Semitendinosus muscle in anterior cruciate ligament surgery: Morphology and function

Purpose: To evaluate the fate of the hamstring muscles in general and the s emitendinosus muscle in particular, after anterior cruciate ligament (ACL) reconstruction with an autologous semitendinosus tendon graft from the ipsi lateral side. Type of Study: Prospective consecutive case series investigat ion . Methods: Included were 16 consecutive patients, 14 male and 2 female, with a mean age of 26 years. The inclusion criterion was chronic unilatera l ACL insufficiency with no concomitant knee ligament injuries. ACL reconst ruction was performed with a quadruple semitendinosus tendon graft using th e EndoButton technique (Acufex, Mansfield, MA). Intraoperatively, muscle sp ecimens were taken from the semitendinosus muscle on the harvested side. Fo llow-up at a minimum of 6 months included clinical examination, isokinetic strength performance, magnetic resonance imaging (MRI) of the thigh and kne e, and ultrasound-guided muscle biopsy procurement from the semitendinosus muscle for histochemical and enzymatic analyses. Results: Of the patients, 75% showed regeneration of their semitendinosus tendons. The neotendons all inserted below the knee joint where they had fused with the gracilis tendo n to a conjoined tendon inserting in the pes anserinus. The semitendinosus muscle had a smaller cross-sectional area on the operated side but none sho wed total atrophy. Less atrophy was present in the patients with a regenera ted semitendinosus neotendon compared with those without regeneration (P = .029). In the latter group the semimembranosus muscle seemed to compensate for this with hypertrophy (P = .019). Cross-sectional muscle fiber areas, t he relative number of each fiber type and oxidative potential as estimated by citrate synthase activity, showed no significant differences between the operated and nonoperated legs. The isokinetic strength of the hamstrings a nd quadriceps was significantly lower in the operated leg than in the nonop erated leg. Conclusions: With this surgical technique, the semitendinosus m uscle can recover and the tendon has, according to the MRI images, a great potential to regenerate after its removal.