Expandable Pedicle Screw Research Articles

Evaluating osteoporosis and bone quality in the aging spine: modern considerations for surgical management in the geriatric population.

Surgical management paradigms of spinal pathologies in the aging population carry inherent substantial risks, with surgical complications being more prevalent among patients with osteoporosis compared to those with normal bone mineral density. In this narrative review, we aim to highlight important clinical understanding and considerations in perioperative evaluation and management of patients elected to undergo spinal surgery. Osteoporosis is a well-defined risk factor for mechanical complications following spinal surgery, and as such, perioperative optimization of bone health in the setting of surgery for geriatric patients remains a critical research area alongside intraoperative surgical augmentation techniques. Surgical techniques to circumvent challenges with instrumentation of poor bone mineral density have included augmentation of pedicle screw fixation, including segmental bicortical screw fixation techniques, cement augmentation with fenestrated screws, or use of expandable pedicle screws to improve bone-implant interface. Judicious selection of treatment modalities and subsequent perioperative optimization is paramount to minimize surgical complications. Contemporary guidelines and evolving paradigms in perioperative evaluation, optimization, and management of the aging spine include the advent of quantitatively evaluating computed tomography (CT) via assessment of the magnitude of Hounsfield units. Prescribing pharmacotherapeutic agents and monitoring bone health requires a multidisciplinary team approach, including endocrinologists and geriatricians to coordinate high-quality care for advanced-age patients who require surgical management of their spinal disorders.

Postfusion effect on pullout strength of pedicle screws with expandablepeek shell and conventional screws.

The pullout performance of various pedicle screws after artificial fusion process was investigated in this study. Normal, cannulated (cemented), novel expandable and normal (cemented) pedicle screws were tested. Polyurethane foams (Grade 10 and Grade 40) produced by casting method were used as test materials. The instrumentation of pedicle screws has been carried out with production of foams, simultaneously. For cemented pedicle screws, 3D models were prepared with respect to the anteriosuperior and oblique radiographs by using PMMA before casting procedure. Pullout tests were performed in an Instron 3369 testing device. Load versus displacement graph was recorded and the ultimate force was defined as the pullout strength sustained before failure of screw. As expected, the pullout strengths of pedicle screws in postfusion are higher than before fusion. Pullout strengths increased significantly by artificial fusion in Grade 10 foams compared to Grade 40 foams. Additionally, while the pullout strengths of normal, cannulated and novel expandable pedicle screws increased by artificial fusion, cemented normal pedicle screws had lower pullout values than before fusion in Grade 40 foams. When the cemented normal pedicle screws are excluded, other screws have almost similar pullout strength level. On the other hand, the pedicle screws have different increasing behaviour also, there is no correlation between each other. As a result, the novel expandable pedicle screws can be used instead of normal and cannulated ones due to their performances in non-cemented usage.

Expandable pedicle screw may have better fixation than normal pedicle screw: preclinical investigation on instrumented L4-L5 vertebrae based on various physiological movements.

Lumbar spine fracture is typically treated by means of screw fixation, the primary aim of which is to reduce fracture by achieving bony union such that the spinal anatomy is restored. Pedicle screw fixation has certain advantages over conventional vertebral screws, e.g. 3-column fixation and improved surgical alignment. However, expandable pedicle screws have been reported to impart better anchorage as compared to conventional pedicle screws, both in case of healthy and osteoporotic bone. The clinical studies notwithstanding, there is a paucity of preclinical investigations on expandable pedicle screws used on lumbar vertebrae. By employing anatomically viable FE models, the present study intended to estimate stress-strain fields of a functional spinal unit (FSU) of intact L4-L5 vertebra and to further compare the same with FSUs instrumented with normal and expandable pedicle screws under different physiological loading condition. The various physiological loading regimes appeared to have significant influence on the overall load transfer in the L4-L5 vertebrae. The expandable pedicle screw predicted marginally improved anchorage as compared to the normal pedicle screws, with more contact area with the bone resulting in higher stresses (~ 1.6MPa) and high strain at the contact sites. This is indicative of improved stability albeit having marginally greater risk of screw pullout. Greater area (15-80%) with peak stresses at the bone-screw interfaces also indicates lesser degree of stress shielding. Thus, stability aside, one may expect to have lower loosening issues too with the use of expandable pedicle screws.

