Spatial characteristics of metacarpal fractures: A quantitative 3D CT study of fall-related versus nonfall-related injuries.

BACKGROUND

In forensic practice, distinguishing fall-related injuries from nonfall-related injuries remains a challenge.

OBJECTIVE

To quantify the parameters of metacarpal fractures to analyze spatial injury patterns in cases resulting from fall-related versus nonfall-related injuries.

METHOD: A total of 50 metacarpal fracture cases (31 fall-related fractures, 125 fragments; 19 nonfall-related fractures, 63 fragments) were included. Digital reduction aligned fractures with healthy anatomy for standardized orientation. Three-dimensional displacement was measured via centroid Euclidean distance, whereas rotational characteristics were assessed using quaternion transformation and inertia tensor-derived angles.

RESULTS

Predominant involvement of the shaft and base of the fourth and fifth metacarpals (MC4, MC5) was observed in a cohort primarily comprising young and middle-aged male trauma patients. The fracture fragments exhibited a distribution pattern characterized by small, scattered fragments at the head, larger and relatively consolidated fragments in the shaft, and intermediate-sized fragments at the base. Both groups demonstrated a significant negative correlation between fragment volume and rotational angle, along with a strong synergistic effect between total displacement and rotational angle. The fall-related injury group exhibited significantly smaller fracture volume (p = 0.0112), greater posterior ulnar displacement (p = 0.0047), and greater rotational angles (p = 0.0097) at the first metacarpal (MC1) base, whereas the MC5 base tended toward palmar displacement (p = 0.0152).

CONCLUSION

Quantitative analysis of metacarpal fracture patterns revealed a synergistic effect between rotation and displacement, with smaller fragment size being correlated with greater rotational deformity. Furthermore, the research also suggests that fractures at the base of MC1 and MC5 may exhibit distinct spatial features when fall-related and nonfall-related injuries are compared, thereby enhancing the understanding of fracture mechanics and supporting forensic evaluations.