Associations between pre-operative radiographic changes and outcomes after total hip replacement for osteoarthritis

Abstract

Purpose: Total hip replacement (THR) is an effective procedure for alleviating pain and improving function in the majority 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. On-going moderate to severe pain has been reported in 8 to 13% of patients and moderate to severe activity limitation in up to 30% of patients at 2 years or more following THR. The purpose of this study was to investigate whether radiographic OA severity was a determinant of pain and disability experienced by people at 1 and 2 years after THR. Methods: Data from a prospective single-centre cohort study of patients (n = 382) undergoing THR between 2006 and 2007 were analysed. Data collection included demographics (age, sex, BMI, ASA score) and surgery details (cementation, surgical approach, femoral head size). The Harris Hip Score (HHS) and the Short Form Health Survey (SF-12) were collected pre-surgery and at 1 and 2 years post-surgery. Pre-operative AP radiographs of the pelvis were read by a single observer using the Kellgren-Lawrence (K-L) and Altman atlases. The main independent variable was the modified K-L (mK-L) grade assessed from the pre-operative radiographs. A K-L grade 3 radiograph with mild joint space (JSN) narrowing was graded 3a, and one with more severe JSN 3b. A K-L grade 4 radiograph (complete loss of joint space) was divided into 4a if there was no bone attrition and 4b if there was any subchondral bone attrition. The outcome variable was the mean clinically important difference (MCID) in the HHS pain and function scores, which was determined based on half the standard deviation (SD) in change in scores. Logistic regression analyses were undertaken to assess the relationships between radiographic features and post-operative pain and function. Results: Of 387 enrolled patients 5 were excluded due to poor quality or radiographs > 6 months leaving 382 TJR cases for inclusion. Follow-up was complete for >95% of patients. The mean (SD) age was 68.9 (9.3) years, 61% were female and the mean BMI was 29.9 (9.0). The change in HHS pain scores from baseline was 27.1 (9.6) at 1 year and 27.1 (9.5) at 2 years. When pain was dichotomised into 2 groups based on the MCID (≥ 5 points), 96% of patients demonstrated a clinically meaningful improvement in pain at 1 and 2 years. The change in function scores from baseline was 16.2 (10.9) and 15.9 (11.8) at 1 and 2 years. When function was dichotomised into 2 groups based on the MCID (≥ 6 points), 81% and 78% of patients demonstrated a clinically meaningful improvement in function at 1 and 2 years. Regression analysis demonstrated significantly lower odds of a clinically meaningful improvement in pain and function for patients with less severe baseline radiographic changes, when compared to severe changes, (mK-L 4b).Table 1Multivariable-adjusted association of modified K&L with Clinically Meaningful Improvement in Pain12 months2 yearsVariableOR (95% CI)POR (95% CI)P*Modified K-L < 3a0.03 (0.00, 0.34)0.0050.05 (0.00, 0.52)0.013*Modified K-L 3b0.10 (0.01, 1.00)0.0500.12 (0.01, 1.21)0.063*Modified K-L 4a0.15 (0.02, 1.36)0.0910.13 (0.01, 1.21)0.073Reference: *Modified K-L 4b, Adjusted for Age, Gender, BMI, ASA Score, pre-operative SF-12, surgical approach, cementation and femoral head size Open table in a new tab Table 2Multivariable-adjusted association of modified K&L with Clinically Meaningful Improvement in Function12 months2 yearsVariableOR (95% CI)POR (95% CI)P*Modified K-L < 3a0.23 (0.08, 0.65)0.0060.13 (0.05, 0.35)< 0.001*Modified K-L 3b0.35 (0.17, 0.75)0.0070.26 (0.12, 0.54)< 0.001*Modified K-L 4a0.30 (0.14, 0.65)0.0020.37 (0.17, 0.80)0.011Reference: *Modified K-L 4b, Adjusted for Age, Gender, BMI, ASA Score, Re-operative SF-12, surgical approach, cementation and femoral head size. Open table in a new tab Reference: *Modified K-L 4b, Adjusted for Age, Gender, BMI, ASA Score, pre-operative SF-12, surgical approach, cementation and femoral head size Reference: *Modified K-L 4b, Adjusted for Age, Gender, BMI, ASA Score, Re-operative SF-12, surgical approach, cementation and femoral head size. Conclusions: We have demonstrated an inverse relationship between the severity of pre-operative radiographic changes and improvement in pain and function at 1 and 2 years in people undergoing primary THR for OA, and suggest that this has important clinical implications for patient selection.