O3256: Early Weightbearing after Proximal Femur Fixation in the Pediatric Population: Is It Safe?

Background: There is a lack of consensus regarding early postoperative weight bearing in pediatric patients after removal of a proximal femur plate due to concerns regarding potential fracture. Post-operative fracture risk is a concern due to the morbidity caused by proximal femur fractures that may occur post-removal. The purpose of this study is to examine the magnitude of forces acting on the proximal femur after plate removal using a biomechanical model to help clinicians elucidate post-operative risk.

Methods: A computer- aided design (CAD) model (Dassault Systems, 2023, solidworks) of a femur was sized according to average height of four age groups (6 yo, 10 yo, 16 yo female, and 16 yo male). These femoral lengths were 305.9 mm, 366.4 mm, 430.2 mm, and 457.1 mm, respectively. A biomechanical study was performed on a computer-generated model femur in each group with a total of 6 circular resections to approximate fixation screw holes. 3.5 mm diameter holes were applied to femurs of the 6 and 10 year old groups. 4.5 mm diameter holes were applied to the 16 year old groups. The model aimed to solve for stresses exerted near the proximal femur and the region near the modeled fixation screw holes whilst subject to physiological loads (50% Body Weight) of each group.

Results: Average stresses near the proximal femur were calculated to be 2.1 MPa, 1.6 MPa, 2.8 MPa, and 2.8 MPa for the 6 yo, 10 yo, 16 yo female, and 16 yo male groups, respectively. The yield strength for cancellous bone is equal to 2.37 MPa. The 16 yo groups exhibit a higher strength near the region of modeled screw holes than those of the younger age groups.

Conclusion: Higher stresses are observed with postoperative weight bearing in the 6 and 10 yo groups. Based on the models, patients between 6 and 10 years old have increased risk of post-operative fracture with early weight-bearing compared to adult-size children in a biomechanical model. Surgeons should therefore protect weightbearing in children under 10 after removal of proximal femur plat