Primary stability of different implants used in conjunction with high tibial osteotomy

High tibial osteotomy in the varus knee has been successfully performed for a long time. Several newer operation techniques have been established in r ecent years. We tested the primary stability of several of these techniques in vitro. Ten human cadaveric fresh-frozen specimens were used that had a mean age of 54 years (range 29-72 years) and a weight of 55-85 kg. All spec imens were harvested, frozen, and subsequently thawed under the same condit ions before testing. The following implants were tested: one-third tubular plate with a cortical screw (AO, Synthes), blade plate with screws (Giebel' s plate, Link), bone staples (osteotomy staples, Krackow staples, Smith & N ephew) and an external fixator (Orthofix). The specimens were mounted in me tal cylinders and then loaded in two different setups: transverse forces we re applied to the osteotomy site by hanging weights parallel to the osteoto my plane in a static-loading frame, and axial forces were applied by a mate rials testing machine (Zwick). Displacement was recorded using a linear var iable displacement transducer (LVDT). The highest stability was achieved by the external fixator and the bone staples. Giebel's blade plate and the on e-third tubular plate were less stable. Retention of an intact medial corte x was a decisive factor in obtaining primary stability. We found that the p rimary stability of the tested devices was generally comparable as long as they were correctly implanted. It was also noted that lateral spacing of th e osteotomized bone should not exceed 3 mm. If the medial cortex is transec ted intraoperatively in lateral osteosynthesis, an additional medial implan t is necessary to ensure sufficient primary stability. For practical reason s it was necessary to neglect the contribution of the soft tissues around t he knee, although all implants were tested under the same conditions. Care should thus be taken when interpreting the results of this study in a clini cal setting.