Biocompatibility and Osteogenic Capacity of Mg-Zn-Ca Bulk Metallic Glass for Rabbit Tendon-Bone Interference Fixation.

Mg-based alloys have great potential for development into fixation implants because of their highly biocompatible and biodegradable metallic properties. In this study, we sought to determine the biocompatibility of Mg60Zn35Ca5 bulk metallic glass composite (BMGC) with fabricated implants in a rabbit tendon-bone interference fixation model. We investigated the cellular cytotoxicity of Mg60Zn35Ca5 BMGC toward rabbit osteoblasts and compared it with conventional titanium alloy (Ti6Al4V) and polylactic acid (PLA). The results show that Mg60Zn35Ca5 BMGC may be classed as slightly toxic on the basis of the standard ISO 10993-5. We further characterized the osteogenic effect of the Mg60Zn35Ca5 BMGC extraction medium on rabbit osteoblasts by quantifying extracellular calcium and mineral deposition, as well as cellular alkaline phosphatase activity. The results of these tests were found to be promising. The chemotactic effect of the Mg60Zn35Ca5 BMGC extraction medium on rabbit osteoblasts was demonstrated through a transwell migration assay. For the in vivo section of this study, a rabbit tendon-bone interference fixation model was established to determine the biocompatibility and osteogenic potential of Mg60Zn35Ca5 BMGC in a created bony tunnel for a period of up to 24 weeks. The results show that Mg60Zn35Ca5 BMGC induced considerable new bone formation at the implant site in comparison with conventional titanium alloy after 24 weeks of implantation. In conclusion, this study revealed that Mg60Zn35Ca5 BMGC demonstrated adequate biocompatibility and exhibited significant osteogenic potential both in vitro and in vivo. These advantages may be clinically beneficial to the development of Mg60Zn35Ca5 BMGC implants for future applications.

Assessment of cardiac adverse events following COVID-19 vaccination by speckle tracking echocardiography.

Cardiac discomfort has been reported periodically in COVID-19-vaccinated individuals. Thus, this study aimed to evaluate the role of myocardial strains in the early assessment of the clinical presentations after COVID-19 vaccination. Totally, 121 subjects who received at least one dose of vaccine within 6 weeks underwent laboratory tests, electrocardiogram (ECG), and echocardiogram. Two-dimensional speckle tracking echocardiography (2D-STE) was implemented to analyze changes in the left ventricular myocardium. After vaccination, 66 individuals (55.4 ± 17.4 years) developed cardiac discomforts, such as chest tightness, palpitations, dyspnea, and chest pain. The ECG readings exhibited both premature ventricular contractions and premature atrial contractions (n = 24, 36.4%), while none of the individuals in the control group manifested signs of cardiac arrhythmia. All had normal serum levels of creatine phosphokinase, creatine kinase myocardial band, troponin, N-terminal pro b-type natriuretic peptide, platelets, and D-dimer. Left ventricular ejection fraction in the symptomatic group (71.41% ± 7.12%) and the control group (72.18% ± 5.11%) (p = 0.492) were normal. Use of 2D-STE presented global longitudinal strain (GLS) and global circumferential strain (GCS) was reduced in the symptomatic group (17.86% ± 3.22% and 18.37% ± 5.22%) compared to the control group (19.54% ± 2.18% and 20.73% ± 4.09%) (p = 0.001 and p = 0.028). COVID-19 vaccine-related cardiac adverse effects can be assessed early by 2D-STE. The prognostic implications of GLS and GCS enable the evaluation of subtle changes in myocardial function after vaccination.

Unraveling the molecular mechanism of collagen flexibility during physiological warmup using molecular dynamics simulation and machine learning.

