Unilateral Screw Research Articles

Radiographic Analysis of Pedicle Screw Retractor-Assisted Transforaminal Lumbar Interbody Fusion for Single-Segment Spondylolisthesis in Adults: A Retrospective Study and Technical Note.

ObjectivesThe objective of this study was to introduce a retractor that can be temporarily installed on unilateral pedicle screws to achieve distraction‐reduction and nerve root protection, and to analyze the efficacy and safety of retractor‐assisted transforaminal lumbar interbody fusion (TLIF) in the treatment of lumbar spondylolisthesis.MethodsThis was a retrospective study of 125 patients who underwent retractor‐assisted TLIF for single‐segment spondylolisthesis from November 2017 to February 2021. Based on morphology, patients were divided into degenerative (N = 66) and isthmic groups (N = 59). Differences in demographics and preoperative characteristics between the groups were analyzed using the independent samples t‐test and χ 2 test. Changes in radiographic parameters (disc height, foramen height, spondylolisthesis degree, slippage length, and segmental lordosis) before and after surgery were compared using the paired samples t‐test. Logistic regression analysis was performed to analyze the relationship between facet joint angle (FJA) and degenerative lumbar spondylolisthesis (DLS).ResultsUnilateral screw retractor‐assisted TLIF significantly corrected spondylolisthesis and improved disc height and segmental lordosis (p < 0.05). There was no significant difference in foramen height between the two sides before and after operation (pre: 15.81 ± 3.58 mm vs 15.69 ± 3.68 mm, p = 0.599; post: 18.65 ± 2.31 mm vs 18.74 ± 2.26 mm, p = 0.516). The degree of spondylolisthesis in the DLS group before surgery was significantly lower than that in the isthmic spondylolisthesis group (17.70 ± 5.62% vs 25.18 ± 9.73%, p < 0.001), whereas a similar degree of correction could be achieved after surgery (5.91 ± 3.12% vs 7.16 ± 5.69%, p = 0.135). FJAs from L3/4 to L5/S1 were significantly smaller in patients with DLS than those in with isthmic spondylolisthesis (p < 0.05). Patients with facet sagittalization were more likely to have DLS (β: −0.101, odds ratio [OR]:0.904, 95% confidence interval [CI]: 0.874–0.934, p < 0.001), while the cut‐off FJA of L4/5 for predicting L4 spondylolisthesis was 53.19.ConclusionsPedicle screw retractor‐assisted TLIF is effective and safe in treating both degenerative and isthmic lumbar spondylolisthesis. The unilateral retractor has the capacity to maintain the disc height achieved by paddle distractors, which optimizes the nerve protection and distractor placement. Patients with an FJA on L4/5 <53.19 were more likely to have DLS.

An early experience of lumbopelvic fixation techniques at Alexandria University

BackgroundThe aim of lumbopelvic fixation is to obtain a solid fusion across the lumbosacral junction. There are many indications for lumbopelvic fixation, namely, spinal deformity in cases requiring long segment fusion, pelvic obliquity, pseudarthrosis at the lumbosacral junction, infection or osteolytic tumors, and pathologic fractures. The classical iliac screws should be contained within the iliac bone but have some disadvantages: excessive soft tissue dissection needed for accurate insertion, screw prominence with patient discomfort, and usually, a side connector is needed to connect the iliac screws to the rest of the construct. Lumbopelvic fixation by insertion of S2 alar-iliac (S2AI) screws was recently described to overcome these disadvantages. In this study, the authors present the initial results for the evaluation of lumbopelvic fixation through the insertion of S2AI screws in 19 consecutive patients operated in the neurosurgery department at Alexandria University.ObjectiveThe aim of the study was to evaluate the efficacy and complications of lumbopelvic fixation through the use of S2 alar-iliac screws.MethodsThe authors conducted a retrospective cohort study of data collected from the database of patients who underwent lumbopelvic fixation through the insertion of S2AI screws from 2016 to 2019 at a single institution.ResultsThere were 19 patients indicated for lumbopelvic fixation, operated by modern instrumentation systems using lumbar pedicle screws and S2 alar-iliac screws. There were 14 females and 5 males. The mean age at the time of the operation was 38.6 ± 19.4 years with a range from 11 to 65 years. There was a total of 37 S2AI screws, screw diameter was 7mm in all cases regardless of age, and the length of the screws ranged from 50 mm in a young female patient (11 years) to 90 mm in an old male patient (60 years). Two screws were inserted per patient except in one case with congenital scoliosis due to the bad bone quality and the multiple iatrogenic wrong paths. Postoperative VAS score for back pain was greatly improved in all patients after the first 6 months of follow-up from 8 ± 1.5 to 3.5 ± 1.2 (paired t-test = 11.182, P<0.001). All patients had a good spinal range of motion to maintain normal daily activities without any significant restrictions after the first 3 months of follow-up. Immediate postoperative radiological follow-up had revealed 2 cases of posterior pelvic breaches and one case with anterior pelvic breach but without clinical manifestations with no need for revision. Two cases of unilateral screw breakout were observed after the first 6 months of follow-up. Removal of screws after the first 6 months was done in one patient with spondylodiscitis due to the unresolved infection and screw pullout.ConclusionThe insertion of S2AI screws is an effective technique for lumbopelvic fixation with a relatively low rate of complications. Pelvic breaches are the commonest complications encountered during the insertion of S2AI screws, although no significant clinical morbidities were reported.

