Anterior plates are used to increase the initial stability of anterior cervical spine fusions; however, plating has been suggested to cause graft stress shielding, leading to reduced fusion rates. The objectives of this study were to quantify the effects of graft size and plating (static versus dynamic) and the role of the posterior elements on load transmission in anterior cervical fusion. A C5 corpectomy was performed on six human cervical spines (C3-C7). An instrumented height-adjustable graft and dynamic cervical plate were used to measure axial load transmission. Each specimen underwent axial compressive testing with dynamic and static plate configurations, optimal and undersized graft heights, and posterior elements intact and removed. Dynamic plating allowed significantly more load transmission by the graft, particularly in the undersized graft configuration. The posterior elements play a significant role in load transmission.
The purpose of this study was to analyze the effect of lumbar spine fusion on the superior adjacent intervertebral disk in the context of disk degeneration, using a nonlinear three-dimensional finite element method. Detailed L3–L5 motion segment models of normal and degenerated intervertebral disks were developed. In fusion models, L4–L5 was fixed by either posterolateral fusion or posterior lumbar interbody fusion (PLIF). Various loading conditions such as compression loading, compression loading plus flexion moment loading, or compression loading plus extension moment loading were applied to study the corresponding stress. Tresca stress on the posterolateral part of intervertebral annulus fiber and von Mises stress on the vertebral endplate (the superior and inferior sides of L3 and L4) were reduced in all degenerated disk models compared with the normal disk models. The PLIF model showed an increase in the percentage change of stress on the vertebral endplate and on the intervertebral annulus fibrosus when flexion and extension moment loadings were applied. This finding suggests that surgeons should consider the risk of exacerbating degeneration of intervertebral disks by undertaking lumbar spine fusion, when degeneration is found in intervertebral disks adjacent to vertebrae requiring fusion.
Despite the frequency of dural tears in spinal surgery, meningitis is a rare complication reported to occur with a frequency of 0.18%. To the best of our knowledge, no case of Acinetobacter baumanii meningitis has been reported in the literature after a dural tear secondary to lumbar spine discectomy. This case highlights the importance of repairing all dural tears and commencing antibiotics that cover uncommon bacteria in those who develop symptoms of meningitis in this setting.
Biomechanical analyses under compression, flexion, and extension loading were performed to evaluate the stability of interbody, posterolateral, posterior, and facet fusions using a nonlinear three-dimensional finite element method. The effects of facet fusion on other lumbar fusions were also examined. A three-dimensional L4-L5 motion segment model was developed that took into consideration the material nonlinearities of ligaments and annular fibers and the contact nonlinearities of facet joints. Of all models of fusion, maximum rigidity was obtained in the interbody fusion model. In the posterolateral, posterior, and facet fusion models under compression, axial displacement and flexion rotation were induced. In combination with facet fusion, the interbody, posterolateral, and posterior fusion models demonstrated a decrease in axial displacement of about 6%, 1%, and 5%, respectively, under compression and a decrease in rotation angle of about 22%, 12%, and 48%, respectively, under flexion-extension loading. Stress concentration moved principally toward the fusion site, indicating increased load transfer across the fusion mass. Our findings suggest that a more solid fixation can be expected from lumbar fusion--especially in posterior fusion--if facet fusion is performed.
Far-out foraminal stenosis with radiculopathy caused by bony spur formation secondary to anomalous articulation between the transverse process and the sacral ala is rarely reported. We report two cases of unilateral far-out foraminal entrapment of the L5 spinal nerve below a transitional vertebra, with a review of the literature. The objective of this work was to describe the management of a rare far-out foraminal stenosis below a transitional vertebra and to evaluate the surgical and conservative procedures and results. In a previous article, decompression was performed through an anterior approach. However, we report no difficulty with decompression using a posterior approach for one patient. The diagnosis was confirmed with computed tomography, magnetic resonance imaging, and selective radiculography. First, selective nerve root blocks were performed in two cases for the purpose of nonoperative treatment. After failure of conservative treatment with selective nerve root block, one patient underwent posterior decompression by resection of the bony spur using a posterior approach. One patient obtained good relief of radicular pain with only selective nerve root block. The other patient obtained good relief of radicular pain after posterior decompression was performed. Posterior decompression through the posterior approach is an easy, safe, and useful treatment for radicular pain caused by an L5 nerve far-out foraminal stenosis below a transitional vertebra when conservative treatments have failed to obtain good relief of radicular pain.
