 years, SD = 11.9), of which 18.3% were male and 81.7% female. The indication for this procedure was primarily due to a diagnosis of osteoarthritis (OA) (91.7%), with other indications including: psoriatic OA (1.7%); intracapsular hip fracture (3.3%); acetabular fracture (1.7%); and hip replacement post-perthes (1.7%).

By 1-year post-operation two patients had withdrawn from the study and a further two patients had passed away from causes unrelated to the operation. By 3-years, a further two patients had withdrawn from the study and one additional patient had passed away due to an unrelated condition (Fig. 2).

3.2. Implant survival

At the 3-year post-operative follow up none of the short stems nor any of the THR constructs had undergone revision surgery. Furthermore, no patients were on the waiting list for a planned revision procedure. The 3-year survival rate for both the femoral stem and THR constructs was therefore 100%.

3.3. PROMs

Descriptive statistics of PROMs at baseline, 1-year post-operation and 3-years post-operation are presented in Table 2.

Table 2.

Mean (M) and Standard Deviations (SD) of PROMs at baseline, 1 year post-operative and 3 years post-operative.

	Oxford Hip Score (OHS)			EQ (5D)-3L Index Score			Harris Hip Score (HHS)
	N	M	SD	N	M	SD	N	M	SD
Baseline	53	18.3	9.8	50	0.350	0.3	32	41.1	15.4
1 Year	54	39.5	10.0	53	0.780	0.3	54	73.6	18.0
P value (baseline to 1 year)	-	<0.001	-	-	<0.001	-	-	-	<0.001
3 Years	48	41.0	8.9	48	0.817	0.2	48	73.3	17.3
P value (baseline to 3 years)	-	<0.001	-	-	<0.001	-	-	-	<0.001

The OHS increased by an average gain of 21.2 (S.D 14.4) at 1-year post-operation in comparison to baseline (p < 0.001). By 3-years post-operation, patients continued to demonstrate improvements in OHS with an average gain of 22.7 (S.D 10.9) from baseline (p < 0.001).

The EQ-5D-3L Index increased by an average gain of 0.430 (S.D 0.416) at 1-year post-operation and by 3-years it demonstrated an average gain of 0.467 (S.D 0.437) (both p < 0.001). Table 3 reports the change in numbers and proportions across the five dimensions of the EQ (5D)-3L for the study cohort. Both the self-care and anxiety/depression dimensions experienced the greatest reduction in reported problems, remaining unchanged at 3 years. The usual activities dimension at 1-year and 3-years was reported to have the least reduction in reported problems. By 3-years, all five dimensions reported a >65% reduction in problems when compared to baseline.

Table 3.

Numbers and proportions reporting problems within the five EQ-5D-3L dimensions: pre-operative, 1 year post-operative and 3 years post-operative.

		Mobility N (%)			Self-Care N (%)			Usual Activities N (%)			Pain/Discomfort N (%)			Anxiety/Depression N (%)
		Pre-Op	1 Year	3 Years	Pre-Op	1 Year	3 Years	Pre-Op	1 Year	3 Years	Pre-Op	1 Year	3 Years	Pre-Op	1 Year	3 Years
Levels	1	4 (7.8)	33 (61.1)	32 (66.7)	24 (47.1)	47 (87)	41 (85.4)	5 (9.8)	29 (53.7)	32 (66.7)	12	30 (56.6)	31 (64.6)	27 (54)	47 (87)	41 (85.4)
	2	47 (92.2)	20 (37)	16 (33.3)	27 (52.9)	713	7 (14.6)	35 (68.6)	24 (44.4)	15 (31.3)	29 (56.9)	21 (39.6)	15 (31.3)	19 (38)	4 (7.4)	6 (12.5)
	3	-	1 (1.9)	-	-	-	-	11 (21.6)	1 (1.9)	1 (2.1)	21 (41.2)	2 (3.8)	2 (4.2)	48	3 (5.6)	1 (2.1)
	Total	51 (100)	54 (100)	48 (100)	51 (100)	54 (100)	48 (100)	51 (100)	54 (100)	48 (100)	51 (100)	53 (100)	48 (100)	50 (100)	54 (100)	48 (100)
	Reporting Problems*	47 (92.2)	21 (38.9)	16 (33.3)	27 (52.9)	713	7 (14.6)	46 (90.2)	25 (46.3)	16 (33.4)	50 (98.1)	23 (43.4)	17 (35.5)	23 (46)	713	7 (14.6)
1 Year	Change in numbers reporting problems	−26			−20			−21			−27			−16
	% Change reporting problems	−55.3%			−74.1%			−45.7%			−54%			−70%
	Rank of dimensions in terms of percentage changes	3			1			5			4			2
3 Years	Change in numbers reporting problems	−31			−20			−30			−33			−16
	% Change reporting problems	−66%			−74.1%			−65.2%			−66%			−70%
	Rank of dimensions in terms of percentage changes	3 =			1			4			3 =			2

By 3-years, the patient-reported HHS had increased by 32.2 (S.D 22.8) in comparison to baseline (p < 0.001). This was a minor reduction of 0.3 when compared to 1-year post-operation.

3.4. Clinical Outcomes

There were two complications reported in the immediate post-operation phase (within 30 days of surgery). They included one dislocation and one case of faecal transplant to manage a Clostridium Difficile infection that was acquired post-operatively.

At the 1-year clinical review, the majority of patients did not report any issues with the operated hip (n = 50, 89.3%). Ongoing issues with the operated hip were reported by 10% of patients, and included reports of persistent pain (n = 4, 7.1%) and trochanteric bursitis (n = 2, 3.6%).

