First ray instability in hallux valgus deformity: a radiokinematic and pedobarographic analysis

Hallux valgus remains a common forefoot condition where different causes may contribute to the pathology. The extent of first ray mobility and, in particular, instability of the first tarsometatarsal joint represents a key argument in the debate on the selection of an appropriate operative treatment. Until now, assessment of first ray instability has relied on clinical examination or static assessment only. For dynamic evaluation in our study, pedobarographic, clinical, and standard weightbearing radiographic findings were correlated with the radiokinematically determined first ray instability in the sagittal plane in hallux valgus patients.

Eight patients with hallux valgus deformity and a clinically unstable first tarsometatarsal joint were enrolled. Seven patients were females; 1 was male. Mean age was 44 years (range, 15-65). Clinical symptoms, American Orthopaedic Foot and Ankle Society forefoot scores, and standard parameters of weightbearing radiographs in 2 planes of the forefoot were recorded. A mobile C-arm fluoroscope with a novel distortion-free flat-screen detector and a pedobarographic platform were synchronized during the rollover process. Fluoroscopic image analysis was performed employing a specific CAD model. Pedobarographic parameters were determined within 8 defined areas of the forefoot contact zone.

The mean dorsiflexion distance and angle of the first ray was 13.9 ± 9.4 mm (range, 6.3 to 34.5) and 5.9 ± 4.0 degrees (range, 2.4 to 14.5). At the first tarsometatarsal joint, the mean maximum dorsiflexion angle was 2.6 ± 1.3 degrees (range, 0.1 to 4.0). The intermetatarsal angle correlated significantly (P = .013) with the radiokinematically determined maximum dorsiflexion. Furthermore, a significant correlation between maximum force transfer to the central (P = .021) and lateral forefoot (fourth metatarsal; P = .032) and first tarsometatarsal joint instability was detected with an unloading of the first metatarsal.

Although our analysis was limited to the sagittal plane only, we can support the notion that an enlarged intermetatarsal angle was associated with increased maximum dorsiflexion of the first ray during gait in hallux valgus patients. Gross instability of the first tarsometatarsal joint during weightbearing was not detectable in our patients, while first tarsometatarsal joint instability increased maximum force transfer to the central forefoot with the potential risk of metatarsalgia.

The results here may shed further light on the role of hypermobility of the first ray on hallux valgus deformity which could have implications for its surgical management.