Sacroiliac joint compression using an anterior pelvic compressor:: A mechanical study in synthetic bone

Objectives: Pelvic external fixation pins placed in the supraacetabular region, directed posteriorly, and mounted with a femoral distractor as a compressor may impart compression forces across the sacroiliac joint. This would be useful for indirect reduction and stabilization of the posterior pelvis. The purpose of this study was to determine the forces achieved by this construct compared with other forms of fixation. Design: Mechanical study. Setting: University laboratory. Patients: Synthetic pelvis models. Intervention: A complete symphyseal and unilateral sacroiliac joint disruption was created in 6 synthetic pelves. Five different fixation constructs were applied, and a pressure-sensitive film (TekScan) was fixed in the sacroiliac joint. Each construct was compressed in a standardized fashion. Main Outcome Measurements: After maximal compression of each trial, the magnitude and regional distribution of the force was recorded. Results: Standard 2-bar external fixation did not allow for any compression across the sacroiliac joint in any specimen. The pelvic compressor delivered 86.3 N (SD, 12.1 N) of force across the sacroiliac joint when the pins were inserted half way, and 85.8 N (SD, 11.0 N) with full pin insertion. Iliosacral screws led to 145 N of compression on average (SD, 69.9 N), but this was not statistically different from the pelvic compressor groups. A C-clamp generated compression of 206 N (SD, 31.9 N), which was significantly greater than both the pelvic compressor groups (P < 0.005). Conclusions: A simple modification of pelvic external fixation, placing a femoral distractor as a compressor on supraacetabular pins, allows for indirect medial translation of the innominate bone and compression across the sacroiliac joint. The force achieved is less than with a C-clamp, but it is safer, involves techniques familiar to most surgeons, and may be useful in the acute management of unstable pelvic fractures.