Abstract
Purpose
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to systematically review comparative studies reporting revision rates, clinical outcomes, or radiographic outcomes of total hip arthroplasty (THA) using collared versus collarless conventional-length uncemented hydroxyapatite (HA)-coated stems.
Methods
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In adherence with PRISMA guidelines, a literature search was performed on Medline, Embase, and Scopus. Comparative clinical studies were eligible if they reported outcomes of collared versus collarless uncemented HA-coated stems for primary THA. Two reviewers screened titles, abstracts, and full-texts to determine eligibility; then performed data extraction; and assessed the quality of studies according to Joanna Briggs Institute (JBI) checklist.
Results
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The search returned 972 records, 486 were duplicates, and 479 were excluded after title/abstract/full-text screening. Three further studies were included from the references of eligible studies and from discussions with subject matter experts, resulting in 11 included studies. The JBI checklist indicated six studies scored ≥7 points and four studies ≥4 points. Pooled data revealed collared stems had significantly lower revision rates (OR = 0.45; 95% CI = 0.31–0.64) and subsidence (MD = −1 mm; 95% CI = −1.6–-0.3), but no significant difference in intraoperative complication rates (OR = 0.94; 95% CI = 0.67–1.32) in the short term to mid-term. Unpooled data indicated that collared stems provide equivalent survival, equivalent or better outcomes, and equivalent or lower complication rates.
Conclusion
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In comparative studies, collared stems have lower revision rates than collarless stems, as well as equivalent or better clinical and radiographic outcomes. Differences could be due to a protective effect that the collar offers against subsidence, particularly in undersized or misaligned stems. Further studies are warranted to confirm long-term results and better understand differences between registry data and clinical studies.
Introduction
Both collared and collarless uncemented femoral stems demonstrated excellent long-term survival and patient-reported outcomes for primary total hip arthroplasty (THA), though there is no clear consensus to date regarding the superiority of one version over the other, or regarding the potential benefits and drawbacks of collars. The Corail stem is the most widely implanted uncemented stem (1, 2, 3), with ample survival data calculated from large cohorts: while the Australian Joint Replacement Registry indicates no significant differences in revision rates at 13 years between the collared and collarless versions (2.4–3.8%) (4), the Norwegian Arthroplasty Register indicates significantly lower revision rates at 10 years for the collared version compared to the collarless version (1.0% versus 2.4%) (5).
Most recent clinical and biomechanical studies that compared collared versus collarless stems demonstrated that the collar could reduce complications (6, 7, 8), migration or subsidence (9, 10, 11), and radiolucent lines or pedestals (12, 13), as well as improve axial and rotational stability (14, 15). While most of these observations are either asymptomatic (not clinically relevant) or theoretical (in vitro but not confirmed clinically), collared stems are now deemed to provide extra safety, particularly in patients with unusual femoral morphology or in challenging surgical circumstances.
The purpose of this meta-analysis was to synthesize, critically appraise and systematically review the literature for comparative studies reporting on revision rates, clinical outcomes, or radiographic outcomes of THA using collared versus collarless conventional-length uncemented hydroxyapatite (HA)-coated stems. The hypothesis was that collared stems provide lower revision rates and better clinical and radiographic outcomes compared to collarless stems, in which case surgeons would have clearer evidence for routine use of one stem design.
Materials and methods
The protocol for this systematic review was submitted to PROSPERO prior to commencement (registration number CRD42022310901) and follows the guidelines established by the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) (16).
Search strategy
The authors conducted a structured electronic literature search on April 5, 2022, using the Medline (PubMed), Embase, and Scopus databases, applying the keywords presented in the Supplemental file (see section on supplementary materials given at the end of this article). After removal of duplicate records, two researchers (TK, ED) each screened the titles and abstracts to determine the suitability for the review against predefined eligibility criteria.
Inclusion criteria
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Prospective or retrospective comparative studies that report on stem survival, stem revisions, clinical outcomes, or radiographic outcomes of collared versus collarless conventional-length uncemented HA-coated stems for primary THA. The collared and collarless stems had to have the same coating and design, with the exception of the collar.
