Spine epidural steroids for patients with lumbar spinal stenosis.

The use of epidural steroid injections to relieve sciatic pain from spinal stenosis is extremely variable and controversial. Drs. Cohen and Kostuik take the position that most studies do not support their use and highlight the potential complications. Dr. Rydevik believes that epidural steroids might be considered as a nonsurgical alternative, especially in elderly patients where surgery carries greater risk.

The use of lower tourniquet inflation pressures in extremity surgery facilitated by curved and wide tourniquets and an integrated cuff inflation system.

Use of the lowest possible cuff inflation pressure should minimize the pathogenic effects of compression beneath the pneumatic tourniquet. Curved tourniquets (designed to fit conically shaped limbs) and wider tourniquets were associated with significantly lower arterial occlusion pressure (AOP) than standard, straight tourniquets on the arms and legs of 26 normal volunteers. These tourniquets were used with an integrated tourniquet inflation system in 29 upper-extremity and 31 lower-extremity surgeries. Mean tourniquet inflation pressures of 183.7 mm Hg and 208 mm Hg were used during various surgical procedures of the arm and leg, respectively. Incomplete hemostasis was associated with elevated systolic blood pressure in several cases, but acceptable surgical hemostasis was achieved by incremental increase of the cuff inflation pressure. Curved cuffs, wide cuffs, and an integrated cuff inflation system should facilitate the use of lower tourniquet inflation pressures in extremity surgery.

Anatomic and technical considerations of pedicle screw fixation.

Pedicle screw systems provide significant and, in many cases, improved and previously unattainable spinal fixation. However, pedicle screw systems represent difficult surgical techniques involving several potential problems and complications. Only by detailed knowledge of the anatomy of the spine, with a clear understanding of the pedicle screw systems implementation, can the risks of complications be minimized.

Effects of reperfusion intervals on skeletal muscle injury beneath and distal to a pneumatic tourniquet.

To date there have been no experimental studies specifically directed at effects of reperfusion intervals on skeletal muscle injury beneath the tourniquet. 99mTechnetium pyrophosphate (Tc 99) incorporation and correlative histology were used to assess injury 2 days after tourniquet application in muscles beneath (thigh) and distal (leg) to the cuff. Tourniquets were applied to rabbit hindlimbs for a total of either 2 or 4 hours. In the 4-hour series, tourniquet compression (either 125 mm Hg or 350 mm Hg cuff inflation pressure) was either continuous or interrupted by 10-minute reperfusion intervals after 2 hours or after every hour of cuff inflation. In the 2-hour series, tourniquet compression (350 mm Hg) was either continuous or interrupted by 10-minute reperfusion intervals after 2 hours or after every hour of cuff inflation. In the 2-hour series, tourniquet compression (350 mm Hg) was either continuous or interrupted by a 10-minute reperfusion interval after 1 hour. Pyrophosphate incorporation (Tc 99 uptake) was significantly greater in the thigh region than in the leg region in all of the 4-hour tourniquet groups. Tc 99 uptake was significantly reduced by reperfusion after each hour of cuff inflation. With 350 mm Hg tourniquet pressure, a reperfusion interval after 2 hours of cuff inflation tended to exacerbate tourniquet compression injury. Reperfusion intervals did not significantly affect Tc 99 uptake in the leg region of these groups. With a 2-hour tourniquet time, Tc 99 uptake in the thigh was significantly decreased by reperfusion after 1 hour of cuff inflation. Previous clinical recommendations, based on serum creatine phosphokinase abnormalities after experimental tourniquet ischemia, probably reflected tourniquet compression injury. Hourly reperfusion limits skeletal muscle injury during extended periods of tourniquet use.

Effects of magnitude and duration of compression on spinal nerve root conduction.

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.

Experimental stretch neuropathy. Changes in nerve conduction under tension.

