# A single lateral hinge screw increased resistance to varus stress after medial closing wedge distal femoral osteotomy in a Sawbones model: A biomechanical analysis

## TL;DR

Adding a lateral hinge screw after a specific bone surgery in a lab model significantly improved resistance to varus stress, but stiffness was unchanged.

## Contribution

Demonstrated that a lateral hinge screw increases failure strength in a biomechanical model of distal femoral osteotomy.

## Key findings

- Maximum load to failure was 72% higher in the hinge screw group compared to the control group.
- No significant difference in stiffness was found between the groups with or without the hinge screw.

## Abstract

To determine the biomechanical effects of a lateral hinge screw on postoperative fracture after medial closing wedge distal femoral osteotomy (MCWDFO). It was hypothesized that adding a lateral hinge screw would significantly increase the failure strength of the hinge.

Twelve Sawbone femurs were used for the study. A biplanar cut was made, a protective lateral hinge pin was placed, and a 5 mm‐closing wedge osteotomy was performed in each specimen. After osteotomy, the hinge pin was removed in six specimens, and in the remaining six specimens, the hinge pin was replaced with a lateral hinge screw. A varus load was then applied utilizing a load frame in a single load‐to‐failure test. Failure was defined as the point just before a substantial drop in the force versus displacement curve. Nonparametric Wilcoxon rank‐sum test was performed to compare maximum load and stiffness between the hinge screw and no hinge screw groups with p < 0.05 considered the threshold of statistical significance.

The maximum load to failure was significantly higher in the hinge screw group versus the control group, 440 ± 70 N versus 256 ± 107 N (mean ± standard deviation), respectively. Load to failure was 72% higher in the hinge screw group versus the no hinge screw group. No significant difference in stiffness was found between the groups.

Using a Sawbone model, the current data showed that placement of a lateral hinge screw significantly increased resistance to varus stress following MCWDFO compared with a construct having no screw. Additionally, no significant difference in stiffness was observed between the group with the hinge screw and the group without the screw. Further investigation should assess the clinical benefit of a hinge screw in reducing surgical morbidity during the postoperative period for patients undergoing a distal femoral osteotomy.

N/A.

In a Sawbone model, placement of a lateral hinge screw significantly increased resistance to varus stress after medial closing wedge distal femoral osteotomy compared with a construct having no screw.