Symptomatic Hallux Valgus Deformities and 1st Tarsometatarsal Joint Morphology

Abstract

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: The pathogenesis of the hallux valgus deformity is still poorly understood. Consistent observations of the 1st tarsometatarsal (TMT) joint as the CORA of hallux valgus raises questions about pathology associated with that joint. Mason and Tanaka studied the 1st TMT joint in cadaveric specimens in 2012, observing three morphological subtypes to the 1st cuneiform articular surface. They noted that specimens with hallux valgus had either a unifacet (37%) or bifacet (63%) appearance, where normal feet had a trifacet appearance. This observation suggests that these bony differences may be responsible for 'instability' that generates the metatarsal deviation into varus, and thus the development of hallux valgus. If true, surgical corrections for hallux valgus deformity should address this TMT joint pathology. Methods: This study was designed to correlate the morphological differences of the TMT joint with symptomatic hallux valgus patients who are seeking surgery. The hypothesis was that the hallux valgus patients would show a majority unifacet and bifacet morphology and have an inclination towards unifacet in younger patients and patients with a larger deformity. The cohort of patients who are in the registered longitudinal study Align3D had their TMT joints harvested in a standard fashion as part of their surgical treatment. These specimens were analyzed for the number of facets by the surgeon at the time of their surgical procedure. This cohort therefore only includes symptomatic hallux valgus patients and eliminates hallux valgus associated with metatarsus adductus. Standard weight-bearing x-rays taken pre-operatively were analyzed for severity of deformities. Functional and Patient Reported Outcome measures were obtained pre-operatively and post-operatively. Results: In this study we observed 143 specimens. Unifacet was observed in 116 specimens (81.1%), bifacet was observed in 26 specimens (18.2%), and trifacet was observed in 1 specimen. Neither X-Ray findings, age, nor Functional Scores suggested a trend in severity in relation to morphological type. Mason & Tanaka's cadaveric study was limited in some respects because of the hardening effect of formaldehyde preservations. Their study represented an elderly population, mean age 86 years, whereas this study represented a much younger population, mean age 40.6, in which patients were able to participate in both X-Ray and clinical scoring. To the best of our knowledge, this is the first time that morphology of the TMT joint has been studied in symptomatic hallux valgus patients who underwent surgery. Conclusion: Symptomatic hallux valgus deformities are associated with a higher likelihood of having a unifacet morphology than previously reported in cadavers (81.1% vs 37%). This morphology may predispose patients to decreased stability resulting in more symptomatic deformity. The number of facets does not seem to correlate with severity of deformity on X-Ray evaluation, nor does it correlate with age. However, the younger age group in our study as compared to Mason and Tanaks's study suggests that morphological differences may even be congenital, leading to later development of deformity.