Subluxation in Mallet Fractures

Data from a prognostic Level IV case series presented Tuesday indicate that articular surface involvement, fragment displacement, and reported interval between injury and treatment are associated with subluxation of the distal interphalangeal joint when treating a mallet fracture. This study also confirms that subluxation is unlikely in fractures that involve less than 39 percent of the articular surface.

The study authors note that although mallet fracture without distal interphalangeal joint subluxation is usually treated nonsurgically, many orthopaedic surgeons recommend surgery when subluxation occurs. The purpose of the study was to evaluate factors associated with distal interphalangeal joint subluxation with mallet fracture. In secondary analyses, the authors looked for differences between initial and late subluxation, as well as for a threshold value of the percentage of articular involvement below which there is no potential for subluxation.

Study methods
ICD-9 codes and text search and review of the medical record were used to identify all adult patients with a mallet fracture in three hospitals between 2004 and 2014. The radiographs and medical records of 383 patients with 392 mallet fractures were reviewed. Seventy-eight mallet fractures had subluxation on the initial radiographs at diagnosis and 19 had subluxation identified on a second set of radiographs during treatment.

Results
In bivariate analysis, fragment size, fragment displacement, reported interval between injury and treatment, and patient age were associated with initial and late subluxation. Multivariable analysis confirmed that each of these factors, except age, was independently associated with subluxation. The researchers found no statistical difference in factors associated with initial or late subluxation. Distal interphalangeal joint subluxation was not observed when the fracture size was less than 39 percent of the total articular surface. According to the statistical model, for each 1 percent increase in total articular surface involvement or 1 percent displacement in fractures with more than 39 percent involvement, the risk of subluxation increased by 4 percent (P = 0.012).

“Subluxation is the only consensus indication for surgical treatment of a mallet fracture,” coauthor David C. Ring, MD, PhD, said. “Our data confirm that a fracture that involves less than 40 percent of the articular surface almost never subluxates. Larger fractures should be monitored more closely, particularly those with greater displacement of the fracture fragment.”          

Dr. Ring’s coauthors of  Paper 112 “Factors Associated with Subluxation in Mallet Fractures” are Ali Moradi, MD; Yvonne Braun, MD; Kamil Oflazoglu, Bsc; Timion Meijs, Bsc; and Neal C. Chen, MD.

Details of the authors’ disclosures as submitted to the Orthopaedic Disclosure Program can be found in the Final Program; the most current disclosure information may be accessed electronically at www.aaos.org/disclosure

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