The Journal of Arthroplasty xxx (2014) xxx–xxx
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Risk factors for Total Hip Arthroplasty Aseptic Revision Monti Khatod, MD a, Guy Cafri, PhD b, Robert S. Namba, MD c, Maria C.S. Inacio, PhD b, Elizabeth W. Paxton, MA b a b c
Department of Orthopaedic Surgery, Southern California Permanente Medical Group, Los Angeles, California Surgical Outcomes and Analysis Unit, Clinical Analysis, Southern California Permanente Medical Group, San Diego, California Department of Orthopaedic Surgery, Southern California Permanente Medical Group, Orange County, California
a r t i c l e
i n f o
Article history: Received 2 December 2013 Accepted 20 January 2014 Available online xxxx Keywords: aseptic revisions total hip arthroplasty Total Joint Replacement Registry risk factors
a b s t r a c t The purpose of this study was to evaluate patient, operative, implant, surgeon, and hospital factors associated with aseptic revision after primary THA in patients registered in a large US Total Joint Replacement Registry. A total of 35,960 THAs registered from 4/2001–12/2010 were evaluated. The 8-year survival rate was 96.7% (95% CI 96.4%–97.0%). Females had a higher risk of aseptic revision than males. Hispanic and Asian patients had a lower risk of revision than white patients. Ceramic-on-ceramic, ceramic-on-conventional polyethylene, and metal-on-conventional polyethylene bearing surfaces had a higher risk of revision than metal-on-highly cross-linked polyethylene. Body mass index, health status, diabetes, diagnosis, fixation, approach, bilateral procedures, head size, surgeon fellowship training, surgeon and hospital volume were not revision risk factors. © 2014 Elsevier Inc. All rights reserved.
Total hip arthroplasty is a successful procedure resulting in reduced pain and stiffness as well as improved function [3,39]. The majority of THA procedures are successful but some fail as a result of aseptic loosening, infection, instability and other factors resulting in revision surgeries. Each year, approximately 50,000 patients undergo a THA revision in the US and this volume is projected to increase dramatically over the next decade [21]. Revision procedures are not only costly but are also associated with an increased risk of complication [24,28]. Identifying the patient, surgical, implant and hospital factors associated with increased risk of revision could potentially reduce the number of revision surgeries. Prior studies that examined risk factors of THA revision have produced conflicting findings. While patient risk factors such as age has been consistently identified as a THA revision risk factor, the effects of body mass index (BMI), diagnosis, gender and other patient factors are less clear. Similarly, studies that have examined implant factors such as bearing surface have produced inconsistent results [10,37,38,42]. In addition, while some studies have identified surgeon and hospital volume as risk factors, other studies have not replicated these findings [2,19,34]. These inconsistent findings emphasize the need for further investigation of THA revision risk factors. Furthermore, THA revision risk factors have not been thoroughly examined in a large, US community-based setting. Therefore, the purpose of this study is to
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.01.023. Reprint requests: Maria C.S. Inacio, PhD, Surgical Outcomes and Analysis Unit, Clinical Analysis, Southern California Permanente Medical Group, 8954 Rio San Diego Dr, Suite 406, San Diego, CA 92108.
evaluate patient, procedure, implant, surgeon, and hospital risk factors associated with aseptic revision after primary total hip arthroplasty in a large US community-based sample. Methods Study Design, Inclusion Criteria, and Data Collection A retrospective analysis of a prospectively followed cohort was conducted. A Total Joint Replacement Registry (TJRR) was used to identify primary THAs performed for any diagnosis between 04/01/ 2001 and 12/31/2010 in a large integrated US healthcare system. Revisions, conversions, and cases with rarely used bearing surfaces (ceramic-on-constrained polyethylene and metal-on-ceramic) were excluded from the analysis. Data collection, participation, and coverage information on the TJRR has been published elsewhere [29–32]. In brief, the TJRR uses both paper and electronic collection processes to capture patient characteristics, implant and surgical information, as well as validated algorithms to capture the outcomes of interest. Patient characteristics, surgeon, hospital and implant information are supplemented with data from several other sources, including the institution's electronic medical records (EMR), administrative claims data, membership information (which contains membership attrition due to health care coverage end or death), a Diabetes Registry, and other institutional departments (e.g. Geographically Enriched Member Socio-demographics). Electronic algorithms are used to search EMR and administrative claims data for re-operations and complications and are validated through EMR review. Intra-operative information is collected by the surgeon at the point of care. Post-operative information is captured using electronic screening algorithms with
0883-5403/0000-0000$36.00/0 – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2014.01.023
Please cite this article as: Khatod M, et al, Risk factors for Total Hip Arthroplasty Aseptic Revision, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.01.023
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EMR review according to published guidelines. The study sample included cases from 50 medical centers and 336 surgeons in 7 US geographical regions (Southern and Northern California, Colorado, Georgia, Hawaii, Northwest, Mid-Atlantic). The voluntary participation of the registry is 90% for the THAs [32]. Outcome of Interest The endpoint of this study was aseptic revisions. Revision was defined as any operation after the index THA where a component is replaced. Aseptic revisions are performed for any reason other than infection related causes. Reasons for revision are recorded by the surgeons in the TJRR operative forms and confirmed via chart review by a trained clinical research associate. Exposures of Interest Risk factors were grouped into patient, procedure, implant, surgeon, and hospital factors. Patient risk factors evaluate were as follows: age (continuous, in 10-year increments), gender, race (white, black, Hispanic, Asian, other/multi), body mass index (BMI) (b30 kg/m2 vs. 30–34 kg/m 2 vs. ≥35 kg/m2), American Society of Anesthesiologists (ASA) score (≤ 2 vs. ≥ 3), diagnosis for surgery (osteoarthritis, rheumatoid arthritis, inflammatory arthritis, and osteonecrosis), and diabetes status (yes vs. no). Procedural factors included whether bilateral procedures (yes vs. no) were performed and the surgical approach used (posterior, anterolateral, direct lateral, or other). Implant attributes evaluated included: fixation type (cemented vs. uncemented vs. hybrid), bearing surface (ceramic-on-ceramic, ceramic-on-conventional polyethylene, ceramic-on-highly cross-linked polyethylene, ceramic-onmetal, metal-on-constrained polyethylene, metal-on-conventional polyethylene, metal-on-(HXLPE), and metal-on-metal), and whether a Depuy's ASR Hip System was used for the procedure. The inclusion of a flag for Depuy ASR Hip System components to the analysis was an attempt to control for the artificial increase in risk of this components' and its attributes risk of revision since this component's recall in August of 2010 [9]. Surgeon variables included average yearly volume (b 30 cases/year vs. ≥30 cases/year) and total joint arthroplasty fellowship training status. Finally, hospital yearly volume (b75 cases/year vs. ≥75 cases/year) was evaluated. Statistical Analysis Frequencies, proportions, mean, and standard deviations (SD) were used to describe the study sample. Crude aseptic revision rates and revision rate per 100 years of observation were calculated. Survival analysis was performed with marginal multivariate Cox models using the robust standard error approach of Lin and Wei to account for surgeon clustering effects. Hazard ratios (HR) and 95% confidence intervals (CI) for the risk of aseptic revision of the exposure variables are reported. To account for missing values of some variables multiple imputations were performed to create 20 versions of the analytic data set and then used Rubin's [35] combining rules to calculate the final parameter estimates and standard errors from the 20 output sets. The imputation model included all covariates as well as the event indicator and the Nelson-Aalen estimator of the cumulative baseline hazard at the time of event or censoring for each case. Significance tests for proportional hazards were based on plots of the standardized score process against time for each covariate and comparing the observed curve to 1000 simulated curves under the assumption of proportional hazards using the listwise deleted data [22]. Data were analyzed using SAS (Version 9.2, SAS Institute, Cary, NC, USA) and alpha = 0.05 was used as the threshold for statistical significance for exposure variables.
