Shape Approximation and Size Difference of the Upper Part of the Talus: Implication for Implant Design of the Talar Component for Total Ankle Replacement

Abstract

The implant design of the talar component for total ankle replacement (TAR) should match the surface morphology of the talus so that the replaced ankle can restore the natural motion of the tibiotalar joint and may reduce postoperative complications. The purpose of this study was to introduce a new 3D fitting method (the two-sphere fitting method of the talar trochlea with three fitting resection planes) to approximate the shape of the upper part of the talus for the Chinese population. 90 models of the tali from CT images of healthy volunteers were used in this study. Geometrical fitting and morphological measurements were performed for the surface morphology of the upper part of the talus. The accuracy of the two-sphere fitting method of the talar trochlea was assessed by a comparison of previously reported data. Parameters of the fitting geometries with different sizes were recorded and compared. Results showed that compared with previously reported one-sphere, cylinder, and bitruncated cone fitting methods, the two-sphere fitting method presented the smallest maximum distance difference, indicating that talar trochlea can be approximated well as two spheres. The radius of the medial fitting sphere R M was 20.69 ± 2.19 mm which was significantly smaller than the radius of the lateral fitting sphere R L of 21.32 ± 1.88 mm. After grouping all data by the average radius of fitting spheres, the result showed that different sizes of the upper part of the talus presented significantly different parameters except the orientation of the lateral cutting plane, indicating that the orientation of the lateral cutting plane may keep consistent for all upper part of the talus and have no relationship with the size. The linear regression analyses demonstrated a weak correlation ( R 2 < 0.5 ) between the majority of parameters and the average radius of the fitting spheres. Therefore, different sizes of the upper part of the talus presented unique morphological features, and the design of different sizes of talar components for TAR should consider the size-specific characteristics of the talus. The parameters measured in this study provided a further understanding of the talus and can guide the design of different sizes of the talar components of the TAR implant.

Statistical shape modeling of mean shape and principal variability of the human talar bone in the Chinese population

“…Clinically, it is well established that male generally has a bigger size of talus than female. 4,32 However, it is noted that at the bottom of the talar head, the mean shape of the female tali extrudes which means that its talar head has a large top-bottom thickness and is therefore more plantar flexed. Therefore, we do not consider the average female shape to be geometrically similar to the average male shape as Liu et al 29 claimed.…”

“…3,7–13 The shape variability of the talus within specific populations is important for accurate diagnosis, treatment planning, and implant design. 3,4,14–17…”

Retrospective Comparison of Midterm Survivorship, Radiographic, and Clinical Outcomes of the INBONE II and Salto Talaris Total Ankle Arthroplasty Systems

“…3,8,11 However, Inman's hypothesis and the basis for this design has been challenged by later studies, which suggest that the Salto Talaris has incongruence between talar and polyethylene components. 9,11,14,17 In contrast to the Salto Talaris, the design of INBONE II is based on the 2-sphere fitting model that is purported to closely approximate the talar trochlea, 17 with improved stability from the first generation of the INBONE (Supplemental Figure S1). 13 We assume that the designs for each implant may explain the major differences in reoperation rates between 2 groups, but we must also acknowledge that other factors, such as implant or polyethylene size, varus or valgus thrust from hindfoot malalignment, and the adequacy of prophylactic resection depending on the surgeon, may have influenced the outcomes in each group.…”

“…3,8,11 However, Inman’s hypothesis and the basis for this design has been challenged by later studies, which suggest that the Salto Talaris has incongruence between talar and polyethylene components. 9,11,14,17…”

Dynamic finite element analyses to compare the influences of customised total talar replacement and total ankle arthroplasty on foot biomechanics during gait

“…The TTR customisation procedure was mimicked by reconstructing a model part of the talar prosthesis from the mirror image data of the contralateral ankle site, which is a common practice in clinical studies in the related field [ 12 , 14 , 21 ]. Because a growing body of evidence indicated that a prosthesis design with a higher approximation to the native ankle anatomy facilitates the restoration of ankle functions [ [21] , [22] , [23] ], we hypothesised that TTR would better reproduce the foot kinematics and force distribution of an intact foot than would TAA. TTR improved ankle motions and reduced foot arch deformation/loadings to the foot segments compared to TAA.…”