Summary

Joint line obliquity (JLO) has an independent and significant effect on peak lateral compartment compressive load during walking after medial opening wedge high tibial osteotomy (HTO).

Abstract

Introduction

Medial opening wedge HTO unloads the medial tibiofemoral compartment (TFC) and increases loads on the lateral TFC. There is no consensus on acceptable limits for JLO after HTO (JLO>4° (Babis et al., 2002) versus JLO>10° (Coventry, 1987)). Apex proximal tibial osteotomy has been shown to increase compressive force on lateral compartment (Wang et al. 2021). This study aimed to quantify the independent effect of JLO versus Hip-Knee-Ankle angle (HKA) on knee bicompartmental compressive loads during walking and guide surgical boundaries to HTO planning. We hypothesized that an increase in compressive load within the lateral TFC would have a direct relationship to post-HTO HKA but also to post-HTO JLO.

Methods

21 medial osteoarthritis patients (Sex: all males; age, 50.9±9.9 years old; height, 1.8±0.1 m; mass, 99.6±18.4 kg; BMI, 30.0±4.6 kg/m2) underwent medial opening wedge HTO for treatment of osteoarthritis. Gait biomechanical data was collected with patients walking at normal speed (motion data, ground reaction force and muscle activity)., Biomechanical and radiographic data were collected pre- and post- surgery to drive computer-simulated musculoskeletal models (Lerner et al., 2015). The radiographic data collected lateral distal femoral angle (LDFA), medial proximal tibial (MPTA) and HKA. JLO was the sum of LDFA and MPTA. Lower-limb muscle forces were computed using inverse dynamics and static optimization. Forces in the knee compartments were computed using Joint Reaction analyses (Steele et al. 2012). Computational pipeline determined the independent contribution of JLO and HKA on knee compartment loads during gait. Knee injury and osteoarthritis outcome score (KOOS) was also collected to evaluate surgery outcomes.

Results

HKA was significantly more valgus after surgery (pre, 7°±3.8° versus post, -2.4°±1.6°; p<0.05). KOOS was significantly improved 12 months after surgery (pre 46.9±17.7; post 72.1±17.9m/s2; p<0.05). MPTA and JLO significantly greater after surgery (MPTA: pre 84.4°±2.8°; post 93.1°±2.3°; p<0.05 ) and JLO: pre 173.7°±2.9°; post 182.0°±3.9°; p<0.05). No difference in walking speed between time (pre, 1.1±0.13m/s2 versus post, 1.1±0.15m/s2; p>0.05). Given a weak correlation between HKA and JLO (r=0.37; p<0.05), multiple regression was used to decouple any confounding effect between these two variables. The isolated JLO effect (apex proximal) induced a 51.7N/° (r=0.71; p<0.05) peak compressive load change on lateral compartment at the first half of stance cycle. The isolated HKA effect (valgising) induced a 83.9N/° (r=0.55; p<0.05) and -76.5 N/° (r=0.63; p<0.05) compressive load change on lateral and medial compartments at early stance, respectively.

Conclusion

The increased compressive loads within the lateral TFC was explained by both the valgising HKA and apex proximal JLO. The decrease in compressive load within the medial compartment was only due to the valgising HKA. These results demonstrated that post-surgical JLO had a significant independent effect on lateral compartment load. HTO planning should consider not just HKA but also JLO to optimize lateral compartment loads and the potential impact on survivorship. Further analysis is necessary to provide clearer guidelines on appropriate boundaries for JLO to avoid compromising HTO outcomes.