Osteoporotic Lumbar Vertebrae Research Articles

Ameliorating effects of bovine colostrum on experimentally induced osteoporotic lumbar vertebrae in female albino rats: a histomorphomeric and scanning electron microscopic study.

Ameliorating effects of bovine colostrum on experimentally induced osteoporotic lumbar vertebrae in female albino rats: a histomorphomeric and scanning electron microscopic study.

Comparison of three different screw trajectories in osteoporotic vertebrae: a biomechanical investigation

BackgroundPedicle screw insertion in osteoporotic patients is challenging. Achieving more screw-cortical bone purchase and invasiveness minimization, the cortical bone trajectory and the midline cortical techniques represent alternatives to traditional pedicle screws. This study compares the fatigue behavior and fixation strength of the cement-augmented traditional trajectory (TT), the cortical bone trajectory (CBT), and the midline cortical (MC).MethodsTen human cadaveric spine specimens (L1 - L5) were examined. The average age was 86.3 ± 7.2 years. CT scans were provided for preoperative planning. CBT and MC were implanted by using the patient-specific 3D-printed placement guide (MySpine®, Medacta International), TT were implanted freehand. All ten cadaveric specimens were randomized to group A (CBT vs. MC) or group B (MC vs. TT). Each screw was loaded for 10,000 cycles. The failure criterion was doubling of the initial screw displacement resulting from the compressive force (60 N) at the first cycle, the stop criterion was a doubling of the initial screw displacement. After dynamic testing, screws were pulled out axially at 5 mm/min to determine their remaining fixation strength.ResultsThe mean pull-out forces did not differ significantly. Concerning the fatigue performance, only one out of ten MC of group A failed prematurely due to loosening after 1500 cycles (L3). Five CBT already loosened during the first 500 cycles. The mean displacement was always lower in the MC. In group B, all TT showed no signs of failure or loosening. Three MC failed already after 26 cycles, 1510 cycles or 2144 cycles. The TT showed always a lower mean displacement. In the subsequent pull-out tests, the remaining mean fixation strength of the MC (449.6 ± 298.9 N) was slightly higher compared to the mean pull-out force of the CBT (401.2 ± 261.4 N). However, MC (714.5 ± 488.0 N) were inferior to TT (990.2 ± 451.9 N).ConclusionThe current study demonstrated that cement-augmented TT have the best fatigue and pull-out characteristics in osteoporotic lumbar vertebrae, followed by the MC and CBT. MC represent a promising alternative in osteoporotic bone if cement augmentation should be avoided. Using the patient-specific placement guide contributes to the improvement of screws’ biomechanical properties.

Can a Deep-learning Model for the Automated Detection of Vertebral Fractures Approach the Performance Level of Human Subspecialists?