Does Laterality Matter? The Effect of Unilateral v. Bilateral Sacroiliac Screw Fixation on Personal Hygiene.

Retrospective comparative analysis of prospective cohort. To determine whether sacroiliac (SI) screw fixation ipsilateral to hand dominance compared to bilateral fixation impacts personal hygiene (wiping) after toileting. Inclusion criteria were adult spinal deformity (ASD) patients with long arthrodesis (≥T12-pelvis) who had undergone primary unilateral or bilateral SI fixation with a minimum of 2-years-follow-up. 117 consecutive patients were included and separated into 2 groups: bilateral SI fixation (BL, n = 61) and unilateral SI fixation (UNI, n = 56), with no difference in age. Of UNI patients, 10.7% (6) performed personal hygiene with a different hand after surgery, compared to 6.6% (4) of patients who received BL fixation (P = 0.422). All UNI patients who switched hands were right-hand dominant, and 5/6 received right-sided fixation. There was no statistical difference found between number of levels fused (<8, 9-11, or >11 levels) and changes in personal hygiene habits. Over a third of patients from both groups had difficulty performing personal hygiene after fusion (UNI = 39.3% BL = 36.1%, P = 0.719). SI screws increase the difficulty of performing personal hygiene; yet, the side of unilateral screws does not significantly change personal hygiene habits when compared to bilateral screw placement. Moreover, the length of the construct does not have a significant impact on ability to perform personal hygiene, cause changes in habits, or require the assistance of another individual. However, among our sample of individuals, bilateral fixation did result in a higher rate of revision instrumentation.

Suitability of the Subaxial Cervical Laminae for Laminar Screws in the Pediatric Population: A Radiologic Anatomical Study

Introduction: The laminar screw method was popularized during recent years. Since no data exist in the literature on its suitability for subaxial levels in the pediatric population, a radiologic anatomical study was planned to evaluate the suitability of the laminae for laminar screws in children. Methods: The laminar thicknesses from C3 to C7 were measured in axial sections in 120 pediatric patients using computed tomography. The patients were divided into 3 age-groups: ages 4–6, 7–9, and 10–12. Each age-group consisted of 20 boys and 20 girls. The suitability of the laminae was evaluated for 3.5-mm-thick commercially available screws and also for the 3-mm screws that could be produced in the future. If the height of the base of the spinous process is ≥ 9 mm, the segment was accepted as suitable for the bilateral screw, and ≥5 mm is for the unilateral screw. Additionally, laminar thickness and length were measured for possible short screws longer than 15 mm in the laminae that were distally thin but proximally thick. Results: The C4 and C5 levels had the thinnest (2.77 ± 0.6 mm and 2.81 ± 0.6 mm, respectively) and C7 had the thickest laminae (4.66 ± 0.6 mm) in all age-groups. No significant differences were found between boys and girls and right and left laminae. According to the age-groups, an increase in laminar thickness was possible by growing, but only C7 laminae thickness was statistically different between 10–12 and 4–6 age-groups (p < 0.001). The last rate of the suitability was 9.1% for the 3.5-mm-thick screws and 13.75% for the 3-mm-thick screws after deletion of the bilateral insertion due to the short base of the spinous process and adding the possible short screws in the distally thin but proximally thick laminae. The rates increased with age, but the only statistically significant difference was found between 4–6- and 10–12-year-old age-groups (p < 0.001). Conclusions: Laminar screws may be suitable for some levels of C7, C6, and C3 even in the young pediatric population. The use of thinner screws (3 mm) may increase the suitability rate. Therefore, laminar screw choice may be considered as a salvage method in pediatric patients, and all laminae may be evaluated individually for suitability. This study did not evaluate the safety and efficacy of the method in children, and these issues must be studied further.

