What Do We Know About the Pathoanatomy of Talar Neck Malunions? Results From a 3D Morphometric Analysis

Abstract

Category: Trauma; Hindfoot Introduction/Purpose: Malunions of the talar neck significantly alter the foot biomechanics and predispose patients to arthrosis and poor functional outcomes. Recent interest has focused on the surgical correction of these deformities, with corrective talar neck osteotomy emerging as a safe and effective treatment for malunions without ankle arthrosis. While a talus malunion is traditionally thought to cause a varus deformity due to the shortening of the medial talar neck, the pathoanatomy of these deformities remains unclear and sparsely reported in the literature. Therefore, this study aimed to investigate the three- dimensional changes in morphometric parameters of the talar neck after malunion and to determine how these changes affect the architecture of the foot. Methods: Adult patients with a talar neck malunion without ankle arthrosis (Rammelt and Zwipp Type 1-3) were prospectively included. Weight-bearing (WB) AP, Lateral and long axial radiographs, and CT scans of both feet were obtained. 3D models of both tali were generated. The malunion side was mirrored and superimposed on the normal side, and distance maps were generated to identify pathoanatomic changes. Deviation of the talar neck in the axial plane (declination angle [DA]), sagittal plane (inclination angle [IA]), coronal plane (torsion angle [TA]) as well as the medial and lateral neck lengths (MNL and LNL) were measured on the 3D talus models using a semi-automated GEOGEBRA script. AP and Lateral Meary’s angle and the hindfoot moment arm (HMA) was determined on WB radiographs. The t-test was used to compare the talar neck parameters, and correlation coefficients were used to determine the association between talar neck parameters and foot radiographic parameters. Results: 10 patients, 6 males, and 4 females, with a mean age of 32.4 years were included. There were 4 cases of Rammelt and Zwipp Type 1 deformity, and 6 cases of Type 3 deformity. Axial plane changes included varus deviation of the talar neck in 8 cases and valgus deviation in 2. Sagittal plane changes included dorsiflexion of the talar neck in 4, neutral alignment in 3 cases, and plantarflexion in 3 cases. The TA was increased in all cases. TA and MNL had a moderate positive correlation with AP Meary’s angle and, and a moderate negative correlation with Lateral Meary’s Angle. DA and MNL had a moderate positive correlation with the HMA. Conclusion: Talar neck malunions are complex three-dimensional deformities resulting in the common varus and dorsiflexion variants, as well as less common valgus and plantarflexion variants. Despite the variation in malunion types, all cases are characterized by an increased TA. Furthermore, the combination of increased TA and DA and decreased MNL leads to forefoot adduction and hindfoot varus. Due to the intricate and diverse three-dimensional nature of these deformities, surgeons must conduct a comprehensive evaluation of the pathoanatomy before planning surgical correction.