Influence of Normal and Pathologic Windlass Mechanism During Dorsiflexion of the Hallux

Category: Midfoot/Forefoot; Other Introduction/Purpose: When the windlass mechanism (WM) is engaged, the plantar aponeurosis (PA) is pulled distally by extension of the first metatarsophalangeal joint (MTPJ1), shortening the sole of the foot and raising the medial longitudinal arch (MLA). It has also been reported that the WM is associated with hallux valgus and hallux rigidus. Although this function has been known for a long time, there are few reports on the movement of the foot bones under pathological conditions. In this study, we used cadaveric feet to compare the movements of the foot bones under three conditions: normal tendon loads, an overpulled Achilles tendon, and a sectioned PA with normal tendon loads. Methods: Ten fresh cadaveric foot specimens were used. The foot was attached to a tibial loading frame with 20% body weight loads applied. Each specimen was scanned in seven configurations (first proximal phalanx angles 0-60°, each 10° apart) and three conditions (normal loads, overpulled Achilles, and sectioned PA) using a LineUP cone-beam computed tomography (CBCT) scanner. The foot bones in the neutral position under normal loading were segmented from the CBCT scan volumes in Mimics Research software v23.0. Bone kinematics between the 20 additional scans were determined via volumetric image registration in custom MATLAB software for each segmented bone. Using additional custom MATLAB code, we calculated the height of the navicular, the MLA angle defined as the three points (the farthest point of the first metatarsal head, the medial process of the calcaneus, and the apex of the navicular tuberosity), and the motion of the joints on the foot in 3D. Results: The height of the navicular was significantly lower at 0, 30, and 60 degrees in the pathological conditions compared to normal (Normal vs overpulled Achilles: 2.9, 3.2, 5.4 mm, p< 0.01, normal vs sectioned PA: 5.2, 5.6, 5 mm, p=0.04, at 0°, 30°, and 60° respectively). The MLA angle was significantly different at all angles for the overpulled Achilles compared to the normal (-3°, -3.5°, -3.6°, p< 0.02). At the tarsometatarsal (TMT) joint, there was no significant differences in any direction. At the cuneonavicular joint, there was less plantarflexion (normal: -6.1, -10.8, overpulled Achilles: -2.8, -6.6, p< 0.01 at 30° and 60° respectively) and less eversion (normal: 24.7, overpulled Achilles: 27.9, p< 0.01 at 60°) in the overpulled Achilles compared to normal. Conclusion: In this study, a three-dimensional model was used to measure the function of the WM. We found that the WM was affected by the pathological conditions of the Achilles tendon and sectioning the PA. The results of this study suggest that WM dysfunction may not affect the TMT joint but does affect the cuneonavicular joint. This might suggest the WM induced MTPJ1 pathologies are driven by the cuneonavicular joint.