The Application Of Computer Simulation In Making Surgical Plan For Correction Of Kyphosis In Ankylosing Spondylitis

BackgroundsAnkylosing spondylitis(AS) is a chronic inflammatory disease. It causesprogressive ossification of the annulus fibrosus and other spinal ligaments thatultimately leads to rigid, kyphotic spine. In few patients, despite adequateconservative treatment, AS may still be lead to a severe fixed thoracolumberkyphotic deformity and a corrective osteotomy may be considered. The pediclesubtraction osteotomy was first described by Thomasen in 1985. In this technique,theposterior elements of vertebra in combination with the posterior wedge of thevertebral body are resected. Correction is achieved by passive extension of spine,thusclosening the posterior osteotomy with an anterior hinge,which made operation moresafety. At present, the surgical techniques are often in use to treat thoracolumberkyphotic deformity caused by AS. But, there is no consensus on the level of theosteotomy and on the exact degree of correction required. Therefore,there is a needfor a method of deformity planning for sagittal plane corrective osteotomies of thespine in AS. In recent years.computer technology has become more and more usefulin surgery and the computer assisted orthopaedic surgery has become a new but rapidly de veloping field. It's potential advantages include the increase of accuracy ofsurgical procedures, less invasive operations, better planning and simulation,reductiong of radiation exposure,and so on.The study include two parts. In the first part,we assess the outcomes of lumbarspinal pedicle subtraction osteotomy on single segment for correction of kyphosis inankylosing spindylitis.In the second part, a newly computer assisted operationplanning procedure are presented for deformity planning of sagittal plane correctiveosteotomies of the spine in AS. Objectives1. To assess the outcomes of lumbar spinal pedicle subtraction osteotomy on singlesegment for correction of kyphosis in ankylosing spindylitis.2. To Discuss the application of computer simulation of spinal osteotomy in makingsurgical plans for patients with kyphosis deformity due to ankylosing spondylitis.Methods1. 17 patients were treated with L2 or L3 pedicle subtraction osteotomy and internalfixation by pedicle screw system. All the patients underwent X-ray examinationsin standing position before and after the operations. The angles of total spinalkyphosis, thoracic kyphosis, thoracolumbar kyphosis,lumbar lordosis and sacralslope were measured and the preoperative and postoperative differences werecompared.2. 4 patients underwent CT scan before and after the operation and the collected datawere put into the Mimics 10.01 to reconstruct 3D images. Virtual vertebrectomieswere carried out on the models to guide actual operations. The corrected angle,the width of the lamina, the width of resected lumbar posterior marginal bone was predicted. In the model of virtual vertebrectomies and postoperativereconstructed ,the total spinal kyphosis angle, the distance between the cervical line on centerpoint of C7 and posterior-superior part of Sl , the distance of thespinous process and the distance of both sides of transverse process were measured and and compared.Results1. All the seventeen operations were well complete. The mean time of operationswas 2.5h and the mean bleeding was 950ml. The lumbar lordosis angle increase from 11.1±15.8°to 44.1±13.7°, the total spinal kyphosis angle and thethoracolumbar kyphosis angle improve from 40.2±13.9°and 30.2±7.8°to 5.4±14.2°and 19.8±12.2°respectively, the sacral slope increase from 10.7±11.8°to 25.7±10.2°,whereas thoracic kyphosis angle remained relative stable.2. The seven models was successfully reconstructed and virtual vertebrectomieswere well completed in every case. The mean predictive value of the correctedangle, the width of the lamina, the width of resected lumbar posterior marginalbone were 26.69°, 27.22mm,and 14.81mm. The mean predictive value of thetotal spinal kyphosis angle, the distance between the cervical line on centerpointof C7 and posterior-superior part of SI , the distance of the spinous process andthe distance of both sides of transverse process were 15.66°, 45.23mm, 63.43mm,51.44mm,48.97mm,while the mean real values were 14.21°, 44.85mm, 63.18mm,50.95mm,49.56mm.Conclusions1. Lumbar spinal pedicle subtraction osteotomy on single segment is a satisfactoryand reliable technique for correction of kyphosis in ankylosing spindylitis and the average correction of lumbarlordosis was 32.9°.2. Computer simulation of vertebrectomy can directly and accurately reflect thecorrection effects before surgery. The method of computer assisted operationplanning procedure is feasible and convenient for defining the best surgical plan.