First Tarsometatarsal Joint Mobility in Hallux Valgus

Abstract

Category: Bunion Introduction/Purpose: Hypermobility of the tarsometatarsal (TMT) joint has been much debated, but is considered to be an important factor in hallux valgus. However to date, studies investigating such hypermobility have been limited to two-dimensional (2D) evaluations using plain X-ray images or to mobility in the sagittal plane. Three-dimensional evaluation should offer more accurate pathological information given that deformity of the hallux valgus occurs in three dimensions. This study evaluated mobility of the first TMT joint in 3D using weight-bearing computed tomography (CT) and an original weight-bearing device (Figure) and then examined its correlation with the hallux valgus angle and intermetatarsal angle in hallux valgus patients. Methods: Ten feet of 10 hallux valgus patients and 10 feet of 10 healthy volunteers without foot disease (control group)were examined. Mean age of the two groups was 58.2 years and 55.9 years, respectively. The hallux valgus angle was 43.2° and 14.1° and the intermetatarsal angle was 22.1° and 9.3°, respectively. CT was performed under two conditions: non-load with the ankle in a neutral position and full-body weight-bearing load. Three-dimensional models of each bone were reconstructed by segmentation, the positions of each bone were adjusted, and the extent of first metatarsal displacement relative to the medial cuneiform was measured in 3D. We defined orthogonal coordinate axes(X-axis, Y-axis, Z-axis), the motion around the X-axis, Y- axis, and Z-axis was defined as plantar flexion/dorsiflexion, inversion/eversion, and adduction/abduction respectively. Data were compared between the hallux valgus and healthy control groups using Student’s t-test. In hallux valgus patients, mobility of the first TMT joint was compared with the hallux valgus angle and intermetatarsal angle using Pearson’s correlation coefficient. Results: Dorsiflexion (X-axis), inversion (Y-axis), and adduction (Z-axis)were significantly different between the hallux valgus patients and control subjects (p < 0.05). In the hallux valgus patients, there was no large correlation between mobility of the first TMT joint and either hallux valgus angle (X-axis: г=0.21 p=0.55, Y-axis: г=0.11 p=0.75, Z-axis: г=0.10 p=0.78) or intermetatarsal angle (X-axis: г=0.40 p=0.25, Y-axis: г=0.10 p=0.78, Z-axis: г=0.53 p=0.11). Conclusion: We were able to analyze 3D changes in the load on the foot in detail. Hallux valgus patients showed hypermobility of the first TMT joint not only in dorsiflexion (sagittal motion), but also in inversion and adduction. However, larger hallux valgus and intermetatarsal angles did not affect mobility of the first TMT joint. Therefore, the magnitude of hallux valgus deformity may correlate with other joint mobility or complex mobility of first ray. Our technique and findings help to clarify the nature of the pathology of hallux valgus and should assist in the selection and development of treatment methods.