External patellotibial transfixation: indications, operative technique and outcome.

Patellotibial transfixation with the MPT fixator is a new method of external stabilisation for lesions of the extensor mechanism of the knee joint. The biomechanical principle is the external transmission of tensile forces in the quadriceps muscle from the patella to the lower thigh and the translation of these forces into extension of the knee joint. The construction is an external patellotibial frame. In fitting method A, a Steinmann pin with central thread is inserted transversely through the patella and proximal tibia. Connection is made via laterally positioned rods with rotatable fixator jaws. In fitting method B, a Schanz screw is inserted sagittally into the proximal tibia and connected to the tibiocentral fixator jaw. In the frame construction a threaded pin is tightened into the fixator jaw. The MPT fixator is mostly used to secure suture repairs and transosseous refixations of the patellar ligament, or to reconstruct neglected patellar tendinous or osseous lesions of the distal extensor apparatus when functionally stable results cannot be obtained by osteosynthesis. The advantages of patellotibial transfixation are that: (1) a minimum of internal allogenic material is required to reconstruct the extensor apparatus and the repair is protected against excessive strain; (2) immediate functional post-operative therapy with an unlimited range of motion and early full weight-bearing is possible. Between 1990 and 1997 the MPT fixator was here used on 74 patients, 51 of whom had an acute lesion of the extensor mechanism, 19 lesions had either been neglected or subjected to an earlier operation. Among 20 of the acutely injured knee joints there were other serious associated injuries. Fitting method A was used in 48 patients and fitting method B in 26 patients. In four patients the operation was followed by severe infection, owing to the fixator in two cases. The remaining 70 patients wore the system for an average of 7.3 weeks. Eight patients with caudal comminuted fractures who had had segmental patellectomy and transosseous refixation of the patellar tendon and 15 patients who had had transosseous suture refixation of the patellar ligament after rupture at the lower pole or suture repair after intraligamentous rupture, were followed up isokinetically and radiologically with IKDC scoring for an average of 49.3 months after the operation. The outcome was classified as normal or close to normal in 19 patients and as abnormal in four. Isokinetically only five of the 23 had a 10-20% deficiency in the strength of the extensor muscles of the operated leg in comparison to the opposite side. External patellotibial transfixation with the MPT fixator produced good operative results in re-establishing the continuity of the distal extensor apparatus of the knee joint and is an effective alternative to patellotibial cerclage with wire or synthetic ligament.