Operative diagnosis for revision total hip arthroplasty is associated with patient-reported outcomes (PROs)

In this observational cohort study, we used prospectively collected data from the Mayo Clinic Total Joint Registry, a large U.S. institutional registry that collects data on every patient who undergoes hip arthroplasty at the Mayo Clinic, Rochester [13, 14]. At 2- and 5-years validated pain and function surveys are administered to patients at the clinic visit, by mail or on the telephone, by trained, registry staff. The Mayo Hip questionnaire has been validated [13‐15]. Several papers using these data have been published [8, 16]. Patients were included in this study if they underwent revision THA between 1993 and 2005 and completed either a 2- or 5-year patient survey. The study was approved by the Mayo Clinic Institutional Review Board.

We used the Mayo Hip questionnaire, a validated instrument [13‐15], as the source for both PROs of interest, overall moderate-severe ADL limitation and moderate-severe pain 2- or 5-years after revision THA. We categorized the responses to limitations in seven activities including walking, climbing stairs, putting on shoes/socks, picking up objects from the floor, sitting, getting in/out of the car, rising from chair into ‘no’ , ‘mild’ , ‘moderate’ or ‘severe’ limitation for each activity. Presence of ≥3 activities with moderate or severe limitation was classified as overall moderate-severe ADL limitation (reference, no/mild ADL limitation), as previously [8, 17]. The pain question, similar to the pain question in Harris Hip Score, a validated THA outcome instrument [18‐20], stated “How much pain do you have in your operated hip?” Patients could respond- ‘none’ , ‘mild’ , ‘moderate’ or ‘severe’. None/mild pain was the reference category and moderate and severe categories were combined into moderate-severe pain, based on an a priori decision before data analyses, as in previous studies [8, 16]. These a priori decisions were based on recommendations from an experienced orthopedic surgeon (D.G.L.), who viewed moderate-severe ADL limitation or pain as undesirable outcomes of arthroplasty.

Operative diagnosis was the main predictor of interest. Based on a priori decision, diagnoses were lumped into 3 categories, as previously [8, 21‐23]: (1) loosening, wear or osteolysis; (2) dislocation, bone or prosthesis fracture, instability or non-union; and (3) failed prior arthroplasty with components removed or infection.

Since several clinical, demographic and implant related factors have been previously shown to be associated with outcomes after THA, they were included in the analyses as covariates and potential confounders [8, 11, 16]. These included: (1) demographic factors- age and gender; (2) clinical factors - body mass index (BMI) [24], American Society of Anesthesiologists (ASA) class [25, 26], depression, anxiety and medical comorbidity which was assessed by Deyo-Charlson index, a validated comorbidity measure [27], consisting of 17 comorbidities [28, 29], based on the presence of International Classification of Diseases- ninth revision (ICD)-9 codes; (3) distance from the medical center; and (4) preoperative limitation in 7 ADLs or preoperative pain, in the respective model. As previously, age was categorized into ≤60, 61–70, 71–80 and >80, BMI into ≤25, 25.1-29.9, 30–34.9, 35–39.9 and ≥40, ASA class into I-II vs. III-IV [8, 16] and distance from the medical center into 0–100 miles, >100-500 miles, >500 miles [24, 30, 31]. Depression and anxiety were assessed by the presence of ICD-9 codes in medical records before the THA.

Data on the dates of the THA, demographic details (age, gender), BMI, ASA class, operative diagnosis, distance from the medical center and preoperative limitation in 7 ADLs and preoperative pain were obtained from the Mayo Total Joint Registry, since they are captured for every patient. ICD-9 codes for the Deyo-Charlson comorbidities, anxiety and depression were obtained from linked Mayo Clinic electronic databases.

We anticipated non-response at both 2- and 5-years, higher at 5- than 2-years. We minimized confounding bias by including multiple covariates known or suspected to be associated with use of ADL limitation or pain after THA.

Our plan was to assemble a large enough sample to study without having too long a study period, therefore we chose all eligible patients from 1993 to 2005. We did not perform any formal sample size calculations.

We used univariate and multivariable logistic regression models to assess the association of operative diagnosis with the odds of moderate-severe ADL limitation and moderate-severe pain at both 2- and 5-years post-revision THA. Logistic regressions were performed using a generalized estimating equations (GEE) approach to adjust the standard errors for the correlation between observations on the same subject due to both hips having been replaced and/or multiple operations on the same hip. The multivariable model included age, gender, BMI, ASA class, anxiety, depression, Deyo-Charlson index, distance from the medical center and preoperative limitation in 7 activities or preoperative pain (in respective models). Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. A p-value ≤ 0.05 was considered statistically significant. We decided a priori to perform only four multivariable analyses for moderate-severe ADL limitation and moderate-severe pain at 2- and 5-years to avoid multiple comparisons, which would be needed, had we chosen individual ADLs as outcomes. Descriptive univariate analyses of each ADL were examined as exploratory analyses and presented in an Additional file 1. Sensitivity analyses were performed for the ADL limitation outcome (significantly associated), by adjusting the main multivariable-adjusted model additionally for ipsilateral knee involvement (model 1) or for ipsilateral knee involvement and preoperative index hip pain (model 2).

At 2-year and 5-years post revision THA, moderate-severe overall ADL limitation was reported by 51% and 53% with loosening/wear/osteolysis, 66% and 65% with dislocation/fracture/instability/non-union, and 68% and 65% with failed prior arthroplasty/infection (Table 2). Moderate-severe pain at 2- and 5-years was reported by 18% and 19%, 18% and 23% and 18% and 23%, respectively (Table 2). Limitation in each ADL is shown in Additional file 1.

Compared to patients with loosening/wear/osteolysis, patients in the other two operative diagnoses categories were twice as likely to report moderate-severe overall ADL limitation 2-years after revision THA (Table 2). At 5-years, patients in either of the two diagnostic categories were 1.6-times as likely to report moderate-severe ADL limitation each, respectively. There were no significant differences in moderate-severe pain by diagnostic category at 2- and 5-years after revision THA (Table 2).

In analyses adjusted for 15-additional variables including preoperative limitations in 7 ADLs, compared to patients with loosening/wear/osteolysis, patients with dislocation/fracture/instability/non-union had significantly higher odds (2.2-times; p = 0.002) of moderate-severe ADL limitation at 2-years post-revision THA (Table 3); those with failed prior arthroplasty/infection showed a trend towards significance with odds ratio of 1.6 (p = 0.06). At 5-years, differences were no longer significant for moderate-severe ADL limitation by diagnosis, after multivariable adjustment. As in the unadjusted analyses, moderate-severe pain did not differ significantly by diagnostic category, at 2- or 5-years in multivariable adjusted analyses, with one exception, i.e. failed prior arthroplasty/infection had a trend towards significance with odds ratio of 1.9 (p = 0.07).

Sensitivity analyses that additionally adjusted for ipsilateral knee involvement (model 1) and ipsilateral knee involvement and preoperative index THA pain severity (model 2) showed that the interpretation or significance level did not change for the associations with moderate-severe ADL limitations at 2-years (Table 4).