Three-Dimensional Analysis of Windlass Mechanism Using Loading Computed Tomography in Patients With Hallux Rigidus and Healthy Volunteers

Abstract

Category: Midfoot/Forefoot; Basic Sciences/Biologics Introduction/Purpose: The windlass mechanism (WM) increases the height of the medial longitudinal arch (MLA) of the foot by tensing the plantar aponeurosis during dorsiflexion of the metatarsophalangeal (MTP) joint. We speculated that this mechanism may be deeply involved in the pathogenesis of forefoot diseases such as hallux rigidus (HR). These conditions are three- dimensional (3D) deformities including rotational deformity, but the role of the WM has been evaluated only two-dimensionally by measuring the height of the navicular on lateral plain radiographs. The purpose of this study was to analyze in detail the WM of normal and HR feet in 3D. Methods: Participants were 14 patients with HR (17 feet) and 13 volunteers (21 feet). The volunteers had no history of foot disease or trauma, whereas the patients with HR had Coughlin and Shurnas classification I or II. Computed tomography (CT) of the foot with a load equivalent to the participant’s body weight was performed. Imaging was performed with the 1st MTP joint in the neutral position and dorsiflexed 30 degrees. 3D models were created using the software Mimics Research 17.0. Next, we used the iterative closest point (ICP) algorithm, which allows 3D objects to be superimposed without specifying anatomical feature points. Then, we performed 3D measurements of the (1) rotation of each bone in the MLA with respect to the tibia, (2) rotation of the distal bone in each joint of the MLA, and (3) changes in the height of the geometric center of the navicular. Results: At the calcaneus, navicular and medial cuneiform, the HR group showed less inversion, adduction than healthy group. (P < 0.05) At the talonavicular joint, the navicular was 3.7° inversion, 2.9° adduction in the healthy group and 2.4°inversion, 1.3° adduction in the HR group. At the talocalcaneal joint, the calcaneus was 1.7° inversion, 1.5° adduction in the healthy group and 0.9°inversion, 0.6° adduction in the HR group. In the talonavicular and talocalcaneal joint, the HR group showed less inversion and adduction than control. (P < 0.05) With dorsiflexion of the hallux, the height of the navicular increased by 2.1 mm in the healthy group and 1.3 mm in the HR group. There was a significant difference (P < 0.05) between the two groups. Conclusion: In both groups, the calcaneus, navicular, and medial cuneiform bones moved not only in the sagittal plane but also in the frontal plane. But the movement of the talonavicular and talocalcaneal joints and the change in height of the navicular were significantly reduced compared with the healthy group. In other words, in the HR group, the motion of the midfoot and hindfoot was limited, suggesting that there may be a close relationship between WM dysfunction and midfoot and hindfoot motion. This study indicates that the dysfunction of the WM may have been a clue to the cause of HR.