Correlation of dorsiflexion angle and plantar pressure following arthrodesis of the first metatarsophalangeal joint.

Background: The correlation between angle of fusion of the first metatarsophalangeal (1MTTP) joint and pressures under metatarsal heads and hallux has not been well characterized. The main purpose was to investigate the correlation between fusion dorsiflexion angle of the 1MTTP joint and plantar pressures under the first metatarsal head and hallux during gait.

Methods: Patients who underwent arthrodesis of the 1MTTP joint from 2005 to 2010 were seen for a follow-up examination. Of 27 patients, 15 (22 feet) with a mean follow-up of 26.2 months were evaluated in the study. Main outcomes included the fusion clinical and radiological dorsiflexion angles and the mean and maximum dynamic plantar pressures under all 5 metatarsal heads and under the hallux. Plantar pressures were measured through an in-shoe system while patients walked normally along a corridor.

Results: The dorsiflexion angle was positively correlated with mean dynamic plantar pressures under the first metatarsal head: P = .02 (r = 0.5) for clinical angle, and P = .01 (r = 0.58) for radiological angle. Patients with 15 degrees or more of clinical dorsiflexion angle demonstrated higher mean dynamic plantar pressure under the first metatarsal head (P = .05) and higher maximum dynamic plantar pressure under the second metatarsal head (P = .04) compared with patients with less than 15 degrees. In contrast, the latter patients demonstrated higher mean dynamic plantar pressure beneath the hallux (P = .04). Patients with 30 degrees or more of radiological dorsiflexion angle demonstrated significantly higher mean dynamic plantar pressure under the first metatarsal head (P = .04) compared with patients with less than 30 degrees.

Conclusion: Higher dorsiflexion angles correlate with higher plantar pressures under the first metatarsal head. Lower dorsiflexion angles increase plantar pressures beneath the hallux during gait.

Clinical Relevance: Significant increase in plantar pressure under the first metatarsal head may be avoided by performing the arthrodesis of the 1MTTP joint below 30° and 15° for the radiological and clinical dorsiflexion angles, respectively.