Adolescent Femoroacetabular Impingement: Gender Differences in Hip Morphology

Purpose: To compare the hip morphology of adolescent male patients and female patients who underwent hip arthroscopy for femoroacetabular impingement (FAI) and determine if gender differences exist.

Methods: We retrospectively reviewed the records of 177 adolescents, aged 13 to 18 years, who were treated for FAI with hip arthroscopy. We examined and analyzed preoperative magnetic resonance imaging (MRI) scans and plain radiographs, measuring the lateral center-edge angle, Tönnis angle, and alpha angle. The intraclass correlation coefficient between readers was calculated. We created multiple linear regression models incorporating age, gender, and body mass index (BMI) with the radiographic measurements. Intraoperative findings using the Outerbridge grading system, as well as procedure performed, were documented. We compared these findings with our preoperative imaging measurements using the χ² test and the Wilcoxon rank sum test.

Results: The intraclass correlation coefficient showed moderate to strong agreement between the 3 image readers. The BMI- and age-adjusted mean alpha angle was higher in male patients than female patients on both plain radiographs (55.9° vs 45.2°, P < .0001) and axial oblique MRI scans (54.1° vs 42.5°, P < .0001). An alpha angle greater than 55° was found in 38.9% of male patients compared with only 1% of female patients (P < .0001). The lateral center-edge angle and Tönnis angle on MRI scans and plain radiographs displayed no statistically significant differences between genders after we controlled for BMI and age. Male patients were more likely to have chondral damage intraoperatively than female patients (56.3% vs 32.5%, P = .0041).

Conclusions: Distinct differences between genders were seen both on preoperative imaging and at the time of hip arthroscopy. We found that male patients with FAI displayed a larger mean alpha angle, and therefore a more severe cam-type deformity, than female patients. Our study also found that male patients were more likely to show evidence of chondral damage than female patients at the time of surgery.

Level of evidence: Level IV.