Results A total of 36,834 primary THAs were included in the study. During the 2.9-years (interquartile range 1.2–5.1 years) median follow-up of the cohort 1898 (5.2%) cases died and 3262 (8.9%) terminated their membership. Table 1 has the sample patient descriptive characteristics. The cohort mean age was 65.5 years old (SD = 11.7) and was mostly female (57.4%) and white (74.0%). The most common diagnosis of the cohort was osteoarthritis (91.2%, N = 33578) followed by osteonecrosis (6.5%, N = 2388). The prevalence of diabetes was 18.7% (N = 6900) and 15.7% (N = 5778) of the sample was considered morbidly obese. Same-day bilateral procedures were performed in 1.2% (N = 426) of the cases and the most commonly used approach was posterior (75.9%, N = 27974). Uncemented implants were used in 80.8% (N = 29762) of the cases and femoral head sizes ≥36 mm were used in 42.0% (N = 15472) of the cases. The most used bearing surface was metal-on-HXLPE (56.0%, N = 20631), followed by ceramic-on-HXLPE (21.0%, N = 7738). ASR Hip Systems were used in 663 cases (1.8%). Most procedures were performed by surgeons without a TJR fellowship (61.0%, N = 22450), by high-volume surgeons (69.1%, N = 25456), in high-volume hospitals (96.0%, N = 34745). See Table 2 for details on procedure, implant attributes, and surgeon and hospital characteristics. During the study period 635 cases (1.7%) were revised due to aseptic reasons. The revision rate per 100 years of observation is 0.52
Table 1 Overall Sample Patient Characteristics and by Revision Status, 2001–2010.
Total, N (%) Total Age years, mean (SD) Age category, years b65 ≥65 Unknown Gender Male Female Unknown Race Asian Black Hispanic Multi-race Native American Other White Unknown Diabetes No Yes BMI kg/m2, mean (SD) BMI category, kg/m2 b30 30–34 ≥35 Unknown ASA score category 1 and 2 ≥3 Unknown Diagnosis Osteoarthritis Osteonecrosis Rheumatoid arthritis Post-traumatic arthritis
Not Revised, N (%)
Revised, N (%)
P value
36,834 (100.0) 36,199 (98.3) 65.5 (11.7) 65.5 (11.7)
635 (1.7) 64.5 (12.3)
16,673 (45.3) 20,156 (54.7) 5 (b0.1)
16,361 (98.1) 19,833 (98.4) 5 (100.0)
312 (1.9) 323 (1.6) 0 (0.0)
0.049
15,696 (42.6) 21,134 (57.4) 4 (b0.1)
15,469 (98.6) 20,726 (98.1) 4 (100.0)
227 (1.4) 408 (1.9) 0 (0.0)
b0.001
1283 (3.5) 2711 (7.4) 2448 (6.6) 204 (0.6) 68 (0.2) 400 (1.1) 27,263 (74.0) 2457 (6.7)
1273 2666 2421 197 68 394 26,743 2437
10 (0.8) 45 (1.7) 27 (1.1) 7 (3.4) 0 (0.0) 6 (1.5) 520 (1.9) 20 (0.8)
0.002
29,934 (81.3) 6900 (18.7) 29.3 (5.9)
29,423 (98.3) 6776 (98.2) 29.3 (5.9)
511 (1.7) 124 (1.8) 29.6 (6.2)
0.605
21,574 (58.6) 8758 (23.8) 5778 (15.7) 724 (2.0)
21,203 8618 5668 710
371 140 110 14
(1.7) (1.6) (1.9) (1.9)
0.383
23,040 (62.5) 12,804 (34.8) 990 (2.7)
22,640 (98.3) 12,581 (98.3) 978 (98.8)
400 (1.7) 223 (1.7) 12 (1.2)
0.969
33,578 (91.2) 2388 (6.5) 753 (2.0) 359 (1.0)
33,025 2336 731 350
553 (1.6) 52 (2.2) 22 (2.9) 9 (2.5)
b0.001 0.078 0.011 0.252
(99.2) (98.3) (98.9) (96.6) (100.0) (98.5) (98.1) (99.2)
(98.3) (98.4) (98.1) (98.1)
(98.4) (97.8) (97.1) (97.5)
SD = standard deviation; BMI = body mass index; ASA = American Society of Anesthesiologists.
Please cite this article as: Khatod M, et al, Risk factors for Total Hip Arthroplasty Aseptic Revision, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.01.023
M. Khatod et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
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Table 2 Procedure, Implants, Surgeon, and Hospital Characteristics of Overall Sample and by Revision Status, 2001–2010. Total, N (%) Total Procedure characteristics Bilateral No Yes Surgical approach Anterolateral Direct lateral Posterior Other Unknown Implant attributes Fixation Uncemented Hybrid Cemented Unknown Femoral head size (mm) ≥36 b36 Unknown Bearing surface Ceramic-on-ceramic Ceramic-on-conventional polyethylene Ceramic-on-HXLPE Ceramic-on-metal Metal-on-constrained Metal-on-conventional polyethylene Metal-on-HXLPE Metal-on-metal Unknown ASR Hip System (Depuy) No Yes Surgeon and hospital characteristics Surgeon TJA fellowship training No Yes Unknown Surgeon annual volume (cases/year) b30 ≥30 Site annual volume (cases/year) b75 ≥75
Not Revised, N (%)
Revised, N (%)
36,834 (100)
36,199 (98.3)
635 (1.7)
36,408 (98.8) 426 (1.2)
35,782 (98.3) 417 (97.9)
626 (1.7) 9 (2.1)
0.535
3591 478 27,974 219 4572
(9.7) (1.3) (75.9) (0.6) (12.4)
3537 468 27,477 213 4504
(98.5) (97.9) (98.2) (97.3) (98.5)
54 (1.5) 10 (2.1) 497 (1.8) 6 (2.7) 68 (1.5)
0.402
29,762 4099 212 2761
(80.8) (11.1) (0.6) (7.5)
29,272 4013 205 2709
(98.4) (97.9) (96.7) (98.1)
490 (1.6) 86 (2.1) 7 (3.3) 52 (1.9)
0.023
15,472 (42.0) 20,689 (56.2) 673 (1.8)
15,278 (98.7) 20,261 (97.9) 660 (98.1)
194 (1.3) 428 (2.1) 13 (1.9)
b0.001
510 129 7738 110 54 1818 20,631 4992 852
490 122 7622 107 52 1748 20,317 4904 837
(96.1) (94.6) (98.5) (97.3) (96.3) (96.1) (98.5) (98.2) (98.2)
20 (3.9) 7 (5.4) 116 (1.5) 3 (2.7) 2 (3.7) 70 (3.9) 314 (1.5) 88 (1.8) 15 (1.8)
b0.001
36,171 (98.2) 663 (1.8)
35,562 (98.3) 637 (96.1)
609 (1.7) 26 (3.9)
b0.001
22,450 (61.0) 14,378 (39.0) 6 (b0.1)
22,037 (98.2) 14,157 (98.5) 5 (83.3)
413 (1.8) 221 (1.5) 1 (16.7)
0.029
11,378 (30.9) 25,456 (69.1)
11,148 (98.0) 25,051 (98.4)
230 (2.0) 405 (1.6)
0.003
1478 (4.0) 35,356 (96.0)
1454 (98.4) 34,745 (98.3)
24 (1.6) 611 (1.7)
0.763
(1.4) (0.3) (21.0) (0.3) (0.1) (4.9) (56.0) (13.6) (2.3)
P value
TJA = total joint arthroplasty; HXLPE = highly cross-linked polyethylene.
