Exploring morphological variations and clinical significance of interconnections between flexor hallucis longus and flexor digitorum longus tendons

Abstract

Background: The tendons of the flexor hallucis longus (FHL) and flexor digitorum longus (FDL) are commonly utilized in reconstructive foot surgery to address deformities. These tendons intersect on the plantar surface and exhibit varying interconnections that can significantly impact graft length and complicate the tendon harvesting process. The objective of this study was to comprehensively categorize these interconnections using a modified classification system and precisely determine their positional relationships with surgically significant bony landmarks. Methods: Sixty embalmed feet of 30 cadavers were studied to analyze the interconnections between FHL and FDL in the planta pedis, classify them in a modified classification system and measure distances to surgically relevant anatomic landmark. Results: The study revealed three primary types of interconnections. Type I, representing a proximal-to-distal connection from the FHL to the FDL, was observed in 85% of the feet. Type II, signifying a proximal-to-distal connection from the FDL to the FHL, was found in 11.66% of the feet. Type III, characterized by a crossed connection, was identified in 3.33% of the feet. The average point of branching for the FHL and FDL tendons was situated 4.5 cm and 3.5 cm distal to the navicular tuberosity, respectively. Conclusion: The presence of atypical proximal-to-distal interconnections from the FHL to the FDL may play a role in preserving residual function in the lesser toes following FDL transfer procedures. Awareness of anatomical variations in the location of these interconnections is crucial for preserving them during surgical interventions, ultimately mitigating the risk of functional impairment in the lateral toes post-tendon grafting.

Keywords

• Flexor digitorum longus
• Flexor hallucis longus
• Interconnection
• Tendon grafting