Figure 4.

Primary cam morphology definition. Primary cam morphology is a cartilage or bony prominence (bump) of varying size at any location around the femoral head-neck junction of the hip, which changes the shape of the femoral head from spherical to aspherical. It occurs most often in asymptomatic male athletes in both hips. The preferred outcome measure for research on primary cam morphology aetiology is a cartilage or bone alpha angle as a continuous variable on radial MRI along the axis of the femoral neck, using 30° intervals from 12 o'clock to 11 o'clock positions, reported per hip, per person or both. In addition to a continuous alpha angle, a dichotomous alpha angle (using a threshold of ≥60°) can be useful in clinical practice or research. Primary cam morphology develops during skeletal maturation in young adolescents (with no current or previous hip disease), as a normal physiological response to high-load sporting activity and other unconfirmed risk factors. Illustrations from Dijkstra et al. (2021)⁵