Posterior Screw Fixation Research Articles

Does the Cage Position in Transforaminal Lumbar Interbody Fusion Determine Unilateral versus Bilateral Screw Placement?: A Review of the Literature.

This literature review examines the relative placement of the interbody cage with respect to the unilateral screw construct to address the need for bilateral screw placement versus unilateral screw placement. Transforaminal lumbar interbody fusion (TLIF) has become a widely used technique for correcting lumbar intervertebral pathologies. This review addresses the necessity for further study on the effects of the relative position of intervertebral cage placement on the outcome of lumbar spine surgery after TLIF with unilateral pedicle screw fixation. Previous studies have addressed various factors, including posterior screw fixation, cage size, cage shape, and number of levels fused, that impact the biomechanics of the lumbar spine following TLIF. A simple survey of the literature was conducted. A search of the English literature was conducted using the keywords ‘TLIF,’ ‘transforaminal lumbar interbody fusion,’ ‘graft placement,’ ‘graft position,’ ‘cage position,’ ‘cage placement,’ ‘unilateral pedicle screw,’ ‘unilateral TLIF cage placement,’ ‘lumbar biomechanics,’ ‘lumbar stability,’ ‘lumbar fusion,’ and ‘lumbar intervertebral cage’ with various combinations of the operators ‘AND’ and ‘OR’ and no date restrictions. Seventeen articles in the English literature that were most relevant to this research question were identified. To the best of our knowledge, there are no published data addressing the effects of cage placement relative to the unilateral screw on lumbar stability in TLIF with unilateral pedicle screw fixation. Investigation of the effects of cage placement is, thus, warranted to achieve optimal clinical outcomes in patients undergoing TLIF with unilateral pedicle screw fixation.

Prospective Multicenter Study of a Multistep Screw Insertion Technique Using Patient-Specific Screw Guide Templates for the Cervical and Thoracic Spine.

A prospective clinical study of a multistep screw insertion method using a patient-specific screw guide template system (SGTS) for the cervical and thoracic spine. To evaluate the efficacy of SGTS for inserting screws into the cervical and thoracic spine. Posterior screw fixation is a standard procedure for spinal instrumentation; however, screw insertion carries the risk of injury to neuronal and vascular structures. Preoperative bone images of the computed tomography (CT) scans were analyzed using 3D/multiplanar imaging software, and the screw trajectories were planned. Plastic templates with screw-guiding structures were created for each lamina using 3D design and printing technology. Three types of templates were made for precise multistep guidance, and all the templates were specially designed to fit and lock onto the lamina during the procedure. In addition, plastic vertebra models were generated, and preoperative screw insertion simulation was performed. This patient-specific SGTS was used to perform the surgery, and CT scanning was used to postoperatively evaluate screw placement. Enrolled to verify this procedure were 103 patients with cervical, thoracic, or cervicothoracic pathologies. The SGTS were used to place 813 screws. Preoperatively, each template was found to fit exactly and to lock onto the lamina of the vertebra models. In addition, intraoperatively, the templates fit and locked onto the patient lamina, and the screws were inserted successfully. Postoperative CT scans confirmed that 801 screws (98.5%) were accurately placed without cortical violation. There were no injuries to the vessels or nerves. The multistep, patient-specific SGTS is useful for intraoperative pedicle screw (PS) navigation in the cervical and thoracic spine. This method improves the accuracy of PS insertion and reduces the operating time and radiation exposure during spinal fixation surgery. 3.

Long-Term Minimum Clinically Important Difference in Health-Related Quality of Life Scores After Instrumented Lumbar Interbody Fusion for Low-Grade Isthmic Spondylolisthesis

