Effect of substance P on mechanosensitive units of tissues around and in the lumbar facet joint

Effect of smartphone use on cervical spine stability

Using a smartphone often involves a sustained head-forward tilt posture, which may deteriorate the mechanism of muscle reaction efficiency or reduce the stiffness of connective tissues of the cervical spine. These changes in muscular and connective tissues can impair cervical spine stability and contribute to developing neck pain symptoms. In this experiment, change in the cervical spine stability associated with a sustained smartphone use posture was evaluated by quantifying the effective stiffness and the reflexive responses of the head to sudden perturbations. Seventeen young smartphone users maintained their heads tilted forward approximately 30° for 30 min while watching videos on their smartphones in sitting. Data show that the measures of cervical spine stability did not change significantly after the smartphone use task despite developing mild to moderate neck and upper body discomfort symptoms. Study findings imply that keeping the head tilt posture for 30 min for smartphone use did not significantly alter spinal stability, rejecting its association with neck discomfort.

Enhancing Annular Fissures and High-Intensity Zones: Pain, Internal Derangement, and Anesthetic Response at Provocation Lumbar Discography

BACKGROUND AND PURPOSE

A high-intensity zone identified on preprocedural MR imaging is known to correlate with pain at provocation lumbar discography. The correlation between enhancing annular fissures and pain at provocation lumbar discography has not been comprehensively evaluated. The purpose of this study was to assess the pain response and imaging features at enhancing annular fissure nonoperated disc levels identified on preprocedural MR imaging with comparison with the high-intensity zone and nonenhancing disc levels in patients referred for provocation lumbar discography.

MATERIALS AND METHODS

One-hundred nonoperated discs in 44 patients were retrospectively evaluated for an enhancing annular fissure on sagittal postcontrast T1-weighted pre-discogram MR imaging. Enhancing annular fissure discs were graded on the sagittal T2-weighted sequence (Grade 4: like CSF to Grade 1: negative/barely visible) for high-intensity-zone conspicuity. High-intensity-zone detection was performed independently. In the primary assessment, enhancing annular fissure and high-intensity zones were associated with pain response at provocation lumbar discography. Additional analysis included intradiscal anesthetic response and postdiscogram CT appearance.

RESULTS

Thirty-nine discs demonstrated an enhancing annular fissure, with 23/39 demonstrating a high-intensity zone. The presence of a high-intensity zone predicted severe pain (concordant + nonconcordant; P = .005, sensitivity of 40%, specificity of 94%) and concordant pain (P = .007, sensitivity of 39%, specificity of 86%) at provocation lumbar discography. Enhancing annular fissures without a detected high-intensity zone were more frequently observed among severely painful (50%) and concordant (36%) discs than among discs negative for pain (9%; P = .01). This finding resulted in a substantially greater overall sensitivity of enhancing annular fissures for severe (P < .001, 64%) and concordant pain (P = .008, 61%), significantly improving the overall predictive ability of a high-intensity zone alone. A high-intensity zone went undetected in 9/11 Grade 1 disc levels with concordant pain present in 7/9.

CONCLUSIONS

Consideration of enhancing annular fissures on preprocedural MR imaging substantially improves the prediction of severe/concordant pain in provocation lumbar discography.

Motion Characteristics of the Functional Spinal Unit During Lumbar Disc Injection (Discography) Including Comparison Between Normal and Degenerative Levels

OBJECTIVE

While provocation lumbar discography has been used to identify discs responsible for low back pain, the biomechanical effects of disc injection have received little attention. The purpose of this study was to assess the motion of the functional spinal unit including the endplate and facet/pedicle region during disc injection including comparison between normal and degenerative discs.

SUBJECTS

Subjects represent 91 consecutive patients referred for discography with chronic low back pain.

METHODS

Lateral projection vertebral motion was retrospectively analyzed at 232 levels (normal: 76 [32.8%], degenerative: 156 [67.2%]). Pre- and postinjection fluoroscopic images were size scaled, and lower endplates were superimposed on separate PowerPoint images. Upper endplate and facet/pedicle motion was separately and independently analyzed on toggled PowerPoint images, subjectively graded as prominent, intermediate, questionable/uncertain, or no motion. Disc morphology was graded using the anteroposterior/lateral postinjection disc appearance (Adams criteria).

RESULTS

Prominent or intermediate endplate and facet/pedicle motion was identified at most lumbar levels with substantial overall agreement (degenerative: κ = 0.93, 95% confidence intervals [CI] = 0.87-1.00; normal: κ = 0.80, 95% CI = 0.61-1.00). Degenerative levels were strongly associated with a lower degree of endplate and facet/pedicle motion compared with normal: ("prominent" motion grade: endplate: 61% [95/156] vs 89% [68/76], P < 0.001; facet/pedicle: 60% [93/156] vs 88% [67/76], P < 0.001).

CONCLUSION

Disc injection expands the disc space inducing endplate motion, pedicle motion, and facet translation in almost all normal and most degenerate levels. Disc injection therefore biomechanically "provokes" the entire functional spinal unit. When provoked pain is encountered during lumbar discography, contribution from the associated facet joint and myotendinous insertions should be considered.

The Diagnostic Accuracy of Gluteal Trigger Points to Differentiate Radicular From Nonradicular Low Back Pain

OBJECTIVES

Low back pain (LBP) is highly prevalent and costly to the society. Previous studies have shown an association between radicular LBP and trigger points (TrPs) in the superior-lateral quadrant of the gluteal area (GTrP). The objective of current study was to evaluate the diagnostic value of GTrP to predict nerve root involvement among patients with LBP.

MATERIALS AND METHODS

In a prospective, diagnostic accuracy study 325 consecutive patients with LBP were recruited. At first step, patients were evaluated for the presence or absence of the GTrP. A different investigator, blinded to the GTrP findings, then performed history taking and physical examination. Subsequently, all patients underwent a lumbar spine magnetic resonance imaging and, when indicated, electrodiagnostic tests. On the basis of the clinical and ancillary tests findings, a multidisciplinary panel of experts (the "reference standard"), blinded to the GTrP evaluation, allocated patients to radicular versus nonradicular LBP groups. The agreement between the GTrP findings, as a diagnostic test and the reference standard allocation was evaluated in a 2 by 2 contingency table.

