Association Between Total Hip Replacement Characteristics and 3-Year Prosthetic Survivorship : A Population-Based Study

Importance  Total hip replacement (THR) is successful in treating hip arthritis. Prosthetic survivorship may depend on characteristics of the implant, notably THR fixation technique and bearing surface type.

Objective  To compare THR short-term survivorship according to cement type and bearing surface.

Design, Setting, and Participants  The cohort included all French patients aged 40 years or older covered by the general scheme of the French national health insurance system who had undergone THR from April 1, 2010, through December 31, 2011, for arthritis, according to French national health insurance databases. The cohort was followed up until December 31, 2013. The THR survivorship was assessed according to cement type and bearing surface in univariate and multivariate Cox proportional hazards regression models adjusted for patient and implanting center characteristics.

Exposures  Antibiotic-free cemented THRs and antibiotic-impregnated cemented THRs were compared with uncemented THRs. Ceramic-on-ceramic (CoC), ceramic-on-polyethylene (CoP), and metal-on-metal (MoM) THRs were compared with metal-on-polyethylene (MoP) THRs.

Main Outcomes and Measures  Revision, including any surgical reintervention in which the implant or any of its components was changed or removed.

Results  The study cohort comprised 100 191 individuals: mean age at baseline, 69.5 years; women, 56.6%; uncemented THR, 74.8%; antibiotic-free cemented THR, 3.8%; antibiotic-impregnated cemented THR, 21.4%; CoC, 40.9%; MoP, 33.9%; CoP, 20.8%; and MoM, 4.4%. During the median 33-month follow-up period, 3142 individuals underwent prosthetic revision. Antibiotic-impregnated cemented THRs had a better prognosis than uncemented THRs: cumulative revision rates were 2.4% and 3.3%, respectively (P < .001), and the multivariate adjusted hazard ratio was 0.75 (95% CI, 0.67-0.84; P < .001). This association was particularly significant in women. The CoP and CoC THRs were no different from the MoP THR. The MoM THR had slightly shorter survivorship compared with the MoP THR (adjusted hazard ratio, 1.20; 95% CI, 1.01-1.43; P < .001).

Conclusions and Relevance  Characteristics of THR are related to early prosthetic revision: antibiotic-impregnated cemented THRs have a better prognosis and MoM THRs a worse one. These findings are useful in helping surgeons select a THR fixation technique and helpful for both patient and surgeon in the decision-making process.

Total hip replacement (THR) to replace a damaged coxofemoral joint has become one of the most common and successful surgical procedures in modern practice. Primary or secondary degenerative osteoarthritis is the main indication,¹ but THR is also used in patients with rheumatoid arthritis or avascular necrosis and after trauma, which is common in elderly populations, especially women older than 80 years.² The number of THR procedures has substantially increased in all industrialized countries in recent decades,^3,4 largely because of the aging of the population. A range of implant designs and materials are available, but 2 particularly important decisions that the surgeon has to make are which fixation technique to use (eg, uncemented, both-sides cemented [antibiotic-impregnated or antibiotic-free cement], hybrid, or reverse hybrid)^5-11 and which bearing couple^5-11 to choose. The bearing surface can consist of a ceramic or metal femoral head with ceramic, metal, or polyethylene on the acetabular side.

Although results are generally good, revision is sometimes necessary (approximately 1% per year^12-14). Prosthetic revision is a longer and more complex operation than primary arthroplasty and has a higher incidence of postsurgical complications.^15,16 Hence, understanding the factors associated with early prosthetic survivorship constitutes a public health issue.

Survivorship and reliability of THR can be assessed and compared by means of observational studies based on national data derived from registries or health insurance systems. The few registries^5-11 and clinical studies^17-26 available have found that THR characteristics could be related to revision risk. However, results have been inconsistent, and none of these studies have compared prosthetic survivorship according to cementation type and bearing surface independently of other THR revision risk factors. Some studies^17-22 have compared uncemented and cemented THRs, but these ignored both antibiotic use and bearing surface. Others^23,24 have compared cement with and without antibiotic but did not take bearing surface into account. Others still have compared revision rates with different bearing surfaces^8,11,25,26 but did not take fixation technique into account.

