P3A351: Adolescents with a Hip Avulsion Fracture Have Significantly Higher Odds of Femoroacetabular Impingement Compared to Controls

Background: The apophyseal hip avulsion fracture is an injury presenting in the adolescent athlete population. No prior studies have investigated the pelvic morphology of patients with avulsion fractures to assess for conditions such as femoroacetabular impingement (FAI). The purpose of this study is to use CT imaging to radiographically analyze hip morphology in avulsion fracture patients compared to control hips that are matched by age and sex. Significant differences in radiographic measurements may suggest a predisposition to hip avulsion fractures based on morphology.

Methods: After institutional review board approval, all cases of apophyseal avulsion fractures about the hip from January 2005 to July 2020 were retrospectively reviewed from the electronic medical records at a tertiary care pediatric center. Patients ages 10 to 19 at baseline visit who had an acute avulsion injury with CT imaging were included in the study. Patients with neuromuscular, osteo-metabolic, bone fragility syndrome, or pathologic fracture were excluded. A total of 34 hips (34 patients) were available for analysis. The avulsion fracture cohort was matched in a 1:2 ratio to control hip CT scans based on age and sex. Cranial acetabular version (AV), central AV, lateral center edge angle (LCEA), and alpha angles (AA)—posterior superior, superior, anterior superior, anterior—were measured for all subjects. Demographic data was also collected.

Radiographic measurements were compared between the avulsion cohort and matched controls using independent sample Wilcoxon rank sum tests. A logistic regression model was run to estimate the effect of the presence of avulsion fracture on the likelihood of impingement, defined as any alpha angle greater than 55°.

Results: Thirty-four hips with avulsion fractures were matched to 68 hips without avulsion fractures for analysis. Bivariate analysis found no difference between the avulsion group and control group with respect to age, sex, or BMI percentile. The mean age of fracture patients was 10 years (range, 10.4 to 18.7 years).

Logistic regression found that avulsion fracture subjects had 2.5 times the odds of impingement (OR=2.5; 95% CI=1.05-5.78; p=0.04) compared to controls. The anterior superior AA was 5° higher for the avulsion cohort compared to controls (median, 58° vs 53°; p=0.03).

Additional findings included a 2° lower superior AA (median, 40° vs 42° v; p=0.03) and 3° higher central AV (median, 17° vs 14°; p=0.03) for the avulsion group compared to controls.

Conclusion: Our findings demonstrate that patients who had an apophyseal avulsion fracture about the hip are significantly more likely to show radiographic evidence of femoroacetabular impingement when compared to matched controls. This data may represent a morphologic predisposition to avulsion fractures among adolescents with FAI.