Distal Anatomical Relationship of the Flexor Hallucis Longus and Flexor Digitorum Longus Tendons

Background: The distal attachment of the flexor hallucis longus (FHL) tendon with the flexor digitorum longus (FDL) tendon varies antomically. The presence of a strong link between the two tendons can preserve distal function if one of the tendons is used for transfer. Methods: Twenty-four cadaver legs were dissected, and the distal relationship of the FHL tendon with the FDL tendon was analyzed. The width of the tendons and their attachments were measured to the closest 0.5 mm. Results: Three different configurations were found. In type 1, a tendinous slip branched from the FHL to the FDL (10 of 24 feet). In type 2, a slip branched from the FHL to the FDL and another from the FDL to FHL (10 of 24). In type 3, no attachment was present (four of 24). In four cadavers the attachment was different in the right and left feet. Conclusion and Clinical relevance: The absence of a cross connection between the two tendons in the foot may be more frequent than previously reported. Three configurations of the anatomical relationship of the distal FDL to FHL tendons were found in this study with a small sample size. Based on these findings, to preserve the distal function of the FDL after transfer of the proximal FDL tendon, routine tenodesis should be done or a wider exposure and tenodesis in type 3 variations.