Novel approach to determine components size in a total ankle replacement

As a total ankle replacement (TAR) prosthesis has been developed and improved in terms of design and surgical technique, it could be expected to lead to a successful functional outcome in the ankle joint. However, several complications of the TAR procedure may be often caused by an incomplete understanding of the abnormal biomechanics of the ankle joint and the prosthesis design of the TAR. This study was performed to suggest a novel approach to determine the TAR prosthesis size by using an orthopedic digital templating software based on a comparison between X-ray and CT images. This study was examined in a novel approach to determine the prosthesis size by using an orthopedic digital templating software (Orthoview™, Florida, USA) based on the comparison between X-ray and CT images. A total 6 types of clinical foot and ankle images were obtained from x-ray and CT of 55 subjects in the coronal and sagittal plane. The x-ray images magnified as 100% and 115% based on the CT images. All subjects were diagnosed to the ankle osteoarthritis with stage 2-4 according to Takakura's ankle OA classification. To predict the appropriate component sizes of the TAR prosthesis, the same TAR prosthesis (HINTEGRA, Newdeal, France) was chosen, and the tibial and the the talar component sizes were selected until by adapting to the osteotomized range of the tibia and talus. The unskilled surgeons predicted the sizes of the TAR components before procedure by using the orthopedic digital templating software. These predicted sizes were then compared with the selected sizes by the specialist surgeon during the procedure. The Cohen's Kappa correlation coefficient was applied to statistically analyze the agreement between the predicted and selected sizes of the TAR components for unskilled and specialist surgeons, respectively. On the CT images, the average agreement rate was relatively higher than on the x-ray images at over 77%. Especially, highest agreement rate was shown at the tibial component in the coronal plane with almost 80%, followed by over 75% in the sagittal plane. In the talar part, the agreement rate was shown to be over 76% in the coronal and sagittal plane, respectively. Overall, the predicted size from the CT image was more consistent with the size selected by the specialist surgeon than the X-ray image. In conclusion, the application of the orthopedic digital templating software based on CT images may expect to provide more complete and detailed visualization to predict the appropriate size of the TAR components than conventional X-ray images which would be limited by relatively lower sensitivity and specificity as well as overlapping the adjacent bones.