Physical activity during adolescence and the development of cam morphology: a cross-sectional cohort study of 210 individuals

Abstract

Introduction: Cam morphology is a strong risk factor for the development of hip pain and osteoarthritis. It is increasingly thought to develop in association with intense physical activity during youth; however, the aetiology remains uncertain. The study aim was to characterise the effect of physical activity on morphological hip development during adolescence.

Methods: Cross-sectional study of individuals aged 9-18 years recruited from Southampton Football Club Academy (103 male) with an age-matched control population (52 males and 55 females). Assessments included questionnaires and 3 Tesla MRI of both hips. Alpha angle, epiphyseal extension and epiphyseal tilt were measured on radial images.

Results: Alpha angle and epiphyseal extension increased most rapidly between ages 12 and 14 years. Soft-tissue hypertrophy at the femoral head-neck junction preceded osseous cam morphology and was first evident at age 10 years. The greatest increase and highest absolute values of alpha angle and epiphyseal extension were colocalised at 1 o'clock. Maximum alpha angles were 6.7 degrees greater in males than females (p=0.005). Compared with individuals who play no regular sport, alpha angles were 4.0 degrees higher in individuals who play sport for a school or club (p=0.041) and 7.7 degrees higher in individuals competing at a national or international level (p=0.035). There was no association with leg dominance .

Conclusions: Sporting activity during adolescence is strongly associated with the development of cam morphology secondary to epiphyseal hypertrophy and extension with a dose-response relationship. Males participating in competitive sport are at particularly elevated risk of developing cam morphology and secondary hip pathology.

Keywords: MRI; football; hip; physical activity; sport.

Figure 1

Soft tissue hypertrophy at the head-neck junction preceded epiphyseal extension and osseous cam morphology (A). Alpha angle was calculated by drawing a line from the centre of a best-fit circle surrounding the femoral head to the midpoint of a line transecting the narrowest portion of the femoral neck. A further line was then drawn from the centre of the best-fit circle to where the contour of the femoral head first exits this circle. The alpha angle is the angle between these two lines and was measured for cartilage (B) and bone (C). Epiphyseal extension (D) was quantified by measuring the distance from the medial femoral head to the most distal extent of the epiphysis along a line parallel to the axis of the femoral neck as was created when measuring the alpha angle. This distance was then divided by the diameter of the femoral head to produce a standardised ratio. Epiphyseal tilt was assessed as the ratio between epiphyseal extension on opposing sides of the femoral head (X/Y).

Figure 2

Bone (A–E) and cartilage (F–J) alpha angle vs age in all participants at 11 o’clock (A and F), 12 o’clock (B and G), 1 o’clock (C and H), 2 o’clock (D and I) and 3 o’clock (E and J) with polynomial regression fit and 95% CI.

Figure 3

Maximum cartilage alpha angle with age for participants who play no regular sport (‘no sport’), play sport for their school or a club team (‘sport’) or compete at a national or international level (‘athlete’). Polynomial regression fit with 95% CI.

Figure 4

Three-dimensional water selective fluid (WATSf) MRI of SFC player aged 16 years with pronounced cam morphology. Epiphyseal hypertrophy and extension is maximal at 1 o’clock but also present in adjacent positions: 12 o’clock (A), 1 o’clock (B), 2 o’clock (C) and 3 o’clock (D).