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 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 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 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.

Objective To summarize the surgical techniques and results of displaced complex ac-etabular fractures.Methods Ninety-eight cases of complex type o f acetabular fracture with dislocation were treated with open reduction and inte rnal fixation from March 1990to Sept ember 1999.Of the 98cases,fractures of the posterior column an d wall was seen in 9cases,T -shaped in28cases,transverse and posterior wall in 22cases,anterior and hemi-transverse in 2cases,both column in 37cases.Kocher -Langenbeck approach was adopted in 28cases,ilio-inguinal approach in 21cases,extended iliofemoral approach in 16cases,and double approachs(K -L +ilio-inguinal)in 33cases.Results Sixty-two cases(63.3%)had anatomic reduction,32cases(32.7%)satisfactory reduction,4cases(4.1%)unsatisfactory reduction.The rates of anatomic reduction in the early 4.5years and the latest 4.5years of this study were 50.0%and72.4%respectively.Seventy-eight cases were followed up from 2to 10yea rs,excellent and good rate for clinical results in anatomic and non-anatomic reduction group were 83.9%and 36.4%respectively,the difference was very significant (P

Objective To review and analyze the complications of spondylolisthesis treated wi th BAK interbody fusion cages.Methods One hundred and eighteen patients wi th spondylolisthesis were treated with BAK interbody fusion ca ges,the intraoperative and postoperative complications were reviewed,which include dural tear,nerve root injury,unsatisfactory cage position,cage retropulsion,cage subsidence and postlaminectomy adhesive arachnoiditis.Results The intraoperative complication ra te was 11%and the most commonly seen were dural tear 4c ases(3.4%),nerve root damage 3cases(2.5%)and unsatisfactory cage position 9cases(7.6%),2cases had both dural tear and unsatisfactory cage position,1patient had both nerve root injury and unsatisfactory cage position.The postoperative c omplication rate was 7.6%,which chiefly consisted of cage retropuls ion 3cases(2.5%),cage subsidence 4cases(3.4%),and postlaminec-tomy adhesive arachnoiditis 2cases(1.7%),2cases of cage retropulsion and 2ca ses of cage subsidence show partial nonunion,2cases of cage subsidence had arachnoiditis.Conclusion As a new technique,lumbar interbody fusion with BAK cages are r apidly gaining popularity,however,the complications described here suggest the importance of selection s of surgical indications and proper manipulations.[

0.05).2)a.There was no severe side effects related to cement in 20dogs,and no pulmonary embolic necrosis was found in autopsy.Cement leakage was frequent which occupied the spinal canal no mo re than 1/4of the median sagittal dia meter without major neurological complication.The epidural leaks we re related to the vertebral morpholo gy.b.The average peak temperatures were 70.5℃at the core,53.5℃at the in terface,40.8℃at the anterior corte x,and 40.5℃in the spinal canal.The temperature above 50℃lasted for 2.9minutes at the core,and 1.3minutes at the interface.In pathological examination,necrosis of osteocytes was found focally at t he periphery of the cement,and resid ual bone in this area showed signs of acti ve remodeling.3)The procedure was technically successful in all pa-tients,with an average injection am ount of 6.3ml cement per vertebral body.No clinically significant com-plications were noted.The 3slight e pidural leaks,1slight neural foram ina leak,and 5paravertebral leaks detected with CT had no clinical importance.Partial or complete pain relief was achieved in all patients as-sociated with improved mobility,an d 1patient experienced transitory worsening of pain followed by significant pain relief.Patients with vertebra l haemangioma or compression fractu res were discharged in 1-4days(average,1.6days)after the procedure.Of the 26patien ts,22were followed up from 6to 24mon ths(average,13.5months),partial or complete pain relief were sustained in 21cases,the other one experienced relapse of pain following partial pain relief,which was related to the deterioration of the metastases.Con-clusion Minimal invasive PVP is a valuable alternative in the treatment of painfu l vertebral haemangioma,osteoporotic vertebral fractures,and osteolytic metastases or myelom a,providing acute pain relief and ea rly mobilization in appropriate patien ts.[