Despite its growing popularity, no comparative studies have explored the minimum clinically important difference (MCID) of health-related quality of life scores following lumbar interbody fusion (LIF) performed on a single-level adult low-grade isthmic spondylolisthesis (LGIS). The purpose of this study is to investigate factors related to MCID of health-related quality of life scores following instrumented LIF performed on a single-level adult LGIS. Consecutive patients who underwent instrumented LIF for single-level LGIS were reviewed. The inclusion criteria were adult patients who underwent L4-5 or L5-S1, underwent anterior lumbar interbody fusion or transforaminal lumbar interbody fusion with a posterior screw fixation, and had a minimum 36-month postoperative follow-up period. MCID was defined as having an improved score of visual analog scale (VAS) back and leg pain >3 and Oswestry Disability Index (ODI) >12. Patients were subdivided into groups named "achievement" (A) and "nonachievement" (N) depending on their postoperative MCID for each health-related quality of life score category. One-hundred and five patients met the inclusion criteria. The overall achievement of MCID for VAS back, leg, and ODI was 80%, 73.3%, and 82.9%. MCID-VAS leg and ODI were less achieved at the L5-S1 level than at the L4-5 level. Postoperatively, disk height was higher and segmental lordosis (SL) was lower in group A of MCID-VAS leg. SL was lower in group A of MCID-ODI. We postulate that excessive SL does not affect lumbar lordosis; rather, it can result in lowering posterior disk height. The decrease in posterior DH may lead to a decreased foraminal height that, in turn, can lead to nerve root compression. Proper restoration of disk height and bone fusion is more important than restoration of more segmental lordosis or slip reduction for isthmic spondylolisthesis.

Anatomical variations of vertebral artery and C2 isthmus in atlanto-axial fusion: Consecutive surgical 100 cases

VA anomalies in extra- and intraosseous regions of the craniovertebral junction (CVJ) is considered very carefully during the posterior screw fixation for the atlantoaxial instability (AAI). This study aims to compare the incidence and variations of VA anomalies, isthmus and pedicle size of C2 in 100 patients with AAI due to congenital skeletal anomaly (CSA) and acquired disease by using three-dimensional CT angiograms (3D CTA) before surgery. The CSA group contained 48 patients and the acquired disease group consisted of 52. In the CSA group, Os odontoideum was the major cause with 43 patients. The causes of acquired disease were RA in 16 patients and OA in 36 patients. Five patients had the anomalous VA in only CSA group; fenestration 2 patients and persistent first intersegmental (PFIS) artery 3 patients. Between CSA and acquired disease groups, no significant differences were found in the isthmus height, internal height, and pedicle width of C2 except the right internal height that is bigger in CSA group. The high-riding VA (isthmus height <4 mm or internal height <2 mm) had no significant difference between CSA group (27.1%) and acquired disease group (34.6%). However, in acquired disease group, patients with rheumatoid arthritis had smaller left internal height (4.21 ± 1.63 vs. 5.51 ± 1.83 mm) and pedicle width (4.11 ± 1.05 vs. 5.05 ± 1.66 mm) of C2 than those of patients with degenerative osteoarthritis. Therefore, in the case of atlantoaxial fusion, we should contemplate VA anomaly and the high-riding VA, especially in patients with CSA and RA.

Posterior Subaxial Cervical Spine Screw Fixation: A Review of Techniques.

Study Design:A narrative literature review.Objectives:To review the surgical techniques of posterior screw fixation in the subaxial cervical spine.Methods:A broad literature review on the most common screw fixation techniques including lateral mass, pedicle, intralaminar and transfacet screws was performed on PubMed. The techniques and surgical nuances are summarized.Results:The following techniques were described in detail and presented with illustrative figures, including (1) lateral mass screw insertion: by Roy-Camille, Louis, Magerl, Anderson, An, Riew techniques and also a modified technique for C7 lateral mass fixation; (2) pedicle screw fixation technique as described by Abumi and also a freehand technique description; (3) intralaminar screw fixation; and finally, (4) transfacet screw fixation, as described by Takayasu, DalCanto, Klekamp, and Miyanji.Conclusions:Many different techniques of subaxial screw fixation were described and are available. To know the nuances of each one allows surgeons to choose the best option for each patient, improving the success of the fixation and decrease complications.

Hollow modular anchorage (HMA) screws for anterior transvertebral fixation in high-grade spondylolisthesis cases requiring 360 degrees in-situ fusion

