Simultaneous anterior and posterior compression of the pelvic ring with external fixation using a pre-tensed curved bar: A biomechanical study

Abstract Introduction External fixators continue to be essential tools in the urgent treatment of pelvic fractures for compression and stabilization of the pelvic ring. Current systems fail to produce simultaneous anterior and posterior compression. A modified application of an existing curved bar fixator is proposed using a specifically designed tensioner to pre-tense the bar prior to its connection to Schanz screws. Subsequent pre-tension release and elastic recovery of the bar could potentially compress the pelvis. The aim of this work was to determine if the modified application could produce greater simultaneous compression across the sacroiliac joint and the symphysis of an unstable fractured pelvis than the standard application without pretension. Materials and methods Six synthetic pelvis models with symphyseal and unilateral sacroiliac joints disruptions, simulating a Tile type C pelvic ring fracture, were used. Each specimen was stabilized using two 5 mm × 250 mm supra-acetabular Schanz pins, a couple of open adjustable clamps and a semicircular carbon fibre rod applied without and with pre-tension. Two distances from bar to bone and three levels of pretension were compared. Each pelvis was tested with the six possible parameter combinations. Compressive forces at the disrupted joints were measured using pressure sensitive film sensors. Results The modified application produced forces significantly higher than the minimal compression achieved with standard application. At the sacroiliac joint, after pre-tension release, mean compressive forces measured ranged from 28.7 to 85.6 N. The closest bar-to-bone distance always produced a significantly higher force; similarly, a significant increase in compression was found as the pre-tension level rose. At the symphysis, mean compressive forces between 35.3 N and 49.0 N were determined. No significant variations were seen with changes of any of the two factors analyzed Conclusions To pre-tense a semi-circular bar before its use for external fixation of the fractured pelvis, is an effective means of applying compression simultaneously through the sacroiliac joint and the symphysis. The proposed method generates the highest compressive forces at the sacroiliac joint when the rod is subject to the highest pre-tension level not producing subluxation and is subsequently positioned as close as possible to the bone depending on patient's condition.