Surgical treatment of avulsion fracture of the posterior cruciate ligament and postoperative management.

BACKGROUND: Avulsion fractures of the posterior cruciate ligament have long been regarded as rare injuries. In the past, it was common practice to use cast immobilization as an external adjunct after open reduction and internal fixation of fractures. METHODS: Sixteen patients with displaced avulsion fractures of the posterior cruciate ligament were treated with open reduction and internal fixation between August 1989 and July 1993. Malleolar screws were chosen as fixation devices in 14 patients. In the other two, pull-through sutures were used because the size of the fractured fragments was too small to obtain purchase of screws. The postoperative management protocol evolved from an initial regimen of 6 weeks' immobilization in a cast with the knee flexed to 40 degrees for the first five patients (group I), to 4 weeks' immobilization in a cast for the next six patients (group II), to the present protocol of immediate postoperative range of motion (40-70 degrees) with muscle-strengthening exercises in a functional brace for the last five patients (group III). The average follow-up period was 36 months (range, 24-58 months). Hughston's criteria were used to assess the clinical results. RESULTS: Overall, there were 12 (75%) good and 4 fair (25%) results. There was no poor result. CONCLUSION: Avulsion fractures of the posterior cruciate ligament should be treated with open reduction and stable internal fixation if any displacement is seen on initial radiographs at presentation. With the use of functional brace and aggressive postoperative rehabilitation program (i.e., immediate range of motion of 40-70 degrees with muscle-strengthening exercises), satisfactory results can be expected and achieved.

The effects of cyclic stretching on tensile properties of the rabbit's skeletal muscle.

OBJECTIVE: To define the threshold of muscle injury with cyclic passive stretch. DESIGN: The changes in the load-deformation curve of muscle-tendon unit were monitored until the failure point by an in vivo rabbit model. BACKGROUND: Muscle injuries range in severity from a simple strain to complete rupture. Although strains occur more frequently than complete failures, only a few studies have investigated the phenomena of these sub-failure injuries. Monitoring of the continuum for stretch-induced injury allows us to define the threshold of stretch injury. METHODS: Thirty rabbits' triceps surae muscle-tendon unit preparations were used. One of the pairs (control) was stretched until failure; the other (experimental) was first cyclic stretched to either 12, 20 or 25% of the initial length of the muscle-tendon unit and then stretched to failure. Comparisons were made between the load-deformation curves of the experimental and control specimens. RESULTS: When cyclic stretched to 12 or 20%, there were no significant changes existed in the biomechanical parameters except the deformation at the peak load. In contrast, all the biomechanical parameters except the ration of the energy absorption changed significantly after 25% strain cyclic stretch. CONCLUSIONS: A threshold for stretch-induced injury does exist. This can be reproduced at the 25% strain of the triceps surae muscle-tendon unit.