RESULTS

The specificity of the GTrP test was 91.4% and its sensitivity was 74.1%. The area under the receiver operating characteristic curve was 0.827 (0.781 to 0.874). Positive likelihood ratio was 8.62 and negative likelihood ratio was 0.28. Positive and negative predictive values were 91.9% and 72.7%, respectively.

DISCUSSION

As a clinical finding, TrPs in superior-lateral quadrant of gluteal area are highly specific indicators for radicular LBP. Incorporating these TrPs evaluation in routine physical examination of patients with LBP could decrease the need for more costly, time-consuming, and invasive diagnostic tests.

Cellular supplementation technologies for painful spine disorders

Low back pain affects more than 80% of adults. A proportion of these adults develops chronic low back pain (CLBP) and becomes disabled by their condition. CLBP is expensive to diagnose and treat and in terms of associated loss of productivity in the work place setting by affected individuals. Although challenging, the source of CLBP can be identified. Contemporary literature contains several studies that have established prevalence estimates for various structural sources of CLBP. In young adults, the intervertebral disk is a common source of CLBP, once it incurs annular injury that heals incompletely. Effective treatment for painful disks currently is an unmet clinical need. In older adults, the facet and sacroiliac joints are more commonly responsible for CLBP. Although certain minimally invasive techniques do exist for these painful joints, an effective restorative intervention has yet to be established. Annular injury precipitates a physiologic response that can lead to a catabolic state within the disk that impairs disk restoration. Cell loss is a feature of this process as well as the pathophysiology associated with painful facet and sacroiliac joints. Cellular supplementation is an attractive treatment strategy to initiate the repair of an injured lumbosacral structure. The introduction of exogenous cells may lead to increased extracelluar matrix production and reduced pain and disability in diskogenic CLBP. Compelling data in animal studies have been produced, stimulating Food and Drug Administration-regulated trials in humans. Numerous questions remain regarding cell viability and sufficient native nutrients to support these cells. Clinical research protocols have focused predominantly on diskogenic CLBP, and very few have addressed painful facet and/or sacroiliac joints.

Neuronal hyperexcitability in the dorsal horn after painful facet joint injury

Excessive cervical facet capsular ligament stretch has been implicated as a cause of whiplash-associated disorders following rear-end impacts, but the pathophysiological mechanisms that produce chronic pain in these cases remain unclear. Using a rat model of C6-C7 cervical facet joint capsule stretch that produces sustained mechanical hyperalgesia, the presence of neuronal hyperexcitability was characterized 7 days after joint loading. Extracellular recordings of spinal dorsal horn neuronal activity between C6 and C8 (117 neurons) were obtained from anesthetized rats, with both painful and non-painful behavioral outcomes established by the magnitude of capsule stretch. The frequency of neuronal firing during noxious pinch (p<0.0182) and von Frey filaments applications (4-26g) to the forepaw was increased (p<0.0156) in the painful group compared to the non-painful and sham groups. In addition, the incidence and frequency of spontaneous and after discharge firing were greater in the painful group (p<0.0307) relative to sham. The proportion of cells in the deep laminae that responded as wide dynamic range neurons also was increased in the painful group relative to non-painful or sham groups (p<0.0348). These findings suggest that excessive facet capsule stretch, while not producing visible tearing, can produce functional plasticity of dorsal horn neuronal activity. The increase in neuronal firing across a range of stimulus magnitudes observed at day 7 post-injury provides the first direct evidence of neuronal modulation in the spinal cord following facet joint loading, and suggests that facet-mediated chronic pain following whiplash injury is driven, at least in part, by central sensitization.

Is activation of the back muscles impaired by creep or muscle fatigue?

STUDY DESIGN

Intervention study on healthy human subjects.

OBJECTIVE

To determine whether reflex activation of the back muscles is influenced by muscle fatigue or soft tissue creep in the spine.

SUMMARY OF BACKGROUND DATA

Reflex contraction of the back muscles normally acts to limit spinal flexion, and hence protect the underlying spine from injury. However, repeated flexion allows bending moments on the spine to increase. Impaired reflexes as a result of fatigue or soft tissue creep may be contributing factors.

METHODS

A total of 15 healthy volunteers (8 females/7 males aged 23-55 years) underwent 2 interventions, on separate days: (a) sitting flexed for 1 hour to induce creep and (b) performing the Biering-Sorensen test to induce back muscle fatigue. Before and after each intervention, reflex activation of the erector spinae in response to sudden trunk flexion (initiated by a Kin-Com dynamometer) was monitored bilaterally at T10 and L3 using surface electromyography (EMG) electrodes. These recordings indicated the onset latency of reflex activation, the peak EMG, and time to peak, at each site. Measurements before and after each intervention and between muscle sites were compared using a 2-way repeated measures Analysis of Variance.

RESULTS

Spinal creep was confirmed by an increase in maximum flexion of 2.3 degrees +/- 2.5 degrees (P = 0.003), and fatigue by a significant fall in median frequency at one or more sites. Following creep, onset latency increased from 60 +/- 12 milliseconds to 96 +/- 26 milliseconds (P < 0.001) but there was no change in peak EMG or time to peak EMG. Differences between sites (P = 0.004) indicated greater latencies in lumbar compared to thoracic regions, especially after creep. Muscle fatigue had no significant effects on any of the measured parameters.

CONCLUSION

Prolonged spinal flexion can impair sensorimotor control mechanisms and reduce back muscle protection of the underlying spine. The effect is due to time-dependent "creep" in soft tissues rather than muscle fatigue.

Prospective pilot study of painful lumbar facet joint arthropathy after intra-articular injection of hylan G-F 20

OBJECTIVE

To examine changes in pain, disability, and medication usage over time from baseline to up to 12 months after facet joint injection of hylan G-F 20.

DESIGN

Prospective, uncontrolled, pilot study.

SETTING

University spine center.

PARTICIPANTS

Fifteen patients (12 females), mean age of 57 years (standard deviation = 12.5), with a median duration of low back pain of 24 months (interquartile range = 11-66).

