Effect of muscle preserved on tendon graft on intra-articular healing in anterior cruciate ligament reconstruction

The aim of this study was to determine the impact on intra-articular healing of muscle tissue retained on tendon grafts used for anterior cruciate ligament (ACL) reconstruction.

In an animal study on 40 New Zealand rabbits, a semi-tendon/semi-muscle graft (SSG) and a total tendon graft (TTG) were individually harvested from the Achilles tendons in each animal. After transecting the ACLs in both knees of each rabbit, SSG and TTG were randomly used on bilateral sides of the knee for ACL reconstruction. After 2, 4, and 8 weeks, functional scoring, gross observations, and histological evaluations of the repaired knees were performed (each time point; n = 10). Biomechanical testing was conducted on remaining animals at 8 weeks (n = 10).

At 2, 4, and 8 weeks after surgery, there were no statistically significant differences in functional scores between the SSG group and TTG group (n.s.). As healing progressed, skeletal muscle on the SSG was gradually absorbed with a corresponding decrease in graft diameter, compared to TTG, at each time point (P < 0.001). However, healing and incorporation of the intra-articular graft in the SSG were more apparent than those in the TTG, based on histology. The vascularity and cellularity in the center of the sample were significantly greater in the SSG group than the TTG group at all the time points (P < 0.01). At 8 weeks, the SSG group’s ultimate failure load, yield load, and elongation at failure were significantly less than for the TTG group (P < 0.01). There were no significant differences in stiffness between the two groups with biomechanical testing (n.s.).

Results of this study indicate that muscle left on tendon grafts promotes intra-articular healing and remodeling of the graft in a rabbit model. However, excessive amounts of retained skeletal muscle weaken tendon graft’s strength for ACL reconstruction. Preserving small amounts of muscle on tendon grafts is feasible for improving the biological success of ACL reconstruction in humans.