Exclusion criteria
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Studies that did not report on clinical or radiographic outcomes of collared versus collarless stems;
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Studies on uncemented stems that are not coated in HA;
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Studies on cemented, short, or long stems;
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Non-comparative studies or case series;
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Case reports, reviews, editorials, expert opinions, letters to the editor, or conference proceedings;
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Studies that reported on animals, in vitro experiments, or in silico simulations;
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Studies written in languages other than English, to avoid translation errors.
Study selection
Full-text review of studies meeting the criteria in the initial screening was carried out by two researchers (TK, ED) and any disagreement about the final eligibility of studies was resolved by review and consensus, or by involving a third researcher (SRP). Subject matter experts (TASS, JPV, MPB), consisting of two active and one retired high-volume hip surgeons, were consulted to further establish relevant studies not captured by the database searches.
Data extraction and quality assessment
Data extraction was performed by two researchers independently and their results compared to ensure accuracy. Where there was disagreement between the researchers, consensus was achieved by discussion and review, or by involving a third researcher. The following data was extracted from the included studies: author(s), journal, year of publication, ethical approval, and conflicts of interest. Cohort characteristics were retrieved, including indication for surgery, number of patients, sex, age, and body mass index (BMI). Follow-up time, clinical outcomes, radiographic outcomes, complications, reoperations, revisions, and survival were retrieved.
When relevant data was missing from the included articles, the authors were contacted by email, LinkedIn, and Research Gate, each up to three times to request missing data.
Methodological quality of the eligible studies was assessed by two researchers according to the Joanna Briggs Institute (JBI) clinical appraisal tools for cohort studies (17). The cohort study checklist was modified by removing question 6, ‘Were the groups/participants free of the outcome at the start of the study (or at the moment of exposure)?’ as it was not applicable for any of the included studies. Any discrepancies in appraisal were resolved through discussion and consensus between the two researchers, or by involving a third researcher.
Statistical analysis
Outcomes that were consistently reported in two or more studies were tabulated. Binary outcomes were reported as proportions. Continuous outcomes were reported as means, standard deviations, and ranges. Outcomes that were consistently reported in three or more studies were pooled and presented in forest plots, indicating odds ratios (OR) for binary outcomes and mean differences (MD) for continuous outcomes. Heterogeneity was evaluated by visual inspection of forest plots and by using the I 2 statistic and its connected χ 2 test, to provide a measure of the degree of inconsistency across studies (18). Pooled estimates of OR and their 95% confidence intervals (95% CI) were calculated via Freeman–Tukey double arcsine transformation using inverse-variance weighting within a random-effects model framework. Test statistics and 95% CI were adjusted using the Hartung–Knapp method. In the case of zero cells (i.e. no outcome events), a continuity correction was applied by adding 0.5 to all cells of the contingency table. Pooled estimates of MD and their 95% CI were calculated using a random-effects model framework. In cases where the range was available, but the standard deviation was not, the latter was calculated according to Hozo et al. (19). P-values <0.05 were considered statistically significant. Statistical analyses were performed using R version 4.1.3 (R Foundation for Statistical Computing, Vienna, Austria) using the meta package.
Results
Literature search
The systematic search returned 972 records, of which 486 were duplicates, leaving 486 records for screening. A total of 446 records were excluded by examining their titles and/or abstracts, leaving 40 records for full-text review. Twenty-nine studies were excluded after full-text review: ten because they reported on non-conventional-length (short, long) or non-HA-coated stems (20, 21, 22, 23, 24, 25, 26, 27, 28, 29), eight because they compared collared versus collarless stems with different designs or coatings (30, 31, 32, 33, 34, 35, 36, 37), five because they were letters to the editor, technical notes, or correspondence (38, 39, 40, 41, 42), three because they did not report on any outcomes (14, 43, 44), one because it compared hemiarthroplasty versus THA (45), one because it was a cadaveric study (46), and one because it was a non-comparative study (47). A further three articles were excluded because the outcomes of interest were not presented separately for collared versus collarless stems (the authors were contacted at least three times but none responded) (4, 6, 48).