METHODS

Patients who fulfilled inclusion criteria underwent diagnostic blocks with local comparative anesthetics at one unilateral facet joint (FJ). Those with a true positive response underwent 2 1.0-mL intra-articular hylan G-F 20 injections, 10 days apart, into the painful FJ. A third hylan G-F 20 injection was offered to patients dissatisfied with the results obtained with the first 2 injections.

MAIN OUTCOME MEASURES

Visual analog scale (VAS) (average, standing, walking), Oswestry Disability Index (ODI), SF-36, finger to floor distance (FTF), tolerance (standing, sitting, walking), analgesic usage, and patient satisfaction collected at baseline, 7-10 days, and at 1-, 3-, 6-, and 12-months follow-up.

RESULTS

Repeated measures mixed-models indicated that VAS (average, standing, walking [P all < .005]), ODI (P = .029), SF-36 (P = .013), FTF (P = .032), and sitting tolerance (P = .020) all showed significant changes from baseline up to 6 months and were not sustained at 12 months; with the exception of the baseline to 12-month difference for FTF. There was not evidence of changes over time in standing (P = .085) or walking (P = .084) tolerance. Satisfaction initially increased from baseline (0%) to 7-10 days (64%) but declined over time (36% at 12 months). As compared with baseline (80%), analgesic usage decreased nominally over time showing significant decreases at 6 months (33%, P = .0253) and increased slightly at 12 months (45%).

CONCLUSIONS

Viscosupplementation for lumbar FJ arthropathy with hylan G-F 20 is associated with modest efficacy that predominately lasts up to 6 months. Limitations include a small sample size and lack of both a control and blinding. Larger, randomized, controlled studies are indicated to better clarify its clinical safety, efficacy, and utility.

[Non-specific lower back pain: In search of the origin of pain]

Lower back pain is a condition considered benign and with a specific cause determined only in 15% of patients. In the past years this concept has varied, because many papers have described no benign condition leading to back pain, citing their capacity to cause disability. Through many different diagnostic techniques it is possible to identify the structures capable of producing back pain. This identification, and the level of evidence of the interventional techniques, is the aim of this paper.

Substance P and its receptors in bone metabolism

Accumulating evidence on bone physiopathology has indicated that the skeleton contains numerous nerve fibers and its metabolism is regulated by the nervous system. Until now, more than 10 neuropeptides have been identified in bone. Substance P (SP) is a neuropeptide released from axons of sensory neurons, belongs to the tachykinin family and plays important roles in many physiological and pathological processes by acting as a neurotransmitter, neuromodulator, or trophic factor. It activates signal transduction cascades by acting on the neurokinin-1 receptor (NK(1)-R). Previous studies have confirmed that the SP-immunoreactive (IR) axons innervate bone and adjacent tissues, and that their density varies depending on the regions and physiological or pathological conditions. Over the past few decades, it has been found that SP takes part in the stimulation of bone resorption, and its receptors have been demonstrated to be located in osteoclasts. Notably, in studies of skeletal ontogeny, SP-IR axons have been shown to appear at an early stage, mostly coinciding with the sequence of long bone mineralization. These findings, together with data obtained from chemically or surgically targeted nerve deletions, strongly suggest that SP is a potent regulator of skeletal physiology. The specific distribution of SP-IR nerve fibers, the different amount of SP within regions, and the various levels of expression of NK(1)-R in targeted cells presumably related to and participate in bone metabolism. It can be predicted that the indirect roles of SP through other cytokines are as important as its direct roles in bone metabolism. This new regulating pathway of bone metabolism would have enormous implications in skeletal physiology and the relevant research might present curative potentials to a spectrum of bone diseases.

Biomechanics of the posterior lumbar articulating elements

✓The clinical success of lumbar spinal fusion varies considerably, depending on techniques and indications. Although spinal fusion generally helps to eliminate certain types of pain, it may also decrease function by limiting patient mobility. Furthermore, spinal fusion may increase stresses on adjacent nonfused motion segments, accelerating the natural degeneration process at adjacent discs. Additionally, pseudarthrosis, that is, incomplete or ineffective fusion, may result in an absence of pain relief. Finally, the recuperation time after a fusion procedure can be lengthy.

The era of disc replacement is in its third decade, and this procedure has demonstrated promise in relieving back pain through preservation of motion. Total joint replacement with facet arthroplasty of the lumbar spine is a new concept in the field of spinal surgery. The devices used are intended to replace either the entire functional spinal unit (FSU) or just the facets. These devices provide dynamic stabilization for the functional spinal segment as an adjunct to disc replacement or laminectomy and facetectomy performed for neural decompression. The major role of facet replacement is to augment the instabilities created by the surgical decompression or to address chronic instability. Additionally, facet joint replacement devices can be used to replace the painful facet joints, restore stability, and/or to salvage a failed disc or nucleus prosthesis without losing motion.

In this paper the authors review and discuss the role of the lumbar facet joints as part of the three-joint complex and discuss their role in intersegmental motion load transfer and multidirectional flexibility in a lumbar FSU.

Basic Science Research Related to Chiropractic Spinal Adjusting: The State of the Art and Recommendations Revisited

OBJECTIVE

The objectives of this white paper are to review and summarize the basic science literature relevant to spinal fixation (subluxation) and spinal adjusting procedures and to make specific recommendations for future research.

METHODS

PubMed, CINAHL, ICL, OSTMED, and MANTIS databases were searched by a multidisciplinary team for reports of basic science research (since 1995) related to spinal fixation (subluxation) and spinal adjusting (spinal manipulation). In addition, hand searches of the reference sections of studies judged to be important by the authors were also obtained. Each author used key words they determined to be most important to their field in designing their individual search strategy. Both animal and human studies were included in the literature searches, summaries, and recommendations for future research produced in this project.

DISCUSSION

The following topic areas were identified: anatomy, biomechanics, somatic nervous system, animal models, immune system, and human studies related to the autonomic nervous system. A relevant summary of each topic area and specific recommendations for future research in each area were the primary objectives of this project.

CONCLUSIONS

The summaries of the literature for the 6 topic sections (anatomy, biomechanics, somatic nervous system, animal models, immune system, and human studies related to the autonomic nervous system) indicated that a significant body of basic science research evaluating chiropractic spinal adjusting has been completed and published since the 1997 basic science white paper. Much more basic science research in these fields needs to be accomplished, and the recommendations at the end of each topic section should help researchers, funding agencies, and other decision makers develop specific research priorities.

