Mobility of the first metatarsal-cuneiform joint in patients with and without hallux valgus: in vivo three-dimensional analysis using computerized tomography scan

BACKGROUND Hallux valgus (HV) deformity is closely correlated to the hypermobility of the first metatarsal-cuneiform joint, but adequate understanding of the three-dimentional (3D) mobility of this joint in normal or HV feet is lacking. This study was conducted to investigate the mobility of the first metatarsal-cuneiform joint in multiple planes during body weight-bearing conditions for both normal and HV patients. METHODS A total of 10 female volunteers (20 feet) and 10 female HV patients (20 feet) participated in this study. Using a custom-made foot-loading device, computerized tomography (CT) scans of each pair of feet were taken under both unloaded and body weight-bearing conditions. 3D models were reconstructed for the first metatarsal and the medial cuneiform. Rotational and translational motions of the first metatarsal-cuneiform joint in multiple planes from unloaded to loaded conditions were quantitatively evaluated by reverse-engineering software. RESULTS During body weight-bearing conditions, the first metatarsal-cuneiform joint in HV feet dorsiflexed at an average of 2.91° (standard deviation, SD 1.71) versus 1.18° (SD 0.47) in controls (t = 4.158, P = 0.001); supinated 2.17° (SD 2.28) versus 0.98° (SD 0.81) in controls (t = 2.080, P = 0.045); and internally rotated 2.65° (SD 2.22) versus 0.96° (SD 0.57) in controls (t = 3.114, P = 0.006). Moreover, the joint in HV feet widened significantly compared with the controls (t = 2.256, P = 0.030) and tended to translate more in the dorsal-plantar direction (t = 1.928, P = 0.063); the translation in the medial-lateral direction was not significantly different between the two groups. CONCLUSIONS During weight-loading process, the first metatarsal-cuneiform joint turns dorsiflexed, supinated, and internally rotated. For HV feet, hypermobility of the first metatarsal-cuneiform joint can be observed in multiple planes. This study promotes further understanding of the physiological and pathological mobility of the first metatarsal-cuneiform joint.