Anatomic features associated with femoroacetabular impingement are equally common in hips of old and young asymptomatic individuals without CT signs of osteoarthritis.

OBJECTIVE: The purpose of this article is to evaluate and compare the prevalence and measurement values of CT signs of femoroacetabular impingement (FAI) in asymptomatic hips without CT signs of osteoarthritis between two age groups: younger than 40 years and older than 60 years. SUBJECTS AND METHODS: We prospectively included patients undergoing thoracoabdominopelvic MDCT for nonorthopedic indications with asymptomatic hips and excluded hips with signs of osteoarthritis seen on CT. Two age groups including 75 hips each were enrolled (< 40 years old: mean age, 31 years; 15 women; > 60 years old: mean age, 66 years; 21 women). Two observers independently performed the image analysis. Prevalences and quantitative values of the cam (alpha angle and femoral head-neck offset) and pincer (acetabular version angle, acetabular index, lateral center-edge angle, crossover sign, and posterior wall sign) FAI morphotypes were compared using both difference and equivalence tests. Intraobserver agreement was assessed. RESULTS: The prevalence of CT signs of FAI were high and showed great variation depending on the signs and cutoff values, in both groups (9-63% for cam; 3-50% for pincer). The prevalence and measurement values of CT signs of the cam morphotype were equivalent between the two age groups. The prevalence and measurement values of CT signs of the pincer morphotype were statistically equivalent between the age groups except for the acetabular version angle, lateral center-edge angle, and crossover sign for which no statistical difference was found, but statistical equivalence was not reached. Interobserver and intraobserver agreement were moderate to almost perfect (κ = 0.72-0.89; intraclass correlation coefficient, 0.42-0.94). CONCLUSION: The prevalence and measurement values of most CT signs of FAI morphotypes were high and equivalent between the two age groups of patients with asymptomatic nonosteoarthritic hips.