Vertebral fractures are the most common osteoporotic fractures in older individuals. Recent studies suggest that the performance of artificial intelligence is equal to humans in detecting osteoporotic fractures, such as fractures of the hip, distal radius, and proximal humerus. However, whether artificial intelligence performs as well in the detection of vertebral fractures on plain lateral spine radiographs has not yet been reported. (1) What is the accuracy, sensitivity, specificity, and interobserver reliability (kappa value) of an artificial intelligence model in detecting vertebral fractures, based on Genant fracture grades, using plain lateral spine radiographs compared with values obtained by human observers? (2) Do patients' clinical data, including the anatomic location of the fracture (thoracic or lumbar spine), T-score on dual-energy x-ray absorptiometry, or fracture grade severity, affect the performance of an artificial intelligence model? (3) How does the artificial intelligence model perform on external validation? Between 2016 and 2018, 1019 patients older than 60 years were treated for vertebral fractures in our institution. Seventy-eight patients were excluded because of missing CT or MRI scans (24% [19]), poor image quality in plain lateral radiographs of spines (54% [42]), multiple myeloma (5% [4]), and prior spine instrumentation (17% [13]). The plain lateral radiographs of 941 patients (one radiograph per person), with a mean age of 76 ± 12 years, and 1101 vertebral fractures between T7 and L5 were retrospectively evaluated for training (n = 565), validating (n = 188), and testing (n = 188) of an artificial intelligence deep-learning model. The gold standard for diagnosis (ground truth) of a vertebral fracture is the interpretation of the CT or MRI reports by a spine surgeon and a radiologist independently. If there were any disagreements between human observers, the corresponding CT or MRI images would be rechecked by them together to reach a consensus. For the Genant classification, the injured vertebral body height was measured in the anterior, middle, and posterior third. Fractures were classified as Grade 1 (< 25%), Grade 2 (26% to 40%), or Grade 3 (> 40%). The framework of the artificial intelligence deep-learning model included object detection, data preprocessing of radiographs, and classification to detect vertebral fractures. Approximately 90 seconds was needed to complete the procedure and obtain the artificial intelligence model results when applied clinically. The accuracy, sensitivity, specificity, interobserver reliability (kappa value), receiver operating characteristic curve, and area under the curve (AUC) were analyzed. The bootstrapping method was applied to our testing dataset and external validation dataset. The accuracy, sensitivity, and specificity were used to investigate whether fracture anatomic location or T-score in dual-energy x-ray absorptiometry report affected the performance of the artificial intelligence model. The receiver operating characteristic curve and AUC were used to investigate the relationship between the performance of the artificial intelligence model and fracture grade. External validation with a similar age population and plain lateral radiographs from another medical institute was also performed to investigate the performance of the artificial intelligence model. The artificial intelligence model with ensemble method demonstrated excellent accuracy (93% [773 of 830] of vertebrae), sensitivity (91% [129 of 141]), and specificity (93% [644 of 689]) for detecting vertebral fractures of the lumbar spine. The interobserver reliability (kappa value) of the artificial intelligence performance and human observers for thoracic and lumbar vertebrae were 0.72 (95% CI 0.65 to 0.80; p < 0.001) and 0.77 (95% CI 0.72 to 0.83; p < 0.001), respectively. The AUCs for Grades 1, 2, and 3 vertebral fractures were 0.919, 0.989, and 0.990, respectively. The artificial intelligence model with ensemble method demonstrated poorer performance for discriminating normal osteoporotic lumbar vertebrae, with a specificity of 91% (260 of 285) compared with nonosteoporotic lumbar vertebrae, with a specificity of 95% (222 of 234). There was a higher sensitivity 97% (60 of 62) for detecting osteoporotic (dual-energy x-ray absorptiometry T-score ≤ -2.5) lumbar vertebral fractures, implying easier detection, than for nonosteoporotic vertebral fractures (83% [39 of 47]). The artificial intelligence model also demonstrated better detection of lumbar vertebral fractures compared with detection of thoracic vertebral fractures based on the external dataset using various radiographic techniques. Based on the dataset for external validation, the overall accuracy, sensitivity, and specificity on bootstrapping method were 89%, 83%, and 95%, respectively. The artificial intelligence model detected vertebral fractures on plain lateral radiographs with high accuracy, sensitivity, and specificity, especially for osteoporotic lumbar vertebral fractures (Genant Grades 2 and 3). The rapid reporting of results using this artificial intelligence model may improve the efficiency of diagnosing vertebral fractures. The testing model is available at http://140.113.114.104/vght_demo/corr/. One or multiple plain lateral radiographs of the spine in the Digital Imaging and Communications in Medicine format can be uploaded to see the performance of the artificial intelligence model. Level II, diagnostic study.

Influence of cement-augmented pedicle screws with different volumes of polymethylmethacrylate in osteoporotic lumbar vertebrae over the adjacent segments: a 3D finite element analysis

BackgroundPolymethylmethacrylate (PMMA) is commonly used for cement-augmented pedicle screw instrumentation (CAPSI) to improve the fixation stability and reduce the risk of screw loosening in the osteoporotic thoracolumbar spine. Biomechanical researches have shown that various dose of cement (1-3 ml) can be injected to enhance screw stability. To date, there have been no studies on the relationship between adjacent segment degeneration and the volume of PMMA. This study aimed to explore the influence of CAPSI with different volumes of PMMA in osteoporotic lumbar vertebrae over adjacent segments by using finite element analysis.MethodsSeven different finite element models were reconstructed and simulated under different loading conditions, including (1) an intact model, (2) three single-level CAPSI models with different volumes of PMMA (1, 1.73, and 2.5 ml), and (3) three double-level CAPSI models with different volumes of PMMA (1, 1.73, and 2.5 ml). To improve the accuracy of the finite element analysis, the models of the injectable pedicle screw and bone cement were created by using a three-dimensional scanning machine and the CAPSI patient’s CT data, respectively. The range of motion (ROM), the stress of intervertebral discs, and the stress of facet in the adjacent segment were comparatively analyzed among the different models.ResultsThe ROMs of the different segments were compared with experimental data, with good agreement under the different load conditions (21.3°, 13.55°, 13.99°, and 6.11° in flexion, extension, bending, and rotation at L3-S1 level, respectively). Compared with the intact model, the ROM, disc stresses, and facet stress in adjacent segments were found to be higher in the six operative models. Otherwise, with a larger volume of PMMA injected, the ROM, disc stresses, and facet stress slightly increased at the adjacent segment. However, the differences were insignificant with the biggest difference less than 3.8%.ConclusionsCAPSI could increase the incidence of disk degeneration in the adjacent segment, while within a certain range, different volumes of PMMA provided an approximate impact over the adjacent segment degeneration.

