Prognostic Factors of Hip Replacement During a 2-Year Period in Patients Undergoing Supervised Education and Exercise Therapy. A Prognostic Model Study of 3,657 Patients with Hip Osteoarthritis

Purpose: The objectives were to: 1) describe the rate of total hip replacement (THR) and 2) identify prognostic factors for receiving THR within two years in patients with hip osteoarthritis (OA) participating in a supervised patient education and exercise therapy program. Methods: Patients aged 45 or older with hip OA enrolled in Good Life with osteoArthritis in Denmark (GLA:D®) from July 1st, 2014 to March 1st, 2017 were included in the study (n=3,965). GLA:D® is an 8-week supervised education and exercise therapy program provided to people with symptoms associated with knee or hip OA. Information on THR was collected via surgical codes from The Danish National Patient Registry. Questionnaires were filled in by clinicians and patients and potential prognostic factors included demographic and disease-specific baseline characteristics as well as measures of baseline physical function, physical activity and quality of life (QoL). The proportion of patients receiving THR during the 2-year period was evaluated using a Kaplan-Meier plot. A multivariable Cox proportional hazards model was developed using backward stepwise elimination and age as the time scale. The final model’s beta estimates were bootstrapped to check the internal validity of the model. Lastly, we calculated Harrell’s c-index to evaluate the discriminative ability of the model. Results: Three hundred and eight patients were excluded due to THR in the index hip at baseline or incomplete data for the predictor variables and we therefore included 3,657 patients. The mean age was 66.5 years (SD 8.6), and 2,687 (73%) were women. During the study period 1,114 patients (30%) received a THR. One hundred patients reported being waitlisted for THR at baseline, and of these 60 received a THR. Fig. 1 illustrates the rate of THR within the study period. Results of the multivariable Cox regression model is presented in table 1. Self-reported radiologic hip OA compared to no known radiologic hip OA predicted THR within the two years follow-up with a HR of 2.34 (95% CI 1.88-2.91) and being waitlisted for surgery predicted THR with a HR of 2.19 (95% CI 1.68-2.85). Use of pain medication, joint replacement in the other hip or in the knees, and lower hip-related QoL evaluated using the quality-of-life subscale score from Hip Disability and Osteoarthritis Outcome Score (HOOS QoL) were also prognostic factors. Variables reflecting poor health status e.g. comorbidities and smoking, which has previously demonstrated to be associated with an increased risk of complications during surgery, were associated with a lower hazard ratio for THR. The internal validation revealed low bias, and the discriminative ability of the model was acceptable (Harrell’s c-index=0.7).Table 1Multivariable Cox regression analysis on the relationship between baseline variables and Time-to-Surgery in the final model.Baseline patient characteristic (candidate prognostic factor)Hazard Ratio (95% CI)Male (vs. female)1.36 (1.19-1.55)BMI, kg/m20.99 (0.97-1.0)Smoking (vs. no smoking)0.74 (0.59-0.92)At labor marked (vs. retired)1.23 (1.01-1.51)Use of pain medication the last 3 months (vs. no pain medication)1.31 (1.12-1.54)Self-reported radiologic OA (vs. no known radiologic OA)2.34 (1.89-2.91)Two or more comorbidities (vs. none)0.79 (0.67-0.93)Waitlisted for surgery (vs. not waitlisted)2.19 (1.68-2.85)Joint replacement in other hip or knees (vs. no previous THR/TKR)1.46 (1.22-1.75)Bilateral hip symptoms (vs. unilateral symptoms)0.77 (0.66-0.89)Widespread pain (numeric: 0-56 possible pain areas)0.94 (0.92-0.95)Hip pain (VAS 0-10, converted from a 0-100 scale)1.07 (1.04-1.11)HOOS* QoL score (0-100)0.98 (0.97-0.98)ASES**(10-100)1.00 (0.99-1.00)40 meters walk test (second)1.01 (1.00-1.01)*Quality of life subscale score from the Hip disability and osteoarthritis Outcome score**ASES: Arthritis Self-Efficacy Scale. Higher scores indicate higher self-efficacy Open table in a new tab *Quality of life subscale score from the Hip disability and osteoarthritis Outcome score**ASES: Arthritis Self-Efficacy Scale. Higher scores indicate higher self-efficacy Conclusions: In patients with hip OA participating in supervised education and exercise therapy, 30% had a THR within two years. Of those waitlisted for THR at baseline, only 60% underwent surgery. A range of modifiable and non-modifiable prognostic factors for 2-year THR were identified.