Total En Bloc Spondylectomy For Treating Thoracolumbar Tumors And Its Related Research

PartⅠ:Treatment of thoracolumbar tumors with total en bloc spondylectomy:the oncologic and stability reconstructive resultsBackground Primary spinal tumors are relatively rare. Benign spinal tumors account for 1% of all primary osseous tumors, and nearly 5% for all malignant tumors. However spinal tumors cannot treated through en bloc resection of tumor segment as long bone tumors of limb because of the special anatomic structure of spine including anterior abut great vessels and visceral organs, bilateral nerve roots and spinal cord in spinal canal. Once the spinal tumor recurs, the possibility of resecting the recurred tumor is slim. As s result, the treatment of spinal tumors has been a thorny difficult problem for many years with extreme surgical difficulty, high relapse incidence and poor prognosis. Recently, with development of imageology, adjunctive therapy, surgical techniques and reconstructive instruments, the surgical staging systems for spinal tumors have been proposed according to their characteristics and the total spondylectomy has been developed that made it possible to resect spinal tumor radically. Two methods were prevalent between late 1960s and late 1980s, named "piecemeal resection" and "eggshell technique" which developed by Heinig in 1970s, but both are intralesional resection and the postoperative relapse incidence is pretty high. In the late 1970s and early 1980s, en bloc spondylectomy was first put forward by Stener and Roy-Camille. Then in mid 1990s one Japanese scholar Tomita proposed improved total en bloc spondylectomy (TES) through posterior approach and brought forward their own surgical classification system for spinal tumors. The spine was divided into two parts (anterior vertebral body and posterior spinal accessory) by cutting off bilateral pedicle though posterior approach. The prognosis of spinal tumors is better than befor after this technique has been used preliminarily. It was not until 2006 that we began learning this technique from one translated articles of Tomita and developing it in China.Objective To improve the technique and the surgical instruments of total en bloc spondylectomy and to observe the therapeutic effect of spinal tumors and the results of stability reconstruction using this technique.Method From January 2007 to October 2009 there were 15 patients with thoracolumbar tumors,9 males and 6 females, with average 43 years old (range:19～63 years). Tumors were distributed in T8 (n=2), T9 (n=1), T10 (n=2), T12 (n=3), Li (n=2), L,4(n=2), L2 (n=l) and L3 (n=2). There were haemangiomas (n=4), giant cell tumors of bone (n=5), aneurysmal bone cyst (n=1), Ewing's sarcoma (n=1), plasmocytoma (n=1), neuroblastoma (n=1), osteoblastoma (n=1), Metastatic malignant fibrous histiocytoma (n=1). According to Tomita classification system there were 1 type-3,7 type-4,5 type-5,2 type-6. According to WBB surgical staging system, tumors located in 4-9 sectors in 3 cases, in the vertebral body crossing 4 sector or 9 in 9 cases and crossing 4 and 9 sectors in 3 cases. Preoperative Frankel grading showed grade A in 1 case, grade C in 1, grade D in 7, grade E in 6. The average VAS score was 5.2. All the 15 patients were treated with improved total en bloc spondylectomy under electrophysiological monitoring of spinal cord. The operations were successful in 12 patients and unsuccessful in 3 which spinal tumors were resected piecemeal.4 patients were treated through one-stage combined anteroposterior approach and 11 patients through one-stage posterior approach. The anterior reconstructions included titanium mesh cages filled with bone or bone cement in 13 cases, titanium mesh cage with strengthened rings in 1 case and artificial vertebral body replacement in 1 case. The posterior reconstruction included multiple segmental fixation with pedicle screw-rod system in 12 cases and short segmental fixation in 3 cases. The massive bone auto-graft was employed in 8 cases. Patients began ambulation after being in bed for 1-3 months postoperatively. The follow-up contents contained operative time, blood loss, local pain, recovery of spinal cord function, tumor recurrence, bone fusion and spinal stability.Results Some new surgical instruments were designed by ourselves according to operating conditions. In 12 patients performed total en bloc spondylectomy successfully, the duration of surgery was from 340 to 610 min (average,466.7 min), the blood loss was from 3000 to 10200 ml (average,5200 ml) and the blood transfusion was from 2800 to 9600 ml (average,4350 ml). The complications