A new transpedicular lag screw fixation for treatment of unstable Hangman\u2019s fracture: a minimum 2-year follow-up study

BackgroundA new C2 transpedicular lag screw designed by our team has been used in human cadaver spines for biomechanical testing, and the results showed that the biomechanical properties of the new C2 transpedicular lag screw were better than ordinary screws. The objective of this study is to analyze the clinical efficacy and safety of the new C2 transpedicular lag screw fixation for the treatment of unstable Hangman’s fracture.MethodsFrom March 2013 to June 2017, 25 patients who had unstable Hangman’s fractures were operated on with a new C2 transpedicular lag screw fixation. The patients included 18 males and 7 females whose ages ranged from 31 to 62 years (average 45.4 ± 9.3 years). The cause of the injury was a traffic accident in 17 patients and a fall from height in 8 patients. Other associated lesions included rupture of the spleen (1 patient) and rib fractures (2 patients). According to the Levine-Edwards classification, 17 patients were type II and 8 patients were type IIA, and according to the Frankel Neurological Performance scale, 8 cases and 17 cases were graded as spinal cord injury D and E, respectively. Twenty-three cases received bilateral screw fixation, and 2 cases had unilateral screw fixation because another pedicle was chipped. The whole procedure was accomplished with monitoring by “C”-arm fluoroscopy.ResultsThe mean follow-up time was 36 ± 12 months and ranged from 24 to 60 months. No obvious symptomatic or radiologic postoperative complications were found during the follow-up period. Six cases were restored from D to E while 2 cases remained D according to the American Spinal Injury Association (ASIA) grade. Pre- and postoperative visual analogue scale (VAS) and Neck Disability Index (NDI) were statistically different (P < 0.001). Osseous union was achieved in all cases, and the range of cervical motion recovered to the normal level up to the last follow-up.ConclusionsThe primary clinical and radiographic efficacies of a new C2 transpedicular lag screw fixation for the treatment of unstable Hangman’s fracture were satisfactory. This approach could be considered a simple, effective, reliable, and economic surgical method for managing unstable Hangman’s fractures.

Unilateral Pedicular Screws and Interbody Lumbar Spine Fusion in Unilateral Degenerative Pathology (Technique and Outcome)

Introduction: Lumbar degenerative diseases (LDD) is considered a common disease. Lumbar pedicular screw fixation and interbody fusion is one of the com¬monly used and effective surgical method in management of single-level lumbar degenerative diseases. Although bilateral pedicular screw (PS) fixation after lumbar interbody fusion is accepted as a standard surgical procedure providing rigid fixation with a great biomechanical stability and clinical benefits, the rigidity of bilateral (PS) fixation can cause device-related osteoporosis of the vertebrae which makes the adjacent segment prone to load and motion-induced degeneration. Therefore, the concept of using less rigid systems of fixation has been advocated. Aim of study: To evaluate effectiveness of unilateral pedicular screws fixation and interbody fusion in unilateral degenerative spine pathology. Patients and methods: This study included 34 patients with single level degenerative lumbar spine disease who were subjected to transforaminal interbody lumbar fusion (TILF) and unilateral transpedicular screws fixation between July 2017 and March 2019 in Ain Shams University hospitals. Results: The study was conducted on 34 patients with age ranging between 32-56 years (mean 45.12±7.80 years). There were 17 male and 17 female in this study. When comparing VAS back pain preoperatively and at postoperative intervals of 1,6 and 12 months, it showed highly significant improvement (P-value 0.000). Also when comparing VAS of leg pain preoperatively and at postoperative intervals of 1,6 and 12 months duration, it showed highly significant improvement (P-value 0.000). ODI preoperatively and at postoperative intervals of 1,6 and 12 months showed also highly significant improvement (P-value 0.000). Regarding the fusion rate, at 6 months postoperative 61.8% (21) of the patients had fusion grade 1,26.5% (9) of the patients had fusion grade 2 and 11.8% (4) of the patients had fusion grade 3. While at 12 months postoperative the percent of grade 1 fusion increased to become 85.3% (29 patients) and the rest were grade 2 fusions (14.7%) with no patients with grade 3 fusion. Conclusion: Unilateral pedicular screws and interbody fusion is a good modality of treatment for unilateral degenerative spine pathology.