for THA cases. The cumulative survival for all-cause revisions at 8 years is 96.4% (95% CI 95.9%–96.7%), and for aseptic revisions only at 8 years, was 96.9% (95% CI 96.5%–97.3%). The main reasons for revision among aseptic cases were instability (49.8%), aseptic loosening (14.2%), and peri-prosthestic fracture (11.3%), followed by polyethylene insert wear (4.3%) (Table 3). In the model including ASR Hip Systems, tests of proportional hazards identified violations for ASR and diabetes. We stratified on each of these variables to determine the point in time when the relationship among the hazards changed (see Figs. 1 and 2). We then created a time-dependent covariate based on interactions between each of these variables and separate dummy indicators of time (based on the time points identified above). These time-dependent effects were then included in our multivariable analysis alongside all other exposure variables (Table 4). For each 10-year increase in age the hazard decreased by a factor of 0.91 (95% CI 0.84–0.99). Females were found to be associated with a 1.35 (95% CI 1.14–1.60) higher risk of revision compared to males. THAs performed in Hispanic (HR = 0.49, 95% CI 0.31–0.78) and Asian (HR = 0.35, 95% CI 0.17–0.72) patients compared to whites had a lower risk of revision. THAs with ceramicon-ceramic bearing (HR = 1.87, 95% CI 1.09–3.22), ceramic-onconventional polyethylene (HR = 2.17, 95% CI 1.04–4.52), and
metal-on-conventional polyethylene (HR = 1.81, 95% CI 1.34–2.44) had a higher risk of revision than metal on HXLPE. Diabetes diagnosis did not have a significant time-dependent effect, which can be explained by misspecification of the functional form of the interaction, confounded effects with the time-dependent ASR Hip System effect, and/or differences between the listwise deleted data and the imputed data. The recalled ASR Hip System was found to have an increased risk over time of failure compared to all other component brands (ASR by time interaction: HR = 9.13, 95% CI 4.01–20.77). Specifically, at less than 500 days ASR Hip Systems appear harmless relative to other components (HR = 0.97, 95% CI 0.19–5.04), but after 500 days they have an 8.84 (95% CI 2.55, 30.62) greater risk of failure than other components. Comparison of the magnitude of the HRs in a model with and without ASR Hip Systems revealed similar findings (data not shown). Discussion In a large US cohort of primary THAs, cumulative aseptic survival at 8 years was 96.7% and aseptic revision per 100 observation years was 0.52. Instability and aseptic loosening accounted for the majority of the reasons for aseptic revisions (49.7% and 13.9% respectively).
Please cite this article as: Khatod M, et al, Risk factors for Total Hip Arthroplasty Aseptic Revision, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.01.023
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Table 3 Crude Revision Rate, Revision Rate/100 years of Observation, and Reasons for Aseptic Revision, 2001–2010. Total Sample Crude revision rate, N (%) Revision rate/100 years of observation, total years (rate/100 years) Reasons for Revision Instability Aseptic loosening Peri-prosthetic fracture Polyethylene insert wear Leg length inequality Component fracture Osteolysis Metallosis Hematoma Cup malposition Wound drainage Seroma Wound dehiscence Other
635 (1.7) 12,1716 (0.52)
N
%
316 90 72 27 22 11 11 8 8 9 3 1 1 70
49.8 14.2 11.3 4.3 3.5 1.7 1.7 1.3 1.3 1.4 0.5 0.2 0.2 11.0
Patient, implant, surgeon and hospital risk factors of THA revisions are described below. Patient Factors Similar to other studies, we found that older age was associated with a lower risk of revision THA [7,8,34,36]. Our results were also consistent with other studies that did not find an association of BMI or diabetes with aseptic revision [13,16]. Similar to studies that have reported race as a risk factor for THA medical complications [40], we found that while Hispanic and Asian race have a lower risk of revision, black and white patients have a similar risk of aseptic revision. Malik et al [25] have noted genetic differences in revision risk among THA patients which may play a role in racial differences. In contrast to a recent US study and a meta-analysis, females in our study had a higher risk of THA failure [20,34]. The different findings could be due to the samples used in the studies, the time when the cohorts had their procedures, the follow-up of the studies, and the definitions of failure used by the studies. A higher risk of revision in women may be partially attributed to smaller size implants used in female patients (smaller femoral heads) resulting in a higher rate of instability [6,12] and possibly in higher revision rates.
Fig. 1. Survival curves for diabetics vs. non-diabetic patients, 2001–2010.
Fig. 2. Survival Curves for ASR Hip System components compared to all other primary THA components, 2001–2010.
While we did not find worse general health status, measured by ASA in our study, to be associated with revision within our study, other studies have found support for higher risk of THA based on comorbid status [18,23,28,34]. These finding may be explained by the use of a different general health index score used and restriction to elective primary THA surgeries within our study. In a study by Wright et al [43], where ASA was evaluated, findings were similar to ours. Several studies also suggest that indication for primary surgery is a predictor of THA revision [8,18,34,41]. However, we did not find diagnosis to be a predictor after adjusting for other patient, implant and surgical factors. These inconsistencies may also be related to our inclusion criterion of only elective THAs. Other studies have also produced conflicting results on the importance of diagnosis in risk of revision [3,11] suggesting the need for further research. Implant and Technique Factors Within our study, conventional polyethylene inserts and ceramicon-ceramic articulations had a higher risk of revision comparison to highly cross-linked polyethylene. Conventional polyethylene has been shown to perform clinically worse than HXLPE in both singlecenter trials and registry data [17,27]. Ceramic-on-ceramic outcomes were also shown to be at higher risk of revision in the National Joint Registry for England and Wales, but have not been shown in other clinical trials and in the US population [5,17,33]. These findings emphasize the importance of THA articulation in implant selection. In contrast to findings reported by Australia and England and Wales [1,38], metal-on-metal articulations did not have an increased risk of revision in our study. However, the ASR implant had a drastic increase in risk of revision after 500 days. This finding is consistent with a recent study based on Medicare administrative data [5]. Of importance, is the significant spike in the revision of metal-on-metal implants at 6 and 7 years reported by both the Australian and England Wales arthroplasty registries, and a longer follow-up period than that of our cohort and in the Medicare sample study. Additional length of follow-up may produce similar findings within our TJRR and further studies are underway to monitor the cohort of patients with these bearings. While several registries and studies suggest that surgical approach and head size influence risk of dislocation [4,6,12,15], we did not discover an increased risk for aseptic revision in our study. However, the endpoint for our study was aseptic revision as opposed to dislocation which may explain the differences in findings. Many postoperative
Please cite this article as: Khatod M, et al, Risk factors for Total Hip Arthroplasty Aseptic Revision, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.01.023
M. Khatod et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
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Table 4 Associations of Patient, Procedure, Implant, Surgeon, and Hospital Risk Factors With Risk of Aseptic Total Hip Arthroplasty Revision (Hazard Ratio and 95% Confidence Interval).
