Biomechanical Study of the Quadrupled Gracilis Tendon Graft for the Anterior Cruciate Ligament Reconstruction

Background/Objectives: To compare the morphological and biomechanical properties of a quadrupled gracilis (4GR) graft with two standard hamstring grafts for anterior cruciate ligament (ACL) reconstruction: a quadrupled semitendinosus (4ST) graft and a doubled semitendinosus–gracilis (2ST2GR) graft. Methods: Tendon specimens were obtained from 30 cadaveric donors (mean age, 42.6 years; range, 21–56 years). Tendon and graft dimensions were measured before biomechanical testing. Grafts underwent standardized preconditioning followed by load-to-failure testing at a displacement rate of 20 mm/min. Differences between graft types were analyzed using a generalized linear mixed-effects model, with results expressed as estimated marginal means with 95% confidence intervals (CI). Results: The mean 4GR graft length was 64.7 (95% CI, 61.6–67.8) mm, with 80% exceeding 60 mm. Graft diameter was greatest in the 4ST group, intermediate in the 2ST2GR group, and smallest in the 4GR group (7.98 [95% CI, 7.67–8.29], 7.41 [95% CI, 7.12–7.70], and 6.12 [95% CI, 5.89–6.36] mm, respectively). The 4ST graft demonstrated significantly greater maximum force than both the 4GR and 2ST2GR grafts, whereas no significant difference was observed between the 4GR and 2ST2GR grafts. In contrast, tensile strength was significantly higher in the 4GR grafts than in both the 4ST and 2ST2GR grafts. Stiffness was significantly higher in the 4ST grafts than in the 4GR grafts, whereas Young’s modulus was significantly higher in the 4GR grafts than in the 4ST grafts. Conclusions: The 4GR graft provided sufficient length for all-inside ACL reconstruction in most specimens. Despite its smaller diameter and lower absolute load-bearing capacity than 4ST, the 4GR graft demonstrated higher tensile strength and Young’s modulus, indicating favorable intrinsic mechanical properties. These findings may help inform graft selection in selected reconstructive procedures.