Reconstructed patellar tendon length after proximal tibia prosthetic replacement.

A common problem after proximal tibia prosthetic reconstruction is insufficient extensor mechanism or extensor lag. Maintaining the reconstructed patellar tendon length is an important way to minimize extensor lag. We measured the patellar tendon length and extensor lag serially. From 1994-2003, seven consecutive patients with malignant bone tumors of the proximal tibia had prosthetic reconstruction. The extensor mechanism was reconstructed by reattachment of the patellar tendon to the prosthesis with a synthetic material and augmented by a gastrocnemius flap. The patellar tendon length was measured according to the Insall-Salvati ratio. The ratios at 30 degrees knee flexion decreased immediately postoperatively, and reverted to almost the same preoperative values within 18 months. The mean ratios at 60 degrees knee flexion are significantly greater than 30 degrees at 6 months postoperatively. These findings indicate that the patellar tendon stretched, whereas the extensor lag improved continuously for 12 months postoperatively. In the revision at 22 months postoperatively, although the patellar tendon was not reattached to the replaced prosthesis, the ratio and the extensor lag had not worsened. These results show that providing strong continuity of the patellar tendon, gastrocnemius flap, and leg extensors can decrease the extensor lag, although the patellar tendon stretches.