Biomechanical stability of high tibial opening wedge osteotomy: internal fixation versus external fixation

The goal of our study was to evaluate stability of internal fixation with a plate compared to external fixation in an opening wedge high tibial osteotomy model. Significance. To our knowledge, this is the only study to compare internal plate to external fixation in an opening wedge osteotomy model. The design of this cadaver study limits its direct application to clinical practice.

In each of the six pairs of fresh-frozen human cadaver knees one specimen was randomly assigned to internal plate fixation while the other was stabilized with an external fixation. The osteosynthesis plate incorporated a 12.5mm block that distracted the medial tibial cortices. Each knee was loaded on a mechanical testing machine to 700 N for 10,000 cycles to simulate immediate full weight bearing in a walking individual.

The internal plate osteosynthesis provided significantly greater stiffness and smaller loss of correction (1.60mm) than the external fixation (3.22 mm) under cyclic loading condition (P<0.05). For static loading, the mean value of stiffness resulting in failure for the internal plate and external fixation, were respectively, 938 N/mm and 459 N/mm. Load to failure also showed two times greater stiffness in the plate osteosynthesis group. No hardware failure was observed in either construct.

Plate fixation was superior to external fixation in maintaining correction. However, progressive adjustment of the distraction with the external fixator allows precise "fine-tuning" during the healing process that is not possible with internal fixation.