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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 non-threaded 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 non-threaded 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. (J Am Vet Med Assoc 1996;208:883–887)

Free access
in Journal of the American Veterinary Medical Association