In vitro biomechanical study of femoral torsion disorders: effect on femoro-tibial kinematics.

Background: Gonarthrosis is a degenerative disease mainly found in elderly persons. Frontal plane deviations are known to induce lateral and medial gonarthrosis. Nevertheless, patients suffer from gonarthrosis without frontal deviations. Lower limb torsions disorders have been considered as a factor inducing lateral and medial gonarthrosis. This paper reports an in vitro study aiming at quantifying the relationships between experimental femoral torsion disorders and femoro-tibial kinematics.

Methods: Five fresh-frozen lower limbs were used. Specimens were fixed on an experimental jig and muscles were loaded. A six-degree-of-freedom Instrumented Spatial Linkage was used to measure femoro-tibial kinematics. Experimental femoral osteotomies were performed to simulate various degrees of medial and lateral torsion. Internal tibial rotation, abduction/adduction and proximo-distal, medio-lateral and antero-posterior translations were measured during knee flexion.

Findings: Internal tibial rotation and abduction/adduction were significantly influenced (P<0.001) by femoral torsion disorder conditions. Medial femoral torsion increased tibial adduction and decreased internal rotation during knee flexion. Opposite changes were observed during lateral femoral torsion. Concerning translations, medial femoral torsion induced a significant (P<0.05) decrease of medial translation and inversely for lateral femoral torsion. No interactions between femoral torsion disorders and range of motion were observed.

Interpretation: Our results showed that medial and lateral femoral torsion disorders induced alterations of femoro-tibial kinematics when applied in normally aligned lower limbs. These results highlight a potential clinical relevance of the effect of femoral torsion alterations on knee kinematics that may be related to the development of long-term knee disease.