The Otto Aufranc Award. On the Etiology of the Cam Deformity: A Cross-sectional Pediatric MRI Study
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Femoroacetabular impingement (FAI) has been recognized as a common cause of hip pain as well as a cause of hip arthritis, yet despite this, little is known about the etiology of the cam morphology or possible risk factors associated with its development.
The purposes of our study were to determine when the cam morphology associated with FAI developed in a cross-sectional cohort study of pediatric patients pre- and postphyseal closure using MRI and whether increased activity level during the period of physeal closure is associated with an increased likelihood that the cam deformity will develop.
Alpha angles were measured at the 3 o’clock (anterior head-neck junction) and 1:30 (anterosuperior head-neck junction) positions in both hips with a cam deformity defined as an alpha angle ≥ 50.5° at the 3 o’clock position. Forty-four volunteers (88 hips) were studied: 23 with open physes (12 females, mean age 9.7 years; 11 males, age 11.7 years) and 21 with closed physes (five females, age 15.2 years; 16 males, age 16.2 years). Daily activity level using the validated Habitual Activity Estimation Scale was compared for patients in whom cam morphology did and did not develop.
None of the 23 (0%) patients prephyseal closure had cam morphology, whereas three of 21 (14%, p = 0.02; all males) postclosure had at least one hip with cam morphology. Daily activity level was higher (p = 0.02) for patients with the cam morphology (7.1 hours versus 2.9 hours). Mean alpha angles at the 3 o’clock head-neck position were 38° (95% confidence interval [CI], 37.2°–39.1°) in the open physes group and 42° (95% CI, 40.16°–43.90°) in the closed physes group; at the 1:30 head-neck position, they were 45° (95% CI, 44.0°–46.4°) in the open physes group and 50° (47.9°–52.3°) in the closed physes group.
The fact that cam morphology was present exclusively in the closed physeal group strongly supports its development during the period of physeal closure with increased activity level as a possible risk factor.
Level of Evidence
Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.
KeywordsSlip Capital Femoral Epiphysis Alpha Angle Femoroacetabular Impingement Increase Activity Level Closed Physis
We acknowledge the contributions of the Children’s Hospital of Eastern Ontario Bone Health Research Team, Steve Anderson, and Kyle Kemp, who have been integral to the completion of the study.
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