Patient Age (increasing 10-year increments) Female vs. male Race: black vs. white Race: Hispanic vs. white Race: Asian vs. white Race: other (includes Native American and multi-race) ASA score: ≥3 vs. ASA 1 and 2 Diabetes (yes vs. no) Diabetes * time interaction (reference: time ≥1461 days) BMI: between 30 and 35 kg/m2 vs. b30 kg/m2 BMI: N35 kg/m2 vs. b30 kg/m2 Osteoarthritis (yes vs. no) Osteonecrosis (yes vs. no) Post-traumatic arthritis (yes vs. no) Rheumatoid arthritis (yes vs. no) Procedure Bilateral (yes vs. no) Surgical approach: anterolateral vs. posterior Surgical approach: direct lateral vs. posterior Surgical approach: other vs. posterior Implant attributes and implants Fixation: hybrid vs. uncemented Fixation: cemented vs. uncemented Femoral head size:b36 mm vs. ≥36 mm Bearing surface: ceramic-on-ceramic vs. metal-on-HXLPE Bearing surface: ceramic-on-conventional polyethylene vs. metal-on-HXLPE Bearing surface: ceramic-on-HXLPE vs. metal-on-HXLPE Bearing surface: ceramic-on-metal vs. metal-on-HXLPE Bearing surface: metal-on-constrained vs. metal-on-HXLPE Bearing surface: metal-on-conventional vs. metal-on-HXLPE Bearing surface: metal-on-metal vs. metal-on-HXLPE Depuy's ASR Hip System vs. no Depuy's ASR Hip System component Depuy's ASR Hip System * time interaction (reference: time b500 days) Surgeon and hospital Surgeon fellowship (yes vs. no) Surgeon annual volume: b30 cases vs. ≥30 cases Site annual volume: b75 cases vs. ≥75 cases
HR
Low 95% CI
High 95% CI
P Value
0.91 1.35 0.83 0.49 0.35 1.35 1.07 1.12 0.96 0.94 1.01 0.72 0.92 1.10 1.18
0.84 1.14 0.60 0.31 0.17 0.59 0.89 0.59 0.50 0.78 0.82 0.46 0.59 0.57 0.67
0.99 1.60 1.14 0.78 0.72 3.08 1.29 2.13 1.83 1.13 1.25 1.13 1.44 2.11 2.08
0.037 b0.001 0.249 0.002 0.004 0.473 0.490 0.729 0.901 0.507 0.899 0.155 0.719 0.782 0.564
1.42 0.94 1.12 1.36
0.65 0.53 0.56 0.60
3.12 1.67 2.24 3.08
0.382 0.840 0.746 0.462
0.83 1.59 1.29 1.87 2.17 0.85 1.90 2.45 1.81 1.06 0.97 9.13
0.61 0.74 1.00 1.09 1.04 0.66 0.82 0.83 1.34 0.75 0.42 4.01
1.15 3.41 1.67 3.22 4.52 1.10 4.42 7.20 2.44 1.51 2.21 20.8
0.261 0.230 0.054 0.023 0.039 0.220 0.134 0.104 0.001 0.735 0.938 b0.001
1.01 1.18 1.10
0.75 0.91 0.58
1.35 1.53 2.07
0.962 0.221 0.769
HR = hazard ratio; CI = confidence interval; BMI = body mass index; ASA = American Society of Anesthesiologists; HXLPE = highly cross-linked polyethylene.
dislocations are treated with closed reduction without revision surgery making revision surgery a less sensitive outcome for femoral head and surgical approach analysis. Surgeon and Hospital Factors Unlike other studies that have found surgeon fellowship training and hospital volume [14,23,34] our study did not identify these as independent risk factors for revision. Our classification of lower- and higher-volume surgeons may not be sensitive enough to pick up differences as other studies compared surgeons with less than 10 cases per year to surgeons with over 100 annual cases. Similar issues surrounding classification of volume may explain differences in hospital volume findings. Manley et al [26] also found no association with hospital volume and total hip revision rates when evaluating the Medicare claims data. Strengths and Limitations A strength of this study is the large contemporary cohort of over 36,000 patients. The diversity of the sample, including patient, surgeon and facility, making the results generalizable to the greater population is also a strength of this study. In addition, this is a prospectively monitored cohort with outcomes that are validated through chart review ensuring a high level of data accuracy. The level of detail in patient and surgical information presented in the current study is not available in other larger samples of THAs. In the absence of randomization, this level of detailed information allows us to better
address the issue of confounding in this observational study. Limitations of this study include its observational nature, some missing data, attrition in the cohort, and the possibly the choice of some of the data definitions used in our analysis. Our data are observational and therefore causality cannot be established from our analysis. Some missing information in our data could lead to information bias, however, our use of multiple imputation minimizes the likelihood of obtaining these biased estimates and maximizes efficiency. Another form of missing data occurs because patients leave the health plan or die. Our survival analysis model treats these individuals as censored and assumes that all individuals who are censored are from the same population as individuals who are not censored (i.e., the survival in the two groups is the same after conditioning on the covariates), which is a reasonable assumption. Certain definitions used in our study (such as high- and low-volume surgeons, diabetic status of patients) are not necessarily standard criteria used throughout the literature and should not therefore be interpreted as such. Additional limitations of the study include our relatively short follow-up period and the lack of patient-reported and radiographic outcomes which may be a more sensitive measure of early THA failure. Conclusion THA cumulative aseptic survival at 8 years was 96.7%. Patient factors affecting THA aseptic revision included gender and race. Certain bearing surfaces were also found to be risk factors of aseptic revision.
Please cite this article as: Khatod M, et al, Risk factors for Total Hip Arthroplasty Aseptic Revision, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.01.023
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20. Katz JN, Wright EA, Wright J, et al. Twelve-year risk of revision after primary total hip replacement in the U.S. Medicare population. J Bone Joint Surg Am 2012;94:1825. 21. Kurtz S, Ong K, Lau E, et al. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007;89:780. 22. Lin DY, Wei LJ, Ying Z. Checking the Cox model with cumulative sums of martingale-based residuals. Biometrika 1993;80:557. 23. Losina E, Barrett J, Mahomed NN, et al. Early failures of total hip replacement: effect of surgeon volume. Arthritis Rheum 2004;50:1338. 24. Mahomed NN, Barrett JA, Katz JN, et al. Rates and outcomes of primary and revision total hip replacement in the United States Medicare population. J Bone Joint Surg Am 2003;85-A:27. 25. Malik MH, Bayat A, Jury F, et al. Genetic susceptibility to hip arthroplasty failure— association with the RANK/OPG pathway. Int Orthop 2006;30:177. 26. Manley M, Ong K, Lau E, et al. Effect of volume on total hip arthroplasty revision rates in the United States Medicare population. J Bone Joint Surg Am 2008;90:2446. 27. Nikolaou VS, Edwards MR, Bogoch E, et al. A prospective randomised controlled trial comparing three alternative bearing surfaces in primary total hip replacement. J Bone Joint Surg Br 2012;94:459. 28. Ong KL, Lau E, Suggs J, et al. Risk of subsequent revision after primary and revision total joint arthroplasty. Clin Orthop Relat Res 2010;468:3070. 29. Paxton E, Inacio M, Slipchenko T, et al. The Kaiser Permanente National Total Joint Replacement Registry. The Permanente Journal 2008;12:12. 30. Paxton E, Namba R, Maletis G, et al. A prospective study of 80,000 total joint and 5,000 anterior cruciate ligament reconstruction procedures in a community-based registry in the United States. The Journal of Bone and Joint Surgery 2010;92 (Supplement 2):117. 31. Paxton EW, Inacio MC, Khatod M, et al. Kaiser Permanente National Total Joint Replacement Registry: aligning operations with information technology. Clin Orthop Relat Res 2010;468:2646. 32. Paxton EW, Inacio MCS, Kiley ML. The Kaiser Permanente Implant Registries: effect on patient safety, quality improvement, cost effectiveness, and research opportunities. Perm J 2012;16(2):33. 33. Pivec R, Johnson AJ, Mears SC, et al. Hip arthroplasty. Lancet 2012;380:1768. 34. Prokopetz JJ, Losina E, Bliss RL, et al. Risk factors for revision of primary total hip arthroplasty: a systematic review. BMC Musculoskelet Disord 2012;13:251. 35. Rubin DB. Multiple imputation for nonresponse in surveys. New York: Wiley; 1987. 36. Santaguida PL, Hawker GA, Hudak PL, et al. Patient characteristics affecting the prognosis of total hip and knee joint arthroplasty: a systematic review. Can J Surg 2008;51:428. 37. Sedrakyan A, Normand SL, Dabic S, et al. Comparative assessment of implantable hip devices with different bearing surfaces: systematic appraisal of evidence. BMJ 2011;343:d7434. 38. Smith AJ, Dieppe P, Vernon K, et al. Failure rates of stemmed metal-on-metal hip replacements: analysis of data from the National Joint Registry of England and Wales. Lancet 2012;379:1199. 39. Soderman P, Malchau H, Herberts P. Outcome after total hip arthroplasty: part I. General health evaluation in relation to definition of failure in the Swedish National Total Hip Arthoplasty register. Acta Orthop Scand 2000;71:354. 40. Soohoo NF, Farng E, Lieberman JR, et al. Factors that predict short-term complication rates after total hip arthroplasty. Clin Orthop Relat Res 2010;468:2363. 41. Stea S, Bordini B, De Clerico M, et al. First hip arthroplasty register in Italy: 55,000 cases and 7 year follow-up. Int Orthop 2009;33:339. 42. Voleti PB, Baldwin KD, Lee GC. Metal-on-metal vs conventional total hip arthroplasty: a systematic review and meta-analysis of randomized controlled trials. J Arthroplasty 2012;27:1844. 43. Wright EA, Katz JN, Baron JA, et al. Risk factors for revision of primary total hip replacement: results from a national case–control study. Arthritis Care Res (Hoboken) 2012;64:1879.
