Properties and Function of the Flexor Hallucis Capsularis Interphalangeus Tendon

Abstract

The fibrocartilagenous plantar plates of the forefoot are biomechanically important, forming the primary distal attachment for the plantar aponeurosis. They are integral to the function of the windlass mechanism in supporting the arches of the foot in gait. Dissection of the cadaveric hallux revealed an organised sagittal thickening of the dorsal side of the Flexor Hallucis Longus (FHL) sheath, which attached the interphalangeal plantar plate to the metatarsophalangeal (MTP) plantar plate. A description of a similar structure was made by McCarthy et al. in 1984 when it was termed the Flexor Hallucis Capsularis Interphalangeus (FHCI)-however, it has not been researched since, and we aim to study it further and identify its characteristics. Methods Eight specimens were dissected from four cadavers. Two were stained and examined under microscope and both polarized and non polarized light. The remaining 6 were subjected to micrometer testing of their tensile properties. Results Both the histological features and mechanical properties were consistent with tendon like substance, with cross sectional area, ultimate tensile strength and stiffness varying between specimens. Conclusions Based on its location and properties, the FHCI tendon may be involved in limiting dorsiflexion of the first MTP joint and could have clinical relevance in pathological processes around both the first and second MTP joints.