Biomechanical and morphometric features of long flexor tendons of toes: a cadaveric study

Tendons of flexor hallucis longus (FHL) and flexor digitorum longus (FDL) can be used as grafts. Slips from FHL to FDL have been reported to contribute to flexion function of toes.Aim of the study was to determine the contribution of FHL slips to function of small toes by biomechanical aspects. It was also aimed to determine the lengths of FHL and FHL tendon grafts harvested by different surgical techniques.Thirteen fresh frozen amputee legs were dissected. Some classification regarding connection types between FDL and FHL tendons, and contribution of FHL slips to long flexor tendons of toes were classified. Lengths of FHL and FDL tendon grafts, harvested by different surgical procedures, were measured by digital caliper. Biomechanical features of tendons and slips were evaluated with the help of tensile test device. All measurements were statistically analyzed. Connections between FHL and FDL tendons were classified as two types. Type I: slips from FHL to FDL in 11 cases. Type II: cross connections in 2 cases. FHL slips contributed into the long flexor tendons of second and third toes. Biomechanical features of tendons of second to four toes were similar to each other regarding stiffness, tensile strength, Young modulus, maximum stress. The same properties of these toes were significantly different from fifth toe. No statistical difference was found between FHL and FDL tendons. Lengths of FDL grafts, harvested by medial and plantar approaches were 6:16 cm and 9:05 cm, respectively. Lengths of FHL grafts, harvested by single, double and minimal invasive techniques were 5:08 cm, 7.02 cm and 20:16 cm, respectively. By this study, biomechanical features of the slips between FHL and FDL tendons, and long flexor tendons of toes were revealed. In addition, functional effects of these structures on toes were evaluated