Unilateral short-segment screw fixation and bone graft fusion for special upper cervical spine injury

Objective To investigate the clinical effect of posterior unilateral short segment screw fixation and bone graft fusion in the treatment of special upper cervical spine injuries. Methods A retrospective case series study was conducted to analyze the clinical data of 15 patients with upper cervical spine injury admitted to Shanxi Bethune Hospital from July 2012 to May 2017. There were nine males and six females, aged 10-69 years [(41.9±20.9)years]. There were eight patients with traumatic atlantoaxial dislocation, one with congenital atlantoaxial dislocation, two with atlantoaxial dislocation with nonunion of odontoid process, three with Anderson type II odontoid process fracture, and one with old odontoid process fracture. All patients had cervico-occipital pain to different degrees, slender unilateral pedicle and distinct stenosis of vertebral artery. All patients were treated with posterior unilateral screw fixation and bone graft fusion. The injury of spinal cord and vertebral artery, operation time and intraoperative blood loss were recorded. Visual analogue scale (VAS) was used to evaluate pain before and after operation, and Japanese Orthopaedic Association (JOA) score was used to evaluate spinal cord function and postoperative improvement rate before and at the last follow-up. The position of internal fixation and fusion of bone graft were observed by X-ray after operation. Results All 15 patients were followed up for 6-36 months [(20.4±8.6)months]. All the screws were implanted successfully at the first time, without spinal cord or vertebral artery injury. The operation time was 100-210 minutes [(131.3±32.0)minutes], and the intraoperative blood loss was 100-450 ml [(203.1±104.0)ml]. Preoperative VAS score was (7.9±0.9)points, and postoperative VAS score was (3.7±0.8)points (P<0.01). Preoperative JOA score was (12.1±4.4)points, and the JOA score at postoperative follow-up was (16.1±1.4)points, with the improvement rate of 68%. Postoperative X-ray showed good recovery of cervical spine sequence. One patient developed loosened internal fixation after the neck brace protection was removed one month after surgery, and the patient recovered after timely second surgical fixation and fusion. The remaining 14 patients did not have loosened internal fixation, fracture or loss of reduction, with bone fusion 6-12 months after surgery. Conclusion Posterior cervical unilateral short-segment screw fixation and bone graft fusion can restore cervical stability, relieve pain, and improve function recovery, which can be used as a complementary procedure to treat upper cervical spine injury with anatomic structure variation. Key words: Cervical vertebrae; Spinal fusion; Surgical procedures, operative

243. The effect of sacroiliac fusion and pelvic fixation on rod strain in thoracolumbar fusion constructs: a biomechanical investigation

BACKGROUND CONTEXT Hardware failure is a multifactorial and challenging problem frequently encountered by spinal surgeons. A common cause of construct failure is the mechanical strain that results from excessive force placed on the spine. In implanted hardware, increased rod strain can lead to construct failure and rod fracture. Clinically significant rod fractures are associated with loss of correction as well as new onset radiculopathy, pain, radiographic signs of pseudarthrosis, and the need for surgical revision. PURPOSE To investigate the effect of sacroiliac joint (SIJ) fusion and iliac fixation on distal rod strain in thoracolumbar fusions. STUDY DESIGN/SETTING In vitro biomechanical study METHODS Seven fresh-frozen human cadaveric specimens (T9–Pelvis) were used. Six operative constructs were tested to investigate changes in rod strain at L5–S1 and S1–Ilium rods: posterior pedicle screws and rods from T10–S1 (PS); PS+bilateral iliac screw fixation; PS+unilateral iliac screw fixation; PS+UIS+3 unilateral SIJ screws; PS+3 unilateral SIJ screws; and PS+6 bilateral SIJ screws. Uniaxial strain gauges were used to measure surface strain of rods during flexion-extension motion. RESULTS In flexion-extension, bilateral iliac screws added significant strain to L5–S1 when compared to long fusion constructs that ended at S1 (PS) (p CONCLUSIONS This biomechanical study examined the effect of pelvic fixation and SIJ fusion on distal rod strain in thoracolumbar fusions. Results showed that additional fixation below S1 to the pelvis significantly increased rod strain. Unilateral pelvic screws had the highest rod strain while SIJF did not affect rod strain. The authors believe these findings can help guide surgeons when associated risk of rod failure needs to be considered. FDA DEVICE/DRUG STATUS SI-LOK Screws (Approved for this indication).

