Why Cam Morphology Forms During the Growth Spurt and the Role of Load

During the second growth spurt, around 12 to 14 in boys, IGF-1 and growth hormone make bone most responsive to load. A hip rotationplasty, where a proximal tibia placed in the acetabulum takes on the shape of a femoral head, shows how plastic growing bone is. Among 63 professional soccer players, those training four or more times a week before age 12 had more cam morphology: 64% against 40% with an alpha angle above 60 degrees, and 30% against 12% above 78 degrees. The Oxford study showed the same gradient from academy players to amateur players to non-athletic controls. In a finite element model of a 12-year-old hip, loading in flexion and external rotation stimulated bone formation where cam morphology develops. In a horizontal growth plate the same loads halted lateral growth, which may tilt the plate until shear stress triggers bone formation. Cohort data showed growth plate extension and cam growth occurring together. Cam morphology appears to be an adaptive response to the type and frequency of loading; whether it can be prevented needs further research.