Novel augmentation technique of percutaneous pedicle screw fixation using hydroxyapatite granules in the osteoporotic lumbar spine: a cadaveric biomechanical analysis.

Percutaneous pedicle screw (PPS) fixation has been commonly used for various spine surgeries. Rigid PPS fixation is necessary to decrease the incidence of screw loosening in osteoporotic spine. Recently, we have reported biomechanical advantages of augmentation technique using hydroxyapatite (HA) granules for PPS fixation in synthetic bone. However, its biomechanical performance in augmenting PPS fixation for osteoporotic spine has not been fully elucidated. The aim of the present study is to perform a cadaveric biomechanical analysis of PPS fixation augmented with HA granules. Thirty osteoporotic lumbar vertebrae (L1-L5) were obtained from 6 cadavers (3 men and 3 women; age 80 ± 9years; bone mineral density 73 ± 9mg/cm3). The maximal pullout strength and maximal insertion torque were compared between the screws inserted into the vertebrae with and without augmentation. In toggle testing, the number of craniocaudal toggle cycles and maximal load required to achieve the 2-mm screw head displacement were also compared. The maximal pullout strength in the screws augmented with HA granules was significantly greater compared to those without augmentation (p < 0.05). The augmentation significantly increased the maximal insertion torque of the screws (p < 0.05). Moreover, the number of toggle cycles and the maximal load required to reach 2mm of displacement were significantly higher in the augmented screws (p < 0.05). The PPS fixation was significantly enhanced by the augmentation with HA granules in the osteoporotic lumbar spine. The PPS fixation augmented with HA granules might decrease the incidence of screw loosening and implant failure in patients with osteoporotic spine.

A bicortical pedicle screw in the caudad trajectory is the best option for the fixation of an osteoporotic vertebra: An in-vitro experimental study using synthetic lumbar osteoporotic bone models

BackgroundIn pedicle screw fixation, the optimal depth and trajectory of insertion are controversial, and this might be because of the wide variations in specimens. The present study aimed to investigate the biomechanically optimal depth and trajectory of screw insertion using synthetic lumbar osteoporotic vertebrae. MethodsA total of 27 synthetic osteoporotic lumbar vertebrae (L3) were used to ensure standard vertebral quality and shape. Pedicle screws having two different lengths (unicortical: to the center of the vertebra; bicortical: to the anterior cortex of the vertebra) were inserted in the following three different trajectories: 1) straight-forward (parallel to the superior endplate), 2) cephalad (toward the anterosuperior corner), and 3) caudad (toward the anteroinferior corner). Maximum insertional torque and pull-out strength were measured. FindingsFor the straight-forward, cephalad, and caudad trajectories, the maximum insertional torque (Ncm) values of unicortical screws were 144.4, 143.1, and 148.9, respectively, and those of bicortical screws were 205.5, 156.2, and 207.8, respectively. The maximum insertional torque values were significantly higher for bicortical screws than unicortical screws (p < 0.001). Additionally, regarding bicortical screws, the maximum insertional torque values were significantly lower for the cephalad trajectory than other trajectories (p = 0.002). The pull-out strength (N) values of bicortical screws for the straight-forward, cephalad, and caudad trajectories were 703.3, 783.9, and 981.3, respectively. The pull-out strength values were significantly lower for the straight-forward trajectory than other trajectories (p = 0.034). InterpretationA bicortical pedicle screw in the caudad trajectory might be the best option to improve fixation in an osteoporotic lumbar vertebra.

Biomechanical study of injectable hollow pedicle screws for PMMA augmentation in severely osteoporotic lumbar vertebrae: effect of PMMA distribution and volume on screw stability.