5. A biomechanical investigation of the sacroiliac joint in the setting of lumbosacral fusion: the impact of pelvic fixation vs sacroiliac joint fixation

BACKGROUND CONTEXT The sacroiliac (SI) joint is a known source of lower back pain. Randomized clinical trials support sacroiliac fusion over conservative management for sacroiliac joint dysfunction. Clinical experience suggests degeneration of the sacroiliac joint in the setting of lumbosacral fusions. However, there are limited biomechanical studies to understand the effect of lumbosacral fusion on the sacroiliac joint. This study is a biomechanical investigation to understand the effect of pelvic vs sacroiliac joint fixation on the sacroiliac joint in lumbosacral fusion. Furthermore, researchers studied the effect of lumbosacral fixation on the SI joint in the absence of pelvic and SI joint fixation. PURPOSE To determine the immediate stability of various lumbopelvic fixation constructs. STUDY DESIGN/SETTING In-vitro biomechanical range of motion testing. METHODS Seven fresh-frozen human cadaver specimens were used. There was one intact and 6 operative constructs: (1) posterior pedicle screws and rods from T10–S1 (PS); (2) PS+bilateral iliac screw fixation (BIS); (3) PS+unilateral iliac screw fixation (UIS); (4) PS+UIS+3 contralateral unilateral SIJ screws (UIS+3SIJ); (5) PS+3 unilateral SIJ screws (3SIJ); and (6) PS+6 bilateral SIJ screws (6SIJ). A custom-built 6 degrees-of-freedom (6DOF) testing apparatus was used to simulate 3 bending modes: flexion extension (FE), lateral bending (LB), axial rotation (AR). Range of motion was recorded at L5–S1 and sacroiliac joint. RESULTS All 6 operative constructs had significantly reduced ROM at L5–S1 compared to the intact specimen in all 3 bending modes (p CONCLUSIONS This biomechanical investigation demonstrated the effects of various fusion constructs using pelvic and sacroiliac fixation in lumbosacral fusion. It adds biomechanical evidence to the literature showing adjacent segment stress in the SIJ in fusion constructs to S1. Unilateral pelvic fixation or SIJ fusion led to appreciable but nonsignificant reduction to the unfused contralateral SIJ. Finally, bilateral pelvic fixation showed the greatest significant reduction of movement at L5–S1 and was equivalent to bilateral sacroiliac fusion in reducing SIJ motion. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

Anterior Hollow Screw Fixation Combined with Posterior Lateral Mass Screws Fixation to Treat A Huge Tear Drop Fracture of The Axis

Teardrop fracture of axis is rarely seen, especially the huge type. The surgical approach is controversial and individualized in the literature. We reported a special case to share our experience of anterior hollow screw fixation combined with posterior unilateral lateral mass screws fixation to treat a huge teardrop fracture of the axis (HTDFA). A 42-year-old male was referred to our department; he presented neck pain after a vehicle accident. Neck movement was limited with no neurological compromise. Cervical x-rays showed a huge tear drop fracture of the anterior–inferior corner of the axis，the lower cervical spine degeneration and poor cervical curvature. Cervical CT confirmed the avulsed ratio of inferior endplate of axis up to 62%. Cervical MRI showed the anterior longitudinal ligament disruption associated with disk injury and instability of C2-3. In order to save the motion segment of C2-3 and decrease the possibility of lower cervical degeneration if C2-3 fusion occurs, a surgical plan involving anterior reduction, hollow screw fixation combined with posterior unilateral mass screws fixation was performed. The 3 months postoperative x-ray and CT scan showed the tear drop fragment had completely healed. The internal fixations were removed timely for 6 months after surgery. The patient had an excellent function of cervical spine without any clinical symptoms. The 12 months postoperative X-ray showed radiographic union of the bony fragment and a good motion range without any instability. We conclude that anterior hollow screw fixation combined with posterior unilateral lateral mass screws fixation can be the treatment of choice for HTDFA

Unilateral pedicle screw fixation and lumbar interbody fusion under the Quadrant tunnel for the treatment of prolapsed lumbar disc herniation in young patients

