Purpose: Femoroacetabular impingement (FAI) is a precursor to osteoarthritis (OA) of the hip. To investigate the fate of impingement abnormalities we analyzed the contralateral hip in patients undergoing THA for advanced FAI. Our purpose was to determine the bilaterality of FAI abnormalities, and to describe the prognosis of these deformities.

Method: We reviewed 508 patients ≤50 years of age treated with THA. Radiographic review identified 70 hips that had OA secondary to FAI (71% cam, 5% pincer, 24% combined). Bilaterality was determined radiographically, and the fate of the contralateral hip was analyzed by determining radiographic presence and progression of OA, and the need for subsequent THA.

Results: 71% of the patients were male and the average age was 43.2 years. The contralateral hip was analyzed on radiographs over an average 9 year period (range, 4–30 years). 100% of the contralateral hips had radiographic features of FAI. 49 (70%) of the contralateral hips demonstrated degenerative disease. 14 had advanced OA at presentation, 41 had progressive joint space narrowing, 25 had progression of Tonnis OA grade and 26 underwent subsequent THA. Statistical analysis showed that alpha angle, LCEA, joint space width, and head-neck ratio have strong predictive value for subsequent THA (p< 0.05).

Conclusion: This study demonstrates that FAI abnormalities are commonly bilateral and are associated with OA progression in the majority of hips. Patients diagnosed with FAI should have both hips monitored, and joint preservation surgery or THA considered when appropriate.