Pain generation in lumbar and cervical facet joints

Facet joints are implicated as a major source of neck and low-back pain. Both cervical and lumbar facet syndromes have been described in the medical literature. Biomechanical studies have shown that lumbar and cervical facet-joint capsules can undergo high strains during spine-loading. Neuroanatomic studies have demonstrated free and encapsulated nerve endings in facet joints as well as nerves containing substance P and calcitonin gene-related peptide. Neurophysiologic studies have shown that facet-joint capsules contain low-threshold mechanoreceptors, mechanically sensitive nociceptors, and silent nociceptors. Inflammation leads to decreased thresholds of nerve endings in facet capsules as well as elevated baseline discharge rates. Recent biomechanical studies suggest that rear-end motor-vehicle impacts give rise to excessive deformation of the capsules of lower cervical facet joints. Still unresolved is whether this stretch is sufficient to activate nociceptors in the joint capsule. To answer this question, recent studies indicate that low stretch levels activate proprioceptors in the facet-joint capsule. Excessive capsule stretch activates nociceptors, leads to prolonged neural afterdischarges, and can cause damage to the capsule and to axons in the capsule. In instances in which a whiplash event is severe enough to injure the joint capsule, facet capsule overstretch is a possible cause of persistent neck pain.

Neural response of cervical facet joint capsule to stretch: a study of whiplash pain mechanism

Cervical facet joints are implicated as a major source of pain after whiplash injury. The purpose of this study was to investigate the proposed capsule strain injury mechanism of whiplash pain using neurophysiologic methods. Strain thresholds, threshold distribution, saturation strains and afterdischarge responses of capsule neural receptors were characterized in vivo. Goat C5-C6 facet joint capsules were used to identify and characterize capsule receptors in response to controlled uniaxial stretch by recording C6 dorsal rootlet nerve discharge. The joints were stretched at 0.5 mm/sec in a series of tests with 2 mm increments until the capsule ruptured. Ninety-two identified units were responsive to physiologic or noxious stretch while 28 were silent receptors. Among the 50 characterized responsive units, 42 showed low strain thresholds at 10.2+/-4.6% while 8 had high strain thresholds at 47.2+/-9.6%. Further, 35 of the 42 low-threshold units displayed discharge saturation at various strains (44.2+/-16.7%). A significant finding was that twelve low-threshold units exhibited afterdischarge for greater than 30 sec after stretch release at 36.6+/-12.5% strains, and displayed longer-lasting afterdischarge (greater than 4 min) at higher strains (39.0+/-14.4%) with significant difference (p = 0.019) in strains. Two high-threshold units had afterdischarges for greater than 30 sec or 4 min at 50.3+/-5.9% and 57.7+/-10.6% strains, respectively. In addition, the spatial distribution of the 42 low-threshold receptors demonstrated that the receptors on the joint gap were more strain-sensitive, with significantly lower strain thresholds compared to the rostral and caudal regions. No significant difference in strain threshold was observed in the medial-lateral direction. When compared to the reported strains that facet joint capsules experienced in whiplash (35-60%) and the reported capsule subfailure strains (35-67%), the low strain thresholds are substantially lower whereas the high thresholds and afterdischarge strains are within that range. Thus, low threshold units appear to signal proprioception within the physiologic range. High threshold units likely signal nociception (pain sensation) while afterdischarge may signal capsule strain injury and contribute to persistent pain.

Material properties of the human lumbar facet joint capsule

The human facet joint capsule is one of the structures in the lumbar spine that constrains motions of vertebrae during global spine loading (e.g., physiological flexion). Computational models of the spine have not been able to include accurate nonlinear and viscoelastic material properties, as they have not previously been measured. Capsules were tested using a uniaxial ramp-hold protocol or a haversine displacement protocol using a commercially available materials testing device. Plane strain was measured optically. Capsules were tested both parallel and perpendicular to the dominant orientation of the collagen fibers in the capsules. Viscoelastic material properties were determined. Parallel to the dominant orientation of the collagen fibers, the complex modulus of elasticity was E*=1.63MPa, with a storage modulus of E'=1.25MPa and a loss modulus of: E" =0.39MPa. The mean stress relaxation rates for static and dynamic loading were best fit with first-order polynomials: B(epsilon) = 0.1110epsilon-0.0733 and B(epsilon)= -0.1249epsilon + 0.0190, respectively. Perpendicular to the collagen fiber orientation, the viscous and elastic secant moduli were 1.81 and 1.00 MPa, respectively. The mean stress relaxation rate for static loading was best fit with a first-order polynomial: B (epsilon) = -0.04epsilon - 0.06. Capsule strength parallel and perpendicular to collagen fiber orientation was 1.90 and 0.95 MPa, respectively, and extensibility was 0.65 and 0.60, respectively. Poisson's ratio parallel and perpendicular to fiber orientation was 0.299 and 0.488, respectively. The elasticity moduli were nonlinear and anisotropic, and capsule strength was larger aligned parallel to the collagen fibers. The phase lag between stress and strain increased with haversine frequency, but the storage modulus remained large relative to the complex modulus. The stress relaxation rate was strain dependent parallel to the collagen fibers, but was strain independent perpendicularly.

Neurophysiological and biomechanical characterization of goat cervical facet joint capsules

Cervical facet joints have been implicated as a major source of pain after whiplash injury. We sought to identify facet joint capsule receptors in the cervical spine and quantify their responses to capsular deformation. The response of mechanosensitive afferents in C5-C6 facet joint capsules to craniocaudal stretch (0.5 mm/s) was examined in anaesthetized adult goats. Capsular afferents were characterized into Group III and IV based on their conduction velocity. Two-dimensional strains across the capsules during stretch were obtained by a stereoimaging technique and finite element modeling. 17 (53%) Group III and 14 (56%) Group IV afferents were identified with low strain thresholds of 0.107+/-0.033 and 0.100+/-0.046. A subpopulation of low-strain-threshold afferents had discharge rate saturation at the strains of 0.388+/-0.121 (n=9, Group III) and 0.341+/-0.159 (n=9, Group IV). Two (8%) Group IV units responded only to high strains (0.460+/-0.170). 15 (47%) Group III and 9 (36%) Group IV units could not be excited even by noxious capsular stretch. Simple linear regressions were conducted with capsular load and principal strain as independent variables and neural response of low-strain-threshold afferents as the dependent variable. Correlation coefficients (R2) were 0.73+/-0.11 with load, and 0.82+/-0.12 with principal strain. The stiffness of the C5-C6 capsules was 16.8+/-11.4 N/mm. Our results indicate that sensory receptors in cervical facet joint capsules are not only capable of signaling a graded physiological mechanical stimulus, but may also elicit pain sensation under excessive deformation.

