Three-dimensional geometric analysis of the talus for designing talar prosthetics

Abstract

Proper understanding of the complex geometric shape of the talus bone is important for the design of generic talar body prosthetics and restoration of the proper ankle joint function after surgery. To date, all talus implants have been patient-specific with the limitation that complex computer modeling is required to produce a mirrored image from the unaffected opposite side followed by machining a patient-specific prosthesis. To develop an "off-the-shelf" non-custom talar prosthesis, it is important to perform a thorough investigation of the geometric shape of the talus bone. This article addresses the applicability of a scaling approach for investigating the geometric shape and similarity of talus bones. This study used computed tomography scan images of the ankle joints of 27 different subjects to perform the analysis. Results of the deviation analyses showed that the deviation in the articulating surfaces of the talus bones was not excessive in terms of talus size. These results suggest that a proposed range of five implant sizes is possible. Finally, it is concluded that the talus bones of the ankle joints are geometrically similar, and a proposed range of five implant sizes will fit a wide range of subjects. This information may help to develop generic talus implants that might be applicable to patients with a severe talus injury.

Investigation of the Average Shape and Principal Variations of the Human Talus Bone Using Statistic Shape Model

“…More specifically, our findings revealed that changes in PC1 can result in up to 81% of points in the male talus and 84% of points in the female talus to deviate more than 1 mm. Thus, PC1 can be considered as a scale amongst tali; its role as a major contributor has been confirmed and widely made use of in previous studies (Islam et al, 2014 ; Trovato et al, 2017 ; Zhao et al, 2019 ). In contrast, as the second major contributor, PC2 leads to a lower percentage of deviations greater than 1 mm: 55% of the deviations for male tali and 36% for female tali ( Figure 5 ).…”

“…Earlier studies have investigated the morphology of the talus by either using anatomical landmarks to capture the characteristics of the talus (Mahato, 2011 ), or by performing 3D deviation analysis in a software (Islam et al, 2014 ). Not only would these methods involve extensive manual work, but would also be prone to errors and inconsistencies (Stagni et al, 2004 , 2005 ; Hayes et al, 2006 ).…”

“…When it comes to the design of a customized talus implant, a CT scan with 1 mm cuts of the healthy unaffected talus is performed (Islam et al, 2014 ). The image is segmented and an STL file is created and then mirrored, which is followed by either milling or 3D printing of the talar prosthesis.…”

“…(Trovato et al, 2017 ) recently quantified detailed 3D deviations among talus bones and determined that talus shape is similar between patients and that a universal talus implant in various sizes could appropriately fit the vast majority of patients. Initially, Islam et al ( 2014 )'s 3D deviation analysis of 27 patients showed that all tali are geometrically similar, and thus proposed to a series of five implant sizes to represent a wide range of subjects using the scale of one talus template. Subsequently, Trovato et al ( 2017 ) used the same method, but expanded the subject size to 91 (50 males and 41 females), and created a series of 10 unisex talus implants.…”

Analysis of a generic talar prosthetic with a biological talus: A cadaver study

“…This requires a generalization of the geometry of the talus. Islam et al 15 proposed an implant in five sizes; however, that study had limitations including a small sample size (n = 27), lack of a diverse sample selection such that the female population was severely underrepresented, a randomly selected reference implant, and an incremental jump in size of volume (which will be more significant in the smaller sizes as volume is a cubic function). Trovato et al 8 improved upon this study by increasing the sample size (n = 91) with 45% of the subjects being female, selectively choosing the reference implant, and using incremental jump in the cube root of the volume between sizes.…”