Physiological warmup plays an important role in reducing the injury risk in different sports. In response to the associated temperature increase, the muscle and tendon soften and become easily stretched. In this study, we focused on type I collagen, the main component of the Achilles tendon, to unveil the molecular mechanism of collagen flexibility upon slight heating and to develop a model to predict the strain of collagen sequences. We used molecular dynamics approaches to simulate the molecular structures and mechanical behavior of the gap and overlap regions in type I collagen at 307 K, 310 K, and 313 K. The results showed that the molecular model in the overlap region is more sensitive to temperature increases. Upon increasing the temperature by 3 degrees Celsius, the end-to-end distance and Young's modulus of the overlap region decreased by 5% and 29.4%, respectively. The overlap region became more flexible than the gap region at higher temperatures. GAP-GPA and GNK-GSK triplets are critical for providing molecular flexibility upon heating. A machine learning model developed from the molecular dynamics simulation results showed good performance in predicting the strain of collagen sequences at a physiological warmup temperature. The strain-predictive model could be applied to future collagen designs to obtain desirable temperature-dependent mechanical properties.

Biomechanical Comparison between Isobar and Dynamic-Transitional Optima (DTO) Hybrid Lumbar Fixators: A Lumbosacral Finite Element and Intersegmental Motion Analysis.

Biomechanical performance of longitudinal component in dynamic hybrid devices was evaluated to display the load-transfer effects of Dynesys cord spacer or Isobar damper-joint dynamic stabilizer on junctional problem based on various disc degenerations. The dynamic component was adapted at the mildly degenerative L3-L4 segment, and the static component was fixed at the moderately degenerative L4-L5 segment under a displacement-controlled mode for the finite element study. Furthermore, an intersegmental motion behavior was analyzed experimentally on the synthetic model under a load-controlled mode. Isobar or DTO hybrid fixator could reduce stress/motion at transition segment, but compensation was affected at the cephalic adjacent segment more than the caudal one. Within the trade-off region (as a motion-preserving balance between the transition and adjacent segments), the stiffness-related problem was reduced mostly in flexion by a flexible Dynesys cord. In contrast, Isobar damper afforded the effect of maximal allowable displacement (more than peak axial stiffness) to reduce stress within the pedicle and at facet joint. Pedicle-screw travel at transition level was related to the extent of disc degeneration in Isobar damper-joint (more than Dynesys cord spacer) attributing to the design effect of axial displacement and angular rotation under motion. In biomechanical characteristics relevant to clinical use, longitudinal cord/damper of dynamic hybrid lumbar fixators should be designed with less interface stress occurring at the screw-vertebral junction and facet joint to decrease pedicle screw loosening/breakage under various disc degenerations.

Kinematic strategies for obstacle-crossing in older adults with mild cognitive impairment.

Introduction: Mild cognitive impairment (MCI) is considered a transitional stage between soundness of mind and dementia, often involving problems with memory, which may lead to abnormal postural control and altered end-point control when dealing with neuromechanical challenges during obstacle-crossing. The study aimed to identify the end-point control and angular kinematics of the pelvis-leg apparatus while crossing obstacles for both leading and trailing limbs. Methods: 12 patients with MCI (age: 66.7 ± 4.2 y/o; height: 161.3 ± 7.3 cm; mass: 62.0 ± 13.6 kg) and 12 healthy adults (age: 67.7 ± 2.9 y/o; height: 159.3 ± 6.1 cm; mass: 61.2 ± 12.0 kg) each walked and crossed obstacles of three different heights (10, 20, and 30% of leg length). Angular motions of the pelvis and lower limbs and toe-obstacle clearances during leading- and trailing-limb crossings were calculated. Two-way analyses of variance were used to study between-subject (group) and within-subject (obstacle height) effects on the variables. Whenever a height effect was found, a polynomial test was used to determine the trend. A significance level of α = 0.05 was set for all tests. Results: Patients with MCI significantly increased pelvic anterior tilt, hip abduction, and knee adduction in the swing limb during leading-limb crossing when compared to controls (p < 0.05). During trailing-limb crossing, the MCI group showed significantly decreased pelvic posterior tilt, as well as ankle dorsiflexion in the trailing swing limb (p < 0.05). Conclusion: Patients with MCI adopt altered kinematic strategies for successful obstacle-crossing. The patients were able to maintain normal leading and trailing toe-obstacle clearances for all tested obstacle heights with a specific kinematic strategy, namely increased pelvic anterior tilt, swing hip abduction, and knee adduction during leading-limb crossing, and decreased pelvic posterior tilt and swing ankle dorsiflexion during trailing-limb crossing. The current results suggest that regular monitoring of obstacle-crossing kinematics for reduced toe-obstacle clearance or any signs of changes in crossing strategy may be helpful for early detection of compromised obstacle-crossing ability in patients with single-domain amnestic MCI. Further studies using a motor/cognitive dual-task approach on the kinematic strategies adopted by multiple-domain MCI will be needed for a complete picture of the functional adaptations in such a patient group.

