A 3D Surface Mapping-Based Morphology Study of the Cartilaginous Surfaces of the 1st TMT Joint

Abstract

Category: Midfoot/Forefoot; Other Introduction/Purpose: The first tarsometatarsal (TMT) joint plays a crucial role in maintaining the stability of the midfoot and medial column. Disorders of this joint are associated with hallux valgus, hallux rigidus, flatfoot, Lisfranc injury and arthritis, and many others. It has been proven that there is a high variability in the morphology of the joint which may be related to joint stability thereby leading to certain deformities. Understanding the morphology of the articular surfaces comprising the joint is necessary. While prior studies have used XR and CT to analyze the joint[1], we present our work using 3D surface mapping to evaluate the cartilaginous articulation of the1st TMT joint. Methods: 22 fresh-frozen cadaveric feet without trauma nor surgery or significant deformities were dissected to expose the medial cuneiform (MeC) and 1st metatarsal (MT) bones, and the articular surfaces of the 1st TMT joint. Surface mapping of the articular surfaces and the two bones was completed using an Artec Space Spider 3D scanner and Mmics. Further digital analysis was completed using GeoMagic Studio 10. Results: Means and Standard Deviations (SDs) of the articular surface and the bone length were summarized in Table 1. The average articular area of the 1st TMT joint was 337.26 (±63.43) mm 2 on MeC, and 337.94 (±66.16) mm 2 on the 1st MT, with the length of the bones measured 25.50 (±2.56) mm for MeC and 63.93 (±4.22) mm for the 1st MT. There were statistically significant linear correlation between the articular-area and the length of the bone on both sides. 1 mm bone length increase was correlated with 11.48 mm 2 articular-area increase on MeC; and 10.33 mm 2 articular-area increase on 1st MT. (Figure 1,2) There were three types of morphologies of the 1st TMT joint (Type 1, with 2 facets linked to each other; Type 2, with 2 facets separated; Type 3, 1 large dorsal facet and two separate smaller facets inferiorly). The facet pattern is more obvious on the 1st MT than the MeC side. (Figure 3) Conclusion: Previous studies of the 1st TMT morphology were done using either direct manual measurements with descriptive reporting which does not reflect the exact contour of the joint, or XR/WBCT which cannot demonstrate the cartilaginous articulation. This study used a novel technique of surface mapping which overcame the above issues. The remodeled cartilaginous articular surfaces provide foundations for further comparison study, as well as integration of 3D surface mapping with weight- bearing CT analysis, which is currently under investigation by our research group. This will provide important information for diagnosis, surgical planning, and follow-up treatment for relevant disorders.