The otto aufranc award. on the etiology of the cam deformity: A cross-sectional pediatric MRI study

Abstract

Background: 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. Questions/purposes: 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. Methods: 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. Results: 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. Conclusions: 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. © 2013 The Association of Bone and Joint Surgeons®.