The author presents a case in which a severe chronic thoracolumbar kyphotic posttraumatic deformity was corrected by a one-block spondylectomy with spine shortening, using a posterior approach. A 19-year-old paraplegic woman was admitted with a chronic deformity of the thoracolumbar spine due to a telescoped posterior dislocation of L1 on T12, which had occurred 8 months earlier. Single reduction by axial traction was impossible. Surgical correction was achieved by means of a total, one-block, L1 spondylectomy and end-to-end apposition of the T12 inferior platform onto the L2 superior platform. This was performed through a posterior approach. The reduction was fixed by a pedicular instrumentation extended from T10 to L4. To our knowledge, this is the first documented case in which the spondylectomy was performed in a single block including the vertebral body and posterior arch in the same piece. Five years following surgery, the clinical result is excellent with complete correction of the deformity and solid interbody vertebral fusion. The complete transection of the spinal cord permitted this aggressive approach, which would have not been possible in other types of pathology.
The computed tomography (CT) studies of the cervical spine from 50 males and 50 females were reviewed to provide morphometric data on a variety of anatomic parameters relevant to anterior cervical reconstruction and fixation. Measurements were made of the vertebral body width and midsagittal anteroposterior (AP) diameter and the distance between the medial borders of the longus coli muscles. Distances between adjacent endplates were also measured, both at their midpoint and at the anterior margin. Widths of the vertebral bodies measure 24.6 +/- 2.4 and 23.0 +/- 2.4 mm in males and females, respectively, with the narrowest measuring 17 and 14, respectively. The average midsagittal AP diameter of each vertebral body in males was approximately 17-18 mm, with the smallest AP diameter measured to be 13 mm. The average midsagittal AP diameter of each vertebral body in females was approximately 15-16 mm, with the smallest being 10 mm. CT scanning provides excellent osseous detail for the measurement of such parameters, and with its widespread use in the evaluation of cervical disorders, large numbers of patients can be reviewed.
The purpose of this study was to determine the locations and loci of instantaneous axes of rotation (IARs) of the T10-T11 motion segment in flexion and extension. An anatomically accurate three-dimensional model of thoracic T10-T11 functional spinal unit (FSU) was developed and validated against published experimental data under flexion, extension, lateral bending, and axial rotation loading configurations. The validated model was exercised under six load configurations that produced motions only in the sagittal plane to characterize the loci of IARs for flexion and extension. The IARs for both flexion and extension under these six load types were directly below the geometric center of the moving vertebra, and all the loci of IARs were tracked superoanteriorly for flexion and inferoposteriorly for extension with rotation. These findings may offer an insight to better understanding of the kinematics of the human thoracic spine and provide clinically relevant information for the evaluation of spinal stability and implant device functionality.
Summary: Nerve root anomalies are frequently underrecognized on advanced imaging studies and may account for some percentage of failed spinal surgical procedures. The conjoined nerve root represents the most common nerve root anomaly. It is a well-known cause of false-positive readings for bulging and herniated disks in patients with purely axial neuroimaging studies. A retrospective evaluation of consecutive microsurgical lumbar diskectomies in 80 patients during a 5-year period was undertaken. A total of four patients (5%) were found intraoperatively to have evidence of a conjoined nerve root by the classification of Neidre. None was diagnosed preoperatively. Coronal magnetic resonance imaging offers the best means of visualizing a conjoined nerve root. The chance for a successful operation can be significantly enhanced if the surgeon is prepared to encounter this pathology.
Expansive laminoplasty of the cervical spine was performed for 15 patients with subaxial lesion (SAL) in rheumatoid arthritis (RA) with or without symptomatic occipitocervical pathology. Clinical results were satisfactory, and radiographic evaluation revealed that the range of movement of the cervical spine decreased to 56.3%, spinal alignment was well preserved, and intervertebral slipping advanced only slightly. Therefore, expansive laminoplasty is shown to be clinically effective in decompressing the subaxial spinal cord without the need for fusion of this region, yet it avoids exacerbating or creating significant instability. We found that it can serve as a useful procedure for treating spinal cord compression caused by SAL in RA. For patients with upper cervical instability, laminoplasty with upper cervical fusion appears to be an effective option. In a case in which kyphosis was observed preoperatively, its deformity became worse after laminoplasty. Thus, it may be advisable to consider subaxial fusion in such cases.
