The purpose of this study was to evaluate the biomechanical properties of commonly used autogenous transplants for the surgical stabilization of chronic lateral ankle instability. We dissected the transplants (peroneus longus, peroneus brevis, Achilles and plantaris tendon, periosteal flap, fascia, corium) and the anterior talofibular ligament from 13 fresh anatomic specimens. After laser-assisted measurement of the transplant diameter, we assessed their biomechanical properties with a universal testing device. Biomechanical stability of the peroneus longus, peroneus brevis, and Achilles tendons was significantly higher than the other transplants. The stability parameters of the periosteal flap were in the range of the anterior talofibular ligament but inferior to the tendons. The application of a transplant with low biomechanical stability, such as the periostal flap, requires more postoperative immobilization as in a strong orthosis or cast.

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A variety of points of insertion and implantation techniques are recommended for inserting screws into the os sacrum. On the basis of 16 complete human sacrum specimens the following axial pull-out tests were performed: 1. Insertion of convergent measuring screws, 6.0 mm and 7.0 mm in outside diameter respectively, into the body of vertebra S1 using a monocortical and bicortical technique respectively with perforation of the ventral cortex. 2. Insertion of divergent screws into the ala sacralis at the level of S1 with 6-mm and 7 mm screws respectively, using a monocortical technique without perforation of the ventral cortex. 3. Insertion of convergent 6-mm screws into the body of vertebra S2 using a monocortical and bicortical technique respectively with perforation of the ventral cortex. The highest axial pull-out force was reached using convergent 6-mm screws inserted into the body of vertebra S1 using the bicortical technique with perforation of the ventral cortex (2392.4 N). The use of a 7.0-mm screw in the same implantation technique did not result in higher pull-out forces (2274.7 N). The monocortical technique reached a pull-out force of 1657.53 N with a 6-mm screw and 1505.64 N with a 7-mm screw. Convergent insertion of 6-mm screws into the body of S2 resulted in pull-out forces of 537.02 N using a bicortical and only 297.71 N using a monocortical technique. Divergent insertion of screws into the ala sacralis reached a maximal pull-out force of 495.47 N using 6-mm screws and 449.79 N using 7-mm screws. These data resulted from a monocortical implantation technique without perforation of the ventral cortex of the ala sacralis. The results of the present biomechanical study show that convergent bicortical implantation in the body of S1 is the most stable technique for screw fixation in the sacrum. The use of 7-mm rather than 6-mm screws did not lead to increased primary stability. Anatomic studies have shown that a safe area exists in the region of the ventral promontory, so this implantation technique appears to be unobjectionable.

High tibial osteotomy in the varus knee has been successfully performed for a long time. Several newer operation techniques have been established in recent 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 specimens were harvested, frozen, and subsequently thawed under the same conditions 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 & Nephew) and an external fixator (Orthofix). The specimens were mounted in metal cylinders and then loaded in two different setups: transverse forces were applied to the osteotomy site by hanging weights parallel to the osteotomy plane in a static-loading frame, and axial forces were applied by a materials testing machine (Zwick). Displacement was recorded using a linear variable displacement transducer (LVDT). The highest stability was achieved by the external fixator and the bone staples. Giebel's blade plate and the one-third tubular plate were less stable. Retention of an intact medial cortex was a decisive factor in obtaining primary stability. We found that the primary stability of the tested devices was generally comparable as long as they were correctly implanted. It was also noted that lateral spacing of the osteotomized bone should not exceed 3 mm. If the medial cortex is transected intraoperatively in lateral osteosynthesis, an additional medial implant is necessary to ensure sufficient primary stability. For practical reasons it was necessary to neglect the contribution of the soft tissues around the knee, although all implants were tested under the same conditions. Care should thus be taken when interpreting the results of this study in a clinical setting.

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