The strength of the central third patellar tendon graft. A biomechanical study

Thirty-seven bone-patellar tendon-bone composite grafts from the knees of 21 human cadavers were tested to failure. Average donor age was 28 years. The composites were divided into 4 groups: 3 groups with 10 grafts (5 pairs) and 1 group with 7 grafts from 6 donors. In Group 1 we tested 10- versus 15-mm wide grafts that were used without twisting; Group II, 10-mm wide grafts without twisting versus 10-mm wide grafts that were twisted 90 degrees; Group III, 10-mm wide grafts twisted 90 degrees versus 10-mm wide grafts twisted 180 degrees; and Group IV, 10- versus 7-mm wide grafts that were not twisted. The tests were performed using a newly described potting technique and clamp system and a servohydraulic testing machine with an elongation rate of 5 cm/sec. The results of this study suggest that the central third of the patellar tendon is stronger than previously reported. The mean ultimate load of a 15-mm bone-patellar tendon-bone composite was 4389 N (+/- 708); of the 10-mm wide composites, 2977 N (+/- 516); and of the 7-mm composites, 2238 N (+/- 316). Twisting the graft 90 degrees increased the strength (P < 0.05). Further twisting to 180 degrees had no significant effect compared with twisting 90 degrees. This study supports the practice of using smaller (10 mm) bone-patellar tendon-bone grafts to avoid the potential complications of patellar fracture and graft impingement in the notch.