We developed an animal model of stretch injury to nerve in order to study in vivo conduction changes as a function of nerve strain. In 24 rabbits, the tibial nerve was exposed and stretched by 0%, 6% or 12% of its length. The strain was maintained for one hour. Nerve conduction was monitored during the period of stretch and for a one-hour recovery period. At 6% strain, the amplitude of the action potential had decreased by 70% at one hour and returned to normal during the recovery period. At 12% strain, conduction was completely blocked by one hour, and showed minimal recovery. These findings have clinical implications in nerve repair, limb trauma, and limb lengthening.

The effects of compression on the physiology of nerve roots.

The spinal roots connect the central and peripheral nervous systems. In doing so, the nerve roots pass through the spinal column, where they are located in narrow spaces, close to vertebrae and intervertebral discs. At these locations, nerve roots can be subjected to mechanical compression in association with, for example, disc herniation, spinal stenosis and spine trauma. In this article, basic aspects of the anatomy and physiology of nerve roots are reviewed. Nerve fiber arrangements, connective tissue layers and blood supply are described. The effects of compression on nerve root structure and function are summarized, based on experimental studies involving analyses of nerve function, nutrition, including blood flow, and edema formation in the nerve root. Pain mechanisms in nerve root compression are reviewed in relation to various clinical conditions.

Stress relaxation of a peripheral nerve.

This study determines the change in tension after an acute nerve lengthening, as would occur in peripheral nerve repair. Stress relaxation, a viscoelastic property, was studied with the use of 24 rabbit tibial nerves. The nerves were divided into three groups and were stretched 6%, 9%, or 12% beyond their original resting length. The mean 1-hour stress relaxations for the three groups were 48%, 34%, and 34%, respectively. Nerve stress relaxation was significantly greater at 6% strain than at 9% or 12% strain. These biomechanical findings have important clinical implications for nerve-stretch injury and for nerve repair.

Muscle injury induced beneath and distal to a pneumatic tourniquet: a quantitative animal study of effects of tourniquet pressure and duration.

Previous recommendations regarding the "safe" period of tourniquet hemostasis were based largely on studies of ischemia distal to the tourniquet. This study quantitatively analyzed skeletal muscle injury induced beneath and distal to a pneumatic tourniquet applied to the hindlimbs of rabbits for 1, 2, or 4 hours with a cuff inflation pressure of 125, 200, or 350 mm Hg. Technetium Tc 99m pyrophosphate incorporation after systemic injection (Tc 99 uptake) and correlative histology were used to evaluate tissue damage 2 days after tourniquet application. Compared with the contralateral control limbs, compression and ischemia induced statistically significant increases in Tc 99 uptake in the thigh and leg regions of all groups. Pyrophosphate incorporation was significantly greater in the thigh region than in the leg region after 2 hours of compression in the 200 and 350 mm Hg pressure groups and following 4 hours of compression in all pressure groups. Focal and regional fiber necrosis and degeneration were observed in thigh muscles after 2 hours of tourniquet compression. Two hours of continuous tourniquet application at clinically relevant cuff inflation pressures induced significant skeletal muscle necrosis beneath the tourniquet. Use of the lowest possible inflation pressure for a limited duration should minimize the degree of tissue injury caused by tourniquet application.

Effects of acute, graded compression on spinal nerve root function and structure. An experimental study of the pig cauda equina.

A well-controlled experimental model for analysis of compression-induced functional changes of the porcine cauda equina is presented. The model allows for electrophysiologic investigation of a variety of neurophysiologic changes induced by nerve root deformation. At an acute pressure threshold of 50-75 mm Hg, changes in both afferent and efferent conduction are induced. With higher compression pressure, a differential recovery in afferent and efferent conduction is seen.

Compressive neuropathy of spinal nerve roots. A mechanical or biological problem?

Pathophysiologically, nerve root pain production is a complex issue. For many years, mechanical compression has been regarded as the sole cause for such pain. There are indications, however, that other factors, such as intraneural inflammation, may be of importance in this context. In this article, four cases are presented in which nerve root related pain gradually resolved without any proven change in the mechanical deformation of the involved nerve root. The data presented here suggest that mechanical compression, per se, may not always be the sole cause of radicular pain and dysfunction. These findings suggest that improvement is needed in our understanding of the pathophysiology of nerve root compression and inflammation.

