Outcome of total hip arthroplasty, but not of total knee arthroplasty, is related to the preoperative radiographic severity of osteoarthritis

BACKGROUND AND PURPOSE There is no consensus on the impact of radiographic severity of hip and knee osteoarthritis (OA) on the clinical outcome of total hip arthroplasty (THA) and total knee arthroplasty (TKA). We assessed whether preoperative radiographic severity of OA is related to improvements in functioning, pain, and health-related quality of life (HRQoL) 1 year after THA or TKA. PATIENTS AND METHODS This prospective cohort study included 302 THA patients and 271 TKA patients with hip or knee OA. In the THA patients, preoperatively 26% had mild OA and 74% had severe OA; in the TKA patients, preoperatively 27% had mild OA and 73% had severe OA. Radiographic severity was determined according to the Kellgren and Lawrence (KL) classification. Clinical assessments preoperatively and 1 year postoperatively included: sociodemographic characteristics and patient-reported outcomes (PROMs): Oxford hip/knee score, hip/knee injury and osteoarthritis outcome score (HOOS/KOOS), SF36, and EQ5D. Change scores of PROMs were compared with mild OA (KL 0-2) and severe OA (KL 3-4) using a multivariate linear regression model. RESULTS Adjusted for sex, age, preoperative scores, BMI, and Charnley score, radiographic severity of OA in THA was associated with improvement in HOOS "Activities of daily living", "Pain", and "Symptoms", and SF36 physical component summary ("PCS") scale. In TKA, we found no such associations. INTERPRETATION The decrease in pain and improvement in function in THA patients, but not in TKA patients, was positively associated with the preoperative radiographic severity of OA.