Fenestrated Screw Research Articles

Fenestrated screws in osteoporotic spine—Is there an association between the cement distribution and DEXA scan T score?

Abstract Purpose: Cement distribution in spinal stabilization with fenestrated screws is unpredictable in patients with osteoporosis. The objective of our study was an assessment of cement distribution while using fenestrated screws and to establish an association between cement distribution and the Dual Emission X-ray Absorptiometry (DEXA) scan T scores. Materials and Methods: Osteoporotic patients who underwent spinal stabilization with fenestrated screws by a single surgeon with a minimum follow-up of one year were included. Cement distribution (four zones comprising the vertebral body and the pedicle), a pattern of distribution (concentrated or scattered) and cement leakage were assessed on CT scans. Patients were categorized into two groups based on their DEXA scan T scores to test an association between the pattern of distribution of cement and the scores. Clinical improvement was determined using visual analogue scale and Oswestry disability index scores. Results: A total of 126 screws were analyzed in 20 patients with a mean age of 69 years and a mean follow-up of 18 months. Out of 126 screws, 114 (90.47%) had cement in Zones 1 and 2. In total, 58 screws had a concentrated pattern of distribution of cement, whereas 68 screws had a scattered distribution, and the odds ratio of a scattered pattern of distribution was 6.31:1 if the DEXA scan T score was “below (−)3.0.” Clinical improvement was calculated in percentage of change from the preoperative value (mean % visual analogue scale change = 65.13 ± 7.59 and mean % Oswestry disability index change = 43.14 ± 7.24). Conclusion: The pattern of cement distribution in fenestrated screws relates well with the DEXA scan T scores and their usage should be strongly considered in patients with poorer scores. However, there is no relevant difference between the pattern of distribution and the clinical outcome.

437 Percutaneous Juxtapedicular Cement Salvage of Failed Pedicle Screws: A Cadaveric Biomechanical Study

INTRODUCTION: Posterior spinal fixation with pedicle screw-based constructs is the gold standard for stabilizing the thoracolumbar spine; however, these constructs sometimes fail due to fatigue loading, necessitating revision surgery. A common hardware revision strategy involves open surgery for screw upsizing, with or without cement augmentation, and extension of fusion. Others have described good clinical outcomes following percutaneous juxtapedicular cement salvage of failing pedicle screws. The relative biomechanical properties of these various approaches has not been evaluated. METHODS: Thirty-two fresh, un-embalmed vertebrae from four cadaveric thoracolumbar spines were used for the study. The study was conducted in two phases. The first phase involved primary pedicle screw insertions and pullout strength testing to model critical pedicle screw failure. The second phase involved revision of failed pedicle screws followed by pullout testing. The four revision cohorts were: 1) Screw Upsizing, 2) Vertebroplasty (cement augmentation with replacement of primary screw), 3) Fenestrated Screws with cement augmentation, and 4) Juxtapedicular Cement Salvage. RESULTS: There was no statistically significant difference in primary fixation strength between the cohorts. The Screw Upsizing cohort exhibited inferior pullout strength compared to the other groups which involved cement augmentation. There was no significant difference in pullout strength between Vertebroplasty, Fenestrated Screws, or Juxtapedicular Cement Salvage cohorts. CONCLUSIONS: Cement augmentation confers superior pullout strength compared to screw upsizing only. The key finding of this study is that the technique of percutaneous juxtapedicular cement salvage is biomechanically non-inferior to other revision strategies that require an open procedure to perform.

Biomechanical Comparison and Three-Dimensional Analysis of Cement Distribution Patterns for Different Pedicle Screw Designs.