Full-text screening left eight eligible studies (5, 9, 10, 11, 12, 13, 49, 50), and by checking their references, two more relevant studies were identified (51, 52). These two studies did not appear in the original search; one was not indexed in any of the databases searched (52), while the other did not contain the keywords ‘hip replacement’ or ‘hip arthroplasty’ (51). A further study (53) was identified from discussion with subject experts (TASS, JPV, MPB); this study did not appear in the original search because the subgroup analysis comparing collared versus collarless stems was not mentioned in the abstract. Therefore, 11 studies (5, 9, 10, 11, 12, 13, 50, 51, 52, 53, 54) were included in this systematic review, all of which reported at least one clinical or radiographic outcome of primary THA using collared versus collarless conventional-length uncemented HA-coated stems (Fig. 1).
Flowchart of the study selection procedure.
Citation: EFORT Open Reviews 9, 4; 10.1530/EOR-22-0091
Characteristics of the included studies
The eleven included studies reported on a combined total of 33 840 THA procedures performed between 1986 and 2019 in Europe (n = 10) and North America (n = 1) (Table 1). Mean age of the included patients was reported in all but two studies and ranged between 51 and 68 years (Table 2). In all studies, the stem implanted was the Corail (DePuy Synthes, West Chester, PA, USA) (Table 2). The Corail stem is straight and tapered, with a quadrangular cross-section, and it is classified as a B2 stem according to Radaelli et al. (55). It is available in a variety of options and offsets (standard offset, high offset, and coxa vara); where studies presented data separately for standard offset stems, data for other stem models were not presented.
Characteristics of the included studies.
| Reference | COIs | Funding | Ethical approval | Country | Study design | Institution | Time period |
|---|---|---|---|---|---|---|---|
| Dammerer et al. (49) | N | N | Y | Austria | Retrospective | Monocentric | 2013–2017 |
| Melbye et al. (5) | N | N | Y | Norway | Multicentric | 2008–2018 | |
| Wirries et al. (11) | N | N | Y | Germany | Retrospective | ||
| Karayiannis et al. (12) | Y | Y | Ireland | Retrospective | April 2006–August 2009 | ||
| Magill et al. (13) | Y | Y | Ireland | 2005–2010 | |||
| Perelgut et al. (9) | Y | N | Y | Canada | RCT | Monocentric | January 2018–July 2019 |
| Ries et al. (10) | N | N | Y | Germany | Retrospective | Monocentric | August 2009–December 2010 |
| Jacquot et al. (53) | Y | N | Y | France | Retrospective | Monocentric | 1986–1990 |
| Al-Najjim et al. (51) | N | Y | UK | Retrospective | Monocentric | August 2007–February 2010 | |
| Magill et al. (50) | Y | Y | Ireland | Retrospective | Monocentric | August 2005–March 2015 | |
| Sudhahar et al. (52) | UK | Retrospective | November 2003–February 2006 |
COIs, conflicts of interest; N, no; Y, yes; RCT, randomized controlled trial.
Patient demographics in the included studies.