Objective: 360 degrees in-situ fusion for high-grade spondylolisthesis showed satisfying clinical long-term results. Combining anterior with posterior surgery increases fusion rates. Anteriorly inserted transvertebral HMA screws could be an alternative to strut graft constructs or cages, avoiding donor site complications. In addition, complete posterior muscle detachment is avoided and the injury risk of neural structures is minimized. This study investigates the use of HMA screws in this context.Material and methods: Five consecutive patients requiring L4-S1 in-situ fusion for isthmic spondylolisthesis (four Grade 3 and one Grade 4) were included. The L5/S1 level was fused with an HMA screw filled with local bone and bone morphogenic protein (BMP2), inserted via the L4/5 disc space level. An L4/5 stand-alone interbody fusion with additional minimal invasive posterior screw fixation was added.Results: Transvertebral insertion of the HMA device was accomplished via a retroperitoneal approach to L4/L5 in all cases without exposure of L5/S1. Blood loss ranged from 150 ml–350 ml. No intraoperative complication occurred. One patient developed posterior wound infection requiring debridement. Solid fusion was confirmed with a CT scan after 6 months in all patients. All patients improved to unrestricted activities of daily living with two being limited by occasional back pain.Conclusions: HMA screws allow for effective lumbosacral fusion via a limited anterior exposure. This is technically easier than posterior exposure of the lumbosacral junction in high-grade spondylolisthesis requiring 360 degrees fusion.

Paper #16 - Lateral Trochlear Ridge: A Non-Articulating Safe Zone for Anterior-To-Posterior Screw Placement for Capitellum and Trochlea Fractures

Introduction: Distal humerus capitellar shear fractures are rare yet difficult to treat due to the complex fracture patterns and the osteochondral nature of the fragments, limiting optimal screw placement. Current instrumentation options (posteriorly-directed headless screws or retrograde screws) often result in poor fixation in these osteochondral fragments. The use of anterior to posterior screw fixation without countersinking the screw head would potentially improve the fixation strength of this complex fracture pattern. However, this technique is avoided due to concerns of articular impingement and cartilage damage. We set out to determine if there is a safe zone for fixation along the anterior lateral trochlea ridge (aLTR), and to ultimately to map this safe zone to guide screw placement.

Efficacy study of thoracolumbar fracture combined spinal cord compression with pedicle screw fixation and injured vertebral bone graft and facet joint grafting in the treatment of percutaneous multinuclear interspace approach

Objective To investigate the clinical efficacy of pedicle screw fixation and injured vertebral bone graft and facet joint grafting in the treatment of thoracolumbar fractures with spinal cord compression. Methods A prospective controlled study was conducted to analyze the clinical data of 60 patients with thoracolumbar fractures complicated with spinal cord compression from January 2015 to April 2017 in Shenzhen Pingle Orthopedic Hospital. The patients were divided into two groups in random number table method. Each group of 30 cases. The patients in the observation group were treated with pedicle screw fixation and injured vertebral bone graft and facet joint grafting in the observation group. The patients in the control group were treated with traditional posterior approach root screw fixation and transverse bone graft was performed. Tactile, vertebral height, motion and Cobb′s angle of the two groups were evaluated preoperatively and one month after operation. The patients were followed up by phone for six months. The ASIA score of the American Spinal Injury Association was used to evaluate the neurological function recovery of the two groups to observe the curative effect. Using SPSS 13.0 statistical software analysis, count data were expressed as percentage, measurement data were expressed by (±s), the two groups were compared using t test. Results The tactile sensation, vertebral height, motion and Cobb′s angle in observation group were significantly higher than those before operation (59.4 ± 17.3) scores, (58.8 ± 16.6) scores, (55.8 ± 23.6) scores and (54.5° ± 21.4°) scores respectively], in the control group [(75.6 ± 14.9) scores, (72.4 ± 14.5) scores, (76.8 ± 23.3) scores, (76.2° ± 23.5°)], with statistical differences (P<0.05). After the observation group was followed up for one month, the neurological function recovery was better than that of the control group (P<0.05). Conclutions Pedicle screw fixation and injured vertebral bone grafting via percutaneous multifidus muscle interspace can play an important role in the treatment of thoracolumbar fractures with compression of the spinal cord. It can significantly relieve spinal cord compression in patients. Key words: Thoracic vertebrae; Lumbar vertebrae; Fractures, bone; Pedicle screw; Vertebral bone graft

Closed Reduction in a "Hyperextended Supine Position" with Percutaneous Transsacral-Transiliac and Iliosacral Screw Fixation for Denis Zone III Sacral Fractures.

