[Influence of knee replacement arthroplasty on modalities of weight transfer during the lateral step]

The aim of this work was to study the relations between equilibrium and movement in patients after total knee arthroplasty. A previous study, conducted in patients with unilateral knee osteoarthritis, had shown that the timing of the events occurring during a side-step was modified in an asymmetrical way according to the supporting leg with respect to the affected one.

A kinetic and kinematic analysis was performed in a population of 9 patients before and after total knee arthroplasty and in 11 control subjects, using an ELITE system and two AMTI force-plates. The different phases (i.e. postural, monopodal, landing and stabilization) of a side step were studied.

Before surgery, the postural phase was longer and the monopodal phase was shorter in knee arthritis patients when the affected leg was the supporting one than when the sound leg was supporting. Total step duration and landing-stabilization phase duration were longer in patients no matter which leg was supporting than in control subjects. After total knee arthroplasty, the postural phase remained longer when the operated leg was supporting than when the sound leg was supporting. Altered proprioception can provide an explanation for this result. However, the duration of the postural phase decreased significantly when the operated leg was supporting as compared to when the affected leg was supporting before surgery. The duration of the monopodal phase was the same when the operated leg was supporting than when the sound limb was supporting and increased significantly as compared to when the affected leg was supporting before surgery. This result can be related to the decrease of pain which was observed in all patients after surgery. The duration of the landing-stabilization phase and the total movement duration remained longer in patients after surgery no matter which leg was supporting than in control subjects.

This study shows that relations between equilibrium and movement tend to become symmetrical with respect to the leg used as supporting one in patients after undergoing total knee arthroplasty but remain different from those of control subjects. This movement analysis method enables to determine and to quantify differences in patients before and after undergoing total knee arthroplasty and thus provides additional information for the functional evaluation of patients with total knee prosthesis.