Evaluation of Articular Morphology and Congruency using a Combination of 3 Dimensional CT Based Bone Segmentation and Joint Surface Mapping

Abstract

Category: Hindfoot; Ankle; Other Introduction/Purpose: Recently joint congruence has been given a lot of focus in studies evaluating foot and ankle deformities. XR and WBCT scans are the commonly used techniques, however, neither can accurately reflect articular surfaces particularly in joints where only partial bone surfaces are covered by articular cartilage. This study introduced a novel technique using 3D surface mapping and CT bone segmentation to assess articular morphology and congruence of the calcaneocuboid (CC) joint. Methods: A CT scan of a fresh frozen cadaveric foot without trauma history nor deformity was taken and then the calcaneus and cuboid bones were dissected free with all soft tissue removed. Segmentation and reconstruction of the calcaneus and cuboid from the CT scan was performed using Materialise Mimics. Surface mapping and digital reconstructions of the calcaneus and cuboid bones as well as the calcaneocuboid articular surfaces were then obtained using an Artec Space Spider 3D scanner. Both the CT and surface mapping reconstructions were imported into Geomagic Studio 10 where the reconstructed calcaneus via CT was merged with the reconstructed calcaneus via surface mapping. The same procedures were performed with the reconstructions of the cuboid. Then cartilage surfaces from the calcaneocuboid joint of the surface mapping reconstruction were outlined on and compared to the bone surfaces underneath. Results: The articular surfaces of the calcaneocuboid joint were shaped according to the bone contour noting however that on both sides, the articular surface did not fully match the bone surface. On the calcaneal side, the dimension of the bone surface was 357.72 mm 2 , while the articular surface was 300.92 mm 2 (percentage of bone covered by cartilage: 84.12%). On the Cuboid side, the dimension of the bone surface was 372.41 mm 2 while the articular surface was 302.60 mm 2 (percentage of bone covered by cartilage: 81.25%). When restoring the articulation of the reconstructed calcaneus and cuboid, there was incongruence of the two bone surfaces with the dorsolateral corner of the calcaneus and the plantarmedial corner of the cuboid uncovered by its contralateral bone. The same applied to the articular surfaces but at a smaller uncovering level (Figure 1). Conclusion: Even with 3D CT segmentation and reconstruction of articulating bones, one has no knowledge of the precise articular surface of a joint. 3D surface scanning is a reliable method to study morphology of the cartilage surface of a joint. 3D CT reconstruction combined with 3D surface mapping is a useful tool for studying both the bony surface and the cartilage surface of a joint. This study has implications for treatment of any joint in the foot which appears subluxated on XR or CT scans and where this may represent the normal bone morphology but not true subluxation. Articular congruence study under weightbearing condition is currently under investigation by our research group.