Assessment of Foot Alignment in Patients with Hallux Rigidus: the Role of Weightbearing CT scan

Abstract

Category: Midfoot/Forefoot Introduction/Purpose: An association between hallux rigidus and metatarsus elevates has been reported in the literature. These findings were based on standard weightbearing radiographs, but have not found general consensus among foot and ankle surgeons. The aims of this study were to 1) assess foot alignment in patients affected by hallux rigidus using 3D reconstructions from a weighbearing CT scan and 2) assess intra and interobserver reliability of weightbearing CT scan imaging (pedCAT, Curvebeam, Warrington, USA). Methods: In this prospective consecutive study, 50 patients with hallux rigidus underwent a weightbearing CT scan. The control group consisted of 50 consecutive patients that underwent a weightbearing CT scan for other reasons (i.e. assessing ankle fusion union, subtalar fusion union, etc). The following angles were measured by 2 investigators: 1st metatarsal length, 2nd metatarsal length, declination of the 1st and 2nd metatarsal, 1st-2nd intermetatarsal angle, hallux valgus angle, and foot width. Each investigator measured each foot twice, 1 month apart. The mean of the values was used for statistical analysis. Results: Intra and interobserver reliability was excellent. There was a statistically significant difference between the declination ratio (1st to 2nd metatarsal) in the hallux rigidus group (0.81) compared to the control group (0.92). Hallux valgus angle was also significantly lower in the hallux rigidus group (12 degrees) compared to the control group (15 degrees). Finally, patients with stages 1 and 2 according to Coughlin & Shurnas classification has significantly higher declination ratios compared to stages 3 and 4. Conclusion: Patients with hallux rigidus demonstrated a lower declination of the first-to-second metatarsal, indicating metatarsus elevatus. While it was not possible to determine whether the elevatus caused or was a result of hallux rigidus, it appears that metatarsus elevatus correlates with the severity of the arthritis. The smaller hallux valgus angle in the hallux rigidus population indicates that true hallux rigidus in association with a true bunion is unlikely. Finally, weightbearing CT imaging proved to be a reliable method of assessing foot alignment.