A computational biomechanical investigation of posterior dynamic instrumentation: combination of dynamic rod and hinged (dynamic) screw.

Currently, rigid fixation systems are the gold standard for degenerative disk disease treatment. Dynamic fixation systems have been proposed as alternatives for the treatment of a variety of spinal disorders. These systems address the main drawbacks of traditional rigid fixation systems, such as adjacent segment degeneration and instrumentation failure. Pedicle-screw-based dynamic stabilization (PDS) is one type of these alternative systems. The aim of this study was to simulate the biomechanical effect of a novel posterior dynamic stabilization system, which is comprised of dynamic (hinged) screws interconnected with a coiled, spring-based dynamic rod (DSDR), and compare it to semirigid (DSRR and RSRR) and rigid stabilization (RSRR) systems. A validated finite element (FE) model of L1-S1 was used to quantify the biomechanical parameters of the spine, such as range of motion, intradiskal pressure, stresses and facet loads after single-level instrumentation with different posterior stabilization systems. The results obtained from in vitro experimental intact and instrumented spines were used to validate the FE model, and the validated model was then used to compare the biomechanical effects of different fixation and stabilization constructs with intact under a hybrid loading protocol. The segmental motion at L4-L5 increased by 9.5% and 16.3% in flexion and left rotation, respectively, in DSDR with respect to the intact spine, whereas it was reduced by 6.4% and 10.9% in extension and left-bending loads, respectively. After instrumentation-induced intradiskal pressure at adjacent segments, L3-L4 and L5-S1 became less than the intact in dynamic rod constructs (DSDR and RSDR) except in the RSDR model in extension where the motion was higher than intact by 9.7% at L3-L4 and 11.3% at L5-S1. The facet loads were insignificant, not exceeding 12N in any of the instrumented cases in flexion. In extension, the facet load in DSDR case was similar to that in intact spine. The dynamic rod constructions (DSDR and RSDR) led to a lesser peak stress at screws compared with rigid rod constructions (DSRR and RSRR) in all loading cases. A dynamic construct consisting of a dynamic rod and a dynamic screw did protect the adjacent level from excessive motion.

Bilateral late remote cerebellar hemorrhage as a complication of a lumbo-peritoneal shunt applied after spinal arteriovenous malformation surgery.

BACKGROUND/OBJECTIVE: Cerebellar hemorrhage is a very infrequent and unpredictable complication of spinal surgery. To the best of our knowledge, cerebellar hemorrhage resulting from the insertion of a lumbo-peritoneal shunt through which cerebrospinal fluid (CSF) is slowly drained has not been documented to date. METHODS: Case report. RESULTS: A 47-year-old woman presented with lower extremity weakness. Spinal arteriovenous malformation was diagnosed, and she underwent surgery. Her neurologic status improved; however, CSF collected subcutaneously as a cyst and leaked 21 days after surgery. The patient underwent urgent surgery during which the dural defect was repaired and a lumbo-peritoneal catheter was put in place to treat the CSF leakage. The lumbo-peritoneal drainage system was removed when bilateral cerebellar hemorrhage was seen 12 days later. Physical therapy was stopped, and conservative treatment was initiated consisting of bed rest, analgesics, sedatives, and careful monitoring of blood pressure. The patient's headache gradually resolved; physical therapy was restarted to rehabilitate this patient with paraparesis. CONCLUSIONS: Remote cerebellar hemorrhage seems to be life threatening and entails significant morbidity. Cerebellar symptoms, and even a late sudden headache after spinal surgery, may be signs of remote cerebellar hemorrhage, which is a rare complication.

Idiopathic spinal cord herniation: case report and review of the literature.

