Objective To investigate the stress characteristics of atlanto-axial bony structure under conditions of anteflexion,posterior extension,lateral flexion,and rotation after artificial atlanto-odontoid joint arthroplasty using three-dimensional finite element method and to improve the orientation of artificial atlantoodontoid joint from perspective of stress.Methods A three-dimensional finite element model of prosthetic atlanto-odontoid joint arthroplasty was created from CT images of the artificial atlantoodontoid joint and cervical vertebrae using software Mimics,Freeform,and Ansys.Stress characteristics of the model dealt with proneness,posterior extension,lateral flexion,or rotation loads were observed.Biomechanical performance of the bony structure of the model was analyzed and the orientation in improving the prosthesis was discussed.Results Anteflexion loading produced a maximum stress of 0.138 ×l08 N/m2 at the junction of lateral mass and posterior arch of the atlas,and 0.201 × 108 N/m2 at axial nail hole,contact point of plates with the axis,and posterior arch of the axis.Posterior extension loading produced a maximum stress of 0.666 × 107 N/m2 at junction of lateral mass and posterior arch of the atlas and 0.254 × 108 N/m2 at arch of the axis.Besides,stress concentration occurred at atlantoaxis nail hole.Right bending produced a maximum stress of 0.124 × 108 N/m2 at nail hole of right mass of atlas and 0.178 × 108 N/m2 at right contact point of the axis with plates.Right rotation produced a maximum stress of 0.847 × 107 N/m2 at junction of lateral mass and posterior arch of the atlas and 0.170 × 109 N/m2 at contact point of the axis with plates.The finite element model comprised 28 620 nodes and 107 441 units and provided good defining of the structural properties of artificial atlanto-odontoid joint arthroplasty.Under different loading conditions,the stress was mainly distributed in contact point of the vertebral body with plates,nail holes,junction of lateral mass and posterior arch of the atlas,and axial pedicle.Conclusions Prosthetic atlanto-odontoid joint scatters a part of the stress and alters the stress distribution of the atlas and axis from the intact condition.Finite element method can obtain complete analysis of the stress distribution of the artificial atlanto-odontoid joint arthroplasty.

Objective To evaluate the effect of type Ⅱ odontoid fracture,type Ⅰ Hangman fracture,C2-C3 disc injury on stability of C1-C2 and C2-C3 segments and investigate the clinical significance.Methods Ten fresh-frozen cadaveric cervical specimens (5 men and 5 women; 25-45 years of age,mean 35.7 years) were selected to test the stability of C1-C2 and C2-C3 segments in the settings of intact condition (control group),type Ⅰ Hangman fracture,type Ⅱ odontoid fracture,type Ⅰ Hangman fracture + type Ⅱ odontoid fracture,type Ⅰ Hangman fracture + type Ⅱ odontoid fracture + C2-C3 disc injury.Range of motion (ROM) and neutral zone (NZ) of those segments were measured.Results Compared with the intact condition,type Ⅰ Hangman fracture produced no significant variations in C1-C2 ROM in all loading modes and C2-C3 ROM during left and right lateral bending; type Ⅱ odontoid fracture produced no significant variations in C2-C3 ROM in all loading modes and C1-C2 ROM during left and right rotation; type Ⅰ Hangman fracture + type Ⅱ odontoid fracture revealed no significant variations in C1-C2 ROM during left and right rotation and C2-C3 ROM during extention; type Ⅰ Hangman fracture + type Ⅱ odontoid fracture + C2-C3 disc injury produced no significant variations in C1-C2 ROM during left and right lateral bending and extension-flextion and C2-C3 ROM in all loading modes (P ＜ 0.05).Conclusions Type Ⅰ Hangman fracture can reserve C1-C2 segmental left and right rotation and extension-flextion; type Ⅱ odontoid fracture can reserve C1-C2 segmental left and right lateral bending and extension-flextion; type Ⅰ Hangman fracture + type Ⅱ odontoid fracture + C2-C3 disc injury can reverse atlantoaxial rotationary stability and C1-C3 segmental stability in all directions.This study provides the biomechanical basis for clinical treatments and the related researches of internal fixation.