The aim of this study was to examine the early effect of the choice of fixation technique and bearing surface on THR survivorship in a population-based cohort, exploiting the data from the French national health insurance system linked to hospital discharge databases.^27-33

We used Système National d'Information Inter-Régimes de l'Assurance Maladie (SNIIRAM), the French National Health Insurance Information System.³⁴ This system covers the entire French population, with different schemes based on employment situation. We limited exploitation of the data from the beneficiaries of the general scheme (approximately 77% of the population) for whom SNIIRAM comprehensively records—with dates—outpatient drugs (Anatomical Therapeutic Classification codes) and medical devices prescribed, as well as reimbursed services and procedures. The database does not stipulate the medical indication for each reimbursement but contains patients’ demographic, administrative, and medical details (including any long-term conditions, such as diabetes mellitus, cancer, or cardiovascular disease) and the date of their death. An anonymous, unique identifier for each patient links SNIIRAM information to a national hospital discharge database (Programme de médicalisation des systèmes d'information), which covers all hospitals and provides reasons for admission (in International Statistical Classification of Diseases, 10th Revision [ICD-10] format).

The eligible population comprised patients 40 years or older who had a first unilateral primary THR for osteoarthritis from April 1, 2010, through December 31, 2011 (20 months). Not included were patients who underwent a first primary THR for trauma or bone cancer, underwent bilateral THR or prosthetic revision before the inclusion period, or did not receive medical reimbursement after the index THR. The study cohort comprised 107 382 patients. The THR characteristics were missing for 7191 who were excluded from subsequent analyses, leaving 100 191 patients (Figure 1); 40 878 of these were enrolled in 2010 and 59 313 in 2011.

Approval from the French data protection agency (Commission nationale de l’informatique et des libertés) was obtained for this study. Informed consent was not required because information was collected anonymously.

The outcome was THR revision (including any surgical reintervention in which the implant or any of its components was changed or removed). Observations were right-censored on December 31, 2013, if neither revision nor death had yet occurred.

Four types of fixation technique are commonly available: uncemented, both-sides cemented, hybrid (femoral component cemented and acetabular component uncemented), and reverse hybrid (femoral component uncemented and acetabular component cemented). The last technique only concerned 1.5% of the cohort, who were excluded from the study. We pooled patients with hybrid and both-sides cemented THRs so the 3 fixation technique groups were (1) uncemented, (2) antibiotic-free cement, and (3) antibiotic-impregnated cement. Four bearing couples were analyzed: ceramic-on-ceramic (CoC), ceramic-on-polyethylene (CoP), metal-on-metal (MoM), and metal-on-polyethylene (MoP).

We collected and controlled for a series of patient and implantation center characteristics known to be or suspected of being associated^35-39 with a risk of complications after joint replacement. Patients’ sociodemographic variables—namely, age, sex, social deprivation index,⁴⁰ and date of death—were obtained from the SNIIRAM database.

At baseline, treatments were identified with prescriptions (Anatomical Therapeutic Classification codes) reimbursed at least once within 90 days of inclusion, namely, benzodiazepines, antihypertensive agents, osteoporosis treatments, oral corticosteroids, lipid-lowering agents, or antidepressants. Diabetes and morbid obesity were defined (ICD-10 categories) on the basis of hospital discharge reports or long-term condition recorded during the year before inclusion together with relevant prescriptions. Center activity was defined as the mean number of hip arthroplasty procedures (both primary and revision) performed per month during the inclusion period. Whether the implantation center was private or public and the duration of the hospital stay (in days) were also defined.

Continuous variables were not normally distributed and have been categorized. Characteristics of patients, implanting centers, and hospital stays were thus compared according to the 3 THR cement types and 4 bearing surface types using a χ² test. Kaplan-Meier survival analysis and a log-rank test were used to assess differences in cumulative revision risk according to cement type and bearing surface.

Hazard ratios (HRs) for revision with 95% CIs related to THR characteristics were assessed using univariate Cox proportional hazards regression models and then a multivariate Cox proportional hazards regression model to adjust for possible confounding factors: sex; age at implantation, classified as young (40-59 years), middle-aged (60-74 years), or elderly (≥75 years); social deprivation index⁴⁰ (quintiles); diabetes; morbid obesity; medical treatments; public or private; center activity (tertiles); and duration of stay (3 groups).