BACKGROUND: Idiopathic spinal cord herniation (ISCH) is a rare cause of progressive myelopathy frequently present in Brown-Séquard syndrome. Preoperative diagnosis can be made with magnetic resonance imaging (MRI). Many surgical techniques have been applied by various authors and are usually reversible by surgical treatment. METHODS: Case report and review of the literature. FINDINGS: A 45-year-old woman with Brown-Séquard syndrome underwent thoracic MRI, which revealed transdural spinal cord herniation at T8 vertebral body level. During surgery the spinal cord was reduced and the ventral dural defect was restorated primarily and reinforced with a thin layer of subdermal fat. The dural defect was then closed with interrupted stitches. RESULTS: Although neurologic status improved postoperatively, postsurgical MRI demonstrated swelling and abnormal T2-signal intensity in the reduced spinal cord. Review of the English language literature revealed 100 ISCH cases. CONCLUSIONS: ISCH is a rare clinical entity that should be considered in differential diagnosis of Brown-Séquard syndrome, especially among women in their fifth decade of life. Outcome for patients who initially had Brown-Séquard syndrome was significantly better than for patients who presented with spastic paralysis. Although progression of neurologic deficits can be very slow, reduction of the spinal cord and repair of the defect are crucial in stopping or reversing the deterioration.

Motion analysis study on sensitivity of finite element model of the cervical spine to geometry.

Numerous finite element models of the cervical spine have been proposed, with exact geometry or with symmetric approximation in the geometry. However, few researches have investigated the sensitivity of predicted motion responses to the geometry of the cervical spine. The goal of this study was to evaluate the effect of symmetric assumption on the predicted motion by finite element model of the cervical spine. We developed two finite element models of the cervical spine C2-C7. One model was based on the exact geometry of the cervical spine (asymmetric model), whereas the other was symmetric (symmetric model) about the mid-sagittal plane. The predicted range of motion of both models-main and coupled motions-was compared with published experimental data for all motion planes under a full range of loads. The maximum differences between the asymmetric model and symmetric model predictions for the principal motion were 31%, 78%, and 126% for flexion-extension, right-left lateral bending, and right-left axial rotation, respectively. For flexion-extension and lateral bending, the minimum difference was 0%, whereas it was 2% for axial rotation. The maximum coupled motions predicted by the symmetric model were 1.5° axial rotation and 3.6° lateral bending, under applied lateral bending and axial rotation, respectively. Those coupled motions predicted by the asymmetric model were 1.6° axial rotation and 4° lateral bending, under applied lateral bending and axial rotation, respectively. In general, the predicted motion response of the cervical spine by the symmetric model was in the acceptable range and nonlinearity of the moment-rotation curve for the cervical spine was properly predicted.

Determination of the biomechanical effect of an interspinous process device on implanted and adjacent lumbar spinal segments using a hybrid testing protocol: a finite-element study.

OBJECT The authors evaluated the biomechanical effects of an interspinous process (ISP) device on kinematics and load sharing at the implanted and adjacent segments. METHODS A 3D finite-element (FE) model of the lumbar spine (L1-5) was developed and validated through comparison with published in vitro study data. Specifically, validation was achieved by a flexible (load-control) approach in 3 main planes under a pure moment of 10 Nm and a compressive follower load of 400 N. The ISP device was inserted between the L-3 and L-4 processes. Intact and implanted cases were simulated using the hybrid protocol in all motion directions. The resultant motion, facet load, and intradiscal pressure after implantation were investigated at the index and adjacent levels. In addition, stress at the bone-implant interface was predicted. RESULTS The hybrid approach, shown to be appropriate for adjacent-level investigations, predicted that the ISP device would decrease the range of motion, facet load, and intradiscal pressure at the index level relative to the corresponding values for the intact spine in extension. Specifically, the intradiscal pressure induced after implantation at adjacent segments increased by 39.7% and by 6.6% at L2-3 and L4-5, respectively. Similarly, facet loads at adjacent segments after implantation increased up to 60% relative to the loads in the intact case. Further, the stress at the bone-implant interface increased significantly. The influence of the ISP device on load sharing parameters in motion directions other than extension was negligible. CONCLUSIONS Although ISP devices apply a distraction force on the processes and prevent further extension of the index segment, their implantation may cause changes in biomechanical parameters such as facet load, intradiscal pressure, and range of motion at adjacent levels in extension.

Idiopathic spinal cord herniation at two separate zones of the thoracic spine: the first reported case and literature review.