related to operation comprised hemopneumothorax, intercostal nerve pain, stress ulcer and bleeding and so on. All patients were followed up from 6 to 27 months (average,18 months). The patients with neurological dysfunction recovered from grade A to grade D in 1 patient, and to grade E in others. The average VAS score was 0.5. One patient with plasmacytoma suffered from progression of disease. One died of other reason and all the residual were free from relapse. The stability of spine was evaluated by X-ray and CT three-dimensional reconstruction. The Cobb angle of upper and lower vertebral body adjacent to involved vertebrae in sagittal plane was from-26.7°to 12°(average,-2.77) just postoperatively and. There were 2 patients with screw-rod breakdown and 2 patients with internal fixation loosening. The measurement of titanium mesh cage subsided into adjacent vertebral bodies was average 7.5mm. The Cobb angle of upper and lower adjacent vertebral body of involved vertebrae at the last follow-up or before reoperation was from-17.5°to 57.2°(average,13.69°). The revision surgery was perfomed in 3 patients, through combined anteroposterior approach in 2 and only posterior approach in 1.Conclusion Total en bloc spondylectomy significantly increases the therapeutic effect of spinal tumors, although accompanied with high difficulty and massive bleeding. The application of self-designed instruments ensures the successful completion of the surgery, but in some patients the en bloc resection is extreme difficult because of the massive bleeding, greater paravertebral tumor or entering tumor mass and should not be maintained and piecemeal resection should be performed. After total spondylectomy the reconstruction with titanium mesh cage and pedicle screw-rod system cannot provide sufficient spinal stability with many complications. Improvement of this method is imperative. The anterior reconstruction should be improved instead of the titanium mesh cage and the anterior fixation may be employed if necessary so as to get better support and fusion for anterior and middle columns of spine. Posterior long segment fixation with pedicle screw-rod system and massive bone graft can achieve short-term firm fixation and long-term fusion-stabilization. Thoracolumbosacral orthosis make it possible for patients to ambulate early without failure of internal fixation. Part II:The designing and application of instruments for total en bloc spondylectomyBackground In the middle of 1990s, Japanese scholar Tomita et al. reported total en bloc spondylectomy (TES) for treating spinal tumors that had got good therapeutic effect. TES consisted of en bloc laminectomy and en bloc corporectomy by bilateral pediculotomy through posterior-only approach. In China, It was not until 2006 that we began learning this technique from one translated articles of Tomita and developing it. As a new developed operation, Some new surgical instruments were designed for TES by Tomita's team, which included T-saw, teeth-cord protector, vertebral spatula, T-saw guide. These new instruments ensure this difficult operation performed successfully, but are not easy to get and use in China that hampers TES domestic developing severely.Objective To design, produce and employ initially some new surgical instruments for TES according to the related anatomical measurements and the characters of TES, Method 6 fresh frozen spinal specimens were used to measure to get the height of intervertebral foramen, the height and width of pedicle, the distance between pedicle and nerve roots and dura mater, the transverse diameter, central sagittal diameter and height of vertebral bodies. The vertical distance between anterior vertebral body and dorsal skin was measured on transverse images of CT or MRI. The distance between the incised skin during operations was measured intraoperatively. Then osteotome for pediculotomy, spinal cord protector and vertebral body retractor were designed and applied in TES.Results These three new instruments were produced. The osteotome for pediculotomy with curved head was placed into the intervertebral foramen through the adjacent transverse process and reached the superior edge of pedicle. The direction of osteotomy was from cephalic to caudal along the pedicle and must not be deviated medially. The spinal cord protector, with two openings as saw passages between which the distance was larger than the transverse diameter of spinal cord, was placed between the cord and vertebral body. The saw was constrained into the openings to protect the spinal cord. There were two vertebral body retractors which were placed anterior