A biomechanical evaluation of anterior and posterior tibialis tendons as suitable single-loop anterior cruciate ligament grafts.

PURPOSE Because allograft tendons used to replace a torn anterior cruciate ligament are in short supply, it is useful to explore other possible graft sources. The purpose of this study was to determine whether a graft formed from a loop of either an anterior or posterior tibialis tendon has structural, material, and viscoelastic properties similar to those of a double-looped semitendinosus and gracilis (DLSTG) graft. TYPE OF STUDY Completely randomized design. METHODS Four structural and 3 material properties were determined for each type of graft (n = 10) by measuring the cross-sectional area, looping the tendon(s) over a post, gripping the free ends of the tendon(s) with a freeze clamp, and pulling the graft to failure by using a materials testing system. Two viscoelastic properties were determined for each type of graft (n = 10) by measuring the decrease in load under a constant displacement (i.e., stress relaxation test) and the increase in displacement under a constant load (i.e., creep test). RESULTS For grafts 95 mm in length, the ultimate load and ultimate displacement of a loop of anterior (4,122 N, 12.0 mm) and posterior tibialis (3,594 N, 12.5 mm) tendon were either similar to or significantly greater than those of the DLSTG graft (2,913 N, 8.4 mm) (P =.204 for the posterior tibialis ultimate load and P < or =.007 for the remaining quantities). The stiffness and cross-sectional area of the anterior (460 N/mm, 48.2 mm2) and posterior tibialis (379 N/mm, 41.9 mm2) grafts were similar to those of the DLSTG graft (418 N/mm, 44.4 mm2) (P > or =.283). The tensile modulus, stress at ultimate load, and strain at ultimate load of the anterior tibialis and posterior tibialis grafts were either similar to or significantly greater than those of the DLSTG graft. The decrease in load of the anterior tibialis and posterior tibialis grafts was either greater than or similar to that of the DLSTG graft for the relaxation test (P < or =.066). The increase in displacement of the anterior tibialis (0.3 mm) and posterior tibialis (0.4 mm) grafts was minimally but significantly greater than that of the DLSTG graft (0.2 mm) for the creep test (P < or =.004). CONCLUSIONS The structural, material, and viscoelastic properties of a single loop of anterior tibialis and posterior tibialis tendon are either better than or similar to those of a DLSTG graft. Consequently, single-loop grafts formed from tibialis tendons should function well as a replacement for a torn anterior cruciate ligament.