To explore the clinical effect of unilateral screw fixation and lumbar interbody fusion under the Quadrant tunnel to treat prolapsed lumbar disc herniation in young patients. Between January 2015 and January 2017, 18 young patients with prolapsed lumbar disc herniation were treated with unilateral pedicle screw fixation and lumbar interbody fusion under Quadrant tunnel. Among them, there were 10 males and 8 females, aged from 20 to 28 years old with an average of 22.5 years. The VAS, lumbar JOA scores were compared before sutgery, 1 and 3 months after surgery and at the final follow-up. The improvement of clinical symptoms and bone fusion rate were evaluated according to the improved rate of JOA score and X-rays data at the final follow-up. All 18 patients were followed up from 14 to 34 months with an average of 24.3 months. All incisions got primary healing, and no nerve root injury, screw loose or rupture, threaded fusion cage sink or other complications were found. The postoperative VAS, lumbar JOA scores were improved significantly(P<0.05). Neurologic function improved significantly in the final follow-up. The postoperative JOA improvement rate was excellent in 10 cases, good in 6 cases, and fair in 2 cases. Postoperative bone graft fusion rate was 100% at 3 to 6 months. Unilateral screw fixation and lumbar interbody fusion under the Quadrant tunnel is an effective and safe method in treating prolapsed lumbar disc herniation for young patients, it has advantage of short operation time, small trauma and short hospitalization time. However, the indications should be well considered.

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.

Sacral-Alar-Iliac Fixation in Children with Neuromuscular Scoliosis: Minimum 5-Year Follow-Up.

To investigate the 5-year outcomes of children with neuromuscular scoliosis treated with sacral-alar-iliac screws. We reviewed clinical and radiographic records of patients aged ≤18 years treated by 1 pediatric orthopedic surgeon for neuromuscular scoliosis with spinal fusion using sacral-alar-iliac pelvic anchors. Thirty-eight patients with a minimum 5-year radiographic follow-up (mean, 6.0 ± 1.2 years) were studied. The mean patient age was 13 ± 2.0 years, and 47% were female. The mean number of levels fused was 18 ± 0.7. Two-thirds (66%) of the patients were diagnosed with cerebral palsy. Between the preoperative period and final follow-up, the patients exhibited a mean correction of the major coronal curve of 79% (preoperative, 85° to final, 18°) and a mean 57% correction of the pelvic obliquity (preoperative, 16° to final, 7°). Patients maintained the correction of mean pelvic obliquity from the early postoperative period (6°) to final follow-up (7°). Preoperatively, 76% of the patients had a pelvic obliquity of >10°, compared with 26% of patients postoperatively. There were no cases of neurologic or vascular complications or pseudarthrosis. Radiographs revealed bilateral sacral-alar-iliac screw lucency in 8 patients; 4 of these patients had deep wound infections, and the other 4 were asymptomatic. Unilateral screw fracture was found in 1 patient with an 8-mm-diameter screw (1.3%; 1 of 76 screws); the patient was observed and remained asymptomatic. There were no cases of set screw displacement, screw back-out, or rod dislodgement. Sacral-alar-iliac screws are safe and effective pelvic anchors for use in children with neuromuscular scoliosis.

Unilateral atlantoaxial pedicle screw fixation plus structural iliac bone graft for treatment of unstable atlas fractures

Objective To evaluate the efficacy of unilateral atlanto-axial transpedicle screw fixation plus iliac bone graft for treatment of unstable atlas fractures combined with unilateral pedicle dysplasia or comminuted fractures. Methods A retrospective case control study was made on 44 patients with unstable atlas fractures surgically treated between January 2012 to June 2016. Unilateral atlanto-axial transpedicle screw fixation combined with iliac bone graft was performed for 22 patients combined with unilateral pedicle dysplasia or comminuted fractures in Group A[15 males, seven females; (37.5±13.4)years], and bilateral atlanto-axial transpedicle screw fixation combined with iliac bone graft was performed for 22 patients without unilateral pedicle dysplasia or comminuted fractures in Group B [14 males, eight females; (38.1±13.3)years]. Between-group differences were compared concerning operation time, intraoperative blood loss, length of hospital stay, success rate of screw placement, postoperative atlanto-axial stability, surgery-related complications, visual analog scale (VAS), Japanese orthopedic association score (JOA) and bone fusion. Results Mean duration of follow-up was 28.4 months (range, 14-48 months). In Group A, operation time was (123.4±18.2)min, blood loss was (218.5±80.2)ml, hospital stay was (7.1±1.0)d, success rate of screw placement was 100%, postoperative atlanto-axial stability of all patients was obtained, and no complications occurred. In Group B, operation time was (173.4±12.4)min, blood loss was (318.2±61.7)ml, hospital stay was (7.2±0.8)d, success rate of screw placement was 100%, postoperative atlanto-axial stability of all patients was obtained, and no complications occurred. There were significant differences in operation time and blood loss between the two groups (P 0.05). Conclusion Both treatments are effective, but unilateral atlanto-axial transpedicle screw fixation combined with iliac bone graft is associated with relatively shorter operation time and less blood loss and hence is considered as a better choice for treatment of unstable atlas fractures. Key words: Atlanto-occipital joint; Spinal fractures; Spinal fusion; Pedicle screws

