High tibial osteotomy is the known surgery in treatment for varus deformity and Uni-compartmental osteoarthritis (OA) of the knee. A biomechanical study showed the post-operative mechanical axis angle between 0 and 3 degrees valgus not only unloaded the medial compartment but also caused no significant increase in the lateral compartment contact pressure and loading and probable subsequent lateral compartment OA. The purpose of this study is to evaluate the clinical and radiological results of OWHTO and our planning method based on MAD measurement in the patients with varus deformity and uni-compartmental knee OA to achieve a reliable correction without lateral compartment overloading.

Methods

A retrospective case-series of patients with Kellgren- Lawrence classification (KL) grade 3 or above (14 patients and 14 limbs) was performed. Radiographic parameters were mechanical axis deviation (MAD), mechanical axis angle (MAA), medial proximal tibial angle (MPTA), Caton-Deschamps Index (CDI), posterior proximal tibial angle (PPTA), and joint line obliquity angle (JLOA). MAD measurements were used for planning. The pre-operative goal was correction of the mechanical axis to pass laterally to the lateral tibial spine. Accuracy of MAD correction was calculated with the preplanned goal. SF-36 score was obtained for clinical performance.

Results

The mean change in MAD was 26.6mm medial from midline to 12.1 lateral from midline (p < 0.001). The MAA changed from 7.35 to -3.5 (p < 0.001). The MPTA improved from 83.7 degrees to 93.1 degrees (p < 0.001), and the PPTA changed from 80.4 degrees to 77.3 degrees (p < 0.0001). The CDI changed from 1.03 to 0.8 (p < 0.0001), and patients did not experience patellofemoral pain. The JLOA improved from 2.7 to 1.3 degrees. The mean SF-36 scores showed significant improvement from 65.2 pre-Op to 82.2 post-Op (p < 0.05). The accuracy of MAD correction was 98.3%

Conclusion

OWHTO considerably improved the clinical outcome for uni-compartmental knee OA. The planning technique based on the measurement of MAD used in study provides accurate and reliable results besides prevention of lateral compartment overloading.