Segmental Tissue Speckle Tracking Predicts the Stenosis Severity in Patients With Coronary Artery Disease.

OBJECTIVE: Two-dimensional speckle tracking echocardiography (2D-STE) has been used as a diagnostic tool for coronary artery disease (CAD). However, whether vessel supplied myocardial strain and strain rate (SR) predict the severity of coronary artery stenosis in patients with CAD is unknown. This study aimed to investigate correlation of cardiac mechanical parameters in tissue speckle tracking measurements with coronary artery stenosis diagnosed by cardiac catheterization in patients with clinically diagnosed CAD. METHODS AND RESULTS: Among 59 patients analyzed, 170 vessels were evaluated by coronary angiography and the corresponding echocardiography to quantify left ventricular myocardial strain and SR. The average longitudinal strain and SR of the segmental myocardium supplied by each coronary artery were calculated to achieve vessel myocardium strain (VMS) and strain rate (VMSR). The VMS and VMSR at each of four severity levels of stenosis showed significant differences among groups (p = 0.016, and p < 0.001, respectively). The strain and SR in vessels with very severe stenosis (≥75%, group IV; n = 29), 13.9 ± 4.3, and 0.9 ± 0.3, respectively, were significantly smaller than those of vessels with mild stenosis ≤ 25%, group I; n = 88, 16.9 ± 4.9, p = 0.023, and 1.2 ± 0.3, p = 0.001, respectively. The SR in vessels with moderate stenosis (26-49%, group II; n = 37), 1.0 ± 0.2, was significantly smaller than that in vessels with mild stenosis vessels (p = 0.021). The lower VMS and VMSR, the higher possibility of severe coronary stenosis is. The VMS and VMSR lower than 13.9 ± 4.3 and 0.9 ± 0.3, respectively predicted the severe coronary stenosis. The VMS and VMSR higher than 16.9 ± 4.9 and 1.2 ± 0.3, respectively predicted mild or no coronary artery stenosis. CONCLUSIONS: The actual stenosis rate in catheterization demonstrates that this technique was able to assess coronary artery condition. Thus, the application of a non-invasive method of 2D-STE to evaluate and simplify diagnosis of CAD is feasible.

Observation of the ultrastructure of anterior cruciate ligament graft by atomic force microscopy.

This study presented the fibril ultrastructure of retrieved grafts from the reconstruction of anterior cruciate ligament (ACL) using atomic force microscopy (AFM). The tapping mode images of the AFM were taken from different areas of the longitudinally cut grafts. Regular arrangement of collagen fibrils was found in certain areas of the graft. In many areas, however, the fibrils were not well arranged in a single direction, with some smaller fibrils oriented vertically to larger parallel fibrils. The crossing and tangling of fibrils in ACL grafts was well represented in the three-dimensional AFM image. This abnormality of graft ultrastructure might indicate the possible alteration of the mechanical environment after ACL reconstruction. This study demonstrated the suitability and importance of ultrastructure observation of ACL grafts by AFM.

Bone remodeling characteristics of a short-stemmed total hip replacement.

Bone remodeling of a metaphyseal fixed femoral stem, Mayo Conservative Hip (Zimmer International, Warsaw, Ind), was characterized by the dual-energy x-ray absorptiometry and a mathematical remodeling model. The mean age of the patient was 50.8 years, and the mean follow-up was 5.7 years. As anticipated, bony structure underwent significant remodeling after the short-stemmed femoral arthroplasty with resorption proximally and ingrowth distally/laterally. Theoretical prediction further suggested that the remodeling was largely regulated by the mechanical loading distribution pattern determined by implant design.

