50 patients who had undergone ACL reconstruction were randomized to undergo the procedure using either an ipsilateral quadrupled semitendinosus (ST) tendon graft, or an ipsilateral doubled semitendinosus/gracilis graft. The purpose of this study was to observe the regeneration of the ST tendon using ultrasonography in all participants and biopsy data in 3 of these patients. Results indicated that, by 12-18 months, the regenerated semitendinosus tendon was almost identical to the one in the non-operated knee. Tendon insertion was found to be more proximal when both the ST and gracilis tendons were resected, whereas the incidence of neotendon development was higher when the ST tendon was harvested leaving the gracilis tendon intact. Regenerated tendons were also well-vascularized at study completion. Lastly, no pain, subluxation or dislocation was experienced by one patient who had undergone medial patellofemoral ligament reconstruction using the regenerated tendon.