Residual strength of the quadriceps versus patellar tendon after harvesting a central free tendon graft

Purpose: Free tendon grafts for reconstruction of the anterior cruciate ligament have become more prevalent with the desire for reduced morbidity, earlier postoperative rehabilitation, and improved free tendon graft fixation. The central quadriceps tendon autograft is an alternative to bone-patellar tendon-bone and free hamstring autografts. The purpose of this study was to measure the postharvest reduction in quadriceps extensor mechanism strength when a central quadriceps free tendon graft is removed. The strength deficit was compared with that associated with harvesting a central free patellar tendon graft, excluding the effects of harvesting bone blocks. Type of Study: Experimental laboratory study. Methods: Fourteen knee extensor mechanisms were divided into quadriceps and patellar tendon constructs. Constructs were tested to failure in tension in either the intact state or after removing 10-mm wide central free tendon grafts. Failure strengths of the quadriceps and patellar tendon constructs were compared statistically using paired and unpaired t tests. Results: The average strength (+/- SD) measured for the native quadriceps tendon was 3,660 +/- 830 N, decreasing to 2,430 +/- 680 N after removing a partial-thickness 10-mm wide central free graft. The average strength measured for the native patellar tendon was 1,920 +/- 330 N, decreasing to 1,460 +/- 740 N after removing a 10-mm wide central free graft. Conclusions: The tensile strength of the quadriceps tendon is reduced by approximately one third after harvesting a partial-thickness 10-mm. wide central free tendon graft. This postharvest strength of the quadriceps tendon is higher than that of the intact patellar tendon. Clinical Relevance: Surgeons can be assured that harvest of a central quadriceps free tendon graft leaves a stronger extensor mechanism than harvest of a patellar tendon graft.