Effect of cyclic stretching on the tensile properties of patellar tendon and medial collateral ligament in rat.

BACKGROUND: Although dynamic stretching is often prescribed before exercise is undertaken, research has rarely been conducted to determine what effects dynamic stretching has on tendon and ligament injury prevention. The hypothesis is that the mechanical properties of tendon and ligament will increase in an ultimate tensile loading test after sinusoid cyclic stretching. METHODS: Ten paired rat medial collateral ligaments and patellar tendons were used with and without 150 sinusoid cyclic stretching in either side to determine the influence of cyclic stretching on the mechanical behavior of the tendons and ligaments. FINDINGS: The increase in ultimate stress and elastic modulus was significant after sinusoid cycling in both the medial collateral ligaments and the patellar tendons. An adequate sinusoid cyclic stretching could increase the mechanical properties of tendon and ligament under optimization of cyclic strain. INTERPRETATION: A better understanding of the mechanical behavior of tendon and ligament after a series of dynamic stretching prior to exercise may lead to the development of training strategies that could reduce the incidence of injury during sports activities.

Composite Polyelectrolyte Multilayer and Mesoporous Bioactive Glass Nanoparticle Coating on 316L Stainless Steel for Controlled Antibiotic Release and Biocompatibility.

Bacterial infection in wounds or implants can cause osteomyelitis, eventually leading to orthopedic implant failure. In this study, polyelectrolyte multilayer (PEM) coating comprising collagen as the cationic layer, chitosan as the barrier layer and γ-poly-glutamic acid as the anionic layer were fabricated onto a 316L stainless steel substrate by spin coating technique. Tetracycline-loaded 57S mesoporous bioactive glass nanoparticles (57S MBG, SiO2:CaO:P2O5 = 57:33:10 by wt%) were introduced into the γ-poly-glutamic acid layers. Herein, 57S MBG nanoparticles were successfully incorporated into the PEMs with a total thickness of ∼53 µm on 316L stainless steel (SS-PEMs-57S), which exhibited good hydrophilicity with a contact angle of 18.71°. The hardness of SS-PEMs-57S was 0.66 GPa while the Young's modulus was 11.5 GPa; these values are similar to those for the cortical bone. The surface roughness of MBG nanoparticle-incorporated PEMs increased from 231 to 384 nm. Controlled release of tetracycline loaded in MBG nanoparticles resulted in sustained antibacterial effect for up to 7 days, with higher release efficacy at low pH, which may be induced by inflammation or infection. Tetracycline loaded in SS-PEMs-57S showed good bacterial inhibition and maintained good cell viability in rat bone marrow mesenchymal stem cells (BMSCs) in the MTT assay. Moreover, SS-PEMs-57S also promoted mineralization of BMSCs. Therefore, this surface modification technology has great potential for endowing orthopedic implants with antibacterial and osteoconductive properties.

Biomechanical effects of polyaxial pedicle screw fixation on the lumbosacral segments with an anterior interbody cage support.

BACKGROUND: Lumbosacral fusion is a relatively common procedure that is used in the management of an unstable spine. The anterior interbody cage has been involved to enhance the stability of a pedicle screw construct used at the lumbosacral junction. Biomechanical differences between polyaxial and monoaxial pedicle screws linked with various rod contours were investigated to analyze the respective effects on overall construct stiffness, cage strain, rod strain, and contact ratios at the vertebra-cage junction. METHODS: A synthetic model composed of two ultrahigh molecular weight polyethylene blocks was used with four titanium pedicle screws (two in each block) and two rods fixation to build the spinal construct along with an anterior interbody cage support. For each pair of the construct fixed with polyaxial or monoaxial screws, the linked rods were set at four configurations to simulate 0 degrees, 7 degrees, 14 degrees, and 21 degrees lordosis on the sagittal plane, and a compressive load of 300 N was applied. Strain gauges were attached to the posterior surface of the cage and to the central area of the left connecting rod. Also, the contact area between the block and the cage was measured using prescale Fuji super low pressure film for compression, flexion, lateral bending and torsion tests. RESULTS: Our main findings in the experiments with an anterior interbody cage support are as follows: 1) large segmental lordosis can decrease the stiffness of monoaxial pedicle screws constructs; 2) polyaxial screws rather than monoaxial screws combined with the cage fixation provide higher compression and flexion stiffness in 21 degrees segmental lordosis; 3) polyaxial screws enhance the contact surface of the cage in 21 degrees segmental lordosis. CONCLUSION: Polyaxial screws system used in conjunction with anterior cage support yields higher contact ratio, compression and flexion stiffness of spinal constructs than monoaxial screws system does in the same model when the spinal segment is set at large lordotic angles. Polyaxial pedicle screw fixation performs nearly equal percentages of vertebra-cage contact among all constructs with different sagittal alignments, therefore enhances the stabilization effect of interbody cages in the lumbosacral area.

