STRENGTH OF THE PIN-BONE INTERFACE OF EXTERNAL FIXATION PINS IN THE ILIAC CREST - A BIOMECHANICAL STUDY

The iliac crest is a frequent insertion site for external fixation pin s in treating unstable pelvic or acetabular fractures and in iliofemor al distraction for superiorly dislocated hips. The pin-bone interface is critical for the success of treatment, but studies of the iliac cre st are lacking. The purpose of this study was to investigate the stren gth of the pin-bone interface of different pins and different insertio n methods. Four types of commercial pins, Wagner pins, Orthofix cortic al and cancellous screws, and AO pins, were driven into sheep iliac cr ests by 2 methods: the intercortical and the transcortical. Specimens were tested for pullout and bending with an Instron testing machine (M odel 1343) at a extension rate of 0.02 mm/sec to failure. The results revealed that the intercortical method had a stronger pullout force th an the transcortical in all types of screws (p < 0.05), probably cause d by longer insertion in the bone. In the pullout tests, the Wagner pi ns were the strongest and the Orthofix cancellous screws were the weak est. There were no differences in bending. In the iliac crest, the int ercortical method was the better way of driving pins, and the new Orth ofix screws were not proven to be stronger than the Wagner pins, nor w ere the cancellous screws more suitable than the cortical ones.