Elsevier

Journal of Biomechanics

Volume 38, Issue 2, February 2005, Pages 349-355
Journal of Biomechanics

The effect of valgus/varus malalignment on load distribution in total knee replacements

https://doi.org/10.1016/j.jbiomech.2004.02.024Get rights and content

Abstract

Valgus or varus malpositioning of the tibial component of a total knee implant may cause increased propensity for loosening or implant wear and eventually may lead to revision surgery. The aim of this study was to determine the effect of valgus/varus malalignment on tibio-femoral mechanics during surgical trial reduction and simulated gait loading. In seven cadaver legs, posterior cruciate sparing total knee replacements were implanted and tibial inserts representing a neutral alignment and 3° and 5° varus and valgus alignments were sequentially inserted. Each knee with each insert was loaded in a manner representative of a trial reduction performed during knee surgery and loaded in a physiological knee simulator. Simulated gait performed on the simulator demonstrated that internal/external and adduction/abduction rotations showed statistical changes with some of the angled inserts at different points in the walking cycle. Neither medial/lateral nor anterior/posterior translations changed statistically during simulated walking. The pressure distribution and total load in the medial and lateral compartments of the tibial component changed significantly with as little as a 3° variation in angulation when loaded in a manner representative of a trial reduction or with a knee simulator. These results support the need for precise surgical reconstruction of the mechanical axis of the knee and proper alignment of the tibial component. These results further demonstrate that tibial contact pressures measured during a trial reduction method may be predictive of contact mechanics at the higher loading seen in the knee simulator.

Introduction

Coronal malpositioning of the tibial component of total knee replacements may result in severe wear of the polyethylene component, component loosening, and ultimately revision surgery (Hungerford, 1995; D’Lima et al., 2001). Classically, the bone cut for the tibial component is perpendicular to the long axis of the tibia. Malpositioning of the tibial component can occur with a slightly angled cut such that too much bone is removed laterally and too little is removed medially or conversely. Variations in tibial coronal alignment of 3–5° can occur clinically (Maestro et al., 1998; Hungerford et al., 1989; Ritter et al., 1994) and therefore warrant an investigation into its effect on implant loading mechanics.

The purpose of this study was to determine in vitro how variations in tibial component angulation might affect (1) the joint pressure distribution, (2) the medial to lateral tibial component force distribution, and (3) the implant kinematics during simulated walking. We further wanted to compare the pressure and loading distributions when measured in a simulated surgical environment to those obtained using a physiological gait simulator.

Section snippets

Materials and methods

In each of seven left cadaver legs, a posterior cruciate sparing total knee replacement was implanted using standard surgical technique and alignment jigs. Symmetric and balanced flexion and extension gaps of 10 mm were surgically created.

Pressure measurements were made using a 2-mm thick sensor fabricated from a stainless steel plate and conductive ink pressure sensors (Tekscan, Inc., Boston, MA). The sensor consisted of 242 pressure-measuring sensals in both the medial and lateral

Results

Pressure data was obtained for all loading conditions for all inserts in six of the seven knees. Pressure data from the first knee was not included since it was not tested at all combinations of the static load cases. Using the knee simulator, in a static knee stance position near full extension, the neutrally aligned tibial insert distributed pressure evenly between the medial and lateral compartments of the tibial component (Fig. 5). Integration of the pressure data in each compartment

Discussion

This study examined several biomechanical consequences of poor coronal tibial component alignment during surgical trial reduction and simulated gait loading. This variation in coronal tibial alignment is related to, but different from, variations in the relative varus/valgus alignment between the tibia and femur which has been shown by others (Ritter et al., 1994; Jeffery et al., 1991) to be a factor in implant loosening.

The results suggest that under static loading, a tibial malposition of 3°

Acknowledgements

Supported in part by Johnson & Johnson, Professional, Inc.

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