Abstract: Objective To explore an approach of CT rendering and mechanical analysis for rib fracture that was inextricable on X-ray film in legal medical practice. Methods 17 cases with rib fracture undetermined on X-ray chest film in legal medical practice underwent CT scans. The thin slices (0.75 mm or 1mm) of images were reconstructed with smooth and sharp kernel.The multiplanar reformatted images along rib and surface shaded display were obtained to investigate rib fracture. Results All rib fractures were accurately displayed by CT scan and MPR images along rib. The torque that caused rib fracture was divided presumably into vertical and rotary types. The two kinds of rib fracture, composed of vertical and rotary type, were proposed. Conclusion CT scan with thin slice and MPR images can definitely reveal the rib fracture unresolved on X-ray film in legal medical practice. The proposition of two kinds of torque will be help avoid misunderstanding acute rotary type of rib fracture as old healed one.

Key words: rib, fracture, X-ray, computed tomography, mechanics