Evaluation of first metatarsal head declination through a modified distal osteotomy in hallux rigidus surgery. A cadaveric model

Background: First metatarsal osteotomies have been described for treatment of hallux rigidus. Most of these techniques result in declination of the first metatarsal head through shortening of the metatarsal and transfer metatarsalgia may result. Our objective was to evaluate the declination effect of a distal metatarsal osteotomy when different angulations and lateral translations are applied. Materials and methods: A cadaveric study was conducted performing a modified distal oblique osteotomy, which produces head declination while limiting shortening. Several transverse inclination angles (0-10-20-30-40°) were used. Thereafter, plantar translation of the metatarsal head was registered at different lateral displacements (1, 3, 5 mm). Results: Twenty-two specimens were included. Three feet were operated on with a 0° of angulation in the transverse plane, 6 with 10°, 5 with 20°, 5 with 30°, and 3 with 40°. Head declination significantly increased with higher angulation and with greater lateral translations (p< 0.001), but the interrelationship between these two variables did not achieve statistical significance (p= 0.597).In regards to angulation, significant differences in head declination were found between 0° (0.1-0.7 mm), 10°-20° (0.5-1.2 mm) and 30°-40° (1.3-2.4 mm). The metatarsal sesamoid joint was compromised when the osteotomy was performed at a 40° inclination angle. Conclusions: Metatarsal head declination is determined by the inclination angle of the oblique limb of the osteotomy and lateral displacement of the metatarsal head. Our results suggest that the effect of lateral displacement is an independent factor from angulation. The latter may impact surgery planning and may improve clinical outcome by selecting a safer inclination angle when lateral displacement of the metatarsal head is being considered. Level of evidence: Level II-A, systematic review with homogeneity of cohort studies.