| Study/Subgroup | Number of | Females | Age | BMI | |||||
|---|---|---|---|---|---|---|---|---|---|
| Hips | Patients | Mean ± s.d. | Range | Mean ± s.d. | Range | Surgical approach | Type pf stem | ||
| Dammerer et al. (49) | 105 | 60 (57%) | 68 | 22–91 | 27 | 17–51 | |||
| Collared | 85 | Direct anterior or | Corail (KA, KHOA, KLA) | ||||||
| Collarless | 24 | Anterolateral | (KS, KHO) | ||||||
| Melbye et al. (5) | |||||||||
| Collared | 10 335 | 7352 (71%) | 67 ± 11 | Anterior, lateral | Corail (KA) | ||||
| Collarless | 20 871 | 14 271 (68%) | 64 ± 11 | Posterior | (KS) | ||||
| Wirries et al. (11) | 68±12 | 34–90 | 27 ± 5 | 19–44 | |||||
| Collared | 146 | 146 | 98 (67%) | Direct anterior | Corail (KA, KHOA) | ||||
| Collarless | 40 | 40 | 20 (50%) | Anterolateral | (KS, KHO) | ||||
| Karayiannis et al. (12) | |||||||||
| Collared | 50 | Posterior | Corail (KA) | ||||||
| Collarless | 89 | (KS) | |||||||
| Magill et al. (13) | |||||||||
| Collared | 161 | 135 (84%) | 64 | 58–68 | Posterior | Corail (KA) | |||
| Collarless | 159 | 102 (64%) | 65 | 62–68 | (KS) | ||||
| Perelgut et al. (9) | |||||||||
| Collared | 23 | 9 (39%) | 64 ± 8 | 29 ± 5 | Direct anterior | Corail (KA, KHOA) | |||
| Collarless | 26 | 11 (42%) | 65 ± 8 | 30 ± 5 | (KS, KHO) | ||||
| Ries et al. (10) | |||||||||
| Collared | 32 | 32 | 24 (75%) | 68 ± 10 | 28 ± 6 | Anterolateral | Corail (KA, KLA) | ||
| Collarless | 199 | 199 | 106 (53%) | 64 ± 9 | 29 ± 6 | Posterior | (KS, KHO) | ||
| Jacquot et al. (53) | 320 | 153 (48%) | 63 ± 11 | 20–89 | 26 ± 4 | 16–41 | Anterolateral | Corail | |
| Collared | 77 | ||||||||
| Collarless | 270 | ||||||||
| Al-Najjim et al. (51) | Corail | ||||||||
| Collared | 66 | 62 | 38 (60%) | 68 | 40–88 | 28 ± 5 | |||
| Collarless | 55 | 51 | 28 (52%) | 66 | 38–77 | 28 ± 4 | |||
| Magill et al. (50) | Posterior | Corail (KA) | |||||||
| Collared | 917 | (KS) | |||||||
| Collarless | 133 | ||||||||
| Sudhahar et al. (52) | |||||||||
| Collared | 43 | 41 | 51 | 31–68 | Lateral | Corail | |||
| Collarless | 39 | 37 | 53 | 40–68 | Lateral | ||||
Quality assessment using the JBI 10-point checklist indicated that seven studies (5, 9, 12, 13, 50, 51, 53) scored ≥7 points, four studies (10, 11, 52, 54) scored 4–6 points, and no studies scored ≥3 points (Table 3).
Quality assessment of the included studies.
| Q1 | Q2 | Q3 | Q4 | Q5 | Q6 | Q7 | Q8 | Q9 | Q10 | |
|---|---|---|---|---|---|---|---|---|---|---|
| Dammerer et al. (49) | Yes | Yes | Yes | Yes | No | Yes | Yes | No | No | No |
| Melbye et al. (5) | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | NA | Yes |
| Wirries et al. (11) | Yes | Yes | Yes | No | No | Yes | No | Yes | NA | No |
| Karayiannis et al. (12) | Yes | Yes | Yes | Yes | No | Yes | Yes | Yes | No | Yes |
| Magill et al. (13) | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | NA | Yes |
| Perelgut et al. (9) | Yes | Yes | Yes | Yes | No | Yes | Yes | NA | NA | Yes |
| Ries et al. (10) | Yes | Yes | Yes | Yes | No | Yes | No | Yes | NA | No |
| Jacquot et al. (53) | Yes | Yes | Yes | No | No | Yes | Yes | Yes | Yes | Yes |
| Al-Najjim et al. (51) | Yes | Yes | Yes | No | No | Yes | Yes | Yes | NA | Yes |
| Magill et al. (50) | Yes | Yes | Yes | Yes | No | Yes | Yes | No | Yes | Yes |
| Sudhahar et al. (52) | NA | Yes | Yes | No | No | Yes | Yes | Yes | NA | NA |
NA, not applicable.
