Defining Nonunion for Metacarpal Fractures: A Systematic Review.

Purpose: Our purpose was to assess how nonunion of the metacarpals has been defined in prior investigations with respect to both clinical and radiographic criteria. We hypothesized that the definitions of nonunion would be highly variable. Methods: A systematic review was conducted using MEDLINE and Embase databases for clinical articles related to the treatment of metacarpal fractures (surgical and nonsurgical) from 2010 to 2021. Included articles were searched to assess how nonunion was defined based on clinical and radiographic criteria. We assessed the treatment type, method of union assessment, time to union, and incidence of union as well as article factors such as the following: date of publication, level of evidence, and publishing journal. Results: A total of 641 articles were identified, of which 102 were included for a definition of nonunion and 97 were included for the assessment of clinical management and outcomes. Of the included articles, 62% contained level IV evidence. A definition of nonunion was provided in 47% of the articles. Radiographic criteria alone, clinical criteria alone, or a combination of the 2 was used in 22%, 6%, and 19% of the cases, respectively, to define nonunion. The most common definition of nonunion was presence of fracture-site tenderness (with no time defined) in 20 articles (20%), followed by lack of radiographic healing at 6 months (15%). In the 97 included articles, the total number of fracture cases was 4,435 and nonunion was reported in 0.45%. Cases with nonunion were reported in a total of six articles that used a variety of treatment modalities. Conclusions: The definition of metacarpal nonunion remains highly variable and lacks standardization with respect to clinical and radiographic criteria. Clinical relevance: Standardizing the definition of nonunion for metacarpal fractures would allow for more accurate assessments of the incidence of this complication and may aid in improving diagnostic and management strategies.