THE STUDIES OF MECHANICAL CONTRIBUTION OF PINS OF WRIST EXTERNAL FIXATOR USING MECHANICAL MODEL, CADAVER MODEL AND IN VIVO PATIENT MODEL

摘要

Wrist external fixator (WEF) is widely used in unstable distal radius fracture. The mechanical properties of WEF were thoroughly studied by many authors. The researches of external skeletal fixator include the stability of the frame structure, fatigue or failure model of pins, exploration of biomechanical characteristics of pin-bone interface, and the strength of pin clamps. The mechanical models and cadaver bone were frequently used to test the WEF. For most of the studies, the stiffness (or stability) of the construct was the criteria to evaluate the WEF. In these many studies, however, the mechanical contribution of pins was less studied. Due to the non-weight bearing property and prevention of injuries from the soft tissue of peri-wrist, the structure and elements of WEF are designed to be small and slender. It is hence important to find if all pins of WEF were necessary or proper designed. We tested the mechanical function of Traumafix WEF using the mechanical model, the cadaver model and in vivo patient model. The strains of the pins on the top surface were analyzed. The data showed that the load distribution of each pins were different from pins to pins, and from models to models. Our result suggests the distal pins of WEF can be smaller if the space of metacarpal bone is limited.