Nerve function and structure beneath and distal to a pneumatic tourniquet applied to rabbit hindlimbs.

Neurophysiologic and neuropathologic changes were studied in rabbit hindlimbs after 2 hours of pneumatic tourniquet application with either 350 mmHg (n = 18) or 1,000 mmHg (n = 6) cuff inflation pressure. The toe spread reflex was decreased in 66% and absent in 33% of limbs 2 days after 350 mmHg compression, and was absent in all limbs after 1,000 mmHg compression. Compound motor action potential amplitudes (CMAPs), recorded from the abductor hallucis muscle, were significantly decreased with sciatic nerve stimulation 1 hour after 350 mmHg compression. CMAPs returned to baseline values one and two days later, however nerve conduction velocity (NCV) was still significantly decreased in the compressed sciatic nerves of these groups. In contrast, complete nerve conduction block, localized beneath the cuff's distal border, was observed two days after 1,000 mmHg compression, and NCV was still significantly decreased distal to the tourniquet zone. Using light and electron microscopy, scattered axonal degeneration, mild myelin damage, and normal nodes of Ranvier were observed two days after 350 mmHg tourniquet compression. Severe fiber damage and nodal obliteration were noted after 1,000 mmHg tourniquet compression. Although nodal invagination is probably not a significant pathogenic mechanism at clinically relevant tourniquet pressures and durations, functional abnormalities were induced by 2 hour, 350 mmHg tourniquet compression. Such changes probably correlate with clinical electromyographic abnormalities and delayed post-operative recovery following 'routine' extremity surgery using pneumatic tourniquets.

An animal model for the study of neuromuscular injury induced beneath and distal to a pneumatic tourniquet.

A well-controlled animal model is presented for the study of neuromuscular injury induced by a pneumatic tourniquet. This model comprises a curved tourniquet surrounded by a stiff exterior shell, both of which were specifically designed to fit the conical and oblong shape of the rabbit hindlimb. Computed tomographic imaging was used to assess transverse tissue displacement induced by tourniquet compression. The curved tourniquet/shell configuration occluded the distal arterial blood flow to the extremity at a significantly lower cuff inflation pressure than a straight tourniquet of equal width. The magnitude and distribution of tissue pressures in the subcutaneous and deep tissues beneath the tourniquet were similar to those recorded in previous human cadaver studies of tourniquet compression. This animal model will facilitate the quantitation and analysis of tissue injury induced beneath and distal to a pneumatic tourniquet. Such data can help define the critical pressure and time limits for the safe use of pneumatic tourniquets in extremity surgery.

An in vitro mechanical and histological study of acute stretching on rabbit tibial nerve.

Peripheral nerves are often mechanically stretched in association with trauma to extremities, resulting in varying degrees of impairment of nerve function. However, little is known about the biomechanical properties of peripheral nerves and limits of stretching that the nerve may undergo before structural changes occur. Also, the injury pattern of nerves under stretching is poorly understood. In the present study, fresh rabbit tibial nerves (n = 18) were harvested. Nine nerves were stretched to failure in an INSTRON materials testing machine at a rate of 1 cm/min (strain rate of 0.5%/s). Load-deformation and stress-strain curves were determined. Histological examination by light microscopy of the stretched nerves as well as six normal control nerves and three clamped nonstretched control nerves was performed. The results show that the rabbit tibial nerves have an in situ strain of 11.0 +/- 1.5% and exhibit a nonlinear stress-strain relationship. After 20% strain, the curve becomes linear up to failure. The ultimate strain and tensile strength of the nerves were 38.5 +/- 2.0% and 11.7 +/- 0.7 MPa, respectively. At failure, the load dropped suddenly, but the specimens remained grossly intact. Histological analysis of the stretched nerves showed multiple ruptures of perineurial sheaths when compared to controls.

Nerve-roots of the cauda equina. The effect of hypotension and acute graded compression on function.

