Associations between pre-operative radiographic osteoarthritis severity and pain and function after total hip replacement

Total hip replacement (THR) is an effective procedure for alleviating pain and improving function in majority of patients with end-stage osteoarthritis (OA). Clinically, meaningful improvement in pain and function after surgery is not universal, and the reasons for this are unclear. We investigated whether radiographic OA severity was a determinant of pain and disability experienced by patients after THR. The Harris hip score (HHS) was collected pre-operatively and at 1 and 2 years after primary THR (N=382). The main independent variable was the modified Kellgren-Lawrence grade, which was assessed from the pre-operative radiographs. The outcome variable was response to surgery at 1 and 2 years. The minimum important difference (MID) in the HHS pain and function scores were used to determine response to surgery. This was based on achieving half the standard deviation in change in scores at 1 year. Regression models were created to assess the relationships between pre-operative x-ray findings and pain and function. Based on the MID, 96.2 and 95.5 % of patients demonstrated an improvement in pain, and 81.2 and 78.3 % of patients demonstrated an improvement in function at 1 and 2 years. Odds ratios for demonstrating an MID in both pain and functions scores for patients with less severe baseline radiographic changes were significantly lower at 1 and 2 years when compared to those with severe radiographic changes. Patients with less severe pre-operative radiographic hip damage are least likely to have substantial gains in terms of pain relief and improved function as a result of a THR. Level of Evidence: Level III, prognostic study