DOES CLINICAL PRONATION OF THE TOE CORRELATE WITH METATARSAL ROTATION? A RETROSPECTIVE ANALYSIS OF WEIGHTBEARING CT IMAGES

Aims First metatarsal Pronation is increasingly recognised as an important component of Hallux valgus (HV) and can contribute towards intraoperative malreduction, postoperative recurrence and patient reported outcome measures (1,2,3). There are numerous radiological ways to measure metatarsal rotation on plain radiographs and weight bearing CT (WBCT), however there are no clinical tests to evaluate metatarsal pronation pre- or intra-operatively. This study therefore aimed to examine the relationship between clinical pronation of the toe and metatarsal pronation. Methods Single-centre, retrospective analysis over 5 years. Measurements were performed on WBCT images with digital reconstructions to add soft tissues. First metatarsal rotation was measured using the Metatarsal Pronation Angle as previously described (4). Toe rotation was measured by the Phalangeal Condylar Angle (PCA), the angle between the condyles of the proximal phalanx and the floor, and the Nail Plate Angle (NPA), the angle of the base of the nail plate to the floor in the coronal Plane. These were obtained from 50 feet in Hallux valgus patients, and 50 control patients with CTs done for osteochondral lesions without hallux valgus or hindfoot malalignment. Results The HV group comprised 41 women and 9 men, mean age 52.4. Control group, 23 women and 23 male, mean age 40.25. Inter and Intra Observer reliability both excellent (ICC >0.95) for all measurements. When comparing HV vs control, MPA was 11.7 vs 6.0 (p<0.001), PCA 31.8 vs 4.7 (p<0.001), NPA 18.3 vs 6.0 (p<0.0001). NPA correlated with PCA. NPA and PCA correlate with Hallux valgus Angle (p<0.001), but not with MPA (p 0.567). Conclusion These results suggest that clinical toe pronation increases as HV angle increases but not with metatarsal pronation, which therefore cannot be used as a clinical marker. Toe pronation is similar at the base and at the nail, suggesting rotation happens at the MTPJ.