The cam-type deformity of the proximal femur arises in childhood in response to vigorous sporting activity

Abstract

Background: The prevalence of a cam-type deformity in athletes and its association with vigorous sports activities during and after the growth period is unknown.

Questions/purposes: We therefore compared the prevalence and occurrence of a cam-type deformity by MRI in athletes during childhood and adolescence with an age-matched control group.

Patients and methods: We retrospectively reviewed 72 hips in 37 male basketball players with a mean age of 17.6 years (range, 9-25 years) and 76 asymptomatic hips of 38 age-matched volunteers who had not participated in sporting activities at a high level.

Results: Eleven (15%) of the 72 hips in the athletes were painful and had positive anterior impingement tests on physical examination. Internal rotation of the hip averaged 30.1° (range, 15°-45°) in the control group compared with only 18.9° (range, 0°-45°) in the athletes. The maximum value of the alpha angle throughout the anterosuperior head segment was larger in the athletes (average, 60.5° ± 9°), compared with the control group (47.4° ± 4°). These differences became more pronounced after closure of the capital growth plate. Overall, the athletes had a 10-fold increased likelihood of having an alpha angle greater than 55° at least at one measurement position.

Conclusions: Our observations suggest a high intensity of sports activity during adolescence is associated with a substantial increase in the risk of cam-type impingement. These patients also may be at increased risk of subsequent development of secondary coxarthrosis.

Level of evidence: Level II, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Fig. 1A–B

(A) The radial MRI planes, which are perpendicular to the femoral head-neck axis, are defined on a sagittal oblique localizer. (B) The radial cuts rotate clockwise in 30°-intervals around the femoral head-neck axis. The alpha angle measurements were performed throughout the cranial hemisphere from 9 o’clock to 3 o’clock.

Fig. 2A–D

(A) An MRI scan of the femoral head of a 12-year-old boy is shown. The bright enhancement line (white arrow) indicates an open growth plate. (B) The open physis is represented by a broad and dark line on the proton density-weighted sequence. The round circle indicates the spherical contour of the head. The alpha angle is 30°. (C) A MRI scan of the femoral head of a 14-year-old boy is shown with no enhancement of the growth plate indicating a closed physis. (D) The closed physis in the 14-year-old boy is represented by a thin, irregular grey line. The round circle indicates the spherical contour of the head. The alpha angle is 40°.

Fig. 3

The average alpha angles at the different positions of the cranial hemisphere of the femoral head in the athlete and control groups are shown. The two groups were further separated into two subgroups according to an open (n = 27 hips in the athlete group, n = 32 hips in the control group) or closed capital growth plate (n = 45 hips in the athlete group, n = 44 hips in the control group).

Fig. 4A–B

The alpha angles at the 2 o’clock position in (A) a 16-year-old athlete with severe cam-type morphologic features (white arrow) and (B) a 17-year old control subject are shown. The white circle indicates the spherical outline of the head on each figure.

Fig. 5

The distribution of internal rotation in the different age subgroups in the athlete and control groups is shown.