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 pins in treating unstable pelvic or acetabular fractures and in iliofemoral distraction for superiorly dislocated hips. The pin-bone interface is critical for the success of treatment, but studies of the iliac crest are lacking. The purpose of this study was to investigate the strength of the pin-bone interface of different pins and different insertion methods. Four types of commercial pins, Wagner pins, Orthofix cortical and cancellous screws, and AO pins, were driven into sheep iliac crests by 2 methods: the intercortical and the transcortical. Specimens were tested for pullout and bending with an Instron testing machine (Model 1343) at a extension rate of 0.02 mm/sec to failure. The results revealed that the intercortical method had a stronger pullout force than the transcortical in all types of screws (p < 0.05), probably caused by longer insertion in the bone. In the pullout tests, the Wagner pins were the strongest and the Orthofix cancellous screws were the weakest. There were no differences in bending. In the iliac crest, the intercortical method was the better way of driving pins, and the new Orthofix screws were not proven to be stronger than the Wagner pins, nor were the cancellous screws more suitable than the cortical ones.