Cement type and bearing surface are related variables technically: cement is used less often for acetabular cup fixation in MoM and CoC THRs.⁸ These characteristics were therefore included simultaneously in the multivariate Cox proportional hazards regression model.

Assumption of proportional hazards was graphically assessed for each variable. Interactions between THR cement type and age, as well as sex and bearing surface, in association with prosthetic survivorship were investigated.

We performed 2 separate and distinct sensitivity analyses. First, hybrid and cemented THRs were separated for sensitivity analysis, making 5 groups: (1) uncemented THRs, (2) hybrid THRs without antibiotic, (3) hybrid THRs with antibiotic, (4) both-sides cemented THRs without antibiotic, and (5) both-sides cemented THRs with antibiotic.

Second, we considered that THR revision and patient death may be competing risks^41,42: the death of a patient precludes subsequent revision. We therefore conducted a sensitivity analysis by using a competing risks multivariate Cox proportional hazards regression model adjusted for the same variables as the main analysis, fitting the Fine and Gray proportional hazards model.^42,43

During follow-up, some patients underwent a second primary THR on the other hip. It has been pointed out that bilaterally operated (or implanted) on patients can introduce methodologic limits.⁴⁴ We thus investigated the robustness of our results, respecting bilaterality (methods and results in eMaterial and eTables 1, 2, 3, and 4 in the Supplement).

All statistical tests were 2-tailed with an α-risk of 5%. Statistical analyses were performed using SAS statistical software, version 9.4 (SAS Institute Inc).

The mean (SD) age was 69.5 (10.8) years (median age, 71 years; interquartile range [IQR], 62-78 years). The women (56.6% of the enrolled individuals) were significantly older than the men (71.2 vs 67.2 years, P < .001). Implantation was performed at a private sector establishment in 66.3% of cases, and 71.5% of procedures were performed in centers that performed more than 16 procedures per month. Fixation was uncemented in 74.8% of cases, with antibiotic-free cement in 3.8% and antibiotic-impregnated cement in 21.4%. Bearing surfaces were CoC (40.9%), MoP (33.9%), CoP (20.8%), or MoM (4.4%).

Baseline patient characteristics, hospital stay, and bearing surface are presented according to THR fixation technique in Table 1. Neither patient characteristics nor hospital stay were balanced across the 3 THR fixation technique groups: more men and young patients were given uncemented THRs, whereas patients taking medications (apart from oral corticosteroids) had more cemented THRs. Cemented THR was more common in the most privileged quintile of patients. Private centers performed more uncemented THR procedures, and centers with higher activity performed more cemented procedures. Baseline characteristics were also not balanced across the 4 bearing surface groups: covariables associated with fixation technique were also associated with bearing surface (eTable 5 in the Supplement).

The THR fixation technique and bearing surface were closely related (P < .001): cement was used in 11.3% of CoC procedures compared with 40.3% for MoP (Table 1).

During the median 33-month follow-up (IQR, 27-39 years; range, 0.1-44 months), 3142 prosthetic revisions (3.1%) were recorded (41.3% total and 58.7% partial). Univariate survival analysis indicated that using antibiotic-impregnated cement was associated with a significant decrease in the risk of revision compared with uncemented THR (respective cumulative revision rates: 2.4% vs 3.3%; P < .001; HR, 0.74; 95% CI, 0.67-0.81). Revision risk for antibiotic-free cemented THRs was not different compared with uncemented THRs (HR, 0.95; 95% CI, 0.79-1.14) (Figure 2). Both CoC and MoM THRs had poorer prognoses than MoP THRs (HR, 1.11; 95% CI, 1.03-1.21 and HR, 1.32; 95% CI, 1.12-1.56, respectively).