Monitoring the Changes of Material Properties at Bone-Implant Interface during the Healing Process In Vivo: A Viscoelastic Investigation.

The aim of this study was to monitor the changes of viscoelastic properties at bone-implant interface via resonance frequency analysis (RFA) and the Periotest device during the healing process in an experimental rabbit model. Twenty-four dental implants were inserted into the femoral condyles of rabbits. The animals were sacrificed immediately after implant installation or on day 14, 28, or 56 after surgery. Viscoelastic properties at bone-implant interface were evaluated by measuring the implant stability quotient (ISQ) using RFA and by measuring the Periotest values (PTVs) using the Periotest device. The bone/implant specimens were evaluated histopathologically and histomorphometrically to determine the degree of osseointegration (BIC%). The BIC% values at different time points were then compared with the corresponding ISQ values and PTVs. The mean ISQ value increased gradually and reached 81 ± 1.7 on day 56, whereas the mean PTV decreased over time, finally reaching -0.7 ± 0.5 on day 56. Significant correlations were found between ISQ and BIC% (r = 0.701, p < 0.001), PTV and BIC% (r = -0.637, p < 0.05), and ISQ and PTV (r = -0.68, p < 0.05). These results show that there is a positive correlation between implant stability parameters and peri-implant-bone healing, indicating that the RFA and Periotest are useful for measuring changes of viscoelastic properties at bone-implant interface and are reliable for indirectly predicting the degree of osseointegration.

Shock wave treatment shows dose-dependent enhancement of bone mass and bone strength after fracture of the femur.

Shock wave treatment is believed to improve bone healing after fracture. The purpose of this study was to evaluate the effect of shock wave treatment on bone mass and bone strength after fracture of the femur in a rabbit model. A standardized closed fracture of the right femur was created with a three-point bending method in 24 New Zealand white rabbits. Animals were randomly divided into three groups: (1) control (no shock wave treatment), (2) low-energy (shock wave treatment at 0.18 mJ/mm2 energy flux density with 2000 impulses), and (3) high-energy (shock wave treatment at 0.47 mJ/mm2 energy flux density with 4000 impulses). Bone mass (bone mineral density (BMD), callus formation, ash and calcium contents) and bone strength (peak load, peak stress and modulus of elasticity) were assessed at 12 and 24 weeks after shock wave treatment. While the BMD values of the high-energy group were significantly higher than the control group (P = 0.021), the BMD values between the low-energy and control groups were not statistically significant (P = 0.358). The high-energy group showed significantly more callus formation (P < 0.001), higher ash content (P < 0.001) and calcium content (P = 0.003) than the control and low-energy groups. With regard to bone strength, the high-energy group showed significantly higher peak load (P = 0.012), peak stress (P = 0.015) and modulus of elasticity (P = 0.011) than the low-energy and control groups. Overall, the effect of shock wave treatment on bone mass and bone strength appears to be dose dependent in acute fracture healing in rabbits.

Effects of knee position, graft tension, and mode of fixation in posterior cruciate ligament reconstruction: a cadaveric knee study.

