Application of the techniques of pedicle screw fixation in t horacolumbar spine has forcefully promoted the development of spinal surgery. Th e key to the techniques is that the pedicle screw insertion must be located into the sole exact routeway of the three-dimensional-space, that is, into the inn er vertebral body through the pedicle according to the exact arrow plane angle a nd horizontal plane angle. Recently great development has been made in the resea rch on the techniques of pedicle screw insertion in thoracolumbar spine, especia lly in the supervising means during operation. The means have been developed fro m the traditional X-ray perspective or photograph apposition to the application of computer-assisted technique. This paper reviews and discusses the current d evelopment and prospects in the research on the techniques of pedicle screw inse rtion in thoracolumbar spine.

Objective To investigate the causes and clinical significance of cement leakage into disc space during kyphoplasty. Methods Since 2002, 178 patients with osteoporotic vertebral compression fractures underwent kypboplasty and 15 of them were detected intradiscal cement leakage and followed up more than 2 years (mean 2 years and 8 months). The mean injection of cement in these patients was 4.2ml.The series comprised 10 females and 5 males, with an average of 71.2 years old ( range, 54～84 years old).Visual analog scale was used to score back pain pre- and postoperatively. The height and MRI index of the involved disc were recorded and compared. Results The discs involved were as following: T10-11 for 4 cases,T11-12 for 1, T12L1for 4, L1-2 for 2, L2-3 for 3, L3-4 for 1. Cement leakage was detected in the disc above the fractured vertebrae in 10 cases, and in the disc below the fractured vertebrae in 5 patients. The back pain significantly alleviated and the average visual analog scale (VAS) score was decreased from 8.5±2.1 preoper-atively to 3.3±1.4 postoperatively (P< 0.05). The anterior disc height was (5.1±2.1)mm preoperatively and (4.8±1.9) mm at the final follow-up, the middle disc height was (7.4±3.2) mm preoperatively and (7.3±2.9) mm at the final follow-up, the posterior disc height was (4.9±2.5) mm preoperatively and (5.0±1.8) mm at fi-nal follow-up, the heights of intervertebral space were well maintained. The signal intensity decreased and became inconsistent in some discs, and the preoperative MRI index significantly decreased from 25482.4± 3467.5 to 18927.6±2519.4 at the final follow-up (t=1.967,P< 0.05). Conclusion Pain relief is impressive in patients with intradiseal cement leakage during kyphoplasty. However, cement leakage into disc space may accellerate the process of disc degeneration.

Objective To evaluate the long term outcome of spondylolytic spondylolisthesis treated with Steffee system and posterolateral fusion. Methods Thirty- four patients were followed up for an average of 77.2 months. The follow- up study include slipping percentage, slipping angle, heights of intervertebral space and foramen, fusion rate, screw broken rate and clinical outcomes. Results 1) Solid fusion was obtained in 88.2％ of patients. screw broken rate was 2.9％ . 2) Comparison of pre- and post- operative slip showed correction rate of 45.1％ . The heights of intervertebral space and foramen increased, slipping angle decreased. 3) During the period of follow- up, recurrence of deformity was found. 4) The subjective outcome was better than the objective outcome. Conclusion 1) Lumbar spondylolytic spondylolisthesis with radicular symptom need complete decompression and reduction as much as possible. 2) A positive slipping angle indicates significant shearing force and the need of an interbody fusion to restore the weight- bearing capacity. 3) Objective criteria is more suitable to evaluate surgical outcome.

Objective To evaluate the efficacy and safety of balloon kyphoplasty in the treatment of painful multi-vertebral osteoporotic compression fractures. Methods From October 2002 to April 2007, 42 patients (96 vertebrae) with painful multi-vertebral osteoporotic compression fractures underwent kyphoplasty. The group included 14 men and 28 women with an average age of 72.5 years (range 56-91 years). Each pro-cedure included insertion and insertion of balloon, fracture reduction and cement filling under "C"-arm monitoring. Preoperative and postoperative pain level, SF-36 score, vertebral height restoration, local kypho-sis correction and complications were recorded and analysed. Results All 42 patients tolerated the opera-tion well and were followed up for average 31.4 months (range 12-71 months). The mean VAS pain score decreased significantly from 7.1±2.4 preoperatively to 2.7±1.3 postoperatively, the mean height of anterior and medial vertebral body were (1.8±0.5) cm, (1.6±0.6) cm preoperatively and (2.3±0.6) cm, (2.2±0.7) cm postoperatively. No significant change of posterior vertebral height was recorded postoperatively.The mean correction of local kyphosis was 9.2°at each level. 6 of 8 subscahs measured by SF-36, including physical function, role function, bodily pain, vitality, role emotion, mental health, were significantly improved by the operation. Complications were found in 7 patients including 6 cases of cement leakage with no clinical symptoms (intradiscal cement leakage in two cases, paravertebral vessel leakage in two cases, paravertebral leakage in one case and cement leakage into canal in one case), and 1 case of pulmonary embelization with symptoms relieved after conservative treatment. Conclusion Kyphoplasty is effective and relatively safe for multi-vertebral osteoporotic compression fractures.