The Evaluation of a Novel Three-Dimensional Printed Expandable Pedicle Screw Sleeve Insert

When used in combination with decompression, spinal fusion is a successful procedure for treating patients with spinal stenosis and degenerative spondylolisthesis. While a number of auxiliary devices have been proposed to enhance the fixation of the screw within the pedicle and vertebral body, there is conflicting information regarding the efficacy of their use. Therefore, the aim of this study was to determine the ability of a novel expandable pedicle screw to improve the fixation of the pedicle screw within the pedicle and vertebral body. A three-dimensional (3D) printed, screw sleeve was designed that expanded within the pedicle and vertebral body when a standard pedicle screw was inserted into it. The left and right pedicle of ten (N = 10) cadaveric lumbar spine specimens (L3–L5) were randomly assigned to be instrumented with either a pedicle screw and the sleeve or a pedicle screw only. Following instrumentation, the screws were exposed to tensile load at 5 mm/min until failure. The failure force, failure deformation, and area under the force–deformation curve were determined and compared between screw conditions. There were no significant differences between the screws and sleeve, and the screw only conditions for the failure force (p = 0.24), failure displacement (p = 0.10), and area under the curve (p = 0.38). While the novel screw sleeve presented here performed as well as a screw without a sleeve, it was better than other screw augmentation devices reported previously. In addition, it is likely that this device would prove useful as an enhancement to revision.

Bone cement augmentation of the pedicle screw in spinal surgery

Osteoporosis is a common metabolic bone disease in the elderly. It may be one of the factors which contributes to instrumentation failure in spinal surgery. Bone cement augmentation of the pedicle screw is a technique to enhance fixation strength, and it is now mainly applied in patients with osteoporosis and revision surgery, as well as spinal tumor surgery. According to clinical studies, bone cement augmentation can decrease screw loosening rate, prevent correction loss of the spine deformity, and increase the fusion rate. Pedicle screw fracture and pulloutare rare following screw augmentation surgery. The pedicle screw loosening rates following screw augmentation surgery with bone cement are higher in patients with osteoporotic vertebral fracture and lower in patients with spinal degenerative diseases. The main material for bone cement augmentation is Polymethylmethacrylate, and the volume for each screw is about 1-3 ml. Some researchers suggest less volume use in thoracic vertebrae than lumbar vertebrae. Both traditional and cannulated screws can be applied as the augmented pedicle screws, as well as the expandable pedicle screw. Cannulated screws can decrease the risk of bone cement extravasation compared with traditional screws. The mini-mally invasive technique of screw augmentation with bone cement can be used both in primary spinal surgery and augmentation of loosed screws. The main complications of the bone cement augmentation technique are cement leakage and pulmonary cement em-bolism. X-ray fluoroscopy is generally used to detect cement extravasation during the bone cement procedure. The 3D navigation and neurological monitoring are also recommended to reduce cement leakage in some studies. Most local cement leakage events are asymptomatic and need no treatment. Management of pulmonary cement embolism depends on the clinical presentation and the position of the emboli, including regular follow-up, oxygen inhalation, anti-coagulation therapy and embolectomy.

Application value of expansive pedicle screw in the lumbar short-segment fixation and fusion for osteoporosis patients.

Clinical value of expansive pedicle screw in lumbar short-segment fixation and fusion for patients with osteoporosis was investigated. A total of 80 patients with lumbar compression fracture but without obvious nerve compression were selected and divided into the observation group (n=40) and the control group (n=40) using a random number table. The observation group used the expansive pedicle screw, and the control group received conventional pedicle screw fixation and bone graft fusion. In the observation group, the operation and hospitalization time after operation were shorter and the intraoperative bleeding amount was less than that in control group (p<0.05). At 1 week, 1, 3 and 6 months after operation, the observation group had better straight leg raising test (SLRT) scores, higher lower limb sensory scores but lower visual analogue scale (VAS) scores than control group (p<0.05). Besides, the proportions of postoperative infection, dural mater tear, nerve root injury and spinal cord injury during operation in the observation group were lower than those in the control group (p<0.05), and the bone graft fusion rates at 3 and 6 months after operation were obviously superior to those in control group (p<0.05). Moreover, after operation, the spinal stenosis rate in the observation group was lower than that in control group (p<0.05), the vertebral height ratio was larger than that in control group (p<0.05), and the Cobb's angle was smaller than that in the control group (p<0.05). In addition, there was a negative correlation between bone mineral density (BMD) and hospitalization time after operation in the observation group (p<0.05). In conclusion, the internal fixation with expansive pedicle screw for osteoporosis patients with lumbar compression fracture is characterized by short operation time, less intraoperative bleeding, few complications, quick recovery of postoperative neurological function and satisfactory surgical effect. However, reasonable intervention in osteoporosis is also necessary.

