Trapezial Fractures and Associated Fractures of the Ulnar Carpus: A Ring-Bone Model

Fractures of the trapezium are rare; however, the incidence may be under-reported in the literature. The incidence of ulnar-sided carpal body fractures as a concomitant injury has not been reported. Our study aimed to evaluate the incidence of trapezium fractures in conjunction with ulnar-sided carpal body fractures.

Over a five-year period, our electronic records were queried and charts reporting carpal bone fractures were reviewed. All cases of trapezium fracture were evaluated further and presented.

Eight trapezial fractures were identified, representing 8% of all carpal fractures and 26% of all nonscaphoid carpal fractures. Of the eight trapezium fractures identified, five (62.5%) were associated with Bennett fracture and four (50%) were associated with ulnar-sided carpal fractures.

Our study demonstrates a higher incidence of trapezial fractures than previously reported. Previously unreported concomitant ulnar-sided carpal body fractures are reported at a frequency nearly equal to that of concomitant Bennett fractures in our series. We propose a mechanism of injury where the carpal canal and overlying transverse carpal ligament function as a ring-bone construct similar to the pelvis. When a trapezium fracture is identified, we recommend additional evaluation for ulnar-sided injuries of the carpus.