Mallet Fractures with Long Fragment Had Poor Outcomes on Extension Block Pinning

Background: Although extension block pinning for mallet fracture is popular, it occasionally results in poor outcome. We reviewed previous cases to elucidate the factors associated with poor outcome. Methods: From 2012 to 2017, 50 mallet fingers in 50 patients were consecutively repaired by extension block pinning using modified Ishiguro method. Inserted Kirschner-wires (K-wires) were removed at 6 weeks, followed by night splinting in extension. For outcome evaluation, distal interphalangeal (DIP) joint motion was measured and classified as either good or poor. Poor outcome was defined as either > 10° of extension lag or < 40° of active flexion or the presence of DIP joint pain. Associations between outcome and age, affected finger, interval to operation, fragment size (in terms of joint surface and dorsal cortex ratios), and fixation angle were evaluated. Results: 33 fingers (66%) had good outcome and 17 (34%) had poor outcome. Mean age was significantly greater in the poor (50.6 years) than in the good (40.1 years) outcome group (p < 0.05). The dorsal cortex ratio was also significantly larger in the poor than in the good outcome group (p = 0.006), but there was no significant difference between two groups in joint surface ratio. Affected finger, interval to surgery, and fixation angle also did not significantly differ between groups. Conclusions: Fracture fragments with a long dorsal cortex and older age associated with poor outcome following extension block pinning for mallet finger. The dorsal cortex ratio should be evaluated pre-operatively to determine the appropriate treatment method.