Objective To compare the influence of the dynamic device(DD) of pedicle screw fixation and its equivalent rigid device (RD) on bone mineral density and bone structure of the vertebrae. Methods 24 goats were randomly divided into 4 groups: control group, single posterolateral fusion group, dynamic device with posterolateral fusion group and rigid device with posterolateral fusion group. After 24 weeks postoperative observation, the animals were sacrificed and the fixed lumbar spines were harvested. The bone mineral density (BMD) of these harvested specimens was measured by quantitative computed tomography (QCT). Then the L3 segment was embedded in methyl methacrylate and sectioned after alcoholic dehydration. Undecalcified slides (50 ?m in thickness) were stained with toluidine blue. Quantitative histologic analysis was performed in a semiautomatic way. The static parameters consisted of trabecular bone volume (TBV), the mean trabecular plate thickness (MTPT) and mean trabecular spacing (Tb.Sp). The main dynamic histomorphometric parameter, bone mineralization rate (MAR), was calculated by measuring the mean distance between two flurochrome labelings. Results The BMD in the rigid device group decreased significantly compared with control group (P

[Objective]To investigate the influence of pressure on the proliferation of rabbit bone marrow stromal cells(MSCs) and explain the relationship of the hip prosthesis submerge and loosening with continuous pressure after revision of total hip replacement.[Method]A unit of MSCs pressure model was set up to load different pressures on MSCs cultured in vitro.[Result]MSCs showed more proliferation capacity under discontinuous pressure.MTT assay was used to determine the cell proliferation of primarily cultured MSCs under discontinuous pressure.The MSCs OD value of pressured groups was much smaller than the control group at different times.Various magnitudes and durations of the discontinuous pressure could significantly suppress MSCs proliferation with the magnitude-dependent.[Conclusion]At the early period after revision of total hip replacement,patients should lie and exercise on the bed until 6 weeks.Otherwise,the weight-bearing pressure may restrain MSCs proliferation which is harmful to union and may cause prosthesis submerge and loose.

ObjectiveTo analyze the stress contribution of different cement volume to the adjacent vertebral endplates in percutaneous kyphoplasty (PKP) so as to explore the possible mechanism of adjacent vertebral fractures after PKP.Methods The three-dimensional finite element model of osteoporotic thoracolumbar vertebral compression fractures was established to simulate vertebral body partial restoration (80％) with PKP.During the process,two doses of bone cement ( polymethylmethacrylate,PMMA) were filled in the vertebral body (4.0 ml bone cement filling 15％ of the vertebral body volume and 8.0 ml bone cement filling 30％ of the vertebral body volume).Endplate stress under conditions of axial compression,flexion and extension was analyzed. ResultsRegarding the two filling doses in PKP,the adjacent vertebral endplate stress under the above-mentioned conditions was all increased at T11 and L1 vertebral body compared with that before operation.Meanwhile,endplate stress had positive correlation with the cement volume and the stress concentrated largely in the anterior and middle parts of endplate.ConclusionsThe stress of adjacent vertebral endplate is positively correlated with cement volume,with anterior and middle parts of endplate as the stress concentration.The probability of adjacent vertebral fractures shows a rising trend with the increase of cement volume in PKP.

Objective To evaluate the mid-term clinical effects and the imaging changes of Coflex interspinous dynamic internal fixation for low back pain. Methods From February 2007 to June 2009,Coflex interspinous dynamic internal fixation was performed in a consecutive 45 patients. They included 26 males and 19 females, with an average of 51.4 years ranging in age from 45 to 70 years. Thirty-two cases were in L4.5 level, 11 in L5S1 level and 2 in both two levels. The patients were treated with limited laminectomy and implanted with Coflex device. Clinical outcomes were assessed by Oswestry disability index (ODI)scores and Japanese Orthopaedic Association (JOA) questionnaires before and after operation. The imaging examination was obtained to assess height of the intervertebral space, area of the intervertebral foramen,segment movement of the operation level, low lumbar curvature and signal of the lumbar disc on MRI. Results The follow-up time ranged from 10 to 34 months, with an average of 24 months. The ODI scores decreased significantly from 62.82±10.42 preoperatively to 11.80±3.35 postoperatively. The JOA scores were improved remarkably from 9.00±2.63 preoperatively to 24.65±1.86 postoperatively. The proportion with optimal effect was 89% (40 cases). The Cobb angle after operation of L4.5 and L5S1 level was 15.1°±3.9° and 16.3°±3.8° respectively, which was significantly decreased after operation. The range of motion of the L4.5 level increased from 6.5°±1.5° to 8.4°±2.6° while the L5S1 level did not change notedly. The heights of the dorsal intervertebral disc, distance of the spinous processes, intervertebral foramen height and area were significantly higher than those before operation. Conclusion The Coflex interspinous dynamic internal fixation is available to reserve segment movement, to increase intervertebral space height and foramen area. Meanwhile,it is effective to self-repair and prevent degeneration for the disc in adjacent levels.

