Complete Closed Rupture of the Medial Bundle of the Flexor Hallucis Brevis Tendon Off the Medial Sesamoid Insertion
Authors: Materon Solangel Rodriguez , Hodgkins Christopher W. 
Published: November 2022

Category: Midfoot/Forefoot; Basic Sciences/Biologics; Sports; Trauma Introduction/Purpose: Flexor tendon injuries of the hallux are uncommon overall but when they happen, the flexor hallucis longus (FHL) tendon is the most frequent one affected. The rupture of FHL usually results from open injuries and deep cuts in the sole at the base of the toe;4 complete subcutaneous ruptures are extremely rare.5 There are around 36 cases reported of complete or partial closed ruptures of the FHL tendon along its entire course6 and the majority of the partial ruptures correspond to dancers and athletes.7 As far as FHB, we found a few reports of calcific tendinitis of the medial bundle and cases of calcifying tendinitis.8 To the best of our knowledge, this is the only case report of isolated closed rupture of the FHB tendon. Methods: A 33-year-old man, amateur soccer player, presented with mild swelling, ecchymosis, and increasing pain in the left hallux triggered by movement and palpation, relieved by rest. He sustained a direct axial blow and blunt force trauma with a soccer ball plus hyperextension. Standard bilateral weightbearing feet radiographs were normal. Physical exam revealed the left hallux normally aligned but with limited painful motion of 20° each way and no obvious instability. Palpation of the left first metatarsophalangeal joint was tender but not particularly over the sesamoids. MRI revealed an avulsion of the flexor Hallucis Brevis tendon off the proximal aspect of the medial sesamoid accompanied by fluid and edema, effusion in the first MTP joint and bone contusions in the first metatarsal head and dorsal base of the first proximal phalanx. Treatment with a toe spacer and postop sandal with the toe straight with an extension block was decided. Results: Tendon's blood flow around the sesamoids is limited making it susceptible to degenerative rupture. The most common mechanism of complete tendon rupture is direct open injury. Closed rupture is very rare and complete rupture in closed injury is even more. We did not find reports on third degree type of injuries, neither for any kind of isolated rupture of FHB. In our patient's case, dorsiflexion stretched all plantar soft tissue around the first MTP but he was able to do active movement of the great toe probably due to the FHL and lateral FHB insertion integrity. We found few reports of second-degree strain injury of FHL and FHB in a chronic setting, all treated conservatively with partial immobilization and strapping of the hallux to prevent extension. After conservative treatment at 3 months follow-up, our patient presented with no subjective complains, normal motion, stability and alignment of the hallux. Conclusion: Despite an extensive literature search, we did not find a similar injury, and this is probably the first time it is described. As found in our research, the most common injury related to the flexor tendons of the hallux are in soccer players and involve the FHL or both.23 These findings made us conclude that these injuries are either under-diagnosed or exceptional.