Objective To validate the safety and accuracy of a rapid prototyping drill template (RPDT) for posterior atlantoaxial transarticular screw placement and analyze factors for screw deviation.Methods Twelve normal cadaveric cervical spines were examined using 64 slice CT with 1-mm thick scan and data in Dicom format were recorded.After data was processed using software Mimics 10.01 for three-dimensional (3-D) model reconstruction,computer-assisted design of optimum trajactory for atlantoaxial transarticular screw placement was worked out and made into a drill template,where the surface was created as the inverse of axial posterior surface.The drill template was materialized in a rapid prototyping machine and used to place the screws.After surgery,the position of posterior atlantoaxial transarticular screw was evaluated by X-ray and CT scan.Screw entry point,angle and orientation of the optimal and actual trajactory were determined after fitting the position of the pre-operative and post-operative specimen in computer software and the redefining the 3-D coordinate axis.Results Twenty-four screws were implanted with no cortex perforation.Depth of the optimum save screw trajectory for atlantoaxial transarticular fixation was (37.34 ± 2.31) mm on the left side and (37.11 ± 2.21) mm on the right side.Introversion angles of the optimum save screw trajectory was 0° in both sides,but the actual angle was (0.15 ±0.58)°on the left side and (0.11 ±0.46)°on the right side.Elevation angle of the optimum save screw trajectory was (49.35 ± 1.62) °on the left side and (48.83 ± 1.83) ° on the right side,but the actual angle was (49.29 ± 1.68) °and (49.10 ± 1.45) °respectively.Average displacement of screw entry point in the x,y and z axis was respective (0.21 ±0.65) mm,(0.69 ± 1.48) mm and (0.39 ±0.11) mm on the right side,while (0.19 ± 0.66) mm,(0.53 ± 1.45) mm and (0.38 ± 0.13) mm on the left side.There were no statistically significant differences in deviation levels of entry point and orientation between the optimum and actual screw trajectory (P ＞ 0.05).Conclusions Causes for deviation in RPDT-assisted placement of atlantoaxial transarticular screw are mainly intrinsic factors of the hardware and software and human factors in the operation.RPDT is easy in operation and has individualized design,which greatly improves the accuracy of screw placement and reduces screw deviation.RPDT can be widely used in clinical practice.

Objective To explore an ideal screw insertion point and optimal trajectory for anterior axis pedicle screw (AAPS) so as to provide an anatomical basis for AAPS placement.Methods CT scan of the cervical spine was performed for 40 healthy Chinese adults.Then,the CT data were imported into the Mimics software to reconstruct the three-dimensional images of the axes.The data were divided into two groups according to the gender.The following data were measured:pedicle centerline minimal diameter on both left and right sides,pedicle axial length,the distance between entrance point and upper endplate,the distance between entrance point and median sagittal plane,the distance between entrance point and peak of crista lambdoidalis of C2 vertebral body,extraversion angle and sagittal angle.The screw fixation parameters for AAPS were measured using the Mimics software.Results There was no statistical difference between the left and right sides as well as between the genders (P ＞ 0.05).The entrance point for insertion of AAPS was recommended to be on (4.39 ± 0.67) mm from the upper endplate,and on (3.95 ± 0.44) mm from the median sagittal plane.The ideal pedicle axial length was (34.15 ± 2.93) mm,and the pedicle centerline minimal diameter was (7.04 ± 0.87) mm.The distance between the entrance point and the peak of crista lambdoidalis of C2 vertebral body was (1.45 ± 0.19) mm.The ideal extraversion angle was (30.80 ± 2.79) °,and the ideal sagittal angle was (36.35 ± 3.26) ° . Conclusion The ideal insertion pathway of AAPS placement can avoid spinal canal,foramen intervertebrale and other important anatomical structure,which is feasible in regard of anatomy.The insertion point can refer to the peak of crista lambdoidalis of C2 vertebral body.However,AAPS placement should be individualized in term of its anatomy variability.