OBJECTIVEThe purpose of this study was to compare stability of injectable hollow pedicle screws with different numbers of holes using different volumes of polymethylmethacrylate (PMMA) in severely osteoporotic lumbar vertebrae and analyze the relationship between screw stability and distribution and volume of PMMA.METHODSForty-eight severely osteoporotic cadaveric lumbar vertebrae were randomly divided into 3 groups-groups A, B, and C (16 vertebrae per group). The screws used in group A had 4 holes (2 pairs of holes, with the second hole of each pair placed 180° further along the thread than the first). The screws used in group B had 6 holes (3 pairs of holes, placed with the same 180° difference in position). Unmodified conventional screws were used in group C. Each group was randomly divided into subgroups 0, 1, 2, and 3, with different volumes of PMMA used in each subgroup. Type A and B pedicle screws were directly inserted into the vertebrae in groups A and B, respectively, and then different volumes of PMMA were injected through the screws into the vertebrae in subgroups 0, 1, 2, and 3. The pilot hole was filled with different volumes of PMMA followed by insertion of screws in groups C0, C1, C2, and C3. Distributions of PMMA were evaluated radiographically, and axial pull-out tests were performed to measure the maximum axial pullout strength (Fmax).RESULTSRadiographic examination revealed that PMMA surrounded the anterior third of the screws in the vertebral bodies (VBs) in groups A1, A2, and A3; the middle third of screws in the junction area of the vertebral body (VB) and pedicle in groups B1, B2, and B3; and the full length of screws evenly in both VB and pedicle in groups C1, C2, and C3. In addition, in groups A3 and B3, PMMA from each of the screws (left and right) was in contact with PMMA from the other screw and the PMMA was closer to the posterior wall and pedicle than in groups A1, A2, B1, and B2. One instance of PMMA leakage was found (in group B3). Two-way analysis of variance revealed that 2 factors-distribution and volume of PMMA-significantly influenced Fmax (p < 0.05) but that they were not significantly correlated (p = 0.078). The Fmax values in groups in which screws were augmented with PMMA were significantly better than those in groups in which no PMMA was used (p < 0.05).CONCLUSIONSPMMA can significantly improve stability of different injectable pedicle screws in severely osteoporotic lumbar vertebrae, and screw stability is significantly correlated with distribution and volume of PMMA. The closer the PMMA is to the pedicle and the greater the quantity of injected PMMA used, the greater the pedicle screw stability is. Injection of 3.0 mL PMMA through screws with 4 holes (2 pair of holes, with the screws in each pair placed on opposite sides of the screw) produces optimal stability in severely osteoporotic lumbar vertebrae.

Biomechanical comparative study of the stability of injectable pedicle screws with different lateral holes augmented with different volumes of polymethylmethacrylate in osteoporotic lumbar vertebrae

Background ContextPolymethylmethacrylate (PMMA) is widely used for pedicle screw augmentation in osteoporosis. Until now, there had been no studies of the relationship between screw stability and the distribution and volume of PMMA. PurposeThe objective of this study was to analyze the relationship between screw stability and the distribution pattern and injected volume of PMMA. Study DesignThis is a biomechanical comparison of injectable pedicle screws with different lateral holes augmented with different volumes of PMMA in cadaveric osteoporotic lumbar vertebrae. MethodsForty-eight osteoporotic lumbar vertebrae were randomly divided into Groups A, B, and C with different pedicle screws (16 vertebrae in each group), and then each group was randomly divided into Subgroups 0, 1, 2, and 3 with different volumes of PMMA (four vertebra with eight pedicles in each subgroup). A pilot hole was prepared in advance using the same method in all samples. Type A and type B pedicle screws were directly inserted into vertebrae in Groups A and B, respectively, and then different volumes of PMMA (0, 1.0, 1.5, and 2.0 mL) were injected through the screws and into vertebrae in Subgroups 0, 1, 2, and 3. The pilot holes were filled with different volumes of PMMA (0, 1.0, 1.5, and 2.0 mL), and then the screws were inserted in Groups C0, C1, C2, and C3. Screw position and distribution of PMMA were evaluated radiographically, and axial pullout tests were performed to measure maximum axial pullout strength (Fmax). ResultsPolymethylmethacrylate surrounded the anterior one-third of screws in the vertebral body in Groups A1, A2, and A3; the middle one-third of screws in the junction area of the vertebral body and the pedicle in Groups B1, B2, and B3; and the full length of screws evenly in both the vertebral body and the pedicle in Groups C1, C2, and C3. There was no malpositioning of screws or leakage of PMMA in any sample. Two-way analysis of variance revealed that two factors—distribution and volume of PMMA—significantly influenced Fmax (p<.05) but that they were not significantly correlated (p=.088). Fmax values in groups using augmentation with PMMA values significantly improved compared with those in groups without PMMA (p<.05). ConclusionsPolymethylmethacrylate can significantly enhance the stability of different injectable pedicle screws in osteoporotic lumbar vertebrae, and screw stability is significantly correlated with the distribution pattern and the injected volume of PMMA. The closer the PMMA to the pedicle and the greater the quantity of injected PMMA, the greater is the pedicle screw stability. Injection of 2.0 mL of PMMA through screws with four lateral 180° holes or of 1.0 mL of PMMA through screws with six lateral 180° holes increases the stability of pedicle screws.