Q1) Were the two groups similar and recruited from the same population? Q2) Were the exposures measured similarly to assign people to both exposed and unexposed groups? Q3) Was the exposure measured in a valid and reliable way? Q4) Were confounding factors identified? Q5) Were strategies to deal with confounding factors stated? Q6) Were the outcomes measured in a valid and reliable way? Q7) Was the follow up time reported and sufficient to be long enough for outcomes to occur? Q8) Was follow-up complete, and if not, were the reasons to loss to follow-up described and explored? Q9) Were strategies to address incomplete follow up utilized? Q10) Was appropriate statistical analysis used?
Clinical scores and patient-reported outcomes
Postoperative WOMAC was reported in two studies, one favored collared stems (97 ± 5 vs 91 ± 12, P = 0.036) (9), while the other found no difference (97 ± 3 vs 97 ± 3) (11) (Table 4). Postoperative Harris hip score (HHS) was reported in one study, which tended to favor collared stems (87 ± 11 vs 80 ± 16, P = 0.084) (53). Postoperative SF-12 was reported in one study, with physical component scores favoring collared stems (55 ± 3 vs 50 ± 8, P = 0.016), but no significant difference in mental component scores (54 ± 9 vs 57 ± 7, P = 0.196) (9). Postoperative UCLA activity score was reported in one study, with no significant difference (7 ± 2 vs 7 ± 2, P = 0.655) (9).
Clinical data of the included studies.
| Study/sub-group | Follow-up (months) | Post-op WOMAC Score | Complication rate, n (%) | Revision rate, n (%) |
|||
|---|---|---|---|---|---|---|---|
| Mean ± s.d. | Range | Mean ± s.d. | Range | Intra-op | Early post-op | ||
| Melbye et al. (5) | |||||||
| Collared | 72 | 80(1%) | |||||
| Collarless | 48 | 354(2%) | |||||
| Wirries et al. (11) | |||||||
| Collared | 12 | 97±3 | 78–100 | ||||
| Collarless | 12 | 97±3 | 85–100 | ||||
| Perelgut et al. (9) | |||||||
| Collared | 12 | 97±5* | 0 (0%) | ||||
| Collarless | 12 | 91±12* | 0 (0%) | ||||
| Ries et al. (10) | 7 ± 6 | ||||||
| Collared | >2 | 0 (0%) | 0 (0%) | ||||
| Collarless | >2 | 3 (2%) | 0 (0%) | ||||
| Jacquot et al. (53) | 27 ± 1 | 25–30 | |||||
| Collared | 1 (1%)** | ||||||
| Collarless | 11 (4%)** | ||||||
| Al-Najjim et al. (51) | |||||||
| Collared | 12 | 8 (12%) | 1 (2%) | ||||
| Collarless | 12 | 4 (7%) | 1 (2%) | ||||
| Magill et al. (50) | |||||||
| Collared | (60–90) | 0 (0%) | |||||
| Collarless | (60–90) | 3 (2%) | |||||
| Sudhahar et al. (52) | 3 (4%) | ||||||
| Collared | (2–17) | 0 (0%) | 0 (0%) | ||||
| Collarless | (2–27) | 0 (0%) | 2 (5%) | ||||
*Significant difference between collared and collarless stems reported by study; **No significant difference between collared and collarless stems reported by study.
Complications, revisions, and survival
Intraoperative complication rates were reported in three studies (9, 10, 52); meta-analysis on pooled data found no significant difference (OR = 0.94; 95% CI = 0.67–1.32) (Fig. 2). Revision rates were reported in six studies (5, 10, 50, 51, 53); meta-analysis on pooled data favored collared stems (OR = 0.45; 95% CI = 0.31–0.64) (Fig. 3). Since the study by Melbye et al. (5) had a weight of 95.4%, a sensitivity analysis was performed excluding Melbye et al., with pooled data tending to favor collared stems (OR = 0.35; 95% CI = 0.04–3.05) (Fig. 4).