Ostéosynthèse par vis pédiculaires expansives dans les déformations rachidiennes dégénératives associées à une ostéoporose : étude clinique à deux ans de recul

BackgroundOsteoporotic bone offers poor purchase for the instrumentation in patients with degenerative spinal deformity (DSD), which could lead to several complications. Recently, augmentation methods to improve pedicle screw fixation have been proposed. This retrospective study was to investigate the clinical and radiographic outcomes of expandable pedicle screws (EPS) in patients with osteoporotic DSD. HypothesisExpandable pedicle screws (EPS) provide excellent instrument fixation in patients with osteoporotic DSD, improving radiographic and clinical outcomes. Materials and methodsA total of 27 (6 males and 21 females) DSD patients who underwent orthopedics operation with EPS were retrospectively studied. Full-length standing spinal radiographs were obtained in all patients pre- and postoperatively and again at the two-year follow-up. The functional evaluations before operation and at two-year follow-up were graded with Scoliosis Research Society outcomes instrument-22 (SRS-22) and Oswestry Disability Index (ODI) scoring system. ResultsAll patients obtained good corrective outcomes on spinal deformity. The preoperative ODI score was 36.7 % and reduced to 11.9 % at two-year follow-up (P=0.0000). Before operation, the SRS-22 function, pain, appearance and mental scores were 2.7±0.4, 3±0.6, 2.7±0.5 and 2.9±0.6, respectively. The scores at two-year follow-up were significantly improved to 3.8±0.7, 4.2±0.6, 4.3±0.6 and 4.4±0.7, respectively (P=0.0000). The SRS-22 satisfaction score was 4.6±0.4 at two-year follow-up. No instances of screw breakage, loosening or pullout in any patient at follow-up. DiscussionEPS provides excellent instrument fixation in patients with osteoporotic DSD, improving radiographic and clinical outcomes at two-years’ follow-up. Type of studyRetrospective case series study. Level of evidenceIV.

Comparison of the Pullout Strength of Different Pedicle Screw Designs and Augmentation Techniques in an Osteoporotic Bone Model.

Study DesignMechanical study.PurposeTo compare the pullout strength of different screw designs and augmentation techniques in an osteoporotic bone model.Overview of LiteratureAdequate bone screw pullout strength is a common problem among osteoporotic patients. Various screw designs and augmentation techniques have been developed to improve the biomechanical characteristics of the bone–screw interface.MethodsPolyurethane blocks were used to mimic human osteoporotic cancellous bone, and six different screw designs were tested. Five standard and expandable screws without augmentation, eight expandable screws with polymethylmethacrylate (PMMA) or calcium phosphate augmentation, and distal cannulated screws with PMMA and calcium phosphate augmentation were tested. Mechanical tests were performed on 10 unused new screws of each group. Screws with or without augmentation were inserted in a block that was held in a fixture frame, and a longitudinal extraction force was applied to the screw head at a loading rate of 5 mm/min. Maximum load was recorded in a load displacement curve.ResultsThe peak pullout force of all tested screws with or without augmentation was significantly greater than that of the standard pedicle screw. The greatest pullout force was observed with 40-mm expandable pedicle screws with four fins and PMMA augmentation. Augmented distal cannulated screws did not have a greater peak pullout force than nonaugmented expandable screws. PMMA augmentation provided a greater peak pullout force than calcium phosphate augmentation.ConclusionsExpandable pedicle screws had greater peak pullout forces than standard pedicle screws and had the advantage of augmentation with either PMMA or calcium phosphate cement. Although calcium phosphate cement is biodegradable, osteoconductive, and nonexothermic, PMMA provided a significantly greater peak pullout force. PMMA-augmented expandable 40-mm four-fin pedicle screws had the greatest peak pullout force.

Investigation of toggling effect on pullout performance of pedicle screws.