The purpose of this study to explore strategies for reducing cement leakage during cement-augmented pedicle screw fixation, we compared the cement distribution patterns and biomechanical strengths of different types of cement-augmented fenestrated screws and traditional cement-augmented techniques. We compared five screw groups in this study: (1) Cannulated screws (Cann); (2) distal one-hole screws (D1); (3) distal two-hole screws (D2); (4) middle two-hole screws (M2); and (5) traditional screws with a traditional cement injection technique (Trad). The screws were inserted into cancellous bone blocks using a controlled, adequate cement injection pressure (1.6–2.0 kg), and an appropriate cement viscosity. Center to screw tip distance, three-dimensional distribution, and pull-out strength for cement were compared between groups. The average distance between the cement center and the screw tip was highest in the M2 group, suggesting a higher risk of cement leakage into the spinal canal. The Trad group had the highest migration distance in the z-axis, also reflecting a higher risk of leakage into the spinal canal. The D1 group had the highest pull-out strength (253 ± 48.82 N and 797 ± 58.31 N) in bone blocks representing different degrees of osteoporosis, and the D2 group had the second highest pull-out strength in the severe osteoporosis model. Overall, D1 screws appeared to be the best option for optimizing biomechanical function and minimizing the risk of cement leakage into the spinal canal in patients with osteoporotic bone undergoing spinal surgery.

Multilevel Percutaneous Fenestrated Screw Fixation with Bone Cement Augmentation in Adult Lumbar Spinal Deformity

Objective: Fenestrated screw fixation with bone cement augmentation has been demonstrated to increase the pullout strength. Bone cement augmentation is performed to prevent screw failure. Although bone cement screw fixation and fenestrated screw fixation have been compared in many studies, there has been no study on the clinical effects and complication in long level percutaneous bone cement screw fixation. The study aimed to investigate the safety and efficacy of multilevel percutaneous fenestrated screw fixation with bone cement augmentation in the adult lumbar spinal deformity.Methods: We performed a retrospective study of 15 patients who underwent multilevel percutaneous fenestrated screw fixation (PFSF) with bone cement augmentation in a single spine surgeon between January 2018 and December 2020. The incidence of screw failure, body mass index (BMI), bone mineral density (BMD), past history, Visual analogue scale (VAS) score, Oswestry disability index (ODI), sagittal vertical axis (SVA), pelvic Tilt (PT), pelvic incidence (PI), sagittal slope (SS), lumbar lordosis (LL) and Cobbs angle were investigated in the patients.Results: All patients underwent percutaneous screw fixation using a bone cement additive. Mean BMD was –2.0±0.8. The mean percutaneous fenestrated screw fixation level was 6. The mean VAS score changed from 7.14 preoperatively to 4.57 postoperatively (1 month after the surgery), to 3.71 at the last follow-up. The mean ODI changed from 45.21 preoperatively to 32.5 postoperatively, to 27.0 at the last follow-up. The mean LL changed from 23.6 preoperatively to 32.96 postoperatively, to 31.67 at the last follow-up. The mean PT changed from 32.67 preoperatively to 28.11 postoperatively, to 28.70 at the last follow-up. The mean PI - LL changed from 35.20 preoperatively to 22.56 postoperatively, to 22.76 at the last follow-up. The mean Cobb’s angle decreased from 18.30 preoperatively to 6.27 postoperatively, to 5.98 at the last follow-up. The mean SVA changed from 76.65 preoperatively to 46.15 postoperatively, to 48.46 at the last follow-up. The bony fusion rate was 73.3%. There were screw loosening in 4 patients, rod fracture in 1 patient and screw fracture in 3 patients. Among the 3 patients with screw fracture, 1 patient required reoperation. Cement leakage occurred towards the anterior body of the vertebrae in 2 patients but no symptoms were observed.Conclusion: Although the current study examined a small sample with relatively short term follow up periods, our study results demonstrate that multilevel PFSF with bone cement augmentation can result in good clinical and radiological outcomes for lumbar spinal deformity. However, larger size screws or smaller through-hole screws are required to prevent screw fracture.