Forest plot presenting odds ratios of intraoperative complication rates for collared versus collarless stems, including studies by Perelgut et al. (9), Ries et al. (10), and Sudhahar et al. (52).
Citation: EFORT Open Reviews 9, 4; 10.1530/EOR-22-0091
Forest plot presenting odds ratios of revision rates for collared versus collarless stems, including studies by Melbye et al. (5), Ries et al. (10), Jacquot et al. (53), Al-Najjim et al. (51), Magill et al. (50), and Sudhahar et al. (52).
Citation: EFORT Open Reviews 9, 4; 10.1530/EOR-22-0091
Sensitivity analysis excluding the study of Melbye et al. and presenting odds ratios of revision rates for collared versus collarless stems, including studies by Ries et al. (10), Jacquot et al. (53), Al-Najjim et al. (51), Magill et al. (50), and Sudhahar et al. (52).
Citation: EFORT Open Reviews 9, 4; 10.1530/EOR-22-0091
Early postoperative complication rates were reported in two studies (51, 52), but only one study presented complications separately for collared versus collarless stems, and tended to favor collarless stems (12% vs 7%) (51) (Table 4). Late postoperative complication rates were reported in one study, which found no difference (0% vs 0%) (52). Stem survival was reported in two studies (5, 50), but only one presented survival separately for collared versus collarless stems, and found no difference (99% vs 98%) in stem survival at 10 years for any reason as endpoint (5).
Radiographic outcomes
Mean subsidence was reported in four studies; meta-analysis on pooled data favored collared stems (MD = −1 mm; 95% CI = −1.6–−0.3) (9, 11, 51, 56) (Fig. 5). Mean stem misalignment was reported in two studies, both of which tended to favor collared stems (0–2.4º vs 0.6–2.9º) (9, 11) (Table 5). Presence of radiolucent lines was reported in three studies, two of which tended to favor collared stems (2–33% vs 29–38%) (12, 13), while the other found no difference (0% vs 0%) (51). Presence of pedestal formation was reported in one study, which found no difference (0% vs 0%) (52).
Forest plot presenting mean differences in postoperative subsidence for collared versus collarless stems, including studies by Dammerer et al. (49), Wirries et al. (11), Perelgut et al. (9), and Al-Najjim et al. (51).
Citation: EFORT Open Reviews 9, 4; 10.1530/EOR-22-0091
Radiographic data of the included studies.
| Study/subgroup | Mean follow-up (months) | Subsidence (mm) | Stem misalignment (º) | Prevalence of RL, n (%) | ||
|---|---|---|---|---|---|---|
| Mean ± s.d. | Range | Mean ± s.d. | Range | |||
| Dammerer et al. (49) | 25 (8–57) | |||||
| Collared | 1.6 | 0.0–9.9 | ||||
| Collarless | 2.2 | 0.0–12.1 | ||||
| Wirries et al. (11) | ||||||
| Collared | 12 | 0.8 ± 0.7* | 0.0–4.0 | 2.4 ± 1.6 | 0.0–9.5 | |
| Collarless | 12 | 1.7 ± 1.9* | 0.0–10.0 | 2.9 ± 1.5 | 0.2–6.2 | |
| Karayiannis et al. (12) | ||||||
| Collared | >120 | 1 (2%)† | ||||
| Collarless | >120 | 26 (29%)† | ||||
| Magill et al. (13) | ||||||
| Collared | 65 (61–70) | 53 (33%)‡ | ||||
| Collarless | 84 (72–84) | 61 (38%)‡ | ||||
| Perelgut et al. (9) | ||||||
| Collared | 12 | 1.5 ± 2.2 | 0.0 ± 0.4 | |||
| Collarless | 12 | 3.8 ± 3.7 | 0.6 ± 1.6 | |||
| Al-Najjim et al. (51) | ||||||
| Collared | 12 | 0.71 ± 0.9* | 0 (0%)§ | |||
| Collarless | 12 | 1.62 ± 2.1* | 0 (0%)§ | |||
| Sudhahar et al. (52) | ||||||
| Collared | 2–17 | 1.0–6.0 | 1.0–6.0 | |||
| Collarless | 2–27 | 1.0–15.0 | 1.0–4.0 | |||
*Significant difference between collared and collarless stems reported by study; †Significant radiolucent lines (RL) included at least one of the following: (i) any line greater than 1 mm in width; (ii) lines in two or more complete Gruen zones; (iii) any line in Gruen zone 7; ‡No threshold specified; §Any liner greater than 2 mm in width.
