High tibial osteotomy - primary stability of several implants

Introduction: High tibial osteotomy in varus knee has been performed for a long time. Several newer operation techniques have been established in rece nt years. We tested the primary stability of several of these techniques in vitro. Material and methods: 10 human cadaveric fresh-frozen specimens were tested with a mean age of 61 years (range 50-72 years), and weight of 65 to 78 kg . The following implants were tested: One-third-tubular plate with cortical s crew (AO, Synthes), blade plate with screws (Giebel's plate, Link), bone st aples (osteotomy staples, Krackow staples, Smith & Nephew), external fixate ur (Orthofix). The specimens were fixed in metal cylinders and then loaded in two different apparati: Shear forces were applied to the osteotomy site by hanging weights parallel to the osteotomy plane in a static-loading fram e, and axial forces were applied by a materials testing machine (Zwick). Lo ad displacement was recorded by inductive displacement transducers. Results: The highest stability was achieved by the external fixateurs and t he bone staples. Giebel's plate and the one third tubular plate were less s table. Receipt of the medial corticalis was decisive for primary stability of the implants. Conclusion: The clinical significance of the results is limited by the rele vance of the protocol, which for practical reasons did-not account for the soft tissue situation around the knee. Thus, primary stability of the teste d devices was generally comparable as long as they were correctly implanted . It was found, that lateral distance of the osteotomized bone should not e xceed 3 mm. If the medial corticalis sawed, another medial implant is neces sary to ensure sufficient primary stability.