In vitro biomechanical study of femoral torsion disorders: effect on tibial proximal epiphyseal cancellous bone deformation.

PURPOSE: Osteoarthritis (OA) of the knee is a degenerative disease mainly found in elderly population. Valgus deformity seems to be directly related to lateralised gonarthrosis. Contradictory outcomes of surgical series are published in the literature and report satisfactory and unsatisfactory long-term results. Lower limb torsions disorders have been considered as being another factor inducing gonarthrosis. This paper presents an in vitro study aiming at quantifying the relationships between experimental femoral torsion disorders (medial and lateral) and the deformation of the cancellous bone of the proximal tibial epiphysis (CB(TPE)).
METHODS: Five left fresh-frozen lower limbs were used. Specimens were mounted on an experimental jig and muscles were loaded. Six measurement elements, including strain gages, were introduced into CB(TPE) to measure relative deformation. Experimental osteotomy control was performed using a specially devised system allowing various amplitudes of medial and lateral torsion. CB(TPE) deformations were measured during knee flexion movement.
RESULTS: Intra-observer reproducibility of CB(TPE) deformations showed a mean coefficient of multiple correlation of 0.93 and a mean coefficient of variation of 9% for flexion. Intra-specimen repeatability showed a mean RMS difference ranging from 7 to 10% and a mean ICC of 0.98. CB(TPE) deformations were significantly influenced by femoral torsion disorder conditions and range-of-motion (ROM) for most measurement elements. No interaction between torsion condition and ROM was observed. Globally, CB(TPE) deformation in the lateral compartment increased during experimental lateral torsion disorder simulation and decreased during medial torsion simulation. The opposite behaviour was observed in the medial compartment. The decrease and/or increase were not always proportional to the degree of femoral torsional disorder simulated.
CONCLUSION: Experimental results from this study do not fully agree with previously published clinical observations on the femoral torsion disorder. The present quantified results do not support that medial femoral torsion disorder induces an increased lateral tibial deformation, which could be linked to gonarthrosis observed in this compartment. In summary, our results showed that medial and lateral femoral torsion disorder conditions applied in normally aligned lower limb induced a deformation increase in the medial and in the lateral compartment, respectively.