The Development and Analysis of a Generic Talus Bone Prosthetic

• Author / Creator

  Trovato, Alexandra N

• Talar collapse results in incongruity of the ankle joint, resulting in pain, stiffness, and disability. In the past, standard treatment has been surgical fusion or total ankle arthroplasty. These treatments can result in a loss of motion and function of the foot, as well as pseudarthrosis. A solution to the problems associated with these treatments is a talar body implant that replaces the avascular portion of the talus or the talus in its entirety. Presently, there are reports of custom talar implants surgically implanted in patients; however, custom implants increase time between injury and surgery which makes this procedure a less desirable option. This study explores the feasibility of developing a generic talus bone prosthetic for patients in need of talar replacements. The first step in the study was to determine the geometric variation between the shapes of 91 individual tali. Comparisons between three-dimensional geometric talus models were conducted to determine if different tali could be considered the same shape. From these models, the best shape was determined for the female and male template and the two were compared to determine if a unisex implant was feasible. One shape was found for the talus and a unisex implant template in ten sizes was created and found sufficient. The geometric template for the talar implant in multiple sizes was validated by comparing the template to the models. A finite element (FE) model of the ankle joint, calcaneus, and navicular was created and used to investigate the change in contact pressure and distribution on the cartilage surfaces surrounding the talus when a biological talus, a custom, and a generic talar implant were placed in the joint. The results showed that the contact patterns on the surrounding cartilage from the custom implant closely resembled that of the biological talar body patterns, but with smaller areas of higher contact pressures. Although the contact patterns from the generic implant were slightly different than those caused by the biological talus, contact areas and pressures were closer to the biological talus in magnitude than the custom implant. The FE model created was validated by comparing its results to cadaveric results from previous studies. The FE results indicated that a well-designed and appropriately sized generic talus implant closely mimics the original biological talus in terms of contact pressure intensity and distribution. Joint compatibility of the generic implants was verified in human cadaver and FE studies. The implants for the right ankle for ten cadaveric specimens were 3D printed. The cadaveric ankles were scanned with the biological talus in the joint and thereafter with the implant in place of the biological talus. The scans were 3D modelled and the location of the implant within the ankle joint was compared to the location of the biological talus. Seventy percent of the deviations on the talar dome between the biological talus and implant were within the acceptable range. The deviations correlated with the contact areas caused by a 2000N axial load (determined through the FE study). Results showed that there would not be excessive pressure caused by a generic implant. A case study explored the possibility of surgically implanting a generic talus bone prosthetic in a patient with bilateral talar avascular necrosis and collapse of the talar domes. A custom implant was created using CT scans of the patient’s talus, tibia and fibula. The custom and generic implants were compared with the intact portion of the biological talus to determine how the implants would articulate with the calcaneus and navicular. The talar domes of the custom and generic implants were compared to the collapsed domes to determine how the width and height of the dome differed from the collapsed (biological) talar dome. The extreme width of the biological talus and implants were found to determine if the implants would fit in the ankle mortise. Both the generic and custom implant were found to be in the acceptable range deviation range of 1mm, and as such either implant would be acceptable for implantation in the patient to maintain geometric compatibility of the ankle joint. This research demonstrated that a generic talar implant could be a viable option for those in need of a talar replacement.

• Subjects / Keywords

  • Biomechanics
  • Talus
  • Generic prosthetic
  • FEA

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R36Q1SN87

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.