Risk Factors for Union Deformities in Fifth Metatarsal Fractures: A Scoping Review

BackgroundUnion deformities are relatively common in proximal fifth metatarsal (5MT) fractures following both conservative and surgical treatment. Several risk factors have been identified to guide risk prediction and management. This review aimed to summarize factors contributing to delayed or nonunion in 5MT fractures.MethodsA literature search for studies reporting risk factors for 5MT fractures was performed using PubMed/Medline, EMBASE, ScienceDirect, Web of Science, and CINAHL databases. Methodological quality was assessed using the Methodological Index for Non-Randomized Studies (MINORS). Data on bone healing rates, complications, fracture zones, treatment approach, and healing outcomes were collected and summarized.ResultsThe initial search identified 668 articles, of which 13 met inclusion criteria, including over 1000 cases. Multiple risk factors were significantly associated with impaired union in 5MT fractures. Fracture zone (particularly zone 2), a plantar gap >1 mm, small screw diameter, and early return to activity before radiographic healing were the most consistent predictors of delayed or nonunion. Surgical treatment led to faster union but higher rates of delayed union and refracture. Bone grafting and larger screw diameters significantly improved union outcomes.ConclusionHealing outcomes in 5MT fractures are influenced by multiple risk factors, with fracture zone, fracture chronicity, and fixation strategy being the most significant contributors to union deformities. Identifying high-risk patients and tailoring treatment may reduce nonunion and improve recovery. Further high-quality studies are warranted to establish standardized definitions, treatment protocols and risk stratification models.Level of Evidence:Level IV: scoping review.