Background Herein, we demonstrate the clinical results of closed reduction in a hyperextended supine position with transsacral-transiliac (TSTI) and iliosacral (IS) screw fixations for Denis zone III sacral fractures. Patients and Methods Sixteen consecutive patients with Denis zone III sacral fractures who were treated between January 2009 and September 2016 were evaluated. All patients were treated using percutaneous TSTI/IS screw fixation during closed reduction performed with patients placed in a hyperextended supine position with body manipulation. The clinical and radiological results were evaluated, and the neurological outcomes were retrospectively assessed using Gibbon's classification system. The clinical outcomes were evaluated using the German Multicenter Study Group Pelvic Outcome Scale (POS). Results The sacral kyphotic angle was reduced by 18.06° ± 15.26° (mean kyphotic angle: pre-OP, 39.44° ± 20.56°; post-OP, 21.38° ± 7.39°), and fracture translation was reduced by 5.93 ± 4.95 mm (mean fracture translation: pre-OP, 8.69 ± 8.03 mm; post-OP 2.75 ± 3.97 mm). The mean initial Gibbon's score was 3.00 ± 1.32. Among 15 patients with a follow-up duration of over 12 months, the mean reduction loss in the sacral kyphotic angle was 5.87° ± 10.40° and was 1.00 ± 3.00 mm for the fracture translation. The final Gibbon's score was 1.80 ± 1.21, and 73.3% of patients had good results based on the POS score. Conclusions Although closed reduction in a hyperextended supine position with percutaneous posterior screw fixation is associated with some surgical limitations and technical difficulties, the procedure is minimally invasive and highly effective for stabilizing Denis zone III sacral fractures.

Posterior Screw Fixation in Previously Augmented Vertebrae with Bone Cement: Is It Inapplicable?

ObjectiveThe purpose of this study was to determine the feasibility of screw fixation in previously augmented vertebrae with bone cement. We also investigated the influence of cement distribution pattern on the surgical technique.MethodsFourteen patients who required screw fixation at the level of the previous percutaneous vertebroplasty or balloon kyphoplasty were enrolled in this study. The indications for screw fixation in the previously augmented vertebrae with bone cement included delayed complications, such as cement dislodgement, cement leakage with neurologic deficits, and various degenerative spinal diseases, such as spondylolisthesis or foraminal stenosis. Clinical outcomes, including pain scale scores, cement distribution pattern, and procedure-related complications were assessed.ResultsThree patients underwent posterior screw fixation in previously cemented vertebrae due to cement dislodgement or progressive kyphosis. Three patients required posterior screw fixation for cement leakage or displacement of fracture fragments with neurologic deficits. Eight patients underwent posterior screw fixation due to various degenerative spinal diseases. It was possible to insert screws in the previously augmented vertebrae regardless of the cement distribution pattern; however, screw insertion was more difficult and changed directions in the patients with cemented vertebrae exhibiting a solid pattern rather than a trabecular pattern. All patients showed significant improvements in pain compared with the preoperative levels, and no patient experienced neurologic deterioration as seen at the final follow-up.ConclusionFor patients with vertebrae previously augmented with bone cement, posterior screw fixation is not a contraindication, but is a feasible option.

Langerhans Cell Histiocytosis of the Thoracic Spine in an Adult.

We report a case of a 45-year-old man with a complaint of both leg weakness and hypoesthesia. Radiological evaluation revealed an osteolytic lesion of the ninth thoracic vertebra. The patient underwent posterior corpectomy with total excision of the tumor, mesh cage insertion with posterior screw fixation and subsequent radiotherapy. Histology confirmed the diagnosis of Langerhans cell histiocytosis (LCH). This case report presents the diagnostic work-up, histopathological evaluation, and the treatment procedures of rare LCH in the thoracic spine.

Application of Intraoperative O-Arm-Assisted Real-Time Navigation Technique for Spinal Fixation

This study explored the combined use of the O-arm and real-time navigation during spinal fixation. The clinical data for 60 patients undergoing spinal fixation, at Beijing Tsinghua Chang Gung Hospital between May 5, 2015 and May 1, 2017, were retrospectively analyzed. Pre-, intra-, and postoperative imaging findings were assessed. The patients were classified into the occipitocervical fusion (32 cases) and thoracic/lumbar/sacral spine fixation (28 cases, including 6 cases of percutaneous pedicle screw) groups. Lesion resections were performed microscopically. An O-arm, combined with real-time navigation, was used to assess spinal fixation. Efficacy was evaluated using operative times, Xray times, screw positioning, and complications. Within the occipitocervical fusion group, 182 screws were placed in the cervical spine and 96 in the occipital bone. However, 6 screws penetrated the bone cortex and were adjacent to the vertebral arteries, based on O-arm three-dimensional imaging; therefore, the precision rate was 96.7%. Within the thoracic/lumbar/sacral spine fixation group, 148 pedicle screws were implanted, with 4 initially outside the vertebral body, yielding a precision rate of 97.3%. Ten percutaneous pedicle screws were implanted and well positioned. O-arm scans were performed 3 times/patient, with an average of 20–30 min/time. Screw implantation times were 5–7 min (cervical spine), 8–10 min (thoracic spine), and 6–8 min (lumbar spine). Intraoperative O-arm scans, combined with real-time navigation technology, allow real-time observation of screw angles and depths, improving the accuracy and safety of posterior screw fixations and reducing the radiation dose and frequency experienced by patients and surgeons.