Advantage side unilateral posterior C1 and C2 pedicle screw fixation for treatment of unstable Jefferson fractures

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 case-control 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 0.05). 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). 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. Key words: Atlanto-occipital joint; Spinal fractures; Internal fixators; Spinal fusion

The effect of screw tunnels on the biomechanical stability of vertebral body after pedicle screws removal: a finite element analysis

Posterior reduction and pedicle screw fixation is a widely used procedure for thoracic and lumbar vertebrae fractures. Usually, the pedicle screws would be removed after the fracture healing and screw tunnels would be left. The aim of this study is to evaluate the effect of screw tunnels on the biomechanical stability of the lumbar vertebral body after pedicle screws removal by finite element analysis (FEA). First, the CT values of the screw tunnels wall in the fractured vertebral bodies were measured in patients whose pedicle screws were removed, and they were then compared with the values of vertebral cortical bone. Second, an adult patient was included and the CT images of the lumbar spine were harvested. Three dimensional finite element models of the L1 vertebra with unilateral or bilateral screw tunnels were created based on the CT images. Different compressive loads were vertically acted on the models. The maximum loads which the models sustained and the distribution of the force in the different parts of the models were recorded and compared with each other. The CT values of the tunnels wall and vertebral cortical bone were 387.126±62.342 and 399.204±53.612, which were not statistically different (P=0.149). The models of three dimensional tetrahedral mesh finite element of normal lumbar 1 vertebra were established with good geometric similarity and realistic appearance. After given the compressive loads, the cortical bone was the first one to reach its ultimate stress. The maximum loads which the bilateral screw tunnels model, unilateral screw tunnel model, and normal vertebral model can sustain were 3.97 Mpa, 3.83 Mpa, and 3.78 Mpa, respectively. For the diameter of the screw tunnels, the model with a diameter of 6.5 mm could sustain the largest load. In addition, the stress distributing on the outside of the cortical bone gradually decreased as the thickness of the tunnel wall increased. Based on the FEA, pedicle screw tunnels would not decrease the biomechanical stability and strength of the vertebral body. A large diameter of screw tunnel and thick tunnel wall were helpful for the biomechanical stability of the vertebral body.

A prospective clinical study comparing MI-TLIF with unilateral versus bilateral transpedicular fixation in low grade lumbar spondylolisthesis.

Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) has become one of the standard techniques for approaching ipsilateral decompression, anterior column fusion, and posterior stabilization. This procedure is usually accompanied by the placement of bilateral transpedicular screws in the corresponding segment. The purpose of this study was to evaluate the clinical efficacy of unilateral screw fixation compared with bilateral fixation in patients diagnosed with low-grade symptomatic lumbar spondylolisthesis who underwent an MI-TLIF technique. A prospective and comparative study was performed in 67 patients with grade 1 symptomatic lumbar spondylolisthesis. The sample was allocated on both unilateral fixation group (n=33) and bilateral fixation group (n=34). Clinical outcomes were evaluated using Oswestry Disability Index (ODI), visual analogue scale (VAS) for leg and back pain, and Short Form 36 Health Survey (SF-36), preoperatively, and at 1, 3, 6, and 12 months postoperatively. Changes over time and differences between the groups were analyzed. Statistical analyses included: Friedman test, Student's t-test and Mann-Whitney's U. A two-tailed P value of <0.05 was considered significant. During 1-year of evaluation there were no significant clinical differences between both groups. Patients with grade 1 symptomatic lumbar spondylolisthesis treated with MI-TLIF with unilateral screw fixation had similar clinical results than those treated with bilateral fixation at 12 months postoperatively.

