Evaluation of cortical bone damage and axial holding power of nonthreaded and enhanced threaded pins placed with and without drilling of a pilot hole in femurs from canine cadavers.

OBJECTIVE: To evaluate the in vitro axial extraction forces necessary to remove pins and to evaluate mechanical trauma resulting from pin insertion, using various types of pins and insertion techniques.
DESIGN: Prospective, controlled study.
SUBJECTS: Femurs of cadavers of dogs. PROCEDURE: Pins were inserted as follows: 1 nonthreaded pin without drilling of a pilot hole, 1 enhanced threaded pin with drilling of a pilot hole, and 1 enhanced threaded pin without drilling of a pilot hole. After pin insertion, mechanical damage and proper pin insertion was determined by means of radiography. Axial extraction forces were determined for all pins, using a universal testing machine. Mechanical damage was evaluated in 12 additional femurs. After pin insertion, all pins were removed from the bone by use of a low-speed power drill. Samples were sectioned, processed, and evaluated by use of dissecting and scanning electron microscopy.
RESULTS: Using radiography, a significant difference was detected in the number of periosteal trans-cortex fractures between the enhanced threaded and nonthreaded pins. Axial extraction force was not significantly different between the enhanced threaded pins, regardless of insertion technique; however, the axial extraction force was significantly greater for enhanced threaded pins, compared with that for nonthreaded pins. Microfractures only were detected on the periosteum of the trans-cortex of enhanced threaded pins by use of scanning electron microscopy. CLINICAL IMPLICATIONS: We cannot recommend a particular insertion technique to decrease mechanical trauma to the bone and to increase axial extraction force needed for removal of enhanced threaded pins from the femur of dogs.