Abstract
Introduction and Aims: Although the association between femoroacetabular impingement and osteoarthritis is established, it is not yet clear which hips have the greatest likelihood to rapidly progress to end-stage disease. We investigated the possible relation of specific radiological parameters, each indicative of a structural aspect of the hip joint, to progression of osteoarthritis.
Materials and Methods: Pairs of plain anteroposterior pelvic radiographs, spaced at least 10 years apart, of 43 patients (47 hips) with pistol-grip deformity of the femur and mild (Tönnis grade 1) or moderate (Tönnis grade 2) arthritis were reviewed. Radiological measurements included the α-angle, the neck-shaft angle, the Tönnis angle, the centre-edge angle of Wiberg and the anatomical medial proximal femoral angle (MPFA). The presence of the cross-over sign and the posterior wall sign was also recorded. Grading of osteoarthritis was repeated on the final films. A logistic regression analysis model was constructed, to investigate the predictive ability of radiological parameters on progression of osteoarthritis.
Results: Of the 47 hips, 31 (66%) showed evidence of progression of arthritis. There was no difference in the prevalence of progression between hips with initial grade 1 and grade 2 arthritis (p = 0.32). Comparison of the hips that progressed and those that did not revealed a significant difference for the MPFA (82° vs. 85°, p = 0.006) and the presence of the posterior wall sign (39% vs. 6%, p = 0.04) only. The regression analysis model demonstrated a predictive ability of 32% for those two parameters, with an accuracy of 78.3%.
Discussion and Conclusion: Mild-to-moderate osteoarthritis in hips with a pistol-grip deformity will not progress rapidly in all patients. In one third of them, progression will take more than ten years to manifest. Other structural aspects, relating to the geometry of the proximal femur and the acetabulum, influence in part this phenomenon. A hip with cam impingement is not always destined to end-stage arthritic degeneration.
Correspondence should be addressed to Mr Richard Wallace at Musgrave Park Hospital, 20 Stockman’s Lane, Belfast BT9 7JB, Northern Ireland.
