Communications between the tendons of flexor hallucis longus and flexor digitorum longus: a cadaveric study

Tibialis posterior tendon insufficiency in adult acquired flat foot deformity (AAFFD) is treated by reinforcing the posterior tibial tendon (PTT) using grafts from flexor hallucis longus (FHL) and flexor digitorum longus (FDL). The communication between FHL and FDL will influence the length of the graft that can be harvested from FHL and FDL. In this study, we aim to study the patterns of communications between FHL and FDL tendons and the location of Master Knot of Henry (MKH) and point of division of FDL tendons in Indian population.

In this observational descriptive study, 36 formalin-fixed cadavers were sourced from Subbaiah Institute of Medical Sciences, Shimoga, Karnataka, India, and JIPMER, Puducherry, India, during the period of 2017-19. Various parameters of the foot to locate the MKH and point of division of FDL tendons and various types of communications between FHL and FDL were observed.

Among the various types of communications between FHL and FDL tendons, type I was present in 61.76% of cases, type II in 2.94% of cases, type III in 7.35% of cases, type IV in 14.70% of cases, type V in 8.82% of cases, type VI in 0% of cases, type VII in 1.47% of cases and an unusual type in 2.94% of cases.

In the present study done in Indian population, we found that type I variety is present more commonly followed by type IV. FHL and FDL tendon grafts can be lengthened based on the communications between them. In type I variety, the communication can be severed at the FDL end to lengthen the tendon graft for harvest.