Multivariate Cox proportional hazards regression analysis gave a similar association between prosthetic survival and fixation technique as univariate analysis. The THRs that used antibiotic-impregnated cement had a better prosthetic survivorship than uncemented THRs after adjustment for other risk factors for revision, including bearing surface (adjusted HR [aHR], 0.77; 95% CI, 0.70-0.85; P < .001). Antibiotic-free cemented THR survivorship was comparable with that of uncemented THRs (aHR, 0.98; 95% CI, 0.81-1.18). Similar results were observed when bearing surface was excluded from the multivariate model: compared with uncemented THR, respective HRs (adjusted for patient characteristics, treatments, center characteristics, and hospital stay) for cement with and without antibiotic were 0.77 (95% CI, 0.70-0.84) and 0.96 (95% CI, 0.80-1.15). The association between THR survivorship and bearing surface persisted only for MoM THR (aHR, 1.20; 95% CI, 1.01-1.43). Similar results were also observed when fixation technique was excluded from the multivariate model: HRs adjusted for patient characteristics, treatments, center characteristics, and hospital stay (95% CIs) with respect to MoP were 1.08 (0.98-1.18) for CoC, 1.04 (0.94-1.15) for CoP, and 1.20 (1.04-1.46) for MoM.

In univariate analysis, prosthetic survival was significantly associated with sex and age. Revision risk was higher in men than women (HR, 1.10; 95% CI, 1.03-1.19) and in younger patients than older ones (HR, 1.25; 95% CI, 1.14-1.36 and HR, 0.89; 95% CI, 0.82-0.96, respectively) compared with middle-aged patients. Revision risk was higher in medicated patients (apart from antihypertensive and antiosteoporotic drugs). Prognosis was poorer for THRs performed in moderate- or low-activity centers (HR, 1.18; 95% CI, 1.08-1.29 and HR, 1.38; 95% CI, 1.22-1.56, respectively) compared with THRs implanted in high-activity centers (>16 procedures per month). Results in the multivariate Cox proportional hazards regression model were similar to those in the univariate analysis (Table 2).

Significant interaction was observed between cement type and sex: the HR between cement type and revision was significantly lower in women than in men (P for interaction = .01). No significant interactions were detected between fixation technique and age or bearing surface in the association with prosthetic survival (Table 3).

First, sensitivity analysis revealed that the association between THR survivorship and fixation technique is similar when comparing uncemented with hybrid or both-sides cemented THRs (Table 4). Baseline characteristics according to THR fixation technique separated into 5 categories are summarized in eTable 6 in the Supplement.

Second, results of competing risk sensitivity analysis were similar to those in the main analysis. Results from the Fine and Gray model⁴³ are provided in eTable 7 in the Supplement.

Early prognosis in THR with antibiotic-impregnated cement is significantly better than uncemented THR regardless of bearing surface and prosthetic revision risk factors, particularly in women. The association between fixation technique and short-term THR survivorship has the same pattern in both-sides cemented and hybrid THRs; cementing of the femoral stem probably explains most of this observed relation. Short-term THR survivorship is poorer in young patients. The global association between bearing surface and THR revision was not statistically significant; however, focusing on MoM, they had slightly higher revision risk (aHR, 1.20; 95% CI, 1.01-1.43).

The observed rate of 3.1% prosthetic revision after 33 months is consistent with data from international registries.^5-11 Our main findings regarding fixation technique are consistent with previous studies^{17,18,20,21,45}; they also are in agreement with the mechanism revealed by Hailer et al,¹⁷ who observed that uncemented stems were more frequently revised due to periprosthetic fracture within 2 years of surgery. The Swedish registry¹¹ found that, in patients receiving an uncemented stem, periprosthetic fracture was 3-fold higher for patients older than 70 years. The more significant association between cement type and prosthetic survivorship observed in women could be due to a difference in bone quality.^46,47

The event analyzed was prosthetic revision with the main indications of osteoarticular infection, dislocation, and periprosthetic fracture.^8,19 Parvizi et al²³ and Wang et al²⁴ found that using antibiotic-impregnated cement halved the deep infection rate, suggesting that our findings could be due to fewer revisions for reason of infection. To investigate this hypothesis, studies covering both cement type (with and without antibiotic) and indications for revision would be necessary.

With respect to the association between bearing couple and prosthetic survivorship, the finding that MoM THR revision risk is slightly higher than that of MoP, CoC, and CoP is consistent with the findings of previous studies²⁵ and registers,^8,10,11 which found this relation with 10 years of follow-up. Thanks to our large cohort size and despite MoM only representing 4.4% of included THRs, we found similar results with a shorter follow-up. This finding supports the contention that the short-term evolution of THRs should be considered as a point of interest, particularly with studies conducted with nationwide data.