Superior cortical screw in osteoporotic lumbar vertebrae: A biomechanics and microstructure-based study

BackgroundOsteoporosis reduces the bone-screw purchase, potentially reducing pullout strength and other biomechanical properties. However, the existing pedicle screw approach may not compensate for the detrimental effects of decreased vertebral bone mineral density. MethodsTwo methods of screw insertion were performed in thirteen cadaveric osteoporotic lumbar vertebrae: Magerl's method in the left pedicle, and superior cortical screw method in the right (its entry point located vertically 3 mm above Magerl's point). Before screw fixations, the pedicle and its corresponding vertebral body were divided into six equal layers from cranial to caudal by performing micro-CT and tested for microstructure properties, such as bone mineral density, trabecular bone volume fraction, trabecular thickness, trabecular separation and trabecular number. Further, pedicle was horizontally divided into three regions and tested. After screw fixations, microstructure properties of the bone surrounding the screws were analyzed. Finally, the screw pullout strength was tested biomechanically. FindingsThe bone structure is denser in the upper third of the pedicle and its corresponding vertebral body. A similar microstructure is seen within the pedicle. This study reveals that the pullout strength is significantly correlated to the bone mineral density, trabecular bone volume fraction and trabecular thickness. Biomechanical test showed pullout strength in the superior cortical screw group with mean 613.3 N (SD 200.4) was 22.4% higher than that in the Magerl group with mean 501.2 N (SD 256.6). InterpretationThe superior cortical screw method can be a reliable alternative, to provide better pullout strength for posterior lumbar instrumentation, especially in osteoporotic patients.

Multilevel Contiguous Osteoporotic Lumbar Compression Fractures: The Relationship of Scoliosis to the Development of Cascading Fractures.

Osteoporotic patients can present with either single or multiple fractures secondary to repeated falls and progressive osteoporosis. Multiple fractures often lead to additional spinal deformity and are a sign of more severe osteoporosis. In the thoracic spine, multiple fractures are associated with the development of gradual thoracic kyphosis but neurologic deficits are uncommon. In the lumbar spine, patients with multiple lumbar fractures have more constant lumbar pain, may have symptoms related to concurrent lumbar stenosis or degenerative scoliosis, and may present with radiculopathy, especially with fractures at L4 and L5. In a review of a series of patients with recurrent multiple lumbar fractures or 'cascading' fractures, it was found that all the patients were female, had severe osteoporosis, often untreated, had a previous history of multiple previous thoracic and lumbar fractures, and all had associated scoliotic spinal deformities ranging from 6o to 50o. It was found that if the curve progressed and the greater the degree of curvature, the more frequently subsequent multiple fractures developed, leading to recurrent acute episodes of pain. Forty percent also had additional sacral insufficiency fractures, an unusually high percentage. Biomechanically, the lumbar spine is both more mobile and supports a larger portion of the spinal load compared to the thoracic spine. The existence or worsening of a lumbar spinal deformity from degenerative lumbar scoliosis shifts the mechanical forces more to one side on already weakened osteoporotic lumbar vertebrae and sacrum, leading to an increased incidence of these fractures. Because of the chronic and uneven lower lumbar spinal load with severe vertebral osteoporosis in certain patients with repeat lumbar fractures and worsening degenerative lumbar scoliosis, there may be a rationale to add preventive vertebroplasty at adjacent vertebral endplates when treating acute recurrent lumbar fractures to decrease the incidence of recurrence in other vertebrae.

Biomechanical comparison of pedicle screw augmented with different volumes of polymethylmethacrylate in osteoporotic and severely osteoporotic cadaveric lumbar vertebrae: an experimental study

