| With the development of surgery, a lot of patients have been cured by selectivesacrectomy. Sacrum is the unique structure which connect lumbar and pelvis, selectivesacrectomy will harm this structure and even damage the whole continuity. We conducted aseries of research, to investigate the biomechanical properties of normal sacrum andmodels after selective sacrectomy in both experimental (cadaveric) and numerical (FEA)approaches, to judge the necessity of reconstruction after sacrectomy, to design a newsacrum prosthesis for reconstruction after total sacrectomy.Part 1OBJECTIVE: To investigate the biomechanical properties of normal sacrum anddifferent levels of partial sacrectomy.METHODS: Six human cadaveric pelves wereplaced on a testing apparatus simulating the posture of sitting. When the superior surfacewas loaded by 0, 200, 400, 600, 800, 1000N in turn after selective resection, which wereabove or below the level of S3, S2, S1 foramina, the main stress value and distribution,displacement and stiffness changes of the sacrum were detected and analyzed. The ultimateload after resection cephalad to the S1 foramina was recorded. RESULTS: The max strainchanged between 552-686μεat sacrum. Stress was mainly distributed above S1.Sacroiliac joint stress and strain did not increase significantly when resection involved theS2 and S3 foramina. As the load increased, the stress and displacement of the pelvisincreased too. When cephalad to the S1 foramina, the ultimate load measured was2042.50±46.25N. After excision of the sacral portion of the sacroiliac joint, the intrajointstress increased on both the sacral and the iliac side. The residual ilium collapsed and moved medially towards the remaining sacrum. CONCLUSIONS: The component aboveS1 is the most important part of stress transduction within the sacroiliac joint. Afterexcision above the foramina of S1, the physiological load beating ability of sacrum washarmed critically, which may result in fracture with normal activity.Part 2OBJECTIVE: To investigate the biomechanical properties of normal sacrum anddifferent levels of partial sacrectomy.METHODS: By using finite element models (FEM)based on CT image data of human pelves, the pelvic mechanical behavior was calculatedsimulating standing on two legs or sitting. The main stress value and stress distributionwere analyzed when the superior surface of the sacrum was loaded. Selective sacrectomywere conducted above or below the level of S3, S2, S1 foramina and one side of sacroiliacjoint. RESULTS: Stress was mainly distributed above S1. Sacroiliac joint stress and straindid not increase significantly when resection involved the S2 and S3 foramina. As the loadincreased, the stress and displacement of the pelvis increased too. Within the sacroiliacjoint, the average stress increased 4.3 times with transection cephalad to the S1 foraminaand 2.1 times with transection caudal to the S1 foramina on the sacral side of the joint byFEM. On the iliac side of the sacroiliac joint, the stress only increased 67.7％and 87.5％.The axial stiffness of the pelvis was decreased 50-60％. With expanded resection stressincreased on the sacral side, while a sudden decrease of approximately 54.3％wasobserved on the iliac side. After excision of the sacral portion of the sacroiliac joint, theintrajoint stress increased on both the sacral and the iliac side. The residual ilium collapsedand moved medially towards the remaining sacrum. CONCLUSIONS: The componentabove S1 is the most important part of stress transduction within the sacroiliac joint. Afterexcision above the foramina of S1, the physiological load bearing ability of sacrum washarmed critically, which may result in fracture with normal activity.Part 3OBJECTIVE: To design a new kind of sacrum prosthesis, which is able to connectlumbar and pelvis, bear the body weight and recover the physiological stress transduction. METHODS: A finite element model of pelvis was developed based on the CT image dataof human pelvises; the main stress distribution was calculated. The main stresstransduction structure showed. The three dimensional numerical model of A new sacrumprosthesis was designed simulating this structure and was measured by finite elementanalysis method. 19 three dimensional numerical model based on CT image data ofdifferent patients was developed and measured simulating reconstruction with the newprosthesis after total sacrectomy. RESULTS: The new sacrum prosthesis was made up ofseveral parts, the sizes of every parts was due to patient's hight and resection degree. Byfinite element analysis, the resected pelvis which was reconstructed with the prosthesisseemed to be a stable structure, the prosthesis restores the stress transduetion prior tosacrectomy. No stress sudden change was detected. CONCLUSIONS: The new designedsacrum prosthesis has the ability of reconstructing pelvises after sacreetomy. Compared tothose already reported, it is more stable, and has the advantage of recovering thephysiological stress transduction.Above all, we concluded that the component above S1 is the most important part ofstress transduction within the sacroiliac joint, after excision above the foramina of S1, thephysiological load bearing ability of sacrum was harmed critically, which may result infracture with normal activity. A new sacrum prosthesis should be encouraged aftersacrectomy to recover the physiological stress transduction. The new sacrum prosthesisdesigned now has the ability to bear the body weight effectively and the stress transductionrecovered with a stable pelvis. |