Our results are in agreement with previous findings about young age and sex,²² morbid obesity,³⁷ and implanting center activity.^8,38,39 The effect we found of benzodiazepine or antidepressant medication and short-term prosthetic revision has not been previously reported in the literature. It might be due to adverse effects (drowsiness and confusion⁴⁸) that increase the risk of falling. Studies focusing on these covariates together with indications for revision would be useful.

The large number of patients, the possibility of comparing prosthetic survivorship according to cement type and bearing surface using a multivariate model, and the ability to adjust survival analysis for known prosthetic revision risk factors are strengths of the study. To our knowledge, no such studies have been performed on a population-based cohort before. The only data available on large populations are those in national registries,^5-11 and previous studies^17,22 only compared cemented and uncemented THR without considering antibiotic THR. Moreover, no previous analyses looked at both fixation technique and bearing couple. Our work, therefore, provides novel information.

Our conclusions might not be applicable to patients who had undergone THR due to trauma or cancer because they were excluded from our study. Because of missing THR characteristics, we excluded 7191 individuals (7.2%) from the analyses. In this group, the revision rate was 2.8%, which is comparable to that in the analyzed individuals, although they differed in terms of sex and age distribution, and more of these excluded patients had undergone implantation in the public sector. Nevertheless, there is no obvious reason to believe that these missing data would be linked to cement type or bearing couple, so we do not think that excluding these patients substantially affected the correlations observed.

Implant survivorship may not be the only relevant outcome after THR: a patient with a failing THR would not have a revision if she died (ie, death might be a competing risk). Gillam et al⁴² found that, if mortality is high, Kaplan-Meier analysis may overestimate the probability of revision. We fitted a Fine and Gray⁴³ competing risk model, which produced results similar to those of the main analysis, so we think mortality probably did not seriously distort the results.

Although prosthetic revision is an unambiguous, objective outcome, it is not the only sign of implant failure⁴⁹; considering revision as the only outcome in implant survivorship has been debated in the orthopedics literature. Other markers, such as quality of life and/or functional improvement, could be used as a secondary outcome, but the SNIIRAM database does not provide such information, and collecting this type of data for a large number of patients would be daunting.

Bilaterality could be mentioned as a limitation⁴⁴ of this study, but we performed additional analyses to investigate the robustness of our results. These complementary approaches are detailed in eMaterial in the Supplement. Their results suggest that bilaterality has probably had very little effect on the results reported. This finding is consistent with the findings of Robertsson and Ranstam⁵⁰ on the revision of knee prostheses.

In addition, the presence of possible residual confounding due to factors not collected in our study cannot be ruled out. Among these, the surgical approach⁵¹ used was not available in the Programme de médicalisation des systèmes d'information database, although some studies have indicated that a lateral approach yields worse outcomes than an anterior or posterolateral approach in primary hip arthroplasty. We also were not able to discern stem length,^52-55 femoral head diameter,⁵⁶ or brand,^8,11,57 all of which may affect THR survivorship. Last, the cost of antibiotic-impregnated cement is also an important issue,^58-60 and medicoeconomic studies would be required to focus on its cost-effectiveness.

Characteristics of THR are related to early implant survivorship. After 33 months of follow-up, antibiotic-impregnated cemented THRs have a better prognosis. Hybrid and both-sides cemented THRs have similar survivorship that is better than that of uncemented THRs. MoM THRs have a slightly worse prognosis. These findings are useful for helping surgeons choose the appropriate THR fixation technique for their patients.

Accepted for Publication: April 7, 2015.

Corresponding Author: Sandrine Colas, MSc, MPH, Department of Epidemiology of Health Products, French National Agency for Medicines and Health Products Safety, 143-147 Blvd Anatole France, F-93285 Saint-Denis Cedex, France (sandrine.brindejonc-colas@ansm.sante.fr).

Published Online: August 19, 2015. doi:10.1001/jamasurg.2015.1325.

Author Contributions: Ms Colas had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Colas, Piriou, Zureik.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Colas, Piriou, Zureik.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Colas, Piriou, Collin.

Administrative, technical, or material support: Piriou.

Study supervision: Zureik.

Conflict of Interest Disclosures: None reported.