Risk of neurovascular injuries in flexor hallucis longus tendon transfers: an anatomic cadaver study

Flexor hallucis longus (FHL) tendon transfer is a frequently used treatment for both posterior tibial tendon insufficiency and chronic Achilles tendinopathy. We observed difficulties in harvesting the FHL tendon that may arise from cross-attachments with the flexor digitorum longus (FDL) tendon near the knot of Henry. The posterior tibial nerve is located nearby the decussation of these tendons. This study examined whether the difficult harvesting may be the cause of nerve injury.

A cadaver study was performed on 24 foot specimens. In all feet, we used a double-incision technique. The FHL tendon was transected in the distal medial midfoot incision and retracted through the posteromedial hindfoot incision. After harvesting the FHL tendon, we exposed the posterior tibial nerve and its lateral and medial plantar branches to identify if any lesion had occurred.

The retraction failed at the first attempt in all specimens because of the presence of cross-attachments between the FHL and FDL tendons. A more extensive dissection of the FHL and FDL tendons was therefore required. We found lesions in 33% of all foot specimens, including two complete ruptures of the medial plantar nerve.

Harvesting of the FHL tendon when transection is made distal to the knot of Henry may cause injuries to the medial and lateral plantar nerves. Experience in this procedure may reduce the risk of nerve injuries but even then nerve lesions remain possible. The clinical significance of these nerve lesions is not described in literature and remains to be determined.