and lateral of the body to pull apart the paraspinal muscles and pleura, protect the big vessels and make enough surgical field. Conclusion The self-designed osteotome for pediculotomy, spinal cord protector and vertebral body retractor can meet the requirement of TES, but there are some shortages to be improved and perfected. PartⅢ:Bio-mechanical analysis of different anterior reconstructions after total spondylectomy and the finite element model establishementBackground After Total spondylectomy the continuity and stability of the spine should be rebuild. Titanium mesh cage, bone graft and pedicle screw-rod fixation is the frequently-used reconstruction currently in China. Due to spinal vertebral body taking about 70%～80% load of the spine, the anterior titanium mesh often collapses into the upper and lower vertebral bodies even when we take the posterior long-segment fixation. In addition to surgical damage of the vertebral end-plate, the main reason is the sharp ends of the ordinary titanium mesh and flat ends cannot adapt to the physiological curvature of the spine that will lead to local stress concentration and titanium mesh perforating end-plate and subsiding into vertebral bodies. In order to enhance the stability of the anterior reconstruction, some new reconstructive instruments have been designed. Titanium mesh with stabilization rings and artificial vertebral body are known widely. But compared to common titanium mesh they are seldom used, the mechanical advantages of them are not clear. Finite element method can summarize the spine structure, material properties, load boundary conditions with mathematical form. The effects of some parameters changing can be observed in the spine and the mechanical change in the spinal physiological and pathological course can be understood. The finite element method can provide more information than in vitro biomechanical test. So the establishment of finite element model of total vertebrectomy and spinal reconstruction will make a good foundation for future research.Objective To study the effect of different anterior reconstructive methods on the primary spinal stability after total spondylectomy and to establish the finite element model of total vertebrectomy and reconstruction.Methods 6 fresh spinal segments from T11 to L3 were used to establish the model of L1 total spondylectomy which were reconstructed by long-segment pedicle screw-rod system posterior and common titanium mesh, titanium mesh with stabilization rings and LIFT vertebral body anterior with primary 50N compression forces. On the bio-mechanical testing machine, we imposed axial compression (500N) and six kinds of pure torque (7.5 Nm) including flexion, extension, left and right lateral bending, rotation in order to simulate the physical activity of the spine. We loaded and unloaded circularly three times and the computer system recorded data automatically on the third time. The load-displacement curves were got and the segmental displacements between T12 and L2 were analyzed. The spine specimens (T11～L3) were scanned by CT and the images were imported into Minics software with the format of DCM to generate spine features contours. Through CAD software the true three-dimensional spine reconstruction was completed and real three-dimensional geometric parameters were accessed. Then a finite element models of T11-L3, pedicle-rod system and titanium mesh with auto-bone graft were delveloped throuth Ansys software. After L1 total vertebrectomy, the pedicle screw-rod system and titanium mesh were placed in position. And the finite element model of total spondylectomy and reconstruction was established.Results Under the same posterior long-segment fixation, the three anterior reconstruction methods all achieve the stability same as, even more than the intact spine in axial compression, flexion and lateral bending, but not in extension and rotation. Except for extension, The LIFT vertebral body can provide more stability than the common titanium mesh and the titanium mesh with stabilization rings (P <0.05). The finite element model of L1 total spondylectomy was established successfully, which was reconstructed with posterior long-segment pedicle screw-rod fixation and anterior titanium mensh.Conclusion The spinal physiologic curvature can be restored when the LIFT vertebral body is used to reconstruct the anterior defect after total spondylectomy. It has more mechanical advantages and can provide more stability than the titanium mesh with or without stabilization rings. The development of finite element model of total spondylectomy provides the foundation for future research.