Qualitative and quantitative morphological study of flexor hallucis longus implicated in tendon harvesting and transfer

Abstract

Flexor hallucis longus (FHL) transfer is a widely used technique for reconstruction of Achilles tendinopathies, but the complications such as neurovascular injury and functional loss of toes have been reported. This study aimed to evaluate the morphology of FHL musculotendinous junction (MTJ), location of MKH in reference to the landmarks in foot, type and morphometry of tendinous interconnection between FHL and flexor digitorum longus (FDL) tendons and FHL tendon length in single incision, double incision and minimally invasive techniques. The dissection was performed in 104 embalmed and 62 soft cadaveric feet. The result showed type 1 (87.3%) and type 3 (12.7%) of MTJ morphology. MKH was located proximal to interphalangeal joint of great toe (IP), under navicular tuberosity (NT) and distal to medial malleolus (MM) with medial plantar neurovascular bundle residing closely. Surface localization of MKH from medial end of plantar flexion crease at the base of great toes (MC) was 94.75 ± 8.43% of MC-NT length with a perpendicular distance of 25.11 ± 5.37 mm below MC-NT line. Three types of interconnection (I, II, V) were found. The most frequent type is type I (85.4 %) which had a slip directly from FHL and the mean distance of slip in all type was distal to MKH. In addition, a new type of connection was found in 6.1%. FHL tendon bifurcated into one tendon to the first toe and the other tendon fused with FDL tendon. Four types of slip distribution to lesser toes were defined in this study and type b with a distribution to 2nd and 3rd toes, was the majority. The length of FHL tendon in foot (in-situ) and after it was cut from the insertion (ex-vivo) was longest in minimally invasive technique (83% and 95% of foot length) and it had the moderate positive correlation to foot length. Moreover, there was a significant difference between in situ and ex vivo length in all techniques. In summary, the knowledge of this investigation might be helpful in order to enhance the clinical efficacy of foot and ankle surgery and minimize the potential complications.