Coronal hamate body fractures with dorsal fourth and fifth carpometacarpal joint instability: fracture patterns, injury mechanisms, surgical strategies, and outcomes

INTRODUCTION: Coronal hamate body fractures are rare injuries, and studies regarding their morphology and management are limited. This study analyzed fracture patterns, injury mechanisms, associated injuries, surgical strategy, and clinical outcomes in patients with coronal hamate body fractures involving more than one-third of the articular surface and concomitant carpometacarpal (CMC) joint instability. METHODS: Fifty-eight male patients were retrospectively reviewed. Fractures were classified as dorsal oblique or coronal splitting types based on computed tomography findings. Surgical treatment involved open reduction and multiple screw fixation of the hamate using a K-wire-guided technique, with supplementary Kirschner wire stabilization for associated metacarpal base fractures or CMC joint instability. Radiographic and functional outcomes were evaluated after a minimum follow-up of 6 months. RESULTS: Dorsal oblique fractures (63.8%) occurred more frequently than coronal splitting fractures (36.2%) and were most commonly associated with punching (OR, 4.9; p = 0.01), whereas falls from height were more common in coronal splitting types. Concomitant fractures occurred in 82.8% of cases, most frequently involving the fourth metacarpal base. Among 35 patients with a minimum 6-month follow-up, 34 achieved successful healing. In the 33 patients with functional outcome data, the mean DASH score was 3.0, and mean grip strength was 94.1% of the contralateral side. One patient treated 45 days post-injury showed recurrent subluxation and poorer outcome. No differences in functional outcomes were observed between fracture types. CONCLUSIONS: Coronal hamate body fractures with CMC instability frequently presented as dorsal oblique patterns following punching injuries and were commonly associated with fourth metacarpal base fractures. Open reduction with multiple small-diameter screw fixation through K-wire tracts, combined with supplementary K-wire stabilization, was feasible and provided favorable clinical outcomes. Favorable outcomes were generally observed when anatomical reduction was achieved within 3 weeks after injury, and fracture morphology was not associated with significant differences in clinical outcomes. LEVEL OF EVIDENCE: IV.