Biomechanical stability of a retrotubercle opening-wedge high tibial osteotomy.

In recent years, opening-wedge osteotomy has gained popularity. However, the complication rate reported is high. Opening-wedge osteotomy was modified to remedy the problems seen with the conventional technique including loss of correction, delayed healing, and patella infera. This biomechanical study evaluates the response of a new opening-wedge osteotomy in a static and dynamic mode of human cadavers. Results were compared to the stability of the conventional technique. Six preserved pairs of human cadaveric knees were tested. Specimens of the same pair were randomly assigned to either the modified or conventional osteotomy. Internal fixation was used to ensure precise correction and prevent bone collapse. Each tibia was loaded on a material testing system from 0 to 700 N for 10,000 cycles to simulate immediate full weight bearing in a walking individual. Specimens were then loaded to failure to determine ultimate load and stiffness of the construct. Displacement of the articular fragment and stiffness were measured during dynamic loading. Load to failure, displacement, and stiffness were measured during static testing. The modified osteotomy provided significantly greater stiffness (1392 N/mm) and smaller loss of correction (.68 mm) than the conventional osteotomy (741 N/mm; 1.76 mm) under cyclic loading conditions (P<.05). The modified retrotubercle osteotomy provides greater stiffness than the conventional osteotomy, increasing stability by 62% and minimizing loss of correction to <1 mm. The modified osteotomy eliminates the need for bone graft and provides additional strength to allow accelerated rehabilitation.

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

PURPOSE: 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. MATERIAL AND METHOD: 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. SUMMARY OF RESULTS: 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. DISCUSSION AND CONCLUSION: 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.