Comparative Biomechanical Study Of Lag Screws And Four-hole Reconstruction Plate For Symphysis Pubis Diastasis

Background In the majority of cases, the pelvic fracture was due to a road traffic accident and falls. The rate of pelvic fracture account for 3-8%, but its death rate is beyond 10% and the mutilation rate account for 4-18% . The rate of pelvic fractures with symphysis pubis diastasises is as high as 24%. The common method totreat symphysis pubis diastasises include two-hole dynamic compression plate fixed to the superior symphysis pubis with 2 cancellous screws, four-hole or six-hole reconstruction plate fixed to the superior symphysis pubis with cortical screws. Simonian pointed out that each of the three fixation styles could provide similar stability of pelvic, and their stability had no significant differences. Plates with more holes have no superiority on the pelvic stability. At present, four-hole or six-hole reconstruction plate fixed to the superior symphysis pubis with cortical screws were generally applied to clinic .In 1995, Routt fist reported the fixation of pubis ramus superior with retrograde lag screws. This technique grew practiced gradually in the following years. While percutaneous lag screw fixation of symphysis pubis had a less generalization.which was due to insufficient study.Objective By testing the biomechanics of two kind of fixation, We compared the pelvic stability, and tried to provide a scientific evidence for the clinical application of percutaneous lag screw fixation of symphysis pubis.Materials and Methods: Seven embalmed pelves, along with their spines intact from L5 to the sacrum, the proximal half of both femora, the intact major pelvic ligaments, and the intact hip joints were obtained. The concrete age were unknown, and there were five males and two females. The pelves were loaded vertically in a test machine in a standing posture. The loads were applied through the L5 body to a maximum of approximately 400N while the displacements of the symphysis pubis were recorded. Testing was first performed on intact pelves and then the symphysis pubis, unilateral anterior sacroiliac joint, and ipsilateral sacrospinous and sacrotuberous ligaments were cut. On each pelvis, a Type B1 injury was simulated. The following fixation ware then applied: (1) four-hole reconstruction plate fixed to the superior symphysis pubis with 4 cortical screws, (2) 2 lag screws fix fixed in lateropulsion through the symphysis pubis.Results The study showed that both fixations were able to reduce symphysis pubis gapping compared with the symphysis pubis diastasis. Under the same condition, the symphysis pubis motion (0.221±0.048mm)with intact pevic was the smallest, and the symphysis pubis motion (3.513±0.764mm )with symphysis pubis, unilateral anterior sacroiliac joint, and ipsilateral sacrospinous and sacrotuberous ligaments cut was the largest. The symphysis pubis motions with a four-hole reconstruction plate to the superior symphysis pubis were 0.926±0.201mm. The symphysis pubis motions with two lag screws fix fixed in lateropulsion through the symphysis pubis were 0.912±0.198mm. Their stability were no significant differences (p>0.05).Both had significant differences (p<0.05) with intact pelvic ,but they were obviously stronger than pelves with symphysis pubis diastasis.Conclusion (1) Both the two kinds of fixation can decrease the displacement of symphysis pubis, and it is the key to recovering the stability of pelvic. Both the fixation can be applied in clinic. (2)The stability of two fixations has no significant differences (p>0.05). Cinically, percutaneous lag screw fixation of symphysis pubis is an effective and minimal invasive method to treat the injury of pelvis,.It presents with central fixtion,which fits the pelvic biomechanics much better and meets the minimally ivasive tendency of surgery.