PURPOSE: Many knees exhibit residual ligament laxity after posterior cruciate ligament (PCL) reconstruction, which is believed to be technique related. The purpose of this study was to investigate the optimal graft tension, the best angle of knee flexion, and the mode of fixation in PCL reconstruction. TYPE OF STUDY: Anatomic biomechanical study. METHODS: A testing apparatus with frictionless bearing that allows other degrees of freedom except for flexion and extension of the knee joint was designed. The normal PCL tension at different angles of knee flexion was measured with a force transducer, and the optimal tension of the PCL graft that allows full range of knee motion was studied with a tensiometer in 12 cadaver knees. The modes of fixation failure between interference screw fixation and post fixation were studied with an Instron (Canton, MA) machine in 8 cadaver knees. RESULTS: The lowest PCL tension in normal knees was noted at 20 degrees to 30 degrees of knee flexion and the highest at 90 degrees. The optimal tension of PCL graft, which allows full range of knee motion, was 15 lb (68 N). The average load of graft failure was 417 (179-730) N with interference screw fixation and 367 (149-701) N with post fixation when the patellar bone-tendon-bone graft was tested. There was no statistical difference in the failure load between interference screw fixation and post fixation (P =.753); however, the modes of failure differ. The sites of failure for interference screw fixation were 25% caused by rupture of ligament substance and 75% bone plug pullout; those of post fixation were 25% caused by rupture of ligament substance, 37.5% caused by fracture, and 37.5% as a result of suture breakage. CONCLUSIONS: The results of this study suggested that a 15-lb tension to the graft at 20 degrees to 30 degrees of knee flexion is optimal in PCL reconstruction. There was no statistical difference in the failure load between interference fixation and post fixation despite different modes of fixation failure.

A biomechanical study of the cortex-anchorage vertebral screw.

OBJECTIVE: To obtain a comprehensive understanding on the effect of the improvement of fixation strength and on the optimal design in various geometrical parameters of a new screw system through biomechanical analyses. DESIGN: A new screw with the cortex-anchorage was designed and manufactured to improve the fixation of the instrumentation for osteoporotic spine. There were four expandable wings distributed around the screw after insertion. BACKGROUND: Screw loosening or loss of correction caused by insufficient mechanical stability on the bone-screw interface is frequently found in osteoporotic subjects. Similarly, the removal and replacement of a screw in a revision procedure substantially decreases its mechanical fixation. Since cortex is the most rigid part in the vertebral body, emphasis on the cortex-anchorage may offer an optimal fixation of screws. METHODS: The biomechanical evaluation that consists of the pullout test and the finite element analysis was applied to identify the stabilizing effect and the optimal design for the new screw system. In the pullout experiment, the porcine vertebral body with a hollow block of cancellous bone was proposed to simulate an osteoporotic spine. This osteoporotic model was specially simulated the degeneration and destruction of the cancellous bone in vertebrae. In the finite element analysis, the reduction of elastic modulus was used in various levels of vertebral degeneration. RESULTS: Pulling screws out of vertebral bodies with a hollow block of cancellous bone, the mean pullout force was 729 (SD 159) N for the conventional screws, and 1072 (SD 179) N for the new screw system. The finite element analysis showed that the longer screw with bi-cortex fixation was the better option in reducing the bony stress and increased the stability. As the height of wings changed, the stress distributed on vertebral body indicated the lowest in fixation by a screw with the largest wings. Nevertheless, there existed a least displacement of vertebral body and moderately low stress on wings' lateral end when assembled with the middle size wings. CONCLUSION: The stabilization function of expansive wings of the new screw system was enhanced in the osteoporotic vertebra and better than that of a conventional screw. The finite element analysis showed a middle size wing could help the screw to reduce the risk of failure and to improve the vertebral stability. RELEVANCE: Screw loosening or loss of correction caused by insufficient mechanical stability on the bone-screw interface is frequently found in osteoporotic subjects. From the biomechanical point of view, this study had shown that a new design of screw could improve the fixation of the instrumentation for osteoporotic spine. With further investigations that includes the clinical proof and the development of a cortex-anchorage vertebral screw may provide a valuable alternative to the spinal instrumentation for the patients with osteoporosis.

An electromyographic assessment of the anti-G straining maneuver.

