Thermal response and torque resistance of five cortical half-pins under simulated insertion technique

A model was developed that can quantitate heat generation during placement of half-pins in cortical bone. Five half-pins were tested to assess differences in insertion torque, heat generation, and micro-damage at the pin-bone interface. Thin thermocouple probes were placed 0.5 mm from the track of the pin and within the pin to measure its temperature during insertion. Scanning electron microscopy was used to view the pin-bone interface to assess the microdamage during placement. The design of the tip of the pin influenced insertion torque and heat generation. Higher heat generation was measured when a thermocouple was placed within the pin itself and less was measured when thermocouple probes were placed within bone samples 0.5 mm from the impending pin track. Furthermore, insertion torque and thermal responses were related, but there were no significant differences in microdamage to bone when different pins and drilling/tapping techniques were used. Due to the significant heat generation at the pin-bone interface, proper cooling with saline irrigation should be applied during pin insertion regardless of the design of the pin. The microdamage observed at the surface of the pin track may have significant implications with regard to loosening of pins, but such effects must be studied with in vivo models.