Anterior Placement of Cemented Fenestrated Screws in Conjunction with Anterior Reconstruction in Elderly Patients with Severe Vertebral Collapse and Paraparesis

Background: Elderly patients with severe osteoporosis are prone to sustain osteoporotic vertebral compression fractures (OVCF’s). Sometimes, they undergo significant vertebral collapse and kyphosis, leading to significant canal compromise and neurological deterioration. Case Description: We present a case series of three patients, of which two had OVCF’s of L1 and L3, respectively, while one patient had Koch’s spine D12 and L1. All three cases had severe vertebral collapse leading to kyphosis, severe pain, and canal compromise, neurological deterioration with paraparesis, and bowel bladder involvement. Surgery warranted total corpectomy of fractured vertebrae (anterior vertebral column resection) and reconstruction of the anterior column. Due to the significant degree of osteoporosis, fenestrated screws with bone cement (poly methyl acrylate) were used anteriorly along with vertebral body reconstruction with cage, through a purely anterior approach. This is the first instance of fenestrated screws being used anteriorly to reduce screw pull-out. In view of the strong anterior construct, a posterior surgery to supplement the fixation could be avoided in these thoracolumbar junctional cases. Results: No patient experienced loosening of implants, nor did any patient experience cement-related complications. Although the present follow-up of these patients is short (12 months), the patients are pain free and independently ambulatory. Conclusion: Using fenestrated screws in an anterior location allow vertebral reconstruction with a single surgery in elderly patients with severe osteoporosis, reducing chances of screw pull-out. Bone plugs at the tip to help prevent cement extravasation from the vertebral body. Keywords: Anterior fenestrated screws, Bone cement, Corpectomy, Osteoporotic vertebral compression fracture, Koch’s spine, Screw pull-out.

Perioperative Outcomes of Minimally Invasive Sacroilliac Joint Fusion Using Hollow Screws Through a Lateral Approach: A Single Surgeon Retrospective Cohort Study

Sacroiliac joint (SIJ) pain is a common cause of lower back pain and a significant source of disability in the United States. There is no consensus on the best surgical treatment for SIJ pain that is not responsive to conservative therapy. Minimally invasive fusion of the SIJ using hollow fenestrated screws from a lateral trajectory is a newer technique for SIJ fusion. This study presents perioperative and patient-reported outcomes amongst 62 patients who underwent SIJ fixation with hollow fenestrated screws. We find that mean disability on the Oswestry disability index improved from 52.2% to 34.9% at one-year post-op. Mean operative time was 34±9 minutes and blood loss was 22±35ml. Only six patients required overnight hospitalization. There were two cases of complications requiring operative intervention. We conclude that SIJ fixation using hollow fenestrated screws is a safe and effective procedure for the fixation of the SIJ. Further investigation is warranted to determine the best surgical treatment for SIJ pain.

Fenestrated pedicle screws for thoracolumbar instrumentation in patients with poor bone quality: Case series and systematic review of the literature

ObjectiveTo describe the results of a single-surgeon series and systematically review the literature on cement-augmented instrumented fusion with fenestrated pedicle screws. MethodsAll patients treated by the senior surgeon using fenestrated screws between 2017 and 2019 with a minimum of 6-months of clinical and radiographic follow-up were included. For the systematic review, we used PRISMA guidelines to identify all prior descriptions of cement-augmented instrumented fusion with fenestrated pedicle screws in the English literature. Endpoints of interest included hardware loosening, cement leakage, and pulmonary cement embolism (PCE). ResultsOur series included 38 patients (mean follow-up 14.8 months) who underwent cement-augmented instrumentation for tumor (47.3%), deformity/degenerative disease (39.5%), or osteoporotic fracture (13.2%). Asymptomatic screw lucency was seen in 2.6%, cement leakage in 445, and pulmonary cement embolism (PCE) in 5.2%. Our literature review identified 23 studies (n = 1526 patients), with low reported rates of hardware loosening (0.2%) and symptomatic PCE (1.0%). Cement leakage, while common (55.6%), produced symptoms in fewer than 1% of patients. Indications for cement-augmentation in this cohort included: spine metastasis with or without pathologic fracture (n = 18; 47.3%), degenerative spine disease or fixed deformity with poor underlying bone quality (n = 15; 39.5%), and osteoporotic fracture (n = 5; 13.2%). ConclusionCement-augmented fusion with fenestrated screws appears to be a safe, effective means of treating patients with poor underlying bone quality secondary to tumor or osteoporosis. High-quality evidence with direct comparisons to non-augmented patients is needed.