At the 3-year clinical review, (n = 48, 80%) of patients reported no problems with their operated hip. In comparison to the 1-year follow-up, 5 (8.3%) patients reported issues with the operated hip. The numbers of those with persistent pain had decreased to one patient (1.7%), though those suffering from trochanteric bursitis had doubled to four (6.7%).

Between 1-year and 3-years, additional issues reported by patients, unrelated to the operated hip, included: OA of another joint (n = 5, 8.3%); lower back pain (n = 2, 3.3%); contralateral trochanteric bursitis (n = 1, 1.7%). In addition, one patient reported an issue with bilateral trochanteric bursitis.

4. Discussion

The present study found that no patients who received the Exeter Short 125 mm Stem were revised, suffered an implant related infection or peri-prosthetic fracture in the first 3-years following surgery. The survival rate for the short stem used within this study was 100% at 3-years. These findings are consistent with a similar study performed in Australia¹ comparing short stem implants to that of the standard 150 mm stem which found 7-year revision rates of 3.4% in their short stem cohort and 3.5% in their standard stem cohort.

A study in Hong Kong¹⁴ involving patients of Chinese ethnicity demonstrated the consequences of using standard sized implants in patients who have a smaller femoral canal. They found that when standard stems were used in patients with a narrow femoral canal, 36% of the patients had a cement mantle that was inadequate with depths of less than 2 mm. Some cases required intramedullary reaming for a standard stem to fit which reduced the femoral bone stock. When the combination of reaming and an inadequate cement mantle was investigated, the rate of implant failure was 100% by 9 years. The overall revision rate at 13-years due to aseptic loosening when using oversized implants was much higher (22%) when compared to cases using an implant that was an appropriate size for the patient (1.6%).

A benefit of this study was that both clinical outcomes and PROMs data were analysed in contrast to previous studies that have focused on implant survivorship alone.^1,15 This provides a better understanding of not only the outcome of the implant itself but also of the patient's functional status after receiving it. This is important to consider alongside implant survival because, although patients may not undergo further procedures, they may have low rates of satisfaction due to poor functional recovery. The present study used three different PROMs scores allowing direct comparison to other similar studies and registries that use similar measures. The OHS⁹ is commonly used as part of the National Joint Registry for England, Wales, Northern Ireland and the Isle of Mann (NJR).¹⁶ The patients in this study demonstrated an significant improvement in their OHS score at both 1 and 3 years compared to baseline. The observed improvement at 3 years(22.7)is greater than the minimally clinically important difference (MCID) for the OHS¹⁷ and is similar to the average OHS improvement reported by the NJR PROMs programme which reports an OHS average gain of 22.1 at 6 months post-operation.¹⁶

The EQ-5D-3L scores for all five components of this measure showed a significant reduction in problems reported, with self-care and anxiety related problems reported as the most improved. The EQ-5D-3L index scores demonstrated a significant improvement at 1 and 3 years compared to baseline and were higher than the NJR reported data which reported an increase of 0.449 from baseline at 6 months using the same score.¹⁶ It is also higher than Eq (5D) index reported from another UK based study, which assessed EQ-5D scores for short stem implants post-operatively with follow up of between 24 and 39 months.¹⁸ Although HHS is not used as frequently as the OHS in UK practice, it has been found that these scores show a good level of correlation and that the two can be directly compared.^19,20 The HHS scores in this study also demonstrated a significant improvement at the post-operative time points and were comparable to other large-scale studies looking at the outcomes of standard THRs at 1-year post-operation.²¹

While no serious implant related complications occurred, there were a small number of complications that occurred in the immediate post-operation period and issues that were recorded at the subsequent clinical follow-up appointment. One patient had a dislocation of the joint in the immediate post-operation period, which required return to theatre for closed reduction with no further dislocations or complications related to the operated joint. A meta-analysis²² comparing short stem implants to standard stem implants found that the most common surgery related complications were recurrent dislocation, deep venous thromboembolism, pulmonary embolism and peri-prosthetic infection; none of which were reported by the patients in this study. The meta-analysis also reported on an increased occurrence of thigh pain with those who had received the short stem implant. Although thigh pain was not specifically reported within the present study, a small number of patients reported trochanteric bursitis.

A limitation of this study is the small sample size. As previously discussed, the rate of revision for the short stem implant has been shown from other larger studies to be low^1,6 and so to establish the true revision rate much higher numbers would be required. It is also important to note that follow-up has been completed to 3-post-operation years only and the survivorship for implants such as this is typically much longer.⁷ To obtain a true impression of longevity of the implant and subsequent revision rates, the follow-up of patients should continue to account for this.

We used a number of methods to verify implant survival including patient reports, clinical records and NJR data. For the majority of participants we were able to use all 3 data sources, however, for patients that had died, those that withdrew and those that were uncontactable at 3 years (20% of the cohort) we were only able to use the clinical records and NJR data. While it is conceivable we may have missed a revision using this method, we feel this is unlikely given the mandation of NJR recording and the quality of the data within this national registry.

Short stem implants provide an alternative and viable prosthesis which is particularly useful in those with a narrow femoral canal in whom a longer stem may risk an intra-operative fracture. With increased use of these types of implants, larger patient pools and longer periods of follow-up can further assess the longevity of the short stem implant.

5. Conclusion

This study has demonstrated that the Exeter Short 125 mm stem implants are a safe and effective option for THR. The PROMs data obtained for the patients who received these implants were comparable to the published data relating to patients that receive a THR of any size stem suggesting clinical outcomes are broadly equivalent. There was no increased risk of a serious complication such as peri-prosthetic fracture, loosening or infection for short stem implants nor were there any cases of revision.

Declaration of competing interest

The authors declare there is no conflict of interest.