Predicting the longer term outcomes of total knee arthroplasty Rajiv Gandhi a, ⁎, Herman Dhotar a , Fahad Razak a,b , Peggy Tso a , J. Roderick Davey a , Nizar N. Mahomed a a Division of Orthopedic Surgery, University of Toronto, 399 Bathurst St, Toronto ON, Canada M5T 2S8 b Population Health Research Institute, McMaster University, Canada abstract article info Article history: Received 29 January 2009 Received in revised form 3 June 2009 Accepted 9 June 2009 Keywords: Knee arthroplasty Comorbidity Mental health Outcomes We asked the question of what are the patient level predictors (age, gender, body mass index, education, ethnicity, mental health, and comorbidity) for a sustained functional benefit at a minimum of 1 year follow-up after total knee arthroplasty(TKA). Five hundred fifty-one consecutive patients were reviewed from our joint registry between the years of 1998 and 2005. Baseline demographic data and the outcome scores of the Western Ontario McMaster University Osteoarthritis Index (WOMAC) and Medical Outcomes Short-Form 36 (SF36) scores were extracted from the database. Longitudinal regression modeling was performed to identify the predictive factors of interest. We had 27% of data points missing. The mean follow-up in our cohort was 3.0 years (range 1–8 years) and there were no revisions performed during this time. Clinical outcome scores were found to be relatively constant for 3–4 years after surgery and then demonstrated a gradual decline after that. Older age, year of follow-up, greater comorbidity, and a poorer mental health state at time of surgery were identified as negative prognostic factors for a sustained functional outcome following TKR (P b 0.05). Knowledge of these factors that predict outcomes should be used in setting appropriate patient expectations of surgery. © 2009 Elsevier B.V. All rights reserved. 1. Introduction It has been estimated that 7.5% of the population over the age of 55 years have some degree of knee pain and functional limitation associated with radiographic evidence of osteoarthritis(OA) [1,2]. Total knee arthroplasty(TKA) has been shown to provide reliable pain relief and quality of life improvement in the short and long term [3–6]. Few authors however have evaluated the patient level predictors of an improved longer term outcome in TKA. Knowledge of these factors allows the surgeon to appropriately counsel patients on realistic expectations and potentially determine optimal timing of surgery. Factors such as gender [7], age [7] and mental health status [8,9] have been suggested to negatively impact long term function. Many of these studies present results that have not been adjusted for potential confounders of the relationship between the predictive factor and the outcome. Moreover, no studies have used longitudinal regression, or repeated measures analysis, which is the most powerful analysis as it accounts for all data points from baseline to last follow-up and evaluates the effect of time on an outcome. It is essential to account for the effect of time (and aging) on an outcome as cross-sectional population studies have demonstrated an inverse relationship between SF-36 scores and older age groups [10,11]. The primary objective of our study was to use longitudinal regression modeling to identify the patient level predictors for a sustained functional outcome following TKA for OA at a minimum of The Knee 17 (2010) 15–18 ⁎ Corresponding author. Toronto Western Hospital, East Wing 1-439, 399 Bathurst St, Toronto ON, Canada M5T 2S8. Tel.: +1416 603 5642; fax: +1416 603 3437. E-mail address: Rajiv.gandhi@uhn.on.ca (R. Gandhi). 1 year follow-up. With this analysis, the null hypothesis is that age, gender, body mass index(BMI), education, ethnicity, mental health, and comorbidity do not affect knee arthroplasty outcomes. 2. Materials and methods This study was designed to use longitudinal regression techniques to identify the predictive factors for a sustained functional outcome following TKA. 2.1. Study sample As part of our prospective total joint arthroplasty database, patients are recruited from a single Canadian academic institution, the Toronto Western Hospital, while on a waiting list for primary knee replacement surgery. All patients are consented to participate by a research coordinator not involved in the medical care of the patients. All data are collected by patient self report. Patients not returning for follow-up then had the questionnaires mailed to their home. Phone calls were also subsequently made to encourage full participation. Our inclusion criteria for this study were being age 18 and above, a diagnosis of primary osteoarthritis, and a minimum of 1 year follow- up. All surgeries were unilateral surgeries and were performed by one of two fellowship trained arthroplasty surgeons between the years of 1998 and 2005. Both surgeons used the same implant (Genesis II, Smith and Nephew, Memphis, Tennessee) and used a cemented design. All patients were treated with immediate weight bearing after surgery and an identical postoperative protocol of antibiotics and 0968-0160/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2009.06.003 Contents lists available at ScienceDirect The Knee