BACKGROUND: The anti-G straining maneuver (AGSM), used by aircrew to enhance their +Gz tolerance and to reduce the potential risk of G-induced loss of consciousness, has been recognized as an effective technique. The purpose of this study was to establish an objective tool to evaluate the effectiveness of an aircrew member's AGSM. METHODS: There were 20 healthy subjects who participated in the study, including 8 senior aviation physiological trainers and 12 trainees. The former were familiar with the anti-G maneuver and had experienced high +Gz exposure, the latter had never been exposed to any high +Gz stress before the study. The analytic method of electromyography (EMG) was used to investigate the physical characteristics of the L-1 AGSM. RESULTS: Comparison of the EMG data from the two groups indicated that the mean duration of a breathing cycle of the trainer group was significantly longer than that of the trainee group (p < 0.001). The buccinator was the muscle that had the most rapid firing rate in both groups (p < 0.001). The trainer group had a significantly faster firing rate of the buccinator than the trainee group (p = 0.03). In addition, the trainee group performed the AGSM with a firing sequence of muscles that was different from that of the trainer group. CONCLUSIONS: An automated and quantitative system based on EMG can be used during AGSM training to augment or replace the current subjective evaluation of the trainee's performance.

Biomechanical comparison of axial load between cannulated locking screws and noncannulated cortical locking screws.

The goal of this study was to compare the biomechanical stability of cannulated locking screws and noncannulated cortical locking screws in a periarticular locking plate. Twelve fresh-frozen porcine tibias with a 1-cm gap created distal to the tibial plateau were used to simulate an unstable proximal tibial fracture. All specimens were fixed with a periarticular proximal lateral tibial locking plate and divided into 2 groups based on whether the proximal metaphyseal screw holes of the plate were inserted with either cannulated locking screws or noncannulated cortical locking screws. An axial compressive load was applied to cause failure in each specimen using a materials testing instrument. The axial stiffness and maximum failure strength in axial loading were recorded. Axial stiffness of the constructs using noncannulated cortical locking screw was significantly higher than that of the constructs using cannulated locking screws (P=.006). Axial failure strength of the constructs using noncannulated cortical locking screw was significantly higher than that of the constructs using cannulated locking screws (P=.002). The failure mode observed in all specimens was a permanent screw-bending deformity over the head-shaft junction of proximal metaphyseal screws, irrespective of whether they were cannulated or noncannulated cortical locking screws. Fixation with noncannulated cortical locking screws offered more stability than cannulated locking screws with regard to axial stiffness and failure strength in a porcine model with unstable proximal tibial fractures.

Transpedicle body augmenter in painful osteoporotic compression fractures.

Osteoporotic compression fractures (VCFs) can result in progressive kyphosis and chronic pain. Polymethylmethacrylate has been used for augmentation of VCFs; however, there are cement complications, and long-term fracture healing is unknown. The transpedicle body augmenter (TpBA), a porous titanium spacer, has been reported as an internal support to reconstruct the vertebral body combining short segment fixation in burst fracture. We retrospectively reviewed radiographic and clinical results of TpBA vertebroplasty for single symptomatic VCF in 80 patients. Manual reduction and TpBA vertebroplasty via a paramedian incision with blunt dissection was done. Mean age was 72.3 years (range 51-87 years), and female-male ratio was 66:14. The mean symptom duration was 5 months, and follow-up 44 months. Peri-operative variables and radiographic and clinical results were evaluated. The average operation time was 26.1 min, blood loss 92 cc, and hospitalization 2.3 days. No patient had neurological deterioration. TpBA was found sinking into vertebral body initially, then locked by residual cortex, and finally stabilized within the vertebra. There was no dislodgement of TpBA in the final visit. Sixty-two patients (77.5%) could walk within 3-6 h after operation and the others within 24 h. The anterior vertebral restoration was 8.0 mm initially and 6.1 mm at final follow-up. Wedge angle correction was 11.5 degrees initially and 9.4 degrees at final follow-up. Pain, by the visual analog scale, was 8.6 pre-operatively, 2.5 at day 7 follow-up, and 2.9 at final follow-up. By the questionnaire, 72 of 76 respondents reported a decrease in discomfort after TpBA vertebroplasty, and 63 of 76 patients reported a return to normal activity after operation. The final satisfaction rate was 93.4%. TpBA vertebroplasty led to early and medium-term clinical improvement and anatomic restoration of painful VCFs.