BACKGROUND CONTEXT: Idiopathic spinal cord herniation (ISCH) is a rare cause of progressive myelopathy. Preoperative diagnosis can be made with magnetic resonance imaging (MRI). Many surgical techniques have been applied by various authors, and ISCH is usually reversible by surgical treatment. PURPOSE: To present a case of ISCH in two separate zones at two thoracic levels. To our knowledge, this is the first such case to be published in English literature. We also discuss the clinical findings, surgical procedures, and surgical outcomes for other previously reported cases of ISCH in the literature. STUDY DESIGN: Case report. METHODS: A 52-year-old woman with bilateral lower extremity weakness underwent thoracic MRI, which revealed transdural spinal cord herniation at two separate zones, namely, the T4-T5 and T5-T6 intervertebral disc levels. RESULTS: During surgery, the spinal cord was reduced, the two separate dural defects were connected, and the new single defect was restored then reinforced with a thin layer of fascial graft. The posterior dural defect was then closed with interrupted stitches. The patient's neurologic status was characterized by no changing of the preoperative motor status. Follow-up MRI scans showed that the cord was replaced in the dural sac and showed cord hyperintensity in the herniation levels. The patient could move with a cane at the sixth month postoperatively. CONCLUSIONS: Idiopathic spinal cord herniation is a rare clinical condition that should be considered in the differential diagnosis of paraplegia. Although progression of neurologic deficits can be very slow, reduction of the spinal cord and repair of the defect are crucial to stop or reverse the deterioration. The outcome for patients who initially have Brown-Séquard syndrome is significantly better than for patients who presented with spastic paralysis. To our knowledge, this case study represents the first reported instance in which two separate anterior dural defects caused two levels of anterior spinal cord herniation.

Preserving the ligamentum flavum in lumbar discectomy: a new technique that prevents scar tissue formation in the first 6 months postsurgery.

OBJECTIVE: Postoperative fibrosis is one of the most important causes of failed back surgery syndrome after lumbar disc surgery. Numerous natural and synthetic materials have been investigated as means to prevent or reduce postoperative scarring after these operations. Preservation of the ligamentum flavum for this purpose has not been studied in depth. A prospective, randomized, controlled clinical study was conducted. The aim was to present a new technique for preserving the ligamentum flavum during lumbar discectomy, and to evaluate whether this helps prevent or diminish postoperative fibrosis. METHODS: Twenty patients with unilateral L5-S1 disc herniation were randomly divided into two equal groups. Group A patients underwent classic microlumbar discectomy, and Group B patients underwent the same procedure but with preservation of the ligamentum flavum. Visual analog pain scale (VAPS) scores, Oswestry scale scores, and straight-leg raising angles were recorded preoperatively and at 6 months postoperatively. Differences between the pre-operative and postoperative findings for each group were statistically compared using the Wilcoxon test. Magnetic resonance imaging was also done at 6 months to assess the extent of postoperative fibrosis, and a "scarring grade" was recorded for each patient. The group findings for this were analyzed with Levene's test. RESULTS: Both groups' clinical parameters were significantly improved at 6 months postsurgery. In Group A, the mean pre- and postoperative VAPS scores were 9.2 and 3.2, respectively (P < 0.05); the corresponding mean Oswestry scale scores were 88 and 28.2, respectively (P < 0.05); and the corresponding mean straight-leg raising angles were 290 and 630, respectively (P < 0.05). In Group B, the mean pre- and postoperative VAPS scores were 9.2 and 2.6, respectively (P < 0.05); the corresponding mean Oswestry scores were 85.2 and 22.2, respectively (P < 0.05); and the corresponding mean straight-leg raising scores were 260 and 710, respectively (P < 0.05). The mean scarring grades in Groups A and B were 1.8 and 1.0, respectively (P < 0.05). CONCLUSION: The groups both showed satisfactory clinical outcomes and the improvements were comparable; however, the group with preserved ligamentum flavum showed significantly less local fibrosis at 6 months postoperatively. The authors speculate that this surgical technique provides a physical protective barrier that can reduce or even eliminate fibrosis-related complications after lumbar disc surgery.