Summary

This study provides robust biomechanical evidence that the prophylactic placement of a lateral hinge screw during MCWDFO significantly enhances resistance to varus stress, thereby reducing the risk of lateral hinge fractures.

Abstract

Objectives:

Medial closing wedge distal femoral osteotomy (MCWDFO) is frequently used to correct knee malalignment, particularly in cases of valgus deformity. However, a significant complication associated with this procedure is the occurrence of lateral hinge fractures, which can result in delayed healing, loss of correction, and increased risk of nonunion or malunion. This study aims to evaluate the biomechanical effects of a prophylactic lateral hinge screw in enhancing varus stress resistance following MCWDFO. The objective is to determine
whether the addition of this screw can significantly reduce the incidence and severity of lateral hinge fractures, thereby improving surgical outcomes.

Methods

A controlled laboratory biomechanical study was conducted using twelve fourth-generation composite femur models (Sawbones USA) to simulate the biomechanical environment of MCWDFO. The specimens were divided into two groups: six femurs received a prophylactic lateral hinge screw, and six served as controls without the hinge screw. All specimens
underwent a standardized biplanar MCWDFO, with a consistent alignment correction of 5 mm. A 3.5 mm cortical screw was inserted parallel to the lateral cortex under fluoroscopic guidance in the experimental group. The femurs were then subjected to a single load-to-failure test under varus stress using an MTS 858 Mini Bionix machine. Failure was defined as the point just before a significant drop in the force versus displacement curve, indicating lateral hinge breakage. The maximum load to failure was recorded and analyzed using a paired t-test, with statistical significance set at p<0.05.

Results

The placement of a prophylactic lateral hinge screw resulted in a significant increase in varus stress resistance compared to the control group. The maximum load to failure in the hinge
screw group was 439.7±64.3 N, compared to 255.6±97.9 N in the control group, representing a 67% increase in load-bearing capacity (p<0.05). This substantial enhancement in mechanical stability suggests that the lateral hinge screw effectively reinforces the lateral cortex, thereby reducing the likelihood of hinge fractures during and after MCWDFO.

Conclusions

This study provides robust biomechanical evidence that the prophylactic placement of a lateral hinge screw during MCWDFO significantly enhances resistance to varus stress,
thereby reducing the risk of lateral hinge fractures. The findings suggest that incorporating this technique into routine MCWDFO procedures could improve surgical outcomes by
reducing postoperative complications, promoting faster healing, and minimizing the need for revision surgeries. Given the high incidence of lateral hinge fractures and their associated complications, the prophylactic use of a lateral hinge screw has the potential to become a standard adjunct in knee osteotomies. Future clinical trials are warranted to validate these findings in patient populations and to assess the long-term benefits of this approach.