Relevance of Postoperative Magnetic Resonance Images in Evaluating Epidural Hematoma After Thoracic Fixation Surgery.

It is difficult to evaluate the significant findings of epidural hematoma in magnetic resonance images (MRIs) obtained immediately after thoracic posterior screw fixation (PSF). Prospectively, immediate postoperative MRI was performed in 10 patients who underwent thoracic PSF from April to December 2013. Additionally, we retrospectively analyzed the MRIs from 3 patients before hematoma evacuation out of 260 patients who underwent thoracic PSF from January 2000 to March2013. The MRI findings of 9 out of the 10 patients, consecutively collected after thoracic PSF, showed neurologic recovery with a well-preserved cerebrospinal fluid (CSF) space and no prominent hemorrhage. Even though there were metal artifacts at the level of the pedicle screws, the preserved CSF space was observed. In contrast, the MRI of 1 patient with poor neurologic outcome demonstrated a typical hematoma and slight spinal cord compression and reduced CSF space. In the retrospective analysis of the 3 patients who showed definite motor weakness in the lower extremities after their first thoracic fusion surgery and underwent hematoma evacuation, the magnetic resonance images before hematoma evacuation also revealed hematoma compressing the spinal cord and diminished CSF space. This study shows that epidural hematomas can be detected on MRI performed immediately after thoracic fixation surgery, despite metal artifacts and findings such as hematoma causing spinal cord compression. Loss of CSF space should be considered to be associated with neurologic deficit.

Effects of recombinant human bone morphogenetic protein-2 combined with pedicle screw fixation via dorsal-approach and vertebral body bone graft in treating type A thoracolumbar vertebral fractures

Objective To observe the effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) on patients with type A thoracolumbar fractures treated by pedicle screw fixation via dorsal-approach and vertebral body bone graft. Methods A retrospective case-control study was conducted to analyze the clinical data of 64 patients with type A thoracolumbar fractures treated from June 2012 to July 2015. The patients were divided into control group (32 cases) and research group (32 cases) according to the random number table. There were 22 males and 10 females aged (48.2±11.2)years old in control group. The injury was located at T11 in 2 cases, T12 in 4, L1 in 9, L2 in 7, L3 in 7 and L4 in 3 in control group. There were 24 males and 8 females aged (50.7±11.4) years old in research group. The injury was located at T11in 2 cases, T12in 4, L1in 8, L2 in 8, L3 in 7 and L4 in 3.The control group was treated with posterior pedicle screw reduction, internal fixation and allograft cancellous bone grafting through pedicle of vertebral arch. The research group was treated with rhBMP-2 (mixed with cancellous bone implants) on the basis of the control group. The time of operation, the amount of bleeding during operation, the volume of postoperative bleeding, the amount of postoperative drainage, the recovery of the injured vertebra, the Lane-Sandhu score, the time of fracture healing, and the postoperative complications were compared. Results There was no difference between two groups on operation time, amount of bleeding during operation or amount of postoperative drainage (P>0.05). No difference existed in two groups about Cobb angle and injured vertebral leading edge height at one week after operation (P>0.05). At the time of last follow-up (12 months), in research group, Cobb angle was lower while injured vertebral leading edge height was much higher than that of control group (P 0.05). Conclusion Compared with simple vertebral bone graft, posterior thoracolumbar vertebrae pedicle screw fixation with vertebral bone graft and hBMP-2 treatment for type A thoracolumbar fractures can restore vertebral stability, shorten the time of fracture healing and reduce the incidence of complications. Key words: Spinal fractures; Thoracic vertebrae; Lumbar vertebrae; Bone morphogenetic proteins; Bone transplantation