Background ContextPolymethylmethacrylate (PMMA) is widely used for pedicle screw augmentation in osteoporosis. Intriguingly, there have been no biomechanical comparisons of the stability of pedicle screws augmented with different volumes of PMMA or studies of the relationship between screw stability and volume of PMMA, especially in different degrees of osteoporosis. PurposeThe purposes of the study reported here were to compare screw stability by different volumes of PMMA augmentation, to analyze the relationship between screw stability and PMMA volume, and to make a preliminary determination of the optimum volume of PMMA augmentation for different degrees of osteoporosis. Study DesignThis study is a biomechanical comparison of pedicle screws augmented with various volumes of PMMA in cadaveric lumbar vertebrae. MethodsThirty-six pedicles from 18 osteoporotic lumbar vertebrae were randomly divided into groups A0 through A5, and 36 pedicles from 18 severely osteoporotic lumbar vertebrae were randomly divided into groups B0 through B5. A different volume of PMMA was injected into each one of groups A0 through A5 (0, 0.5, 1.0, 1.5, 2.0, and 2.5 mL, respectively) and into each one of groups B0 through B5 (0, 1.0, 1.5, 2.0, 2.5, and 3.0 mL, respectively), and then pedicle screws were inserted in all vertebrae. After complete solidification of the PMMA, we examined pedicle X-rays, performed axial pullout tests, and determined the maximum axial pullout strength (Fmax) for all samples. ResultsNo PMMA was found around the screws in groups A0 and B0. In groups A1 to A5 and B1 to B5, screws were wrapped by gradually increasing amounts of PMMA. There was no PMMA leakage or screw malpositioning in any samples. The Fmax in groups A1 through A5 increased by 32.40%, 64.42%, 116.02%, 174.07%, and 207.42%, respectively, compared with that in group A0. There were no significant differences in Fmax between groups A0 and A1, A1 and A2, A2 and A3, A3 and A4, and A4 and A5 (p>.05), but there were significant differences in Fmax between any other two groups (p<.05). The Fmax in groups B1 through B5 increased by 23.48%, 48.40%, 106.60%, 134.73%, and 210.04%, respectively, compared with that in group B0. There were no significant differences in Fmax between groups B0 and B1, B0 and B2, B1 and B2, B2 and B3, B3 and B4 (p>.05), but there were significant differences in Fmax between any other two groups (p<.05). There was a significant positive correlation between Fmax and volume of PMMA in both osteoporotic and severely osteoporotic lumbar vertebrae (p<.05). ConclusionsPolymethylmethacrylate can significantly enhance stability of pedicle screws in both osteoporotic and severely osteoporotic lumbar vertebrae. There is a significant positive correlation between screw stability and volume of PMMA. Within a certain range, nevertheless, increasing the volume of PMMA does not significantly improve screw stability. We suggest that 1.5 and 3 mL, respectively, are the volumes of injected PMMA that will optimize pedicle screw stability in osteoporotic and severely osteoporotic lumbar vertebrae.

Improvement on growth of osteoporotic bone tissue around screw and fixation strength of screw induced by stress force from the expanding pedicle screw: dynamic microstructural, histological and biomechanical studies in osteoporotic sheep lumbar vertebrae

Improvement on growth of osteoporotic bone tissue around screw and fixation strength of screw induced by stress force from the expanding pedicle screw: dynamic microstructural, histological and biomechanical studies in osteoporotic sheep lumbar vertebrae

Finite element analysis of osteoporotic lumbar vertebrae L1 under dynamic loading

Finite element analysis of osteoporotic lumbar vertebrae L1 under dynamic loading

The Benefits of Cement Augmentation of Pedicle Screw Fixation Are Increased in Osteoporotic Bone: A Finite Element Analysis

Study DesignBiomechanical study using a finite element model of a normal and osteoporotic lumbar vertebrae comparing resistance with axial pullout and bending forces on polymethylmethacrylate-augmented and non-augmented pedicle screws. ObjectiveTo compare the effect of cement augmentation of pedicle screw fixation in normal and osteoporotic bone with 2 different techniques of cement delivery. Summary of Background DataVarious clinical and biomechanical studies have addressed the benefits of cement augmentation of pedicle screws, but none have evaluated whether this effect is similar, magnified, or attenuated in osteoporotic bone compared with normal bone. In addition, no study has compared the biomechanical strength of augmented pedicle screws using cement delivery through the pedicle screw with delivery through a pilot hole. MethodsThis study was funded by a grant from DePuy Synthes Spine. Normal and osteoporotic lumbar vertebrae with pedicle screws were simulated. The models were tested for screw pullout strength with and without cement augmentation. Two methods of cement delivery were also tested. Both methods were tested using 1 and 2.5 cm3 volume of cement infiltrated in normal and osteoporotic bone. ResultsThe increase in screw pullout force was proportionally greater in osteoporotic bone with equivalent volumes of cement delivered. The researchers found that 1 and 2.5 cm3 of cement infiltrated bone volume resulted in an increase in pullout force by about 50% and 120% in normal bone, and by about 64% and 156% in osteoporotic bone, respectively. The delivery method had only a minimal effect on pullout force when 2.5 cm3 of cement was injected (<4% difference). ConclusionsCement augmentation increases the fixation strength of pedicle screws, and this effect is proportionately greater in osteoporotic bone. Cement delivery through fenestrated screws and delivery through a pilot hole result in comparable pullout strength at higher cement volumes.