Objective of this study is to assess the pullout performance of various pedicle screws in different test materials after toggling tests comparatively. Solid core, cannulated (cemented), novel expandable and solid-core (cemented) pedicle screws were instrumented to the polyurethane foams (Grade 10 and Grade 40) produced in laboratory and bovine vertebra. ASTM F543 standard was used for preparation process of samples. Toggling tests were carried out. After toggling test procedures, pullout tests were performed. Load versus displacement graph was recorded, and the ultimate pullout force was defined as the maximum load (pullout strength) sustained before failure of screw. Anteriosuperior and oblique radiographs were taken from each sample after instrumentation in order to examine screw placement and cement distribution. The pullout strength of pedicle screws decreased after toggling tests with respect to the initial condition. While the cemented solid-core pedicle screws had the highest pullout strength in all test materials, they had the highest strength differences. The cemented solid-core pedicle screws had decrement rates of 27% and 16% in Grade 10 and Grade 40, respectively. There are almost same decrement rate (between 5.5% and 6.5%) for all types of pedicle screws instrumented to the samples of bovine vertebra. The pullout strengths of novel expandable pedicle screws in both of early period and after toggling conditions were almost similar, in other words, the decrement rates of it were lower than other types. According to the data collected from this study, polymethylmethacrylate augmentation significantly decreases pullout strength following the toggling loads. Higher brittleness of cured polymethylmethacrylate has adverse effect on the pullout strength. Although augmentation is an important process for enhancing pullout strength in early period, it has some disadvantages for preserving stabilization in a long time. Expandable pedicle screw with polyetheretherketone shell may be good alternative to polymethylmethacrylate augmentation on both primer stabilization and long-term loading application with toggling.

Implant related complications in patients operated on with expandable pedicle screws and technical solutions for revision surgery

Implant related complications in patients operated on with expandable pedicle screws and technical solutions for revision surgery

Surgical treatment of osteoporotic degenerative spinal deformity with expandable pedicle screw fixation: 2-year follow-up clinical study.

Osteoporotic bone offers poor purchase for the instrumentation in patients with degenerative spinal deformity (DSD), which could lead to several complications. Recently, augmentation methods to improve pedicle screw fixation have been proposed. This retrospective study was to investigate the clinical and radiographic outcomes of expandable pedicle screws (EPS) in patients with osteoporotic DSD. Expandable pedicle screws (EPS) provide excellent instrument fixation in patients with osteoporotic DSD, improving radiographic and clinical outcomes. A total of 27 (6 males and 21 females) DSD patients who underwent orthopedics operation with EPS were retrospectively studied. Full-length standing spinal radiographs were obtained in all patients pre- and postoperatively and again at the two-year follow-up. The functional evaluations before operation and at two-year follow-up were graded with Scoliosis Research Society outcomes instrument-22 (SRS-22) and Oswestry Disability Index (ODI) scoring system. All patients obtained good corrective outcomes on spinal deformity. The preoperative ODI score was 36.7% and reduced to 11.9% at two-year follow-up (p=0.0000). Before operation, the SRS-22 function, pain, appearance and mental scores were 2.7±0.4, 3±0.6, 2.7±0.5 and 2.9±0.6, respectively. The scores at two-year follow-up were significantly improved to 3.8±0.7, 4.2±0.6, 4.3±0.6 and 4.4±0.7, respectively (p=0.0000). The SRS-22 satisfaction score was 4.6±0.4 at two-year follow-up. No instances of screw breakage, loosening or pullout in any patient at follow-up. EPS provides excellent instrument fixation in patients with osteoporotic DSD, improving radiographic and clinical outcomes at two years' follow-up. Retrospective case series study. IV.

Biomechanical study of a newly-designed Y type pedicle screw in osteoporotic synthetic bone

