The purpose of this study was to quantify the forces produced by the growth plates of the adolescent human proximal tibia and distal femur. The postoperative deformations of staples used to treat genu valgum were correlated with similar staple deformations produced by mechanical testing. Staple deformation was measured in sequential radiographs of 35 knees in 20 patients. Mechanical tests were performed on new staples to determine the force necessary to bend the staples to the observed displacements. Based on deformation at final examination, the static equivalent loads exerted at the joint centerline by the growth plates of the proximal tibia and distal femur were 0.5 kN per physis. The estimated corresponding stress was 1 MPa. These results indicated that successful lower limb hemiepiphysiodesis suppressed a longitudinally directed, centrally applied compressive force on the order of body weight.