Influence of Screw Augmentation in Posterior Dynamic and Rigid Stabilization Systems in Osteoporotic Lumbar Vertebrae

Biomechanical cadaveric study. To determine whether augmentation positively influence screw stability or not. Implantation of pedicle screws is a common procedure in spine surgery to provide an anchorage of posterior internal fixation into vertebrae. Screw performance is highly correlated to bone quality. Therefore, polymeric cement is often injected through specifically designed perforated pedicle screws into osteoporotic bone to potentially enhance screw stability. Caudocephalic dynamic loading was applied as quasi-physiological alternative to classical pull-out tests on 16 screws implanted in osteoporotic lumbar vertebrae and 20 screws in nonosteoporotic specimen. Load was applied using 2 different configurations simulating standard and dynamic posterior stabilization devices. Screw performance was quantified by measurement of screwhead displacement during the loading cycles. To reduce the impact of bone quality and morphology, screw performance was compared for each vertebra and averaged afterward. All screws (with or without cement) implanted in osteoporotic vertebrae showed lower performances than the ones implanted into nonosteoporotic specimen. Augmentation was negligible for screws implanted into nonosteoporotic specimen, whereas in osteoporotic vertebrae pedicle screw stability was significantly increased. For dynamic posterior stabilization system an increase of screwhead displacement was observed in comparison with standard fixation devices in both setups. Augmentation enhances screw performance in patients with poor bone stock, whereas no difference is observed for patients without osteoporosis. Furthermore, dynamic stabilization systems have the possibility to fail when implanted in osteoporotic bone.

The Effects of Risedronate and Exercise on Osteoporotic Lumbar Rat Vertebrae and Their Sensory Innervation

Investigation of sensory innervation of rat osteoporotic lumbar vertebrae using in vitro and in vivo models. To investigate (1) sensory innervation of osteoporotic rat vertebrae, (2) effects of risedronate on sensory neurons, (3) effects of osteoporosis treatment on bone mineral densities (BMDs) and the sensory innervation. Osteoporotic patients without fractures sometimes experience vague low back pain of unknown origin. The mechanisms of osteoporosis treatments against the pain are unclear. (1) The expression of calcitonin gene-related peptide (CGRP) immunoreactive (-ir) or transient receptor potential vanilloid 1 (TRPV1)-ir nerve fibers in vertebrae and dorsal root ganglions (DRG) innervating L3 vertebrae of Sprague Dawley rats labeled with neurotracer were examined in control, sham, and ovariectomized (OVX) rats. (2) Cultured rat neonate DRG neurons in media containing different concentrations of risedronate were immunostained for CGRP, and we measured its activity using axonal length and proportion of CGRP-ir neurons. (3) BMDs and CGRP expression in DRG neurons innervating L3 vertebrae were examined in the following 5 groups: sham (treated with saline), OVX (saline), OVX+EXE (treadmill exercise), OVX+RIS (risedronate), and OVX+RIS+EXE (risedronate and exercise). (1) A few CGRP-ir or TRPV1-ir nerve fibers were observed in the bone marrow. CGRP or TRPV1 expression in DRG was elevated in the OVX group (P < 0.05). (2) The axonal length and proportion of CGRP-ir neurons were dose-dependently suppressed (P < 0.05). (3) BMDs improved and the CGRP expression decreased in the risedronate-treated groups (P < 0.05), especially in the OVX+RIS+EXE group. Sensory innervation of osteoporotic rat vertebrae showed increased expression of CGRP and TRPV1 in DRG neurons. Risedronate suppressed activity of CGRP-ir neurons in vitro, improved BMD, and decreased CGRP expression, especially together with exercise in vivo.

Recovery Effects of a 180 mT Static Magnetic Field on Bone Mineral Density of Osteoporotic Lumbar Vertebrae in Ovariectomized Rats

The effects of a moderate-intensity static magnetic field (SMF) on osteoporosis of the lumbar vertebrae were studied in ovariectomized rats. A small disc magnet (maximum magnetic flux density 180 mT) was implanted to the right side of spinous process of the third lumbar vertebra. Female rats in the growth stage (10 weeks old) were randomly divided into 4 groups: (i) ovariectomized and implanted with a disc magnet (SMF); (ii) ovariectomized and implanted with a nonmagnetized disc (sham); (iii) ovariectomized alone (OVX) and (vi) intact, nonoperated cage control (CTL). The blood serum 17-β-estradiol (E2) concentrations were measured by radioimmunoassay, and the bone mineral density (BMD) values of the femurs and the lumbar vertebrae were assessed by dual energy X-ray absorptiometry. The E2 concentrations were statistically significantly lower for all three operated groups than those of the CTL group at the 6th week. Although there was no statistical significant difference in the E2 concentrations between the SMF-exposed and sham-exposed groups, the BMD values of the lumbar vertebrae proximal to the SMF-exposed area statistically significantly increased in the SMF-exposed group than in the sham-exposed group. These results suggest that the SMF increased the BMD values of osteoporotic lumbar vertebrae in the ovariectomized rats.

