Abstract
Background: Understanding of femoroacetabular impingement (FAI) continues to improve. Low-dose computed tomography (CT) is increasingly utilized due to its improved ability to characterize the complex and variable hip morphologies of different FAI patients, compared to plain radiographs. This study defined FAI morphology in adolescents and compared males and females utilizing low-dose CT. Methods: A multi-center, prospective cohort of FAI patients undergoing arthroscopy was performed. Patients 14-18.9 years of age were the focus of the current study. All patients underwent low-dose CT for preoperative planning with radiation exposure, similar to 3-4 AP pelvis radiographs. Localization with a clock-face was utilized (3:00 was anterior and 9:00 posterior). Univariate analysis and multivariable regression were used to determine differences between male and female groups. Results: There were 194 adolescent patients. Utilizing low-dose CT, males had higher alpha angles at 76.7°±10.3° compared to females 63.9°±10.1° (p<0.001). The largest difference was noted at 1:00 and was 72.9°±10.7° for males compared to 56.6°±11.5° for females (p<0.001). When classified into alpha angles <55°, 55-62.9°, and ≥63°, female distribution was 17.3%, 32.7%, 50%, and male distribution was 1.5%, 4.4%, and 94.1%, respectively (p<0001). The location of maximal alpha angle was more anterior in females at 1:21±0:37 and 1:07±0:42, respectively (p=0.002). Females had higher femoral version at 19.1°±8.7° compared to 15.4°±8.4° (p=0.005). Femoral neck-shaft angle was higher in females at 134.4°±4.2° compared to 131.7°±4.4°. Acetabular coverage at 1:30 was lower for females with 57.1%±3.3% compared to males with 59.2%±3.1% (p<0.001). Cranial (1:30) and central (3:00) acetabular version was about 3 degrees higher for females compared to males (p-values <0.05). Regression analysis demonstrated that females had increased coverage at 10:30 (OR: 1.30, CI: 1.06-1.61, p=0.014) and males had increased femoral head diameter (OR: 1.94, CI: 1.49-2.53), p<0.001) and alpha angles at 1:30 (OR: 1.08, CI: 1.02-1.14, p=0.011). Conclusion: Adolescent males and females with symptomatic FAI have significant differences in FAI morphology that are important to recognize. Females have 2.1% less anterior coverage, 2.7% more posterior coverage, about 3° higher cranial and central version, 3.7° higher femoral version, 12.8° lower maximum alpha angle, a more anterior cam location, and 2.7° higher femoral neck-shaft angle.