Anatomy of Flexor Hallucis Longus and Its Relationship with Hallux Valgus: A Cadaveric Study

CATEGORY: Basic Sciences/Biologics; Midfoot/Forefoot INTRODUCTION/PURPOSE: The first ray is an inherently unstable structure that relies on a fine balance between its static and dynamic stabilizers to maintain its alignment. Multiple risk factors have been associated with hallux valgus development. The dynamic stabilizers, particularly the flexor hallucis longus (FHL), has been mentioned as a potential deforming force that could contribute and accentuate hallux valgus deformity due to its spatial situation and insertion morphology. The aim of this study is to describe FHL distal insertion morphology and it spatial relationship with interphalangeal (IP) and metatarso-phalangeal (MTTP) joint. METHODS: 10 fresh frozen cadaver hallux were dissected up to the MTT-F joint, exposing FHL and bony structures, leaving in situ ligamentous attachments. We evaluated FHL distal insertion morphology in terms of width of insertion and distance between insertion borders of the FHL and medial-lateral phalangeal borders. The spatial relationship of the FHL with IP and MTTP joint was measured by the position of the FHL long axis width midpoint in relation to the phalangeal and metatarsal width 1cm proximal to the joint. RESULTS: The FHL mean width of insertion was 12,1mm (range 10-15) SD (+-1,5). All specimens showed a lateral tendon fascicle that was inserted more lateral and distal than the tendon main insertion. Mean lateral distance of insertion to phalangeal border was 3mm (range3-4) SD (+-0,7), mean medial distance of insertion to phalangeal border 5,2mm (range 4-7) SD (+-1,1). FHL long axis width midpoint was on average 12.36% laterally deviated from the osseous midpoint at MTTP joint and 14.07% lateral deviated at IP joint. CONCLUSION: The FHL has a closer insertion to the lateral phalanx border and it long axis midpoint is laterally located in relation to IP and MTTP joint, creating a laterally directed force vector over both joints that could be involved in the pathogenesis of hallux valgus.