Microstructural analysis of a malunited clavicular fracture in a human cadaver.

Clavicle fractures are common, with midshaft fractures accounting for approximately 70-80% of cases. Malunion often occurs following conservative treatment, but the microstructural characteristics of the malunited region remain poorly understood. This case report describes a rare instance of clavicular malunion identified in a 85-year-old male cadaver during a gross anatomy dissection course. Both clavicles were analyzed using radiography, micro-computed tomography (micro-CT), and histology to investigate the microstructural alterations associated with the malunion. Radiographically, the right clavicle demonstrated anterior-posterior displacement and approximately 10% shortening compared with the intact side. Micro-CT analysis revealed decreased tissue mineral density, reduced trabecular bone volume, marked cortical thinning, and elevated structural indices, including the trabecular bone pattern factor and structure model index, suggesting a loss of trabecular connectivity and a transition from plate-like to rod-like architecture. Histological examination showed that the cortical bone at the fractured site exhibited a disorganized bone matrix lacking a lamellar structure, while the intact side displayed a well-organized lamellar pattern with regularly aligned osteocyte lacunae. These findings suggest that microstructural disorganization and decreased mineral density may contribute to reduced bone strength in the malunion region. Because high-resolution peripheral quantitative CT (HR-pQCT) cannot assess the clavicle, this cadaveric micro-CT and histological analysis provide valuable insights into the microstructural characteristics of clavicular malunion that are not accessible through conventional clinical imaging.