Quantitative Analysis of the Degree of Frontal Rotation Required to Anatomically Align the First Metatarsal Phalangeal Joint During Modified Tarsal-Metatarsal Arthrodesis Without Capsular Balancing

The data from 35 consecutive patients with hallux valgus undergoing triplane arthrodesis at the first tarsal metatarsal joint were studied to determine the amount of first metatarsal frontal plane rotation (supination) needed to anatomically align the first metatarsal phalangeal joint on an anterior posterior radiograph without soft tissue balancing at the first metatarsal phalangeal joint. Radiographs were measured both pre- and postoperatively to assess the 1-2 intermetatarsal angle, hallux abductus angle, and tibial sesamoid position (TSP). The mean amount of varus (supination) rotation performed during correction was 22.1° ± 5.2° and the mean amount of intermetatarsal angle reduction achieved after completion of the procedure was 6.9° ± 3.0°. The TSP changed by a mean of 3.3° ± 1.2°. A series of univariate linear regression analyses was performed to analyze the relationship between the frontal plane rotation of the first metatarsal performed during the operation and the preoperative intermetatarsal angle, hallux abductus angle, and TSP. Greater preoperative TSP scores were associated with greater intraoperative varus (supination) rotation required for joint alignment. Direct observation of the alignment changes at the first metatarsal phalangeal joint after metatarsal rotation without distal procedures strengthened the notion that the frontal plane rotational position plays an important role in the bunion deformity.