To evaluate the biomechanical stability of a newly-designed Y type pedicle screw (YPS) in osteoporotic synthetic bone. The osteoporotic synthetic bone were randomly divided into 3 groups ( n=20). A pilot hole, 3.0 mm in diameter and 30.0 mm in deep, was prepared in these bones with the same method. The YPS, expansive pedicle screw (EPS), and bone cement-injectable cannulated pedicle screw (CICPS) were inserted into these synthetic bone through the pilot hole prepared. X-ray film examination was performed after 12 hours; the biomechanical stability of YPS, EPS, and CICPS groups was tested by the universal testing machine (E10000). The test items included the maximum axial pullout force, the maximum running torque, and the maximum periodical anti-bending. X-ray examination showed that in YPS group, the main screw and the core pin were wrapped around the polyurethane material, the core pin was formed from the lower 1/3 of the main screw and formed an angle of 15° with the main screw, and the lowest point of the inserted middle core pin was positioned at the same level with the main screw; in EPS group, the tip of EPS expanded markedly and formed a claw-like structure; in CICPS group, the bone cement was mainly distributed in the front of the screw and was dispersed in the trabecular bone to form a stable screw-bone cement-trabecular complex. The maximum axial pullout force of YPS, EPS, and CICPS groups was (98.43±8.26), (77.41±11.41), and (186.43±23.23) N, respectively; the maximum running torque was (1.42±0.33), (0.96±0.37), and (2.27±0.39) N/m, respectively; and the maximum periodical anti-bending was (67.49±3.02), (66.03±2.88), and (143.48±4.73) N, respectively. The above indexes in CICPS group were significantly higher than those in YPS group and EPS group ( P<0.05); the maximum axial pullout force and the maximum running torque in YPS group were significantly higher than those in EPS group ( P<0.05), but there was no significant difference in the maximum periodical anti-bending between YPS group and EPS group ( P>0.05). Compared with EPS, YPS can effectively enhance the maximum axial pullout force and maximum rotation force in the module, which provides a new idea for the design of screws and the choice of different fixation methods under the condition of osteoporosis.

Percutaneous vertebroplasty, percutaneous kyphoplasty and expansive pedicle screw fixation for repairing primary osteoporotic thoracolumbar fractures

Percutaneous vertebroplasty, percutaneous kyphoplasty and expansive pedicle screw fixation for repairing primary osteoporotic thoracolumbar fractures

A Systematic Review of Treatment Strategies for Degenerative Lumbar Spine Fusion Surgery in Patients With Osteoporosis.

Purpose:To evaluate the current evidence in the literature on treatment strategies for degenerative lumbar spine fusion in patients with osteoporosis.Methods:A systematic review of the literature from 1950 to 2015.Results:The review of the literature yielded 15 studies on the effect of treatment options for osteoporosis on lumbar fusion rates. This study evaluated only degenerative lumbar spine conditions and excluded deformity patients. One study demonstrated an association between low bone mass as measured by Hounsfield units and lower fusion rates. Six studies evaluated perioperative medical treatment of osteoporosis and showed higher fusion rates in patients treated with alendronate and teriparatide. The strongest evidence was for perioperative teriparatide. Eight studies evaluated surgical treatment strategies in patients with osteoporosis and showed that cement augmentation of pedicle screws and expandable pedicle screws demonstrated improved fusion rates than traditional pedicle screws. The strongest evidence was for expandable pedicle screws.Conclusion:There are 15 articles evaluating osteoporosis in patients undergoing lumbar fusion and the highest level of evidence is for perioperative use of teriparatide.

Biomechanical Comparison of Expansive Pedicle Screw and Polymethylmethacrylate-augmented Pedicle Screw in Osteoporotic Synthetic Bone in Primary Implantation: An Experimental Study.