Objective To investigate the clinical outcomes of pedicle screw fixation assisted with the 3D printing positioning guide template for treatment of unstable atlas fractures.Methods A retrospective case series review was made on 10 patients with unstable atlas fractures undergone direct posterior C1 pedicle screw fixation assisted with the 3D printing drill guide template from September 2012 to May 2015.There were 7 males and 3 females,with a mean age of 52.6 years (range,23-75 years).All patients complained of neck pain,stiffness and decreased range of motion without neurologic deficit.Preoperative skull traction was used routinely.After the three-dimension reconstruction of cervical vertebrae,ideal trajectory for C1 pedicle screws was designed with a complementary basal template for posterior surface of atlas corresponding anatomical structure.Then the drill guide template was materialized in a rapid prototyping machine and used during operation.Start point and direction of the ideal and actual trajectories were measured after matching the position of the pre-and post-operative patients' cervical spine.Safety of pedicle screw fixation was assessed in the transverse and sagittal planes of CT scan.Operation time and blood loss were recorded.Visual Analogue Scale (VAS) of neck pain was recorded before operation and 3 months after operation.Clinical efficacy,fracture reduction,stability and surgical complications were reviewed at the follow-up.Results A total of 20 screws were inserted safely.No significant differences existed in deviation of entry point and direction between ideal and actual trajectories (P ＞0.05).Operation time was 60-90 min (mean,75 min) and intraoperative blood loss was 110-300 ml (mean,160 ml).No spinal cord or vertebral artery injury was noted during operation.All patients were followed up for 12-36 months (mean,20.5 months).VAS was improved from preoperative 7.3 (6.3-9.5) points to 1.4 (0.3-2.5) points 3 months after operation (P ＜ 0.05).All patients had normal range of motion of the cervical spine 3 months after operation.Bony fusion was achieved 6 months after operation.At the follow-up,good cervical alignment was maintained with no instrument failure and C1.2 instability.Conclusion For treatment of unstable atlas fractures,direct posterior C1 pedicle screw fixation assisted with the 3D printing drill guide template can improve the precision of screw placement,reduce complications,and preserve the function of the occipital-atlantoaxial junction.

Objective:To study curative effect of Biqi Capsule on lumbar muscle strain. Methods:120 patients who meet the full diagnostic criteria were grouped into the treatment group (66 patients) and the control group (54 patients) at random. The treatment group was treated with Biqi Capsule per os,while the control group was treated with western medicine Composite Chlorzozazone tablets per os.The comprehensive curative effects on the two groups were summarized.Results:The total effective rate of the treatment group and the control group were 92.4% and 79.6% respectively;No significant differences in two groups in statistics (P=0.06).The VAS score of the treatment group and the control group were (0.95?1.63) and (1.83?2.39) respectively.The curative effect was found to be better in the treatment group than that in the control group (P

Objective To observe the correlation of MRI findings with treatment outcome of percutaneous kyphoplasty (PKP) in the acute phase of osteoporotic vertebral compression fracture (OVCF).Methods A total of 101 patients with single-segment OVCF undergone PKP in the acute phase were included in the study.There were 19 males and 82 females, at age range of 61 to 89 years (mean, 69.3 years).According to the T2WI signal intensity, the patients were divided into low signal group (Group A), low-medium signal group (Group B), medium signal group (Group C), and mediumhigh signal group (Group D).visual analogue scale (VAS) was used to evaluating the pain relief.Correlations of MRI signal with vertebral height, vertebral compression ratio, Cobb's angle change in each group were determined.Results All MRI images were shown as low signal in T1WI and high signal in FS-T2WI.On the T2WI images, the signal was medium-high in 14 vertebrae, medium in 18 vertebrae, low-medium in 31 vertebrae, and low in 38 vertebrae.Among four groups, the VAS score, vertebral body height, vertebral compression ratio and Cobb's angle changes before operation showed no statistical difference compared with those after operation (P ＜ 0.05).Conclusions MRI findings are primarily low or medium signal on T2WI images in the acute phase of OVCF, which shows insignificant correlation with effect of PKP.However, PKP is effective in the treatment of OVCF.

Objective To determine the treatment options for teardrop fracture of the axis and discuss the treatment efficacy.Methods Nineteen patients with teardrop fracture of the axis treated from March 2003 to June 2013 were retrospectively reviewed.Teardrop fracture of the axis accounted for 3.9％ of the cervical injuries and 11.4％ of the axis fractures over the same period.There were 15 males and 4 females,at age range of 21-56 years (mean,37.8 years).Injury was caused by traffic accidents in 12 patients,falls in 6,and hit from heavy objects in 1.Cervical imaging examinations (X-ray,CT and MRI) were performed on admission.Thirteen patients were immobilized for 3 to 6 months with the Halovest device,and six patients underwent anterior cervical surgery.No patients had neurologic deficit [American Spinal Injury Association (ASIA) grade E].Visual analogue scale (VAS),implant failure and bone fusion were recorded after operation.Results All patients were followed up for 12-18 months (mean,15.6 months).At the final follow-up,no implant loosening or breakage happened and 18 patients achieved bone union.Neck mobility returned to normal,which showed VAS improved from (7.5 ± 1.2) points to (3.1 ± 1.5) points.ASIA grade E remained in 18 patients,and one patient were progressed to grade D.Conclusions Teardrop fracture of the axis is rare cervical injury,and can be treated conservatively in most cases.However,surgery is often necessary when imaging findings suggest the existence of instability.