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Background Cervical spine injuries (CSI) are considered to be a major trauma with no well-established criteria for the choice of treatment technique. Objective Determine criteria for the choice of surgical technique to address CSI and review current tendencies in stabilization approaches used for CSI. Design Retrospective review and literature survey. Material and methods Retrospective review included 101 CSI cases with 24 craniocervical and 77 subaxial injuries, 48 CSI publications (9 books and guidelines, and 39 articles). The patients were treated with either anterior (ACDF, ACCF) or posterior fixation using screw constructs, or with 360° stabilization. Results Subaxial spine injury accounts for 75 % of all CSI. C2 vertebra injury is the most severe among craniocervical trauma. Posterior C1–C2 fixation with Harms and Magerl techniques remains the method of choice. SLIC and CSISS scoring systems are mostly used to assess subaxial injury. Anterior fixation is common for unstable subaxial injury. Posterior screw fixation has become more common. Conclusion Injuries to the cervical spine at the С2 vertebra fractures are most challenging, and posterior fixation is the method of choice for the operative stabilization. Subaxial injuries require a thorough assessment of posterior supporting complex integrity. Anterior fixation remains the most common method of treatment. Multipillar subaxial injuries require posterior fixation and 360° stabilization in the majority of the cases.

"Direct vision" operation of posterior atlantoaxial transpedicular screw fixation for unstable atlantoaxial fractures: A retrospective study.

The posterior screw fixation in atlas via posterior arch and lateral mass, also called C1 "pedicle" screw, combined with C2 pedicle screw fixiation has shown better biomechanical stability in unstable atlantoaxial fractures. However, its popularization has to fulfill the limitation imposed by anatomical characteristics. The aim of this study was to explore the manipulation, effect, and safety of the atlantoaxial transpedicular screw fixation under "direct vision" for the treatment of unstable atlantoaxial fracture. All the patients diagnosed with unstable atlantoaxial fracture, who received surgery treatment of C1,C2 internal fixation from January 2012 to December 2014 were reviewed. Only these patients that were diagnosed with atlantoaxial unstability secondary to trauma and were treated with atlantoaxial transpedicular screw fixation under "direct vision" and iliac autograft were included. The safety of transpedicular screw placement, postoperative outcome, atlantoaxial stability, autograft fusion, and complications was observed and analyzed retrospectively. The pain visual analog scale (VAS) and the Japanese Orthopedic Association (JOA) score were used as surgical curative effect evaluation standards. We reviewed a total of 92 patients diagnosed with unstable atlantoaxial fracture, who received surgery treatment of C1,C2 internal fixation from January 2012 to December 2014, and 87 patients were treated with atlantoaxial transpedicular screw fixation under "direct vision" and were included this analysis. A total of 306 transpedicular screws in atlas and axis were placed successfully. All cases were followed-up >12 months. The overall breach rate was 11.36%. None of the breaches resulted in new-onset neurological sequela. The neurological status in cases with bilateral upper extremities numbness and lower extremities weakness had improved after surgery. At the latest follow-up, the neck VAS and JOA scores were significantly improved (P < .01) than those preoperatively. No cases demonstrated implantation failure and bone graft absorption on the postoperative x-ray films and CT scans. Atlantoaxial transpedicular screw fixation under "direct vision" and iliac autograft for the treatment of unstable atlantoaxial fracture has shown simple manipulation and efficient performance. Thus, the technique of C1-C2 fixation is feasible in treating unstable atlantoaxial fracture.

Role of 3D printing positioning guide template in pedicle screw fixation of unstable atlas fractures

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-atlanto-axial junction. Key words: Atlas; Fracture fixation, internal; Rapid prototyping

Efficacy of one-stage posterior-anterior approach for treatment of severe thoracolumbar fractures