Comparison of curative effect of unilateral and bilateral vertebral pedicle screw instrumentation for treatment of thoracolumbar burst fractures

Objective To compare the efficacy of unilateral and bilateral pedicle screw instrumentation for treatment of thoracolumbar burst fractures. Methods A retrospective case-control analysis was made on 50 patients with thoracolumbar burst fractures free from neurological deficit admitted between January 2008 and October 2013. There were 37 males and 13 females, aged from 24 to 51 years (mean, 36 years). Injuries were caused by high falls in 23 patients, traffic accidents in 18 and crashing accidents in 9. Distribution of the injured segment was T11 in 6 patients, T12 in 16, L1 in 20 and L2 in 8. Based on the surgical procedures, the patients were assigned to unilateral pedicle screw fixation group (n=35) and bilateral pedicle screw fixation group (n=15). Operation time, intraoperative blood loss and hospital length of stay were recorded. Visual analogue scale (VAS), Oswestry disability index (ODI), kyphotic angle and anterior vertebral height were evaluated before surgery, after surgery and at 1-year follow-up. Results No screw lessening, screw breakage or infection occurred at 1-year follow-up. Unilateral and lateral pedicle screw instrumentation groups revealed no significant differences in operation time [(81.4± 10.0)min vs. (83.3±13.6)min], intraoperative blood loss [(194.0±65.4)ml vs. (212.0±61.9)ml] and hospital length of stay [(10.3±1.3)d vs. (9.9±1.5)d] (P>0.05). After operation, VAS and ODI in unilateral pedicle screw instrumentation group (3 points, 73.9) showed no significance from these in lateral pedicle screw instrumentation group (2 points, 72.1) (P>0.05). VAS was within 1 point and ODI was within 20 at 1-year follow-up, showing no significant differences between the two groups (P>0.05). After operation, correction of kyphotic Cobb angle and restoration of anterior vertebral body height in unilateral pedicle screw instrumentation group (8°, 26.7%) showed no significance from these in lateral pedicle screw instrumentation group (11°, 32.1%) (P>0.05). Loss of local kyphotic Cobb angle and anterior vertebral body height in unilateral pedicle screw instrumentation group (2°, 3%) showed no significance from these in lateral pedicle screw instrumentation group (1°, 2%) at 1-year follow-up (P>0.05). Conclusion Both methods have comparable efficacy in restoring vertebral height and improving spinal kyphosis for treatment of thoracolumbar burst fractures. Key words: Spinal fractures; Fracture fixation, internal; Pedicle screws

Use and modifications of cervical and upper thoracic laminar screws in posterior stabilization.

Laminar screw technique is used to stabilize C2 and other levels when other techniques cannot be performed. The patients underwent laminar screws at cervical and upper thoracic levels in our clinic during 5 yearswere evaluated retrospectively. In 25 patients, 6 to 82 years old,total 54 laminar screws were used. Most frequent diagnoses were cervical spinal stenosis and craniovertebraljunction anomalies.There were handicaps to perform other type of screwsin 19 out of 25 screws during first 4 years, and 9 out of 29 in the last year (p=0.0009).Two modifications were performed in some cases. In 4 segments with thin lamina, a shorter screw was performed to leave clear the thinnest part, and in 3 C2 levels with almost full length bifid spinous process,shorter screws were inserted from medial sides of the bifid processes with a more vertical orientation. There was ventral cortex penetration in 11 screws without new neurological deficits. One of them was removed because of its full thickness insertion into the spinal canal.Fusion rate was 75% in 16 patients followed radiologically longer than 6 months.In one patient out of 4 without fusion, unilateral screw was loosened, and in others laminar screws were not loosened. Laminar screw technique is easy, safe and effective at C2, C7 and upper thoracic levels. Some modifications may be required due to the anatomical variations.It can be used at other subaxial levels also in theselected cases that other techniques could not be performed.

Modified translaminar screw fixation in the cervicothoracic junction (C7-T2): a technical note.

To describe and illustrate a modified technique for using translaminar screw in the cervicothoracic junction (C7-T2). 12 patients (8 males and 4 females, average age was 52years) underwent insertion of unilateral or bilateral translaminar screws by using our modified technique. With this modified technique, a tiny unicortical "hole" was made at the middle of the contralateral lamina, and the screw can be directly visualized through the unicortical "hole" to prevent violating the spinal canal. With this modified technique, the mean operation time was 205min (range 145-360) and mean estimated blood loss was 445ml (range 260-1250). The mean length of the laminar screws was 27 (range 24-30) mm. The results of the 12 patients with an average follow-up of 17 (6-33) months demonstrated this modified technique to be safe and effective in the fixation of cervicothoracic junction. In this modified technique, a tiny unicortical "hole" which was made at the middle of the dorsal lamina of cervicothoracic junction (C7-T2). By directly visualizing the screw inserting against the dorsal cortices of the lamina, this modified technique can reduce the risk of violation of the spinal canal and shorten the operation time.