The aim of this work was to add to the body of data on the frequency and severity of degenerative radiographic findings at adjacent levels after anterior cervical interbody fusion and on their clinical impact and to contribute to the insights about their pathogenesis. One hundred eighty patients who were treated by anterior cervical interbody fusion and who had a follow-up of >60 months were clinically and radiologically examined by independent investigators. For all patients, the long-term Odom score was compared with the score as obtained 6 weeks after surgery. For myelopathic cases, both the late Nurick and the Odom score were compared with the initial postoperative situation. For the adjacent disc levels, a radiologic "degeneration score" was defined and assessed both initially and at long-term follow-up. At late follow-up after anterior cervical interbody fusion, additional radiologic degeneration at the adjacent disc levels was found in 92% of the cases, often reflecting a clinical deterioration. The severity of this additional degeneration correlated with the time interval since surgery. The similarity of progression to degeneration between younger trauma patients and older nontrauma patients suggests that both the biomechanical impact of the interbody fusion and the natural progression of pre-existing degenerative disease act as triggering factors for adjacent level degeneration.
Despite the frequency of dural tears in spinal surgery, meningitis is a rare complication reported to occur with a frequency of 0.18%. To the best of our knowledge, no case of Acinetobacter baumanii meningitis has been reported in the literature after a dural tear secondary to lumbar spine discectomy. This case highlights the importance of repairing all dural tears and commencing antibiotics that cover uncommon bacteria in those who develop symptoms of meningitis in this setting.
A retrospective review of 12 patients who were victims of penetrating trauma with a bullet or bullet fragments lodged within the intervertebral disk space was conducted. The objective of the review was to evaluate the potential systemic effects of lead resorption at long-term follow-up. Literature regarding the potential for lead toxicity due to retained bullet fragments within the intervertebral disk space is lacking. Between January 1969 and June 1993, a total of 238 patients with a gunshot wound to the spine were identified. Twelve of the 238 were found to have a bullet or bullet fragments within the intervertebral disk space. All patients were fully screened for evidence of plumbism. The average age at time of gunshot injury was 35.8 years; the average time for follow-up was 7.8 years. One of the 12 patients showed clinical evidence of plumbism. The patient subsequently underwent a partial laminectomy and diskectomy with excision of the bullet fragments. The patient's complaints, specific for plumbism, resolved 2 months postoperatively. We conclude that patients with retained lead-based bullet fragments in the intervertebral disk should be educated about the rare potential for plumbism due to partial bullet fragment resorption and that long-term observation for this disorder is recommended.
Studies reported previously in the literature have described the importance of material variation on the cervical responses and have examined some effects by varying the material properties, but there is no systematic approach using statistical methods to understand the influence of material variation on a cervical spine model under a full range of loading conditions, especially under compression and anterior and posterior shear. A probabilistic design system based on Monte Carlo simulation methods using Latin hypercube sampling techniques is used to analyze the material sensitivity of a C4-C6 cervical spine model involving 13 uncertain input parameters on the biomechanical responses and disc annulus stresses under compression, anterior shear, posterior shear, flexion, extension, lateral bending, and axial rotation. The loading types and range of values were as follows: compression, 0-1 mm; anterior shear, 0-2 mm; posterior shear, 0-3.5 mm; flexion, extension, lateral bending, and axial rotation, 0-1.8 Nm with 73.6-N preload. For each case, the load-deflection and key stress values at various spinal components were captured after each load step. The model was also validated under the same conditions. The minimum and maximum predicted responses were within the range of the experimental data. Ignoring compression loading, the combined effects on the biomechanical responses of the cervical ligaments under the remaining loads are enormous. Their total impacts are almost equal to or slightly less than the influence of disc annulus. Results show that the fiber mechanical properties did not have a significant effect on the compressive stiffness. This study reveals important features that help us identify the critical input parameters and enable us to reduce the development time of a patient-specific biomechanical model.