Discussion
This meta-analysis included eleven comparative clinical studies that reported outcomes of THA using collared versus collarless conventional-length uncemented HA-coated stems, all of which concluded that collared stems were preferable over collarless stems. The pooled data including all six studies that reported revision rates revealed that collared stems have significantly lower revision rates than collarless stems, but when removing the registry study with the largest cohort, the difference between groups was not significant. In addition, the unpooled data indicated that collared stems provide equivalent survival, equivalent or better clinical and radiographic outcomes, and equivalent or lower complication rates. These findings partly support our hypothesis, as collared stems provide lower revision rates and equivalent or better clinical and radiographic outcomes, suggesting that surgeons should consider their routine use. The present findings are in contrast to two registry studies (4, 57) on the Corail stem, that did not meet the criteria for inclusion in this meta-analysis; both performed regression analyses and concluded that the presence or absence of a collar did not significantly influence revision rates, though these studies did not report the numbers or incidences of revisions for each stem model, and could therefore not be included in the present meta-analysis.
The pooled data in the current meta-analysis revealed a significant difference in odds of revision of collared stems, which were less than half the odds of revision of collarless stems (OR = 0.45; 95% CI = 0.31–0.64). Of the six studies (5, 10, 50, 51, 53) from which data was pooled, the registry study by Melbye et al. (5) had a weight of 95%, because it accounted for 31 206 of the 33 037 patients. For this reason, a sensitivity analysis was performed excluding data from Melbye et al., and although the odds ratio decreased further, it was no longer statistically significant (OR = 0.35; 95% CI = 0.04–3.05). This observation illustrates how certain phenomena based on rare events, such as revision rates, might only be ascertained using large cohort studies such as those based on registry data. Of the other studies that reported revision rates, Magill et al. (50) identified three cases of aseptic loosening, but it is interesting to note that 14 of the 15 revised stems for aseptic loosening were undersized, so the failure could be attributed to technical error rather than absence of a collar; in which case the collar may offer a protective effect in cases with undersized stems. Furthermore, Sudhahar et al. (52) reported two stem revisions for instability related to subsidence of 13 mm and 15 mm in the collarless group, but they did not specify if these stems were osseointegrated. Furthermore, the pooled data in the current meta-analysis revealed a significant mean difference in subsidence between the two groups, based on data from four studies, with collared stems resulting in less subsidence than collarless stems (MD = −1 mm; 95% CI = −1.6–−0.3) (9, 11, 51, 56). The overall lower revision rates seen on collared stems could be due to a protective effect that the collar offers against subsidence, particularly in cases with undersized or misaligned stems.
The present meta-analysis focused on cementless HA-coated stems. HA-coated stems have demonstrated good osseointegration and satisfactory clinical outcomes (2, 53, 58, 59), although a few recent studies have found no differences in clinical or radiographic outcomes between stems coated with and without HA (60, 61). Furthermore, a meta-analysis (62) aimed at comparing the effectiveness of HA-coated versus non-HA-coated stems in primary THA analyzed seven randomized controlled trials including 792 hips and concluded that the use of HA-coated stems had no clinical or radiological benefits.
