Growth plate alteration precedes cam-type deformity in elite basketball players

Abstract

Background: Vigorous sporting activity during the growth years is associated with an increased risk of having a cam-type deformity develop. The underlying cause of this osseous deformity is unclear. One may speculate whether this is caused by reactive bone apposition in the region of the anterosuperior head-neck junction or whether sports activity alters the shape of and growth in the growth plate. If the latter is true, then one would expect athletes to show an abnormal shape of the capital growth plate (specifically, the epiphyseal extension) before and/or after physeal closure.

Questions/purposes: We therefore raised three questions: (1) Do adolescent basketball players show abnormal epiphyseal extension? (2) Does the epiphyseal extension differ before and after physeal closure? (3) Is abnormal epiphyseal extension associated with high alpha angles?

Methods: We performed a case-control comparative analysis of young (age range, 9-22 years) male elite basketball athletes with age-matched nonathletes, substratified by whether they had open or closed physes. We measured epiphyseal extension on radial-sequence MRI cuts throughout the cranial hemisphere from 9 o'clock (posterior) to 3 o'clock (anterior). Epiphyseal extension was correlated to alpha angle measurements at the same points.

Results: Epiphyseal extension was increased in all positions in the athletes compared with the control group. On average, athletes showed epiphyseal extension of 0.67 to 0.83 versus 0.53 to 0.71 in control subjects. In the control group epiphyseal extension was increased at all measurement points in hips after physeal closure compared with before physeal closure. In contrast, the subgroup of athletes with a closed growth plate only had increased epiphyseal extension at the 3 o'clock position compared with the athletes with an open [corrected] growth plate (0.64-0.70). We observed a correlation between an alpha angle greater than 55° and greater epiphyseal extension in the anterosuperior femoral head quadrant: the corresponding Spearman r values were 0.387 (all hips) and 0.285 (alpha angle>55°) for the aggregate anterosuperior quadrant.

Conclusions: These findings suggest that a cam-type abnormality in athletes is a consequence of an alteration of the growth plate rather than reactive bone formation. High-level sports activity during growth may be a new and distinct risk factor for a cam-type deformity.

Fig. 1A–C

(A) A radial-sequence MR image of the hip of a 20-year-old basketball player taken at the 2 o’clock position is shown. (B) The diameter (d) of the femoral head, through the center of the head-neck axis, and the distance from a line orthogonal to the diameter to the lateral-most extension of the epiphysis (e) is measured. The epiphyseal extension is defined as e/d. (C) The measurement of the alpha angle on this same MRI slice is shown.

Fig. 2A–B

(A) Radial-sequence MRI planes are perpendicular to the femoral head-neck axis. (B) Positions are defined clockwise with the 12 o’clock position being superior and 3 o’clock position being anterior; 3 h = 3 hours; 6 h = 6 hours; 9 h = 9 hours; 12 h = 12 hours. (Published with permission from Siebenrock KA, Ferner F, Noble PC, Santore RF, Werlen S, Mamisch TC. The cam-type deformity of the proximal femur arises in childhood in response to vigorous sporting activity. Clin Orthop Relat Res. 2011;469:3229–3240.)

Fig. 3

Epiphyseal extension for all athletes and all control subjects is shown for the cranial half of the femoral head-neck junction (9 o’clock through 3 o’clock). Epiphyseal extension is greater in athletes than control subjects for all positions (p < 0.001).

Fig. 4A–B

Epiphyseal extension for athletes and control subjects is shown for (A) open and (B) closed physes. Although there is a marked difference between the two groups when the physis is open, the difference narrows after physeal closure.

Fig. 5A–B

A comparison is shown between epiphyseal extension before and after physeal closure for (A) athletes and (B) control subjects. Athletes with open physes show epiphyseal extensions in the range of their counterparts with closed physes. Control subjects show a relatively uniform increase in epiphyseal extension as the growth plate closes.

Fig. 6

A scatterplot with linear regression line shows the relationship between the alpha angle and epiphyseal extension in the anterosuperior quadrant of all hips (1 o’clock through 3 o’clock positions).