The effect of an interspinous process implant on facet loading during extension

STUDY DESIGN

Facet loading parameters of lumbar cadaver spines were measured during extension before and after placement of an interspinous process implant.

OBJECTIVE

The study was undertaken to quantify the influence of an interspinous implant on facet loading at the implanted and adjacent levels during extension.

SUMMARY OF BACKGROUND DATA

Facet loading is increased during extension and decreased during flexion. Previous studies have demonstrated that interspinous process decompression relieves disc pressure at the implanted level and does not alter disc pressure at the adjacent levels. Facet joints are believed to play a key role in back pain, especially in patients with collapsed discs and increased motion segment mobility resulting in increased facet loading.

METHODS

Seven cadaver spines (L2-L5) were loaded to 15 Nm of extension and 700 N compression with and without an interspinous process implant (X STOP) placed between the L3-L4 spinous processes. Pressure-sensitive film was placed in the facet joints of the implanted and adjacent levels. After loading, the film was digitally analyzed for peak pressure, average pressure, contact area, and force. These values were compared between the intact and implanted specimens at the adjacent and implanted levels using a paired t test (P < 0.05).

RESULTS

The implant significantly reduced the mean peak pressure, average pressure, contact area, and force at the implanted level. The mean peak pressure, average pressure, contact area, and force at the adjacent levels were not significantly different between the intact and implanted specimens with the exception of contact area at the L2-L3 level.

CONCLUSIONS

Interspinous process decompression will unlikely cause adjacent level facet pain or accelerated facet joint degeneration. Furthermore, pain induced from pressure originating in the facets and/or posterior anulus of the lumbar spine may be relieved by interspinous pro-cess decompression. Clinical results from patients with a component of lower back pain suggest that this is a valid conclusion.

Demonstration of substance P, calcitonin gene-related peptide, and protein gene product 9.5 containing nerve fibers in human cervical facet joint capsules

STUDY DESIGN

Human cervical facet joint capsules were evaluated by immunohistochemistry.

OBJECTIVES

To study the neuropeptide innervation of the cadaveric cervical facet joint capsules.

SUMMARY OF BACKGROUND DATA

Various clinical and biomechanical studies indicate a role for cervical facet joint capsules in the etiology of neck pain. However, studies on innervation of these capsules are very limited. There is also a dearth of studies on the neuropeptide nature of this innervation.

METHODS

Facet joint capsules harvested from unembalmed cadavers were studied by the avidin biotin peroxidase method for the presence of nerve fibers. Neuropeptide innervation was investigated by using antisera to substance P and calcitonin gene-related peptide. Antisera to protein gene product 9.5 (PGP 9.5), a general neuronal marker, were also used.

RESULTS

In a study of 12 human cervical facet joint capsules, short segments of substance P were observed in 6 capsules, while fibers reactive to calcitonin gene-related peptide were demonstrated in 7 capsules. Nerve fibers immunoreactive to protein gene product 9.5 were also observed in 9 of the 14 capsules studied. Protein gene product 9.5 reactive fibers were the most extensively distributed fibers, observed as bundles and also as single fibers.

CONCLUSIONS

An abundance of protein gene product 9.5 reactive nerve fibers indicates an extensive innervation of the cervical facet joint capsules. The presence of substance P and calcitonin gene-related peptide reactive nerve fibers in a population of these lends credence to cervical facet joint capsules as a key source of neck pain.

Somatosympathetic reflexes from the low back in the anesthetized cat

In the appendicular skeleton, substantial evidence demonstrates that somatosensory input from deep tissues including limb muscles and joints elicits somatosympathetic reflexes. Much less is known about the presence and organization of these reflexes from the axial skeleton. We determined if mechanical loading of the lumbar spine and lumbar paraspinal muscle irritation reflexively affects postganglionic sympathetic nerve discharge (SND) to the spleen and kidney. In 27 alpha-chloralose-anesthetized cats, the L2-4 multifidus muscles were injected with the inflammatory irritant mustard oil (20%, 60 microl total) and a vertebral load (100% body weight) was applied dorsal-ventral at the L3 spinous process. Mustard oil injection alone without vertebral loading (n = 7) increased mean splenic SND (60%), renal SND (30%), and heart rate (HR; 52 bpm). Mustard oil injection accompanied by the vertebral load (n = 7) increased mean splenic SND (55%), renal SND (16%), and HR (27 bpm). Blood pressure changes were biphasic and could not account for these changes. When the vertebral load accompanied mustard oil, the increases in splenic SND, renal SND, and HR remained elevated in a pattern significantly different from when the vertebral load was absent. Vehicle injection combined with the mechanical load (n = 3) did not change any of the autonomic responses. Similarly, mustard oil injection combined with a mechanical load did not change these responses when either the medial branches of the dorsal rami from T11-L5 had been cut (n = 4) or when the spinal cord had been transected between the second and third cervical vertebrae (n = 6). The results indicate that inflammatory stimulation of multifidus muscle in the low back evokes a somatosympathetic reflex integrated supraspinally in the upper cervical spinal cord or higher. The reflex's afferent arm travels in the medial branch of the dorsal ramus, and its efferent arm can affect sympathetic outflow to the spleen and the kidney as well as HR and BP. A static mechanical load applied to the lumbar spine accompanying the inflammatory stimulus appears to sustain the inflammatory-induced reflex activity.

