Establishment And Electrophysiological Study Of Unstable Pelvic Fracture Model With Sacral Plexus Stretch Injury In Goats

Background:While the main part of sacral plexus located in stable pelvis, the sacral plexus nerve injury as a complication of pelvic fractures is not common in clinic. However, with the development of transportation and industry, the incidence of pelvic fractures is increasing year by year. And incidence of unstable pelvic fractures combined with nerve injury is up to 21%～52%. In the acute phase of trauma, sacral plexus nerve injury was usually missed and not taken seriously, because of severe multiple injuries accompanied by pelvic fractures. Although extensive literature described mechanism and treatment of pelvic fractures combined with nerve injury, the relationship between the displacement of pelvic fractures and sacral plexus stretch injury has not been reported. There are also no reports about animal models and electrophysiological experiments.Objective:1 To determine the main components of sacral plexus and their characteristics by anatomy of pelvis and sacral plexus in goats.2 To establish a reliable unstable pelvic fracture model with sacral plexus stretch injury in goats.3 To detect electrophysiological signals when pelvis is shifted in different orientations and distance.Methods:There are two parts in this study. In the first part, eight goats were selected to undergo CT scan and execute by excess anesthesia. The data of CT scan was imported into Mimics 17.0 software to measure pelvis and vertical and horizontal diameters of neural foramens. Abdominal organs and vessels were removed through ventral midline incision. Then, sacral plexus nerves were exposed to measure length and diameters. Muscles and ligaments around pelvis are separated layer by layer to make clear their traveling and positions of beginning and ending in the pelvis.In the second part, twenty four goats were divided into three groups of eight goats each randomly:in Group A, pelvic longitudinal displacement was induced. In Group B pelvic fracture models with pelvic lateral displacement and the models with pelvic rear shift were made in Group C. After anesthesia, goats were fixed on the homemade pelvic displacement experiment table, cut the left sacroiliac joint and pubic symphysis and related ligaments and muscles to establish unstable pelvic fracture model. The left L6 and Si nerve root and initial segment of sciatic nerve were exposed in the next step. BL-420s Biological Functional Experimental System was opened with the left L6 and Si nerve root and initial segment of sciatic nerve were connected with stimulating and receiving electrodes respectively. The left pelvis was shifted with the speed of 0.25 mm/s. Electrophysiological signals of L6 and Si,including threshold potential, maximum stimulus potential, compound action potential amplitude and signal latency, were recorded when the placement of pelvis was 0,0.5 and 1.0 cm respectively.Results:L6 nerve contributes to femoral nerve, obturator nerve and sciatic nerve respectively. Sciatic nerve branch of L6 nerve,34.75±4.01 mm in length, which is similar to lumbosacral trunk in human, constitutes sciatic nerve with S1 nerve, which is 16.36±4.25 mm in length, and sciatic nerve branch of S2 nerve, which is 12.16±4.02 mm in length. The main soft tissue to stabilize pelvis including ligaments around sacroiliac joint and pubic symphysis, sacrospinous ligament, longissimus muscle, dorsal spine neck muscle, psoas major, psoas minor and muscle tendons around pubic symphysis.With pelvic displacement, threshold potential, maximum stimulus potential and signal latency were gradually increasing, and amplitude became smaller gradually. While displacement up to 0.5 cm, compared with the normal, part of electrophysiological signals changed obviously in Group A and B. There is no statistical difference between signals in Group C and the normal. While displacement up to 1.0 cm, compared with the normal, part of electrophysiological signals changed obviously. Compared with other groups, sacral plexus was damaged most seriously in Group A (P<0.05).There were significant differences between variation of electrophysiology of L,6 and Si in Group A except maximum stimulus potential (P< 0.05) while it changed little (P>0.05). In Group B, the significant differences are amplitude and signal latency. While in Group C, the differences are all signals.Conclusions:1 L6 nerve is involved in composing femoral nerve, obturator nerve and sciatic nerve in goats. The sciatic nerve branch of L6 nerve is consistent with L5 nerve and lumbosacral trunk of human in characteristics. It constitutes the sciatic nerve with S1 nerve and sciatic nerve branch of S2 nerve.2 By this method of fixing goats on the pelvic displacement experiment table and cutting related ligaments, muscles, sacroiliac joint and pubic symphysis, establishment of unstable pelvic fracture model with sacral plexus stretch injury in goats is feasible.3 In A and B Group, electrophysiological signals of sacral plexus changed obviously when pelvic displacement up to 0.5 cm. Sacral plexus stretch injury is the most serious when pelvis occurred longitudinal displacement.