Geometric analysis of the talus and development of a generic talar prosthetic

Background Trauma to the talus can result in fracture, avascular necrosis and structural collapse. Treatment has been limited to surgical fusion and total ankle arthroplasty. Total ankle arthroplasty may not be an appropriate treatment for avascular necrosis while surgical fusion of the joint limits mobility. Custom-made implants have recently been used to address these limitations but have lengthy delays between injury and surgery and higher associated costs. A generic talar prosthesis available in various sizes may serve as a suitable alternative. Methods The geometric variation between shapes of individual tali was determined using 3D geometric models of 91 tali created from CT-scan data. Comparisons were done to determine if tali are one shape. The best shape was determined for each sex, and was compared to determine if a unisex implant would be possible. A geometric template for the implant in multiple sizes was created and compared to the models. Results The average of the average deviation between tali after volume scaling was found to be less than 1 mm on the main articulating surfaces. One shape group was found for the talus. The female and male tali were found to be similar and a unisex implant template was created. Conclusions Ten generic talar implant sizes were determined to be sufficient to match the size and shape of the 91 tali examined in this study.