Three-Dimensional Distance and Coverage Mapping of the First Ray in Hallux Valgus

BackgroundThree-Dimensional Distance and Coverage Mapping (DM and CM) generated through weightbearing CT (WBCT) can aid in understanding the complex articular relationship in hallux valgus (HV). Prior studies have demonstrated that subluxation can occur at the hallux metatarsophalangeal (MTP) and metatarsosesamoid articulation with greater deformities. Little is known however about these parameters at the level of the tarsometatarsal (TMT) joint, particularly as it relates to the concept of TMT instability as a cause for HV. The purpose of this study is to evaluate DM and CM characteristics at the first TMT joint through WBCT in a cohort of HV patients relative to controls.MethodsTwenty-nine feet (14 left and 15 right) from 16 individuals (avg age of 56.6 ± 6.2 yrs) underwent WBCT. Twelve feet were clinically diagnosed with HV, without clinical evidence of TMT instability, and formed the experimental group, while the remaining 17 feet, absent of deformity, served as the control group. For distance maps, spatial relationship of the joint was assessed by sampling the surface of one bone and calculating the shortest distance to the opposing bone. A limit of 4 mm was set to ensure the analysis focuses on relevant anatomical gaps. For coverage maps, the region was defined along the longitudinal axis of the 1^st metatarsal, with 10% of each end defined to be in contact with the opposing bone. The nearest distance was calculated for this region, with regions of 5 mm or less defined as covered and >5 mm defined as uncovered. Sagittal TMT 1 angle was calculated as a marker of TMT instability. Welch's t-test and Mann-Whitney U were used for statistical analysis.ResultsHallux valgus patients demonstrated significantly increased coverage along the dorsal lateral and plantar lateral quadrant of the MTP joint relative to controls (28.59%, P=.002 and 14.47%, P=.007, respectively) and decreased coverage along the dorsal medial and plantar medial quadrant (-42.63%, P=.002 and -46.69%, P<.001, respectively). No differences in distance mapping at the MTP joint or contact and distance mapping at the TMT joint were observed between groups (Table 1). Sagittal TMT 1 angle was higher in the HV group (1.36° vs 0.6°, P=.02).DiscussionThere is notable discrepancy in coverage at the MTP joint in HV patients relative to those without HV, consistent with subluxation of the hallux MTP joint in HV. Contrary to our hypothesis, no discernable difference was noted at the TMT joint with respect to DM and CM. While sagittal plane angulation was higher in HV, it did not result in appreciable changes in contact and distance mapping at the TMT joint.Level of EvidenceIII: Retrospective case control.