手根骨基部関節外骨折に対するプレート固定と髄内スクリュー固定の生体力学的比較

Intramedullary (IM) screws are commonly used for metacarpal shaft and neck fractures, but their application in extra-articular metacarpal base fractures has not been thoroughly evaluated. This study aims to compare the biomechanical performance (load to failure) of IM screw fixation versus dorsal plate fixation for extra-articular fractures at the base of the metacarpal.

Twenty-four cadaveric metacarpals from 12 upper extremities were prepared and randomized to receive either IM screw fixation or dorsal plate fixation following a standardized transverse fracture near the base. All specimens were potted and tested using cantilever bending in a materials testing system. The primary outcome was ultimate load to failure; stiffness was evaluated as a secondary measure.

Dorsal plate fixation demonstrated greater load to failure compared to IM screw fixation when all specimens were analyzed collectively. Subgroup analysis indicated this difference was more pronounced in the thumb metacarpals. In contrast, IM screw constructs consistently exhibited greater stiffness across all specimens, including both thumb and small finger metacarpals.

Dorsal plating offered greater resistance to fracture displacement, while IM screw fixation provided superior construct stiffness. Both fixation methods surpassed expected physiologic loading during hand use, indicating that either approach may be biomechanically acceptable depending on the clinical context.

The IM screws may serve as a biomechanically viable alternative to dorsal plates for extra-articular metacarpal base fractures. These findings may help guide surgical decision-making regarding fixation selection and promote individualized treatment strategies.