Fenestrated Pedicle Screws in Spinal Oncology: Technique and Comparative Retrospective Analysis.

The use of spinal stabilization with decompression has been shown to improve survival, spinal stability, and ambulatory status in patients with metastatic spinal tumors. However, the poor bone quality typically seen in these patients can prevent adequate stabilization. Fenestrated pedicle screws permit augmented fixation via injection of bone cement into the vertebral body upon screw placement, potentially mitigating the difficulties in achieving adequate stabilization in these patients. To compare surgical outcomes of posterior spinal fusion in patients with cancerous spinal lesions between polymethyl methacrylate cement-augmented fenestrated screws and standard pedicle screws. A total of 19 consecutive patients with cancerous spinal lesions receiving posterior spinal fusion (PSF) with pedicle screws from a single surgeon were retrospectively reviewed for demographic information, comorbidities, surgical parameters, and outcomes. Ten patients underwent PSF with cement augmentation, whereas 9 underwent standard PSF. There was no significant difference in demographics, comorbidities, or surgical characteristics. Operative time was significantly greater in the cement-augmented group (302 ± 100 minutes vs 203 ± 55 minutes; P = .015). There was no significant difference in rates of operation or readmission between the cohorts nor was there any significant difference in discharge disposition. There was 1 case of surgical site infection (in a patient with a fenestrated screw) and no cases of cement extravasation. No instances of mechanical hardware failure were recorded. Fenestrated screws confer similar risk profiles as nonfenestrated screws for posterior spinal fusion in patients with spinal cancer. However, fenestrated screws may affect operative time, radiation exposure, and impose risk of cement extravasation. Cement-augmented fenestrated pedicle screws may be a viable option for patients with poor bone quality associated with metastatic disease without significantly increased rates of surgical complications. 3.

Effectiveness and reliability of cannulated fenestrated screws augmented with polymethylmethacrylate cement in the surgical treatment of osteoporotic vertebral fractures.

Background:Implants' stability, especially in osteoporosis patients, is a challenging matter. Nowadays, the adoption of cannulated fenestrated screws augmented with polymethylmethacrylate cement (PMMA CSF) is described by some authors. This single-center, retrospective observational study aims to evaluate the long-term effectiveness, reliability, and mechanical performances of this type of screws in osteoporotic fractures.Materials and Methods:All the patients surgically treated from January 2009 to December 2019 with PMMA CSF were evaluated and submitted to the inclusion and exclusion criteria. Clinical and radiological evaluations were performed at pre- and post-surgery time and at the follow-up (FU). Loss of correction in the sagittal plane (bisegmental Cobb angle), kyphosis angle of the fracture (fractured vertebral angle), loosening of pedicle screws (screw's apex vertebral body's anterior cortex mean gap called SAAC gap and screw's apex vertebral body's superior endplate mean gap called SASE gap), visual analog scale, and Oswestry disability index scores were evaluated.Results:One hundred and sixty-three patients (58 males and 105 females) aged over 65 years affected by vertebral osteoporotic fractures were included in the study. At FU, we do not found significant differences in radiological items in respect to the postoperative period. Only one case of loosening and 18 cases of cement leaking (without neurological impairments) were found. Clinical scores improvement was significant in the interval between preoperative and FU.Conclusions:PMMA CSF seems to can guarantee good efficacy and effectiveness in the surgical treatment of vertebral fractures in osteoporosis.

Effect of Fenestrated Pedicle Screws with Cement Augmentation in Osteoporotic Patients Undergoing Spinal Fusion

