Three Dimensional Analysis of Symmetry and Morphometry of the Bilateral Tarsal Bones Using Weightbearing Computed Tomography

CATEGORY: Hindfoot INTRODUCTION/PURPOSE: Surgical restoration of the morphology of deformed tarsal bones caused by severe arthritis and complex fracture may require surgical procedure such as custom 3D printed total talar replacement, extensive bone reconstruction of complex fractured bones, etc. There are variations in the tarsal bones between individuals and with advances in medical imaging/personalized manufacturing techniques such as additive manufacturing; reliance on the contralateral side of the patient becomes important. The purpose of this study is to evaluate the left to right symmetry characteristics of tarsal bones utilizing weightbearing computed tomography in order to effectively and reliably use the 3D morphology of the contra-lateral foot. METHODS: 15 bilateral data sets from weightbearing CT scans were used from a foot and ankle unit. The images were processed to produce 3-dimensional computer models of the distal tibia, talus, talar dome and calcaneus. The left and right tarsal bones in each pair were first mirror-imaged and then registered using a 3D optimal registration technique. After the registration, a distance-mapping algorithm was used to determine the surface-to-surface distance distribution between the paired and registered bones (Figure 1). Maximum surface-to-surface distance indicated the level of asymmetry between the bones. In addition, the volume and surface area of each bone was established and the percentage difference in volume and surface area were established providing an additional measure of left-to-right asymmetry. Figure 1 – Surface-to-surface distance map shiwing the left-to-right deviations (in millimeters) for a talus and distal tibia for one subject. RESULTS: The results indicated a left-to-right volume mean difference of less than 2.6% for the talus, 3.1% for the distal tibia and 2.3% for the calcaneus. The mean difference of the surface area was 2.4% for the talus, 1.9% for the distal tibia and 1.6% for the calcaneus. The distance mapping showed a maximum average surface-to-surface left-to-right deviation of 0.8 mm for the talus, 0.4 mm for the talar dome, 0.65 mm for the distal tibia and 0.95 mm for the calcaneus. CONCLUSION: Based on the results of this study, morphometric analysis showed high level of bilateral symmetry indicating that restoration of the tarsal bone based on the contra-lateral foot is a feasible and reliable approach. The study established the level of confidence with which such an approach can be implemented.