Objective To compare the clinical efficacy and fusion rate of unilateral and bilateral C1 and C2 pedicle screw fixation of unstable Jefferson fractures.Methods This retrospective casecontrol study enrolled 22 patients with unstable Jefferson fractures admitted between April 2012 and May 2015.There were 18 males and four females,with the mean age of 52.9 years (range,35-67 years).Mean preoperative visual analogue scale (VAS) was 6.09 points (range,4-8 points).According to the American spinal injury association (ASIA) classification,two patients were rated grade D and one patient grade C.Mean Japanese orthopedic association (JOA) score was 12.3 points.Bilateral C1 and C2 pedicle screw fixation was performed for 15 patients (bilateral group).Advantage side unilateral C1 and C2 pedicle screw fixation was performed for seven patients with extremely unstable fracture or narrow pedicle (unilateral group).Operation time,blood loss and surgical complications were recorded.VAS was used to evaluate the improvement of neck pain after operation.ASIA classification and JOA score were used to assess nerve function recovery.Atlanto-dental interval (ADI),srew position and bone fusion were evaluated after operation.Results All patients successfully completed the operation.Operation time was (119.5 ±21.2)min,and blood loss was (280.1 ±83.1)ml.A total of 74 screws were placed and CT scan showed satisfactory position of the screws.No complications were noted either during the operation or after surgery.All patients were followed up for mean 20.7 months (range,13-33 months).VAS was improved in both groups after operation (P ＜ 0.01),and there was no significant difference between the two groups (P ＞ 0.05).Two patients with ASIA grade D in bilateral group were improved to ASIA grade E after operation.One patient with ASIA grade C in unilateral group was improved to ASIA grade D after operation.JOA score increased to mean 15.7 points at last follow-up.ADI were decreased in both groups after operation(P ＜0.05),but there was no significant difference between the two groups (P ＞ 0.05).All patients had bony fusion 6 months after operation,with similar fusion rate between the two groups (P ＞ 0.05).Conclusion Advantage side unilateral screw fixation can be used for the patients with bilateral C1 and C2 pedicle screw fixation failure,for the technique can improve cervical pain and provide relatively high stability and fusion rate.

Objective To evaluate the biomechanical stability of anterior odontoid screw plate (AOSP).Methods Eight fresh-frozen cadaveric cervical spine specimens were subjected to stepwise destabilization of the C1-Ca complex,simulating a type Ⅰ Hangman fracture,type Ⅱ odontoid fracture,and the C2-3 disc injury.Intact specimens,fractured specimens,and fractured specimens with posterior,anterior fixation techniques were divided into six groups:control group (intact),injury group of type Ⅱ odontoid fracture and type Ⅰ Hangman fracture combined with C2-3 disk injury,after anterior cervical plate + odontoid screw + cage (ACP + OS + cage) group,after anterior odontoid screw plate (AOSP) fixation system group,after affixing rods from pedicle screws in C2 to lateral mass screws in C3 + odontoid screw (C2PS + C3LMS +OS) group,after affixing rods from pedicle screws in C1 to pedicle screws in C2 and lateral mass screws in C3 (C1 PS + C2PS + C3LMS) group.The range of motion (ROM) and neutral zone of C1-C2 and C2-C3 segment was tested.Results There was statistically significant difference between the C1PS + C2PS + C3LMS fixation group and the AOSP fixation group of ROMC1-C2 (P ＜ 0.05).During all loading modes,AOSP + Bone graft fixation significantly outperformed the ACP + OS + cage fixation in limiting ROMC2-C3.During flexion and extension,AOSP fixation significantly outperformed the C1PS + C2PS + C3LMS fixation and C2PS + C3LMS + OS fixation in limiting ROMC2-C3.Conclusion The AOSP fixation system has excellent biomechanical performance when dealing with type Ⅰ Hangman fracture,type Ⅱ odontoid fracture,and the C2-3 disc injury,and appear to be a safe and effective technique for dealing with the combined injury.