The influence of hypotension on the function of nerve-roots of the cauda equina under acute graded compression was studied with use of an established porcine model. In twenty adult miniature pigs, the nerve-roots of the cauda equina were compressed at pressures of zero (sham), fifty, 100, or 200 millimeters of mercury, and hypotension was induced with sodium nitroprusside. Compression was maintained for two hours, and a ninety-minute period of recovery followed. The nerve-roots were monitored electrophysiologically throughout the experiment. To assess the effect of compression and hypotension on the function of the nerve-roots, values of afferent and efferent amplitude and nerve-conduction velocity were compared with values in twenty adult miniature pigs that had similar graded compression without hypotension. Hypotension significantly affected efferent and afferent amplitudes at the end of the compression period; the effect remained significant at the end of the recovery period. The most profound effect of hypotension occurred during compression at fifty millimeters of mercury--a pressure that had no effect on the function of the nerves in normotensive animals.

Carpal tunnel syndrome: morphologic changes after release of the transverse carpal ligament.

We describe the morphologic changes that follow division of the transverse carpal ligament in patients with carpal tunnel syndrome. Fifteen hands in 12 patients with carpal tunnel syndrome were studied with magnetic resonance imaging before operation and for 6 weeks after operation. Eight hands were studied at 8 months after operation. Carpal arch width, anterior displacement of the carpal canal contents, and carpal canal volume were measured by use of multiplanar reformation and three-dimensional reconstruction of magnetic resonance images. There was a 24.2 +/- 11.6% increase in carpal canal volume 6 weeks after carpal tunnel release (p less than 0.001). This difference persisted at 8-month follow-up. There was an anterior displacement of carpal canal contents 3.5 +/- 1.9 mm from its original position 6 weeks after operation (p less than 0.001). This palmar displacement persisted at the 8-month follow-up. There was no statistically significant increase in carpal arch width 8 months after carpal tunnel release. We believe that division of the transverse carpal ligament restores median nerve function by increasing the volume of the carpal canal. This volumetric increase results from an anterior displacement of the newly formed transverse carpal ligament and not from a widening of the bony carpal arch.

Pressure increase in the dorsal root ganglion following mechanical compression. Closed compartment syndrome in nerve roots.

Spinal nerve roots including the dorsal root ganglion (DRG) often are mechanically deformed in connection with degenerative and traumatic conditions of the spine. However, the pathophysiology underlying various functional changes, including pain production, in such conditions is incompletely known. In this study, the tissue fluid pressure in the DRG of L5 nerve roots of rats was measured before and after compression. Normal values were found to be 3.7 +/- 0.3 cm H2O (2.7 +/- 0.2 mm Hg). After mechanical compression, the endoneurial fluid pressure in the ganglia rose to 9.6 +/- 1.7 cmk H2O (7.1 +/- 1.2 mm Hg) (P less than 0.001). Histologic examination revealed edema and haemorrhage in the endoneurial space of the DRG. Pressure increase in the DRG as a result of mechanical deformation by, for example, a herniated disc might be expected to reduce blood flow to the sensory nerve cell bodies in the DRG. This may be a mechanism underlying the production of nerve root pain, which previously has not been described.

Proximodistal gradient in endoneurial fluid pressure.

Endoneurial fluid pressure measurements were made in the interstitial space of rat L5 dorsal root ganglia and in the corresponding sciatic nerves. Endoneurial fluid pressure was always higher in the ganglia than in the paired distal nerve. This proximodistal gradient in endoneurial fluid pressure may be the driving force responsible for the proximodistal convection of endoneurial fluid.

Carpal tunnel syndrome. A scientific basis for clinical care.

The series of experimental studies reviewed in this article supports a classification of median nerve compression at the wrist into early, intermediate, advanced, and acute nerve compression. The findings correlate well with experimental studies on the pathophysiology of nerve compression. A patient-specific management approach is recommended based upon the clinical and electrophysiologic findings which can be correlated with previously demonstrated intraneural pathologic changes.