Compressive loading at the end plate directly regulates flow and deformation of the basivertebral vein: an analytical study.

BACKGROUND: Metastatic diseases and infections frequently involve the spine. This is the result of seeding of the vertebral body by tumor cells or bacteria delivered by venous blood from Batson's plexus, which is hypothesized to enter the vertebral body via the epidural veins. Isolated spinal segments deform significantly at the bony end plate when under compression. This deformation could cause a volume change of the vertebral body and may be accompanied by retrograde flow of venous blood. To date, this process has not been investigated quantitatively. The purpose of this study was to determine the volume changes of the vertebral body and basivertebral vein for a vertebral body under compression. METHODS: A three-dimensional finite element mesh model of the L4 segment with both adjacent discs was modified from a 3-D computed tomography scan image. An octagon representing the basivertebral vein was introduced into the center of the vertebral body in the model. Four compressive orientations (1500 N) were applied on the top disc. The volume change of the vertebral body model and the basivertebral vein were then computed. RESULTS: The volume change of the vertebral body was about 0.1 cm3 (16.3% of the basivertebral vein) for the four loading conditions. The maximum cross-sectional area reductions of the basivertebral vein and volume reduction were 1.54% and 1.02%, for uniform compression. CONCLUSION: Our study quantified the small but significant volume change of a modeled vertebral body and cross-sectional areas and that of the basivertebral vein, due to the inward bulging of the end plate under compression. This volume change could initiate the reverse flow of blood from the epidural venous system and cause seeding of tumors or bacterial cells.

Biomechanical analysis of unilateral fixation with interbody cages.

STUDY DESIGN: An in vitro biomechanical study of the stabilizing effects of a different combination of cages and transpedicular instrumentation on experimental degenerative disc disease. OBJECTIVES: To evaluate the biomechanical efficacy of the interbody fusion cage and unilateral posterior instrumentation on the stability of the spine-device construct. SUMMARY OF BACKGROUND DATA: Posterior lumbar interbody fusion (PLIF) has become a clinically established and increasingly popular procedure since its introduction and subsequent modification. Recently, unilateral fixation was reported to have comparable efficacy to bilateral fixation in two- to three-segment posterior instrumentation. This study has been designed to compare biomechanical properties among various spinal fixations, including bilateral versus unilateral fixation with PLIF and cages. METHODS: Thirty porcine L3-L6 spines were separated into six groups. The utilization of one or two cages and unilateral or bilateral instrumentations were reciprocally combined to stabilize the spine with the L4-L5 discectomy, simulating degenerative disc disease. A serial of biomechanical tests, including flexion (5 N-m), extension (5 N-m), compression (250 N), lateral bending (5 N-m), and axial rotation (5 N-m, 25 mm/min), were conducted at the displacement rate of 25 mm/min in five cycles. Stiffness values were derived from loading curves for comparison of spinal stability. RESULTS.: In axial compression, the stiffness of bilateral fixation (BF) and unilateral fixation with two-cage (UF2C) groups were almost identical and only less than that of the bilateral fixation with two cages (BF2C) group. In the flexion, the BF, UF2C, and unilateral fixation with one cage (UF1C) group incurred comparable stiffness to that of the Intact group. In extension, the UF2C group had a comparable stiffness to the BF2C group. In lateral bending, the BF2C group and the UF2C group were the constructs incurring most stiffness. In torsion, the BF group and the UF2C group were less stiff than the BF2C group, but that was statistically insignificant CONCLUSIONS: In the group of unilateral fixation combining PLIF with two cages, the anterior support of cages enabled unilateral instrumentation to restore torsional stiffness and other spinal stability indexes. Considering the initial stability and the load-sharing effect, this study showed that the unilateral fixation combining PLIF and two cages might be a good alternative to spinal fixation.