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Risk factors for Total Hip Arthroplasty Aseptic Revision Monti Khatod, MD a, Guy Cafri, PhD b, Robert S. Namba, MD c, Maria C.S. Inacio, PhD b, Elizabeth W. Paxton, MA b a b c
Department of Orthopaedic Surgery, Southern California Permanente Medical Group, Los Angeles, California Surgical Outcomes and Analysis Unit, Clinical Analysis, Southern California Permanente Medical Group, San Diego, California Department of Orthopaedic Surgery, Southern California Permanente Medical Group, Orange County, California
a r t i c l e
i n f o
Article history: Received 2 December 2013 Accepted 20 January 2014 Available online xxxx Keywords: aseptic revisions total hip arthroplasty Total Joint Replacement Registry risk factors
a b s t r a c t The purpose of this study was to evaluate patient, operative, implant, surgeon, and hospital factors associated with aseptic revision after primary THA in patients registered in a large US Total Joint Replacement Registry. A total of 35,960 THAs registered from 4/2001–12/2010 were evaluated. The 8-year survival rate was 96.7% (95% CI 96.4%–97.0%). Females had a higher risk of aseptic revision than males. Hispanic and Asian patients had a lower risk of revision than white patients. Ceramic-on-ceramic, ceramic-on-conventional polyethylene, and metal-on-conventional polyethylene bearing surfaces had a higher risk of revision than metal-on-highly cross-linked polyethylene. Body mass index, health status, diabetes, diagnosis, fixation, approach, bilateral procedures, head size, surgeon fellowship training, surgeon and hospital volume were not revision risk factors. © 2014 Elsevier Inc. All rights reserved.
Total hip arthroplasty is a successful procedure resulting in reduced pain and stiffness as well as improved function [3,39]. The majority of THA procedures are successful but some fail as a result of aseptic loosening, infection, instability and other factors resulting in revision surgeries. Each year, approximately 50,000 patients undergo a THA revision in the US and this volume is projected to increase dramatically over the next decade [21]. Revision procedures are not only costly but are also associated with an increased risk of complication [24,28]. Identifying the patient, surgical, implant and hospital factors associated with increased risk of revision could potentially reduce the number of revision surgeries. Prior studies that examined risk factors of THA revision have produced conflicting findings. While patient risk factors such as age has been consistently identified as a THA revision risk factor, the effects of body mass index (BMI), diagnosis, gender and other patient factors are less clear. Similarly, studies that have examined implant factors such as bearing surface have produced inconsistent results [10,37,38,42]. In addition, while some studies have identified surgeon and hospital volume as risk factors, other studies have not replicated these findings [2,19,34]. These inconsistent findings emphasize the need for further investigation of THA revision risk factors. Furthermore, THA revision risk factors have not been thoroughly examined in a large, US community-based setting. Therefore, the purpose of this study is to
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.01.023. Reprint requests: Maria C.S. Inacio, PhD, Surgical Outcomes and Analysis Unit, Clinical Analysis, Southern California Permanente Medical Group, 8954 Rio San Diego Dr, Suite 406, San Diego, CA 92108.
evaluate patient, procedure, implant, surgeon, and hospital risk factors associated with aseptic revision after primary total hip arthroplasty in a large US community-based sample. Methods Study Design, Inclusion Criteria, and Data Collection A retrospective analysis of a prospectively followed cohort was conducted. A Total Joint Replacement Registry (TJRR) was used to identify primary THAs performed for any diagnosis between 04/01/ 2001 and 12/31/2010 in a large integrated US healthcare system. Revisions, conversions, and cases with rarely used bearing surfaces (ceramic-on-constrained polyethylene and metal-on-ceramic) were excluded from the analysis. Data collection, participation, and coverage information on the TJRR has been published elsewhere [29–32]. In brief, the TJRR uses both paper and electronic collection processes to capture patient characteristics, implant and surgical information, as well as validated algorithms to capture the outcomes of interest. Patient characteristics, surgeon, hospital and implant information are supplemented with data from several other sources, including the institution's electronic medical records (EMR), administrative claims data, membership information (which contains membership attrition due to health care coverage end or death), a Diabetes Registry, and other institutional departments (e.g. Geographically Enriched Member Socio-demographics). Electronic algorithms are used to search EMR and administrative claims data for re-operations and complications and are validated through EMR review. Intra-operative information is collected by the surgeon at the point of care. Post-operative information is captured using electronic screening algorithms with
0883-5403/0000-0000$36.00/0 – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2014.01.023
Please cite this article as: Khatod M, et al, Risk factors for Total Hip Arthroplasty Aseptic Revision, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.01.023