To determine the cause of neurologic symptoms and signs seen in discitis, the neural histopathologic effects of discitis were investigated in an experimental study carried out on rats. Groups of seven rats each had their intervertebral discs inoculated with either Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, or a control solution. Histopathologic examinations of the spinal cord and nerve roots were performed after 3 weeks. On histopathologic examination, vacuolar myelopathy in the spinal cord and vacuolar neuropathy within the nerve roots near the junction with the spinal cord were found. The severity and form of vacuolar myelopathy varied according to the bacteria used for inoculation. The myelopathy and neuropathy seen in this rat model of bacterial discitis might be the result of an immunologic mechanism and could be responsible for the neurologic signs and symptoms of discitis in patients.
Rigid screw fixation of the axis, for either atlantoaxial fixation or for incorporation of C2 into subaxial cervical constructs, provides significant stability and excellent long-term fusion results but remains technically demanding due to the danger of injury to the vertebral artery. Anatomic variability of the foramen transversarium in the body of the axis can preclude safe transarticular C1–C2 screw placement in up to 20% of patients. Although more recent methods of C2 screw fixation with pedicle screws allow safer fixation in a higher number of patients, there remains a significant risk to the vertebral artery with C2 pedicle screw placement. The author describes a novel technique of C2 rigid screw fixation using bilateral, crossing C2 laminar screws, not previously reported in the literature, which does not place the vertebral artery at risk during C2 fixation. This technique has been successfully used by the author in cases of craniocervical and atlantoaxial fixation as well as for incorporation of C2 into sub-axial fixations. The technique is illustrated, and the author's initial experience in treating 10 patients with crossing, bilateral C2 aminar screws for indications of trauma, neoplasm, pseudarthrosis, and degenerative disease is reviewed. The possible advantages of C2 fixation with C2 laminar screws are discussed.
This retrospective consecutive case study evaluated the effect of anterior plating on multilevel anterior cervical decompressions and fusions in smokers and non-smokers. Multilevel anterior cervical decompression and fusion surgery in smokers provides an important challenge. Higher nonfusion rates in smokers have been reported. Cigarette smoking has been shown to interfere with bone metabolism and revascularization and to suppress bone formation. One hundred six patients underwent anterior cervical decompression and fusion using autografts or allografts and anterior plating. The minimum follow-up was 12 months. The mean age was 50.12 years (+/- 11.72; range, 27 to 80 years). Autografts were used in 90 patients and allograft in 16. The mean level fused was 2.74 (+/- 0.61). Forty-six (45.5%) patients were smokers. Successful fusion was achieved in all but three patients (97.17%). C5 root weakness was seen in four patients (3.8%); two patients experienced acute airway obstruction, of which one required tracheotomy. Temporary recurrent laryngeal nerve palsy developed in three (2.8%) patients. A fusion rate of 97% was achieved in multilevel anterior cervical decompression and fusions using anterior plating. No difference in fusion rates between smokers and nonsmokers was seen. Anterior cervical plating markedly improved the fusion rate in smokers.
The authors describe a patient with severe lower back and left leg pain in the early postoperative period after cardiac surgery. Radiologic examination revealed gas in the spinal epidural space at the level of L4-5. The pain could not be relieved with analgesics and the patient underwent lumber surgery after cardiac surgery. After decompression, the patient improved and was discharged with no symptoms.
Two patients with previously unreported clinically evident myelopathy caused by herniated intervertebral disks are described. These patients had isolated posterior column dysfunction in the lower extremities without motor deficits, abnormal reflexes, spinothalamic sensory abnormalities, or sphincter changes. The level of cord compression was significantly more cranial than suggested by clinical localization, and the results of initial radiographic studies were unremarkable. Study of posterior column dysfunction using somatosensory evoked potentials was helpful in localizing the lesions and guiding appropriate neuroradiologic studies.
Neurogenic dumbbell tumors occur more frequently in the cervical than in the thoracic or lumbar spine. Cervical paravertebral masses usually do not become exceptionally large because they are superficial and are palpated easily. Thoracic tumors can become large before they are detected. The authors describe a large intrathoracic dumbbell tumor arising from the C8 nerve root. The intraspinal tumor was resected through a posterior approach. In the second stage, dividing the clavicle, the intrathoracic component was resected by separating it from the lung. Two years after treatment, the preoperative neurologic deficit had improved except for weakness of muscles innervated by the C8 nerve root. Radiographs showed no residual or recurrent mass at the apex of the lung. Sometimes a retroclavicular location may conceal a large paravertebral mass, such as Pancoast tumors. As described here, the transclavicular approach gave adequate access to the cervicothoracic junction.