Expansive pedicle screws (EPS) and polymethylmethacrylate-augmented pedicle screws (PMMA-PS) were inserted into osteoporotic synthetic bones, which were then tested by radiographic and biomechanical examinations. To compare the stability of EPS and PMMA-PS with that of a conventional pedicle screw (CPS) in an osteoporotic synthetic bone. It is a significant challenge for orthopedic surgeons performing transpedicular fixation in the osteoporotic spine. Prior studies have suggested that both EPS and PMMA-PS can increase the screw stability effectively. However, there are no biomechanical comparisons of EPS and PMMA-PS, especially in primary spinal surgery in osteoporosis. Thirty osteoporotic synthetic bone blocks were divided into 3 groups randomly. A pilot hole was prepared in advance in all samples by the same method. Then, the CPS was inserted directly into the pilot hole in the CPS group; the hole in the PMMA-PS group was first filled with polymethylmethacrylate (PMMA; 2.5 mL) and then inserted with CPS, and the EPS was inserted directly into the blocks in the EPS group. Twenty-four hours later, x-ray and computed tomography examination and axial pullout tests were performed on all samples; the block destructions were then recorded, and the hole diameters were measured. In the CPS group, the screw was surrounded directly by the synthetic bone without any other materials, whereas in the PMMA-PS group, the screw was totally wrapped up by PMMA, and the PMMA was evenly distributed in the synthetic bone around the screw, indicating obvious improvement of the local density around the track. In the EPS group, the anterior part of the EPS presented an obvious expansion in synthetic bone and formed an unguiform structure pressing the surrounding synthetic bone. Screw stabilities in both the PMMA-PS and the EPS groups were significantly enhanced compared with those in the CPS group, and the screw stability in the PMMA-PS group was significantly higher than that in the EPS group. After the pullout tests, the block destructions were the most severe in the PMMA-PS group and the lightest in the CPS group. Hole diameters in the PMMA-PS and the EPS groups were significantly larger than that in the CPS group, whereas the diameter of the hole in the PMMA-PS group was significantly greater than that in the EPS group. EPS can significantly increase the strength of screw fixation compared with CPS in osteoporotic synthetic bone. Although EPS shows a weaker fixation strength compared with PMMA-PS in the osteoporotic synthetic bone, it may still provide an alternative option to prevent screw loosening in the clinical treatment of osteoporosis.

Thoracolumbar fractures: Three column stabilization through posterior only approach

Abstract Introduction The combination of anterior and posterior approaches when indicated in unstable thoracolumbar fractures provides the most stable reconstruction. However, the use of both approaches on a trauma patient is associated with significant morbidity. We evaluated the clinical outcome, morbidity and feasibility of single stage posterior midline approach for decompression and three column stabilization using expandable cage and pedicle screws. Methods The cases of fifteen patients with severe traumatic thoracolumbar fractures/dislocations that were managed with single-stage decompression, reconstruction and three column stabilization using an expandable cage via an entirely posterior approach were included in this study. Data on age, sex, mechanism of injury neurological status, surgical technique, radiological and clinical outcome were reviewed retrospectively. Observation There was no difference between the preoperative and immediate postoperative neurological status of the patients. The average blood loss was 580 ml and average operating time was 4 h 30 minutes. Adequate decompression, fixation and anterior column correction were achieved in all the patients. After a mean follow up period of 21.4 months, no patient complained of local pain and no significant loss of corrections or hardware failure was observed. Conclusion Our experience proves that single stage posterior approach using pedicle screws and an expandable cage is a safe and biomechanically reliable method for treating thoracolumbar fractures.

A new alternative to expandable pedicle screws: Expandable poly-ether-ether-ketone shell

Screw pullout is a very common problem in the fixation of sacrum with pedicle screws. The principal cause of this problem is that the cyclic micro motions in the fixation of sacrum are higher than the other regions of the vertebrae that limit the osteo-integration between bone and screw. In addition to that, the bone quality is very poor at sacrum region. This study investigated a possible solution to the pullout problem without the expandable screws' handicaps. Newly designed poly-ether-ether-ketone expandable shell and classical pedicle screws were biomechanically compared. Torsion test, pullout tests, fatigue tests, flexion/extension moment test, axial gripping capacity tests and torsional gripping capacity tests were conducted in accordance with ASTM F543, F1798 and F1717. Standard polyurethane foam and calf vertebrae were used as embedding medium for pullout tests. Classical pedicle screw pullout load on polyurethane foam was 564.8 N compared to the failure load for calf vertebrae's 1264 N. Under the same test conditions, expandable poly-ether-ether-ketone shell system's pullout loads from polyurethane foam and calf vertebrae were 1196.3 and 1890 N, respectively. The pullout values for expandable poly-ether-ether-ketone shell were 33% and 53% higher than classical pedicle screw on polyurethane foam and calf vertebrae, respectively. The expandable poly-ether-ether-ketone shell exhibited endurance on its 90% of yield load. Contrary to poly-ether-ether-ketone shell, classical pedicle screw exhibited endurance on 70% of its yield load. Expandable poly-ether-ether-ketone shell exhibited much higher pullout performance than classical pedicle screw. Fatigue performance of expandable poly-ether-ether-ketone shell is also higher than classical pedicle screw due to damping the micro motion capacity of the poly-ether-ether-ketone. Expandable poly-ether-ether-ketone shell is a safe alternative to all other expandable pedicle screw systems on mechanical perspective.

Management of osteoporosis in spine surgery.