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EMR review according to published guidelines. The study sample included cases from 50 medical centers and 336 surgeons in 7 US geographical regions (Southern and Northern California, Colorado, Georgia, Hawaii, Northwest, Mid-Atlantic). The voluntary participation of the registry is 90% for the THAs [32]. Outcome of Interest The endpoint of this study was aseptic revisions. Revision was defined as any operation after the index THA where a component is replaced. Aseptic revisions are performed for any reason other than infection related causes. Reasons for revision are recorded by the surgeons in the TJRR operative forms and confirmed via chart review by a trained clinical research associate. Exposures of Interest Risk factors were grouped into patient, procedure, implant, surgeon, and hospital factors. Patient risk factors evaluate were as follows: age (continuous, in 10-year increments), gender, race (white, black, Hispanic, Asian, other/multi), body mass index (BMI) (b30 kg/m2 vs. 30–34 kg/m 2 vs. ≥35 kg/m2), American Society of Anesthesiologists (ASA) score (≤ 2 vs. ≥ 3), diagnosis for surgery (osteoarthritis, rheumatoid arthritis, inflammatory arthritis, and osteonecrosis), and diabetes status (yes vs. no). Procedural factors included whether bilateral procedures (yes vs. no) were performed and the surgical approach used (posterior, anterolateral, direct lateral, or other). Implant attributes evaluated included: fixation type (cemented vs. uncemented vs. hybrid), bearing surface (ceramic-on-ceramic, ceramic-on-conventional polyethylene, ceramic-on-highly cross-linked polyethylene, ceramic-onmetal, metal-on-constrained polyethylene, metal-on-conventional polyethylene, metal-on-(HXLPE), and metal-on-metal), and whether a Depuy's ASR Hip System was used for the procedure. The inclusion of a flag for Depuy ASR Hip System components to the analysis was an attempt to control for the artificial increase in risk of this components' and its attributes risk of revision since this component's recall in August of 2010 [9]. Surgeon variables included average yearly volume (b 30 cases/year vs. ≥30 cases/year) and total joint arthroplasty fellowship training status. Finally, hospital yearly volume (b75 cases/year vs. ≥75 cases/year) was evaluated. Statistical Analysis Frequencies, proportions, mean, and standard deviations (SD) were used to describe the study sample. Crude aseptic revision rates and revision rate per 100 years of observation were calculated. Survival analysis was performed with marginal multivariate Cox models using the robust standard error approach of Lin and Wei to account for surgeon clustering effects. Hazard ratios (HR) and 95% confidence intervals (CI) for the risk of aseptic revision of the exposure variables are reported. To account for missing values of some variables multiple imputations were performed to create 20 versions of the analytic data set and then used Rubin's [35] combining rules to calculate the final parameter estimates and standard errors from the 20 output sets. The imputation model included all covariates as well as the event indicator and the Nelson-Aalen estimator of the cumulative baseline hazard at the time of event or censoring for each case. Significance tests for proportional hazards were based on plots of the standardized score process against time for each covariate and comparing the observed curve to 1000 simulated curves under the assumption of proportional hazards using the listwise deleted data [22]. Data were analyzed using SAS (Version 9.2, SAS Institute, Cary, NC, USA) and alpha = 0.05 was used as the threshold for statistical significance for exposure variables.
Results A total of 36,834 primary THAs were included in the study. During the 2.9-years (interquartile range 1.2–5.1 years) median follow-up of the cohort 1898 (5.2%) cases died and 3262 (8.9%) terminated their membership. Table 1 has the sample patient descriptive characteristics. The cohort mean age was 65.5 years old (SD = 11.7) and was mostly female (57.4%) and white (74.0%). The most common diagnosis of the cohort was osteoarthritis (91.2%, N = 33578) followed by osteonecrosis (6.5%, N = 2388). The prevalence of diabetes was 18.7% (N = 6900) and 15.7% (N = 5778) of the sample was considered morbidly obese. Same-day bilateral procedures were performed in 1.2% (N = 426) of the cases and the most commonly used approach was posterior (75.9%, N = 27974). Uncemented implants were used in 80.8% (N = 29762) of the cases and femoral head sizes ≥36 mm were used in 42.0% (N = 15472) of the cases. The most used bearing surface was metal-on-HXLPE (56.0%, N = 20631), followed by ceramic-on-HXLPE (21.0%, N = 7738). ASR Hip Systems were used in 663 cases (1.8%). Most procedures were performed by surgeons without a TJR fellowship (61.0%, N = 22450), by high-volume surgeons (69.1%, N = 25456), in high-volume hospitals (96.0%, N = 34745). See Table 2 for details on procedure, implant attributes, and surgeon and hospital characteristics. During the study period 635 cases (1.7%) were revised due to aseptic reasons. The revision rate per 100 years of observation is 0.52
Table 1 Overall Sample Patient Characteristics and by Revision Status, 2001–2010.
Total, N (%) Total Age years, mean (SD) Age category, years b65 ≥65 Unknown Gender Male Female Unknown Race Asian Black Hispanic Multi-race Native American Other White Unknown Diabetes No Yes BMI kg/m2, mean (SD) BMI category, kg/m2 b30 30–34 ≥35 Unknown ASA score category 1 and 2 ≥3 Unknown Diagnosis Osteoarthritis Osteonecrosis Rheumatoid arthritis Post-traumatic arthritis
Not Revised, N (%)
Revised, N (%)
P value
36,834 (100.0) 36,199 (98.3) 65.5 (11.7) 65.5 (11.7)
635 (1.7) 64.5 (12.3)
16,673 (45.3) 20,156 (54.7) 5 (b0.1)
16,361 (98.1) 19,833 (98.4) 5 (100.0)
312 (1.9) 323 (1.6) 0 (0.0)
0.049
15,696 (42.6) 21,134 (57.4) 4 (b0.1)
15,469 (98.6) 20,726 (98.1) 4 (100.0)
227 (1.4) 408 (1.9) 0 (0.0)
b0.001
1283 (3.5) 2711 (7.4) 2448 (6.6) 204 (0.6) 68 (0.2) 400 (1.1) 27,263 (74.0) 2457 (6.7)
1273 2666 2421 197 68 394 26,743 2437
10 (0.8) 45 (1.7) 27 (1.1) 7 (3.4) 0 (0.0) 6 (1.5) 520 (1.9) 20 (0.8)
0.002
29,934 (81.3) 6900 (18.7) 29.3 (5.9)
29,423 (98.3) 6776 (98.2) 29.3 (5.9)
511 (1.7) 124 (1.8) 29.6 (6.2)
0.605
21,574 (58.6) 8758 (23.8) 5778 (15.7) 724 (2.0)
21,203 8618 5668 710
371 140 110 14
(1.7) (1.6) (1.9) (1.9)
0.383
23,040 (62.5) 12,804 (34.8) 990 (2.7)
22,640 (98.3) 12,581 (98.3) 978 (98.8)
400 (1.7) 223 (1.7) 12 (1.2)
0.969
33,578 (91.2) 2388 (6.5) 753 (2.0) 359 (1.0)
33,025 2336 731 350
553 (1.6) 52 (2.2) 22 (2.9) 9 (2.5)
b0.001 0.078 0.011 0.252
(99.2) (98.3) (98.9) (96.6) (100.0) (98.5) (98.1) (99.2)
(98.3) (98.4) (98.1) (98.1)
(98.4) (97.8) (97.1) (97.5)
SD = standard deviation; BMI = body mass index; ASA = American Society of Anesthesiologists.
