PATIENT REPORTED OUTCOMES FOLLOWING PRIMARY HIP REPLACEMENT SURGERY: DEVELOPMENT AND INTERNAL VALIDATION OF A PROGNOSTIC TOOL

s / Osteoarthritis and Cartilage 22 (2014) S57–S489 S209 Purpose: Non-steroidal anti-inflammatory agents (NSAIDs) are commonly used to manage symptoms in patients with knee osteoarthritis (OA). While randomized controlled trials have demonstrated efficacy, real world effectiveness of these agents in long term studies is lacking. This study sought to estimate the effectiveness of NSAIDs on symptom management over 4 years among persons with radiographically confirmed OA. Marginal structural models, which take into consideration the likely dual role of indices of disease severity as confounders and intermediary variables, were compared to standard repeated-measure analyses. Methods: We identified NSAID naive participants with radiographic knee OA in the Osteoarthritis Initiative. Participants were evaluated over 4 years. NSAID users included those reporting any use of prescription medication use (i.e., either regular use or as-needed use) at each assessment. Outcome measures included WOMAC Pain, Stiffness and Physical Function. Beta coefficients derived from marginal structural models and generalized estimating equation models represented the average change in outcomemeasures attributed to long term NSAID use. Minimally important clinical differences were a priori set as at least 1.2 for pain, 0.5 for stiffness, and 4.1 for function. Results: Persons with radiographically confirmed OA with long term reports of prescription NSAIDS use experienced improvements in WOMAC Pain: -0.99 (95% Confidence Interval (CI): -2.38 to 0.4); WOMAC Stiffness: -0.64 (95% CI: -1.52 to 0.24); and WOMAC Function: -5.29 (95% CI: -9.7 to -0.89). In contrast, the analysis with generalized estimating equations yields an estimate of -0.03, -0.08 and 0.07 for difference in Pain, Stiffness and Function, respectively. Conclusions: When evaluated using marginal structural models, long term use of NSAIDs showed a modest trend towards relieving symptoms and a clinically significant improvement in function in patients with radiographically confirmed OA, whereas a standard regression models didn’t show such benefits. Studies on the treatment of OA using non-experimental data should consider using marginal structural models when evaluating the overall treatment effect from a timevarying treatment. 366 PATIENT REPORTED OUTCOMES FOLLOWING PRIMARY HIP REPLACEMENT SURGERY: DEVELOPMENT AND INTERNAL VALIDATION OF A PROGNOSTIC TOOL A. Judge yz, R.N. Batra y, D. Murray y, P.A. Dieppe x, M.T. Sanchez-Santos y, G. Thomas y, D. Beard y, M.K. Javaid yz, K. Dreinh€ ofer k{, K. Peter-G€ unther#, C. Cooper yz, N.K. Arden yz. yNIHR Musculoskeletal BioMed. Res. Unit, Univ. of Oxford, Oxford, United Kingdom; zMRC Lifecourse Epidemiology Unit, Univ. of Southampton, Southampton, United Kingdom; x Peninsula Coll. of Med. and Dentistry, Univ. of Plymouth, Plymouth, United Kingdom; k Inst. for Muskuloskeletal Rehabilitation, Charit e Univ.smedizin Berlin, Berlin, Germany; {Dept. of Orthopaedics, Traumatology and Sports Med., Med. Park Berlin Humboldtm€ uhle, Berlin, Germany; Dept. of Orthopaedic Surgery, Univ. Hosp. Carl Gustav Carus, Med. Faculty of the Technical Univ. of Dresden, Dresden, Germany Purpose: Although Total Hip Replacement (THR) is a successful surgical intervention, there are a minority of patients who do not achieve clinically meaningful improvement or whose symptoms get worse following surgery. The aim of this study was to develop a clinical risk prediction tool to predict patient reported outcomes following primary hip replacement surgery. Methods: We obtained data on two prospective cohorts of patients receiving primary THR for osteoarthritis: Exeter Primary Outcomes Study (n 1⁄4 1247); EUROHIP (n 1⁄4 845). The primary outcome was the Oxford Hip Score (OHS). Combining data from two large prospective cohort studies allowed us to take account of a wide and comprehensive range of both traditional and novel risk factors, including patient, radiographic and surgical predictors. Linear regression modelling was used to identify predictors of outcome. For internal validationwe used a combination of multiple imputation and bootstrapping with backward selection. Performance of the predictive model was assessed in terms of calibration and discrimination. Results: Of the radiographic variables pattern of OA was an important determinant of outcome. Those with superomedial, medial or concentric disease had worse outcomes than patients with a superolateral pattern of OA or no reduction in joint space. Arthritis in other joints, and previous surgery on other joints, were associated with worse outcomes. For surgical variables, a posterior surgical approach, and larger femoral component offset had better outcomes. For patient factors, worse preoperative pain/function, increasing age when over age 75, increasing BMI, lower levels of educational attainment and those with worse preoperative SF36 mental health scores, also had worse outcomes. These factors were operationalized into a clinical risk prediction tool. Calibration of the predicted 12-month post-operative OHS, and absolute change in OHS was good. The model showed good discriminatory ability with a bias corrected R-squared of 23.1%. We tested the ability of the model to identify patients with the worst possible outcomes following THR (defined as a change in OHS < 5-points of whom 89 (4.25%) patients met this criterion). Performance of the tool to identify patients with the worst outcomes was good (C-statistic 0.77 95%CI (0.72 to 0.82)). Conclusions: We have developed a clinical risk prediction tool that would provide information on the likely outcomes of hip replacement surgery. Following hip replacement the majority of patients do very well, and only a minority will not achieve clinically meaningful symptomatic change in OHS. The clinical tool performed well in terms of its calibration and discriminatory ability, and identification of those patients with the worst possible outcomes was good. The tool provides individualised risk prediction and allows patients to understand their expected outcomes of surgery – it has the potential to guide patientclinician decision-making. It will now undergo external validation in a new prospective cohort of patients. 367 COURSE OF PHYSICAL FUNCTIONING AND PAIN IN OSTEOARTHRITIS OF THE KNEE OR HIP: A SYSTEMATIC REVIEW M. de Rooij y, M. van der Leeden yz, A. H€ akkinen#x, W.F. Lems ky, L.D. Roorda y, C. Veenhof{, H.C. de Vet #, J. Dekker yy. yAmsterdam Rehabilitation Res. Ctr. j Reade, Amsterdam, Netherlands; zVU Univ. Med. Ctr., Dept. of Rehabilitation Med., Amsterdam, Netherlands; xDept. of Hlth. Sci., Univ. of Jyv€ askyl€ a and Jyv€ askyl€ a Central Hosp., Jyv€ askyl€ a, Finland; kVU Univ. Med. Ctr., Dept. of Rheumatology, Amsterdam, Netherlands; {Netherlands Inst. for Hlth. Services Res., Utrecht, Netherlands; VU Univ. Med. Ctr. EMGO Inst. for Hlth. and Care Res., Dept. of Epidemiology and Biostatistics, Amsterdam, Netherlands; yyVU Univ. Med. Ctr., Dept. of Psychiatry, Dept. of Rehabilitation Med., EMGO Inst., Amsterdam, Netherlands Purpose: (1) The aim of the study was to systematically summarize the literature from March 2005 to January 2013 on the course of physical functioning and pain in patients with OA of the knee or hip and (2) to provide an overview of prognostic factors of physical functioning and future pain for these patients. Methods: A search was conducted in PubMed, CINAHL, Embase and Psych-INFO in January 2013. Eligible studies were prospective cohort studies (minimum follow up was 6 months) that included participants with knee or hip OA diagnosed with radiographically and/or