Osteoporosis is a well-known risk factor for instrumentation failure and subsequent pseudoarthrosis after spinal fusion. In the present systematic review, we analyzed the biomechanical properties, clinical efficacy, and complications of cement augmentation via fenestrated pedicle screws in spinal fusion. We conducted a systematic review in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Reports appearing in the PubMed database up to March 31, 2020 were queried using the key words "cement," "pedicle screw," and "osteoporosis." We excluded non-English language studies, studies reported before 2000, studies that had involved use of cement without fenestrated pedicle screws, nonhuman studies, technical reports, and individual case reports. Twenty-five studies met the inclusion criteria. Eleven studies had tested the biomechanics of cement-augmented fenestrated pedicle screws. The magnitude of improvement achieved by cement augmentation of pedicle screws increased with the degree of osteoporosis. The cement-augmented fenestrated pedicle screw was superior biomechanically to the alternative "solid-fill" technique. Fourteen studies had evaluated complications. Cement extravasation with fenestrated screw usage was highly variable, ranging from 0% to 79.7%. However, cement extravasation was largely asymptomatic. Thirteen studies had assessed the outcomes. The use of cement-augmented fenestrated pedicles decreased screw pull out and improved fusion rates; however, the clinical outcomes were similar to those with traditional pedicle screw placement. The use of cement-augmented fenestrated pedicle screws can be an effective strategy for achieving improved pedicle screw fixation in patients with osteoporosis. A potential risk is cement extravasation; however, this complication will typically be asymptomatic. Larger comparative studies are needed to better delineate the clinical efficacy.

Utility of Cement Augmentation via Percutaneous Fenestrated Pedicle Screws for Stabilization of Cancer-Related Spinal Instability.

Cancer patients experience pathological fractures and the typical poor bone quality frequently complicates stabilization. Methods for overcoming screw failure include utilization of fenestrated screws that permit the injection of bone cement into the vertebral body to augment fixation. To evaluate the safety and efficacy of cement augmentation via fenestrated screws. A retrospective chart review of patients with neoplastic spinal instability who underwent percutaneous instrumented stabilization with cement augmentation using fenestrated pedicle screws. Patient demographic and treatment data and intraoperative and postoperative complications were evaluated by chart review and radiographic evaluation. Prospectively collected patient reported outcomes (PRO) were evaluated at short (2-<6 mo) and long term (6-12 mo). Cement augmentation was performed in 216 fenestrated pedicle screws in 53 patients. Three patients required reoperation. One patient had an asymptomatic screw fracture at 6 mo postoperatively that did not require intervention. No cases of lucency around the pedicle screws, rod fractures, or cement extravasation into the spinal canal were observed. Eight cases of asymptomatic, radiographically-detected venous extravasation were found. Systemic complications included a pulmonary cement embolism, a lower extremity deep vein thrombosis, and a postoperative mortality secondary to pulmonary failure from widespread metastatic pulmonary infiltration. Significant improvement in PRO measures was found in short- and long-term analysis. Cement augmentation of pedicle screws is an effective method to enhance the durability of spinal constructs in the cancer population. Risks include cement extravasation into draining blood vessels, but risk of clinically significant extravasation appears to be exceedingly low.

Augmentation of fenestrated pedicle screws with cement in patients with osteoporotic spine.

Background:Backing out and failure of pedicle screws in patients with osteoporosis is becoming a big problem due to wide use of these screws nowadays.Purpose:The aim of this study is to evaluate the purchase of fenestrated pedicle screws augmented with cement in patients with osteoporosis.Study Design:This was retrospective observational study.Patients and Methods:From May 2015 to January 2016, 25 patients with a poor bone stock condition underwent posterior fixation by fenestrated pedicle screws and cement augmentation. Assessment of pain improvement was done by visual analogue score (VAS) score while the long-term clinical outcome was assessed using Oswestry low back disability questionnaire (Oswestry disability index [ODI]). Implant stability was evaluated by plain radiography. Complications were evaluated in all cases.Results:All patients were followed up clinically and radiographically for a mean age of 24.84 months. There was a significant reduction in pain and improvement of the quality of life as detected using VAS scores and ODI questionnaire consecutively (P < 0.001). No radiological loosening or backing out of screws was observed. Cement leakage occurred in five cases.Conclusion:Augmentation of fenestrated screws with cement provided effective and lasting purchase in patients with osteoporosis. The only clinical complication strictly related to this technique was cement leakage.

Pull-out strength of cemented solid versus fenestrated pedicle screws in osteoporotic vertebrae.