[Objective]To study the changes of biomechanical efficiency of absorbable balloon vertebraplasty associated with pedicle screw system for treatment of thoracolumbar fracture.[Method]Six fresh adult thoracolumbar specimens were harvested and 10 segmental specimens(T_(11)~L_1、 L_(2~4)、 L_(1~3)) were processed.After burst fracture created by free-drop test,the specimens were braced and reduced by APF pedicle screw,then absorbable balloon were placed through the traumatic vertebral pedicle and were infused with autosolidification calcium phosphate cement to process vertebroplasty.The stiffness in middle vertebrae were measured under flexion,extension,lateral flexion and torsion stress before fracture and after absorbable balloon vertebroplasty respectively.[Result]The crushing strength in traumatic vertebrae after vertebroplasty with absorbable saeculi increased showed 8% under flexion,15% under extension and 9.8% under lateral flexion,but with significant increasing under extension(P0.05).[Conclusion](1)absorbable balloon vertebraplasty associated with pedicle screw system conduces to the reconstruction of traumatic vertebrae,and making postoperative spinal biomechanical characteristics approach the level before fracture;(2)Vertebroplasty with absorbable sacculus for treatment of thoracolumbar burst fracture based on the premise that avoid the potential danger induced by leakage of bone cement,and can reestablish intact corporeal structure of traumatic vertebrae and restore their height essentially,so that spinal physiologic curve can be gained to restore and maintain,tardive lumbodorsal pain and spinal cord injury and nerve injury caused by secondary kyphosis can be prevented,this can fundamentally solve complications left over by thoracolumbar burst fracture treated using pedicle screw system simply.The new method prorides a rational method for clinical treatment of thoracolumbar burst fractures.

[Objective]To investigate feasibility and efficacy of clinical application of endoscopic anterior cervical decompression and fusion.[Method]With Metrx MED system and modified working tube and decompression instruments,endoscopic anterior cervical decompression and fusion were performed on 15 patients with cervical spondylotic myelopathy.A paramidline right transverse incision of 2 cm long was made.A channel between the neurovascular and visceral sheath was created through finger dissection.The dilators were inserted sequentially.An original one arm working tube or a modified,shortened working tube with double arms was inserted over the dilators.Then decompression and fusion with autologus graft was performed under endoscope.[Result]Once the tubular retractor was stably fixed throughout the operation,releasing of the discomfort was observed.All the compression tissue such as soft disc tissue or hard osteophyte and anterior longitudinal ligament or dura sac were clearly visualized under the endoscope.Shortened working tube provided improved visual field and increased manipulation space for the decompression instrument.The double arms enhanced stability of the working tube but could not eliminate moving of it during operation.Intraoperative blood loss was 200 ml to 800 ml.The operation lasted 80 to 210 minutes.The incision healed in one week.Postoperative discomfort in laryngeal region was light.All of the cases showed thorough decompression on postoperative MRI films and gained better spinal cord function at postoperative follow-up.No surgery-related complication were encountered.[Conclusion]Endoscopic anterior cervical decompression and fusion based on the use of a working tube is technically feasible.Compared with conventional method,this technique has the advantages of improved intraoperative visualization,thorough decompression,minimal trauma,quicker recovery and improved cosmetic result.Disadvantages waiting for further improving include:limited manipulation space,discomfort and potential hazards to the surrounding structure resulted from moving of the working tube.

Objective To describe the surgical technique for treatment of old traumatic posterior acetabular defects. Methods From March 1990 to March 1998, 6 patients were treated with a full thickness iliac crest autograft to reconstruct their posterior acetabular defects. There were 4 males and 2 females, the average age of the patients was 32 years. The acetabular defects were caused by traffic accident and delayed in treatment for 3 to 11 months. Results The duration of follow up was 2－ 10 years， the function of the hip joints were good in all of the patients, according to the criterion of d Aubigne six points. X－ ray film revealed that although the femoral head was not in exact congruence with reconstructed acetabulum, yet there was no dislocation. Slight degeneration was found in 3 cases. Conclusion Although this procedure did not exactly reproduce the anatomy of the hip joint, it restored the posterior stability, provided bone stock for the hip joints and prevented dislocation of the femoral head. So this procedure is useful for late total hip arthroplasty.