As mentioned previously, two registry studies (4, 57) of the Corail stem have found no associations between revision rates and the presence or absence of a collar; although neither of these studies met the inclusion criteria for inclusion in the present meta-analysis, because they did not report revision rates separately for collared versus collarless stems. The study based on the National Joint Registry for England and Wales (57) examined 35 386 primary THAs implanted with the Corail stem, of which 69% were collarless. The authors reported a total revision rate of 2.4% at 5 years (95% CI, 2.02–2.79%), but regression analyses found no associations between the risk of revision and the presence of a collar. Furthermore, the study based on the Australian Joint Replacement Registry (4) examined 41 265 primary THAs implanted with the Corail stem, of which 54% were collarless, to investigate whether revision rates were associated with stem size. The authors found that the cumulative percent revision at 13 years was 7.7% (95% CI = 5.5–10.7) for stem sizes 8 and 9 and 3.0% (95% CI, 2.4–3.8) for sizes 10–20 (P < 0.001). However, when the revision rates of collared versus collarless femoral stems were compared between the two size groups, the presence of a collar made no difference to the revision rates.
Some surgeons are concerned that collared stems could lead to stem undersizing and/or misalignment, whereas recent evidence revealed more radiolucencies and subsidence with collarless stems (11, 12, 13, 63). Furthermore, a recent indirect meta-analysis including both comparative and non-comparative studies on collared and collarless stems for THA, implanted by direct anterior approach, found that collared stems had significantly lower risk of complications (0.02; 95% CI = 0.001–0.30), and tended to have lower risk of revisions, although this was not statistically significant. In contrast, the current meta-analysis has demonstrated that compared to collarless stems, revision rates were significantly lower for collared stems, that stem alignment was similar (or better), and that the rates of radiolucent lines were similar (or better). A potential drawback of collared stems may be revision surgery, as a well-fixed collared stem could be more challenging to revise than a well-fixed collarless stem, because the collar obstructs insertion of blades or osteotomes along the bone-implant interface (64). Nonetheless, this systematic review only focused on primary THA, and therefore cannot address this question.
The current meta-analysis has a number of limitations. First, the eleven included studies all implanted the Corail stem; therefore, one should be careful when extrapolating findings of this systematic review to other uncemented HA-coated stem designs. Second, the Corail stem is available in a variety of options and offsets; to reduce heterogeneity, the current study focused on reporting outcomes for standard offset stems only; however, this was not possible if studies did not separate outcomes by stem model. Subgroup analysis of high-offset and/or coxa vara stems was not feasible, since only two studies reported outcomes separately for these stem models. Third, the analysis did not account for the morphology of the femur (Dorr type), which may have an influence on short and/or long-term outcomes. Fourth, the comparative studies included did not always present outcomes at the same follow-up time for the collared and collarless groups. Fifth, there was heterogeneity in terms of follow-up across studies, with minimum follow-up varying between 2 and 120 months. Furthermore, the mean follow-up was ≥2 years in only 4 of the 11 included studies, therefore it is not possible to draw solid conclusions on differences in revision rates at mid-term to long term. Sixth, certain studies with relevant outcomes could not be included in the meta-analysis, because the necessary data was not reported separately for collared versus collarless stems. The authors of the current meta-analysis contacted the authors of the relevant clinical studies at least three times but received no response.
Conclusion
This meta-analysis on conventional-length uncemented HA-coated stems revealed that collared stems have lower revision rates than collarless stems in comparative studies, as well as equivalent or better clinical and radiographic outcomes. The differences could be due to a protective effect that the collar offers against subsidence, particularly in cases with undersized or misaligned stems. Further studies are warranted to confirm these results in the long-term, as well as to better understand the differences between registry data and clinical studies.
Supplementary materials
This is linked to the online version of the paper at https://doi.org/10.1530/EOR-22-0091.
ICMJE Conflict of Interest Statement
TASS, JPV, and MB have received royalties and consultancy fees from DePuy-Synthes. SRP, ED, TK, and MS declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the study reported.
Funding Statement
This work was supported by ‘GCS Ramsay Santé pour l’Enseignement et la Recherche’, which provided funding for data collection and manuscript preparation.
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