Injury Mechanism Of Sacral Plexus Resulting From Zone-â…¡ Sacral Fractures: A Cadaveric Study

Objective:The sacrum provides the foundation for lumbar as a weight-bearing platform as well as pelvic ring alignment to protect sacral plexus , iliac vessels and pelvic organs.Injury of sacral plexus leads to poor function of hip,leg,bowel and bladder,which continues to be a major cause of long term morbidity after pelvic disruption. Zone-â…¡sacral fractures with neurologic injury is more common in clinic.This experiment was carried out to study the injury mechanism of sacral plexus resulting from sacral zone-â…¡fractures,trying to develop comprehension,and providing the basis for clinical treatment and prognosis. Method:9 short-term (in a year) embalmed pelves along with their spines intact from L4 to the sacrum,and hip joints with the 1/3 proximal of both femora were obtained from anatomic department of Hebei Medical University.All of these specimens were cleared of belly muscules,organs of pelvic cavity and iliac vessels,preserving sacral plexus carefully and maintaining its connection with pelves.The structure of sacral plexus and relation with sacral foramen,sacroiliac joint,sacrotuberous and sacrospinons ligaments were observed.According to different types of traumatic force,sacral longitudinal fractures are devided into four types:anteroposterior compression,lateral compression,axial compression and complex mecharism.So these specimens were divided into three groups (three in each group).Then with preserving sacral plexus and resecting pubic symphysis, the former three types of fracture models are produced by slitting sacral cortices along to sacral foramens using cut-off saw.After this,according to the characteristic of different types of fracture displacement,quantitative analysis for fracture displacement is carried out to observe the characteristic and the mechanism of sacral plexus injury.Then removing sacral plexus are replaced by proportional diameter silica gel pips fulled with contrast medium,experimental procedure is repeated to observe compressure part and change of courser of sacral plexus attributed to fracture displacement.The experimental datum are analyzed by SPSS10.0 statistic software and obtain result. Results:In anteroposterior compression type of sacral fracture, sacral nerve canal is gradually open and its volume raise.No sacral nerve was opressed in nerve canal.However ilium external rotation prolong sacral nerves distinct level,especial of S1,S4 and more separate of pubic symphsis more prolonged of sacral plexus nerves.At the same time, sharp border of fracture segment stabs nerves obviously,especial L5(6 cases),S1(5 cases) and S2(3 cases).In lateral compression type (with ilium internal rotation) ,sacral canal is being closed and its volume reduced and small free fracture segment result in sacralplexus nerves oppressed,especial of S1,S2(6 cases of each).L5 has no much compression at the outlet of nerve canal,likely to be crushed between diatal and proximal of fracture which make nerve serious compression injury(100%).At the same time loosening of sacral plexus nerves can be observed.The more overlapping of pubic symphsis,the more serious of compression.Axial compression type of sacral fracture is unstable in various direction.In this type, change of sacral canal content has no regularity,however nerves being dragged and being stabed by facture segment border are easy observed in upper and anterior displacement,sometime nerves even be crushed in fracture interspace(3 cases).Among the total,distal segment diaplacement to upper and anterior are more likely to damage sacral plexus.Futhermore axial compression fracture makes some free ,inversion fracture segments in nerve canal which can oppress some sacral nerves(2 cases) .To sum up,nerve injury of this type covers widely and has more serious level,sometime total sacral plexus were damaged.Using proportional diameter silica gel pip instead of nerve,the same result are observed from X-ray image. Conclusion:Sacral plexus is tight conncted with the wall of pelvic cavity and fixed. Zone-â…¡sacral fracture is likely to damage sacral plexus,especially L5,S1.The injury part and severity of sacral plexus are relative to the type,displaced distance and stability of sacral fractures.In clinical surgeon should treat patients of this type positively,that is to say early...