Objective To review the clinical results of cemented and uncemented revision total hip arthroplasty(RTHA). Methods The diagnoses included aseptic loosening of the femoral components in 23 cases, fractures around the tip of loosened femoral components in 3 cases. Of 26 cases, 10 cases(10 hips)underwent RTHA by the use of the second generation cementing techniques, 16 cases(16 hips)underwent uncemented RTHA with a long stem porous coated femoral component assisted with autografting. Results At an average of 6 years of follow- up for cemented RTHA, clinical results were evaluated as excellent or good in 5 hips(50％ ),fair in 3 hips(30％ ) and poor in 2 hips(20％ ), re- revision in 1 hip(10％ ). X－ ray film revealed definite loosening in 2 hips, probable loosening 1 hip, possible loosening 5 hips, and no loosening 2 hips. At an average of 5 years follow- up for uncemented RTHA,clinical results were evaluated as excellent in 9 cases(56％ ),good in 6 cases(38％ ), fair in 1 case (6％ ),no case need rerevision. X－ ray film revealed osseous fixation of the femoral components in 12 cases (75％ ), fibrous stability in 4 cases (25％ ). The apparent reconstitution of femoral bone structure present in the area of previous osteolysis or cortical thinning. Conclusion Clinical results of the uncemented RTHA are significantly superior to that of cemented RTHA. Reconstructing any structural bone loss with cancellous autograft and getting adequate mechanical fixation with a long stem porous- coated prosthesis may contribute to the good results of uncemented RTHA.

Objective To conduct biomechanical study and three dimensional finite element analysis on lumbar spondylolysis and spondylolisthesis treated with single vertebra reduction and fixation system(LSRF), and to evaluate the long term outcome of isthmic spondylolisthesis treated with direct repair and fixation with LSRF. Methods Biomechanical characteristics of LSRF was tested, and three dimensional finite element model of lumbar spondylolysis and isthmic spondylolisthesis was established, the stress of lumbar in spondylolisthesis was observed after fixation and reduction. Thirty two patients with spondylolysis and isthmic spondylolisthesis were treated with direct repair and fixation with LSRF designed by the authors from 1992 to 1995. Eighteen cases had spondylolysis, and the others accompanied with spondylolisthesis. The patients age was 28-46 years, with an average of 36.4 years. Results The biomechanical study and three dimensional finite element analysis showed that LSRF has good ability in reduction and rigid fixation. All patients were followed up for an average of 5.6 years. The latest radiographs showed that bony union occurred in 29 cases. There was no breakage and pullout of screws except dislocation of hook in 2 patients. By Henderson standard, the result was excellent in 22, good in 6, fair in 2, poor in 2. Conclusion LSRF has stronger fixation strength and higher fusion rate. Direct repair and fixation with LSRF is a good procedure for younger and middle aged patients with spondylolysis and isthmic spondylolisthesis.

Objective To study the variability of the parameters of the pedicle screw path and influencing factors of clinical significance. Methods A Picker PQ6000 Spiral CT was used to scan 736 vertebrae from C 3 to L 5 of 118 men and 80 women aged between 17 and 58. The largest transverse diameter, screw path length and e angle (the angle between the axis of the pedicle and sagittal plane) of each pedicle were measured. The contour of the vertebrae and the relationship of the sagittal axis of the spinal process, vertebral body and human body were inspected. Any discrepancy of these axes was measured and recorded. The gender, age, height and weight were recorded at the same time. Results Measurement of the biggest transverse diameter, screw path length and e angle at each vertebral level showed a wide range of value and quantity. Although the screw path length and the transverse diameter of the pedicle showed significant difference between man and woman, further covariance analysis for between subject effects revealed that no inter gender difference existed after the effects of height and weight were removed. Both height and weight showed significant positive correlation with the screw path length and transverse diameter of the pedicle, but no correlation with the e angle. Observation on the deformity of the vertebrae showed that the sagittal axes of the vertebral body and human body was discrepant in 14 thoracic and lumbar vertebrae; the sagittal axes of the spinal process and vertebrae was discrepant in 11 vertebrae; the transverse diameter of the pedicle was smaller than 4 mm in 14 vertebrae below T 9; 4 vertebrae showed lateral convex pedicle. Conclusion The parameters of the pedicle screw path varied in different subjects and different vertebral level with a large variability. The weight and height are two important factors to influence the parameters. Deformity is another factor which may lead to mistake of placement of the pedicle screw. To improve the accuracy of the pedicle screw, individual identification of the entering point and orientation should be considered and in some circumstances even special screws, should be used.