Risk Factors for Nonunion After First Metatarsophalangeal Joint Arthrodesis With a Dorsal Locking Plate and Compression Screw Construct: Correction of Hallux Valgus Is Key.

First metatarsophalangeal joint (MTPJ) arthrodesis is currently the gold standard technique for advanced hallux rigidus. This retrospective study aimed to identify the risk factors for nonunion after first MTPJ arthrodesis with a dorsal locking plate and compression screw construct. Between April 2014 and April 2019, 165 consecutive patients (28 men and 137 women; mean age, 60 (range, 28-84) years) who underwent 178 primary first MTPJ arthrodeses were retrospectively reviewed. All arthrodeses were performed using either a dorsal locking plate with an integrated compression screw (Anchorage CP plate, Stryker, n = 97) or a dorsal locking plate (Anchorage V2 plate, Stryker, n = 81) with a separate compression screw (4 mm cannulated ACE screw). Union was defined as bone bridging across the fusion site on at least 2 of the 3 standard foot radiographs (anteroposterior, lateral, oblique) and no MTPJ movement or pain during clinical examination. Potential risk factors for nonunion were analyzed with the use of univariate and multivariate analyses. The overall nonunion rate was 6.2% (11 of 178 cases). The risk factors identified in the univariate analysis included preoperative hallux valgus deformity, postoperative residual hallux valgus deformity, and diabetes (p < .05). Multivariate analysis confirmed that postoperative residual hallux valgus deformity (odds ratio 6.5; p= .015) and diabetes (odds ratio 7.4; p = .019) are independent risk factors for nonunion after first MTPJ arthrodesis. Diabetes is the most important independent risk factor for nonunion after first MTPJ arthrodesis with a dorsal locking plate and compression screw construct. A residual postoperative hallux valgus deformity is associated with a significantly increased risk for nonunion. It is therefore crucial to correct the hallux valgus deformity to a hallux valgus angle of less than 20°.