KNEE FUNCTION AFTER PATELLECTOMY AND CRUCIFORM REPAIR OF THE EXTENSORMECHANISM

When patellectomy is performed, the objectives should include restorat ion of a moment arm, centralization of the extensor mechanism, adequat e range of motion, and cosmesis. The cruciate repair of the extensor m echanism described in this report has been developed to meet the afore mentioned objectives. Eight patients with 12 patellectomies described herein were examined with Cybex testing of the knee at a follow-up per iod of 18 months to 20 years (mean, 56 months). A four-quadrant tissue dissection of the patellar soft-tissue enclosure was reconstructed in a cruciform pants-over-vest fashion, with the superomedial flap conta ining the vastus medialis insertion on top. This ''soft-tissue'' patel la attempts to provide a greater moment arm than simpler repairs. This study examines whether this construct restored the torque of extensio n while concomitantly facilitating centralization of the extensor mech anism. Cybex testing of both knees examined both extensor and flexor f unction with specific regard to the ratio of extensor to flexor forces . Patients with patellectomies had few subjective complaints, with a m ean knee score of 94 (median, 100). The extensor torque was not comple tely restored and there was a moderate decrease in the quadriceps func tion, both subjectively and objectively as measured by Cybex testing. The authors also found that in patients with unilateral patellectomies , the ratios of extension to flexion function, a parameter not yet rep orted in the literature, were significantly different between the norm al and patellectomized knees. The same extension to flexion ratios wer e seen in patients with bilateral patellectomies. Because patients wit h patellar pathology requiring patellectomy frequently have chronic an d bilateral disease, comparative functional evaluation may be difficul t. The use of the extension-to-flexion ratios may help in the evaluati on of knee function after patellectomy since the flexor muscles provid e an inherent control against which the extensor mechanism can be comp ared.