Biomechanical Strength and Elongation of the T-Block Modification for Bone-Patella Tendon-Bone Allografts.

Abstract

To assess the biomechanical performance of 2 different T-block modifications of bone-patella tendon-bone (BPTB) allografts. The matched knee pairs from 10 human cadavers (mean age 49 years) were fashioned into 30 BPTB allografts and divided into 3 groups (10 each): group 1, standard patella tendon-tibial attachment; group 2, T-block tibial attachment with 10 mm of unattached bone proximal to the patella tendon insertion with 15 mm of tendon attached; group 3, T-block tibial attachment with 15 mm of unattached bone proximal to the patella tendon insertion and 10 mm of tendon attached. A biocomposite interference screw secured each graft into a 10-mm tunnel in 15 pcf polyurethane foam. A 10-N preload was applied followed by 500 cycles of 10- to 150-N loading at 0.5 Hz. Grafts completing cyclic loading were destructively tested at 200 mm/min. Failure load, stiffness, elongation, and failure mode were recorded. Failure loads and elongation for groups 1, 2, and 3 (790, 729, and 700 N; 0.15, 0.16, and 0.19 mm, respectively) were not statistically different (P > .1). Graft stiffness for groups 1 and 2 (214 and 186 N/mm) were not statistically different, but group 3 (170 N/mm) was different from group 1. All group 1 and 2 tests failed by graft pullout as did 8 of 10 from group 3. The other 2 failed by tendon tearing from bone. A T-block BPTB allograft harvested with 10 or 15 mm of unattached bone proximal to the tibial patella tendon insertion has no ultimate failure strength difference after cyclic loading compared with the standard BPTB allograft. The 15-mm T-block showed lower stiffness and more elongation at failure than the standard BPTB allograft whereas the 10-mm T-block exhibited comparable stiffness and elongation measurements to the standard BPTB allograft control specimens. The T-block BPTB allograft construct should increase the availability of BPTB allografts for anterior cruciate ligament reconstruction and facilitate the use of grafts possessing longer tendon segments that are currently being discarded.