Potential sources of neck and back pain in clinical conditions of dogs and cats: a review

Pathological neck and back pain occurs in many medical conditions of dogs and cats. Pain may arise from a variety of structures including the intervertebral discs, facet joint capsules, dorsal root ganglia, vertebral ligaments, the vertebral periosteum, and the meninges. The source of this pain is dependent upon the type of disease process and its location within or surrounding the spinal column. Diseases can directly or indirectly stimulate pain sensors (nociceptors). Inflammatory diseases may hypersensitize these receptors or nociceptive pathways with inflammatory mediating substances such as serotonin, histamine and potassium. Diseases resulting in mechanical compression of nociceptors or nociceptive pathways may also result in neck or back pain. A thorough understanding of spinal pain occurring in dogs and cats will lead to more accurate diagnoses and treatments and may provide information regarding prognoses for various diseases. Evidence pointing to sources of spinal pain taken from scientific and clinical studies of a variety of species including humans is provided. Suspected or known sources of neck and back pain occurring in several clinical conditions of dogs and cats are discussed.

Neurophysiological effects of spinal manipulation

BACKGROUND CONTEXT

Despite clinical evidence for the benefits of spinal manipulation and the apparent wide usage of it, the biological mechanisms underlying the effects of spinal manipulation are not known. Although this does not negate the clinical effects of spinal manipulation, it hinders acceptance by the wider scientific and health-care communities and hinders rational strategies for improving the delivery of spinal manipulation.

PURPOSE

The purpose of this review article is to examine the neurophysiological basis for the effects of spinal manipulation.

STUDY DESIGN

A review article discussing primarily basic science literature and clinically oriented basic science studies.

METHODS

This review article draws primarily from the peer-reviewed literature available on Medline. Several textbook publications and reports are referenced. A theoretical model is presented describing the relationships between spinal manipulation, segmental biomechanics, the nervous system and end-organ physiology. Experimental data for these relationships are presented.

RESULTS

Biomechanical changes caused by spinal manipulation are thought to have physiological consequences by means of their effects on the inflow of sensory information to the central nervous system. Muscle spindle afferents and Golgi tendon organ afferents are stimulated by spinal manipulation. Smaller-diameter sensory nerve fibers are likely activated, although this has not been demonstrated directly. Mechanical and chemical changes in the intervertebral foramen caused by a herniated intervertebral disc can affect the dorsal roots and dorsal root ganglia, but it is not known if spinal manipulation directly affects these changes. Individuals with herniated lumbar discs have shown clinical improvement in response to spinal manipulation. The phenomenon of central facilitation is known to increase the receptive field of central neurons, enabling either subthreshold or innocuous stimuli access to central pain pathways. Numerous studies show that spinal manipulation increases pain tolerance or its threshold. One mechanism underlying the effects of spinal manipulation may, therefore, be the manipulation's ability to alter central sensory processing by removing subthreshold mechanical or chemical stimuli from paraspinal tissues. Spinal manipulation is also thought to affect reflex neural outputs to both muscle and visceral organs. Substantial evidence demonstrates that spinal manipulation evokes paraspinal muscle reflexes and alters motoneuron excitability. The effects of spinal manipulation on these somatosomatic reflexes may be quite complex, producing excitatory and inhibitory effects. Whereas substantial information also shows that sensory input, especially noxious input, from paraspinal tissues can reflexively elicit sympathetic nerve activity, knowledge about spinal manipulation's effects on these reflexes and on end-organ function is more limited.

CONCLUSIONS

A theoretical framework exists from which hypotheses about the neurophysiological effects of spinal manipulation can be developed. An experimental body of evidence exists indicating that spinal manipulation impacts primary afferent neurons from paraspinal tissues, the motor control system and pain processing. Experimental work in this area is warranted and should be encouraged to help better understand mechanisms underlying the therapeutic scope of spinal manipulation.

Mechanosensitive afferent units in the lumbar posterior longitudinal ligament

STUDY DESIGN

The mechanosensitive afferent units in the lumbar posterior longitudinal ligament were investigated in an animal model using an electrophysiologic technique.

OBJECTIVES

The objectives of this study were to identify the mechanosensitive receptive fields in the lumbar posterior longitudinal ligament and to investigate their distribution and characteristics.

SUMMARY OF BACKGROUND DATA

The lumbar posterior longitudinal ligament has a nerve network originating from the sinuvertebral nerve. These fibers are thin, and most of their terminals are free nerve endings. Some immunohistochemical studies have indicated that they are immunoreactive to calcitonin gene-related peptide and/or substance P, suggesting a nociceptive function. Most of these studies investigated morphologic aspects, and there have been few studies employing electrophysiologic techniques to examine mechanosensitive units.

METHODS

We used 13 adult cats. They were anesthetized and then laminectomy was performed. The L5 and L6 dorsal rootlets were draped over a recording electrode. To investigate the receptive fields in the posterior longitudinal ligament, afferent impulses were evoked by mechanical stimulation with a glass probe. When the receptive fields were located, they were stimulated electrically to obtain conduction velocity and were stimulated with a set of 17 nylon filaments to determine their mechanical thresholds.

RESULTS

Thirteen units were identified in the lumbar posterior longitudinal ligament. The majority of the units were located around the intervertebral disc level of the posterior longitudinal ligament. The mean mechanical threshold was 47.04 +/- 15.25 g. According to the conduction velocities of the units, 12 units were classified into Group III (0.5-2.5 m/sec) and one unit into Group IV (2.5-20 m/sec).

CONCLUSION

Mechanosensitive units classified into Group III or Group IV and with a high mechanical threshold (>7.0 g) were thought to act as nociceptive units. All units identified in this study satisfied these criteria. Our result suggests that afferent fibers from the lumbar posterior longitudinal ligament have a principally nociceptive function.