ObjectivesCement augmentation of pedicle screws could be used to improve screw stability, especially in osteoporotic vertebrae. However, little is known concerning the influence of different screw types and amount of cement applied. Therefore, the aim of this biomechanical in vitro study was to evaluate the effect of cement augmentation on the screw pull-out force in osteoporotic vertebrae, comparing different pedicle screws (solid and fenestrated) and cement volumes (0 mL, 1 mL or 3 mL).Materials and MethodsA total of 54 osteoporotic human cadaver thoracic and lumbar vertebrae were instrumented with pedicle screws (uncemented, solid cemented or fenestrated cemented) and augmented with high-viscosity PMMA cement (0 mL, 1 mL or 3 mL). The insertion torque and bone mineral density were determined. Radiographs and CT scans were undertaken to evaluate cement distribution and cement leakage. Pull-out testing was performed with a material testing machine to measure failure load and stiffness. The paired t-test was used to compare the two screws within each vertebra.ResultsMean failure load was significantly greater for fenestrated cemented screws (+622 N; p ⩽ 0.001) and solid cemented screws (+460 N; p ⩽ 0.001) than for uncemented screws. There was no significant difference between the solid and fenestrated cemented screws (p = 0.5). In the lower thoracic vertebrae, 1 mL cement was enough to significantly increase failure load, while 3 mL led to further significant improvement in the upper thoracic, lower thoracic and lumbar regions.ConclusionConventional, solid pedicle screws augmented with high-viscosity cement provided comparable screw stability in pull-out testing to that of sophisticated and more expensive fenestrated screws. In terms of cement volume, we recommend the use of at least 1 mL in the thoracic and 3 mL in the lumbar spine.Cite this article: C. I. Leichtle, A. Lorenz, S. Rothstock, J. Happel, F. Walter, T. Shiozawa, U. G. Leichtle. Pull-out strength of cemented solid versus fenestrated pedicle screws in osteoporotic vertebrae. Bone Joint Res 2016;5:419–426.

Axial pullout strength comparison of different screw designs: fenestrated screw, dual outer diameter screw and standard pedicle screw.

BackgroundThe pullout strength of pedicle screws is influenced by many factors, including diameter of the screws, implant design, and augmentation with bone cement such as PMMA. In the present study, the pullout strength of an innovative fenestrated screw augmented with PMMA was investigated and was compared to unaugmented fenestrated, standard and dual outer diameter screw.MethodsTwenty four thoracolumbar vertebrae (T10-L5, age 60 to 70 years) from three cadavers were implanted with the four different pedicle screws. Twelve screws of each type were instrumented into either left or right pedicle with standard screw paired with unaugmented and dual outer diameter screw paired with augmented fenestrated screw in any given vertebra. Axial pullout testing was conducted at a rate of 5 mm/min. Force to failure (Newtons) for each pedicle screw was recorded.ResultsThe augmented fenestrated screws had the highest pullout strength, which represented an average increase of 149%, 141%, and 78% in comparison to unaugmented, standard, and dual outer diameter screws, respectively. Pullout strength of unaugmented screws was comparable to that of standard screws, however it was significantly lower than dual outer diameter screws.ConclusionsFenestrated screws augmented with PMMA improve the fixation strength and result in significantly higher pullout strength compared to dual outer diameter, standard and unaugmented fenestrated screws. Screws with dual outer diameter provided enhanced bone-screw purchase and may be considered as an alternative technique to increase the bone-screw interface in cases where augmentation using bone cement is not feasible. Unaugmented screws can be left in the pedicle even without cement and provide similar pullout strength to standard screws.

Effect of augmentation techniques on the failure of pedicle screws under cranio-caudal cyclic loading

