Introduction: Recent clinical, morphological and MRI studies have evidenced a potential for regeneration of the tendons of the semitendinous and medial rectus muscles. This is the first article in the world literature describing how these two tendons have been obtained for the second time and have been used for reconstruction of the ACL.

Materials and methods: The study included two men aged 30 and 38 in whom the ACL had been reconstructed (6 and 9 years before, respectively) using the semitendinous (ST) and medial rectus (MR) tendons. The full length and width of the tendons were harvested using a tenotome. The ACL reconstruction was subsequently broken in both patients in a sporting accident. Preoperative MRI was performed in both patients and confirmed the rupture of the ACL and regeneration of the ST and MR. Both tendons were harvested, the macroscopic findings were noted and samples of the tendons were taken for histological study. The regenerated tendons were used to reconstruct the ACL, maintaining their distal attachment and fixing them proximally with a staple.

Results: Macroscopically the regenerated tendons looked nearly normal. Both had regenerated to their normal thickness and length (the diameter of the tunnels in the ACL revision surgery was the same as in the primary surgery).

The histological study showed normal tendinous tissue with a few areas of disorganised collagen bundles, increased proliferation of fibroblasts and formation of capillaries.

After a follow-up of 14 and 17 months, both patients recovered their prior level of sports activity and their knees were stable.

Conclusions: Harvesting the tendons of the semitendinous and medial rectus muscles leads to regeneration of both tendons. Although the biomechanical properties of this regenerated tissue are unknown, clinically it appears to be an appropriate tissue for ACL reconstruction.