Please cite this article as: Khatod M, et al, Risk factors for Total Hip Arthroplasty Aseptic Revision, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.01.023
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Table 2 Procedure, Implants, Surgeon, and Hospital Characteristics of Overall Sample and by Revision Status, 2001–2010. Total, N (%) Total Procedure characteristics Bilateral No Yes Surgical approach Anterolateral Direct lateral Posterior Other Unknown Implant attributes Fixation Uncemented Hybrid Cemented Unknown Femoral head size (mm) ≥36 b36 Unknown Bearing surface Ceramic-on-ceramic Ceramic-on-conventional polyethylene Ceramic-on-HXLPE Ceramic-on-metal Metal-on-constrained Metal-on-conventional polyethylene Metal-on-HXLPE Metal-on-metal Unknown ASR Hip System (Depuy) No Yes Surgeon and hospital characteristics Surgeon TJA fellowship training No Yes Unknown Surgeon annual volume (cases/year) b30 ≥30 Site annual volume (cases/year) b75 ≥75
Not Revised, N (%)
Revised, N (%)
36,834 (100)
36,199 (98.3)
635 (1.7)
36,408 (98.8) 426 (1.2)
35,782 (98.3) 417 (97.9)
626 (1.7) 9 (2.1)
0.535
3591 478 27,974 219 4572
(9.7) (1.3) (75.9) (0.6) (12.4)
3537 468 27,477 213 4504
(98.5) (97.9) (98.2) (97.3) (98.5)
54 (1.5) 10 (2.1) 497 (1.8) 6 (2.7) 68 (1.5)
0.402
29,762 4099 212 2761
(80.8) (11.1) (0.6) (7.5)
29,272 4013 205 2709
(98.4) (97.9) (96.7) (98.1)
490 (1.6) 86 (2.1) 7 (3.3) 52 (1.9)
0.023
15,472 (42.0) 20,689 (56.2) 673 (1.8)
15,278 (98.7) 20,261 (97.9) 660 (98.1)
194 (1.3) 428 (2.1) 13 (1.9)
b0.001
510 129 7738 110 54 1818 20,631 4992 852
490 122 7622 107 52 1748 20,317 4904 837
(96.1) (94.6) (98.5) (97.3) (96.3) (96.1) (98.5) (98.2) (98.2)
20 (3.9) 7 (5.4) 116 (1.5) 3 (2.7) 2 (3.7) 70 (3.9) 314 (1.5) 88 (1.8) 15 (1.8)
b0.001
36,171 (98.2) 663 (1.8)
35,562 (98.3) 637 (96.1)
609 (1.7) 26 (3.9)
b0.001
22,450 (61.0) 14,378 (39.0) 6 (b0.1)
22,037 (98.2) 14,157 (98.5) 5 (83.3)
413 (1.8) 221 (1.5) 1 (16.7)
0.029
11,378 (30.9) 25,456 (69.1)
11,148 (98.0) 25,051 (98.4)
230 (2.0) 405 (1.6)
0.003
1478 (4.0) 35,356 (96.0)
1454 (98.4) 34,745 (98.3)
24 (1.6) 611 (1.7)
0.763
(1.4) (0.3) (21.0) (0.3) (0.1) (4.9) (56.0) (13.6) (2.3)
P value
TJA = total joint arthroplasty; HXLPE = highly cross-linked polyethylene.
for THA cases. The cumulative survival for all-cause revisions at 8 years is 96.4% (95% CI 95.9%–96.7%), and for aseptic revisions only at 8 years, was 96.9% (95% CI 96.5%–97.3%). The main reasons for revision among aseptic cases were instability (49.8%), aseptic loosening (14.2%), and peri-prosthestic fracture (11.3%), followed by polyethylene insert wear (4.3%) (Table 3). In the model including ASR Hip Systems, tests of proportional hazards identified violations for ASR and diabetes. We stratified on each of these variables to determine the point in time when the relationship among the hazards changed (see Figs. 1 and 2). We then created a time-dependent covariate based on interactions between each of these variables and separate dummy indicators of time (based on the time points identified above). These time-dependent effects were then included in our multivariable analysis alongside all other exposure variables (Table 4). For each 10-year increase in age the hazard decreased by a factor of 0.91 (95% CI 0.84–0.99). Females were found to be associated with a 1.35 (95% CI 1.14–1.60) higher risk of revision compared to males. THAs performed in Hispanic (HR = 0.49, 95% CI 0.31–0.78) and Asian (HR = 0.35, 95% CI 0.17–0.72) patients compared to whites had a lower risk of revision. THAs with ceramicon-ceramic bearing (HR = 1.87, 95% CI 1.09–3.22), ceramic-onconventional polyethylene (HR = 2.17, 95% CI 1.04–4.52), and
metal-on-conventional polyethylene (HR = 1.81, 95% CI 1.34–2.44) had a higher risk of revision than metal on HXLPE. Diabetes diagnosis did not have a significant time-dependent effect, which can be explained by misspecification of the functional form of the interaction, confounded effects with the time-dependent ASR Hip System effect, and/or differences between the listwise deleted data and the imputed data. The recalled ASR Hip System was found to have an increased risk over time of failure compared to all other component brands (ASR by time interaction: HR = 9.13, 95% CI 4.01–20.77). Specifically, at less than 500 days ASR Hip Systems appear harmless relative to other components (HR = 0.97, 95% CI 0.19–5.04), but after 500 days they have an 8.84 (95% CI 2.55, 30.62) greater risk of failure than other components. Comparison of the magnitude of the HRs in a model with and without ASR Hip Systems revealed similar findings (data not shown). Discussion In a large US cohort of primary THAs, cumulative aseptic survival at 8 years was 96.7% and aseptic revision per 100 observation years was 0.52. Instability and aseptic loosening accounted for the majority of the reasons for aseptic revisions (49.7% and 13.9% respectively).
Please cite this article as: Khatod M, et al, Risk factors for Total Hip Arthroplasty Aseptic Revision, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.01.023
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Table 3 Crude Revision Rate, Revision Rate/100 years of Observation, and Reasons for Aseptic Revision, 2001–2010. Total Sample Crude revision rate, N (%) Revision rate/100 years of observation, total years (rate/100 years) Reasons for Revision Instability Aseptic loosening Peri-prosthetic fracture Polyethylene insert wear Leg length inequality Component fracture Osteolysis Metallosis Hematoma Cup malposition Wound drainage Seroma Wound dehiscence Other
635 (1.7) 12,1716 (0.52)
N
%
316 90 72 27 22 11 11 8 8 9 3 1 1 70
49.8 14.2 11.3 4.3 3.5 1.7 1.7 1.3 1.3 1.4 0.5 0.2 0.2 11.0
Patient, implant, surgeon and hospital risk factors of THA revisions are described below. Patient Factors Similar to other studies, we found that older age was associated with a lower risk of revision THA [7,8,34,36]. Our results were also consistent with other studies that did not find an association of BMI or diabetes with aseptic revision [13,16]. Similar to studies that have reported race as a risk factor for THA medical complications [40], we found that while Hispanic and Asian race have a lower risk of revision, black and white patients have a similar risk of aseptic revision. Malik et al [25] have noted genetic differences in revision risk among THA patients which may play a role in racial differences. In contrast to a recent US study and a meta-analysis, females in our study had a higher risk of THA failure [20,34]. The different findings could be due to the samples used in the studies, the time when the cohorts had their procedures, the follow-up of the studies, and the definitions of failure used by the studies. A higher risk of revision in women may be partially attributed to smaller size implants used in female patients (smaller femoral heads) resulting in a higher rate of instability [6,12] and possibly in higher revision rates.
Fig. 1. Survival curves for diabetics vs. non-diabetic patients, 2001–2010.
Fig. 2. Survival Curves for ASR Hip System components compared to all other primary THA components, 2001–2010.
