gms | German Medical Science

Objectives/Interrogation: Although a mallet fracture is a common injury, few reports have described bony mallet thumb injuries. We retrospectively investigated bony mallet thumb injuries treated surgically.

Methods: We evaluated 9 patients (6 men, 3 women) who underwent surgery for bony mallet thumb injury between January 2009 and February 2018. The mean age (range) of the patients was 44.9 years (18-80 years), and the surgery was performed 7.2 days (0-18 days) after the injury. The mean follow-up period was 4.8 months (2-14 months).

Results and Conclusions: Based on the Wehbe and Schneider classification of mallet fractures, all patients demonstrated Type I fractures (no joint subluxation). Subtypes A and B were observed in 4 and 5 patients, respectively. Six patients were treated with extension block K-wire pinning using a closed method, and 3 patients were treated with screws. Bone union occurred in 8 patients; however, 1 patient treated with pinning did not show bone union. One patient continued to demonstrate pain with interphalangeal (IP) joint extension. Range of motion and extension lag at the IP joint at the final follow-up were 64.1° (40°-85°) and 3.6° (0°-20°), respectively.

A biomechanical study of mallet fractures has reported that distal phalangeal subluxation is more common with defects involving >40-50% of the joint surface. In this study, although 5 patients demonstrated subtype B fractures (one-third to two-third of articular surface involvement), no patient demonstrated joint subluxation. The retinacular ligament of the IP joint of the thumb (which does not exist in other distal IP joints of fingers) may contribute to joint instability. Bone union did not occur in 1 patient treated with pinning. The fracture fragment observed in bony mallet thumb injuries is relatively larger than that observed with fractures of other fingers. Rigid fixation with screws may be superior to pinning to achieve effective bone union.

In conclusion, joint subluxation is rare in bony mallet thumb injuries despite the large area of joint surface defects. Rigid fixation with screws may be effective to achieve bone union.