Objective To observe the outcomes of one-stage posterior short-level pedicle screw fixation combined with anterior fixation of severe thoracolumbar fractures. Methods A retrospective case series study was performed on 21 patients with severe thoracolumbar fractures stabilized by posterior short-level pedicle fixation combined with anterior internal fixation at one stage from January 2012 to December 2014. There were 16 males and 5 females, at age of 17 and 64 years [(38.7±11.4)years]. The involved segments included T11 in 2 patients, T12 in 5, L1 in 6 and L2 in 8. For AO fracture classification, type A fractures were seen in 4 patients, type B in 7 and type C in 10. Thoracolumbar injury classification and severity score (TLICS) was (8.12±0.87)points (range, 7-10 points). Frankel neurological performance scale was Grade B in 8 patients, Grade C in 11 and Grade D in 2. Operation time, blood loss, nerve function, kyphosis correction and complications were reported. Results Operation time was (234.5±57.3)min (range, 180-360 min), and blood loss was (387.4±124.4)ml (range, 260-950 ml). Time of follow-up was (19.8±3.5)months (range, 14-25 months). Nerve function of 18 patients was improved by at least one Frankel scale. Cobb angle was (4.1±5.3)° at postoperative 3 days and (4.0±4.9)°at the final follow-up, showing significant differences from that before operation [(-9.3±4.2)°] (P<0.05). While the difference of Cobb angle did not differ significantly at postoperative 3 days and at final follow-up. No cerebrospinal fluid leakage, vascular injury, incision infection or nerve function deterioration occurred. Conclusion One-stage posterior short-level pedicle screw fixation combined with anterior decompression and bone graft fixation is characterized by short operation time, few blood loss, good correction of traumatic kyphosis and good neurological recovery, indicating a good surgical choice for severe thoracolumbar fractures. Key words: Thoracic vertebrae; Lumbar vertebrae; Fracture fixation, internal

Design and biomechanical test of a new lateral lumbar intervertebral cage-plate complex instrument

Objective To design a new minimally invasive lateral transpsoas lumbar intervertebral cage-plate complex instrument and evaluate its biomechanical characteristics. Methods The 18 fresh calf lumbar specimens simulated by one-level extreme lateral interbody fusion (XLIF) were randomly divided into three groups as follows: standalone XLIF cage in group A, standalone XLIF cage combined with posterior bilateral pedicle screw fixation in group B, and lateral lumbar intervertebral cage-plate complex instrument in group C. The test states included intactness and solid fixation. The range of motion (ROM) of fusion segment was recorded and comparisons were performed between different simulated constructs in flexion, extension, lateral bending and rotation. Results The three fixation systems were all able to stabilize the surgical segments. The ROM of surgical segment of new lateral lumbar intervertebral cage-plate complex instrument was (2.00±0.28)°, (1.31±0.69)°, (2.17±0.69)°, (2.91±1.12)° respectively, and reduced to 63%, 63%, 45% and 47% of the intact level in flexion, extension, lateral bending and rotation. Apart from the ROM of flexion (P=0.000) and extension (P=0.026), there was no significant difference in ROM between group B and group C. Conclusion The new lateral lumbar intervertebral cage-plate complex instrument can effectively afford a better biomechanical stability of lumbar vertebrae than the standalone XLIF cage in extension, lateral bending and rotation, while it can reduce less ROM in flexion and extension than standalone cage in combination with posterior internal fixation. Key words: Lumbar vertebrae; Biomechanics; Intervertebral fusion cage; Spinal fusion

Safe Zone of Posterior Screw Insertion for Talar Neck Fractures on 3-Dimensional Reconstruction Model.

To investigate the optimal posterior screw placement and the geometry of safe zones for screw insertion in the talar neck. Computed tomography data for 15 normal feet were imported into Mimics 10.01 software for 3-dimensional reconstruction; 4.0-mm-diameter screws were simulated from the lateral tubercle of the posterior process of the talus to the talar head. The range of screw paths trajectories and screw lengths at nine locations that did not breach the cortex of the talus were evaluated. In addition, the farthest (point a) and nearest point (point b) of the safe zone to the subtalar joint at each location, the anteversion angle (angle A), which is parallel to the sagittal plane, and the horizontal angle (angle B), which is perpendicular to the sagittal plane, were measured. The safe zone was mainly between the 30% location and the 60% location; the width of each safe zone was 13.6° ± 1.4°; the maximum height of each safe zone was 7.8° ± 1.2°. The height of the safe zone was lowest at the 30% location (4.5°) and highest at the 50% location (7.3°). The mixed safe zone of all tali was between the 50% location and the 60% location. When a screw was inserted at point a, the safe entry distance (screw length) ranged from 48.8 to 49.5 mm, and when inserted to point b, the distance ranged from 48.2 to 48.9 mm. And inserting a 48.7 mm screw, 5.6° laterally and 7.4° superiorly, from the lateral tubercle of the posterior process of the talus towards the talar head is safest. The safe zone of posterior screw fixation have been defined applying to most talus, assuming the fractures are well reduced, this may strengthen the stability, shorten the operation time and reduce the incidence of surgical complications.