Summary

Anterior closing wedge osteotomy resulted in anterior translation of the weighted center of contact in the lateral compartment of the knee, while anterior opening wedge osteotomy translated contact on the tibia posteriorly in both compartments.

Abstract

Objectives: High posterior tibial slope is a well-established risk factor for graft failure after anterior cruciate ligament (ACL) reconstruction and primary ACL insufficiency. Several biomechanical studies have demonstrated that decreased posterior tibial slope results in decreased forces across the ACL, but the effect of a sagittal plane tibial osteotomy on tibiofemoral joint contact forces have not been quantified. The objective of this study is to quantify the effects of anterior closing and opening wedge osteotomies on tibial plateau contact mechanics of human cadaveric knees during simulated standing and as a function of knee flexion. We hypothesize that anterior closing wedge osteotomy will result in anterior translation of the center of contact and an increase in peak contact stress, while anterior opening wedge osteotomy will translate contact on the tibia posteriorly and decrease peak contact stress.

Methods

Five knees were mounted on a robotic test system [VIVO, AMTI] programmed to apply forces, and moments to mimic level standing. An electronic, intra-articular pressure sensor [Model 4011, Tekscan] was calibrated and attached across the tibial plateau of each knee. Anterior high tibial osteotomies were performed using a standard supra-tubercle approach. Specimen specific half bodyweight was applied to each knee for each condition, and testing was performed at 0°, 15°, 30°, and 45° of flexion. A 7° polymethyl methacrylate (PMMA) cement wedge was fashioned to support the opening wedge. Both osteotomies were fixed using bone staples. Outcomes quantified for the medial and lateral compartments of each knee included: position of contact [calculated as a weighted center of contact (WCoC)], peak contact stress, and contact area.

Results

Opening wedge osteotomy resulted in a posterior translation of the WCoC for both medial and lateral compartments: Posteriorly, the magnitude of change was 1.3mm (range, 1.0-1.5; SD, 0.2) in the medial compartment and 2.1mm (range, 0.4-3.3; SD, 1.2) in the lateral compartment. Closing wedge osteotomy resulted in anterior translation in the WCoC in the lateral compartment (mean 5.2mm, range 3.0-7.2, SD 1.6) but had no effect in the medial compartment (mean 0.2mm, range 0.0-0.5, SD 0.2) for all flexion angles compared to the intact state. There were no significant changes in peak contact stresses for either the medial or lateral compartment between the increased and decreased slope states at all flexion angles (0-45°).

Conclusions

By way of a cadaveric study, augmented with pressure sensors, we accepted our hypothesis that anterior closing wedge osteotomy resulted in anterior translation of the weighted center of contact in the lateral compartment of the knee, while anterior opening wedge osteotomy translated contact on the tibia posteriorly in both compartments. There were no significant changes in peak contact stresses for either the medial or lateral compartments between the increased and decreased slope states at all flexion angles. The proposed study is the first of its kind to assess tibiofemoral joint biomechanics following high tibial ACWO and AOWO and may have significant implications for the potential long-term health of the tibiofemoral joint in this select group of patients.