Abstract
A laboratory study was undertaken to evaluate the effectiveness of alternative methods of fixation of unilateral vertical shear fractures of the pelvis. Prior to experimental testing, a biomechanical analysis was performed to estimate the forces that displace the hemipelvis in the presence of two different patterns of injury: an interforaminal sacral fracture and a disruption of the sacroiliac joint. These lesions were then experimentally created in five unembalmed human pelvises and sequentially fixed with an external Hoffmann frame alone, a Hoffmann frame with sacral bars, or sacral bars with either one or two bone plates placed across the symphysis pubis. Each pelvis/fixator system was mechanically tested by loading along the direction of the resultant muscle force predicted by the biomechanical analysis. During loading the proximal migration of the ilium was continuously recored with a transducer. At intervals during loading, the threeβdimensional displacement of the detached hemipelvis at the pubic symphysis was also measured using a stereophotographic technique. With both the sacral frature and the sacroiliac disruption, the addition of posterior sacral rods substantially increased the strength and rigidity of fixation provided by the Hoffmann fixation frame alone (p < 0.01). In speciments with a sacral fracture, the use of anterior plates with posterior rods restored 65β71% of the strength of the intact pelvis, in comparison with 46% observed with the combination of sacral rods with an anterior Hoffmann frame (p < 0.01). All of the methods of fixation evaluated in this study were less successful in stabilizing the sacroiliac distruption. In this case there was no significant difference between the fixation achieved with one or two anterior bone plates or a Hoffmann frame placed anteriorly in combination with sacral rods placed posteriorly. In both patterns of injury treated with posterior sacral rods, the use of two anterior base plates led to no significant enhancement of the strength or the rigidity of fixation compared with one anterior plate alone.