Search

Study Design: An anatomic cadaveric study to characterize the lumbar intraforaminal nerve root attachments., Objectives: To characterize the intraforaminal nerve root attachments and describe their anatomic relationships and biomechanical properties., Summary of Background Data: Observations during foraminotomies for lateral recess stenosis as well as lateral approaches for far lateral disc herniation have shown dense attachments between the nerve root and adjacent structures. Little or no information has appeared in the literature describing intraforaminal nerve root attachments., Methods: Twelve fresh-frozen human cadaveric lumbar spines were used to study intraforaminal ligamentous structures. Four cadavers were cut into sagittal sections for qualitative description, and eight were used for biomechanical testing. Histologic analyses were performed on samples of the foraminal attachments to assure that they were not vascular or neural structures. Biomechanical testing of the nerve roots with ligamentous attachments was performed measuring load to failure along the anatomic axis of the root., Results: The dissections showed four distinct bands extending radially from the nerve root sleeve. The most prominent nerve root attachment was to the facet capsule posteriorly. Other ligaments fanned out with attachments inferiorly and superiorly to the adjacent pedicles and anteriorly to the intervertebral disc. Biomechanical study of the L3, L4, and L5 nerve roots showed a significant increase in strength at failure with axial traction, progressing from L3 to L5., Conclusions: The results demonstrate that these foraminal ligaments are normal anatomic structures within the intervertebral foramen of the lumbar spine. In addition, they may play a role in limiting motion along the nerve root.

The pathophysiology of sciatica is not completely understood, although our understanding of its causes is increasing. Mechanical alterations combined with inflammatory changes lead to pain. Compression alters nerve root conduction and compromises the nutritional support of spinal nerve roots (through intrinsic and extrinsic vascularity and cerebral spinal fluid percolation). Mechanical forces can lead to intraneural damage and functional changes in nerve roots. Chemical and metabolic effects can create an inflammatory response. Varying causes of inflammation coupled with varying degrees of compression can occur anywhere along the cauda equina or spinal nerve root, including the dorsal root ganglia, and contribute to the pain response and neurologic deficits associated with sciatica.

Study Design: The magnetic resonance artifact susceptibility of traces of surgical aluminum, titanium, and stainless steel in a human spine model was investigated. Metallic filings were deposited in noncontiguous disc spaces in five human thoracic spines before magnetic resonance imaging with spin echo and gradient echo sequences., Objectives: Spin echo and gradient echo sequences were used for quantitate and compare void artifact produced by commonly used surgical metals. This was compared to a liquid paraffin control., Summary of Background Data: No significant susceptibility artifact was seen with any metal in all spin echo sequences, including T1 (TR 600, TE 12), T2 (TR 2000, TE 30), proton density (TR 2000, TE 80), and fast T2 scanning (TR 3800, TE 96, Ef)., Methods: Sagittal magnetic resonance imaging permitted void artifact quantification and comparison between different metallic alloys. Two neuroradiologists, working on a blinded basis, evaluated all data and rated the void susceptibility artifact on a scale of 1 (least) to 4 (greatest)., Results: In general, the magnitude of an imaging artifact during magnetic resonance imaging correlated with the magnetism of the metal. Nickel, found in a larger concentration in 316L than in 304 stainless steel, decreases the magnetic resonance artifact of specific metals because of its ability to stabilize iron in a non-magnetic state. Therefore, the 316L stainless steel yielded less artifact production than 304 stainless steel on gradient echo imaging., Conclusion: If upon gradient echo imaging in the postoperative period significant artifact production is noted, stainless steel deposition should be suspected as the causative agent. In this situation, spin echo techniques should be the first approach for attempting optimal visualization of the spinal cord and soft tissue structures.

