Biomechanical consequences of first metatarsaophalangeal joint arthrodesis on flexor digitorum longus function: A cadaveric study

Abstract

Background: First metatarsophalangeal joint (MTPJ) arthrodesis is a common treatment modality for hallux rigidus with successful outcomes. However, the effect of arthrodesis on flexor digitorum longus (FDL) is poorly understood. The purpose of this study was to investigate this effect in a biomechanical model. Methods: Ten cadaveric trans-knee amputated specimens were studied. Lesser toe range of motion (ROM) and FDL excursion on simulated FDL contraction were measured in the following three scenarios: (1) before 1st MTPJ arthrodesis, (2) after 1st MTPJ arthrodesis, and (3) after the knot of Henry release. Results: 1st MTPJ arthrodesis reduced both mean lesser toe ROM and FDL excursion. However, there was improvement in these parameters after the knot of Henry release. Conclusions: FDL function was reduced following 1st MTPJ arthrodesis. This effect was contributed by soft tissue connections at the knot of Henry, where FDL crosses flexor hallucis longus (FHL). Therefore, with restriction of FHL movement after 1st MTPJ arthrodesis, FDL movement was also restricted. Clinical Relevance: This result improved our understanding of 1st MTPJ arthrodesis biomechanics and suggested potential benefits of the knot of Henry release in 1st MTPJ arthrodesis to improve FDL function, thereby decreasing the rate of metatarsalgia and other associated problems.