Objectives Cam morphology is not completely understood. The aim of this study was threefold: (1) to investigate if cam morphology development is associated with growth plate status; (2) to examine whether cam morphology continues to develop after growth plate closure; and (3) to qualitatively describe cam morphology development over 5-year follow-up.

Methods Academy male football players (n=49) participated in this prospective 5-year follow-up study (baseline 12–19 years old). Anteroposterior and frog-leg lateral views were obtained at baseline (142 hips), 2.5-year (126 hips) and 5-year follow-up (98 hips). Cam morphology on these time points was defined as: (A) visual scores of the anterior head-neck junction, classified as: (1) normal, (2) flattening, and (3) prominence; and (B) alpha angle ≥60°. Proximal femoral growth plates were classified as open or closed. Cam morphology development was defined as every increase in visual score and/or increase in alpha angle from <60° to ≥60°, between two time points. This resulted in 224 measurements for cam morphology development analysis.

Results Cam morphology development was significantly associated with open growth plates based on visual score (OR: 10.03, 95% CI 3.49 to 28.84, p<0.001) and alpha angle (OR: 2.85, 95% CI 1.18 to 6.88, p=0.020). With both definitions combined, cam developed in 104 of 142 hips during follow-up. Of these 104 hips, cam developed in 86 hips (82.7%) with open growth plate and in 18 hips (17.3%) with a closed growth plate. Cam morphology developed from 12 to 13 years of age until growth plate closure around 18 years.

Conclusion Cam morphology of the hip is more likely to develop with an open growth plate.