Influences on the fusimotor-muscle spindle system from chemosensitive nerve endings in cervical facet joints in the cat: possible implications for whiplash induced disorders

The aim of the present study was to establish if there exists reflex connections from ligamentous structures in cervical facet joints and the fusimotor system of dorsal neck muscles. In seven cats, anaesthetized with alpha-chloralose, bradykinin (BK) of concentrations between 12 and 50 microg was injected into the facet joint between C1 and C2. Recordings were made from single muscle spindle afferents (MSA) originating in contralateral trapezius and splenius muscles (TrSp). Fusimotor induced changes in the sensitivity of the muscle spindle afferents were assessed by recording the responses to sinusoidal stretches of the TrSp muscles. The mean rate of discharge and the depth of modulation of a fitted sine were taken as quantitative estimates of the response. A total of 25 MSAs were recorded, and 21 of these showed clear-cut alterations in their responses to the sinusoidal stretches following Bk. injections into contralateral facet joint. The majority of the responding afferents (13/21) showed changes in their responses indicating an increased activity of static fusimotoneurones, although responses of dynamic and mixed static and dynamic nature were also seen. Local anaesthetics applied to the intraarticular receptors abolished the effects. Injection (i.v.) of a general anaesthetic (pentobarbital) abolished the effects. The results show that there exist reflex connections between receptors in cervical facet joints and fusimotoneurones of dorsal neck muscles, and this might be of importance in the pathophysiology behind whiplash associated disorders (WAD).

Differences in repositioning error among patients with low back pain compared with control subjects

STUDY DESIGN

Trunk repositioning error was measured in 20 patients with chronic low back pain and 20 control subjects.

OBJECTIVES

To measure trunk repositioning error as a method of measuring proprioception of the low back and to compare trunk repositioning error in patients with low back pain and in control subjects.

SUMMARY OF BACKGROUND DATA

Although many current low back pain rehabilitation programs incorporate proprioceptive training, very little research has been performed on proprioception of the low back.

METHODS

While standing with the legs and pelvis immobilized, the subject bent the trunk to a predetermined target position and then attempted to replicate the position. Repositioning error was calculated as the absolute difference between the actual target position and the subject-perceived target position. The multiple target positions in the frontal and sagittal planes were tested. Trunk position was measured with a 3Space Tracker, which analyzes the three-dimensional position of the body.

RESULTS

Repositioning error in patients with low back pain was significantly higher than that of control subjects in flexion, and significantly lower than that of control subjects in extension.

CONCLUSIONS

The increase in repositioning error of patients with low back pain during flexion implies that some aspects of proprioception are lost in patients with low back pain. The decrease in repositioning error in patients with low back pain in extension is not as easily explained, but could possibly be caused by increased activation of mechanoreceptors in facet joints.

Innervation of the human costovertebral joint: implications for clinical back pain syndromes

BACKGROUND

The diagnosis of pain in the upper back, shoulder, chest, and arm is often made with considerable confusion and may be accompanied by needless expense and suffering by the patient. Despite the paucity of evidence concerning the tissues and mechanisms responsible for interscapular and atypical chest pain or "pseudo-angina," practitioners of manual therapy maintain that manipulation of the costovertebral elements and associated soft tissues may be helpful in the treatment of these painful conditions.

OBJECTIVE

We have examined the costovertebral complex in humans with respect to the presence of immune-like reactivity to neurofilament protein and the neuropeptide substance P and calcitonin gene-related peptide, markers that reveal the presence of axons in peripheral tissues.

DESIGN

Human costovertebral complexes obtained at autopsy were processed with standard histologic examination and immunocytochemical methods to detect the presence of neurofilaments, substance P, and calcitonin gene-related peptide.

MAIN OUTCOME MEASURES

Outcomes were descriptive and did not require statistical methods.

RESULTS

All costovertebral joints contained innervation within the anterior capsule and synovial tissues. In 4 separate cases, the costovertebral joints contained large intraarticular synovial inclusions or "meniscoids" found to contain small bundles of axons with immune-like reactivity to substance P. Axon bundles were identified in serial section with monoclonal antibodies to neurofilaments as well as with urea-silver nitrate staining.

CONCLUSIONS

The costovertebral joint has been considered a candidate for producing back pain and/or pseudo-angina that may be ameliorated by spinal manipulation. This study has demonstrated that the costovertebral joint has the requisite innervation for pain production in a similar manner to other joints of the spinal column.

Common nerve blocks in chronic pain management

Anesthesiologists have become increasingly involved with the management of chronic pain patients in the operating room, on the surgical floor, and in the outpatient pain facility setting (often interdisciplinary). Based upon the authors' practice of regional anesthesia, the most specific contribution to chronic pain management arguably remains the practice of diagnostic, prognostic, and therapeutic injections of the neuraxis, peripheral nerves, and the autonomic nervous system.

Repositioning error in low back pain. Comparing trunk repositioning error in subjects with chronic low back pain and control subjects

STUDY DESIGN

Repositioning error of the trunk was tested in 20 subjects with chronic low back pain and in 20 control subjects. The 3Space Tracker (Polhemus, Colchester, VT), a device that measures three-dimensional position in space, was used to determine the subject's trunk position.

OBJECTIVES

To determine whether repositioning error is different in subjects with chronic low back pain than in control subjects.

SUMMARY OF BACKGROUND DATA

Proprioception allows the body to maintain proper orientation during static and dynamic activities. In peripheral joint injuries, researchers have demonstrated a loss of some aspects of proprioception and improvement in outcome with retraining. Although the components of proprioception in subjects with low back pain have not been well studied, it is thought that these persons lose some elements of proprioception that can be measured in a quantifiable way. If so, then rehabilitation to improve these deficits is important. In this pilot study, one aspect of proprioception, repositioning error, was examined.

METHODS

The subjects attempted to replicate target positions of the trunk in flexion, extension, lateral bending, and lateral rotation. Repositioning error was calculated as the absolute difference between the actual and the subject-replicated target positions.

RESULTS

No significant difference was found in repositioning error between the control subjects and the persons with chronic low back pain.

CONCLUSIONS

Because proprioception is complex and entails the use of many afferent receptors, it is difficult to measure any one afferent deficiency discretely. The authors believe that this study, in which one aspect of proprioception was measured in an indirect manner, provides important background information on low back position sense. Further studies analyzing aspects of proprioception in subjects with low back pain are recommended.

Neural response of mechanoreceptors to acute inflammation in the rotator cuff of the shoulder joint in rabbits

We examined with electrophysiological techniques the effects of experimentally induced inflammation on the mechanosensitive afferent units in the rotator cuff of the shoulder joint of 21 rabbits. We identified 21 mechanosensitive units belonging to group III. 12 units had mechanical thresholds of > 7.0 g and 9 units had thresholds of < 7.0 g. After injection of inflammatory agents, kaolin and carrageenan, into the joint space, ongoing afferent discharge rates increased in all units. The average discharge rate increased significantly from 7 imp/s to 15 imp/s after injection. 5 units had a decreased mechanical threshold after the injection. Acute inflammation seems to have an excitatory and sensitizing effect on the high- and low-threshold units in the rotator cuff.