Injuries caused by compression of spinal nerve roots are frequently encountered clinically. Experimental studies show that several different factors affect the pathophysiologic changes that occur after these injuries. However, the effect of hypertension in conjunction with graded compression of spinal nerve roots is yet unclear. A previously established porcine model was employed, in which the spinal nerve roots were exposed and compressed by an inflatable balloon. Impulse propagation across the compressed nerve segment was studied by the recording of efferent and afferent nerve action potentials, and nerve conduction velocity. The systemic blood pressure was increased by administration of Neo-Synephrine hydrochloride (phenylephrine HCl) (Winthrop Pharmaceuticals, New York, NY) and elevated 40 +/- 5 mm Hg above the normal (100 +/- 5 mm Hg), and electrophysiologic baseline values were recorded. The spinal nerve roots were then compressed for 2 hours with either 0 (control), 50, 100, or 200 mm Hg. The balloon was deflated and the nerve roots were allowed to recover for 1.5 hours. Impulse propagation was studied every 15 minutes and hypertension was maintained throughout the experiment. The results showed no significant changes of the efferent and afferent nerve action potentials at 0.50 or 100 mm Hg. At 200 mm Hg, efferent and afferent nerve action potentials decreased rapidly and were almost abolished within 20 minutes of compression. Some but not significant recovery was seen of the nerve impulse. Compared to data from normotensive pigs in an earlier experiment, the current study showed that hypertension significantly decreases the susceptibility of the spinal nerve roots to compression at and below 100 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Straight leg raising (SLR) is a useful clinical test to demonstrate an inflammatory compressive process across a spinal nerve root. Several previous studies have attempted to evaluate the effect of SLR on nerve root motion, but the exact direction and amount of this motion is still unclear. Components of the SLR test that have not been adequately addressed include the effect of SLR on the intact dural-nerve root system, motion of the nerve tissues as distinct from the dura, and nerve root strain. Separately, spinal fusion is occasionally used as an adjunct to discectomy to decrease instability and subsequent "nerve root irritation." The effect of a one-level fusion on in situ nerve root biomechanics, however, has not been evaluated. Ten fresh human cadavers underwent posterior lumbar laminectomies. Spinal nerve root motion was studied while a SLR maneuver was performed. Data was recorded photographically and statistically analyzed. The results were as follows: 1) SLR induced both linear motion (0.5-5 mm) and strain (2-4%) in spinal nerves L4, L5, and S1; 2) The dura moved less than the intrathecal nerve root at the pedicle and experienced more strain (P < .05). 3) The nerve roots moved laterally toward the pedicle and thus would move into a posterolaterally herniated disc. 4) Rigid anterior stabilization did not decrease nerve root motion or strain.

Spinal nerve root compression occurs commonly in conditions such as herniated nucleus pulposus, spinal stenosis, and trauma. However, the pathophysiology of the symptoms and signs related to spinal nerve root compression is poorly understood. The purpose of the present study was to assess and compare effects of various pressures and durations of acute compression on spinal nerve root conduction in the pig cauda equina. Efferent conduction (compound motor action potentials) and afferent conduction (compound nerve action potentials) were monitored during compression for 2 or 4 hours with compression pressures of 0 (sham), 50, 100, or 200 mm Hg. Recovery from compression was monitored for 1.5 hours. No significant deficits in spinal nerve root conduction were observed with 0 or 50 mm Hg compression, compared to significant conduction deficits induced by 100 and 200 mm Hg compression. Three-way analysis of variance demonstrated significant effects of compression pressure and duration on conduction at the end of compression and recovery, with a significant difference between efferent and afferent conduction at the end of the recovery period. These observations suggest an interaction between biomechanical and microvascular mechanisms in the production of nerve root conduction deficits. Such information may relate to the motor and sensory dysfunction in clinical conditions associated with spinal nerve root compression.

The three-dimensional organization of the human cauda equina has not been described previously. This is partly due to the difficulties of dissecting individual, unfixed nerve roots. By the use of a newly developed in situ fixation and embedding technique on 15 fresh human cadavers, the cross-sectional anatomy of the cauda equina was defined from L2-L3 to L5-S1. A highly consistent cross-sectional pattern was observed in all specimens. The lower sacral (S2-S5) and coccygeal roots were located in the dorsal aspect of the thecal sac, whereas the lumbar and first sacral roots exhibited an oblique, layered pattern as they ascended. The motor bundle was situated anteromedial to its respective sensory bundle within each layer, Invaginations of arachnoid held the nerve roots in a fixed relationship to one another. This previously undescribed three-dimensional anatomy within the thecal sac may aid in the understanding and treatment of trauma, neurocompressive syndromes, and tumors of the cauda equina.