While we did not find worse general health status, measured by ASA in our study, to be associated with revision within our study, other studies have found support for higher risk of THA based on comorbid status [18,23,28,34]. These finding may be explained by the use of a different general health index score used and restriction to elective primary THA surgeries within our study. In a study by Wright et al [43], where ASA was evaluated, findings were similar to ours. Several studies also suggest that indication for primary surgery is a predictor of THA revision [8,18,34,41]. However, we did not find diagnosis to be a predictor after adjusting for other patient, implant and surgical factors. These inconsistencies may also be related to our inclusion criterion of only elective THAs. Other studies have also produced conflicting results on the importance of diagnosis in risk of revision [3,11] suggesting the need for further research. Implant and Technique Factors Within our study, conventional polyethylene inserts and ceramicon-ceramic articulations had a higher risk of revision comparison to highly cross-linked polyethylene. Conventional polyethylene has been shown to perform clinically worse than HXLPE in both singlecenter trials and registry data [17,27]. Ceramic-on-ceramic outcomes were also shown to be at higher risk of revision in the National Joint Registry for England and Wales, but have not been shown in other clinical trials and in the US population [5,17,33]. These findings emphasize the importance of THA articulation in implant selection. In contrast to findings reported by Australia and England and Wales [1,38], metal-on-metal articulations did not have an increased risk of revision in our study. However, the ASR implant had a drastic increase in risk of revision after 500 days. This finding is consistent with a recent study based on Medicare administrative data [5]. Of importance, is the significant spike in the revision of metal-on-metal implants at 6 and 7 years reported by both the Australian and England Wales arthroplasty registries, and a longer follow-up period than that of our cohort and in the Medicare sample study. Additional length of follow-up may produce similar findings within our TJRR and further studies are underway to monitor the cohort of patients with these bearings. While several registries and studies suggest that surgical approach and head size influence risk of dislocation [4,6,12,15], we did not discover an increased risk for aseptic revision in our study. However, the endpoint for our study was aseptic revision as opposed to dislocation which may explain the differences in findings. Many postoperative
Please cite this article as: Khatod M, et al, Risk factors for Total Hip Arthroplasty Aseptic Revision, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.01.023
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Table 4 Associations of Patient, Procedure, Implant, Surgeon, and Hospital Risk Factors With Risk of Aseptic Total Hip Arthroplasty Revision (Hazard Ratio and 95% Confidence Interval).
Patient Age (increasing 10-year increments) Female vs. male Race: black vs. white Race: Hispanic vs. white Race: Asian vs. white Race: other (includes Native American and multi-race) ASA score: ≥3 vs. ASA 1 and 2 Diabetes (yes vs. no) Diabetes * time interaction (reference: time ≥1461 days) BMI: between 30 and 35 kg/m2 vs. b30 kg/m2 BMI: N35 kg/m2 vs. b30 kg/m2 Osteoarthritis (yes vs. no) Osteonecrosis (yes vs. no) Post-traumatic arthritis (yes vs. no) Rheumatoid arthritis (yes vs. no) Procedure Bilateral (yes vs. no) Surgical approach: anterolateral vs. posterior Surgical approach: direct lateral vs. posterior Surgical approach: other vs. posterior Implant attributes and implants Fixation: hybrid vs. uncemented Fixation: cemented vs. uncemented Femoral head size:b36 mm vs. ≥36 mm Bearing surface: ceramic-on-ceramic vs. metal-on-HXLPE Bearing surface: ceramic-on-conventional polyethylene vs. metal-on-HXLPE Bearing surface: ceramic-on-HXLPE vs. metal-on-HXLPE Bearing surface: ceramic-on-metal vs. metal-on-HXLPE Bearing surface: metal-on-constrained vs. metal-on-HXLPE Bearing surface: metal-on-conventional vs. metal-on-HXLPE Bearing surface: metal-on-metal vs. metal-on-HXLPE Depuy's ASR Hip System vs. no Depuy's ASR Hip System component Depuy's ASR Hip System * time interaction (reference: time b500 days) Surgeon and hospital Surgeon fellowship (yes vs. no) Surgeon annual volume: b30 cases vs. ≥30 cases Site annual volume: b75 cases vs. ≥75 cases
HR
Low 95% CI
High 95% CI
P Value
0.91 1.35 0.83 0.49 0.35 1.35 1.07 1.12 0.96 0.94 1.01 0.72 0.92 1.10 1.18
0.84 1.14 0.60 0.31 0.17 0.59 0.89 0.59 0.50 0.78 0.82 0.46 0.59 0.57 0.67
0.99 1.60 1.14 0.78 0.72 3.08 1.29 2.13 1.83 1.13 1.25 1.13 1.44 2.11 2.08
0.037 b0.001 0.249 0.002 0.004 0.473 0.490 0.729 0.901 0.507 0.899 0.155 0.719 0.782 0.564
1.42 0.94 1.12 1.36
0.65 0.53 0.56 0.60
3.12 1.67 2.24 3.08
0.382 0.840 0.746 0.462
0.83 1.59 1.29 1.87 2.17 0.85 1.90 2.45 1.81 1.06 0.97 9.13
0.61 0.74 1.00 1.09 1.04 0.66 0.82 0.83 1.34 0.75 0.42 4.01
1.15 3.41 1.67 3.22 4.52 1.10 4.42 7.20 2.44 1.51 2.21 20.8
0.261 0.230 0.054 0.023 0.039 0.220 0.134 0.104 0.001 0.735 0.938 b0.001
1.01 1.18 1.10
0.75 0.91 0.58
1.35 1.53 2.07
0.962 0.221 0.769
HR = hazard ratio; CI = confidence interval; BMI = body mass index; ASA = American Society of Anesthesiologists; HXLPE = highly cross-linked polyethylene.
dislocations are treated with closed reduction without revision surgery making revision surgery a less sensitive outcome for femoral head and surgical approach analysis. Surgeon and Hospital Factors Unlike other studies that have found surgeon fellowship training and hospital volume [14,23,34] our study did not identify these as independent risk factors for revision. Our classification of lower- and higher-volume surgeons may not be sensitive enough to pick up differences as other studies compared surgeons with less than 10 cases per year to surgeons with over 100 annual cases. Similar issues surrounding classification of volume may explain differences in hospital volume findings. Manley et al [26] also found no association with hospital volume and total hip revision rates when evaluating the Medicare claims data. Strengths and Limitations A strength of this study is the large contemporary cohort of over 36,000 patients. The diversity of the sample, including patient, surgeon and facility, making the results generalizable to the greater population is also a strength of this study. In addition, this is a prospectively monitored cohort with outcomes that are validated through chart review ensuring a high level of data accuracy. The level of detail in patient and surgical information presented in the current study is not available in other larger samples of THAs. In the absence of randomization, this level of detailed information allows us to better
address the issue of confounding in this observational study. Limitations of this study include its observational nature, some missing data, attrition in the cohort, and the possibly the choice of some of the data definitions used in our analysis. Our data are observational and therefore causality cannot be established from our analysis. Some missing information in our data could lead to information bias, however, our use of multiple imputation minimizes the likelihood of obtaining these biased estimates and maximizes efficiency. Another form of missing data occurs because patients leave the health plan or die. Our survival analysis model treats these individuals as censored and assumes that all individuals who are censored are from the same population as individuals who are not censored (i.e., the survival in the two groups is the same after conditioning on the covariates), which is a reasonable assumption. Certain definitions used in our study (such as high- and low-volume surgeons, diabetic status of patients) are not necessarily standard criteria used throughout the literature and should not therefore be interpreted as such. Additional limitations of the study include our relatively short follow-up period and the lack of patient-reported and radiographic outcomes which may be a more sensitive measure of early THA failure. Conclusion THA cumulative aseptic survival at 8 years was 96.7%. Patient factors affecting THA aseptic revision included gender and race. Certain bearing surfaces were also found to be risk factors of aseptic revision.
Please cite this article as: Khatod M, et al, Risk factors for Total Hip Arthroplasty Aseptic Revision, J Arthroplasty (2014), http://dx.doi.org/ 10.1016/j.arth.2014.01.023
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