Comparison of the efficiency of an extra-articular absorber system and high tibial osteotomy for unloading the medial knee compartment: an in vitro study.

Abstract

The unloading effect of an extra-articular absorber system on the knee joint medial compartment was compared with high tibial osteotomy (HTO) under physiological conditions in vitro. Seven fresh-frozen cadaveric knees were used to test isokinetic flexion-extension motions under physiological loading using a biomechanical knee simulator. Tibiofemoral area contact and peak contact pressures were measured using pressure-sensitive film in the untreated medial compartment. Pressures were measured after KineSpring System implantation and HTO (5° and 10° correction angles) performed with an angular-stable internal fixator (Tomofix). Implantation of the unloading device resulted in significantly decreased medial compartment area contact pressure (Δ0.02±0.01MPa, p=0.001) and peak contact pressure (Δ0.3±0.1MPa, p=0.001) compared with the first test cycle results in the untreated knee. HTO significantly decreased the pressure (p=0.001). Compared with the first test cycle, HTO (5° correction angle) decreased the mean contact pressure by Δ0.03±0.01MPa and peak contact pressure by Δ0.3±0.01MPa. With a 10° correction angle, HTO decreased contact pressure by Δ0.04±0.02MPa and peak contact pressure by Δ0.4±0.1MPa compared with that at the 5° correction angle. Implantation of an extra-capsular unloading device resulted in a significant unloading effect on the medial compartment comparable to that achieved with HTO at 5° and 10° correction angles. Thus, implantation of an extra-articular, extra-capsular absorber could become the method of choice when treating patients with unicompartmental osteoarthritis that cannot be adequately treated by HTO because of their straight-leg axis.