Objective To analyze the incidence and risk factors of contralateral radiculopathy in patients after unilateral transforaminal lumbar interbody fusion (TLIF) surgery.Methods A retrospective study was conducted within 587 patients (average age 57.1 years,range 19-71 years) who underwent unilateral TILF from January 2010 to January 2014 in our hospital,including 334 males and 253 females.Patients were divided into a symptomatic group and an asymptomatic group.The causes of contralateral neurological symptom were evaluated according to the radiological data.The difference of pre-and post-operative contralateral foramen area (CFA),segmental angle (SA) and the clinical treatment outcomes (VAS,JOA score) were compared between two groups.Results Patients were followed up for 9-21 months,average 15.1 months.Post-operative contralateral radiculopathy occurred in 28 (4.8％) of the patients who underwent unilateral TLIF,including contralateral foraminal stenosis in 16 (57.1％,16/28),screw malposition in 5 (17.9％,5/28),contralateral lateral recess stenosis and/or newly developed disc herniation in 3 (10.7％,3/28),hematoma in 1 (3.6％,1/28),cement compression in 1 (3.6％,1/28),and unknown origin in 2 patients (7.1％,2/28).Nineteen (3.2％,19/587) of the 28 patients received revision surgery because of ineffective conservative treatment.Compared with the asymptomatic group,the difference of pre-and post-operative CFA was significantly smaller (-13.8±13.2 mm2) in symptomatic group,while the SA was significantly greater (7.0°±9.8°) in symptomatic group.The JOA score at 3 months after the surgery was significantly improved in asymptomatic group (63.0％±18.1％,P＜0.05).Conclusion The incidence rate of contralateral neurological symptom was 4.8％ in the present study.The potential risk factors associated with contralateral radiculopathy were predominantly contralateral foraminal stenosis and screw malposition.The excessive restoration of SA might have an effect on contralateral nerve compression,which should arouse the attention of the surgeon.

Objective To develop a three-dimensional finite element model of atlantoaxial instability and compare the biomechanical properties of percutaneous anterior transarticular screw (ATS) and posterior transarticular screw (PTS) fixations.Methods A pathologic three-dimensional finite element model of atlantoaxial instability was developed from CT images of the upper cervical spine of volunteers with the aid of softwares,such as Mimics,Freeform,and Ansys.Percutaneous C1-2 ATS and PTS fixation modes were simulated and implanted to the model.Under the preload of 40 N and force moment of 1.5 Nm in anterior flexion,posterior extension,lateral bending,and axial rotation,biomechanical properties of the two fixation modes were compared.Results Under the four loading modalities,both fixation techniques provided maximal inhibition on C1-2 movement.The maximal stress for ATS was larger than that for PTS and maximal displacement for ATS was smaller than that for PTS.Conclusions Both ATS and PTS provide similar outlook and are effective to stabilize the atlantoaxial joint.Biomechanical performance of percutaneous C1-2 ATS is better than that of percutaneous C1-2 PTS.

Objective To evaluate the effect of different preparation processes on preparation of the glial cell line-derived neurotrophic factor(GDNF)loaded microspheres and observe the biological activity of GDNF.Methods With polylactide-co-glycolide(PLGA)as the coating material,the GDNF-loaded microspheres were prepared by using double emulsion(W1/O/W2).Two-factor factorial design variance analysis was done to analyze the effects of the composition proportion of lactic acid(LA)and glycolic acid(GA)in PLGA and the stirring speed of multiple emulsion on particle size,entrapment efficiency,burst release and in vitro release characteristics of the GDNF-loaded microspheres.PC-12 bioassay was employed to detect the biological activity of the released GDNF so as to determine the optimal preparation process.Results The composition proportion of PLGA could affect the microspheres'burst release(P ＜ 0.05),with no effect on particle size and entrapment efficiency.with the higher.With higher proportion of GA,the release speed of GDNF in the microspheres was increased.When the stirring speed of multiple emulsion was increased from 1 000 r/min to 3 000 r/min,the particle size of the microspheres was decrease significantly(P ＜ 0.01),the burst release was increased markedly(P ＜ 0.01)and the in vitro release rate was accelerated.The activity of GDNF in the microspheres could last for about 20 days at 37℃,which was 10 days longer than that of single GDNF.Conclusions Double emulsioncan prepare the GDNF-loaded microspheres with high entrapment efficiency and suitable in vitro release time.In the meantime,the microspheres can extend the validity of GDNF.