Augmentation of pedicle screws is recommended in selected indications (for instance: osteoporosis). Generally, there are two techniques for pedicle screw augmentation: inserting the screw in the non cured cement and in situ-augmentation with cannulated fenestrated screws, which can be applied percutaneously. Most of the published studies used an axial pull out test for evaluation of the pedicle screw anchorage. However, the loading and the failure mode of pullout tests do not simulate the cranio-caudal in vivo loading and failure mechanism of pedicle screws. The purpose of the present study was to assess the fixation effects of different augmentation techniques (including percutaneous cement application) and to investigate pedicle screw loosening under physiological cyclic cranio-caudal loading. Each of the two test groups consisted of 15 vertebral bodies (L1-L5, three of each level per group). Mean age was 84.3years (SD 7.8) for group 1 and 77.0years (SD 7.00) for group 2. Mean bone mineral density was 53.3mg/cm3 (SD 14.1) for group 1 and 53.2mg/cm3 (SD 4.3) for group 2. 1.5ml high viscosity PMMA bone cement was used for all augmentation techniques. For test group 1, pedicles on the right side of the vertebrae were instrumented with solid pedicle screws in standard fashion without augmentation and served as control group. Left pedicles were instrumented with cannulated screws (Viper cannulated, DePuy Spine) and augmented. For test group 2 pedicles on the left side of the vertebrae were instrumented with cannulated fenestrated screws and in situ augmented. On the right side solid pedicle screws were augmented with cement first technique. Each screw was subjected to a cranio-caudal cyclic load starting at 20-50N with increasing upper load magnitude of 0.1N per cycle (1Hz) for a maximum of 5000 cycles or until total failure. Stress X-rays were taken after cyclic loading to evaluate screw loosening. Test group 1 showed a significant higher number of load cycles until failure for augmented screws compared to the control (4030 cycles, SD 827.8 vs. 1893.3 cycles, SD 1032.1; p<0.001). Stress X-rays revealed significant less screw toggling for the augmented screws (5.2°, SD 5.4 vs. 16.1°, SD 5.9; p<0.001). Test group 2 showed 3653.3 (SD 934) and 3723.3 (SD 560.6) load cycles until failure for in situ and cement first augmentation. Stress X-rays revealed a screw toggling of 5.1 (SD 1.9) and 6.6 (SD 4.6) degrees for in situ and cement first augmentation techniques (p>0.05). Augmentation of pedicle screws in general significantly increased the number of load cycles and failure load comparing to the nonaugmented control group. For the augmentation technique (cement first, in situ augmented, percutaneously application) no effect could be exhibited on the failure of the pedicle screws. By the cranio-caudal cyclic loading failure of the pedicle screws occurred by screw cut through the superior endplate and the characteristic "windshield-wiper effect", typically observed in clinical practice, could be reproduced.

Minimally Invasive Technique for PMMA Augmentation of Fenestrated Screws.

Purpose. To describe the minimally invasive technique for cement augmentation of cannulated and fenestrated screws using an injection cannula as well as to report its safety and efficacy. Methods. A total of 157 cannulated and fenestrated pedicle screws had been cement-augmented during minimally invasive posterior screw-rod spondylodesis in 35 patients from January to December 2012. Retrospective evaluation of cement extravasation and screw loosening was carried out in postoperative plain radiographs and thin-sliced triplanar computed tomography scans. Results. Twenty-seven, largely prevertebral cement extravasations were detected in 157 screws (17.2%). None of the cement extravasations was causing a clinical sequela like a new neurological deficit. One screw loosening was noted (0.6%) after a mean follow-up of 12.8 months. We observed no cementation-associated complication like pulmonary embolism or hemodynamic insufficiency. Conclusions. The presented minimally invasive cement augmentation technique using an injection cannula facilitates convenient and safe cement delivery through polyaxial cannulated and fenestrated screws during minimally invasive screw-rod spondylodesis. Nevertheless, the optimal injection technique and design of fenestrated screws have yet to be identified. This trial is registered with German Clinical Trials DRKS00006726.

"NIMS technique" for minimally invasive spinal fixation using non-fenestrated pedicle screws: A technical note.

