In the TMS (Trauma Medullary System) fixation, the pin is oversized to achieve a press-fit within the medullary canal. This ensures stable axial and rotational fixation by preventing micromotion and loosening at the fracture site. An oversized pin enhances mechanical stability without the need for supplementary fixation hardware. This principle is crucial in maintaining proper alignment and promoting effective bone healing during internal fixation. The oversized design also aids in distributing load effectively to the bone.

Reference: Skeletal Trauma, Kenneth A. Egol, Edition 5.