Effect of quadriceps exercise on synostosis following tibial osteotomy with internal fixation: a finite element simulation

Objective. To clarify the influence of quadriceps muscle exercises on the apposed bony surfaces of the tibia after a high tibial osteotomy. The sl:udy was designed so that the instability at the osteotomy could be evaluated by a finite element simulation. Background. A detailed knowledge of the effects of quadriceps exercises on the healing tibia may lead to a solid rationale for exercise prescription. Methods. Using a three-dimensional finite-element method, we calculated displacement at the site of surgical repair of a tibia with an osteotomy and fixation plate attached. Construction of the finite element model of the tibia and subsequent calculations were done with the aid of commercial software. Boundary and loading conditions were calculated for two situations: a straight leg raising exercise and a full knee extension beginning from 90 ° of knee flexion. Results. In the straight leg raising exercise, the surgically cut surfaces were apposed tightly, whether or not an external load was added. For the knee extension exercise, on the other hand, separation occurred when the lower leg began at a full vertical orientation of 90 ° of knee flexion, but as the lower leg diverged from the vertical orientation, compression began to come into play and progressively increased. Conclusions. A position of 90 ° of knee flexion with the lower leg vertical should be considered hazardous to the integrity of the surgically cut and apposed surfaces.