Study Design:Case series.Objective:To reduce the cost of minimally invasive spinal fixation.Background:Minimally invasive spine (MIS) surgery is an upcoming modality of managing a multitude of spinal pathologies. However, in a resource-limited situations, using fenestrated screws (FSs) may prove very costly for patients with poor affordability. We here in describe the Nizam's Institute of Medical Sciences (NIMS) experience of using routine non-FSs (NFSs) for transpedicular fixation by the minimally invasive way to bridge the economic gap.Materials and Methods:A total of 7 patients underwent NFS-minimally invasive spine (MIS) surgery. Male to female distribution was 6:1. The average blood loss was 50 ml and the mean operating time was 2 and 1/2 h. All patients were mobilized the very next day after confirming the position of implants on X-ray/computed tomography.Results:All 7 patients are doing well in follow-up with no complaints of a backache or fresh neurological deficits. There was no case with pedicle breach or screw pullout. The average cost of a single level fixation by FS and NFS was ₹1, 30,000/patient and ₹32,000/patient respectively (‘2166 and ‘530, respectively). At the end of 1-year follow-up, we had two cases of screw cap loosening and with a displacement of the rod cranio-caudally in one case which was revised through the same incisions.Conclusions:Transpedicular fixation by using NFS for thoracolumbar spinal pathologies is a cost-effective extension of MIS surgery. This may extend the benefits to a lower socioeconomic group who cannot afford the cost of fenestrated screw (FS).

Minimally Invasive Spine Metastatic Tumor Resection and Stabilization: New Technology Yield Improved Outcome.

Spinal metastases compressing the spinal cord are a medical emergency and should be operated on if possible; however, patients' medical condition is often poor and surgical complications are common. Minimizing surgical extant, operative time, and blood loss can potentially reduce postoperative complications. This is a retrospective study describing the patients operated on in our department utilizing a minimally invasive surgery (MIS) approach to decompress and instrument the spine from November 2013 to November 2014. Five patients were operated on for thoracic or lumbar metastases. In all cases a unilateral decompression with expandable tubular retractor was followed by instrumentation of one level above and below the index level and additional screw at the index level contralateral to the decompression side. Cannulated fenestrated screws were used (Longitude FNS) and cement was injected to increase pullout resistance. Mean operative time was 134 minutes and estimated blood loss was minimal in all cases. Improvement was noticeable in neurological status, function, and pain scores. No complications were observed. Technological improvements in spinal instruments facilitate shorter and safer surgeries in oncologic patient population and thus reduce the complication rate. These technologies improve patients' quality of life and enable the treatment of patients with comorbidities.

Pedicle Screw Design and Cement Augmentation in Osteoporotic Vertebrae

Experimental, human cadaveric study. To assess the fixation effects of injecting cement augmentation before screw insertion or after insertion of fenestrated screws; the effect of modulating cement viscosity; and the effects of these techniques on screw removal. It seems clear that cement augmentation can enhance pedicle screw fixation in osteoporotic bone. What remains to be demonstrated is the aspects of optimal technique such that fixation is enhanced with the greatest safety profile. Part I: Human osteoporotic vertebrae were instrumented with solid (nonaugmented) screws, solid screws with polymethylmethacrylate (PMMA), partially cannulated fenestrated (Pfen) screws, or fully cannulated fenestrated (Ffen) screws through which PMMA was injected. Screw fixation was tested in pullout. Part II: Ffen screws were augmented with standard low-viscosity PMMA versus high-viscosity PMMA. Part III: Sample cohorts were extracted from vertebrae to assess required torque and characterize difficulty of extraction. Part I: Pfen screws demonstrated the greatest fixation with mean failure force of 690 ± 182 N. All methods of cement augmentation demonstrated significant increases in screw fixation. Part II: Ffen screws did not demonstrate a significant difference in pullout strength when high-viscosity PMMA was used as compared with low-viscosity PMMA. Part III: Mean extraction torque values for solid augmented screws, Ffen screws, and Pfen screws were 1.167, 1.764, and 1.794 Nm, respectively, but these differences did not reach significance. None of the osteoporotic vertebrae sustained catastrophic failure during augmented screw extraction. Polymethylmethacrylate cement augmentation clearly enhances pedicle screw fixation in osteoporotic vertebrae when tested in pure pullout. The technique used for cement injection and choice of specialty screws can have a significant impact on the magnitude of this effect. Fenestrated screws have the capacity to confine cement placement in the vertebral body and may provide enhanced safety from cement extrusion into the spinal canal. It is feasible to inject high-viscosity PMMA through this fenestration geometry, and higher-viscosity cement may enhance the fixation effect.