Acetabular Retroversion and Decreased Posterior Coverage Are Associated With Sports-related Posterior Hip Dislocation in Adolescents
Authors: Novais Eduardo N. , Ferrer Mariana G. , Williams Kathryn A. , Bixby Sarah D. 
Published: September 2018

Abstract

Background
Leverage of the femoral head against the acetabular rim may lead to posterior hip dislocation during sports activities in hips with femoroacetabular impingement (FAI) deformity. Abnormal concavity of the femoral head and neck junction has been well described in association with posterior hip dislocation. However, acetabular morphology variations are not fully understood.

Questions/purposes
The purpose of this study was to compare the acetabular morphology in terms of acetabular version and coverage of the femoral head in adolescents who sustained a posterior hip dislocation during sports and recreational activities with a control group of patients without a history of hip disease matched by age and sex.

Methods
In this case-control study, we identified 27 adolescents with posterior hip dislocation sustained during sports or recreational activities who underwent a CT scan of the hips (study group) and matched them to patients without a history of hip disease being evaluated with CT for possible appendicitis (control group). Between 2001 and 2017, we treated 71 adolescents (aged 10-19 years old) for posterior hip dislocations. During the period in question, we obtained CT scans or MR images after closed reduction of a posterior hip dislocation. One patient was excluded because of a diagnosis of Down syndrome. Twenty-one patients who were in motor vehicle-related accidents were also excluded. Twelve patients were excluded because MRI was obtained instead of CT. Finally, three patients with no imaging after reduction and seven patients with inadequate CT reformatting were excluded. Twenty-seven patients (38%) had CT scans of suitable quality for analysis, and these 27 patients constituted the study group. We compared those hips with 27 age- and sex-matched adolescents who had CT scans for appendicitis and who had no history of hip pain or symptoms (control group). One orthopaedic surgeon and one pediatric musculoskeletal radiologist, not invoved in the care of the patients included in the study, measured the lateral center-edge angle, acetabular index, acetabular depth/width ratio, acetabular anteversion angle (10 mm from the dome and at the level of the center of the femoral heads), and the anterior and posterior sector angles in the dislocated hip; the contralateral uninvolved hip of the patients with hip dislocations; and both hips in the matched control patients. Both the study and control groups had 25 (93%) males with a mean age of 13 (± 1.7) years. Inter- and intrarater reliability of measurements was assessed with intraclass correlation coefficient (ICC). There was excellent reliability (ICC > 0.90) for the acetabular anteversion angle measured at the center of the femoral head, the acetabular version 10 mm from the dome, and the posterior acetabular sector angle.

Results
The mean acetabular anteversion angle (± SD) was lower in the study group at 10 mm from the acetabular dome (-0.4° ± 9° versus 4° ± 4°; mean difference -5°; 95% confidence interval [CI], -9 to -0.3; p = 0.015) and at the center of the femoral heads (10° ± 5° versus 14° ± 4°; mean difference -3°; 95% CI, -6 to -0.9; p = 0.003). A higher proportion of acetabula was severely retroverted in the study group (14 of 27 [52%]; 95% CI, 33%-71% versus four of 27 [15%]; 95% CI, 1%-28%; p = 0.006). The mean posterior acetabular sector angle was lower in the study group (82° ± 8° versus 90° ± 6°; mean difference -8°; 95% CI, -11 to -4; p < 0.001), whereas no difference was found for the anterior acetabular sector angle (65° ± 6° versus 65° ± 7°; mean difference 0.3°; 95% CI, -3 to 4; p = 0.944). There was no difference for the lateral center-edge angle (27° ± 6° versus 26° ± 5°; p = 0.299), acetabular index (5° ± 3° versus 6 ± 4°; p = 0.761), or acetabular depth/width ration (305 ± 30 versus 304 ± 31; p = 0.944) between groups. Acetabular anteversion angle at the center of the femoral heads (11° ± 4° versus 14° ± 4°; p = 0.006) and the posterior acetabular sector angle (86° ± 7 ° versus 91° ± 6°; p = 0.007) were lower in the contralateral uninvolved hips compared with control hips.

Conclusions
Decreased acetabular anteversion angle and posterior acetabular coverage of the femoral head were associated with posterior dislocation of the hip in adolescents with sports-related injury even in the absence of a high-energy mechanism. Further studies are necessary to clarify whether a causative effect exists between acetabular and femoral morphology and the dislocation of the hip in patients with sports-related injuries.

Level of Evidence
Level III, prognostic study.