Objective To discuss the clinical characteristics and treatment of upper cervical spine injuries in the elderly. Methods A retrospective study was done on clinical data of 28 elderly patients ( > 60 years old) with upper cervical spine injuries treated from January 2003 to December 2007. There were 20 males and 8 females, at age range of 60-86 years (mean 68.1 years). Injury causes included slip in 16 patients, traffic injury in eight and fall from height in four. Atlas fractures occurred in five patients and axis ones in 15,of which there were eight patients with odontoid fractures, six with C2 vertebral arch fractures and one with C2 body fractures. Upper cervical spine injury was combined with lower cervical spine injuries in five patients. There were combined atlantoaxial injuries including odontoid fractures combined with lateral atlas fracture in one and edontoid fractures combined with anterior atlas arch fracture in one. Atlantoaxial dislocation occurred in one patient and combined spinal injury in four. Of all, eight patients were treated conservatively, eight with open surgical operation and 12 with minimally invasive surgery. Results The average hospital stay was 16.5 days, with no statistical difference be-tween conservative treatment group and open surgical operation group ( P > 0.05 ). While the average hos-pital stay in minimally invasive surgery group was shorter than that in conservative treatment and open sur-gical operation groups ( P < 0.05 ). Of all, two patients in conservative treatment group and one in open surgical operation group died and the other 25 patients were followed up for average 16.8 months (9-56 months). The satisfaction rate was 50% in conservative treatment group, 72% in open surgical operation group and 75% in minimally invasive surgery group. Complications occurred in four patients in conserva-tive treatment group, three in open surgical operation group and two in minimally invasive surgery group. Conclusions With odontoid fracture the most common injury type, upper cervical spine injuries arema-inly caused by low-energy force and characterized by low mobidity of spinal cord injuries and high possi-bility of missed diagnosis in the elderly patients. The surgical treatment especially minimally invasive surgery can bring good results compared with conservative methods.

Objective To explore different treatment choices for unilateral cervical facet locking. Methods The study involved 32 patients with cervical unilateral facet locking. Successful reduction by the skull traction was done in eight patients, of whom three were fixated by the head and neck chest plas-ter after a month of traction. Five patients were treated with anterior decompression and internal fusion fixation. The other 23 patients resulted in failure of traction and then were treated with anterior reduction, discectomy and internal fusion fixation in 14 patients, subtotal vertebral decompression and bone graft fix-ation in three, posterior open reduction and anterior bone graft fixation in one, posterior reduction, fixation and internal fusion fixation in three and posterior reduction and decompression plus anterior discectomy decompression and bone graft fixation in two. Due to misdiagnosis, one patient was treated with anterior decompression and fusion eight months after injury. Results A follow-up for average 18 months showed cervical instability in two patients who were treated with only traction, without fusion. The patients treated with anterior cervical fusion obtained bone union after 12 weeks, with satisfactory cervical physiological curvature and vertebral height. There were no internal fixation complications or neurological complications. Conclusions The treatment of lower cervical unilateral facet locking needs a compre-hensive considerations on whether there associates with disc injury, posterior column fractures or spinal cord injuries. As for patients with lower cervical unilateral facet locking combined with traumatic cervical disc herniation, the anterior reduction and decompression is the choice of treatment. While for those with-out disc herniation, traction or posterior open reduction and fixation can be carried out directly.

Objective To study the feasibility and clinical effect of percutaneous C2 pedicle lag screw in treatment of Hangman's fracture and define the indications of the technique. Methods There were 9 patients including 5 males and 4 females at average age of 36 years (26-68 years). According to a Levine and Edwards System, there were 5 patients with type Ⅰ hangman' s fracture, 3 with type Ⅱ hangman' s fracture and 1 with type Ⅱ A hangman' s fracture. According to American spinal injury association (ASIA) system, the spinal cord function was ranked at Type D in 2 patients and Type E in 7. All patients achieved anatomic reduction by skull traction. Under general anesthesia, 9 patients were fixed with percutaneons C2 pedicle lag screw. The whole procedure was done under monitoring of "C"-arm fluoroscopy for safety and accuracy. Results All patients obtained bony fusion within 2-3 months, with no infection, neurological deficits, vertebra artery injury or other complications. CondusionsThe percutaneous C2 pedicle lag screw fixation is minimally invasive and effective for treatment of Hangman's fracture. During the course of treatment, the function of upper cervical spine remains unaffected.