Background

Soft tissue laxity around the knee joint has been recognized as a crucial factor affecting correction error during medial open-wedge high tibial osteotomy (MOWHTO). Particularly, the medial laxity, representing the changes in joint line convergence angle (JLCA), affects the soft tissue correction.

Hypothesis/Purpose: Quantify the medial laxity and develop a preoperative planning method that considers the medial laxity.

Methods

This study retrospectively reviewed 139 knees in 117 patients who underwent navigation-assisted MOWHTO from January 2014 to July 2019, for symptomatic medial compartment osteoarthritis with varus alignment >5°. We compared the results of two different preoperative planning methods used: 1) conventional Miniaci and 2) latent medial laxity reduction. We evaluated the incidence of under-correction, acceptable correction, and over-correction. The radiologic parameters were analyzed using the multiple linear regression with a stepwise selection model to establish an equation for the optimal preoperative planning method.

Results

The Miniaci method showed a higher incidence of over-correction (55.3%) than the latent medial laxity reduction method (22.8%) at postoperative 6 months (p=0.0006). The multiple linear regression with a stepwise selection model revealed a high correlation coefficient for the following equation: adjusted preoperative planning correction angle = 0.596 + 0.891 x target correction angle (TCA) - 0.255 x ?JLCA valgus (R2= 0.888). On simplifying, TCA – 1/3?JLCA valgus showed the highest intraclass coefficient (ICC) value (0.991) with the proposed equation. While, the Miniaci method showed a relatively low ICC value of 0.875.

Conclusion

The Conventional Miniaci method has a risk of over-correction after MOWHTO. An equation that is considering medial laxity could help to set a preoperative planning for optimal correction during MOWHTO.