Aim

The most common complication in medial opening wedge high tibial osteotomies is a lateral hinge fracture, with a reported incidence of 20%. Lateral hinge width guidance ranges from 5mm to 15mm and the distance from the apex to the tibial plateau is defined relative to the tibiofibular joint. We sought to analyse the impact of changing the horizontal and the vertical position of the osteotomy apex on fracture risk and type, as well as map Takeuchi fracture types on the rectangular apex profile.

Methods

Artificial bone models and Perspex plates were utilised. For artificial bone models, osteotomy cuts started 40mm from the tibial plateau and the apex was positioned 16mm from the joint line; lateral hinge widths ranged from 4mm to 22mm. For Perspex models, the cut started 40mm from the tibial plateau; the apex from the joint line was varied at 13mm, 16mm and 19mm. At each height, lateral hinge widths ranged from 4mm to 25mm. Wedge opening angle at failure, failure load and fracture type were recorded in an opening-to-failure test in using cameras and an Instron machine. R2 values were calculated to assess correlation.

Results

Reducing the lateral hinge width reduces the overall fracture risk and Takeuchi type III fracture risk. Reducing the osteotomy apex to joint line distance reduces overall fracture risk but increases Takeuchi type III fracture risk. No Takeuchi II fractures were seen. A steep increase in the failure load with increasing hinge width was observed; there was no consistent impact of varying the apex to joint line distance.

Conclusion

Our study has demonstrated the correlation between fracture risk and hinge widths, as supported by different modelling methods. Moving the apex closer to the tibial plateau reduces the overall fracture risk but with an increased risk of type III fractures. A sharp increase in the failure load occurs as the lateral hinge width is increased. By mapping Takeuchi fracture types on the rectangular apex profile, we demonstrate a significant potential for simplifying future analysis of lateral hinge fracture mechanics.