Osteoporosis is a burgeoning clinical problem that is characterized by decreased bone strength and density. It predisposes patients to fragility fractures and debilitating spine deformities. Several complications are associated with spine surgery in patients with osteoporosis, and there is currently no treatment algorithm to guide the spine surgeon. A multidisciplinary approach to treatment of patients with osteoporosis and spine deformity or fracture is encouraged, and preoperative planning is crucial for successful surgical outcomes. Several surgical techniques have been developed to treat osteoporosis-related deformities, including posterior instrumentation with fusion. However, achieving fixation and fusion in these patients can be difficult secondary to poor bone stock. Augmentation methods to improve pedicle screw fixation have evolved, including instrumentation at multiple levels, bioactive cement augmentation, and fenestrated or expandable pedicle screws, but their impact on clinical outcomes remains unknown. Management of osteoporosis in patients undergoing spine surgery is challenging, but with appropriate patient selection, medical optimization, and surgical techniques, these patients can experience pain relief, deformity correction, and improved function.

Balancing Rigidity and Safety of Pedicle Screw Fixation via a Novel Expansion Mechanism in a Severely Osteoporotic Model

Many successful attempts to increase pullout strength of pedicle screws in osteoporotic bone have been accompanied with an increased risk of catastrophic damage to the patient. To avoid this, a single-armed expansive pedicle screw was designed to increase fixation strength while controlling postfailure damage away from the nerves surrounding the pedicle. The screw was then subsequently tested in two severely osteoporotic models: one representing trabecular bone (with and without the presence of polymethylmethacrylate) and the other representing a combination of trabecular and cortical bone. Maximum pullout strength, stiffness, energy to failure, energy to removal, and size of the resulting block damage were statistically compared among conditions. While expandable pedicle screws produced maximum pullout forces less than or comparable to standard screws, they required a higher amount of energy to be fully removed from both models. Furthermore, damage to the cortical layer in the composite test blocks was smaller in all measured directions for tests involving expandable pedicle screws than those involving standard pedicle screws. This indicates that while initial fixation may not differ in the presence of cortical bone, the expandable pedicle screw offers an increased level of postfailure stability and safety to patients awaiting revision surgery.

Biomechanical evaluation of expansive pedicle screws and injectable absorbable bone cement augmentation in the osteoporotic vertebral environment

Objective To evaluate the fixation strengths of expansive pedicle screws in human cadaveric vertebrae with different bone mineral densities and with the augmentation by newly-developed injectable absorbable bone cement(IABC).Methods Fresh human cadaveric spines used for this study were grouped into 4 levels according to the measurements of bone mineral density:normal,osteopenia,osteoporosis and severe osteoporosis.The vertebrae were bilaterally instrumented with 4 pedicle screw protocols:conventional pedicle screw without augmentation,expansive pedicle screw without augmentation,conventional pedicle screw with augmentation and expansive pedicle screw with augmentation.The statistical method of balanced incomplete randomized blocks was used to assign the pedicles for the 4 protocols,resulting in 9 screws per group per level.Screw pullout tests were conducted.On the load-stroke curve,the maximum pullout strength and stiffness were determined.The differences between groups at the same bone mineral density level but with different screw protocols,or between groups at different bone mineral density levels but with the same screw protocol,were compared.Results Given the same bone mineral density level,the maximum pullout strength and stiffness of expansive screws were significantly higher than those of conventional screws (P ＜ 0.05).When the same type of screw was used,the maximum pullout strength in the augmented group was significantly higher than in the non-augmented group (P ＜ 0.05),but the cement augmentation had insignificant impact on the stiffness of either conventional or expansive pedicle screws (P ＞ 0.05).The pullout strength and stiffness of expansive screws,augmented conventional screws and augmented expansive screws at the osteoporotic level were comparable to those of conventional screws at the osteopenic lcvel (P ＞ 0.05).However,the pullout strength of any of the 4 protocols in the severe osteoporosis group was significantly lower than that of conventional screws in the osteopenia group (P ＜ 0.05).Conclusions Expansive pedicle screws appear feasible and safe in either osteopenic or osteoporotic spines.Augmentation by the newly-developed IABC can further improve the initial fixation strength of either conventional or expansive pedicle screws. Key words: Osteoporosis; Bone screw; Biomechanics; Cement; Pedicle screw augmentation