Biomechanical In Vitro Testing of Human Osteoporotic Lumbar Vertebrae Following Prophylactic Kyphoplasty With Different Candidate Materials

Biomechanical study of human osteoporotic lumbar vertebrae following prophylactic kyphoplasty. To evaluate the potential benefits of different resorbable candidate materials for use in prophylactic kyphoplasty compared with the behavior of polymethylmethacrylate cement. Kyphoplasty using PMMA bone cement for the stabilization of fractured osteoporotic vertebrae has been established as a useful clinical tool. In several studies, consecutive compression fractures have been reported in vertebrae caudal or cranial to those augmented with bone cement. Consequently, some physicians have begun to treat adjacent vertebrae by means of prophylactic augmentation. Biomechanical in vitro testing was performed on 40 human osteoporotic nonfractured lumbar vertebrae. Three types of bone cement (PMMA, 2 different calcium phosphate cements) and one silicon derivative were assessed during compressive and cyclic sinusoidal testing. Each candidate material was applied bipedicularly under fluoroscopic control. Differing processing qualities of the materials led to substantial differences during cement injection, in particular in the amount of cement filling of the vertebrae. However, in comparison to native vertebrae, augmented specimens showed significantly higher compressive failure. No significant differences between vertebral bodies treated with PMMA and those treated with either type of calcium phosphate cement were documented. The biomechanical properties of the vertebrae could not be significantly improved by the silicon derivative. This study demonstrated that calcium phosphate cements displayed identical behavior to PMMA cement with respect to in vitro mechanical qualities. Consequently, from a mechanical viewpoint, calcium phosphate cements may be used in addition to PMMA cement for kyphoplasty and prophylactic kyphoplasty. Silicon derivatives are apparently not recommendable as candidate materials for kyphoplasty.

Primary Pedicle Screw Augmentation in Osteoporotic Lumbar Vertebrae

Pedicle screw pullout testing in osteoporotic and control human cadaveric vertebrae, comparing augmented and control vertebrae. To compare the pullout strengths of pedicle screws fixed in osteoporotic vertebrae using polymethyl methacrylate delivered by 2 augmentation techniques, a standard transpedicular approach and kyphoplasty type approach. Pedicle screw instrumentation of the osteoporotic spine carries an increased risk of screw loosening, pullout, and fixation failure. Osteoporosis is often cited as a contraindication for pedicle screw fixation. Augmentation of the vertebral pedicle and body using polymethyl methacrylate may improve fixation strength and construct survival in the osteoporotic vertebrae. While the utility of polymethyl methacrylate has been demonstrated for salvage of screws that have been pulled out, the effect of the cement technique on pullout strength in osteoporotic vertebrae has not been previously studied. Thirteen osteoporotic and 9 healthy human lumbar vertebrae were tested. All specimens were instrumented with pedicle screws using a uniform technique. Osteoporotic pedicles were augmented with polymethyl methacrylate using either a kyphoplasty type technique or a transpedicular augmentation technique. Screws were tested in a paired testing array, randomly assigning the augmentation techniques to opposite sides of each vertebra. Pullout to failure was performed either primarily or after a 5000-cycle tangential fatigue conditioning exposure. After testing, following screw removal, specimens were cut in the axial plane through the center of the vertebral body to inspect the cement distribution. Pedicle screws placed in osteoporotic vertebrae had higher pullout loads when augmented with the kyphoplasty technique compared to transpedicular augmentation (1414 +/- 338 versus 756 +/- 300 N, respectively; P < 0.001). An unpaired t test showed that fatigued pedicle screws in osteoporotic vertebrae augmented by kyphoplasty showed higher pullout resistance than those placed in healthy control vertebrae (P = 0.002). Both kyphoplasty type augmentation (P = 0.007) and transpedicular augmentation (P = 0.02) increased pullout loads compared to pedicle screws placed in nonaugmented osteoporotic vertebrae when tested after fatigue cycling. Pedicle screw augmentation with polymethyl methacrylate improves the initial fixation strength and fatigue strength of instrumentation in osteoporotic vertebrae. Pedicle screws augmented using the kyphoplasty technique had significantly greater pullout strength than those augmented with transpedicular augmentation technique and those placed in healthy control vertebrae with no augmentation.