The Laboratorial Research And Clinical Significance Of The Acetabulum-impacting THR For Acetabular Dysplasia In The Adult

[Background] In the recent years, there was a new surgical technique forusing the acetabulum-impacting total hip arthroplasty. This technique is newmethod of acetabular plasty for the patients with severe dysplastic hip. howeverthere is no universal criteria for the moving of the acetabular wall entad in the newmethod . The position of the acetabular wall moving entad is vital factors in theeffects of the THR. it will directly affects the longevity of the cup prosthesis. Thepostoperative loosening,prosthesis impingement,pain,wearout, is closelyconnected with the distance of acetabular wall moving entad .How to avoidthese negative factors will be a challenge faced by the clinical surgeons. Throughcoumputer assisted finite element analysis, we can understand the loaddistribution on any region of the reconstructed models. As the devolpement of thecomputer software program, it will be feasible for any researchers to use it toanalyze the complicated biomechanmic problem and carry out the tediouscalculation process. the CAD/CAM assisted custom design is a promising way. [Objective] Based on the CT scan, the pelvic model of acetabular dysplasiawas reconstructed. The distance of the acetabular wall entad ranges from-2~-+7millimetre. On the SolideWorks calculation platform, the distance of theacetabular wall entad was input in each position every 1 millimetre. Thebiomechanic analysis of the effects to the load distribution aroud the acetabularform the different moving position entad was to carry out, in order to find outwhich position is good to the load distribution and define the safe range of theacetabular wall entad. Therefore lay a theoretical foundation for the clinical work.Also, the pelvis of acetabular dysplasia reconstructed model was found throughthe the accuracy of the existed CAD program. The pelvic model will give a betterunderstanding to the load transfer on the pelvic. And it will be an epoch thatcalculating machine simulate the method of clinical operations. [Material and method]1. The three-dimensional reconstruction of the pelvis1.1 The obtain of the CT imagesGEspeedlight 16CT scanned a pelvis from a clinical patient of acetabulardysplasia in the adult. There was 1.25mm between each scanned slice and thetwo-dimensional images of each slice were obtained. All the obtained data wereput into the computer workstation for the later use.1.2 The process of the obtained CT imagesThe two-dimensional images of each slice in the workstation were conversedinto the compact disc files and recorded on 700M CD-R. Through the calculation,we directly gained the CT images and using own developed CAD software carriedon later experiments.1.3 The edge detectiveUse semi-automatic detective system to detect the images' edges.(1)Figured out the average coordinate value of all the detective edge points,namely the middle point in the three-dimensional space.(2)Took the middle point as the crossing point in the coordinate, thetransverse line as the X-axis and the vertical as the Y-axis. Calculated the distancebetween each point and the crossing point. The angles (counter-clockwise)existing in them were also calculated.(3)Confirmed the two beginning point. one is in the outer contour, the otheris in the inner contour.(4)Drew the contour according to the angle.(5)The conversion of two-dimensional images to three-dimensional oneThe originally obtained two-dimensional data were transformed intothree-dimensional picture in order to make the picture more real for observation.2. the three-dimensional reconstruction of cup prostheses2.1 The CLY single-arm three-dimensional measurement device (made inChina measurement technical institution) was used in measuring biologicalacetabular cup prostheses. All measure data were put into the same coordinate.2.2 The three-dimensional reconstruction of the cup prostheses model wasautomatically performed through the SolidWorks 2003.3. The computer simulative comparison biomechanicalExperiment of theinfluence on the load distribution around the acetabular form different position ofthe none-cement acetabular components3.1 the limitation analysis of the pelvic model.3.2 The computer simulative comparison biomechanicalExperiment of theinfluence on the load distribution around the acetabular from different positionmoving-entad of the none-cement acetabular components was carried out and theinterface Mises load distribution,shear load were measured under the one-foot astand condition.[Result]1. The reconstructed pelvic midel of acetabular dtsplasia is helpful tounderstanding the transfer of load on the pelvic. it also provides the refrences forthe custom made pelvic research.the pelvic finite element analysis is provedfeasible by present study.2. The major load distribution area is around the post-superior region in theacetabular.3.Following the acetabular wall entad , Mises loading augmented gradually,shear loading minished gradually.4. Sum up in a few words, Mises load distribution is a vital factor, and thatshear load distribution is a secondary factor, so the range of the acetabular wallentad will be -1~+1 millimitre, especially at +1millimitre.[Conclusion] The distance of the acetabular wall entad from -1~+1millimitreis definited as the safe range, and in the THR surgery of severe acetabulardysplasia, the acetabular wall entad should be put in this range. The reconstructedpelvic midel is helpful to understanding the transfer of load on the pelvis. And itwill be an epoch that calculating machine simulate the method of clinicaloperations. it also provides the pelvic finite element analysis is proved feasibleby present study.