The clinical relevance of biomechanics

Most neurologists are familiar with biomechanics but may be unsure of the relevance of this field to their practice. Actually those involved in musculoskeletal problems are undoubtedly using biomechanical principles. This article is limited to the spine, but the basic principles of biomechanics are applicable to other parts of the body. In this article, we describe the spine and trunk as a biomechanical organ, the biomechanical principles behind back injuries and their importance, the role of biomechanical issues in pain, the utility of clinical tests based on biomechanical principles, the effects of aging, and the future directions in spine biomechanical research.

Phospholipase A2 sensitivity of the dorsal root and dorsal root ganglion

STUDY DESIGN

This study was designed to characterize the effects of phospholipase A2 on the neural response of dorsal root and dorsal root ganglion in the anesthetized New Zealand White rabbit.

OBJECTIVES

To examine the effects of phospholipase A2 on the neural response of somatosensory neurons at the dorsal root ganglion level.

SUMMARY OF BACKGROUND DATA

Phospholipase A2 may be an irritating component of disc tissue that is present in high concentration in painful herniated discs, in synovial fluids, and in sera of rheumatoid arthritis patients. Phospholipase A2 is inflammatory; however, its effects on dorsal roots and dorsal root ganglion response have never been demonstrated.

METHODS

Surgically isolated dorsal roots and dorsal root ganglia from New Zealand White rabbits were investigated by electrophysiologic techniques. Phospholipase A2 doses ranging from 100 to 400 U were applied on the mechanically sensitive segments of the dorsal root ganglia, and responses to varying doses were evaluated in relation to elapsed time.

RESULTS

The application of phospholipase A2 on the dorsal root ganglion resulted in possible neurotoxicity at doses more than 375 U, with no significant effect at lower doses except for recruitment of "silent units" at doses ranging from 200 to 340 U.

CONCLUSIONS

Phospholipase A2 doses comparable to serum concentrations in human rheumatoid arthritis appeared to be neurotoxic when applied to dorsal root ganglia. At lower doses, silent units become activated that were not active before the phospholipase A2 application. These results suggest that dorsal roots and dorsal root ganglion may be impaired by phospholipase A2, leading to sciatica and low back pain.

An immunohistochemical study of innervation of lumbar spinal dura and longitudinal ligaments

STUDY DESIGN

An immunocytochemical study of nerve fibers in lumbar spinal dura and longitudinal ligaments was conducted in New Zealand white rabbits.

OBJECTIVES

To demonstrate the presence of nerve fibers and to establish the presence of nociceptive and sympathetic nerve fibers in lumbar dura and longitudinal ligaments.

SUMMARY OF BACKGROUND DATA

The role of dura as a source of low back pain is still unclear, and the data present a somewhat conflicting picture of the nature of nociceptive innervation in this tissue.

METHODS

An immunocytochemical method was used to study dura and longitudinal ligaments from New Zealand White rabbits.

RESULTS

Numerous fine nerve fibers and some small bundles were demonstrated in both the dura and the longitudinal ligaments. In dorsal dura, the fibers were seen at lateral margins running toward midline. In ventral dura and longitudinal ligaments, the fibers were seen throughout the substance of these tissues. A population of substance P, calcitonin gene-related peptide, and tyrosine hydroxylase-reactive nerve fibers were observed in all the tissues. In addition, fibers exhibiting nicotinamide adenine dinucleotide phosphate diaphorase activity were also observed, indicating the presence of nitric oxide in dura.

CONCLUSIONS

The results clearly demonstrate an extensive distribution of nerve fibers in dura and longitudinal ligaments. The presence of a significant number of putative nociceptive fibers supports a possible role for these structures as a source of low back pain and radicular pain.

The tachykinin NK1 receptor. Part II: Distribution and pathophysiological roles

The tachykinin NK1 receptor is widely distributed in both the central and peripheral nervous system. In the CNS, NK1 receptors have been implicated in various behavioural responses and in regulating neuronal survival and degeneration. Moreover, central NK1 receptors regulate cardiovascular and respiratory function and are involved in activating the emetic reflex. At the spinal cord level, NK1 receptors are activated during the synaptic transmission, especially in response to noxious stimuli applied at the receptive field of primary afferent neurons. Both neurophysiological and behavioural evidences support a role of spinal NK1 receptors in pain transmission. Spinal NK1 receptors also modulate autonomic reflexes, including the micturition reflex. In the peripheral nervous system, tachykinin NK1 receptors are widely expressed in the respiratory, genitourinary and gastrointestinal tracts and are also expressed by several types of inflammatory and immune cells. In the cardiovascular system, NK1 receptors mediate endothelium-dependent vasodilation and plasma protein extravasation. At respiratory level, NK1 receptors mediate neurogenic inflammation which is especially evident upon exposure of the airways to irritants. In the carotid body, NK1 receptors mediate the ventilatory response to hypoxia. In the gastrointestinal system, NK1 receptors mediate smooth muscle contraction, regulate water and ion secretion and mediate neuro-neuronal communication. In the genitourinary tract, NK1 receptors are widely distributed in the renal pelvis, ureter, urinary bladder and urethra and mediate smooth muscle contraction and inflammation in response to noxious stimuli. Based on the knowledge of distribution and pathophysiological roles of NK1 receptors, it has been anticipated that NK1 receptor antagonists may have several therapeutic applications at central and peripheral level. At central level, it is speculated that NK1 receptor antagonists could be used to produce analgesia, as antiemetics and for treatment of certain forms of urinary incontinence due to detrusor hyperreflexia. In the peripheral nervous system, tachykinin NK1 receptor antagonists could be used in several inflammatory diseases including arthritis, inflammatory bowel diseases and cystitis. Several potent tachykinin NK1 receptor antagonists are now under evaluation in the clinical setting, and more information on their usefulness in treatment of human diseases will be available in the next few years.

Effects of phospholipase A2 on lumbar nerve root structure and function

STUDY DESIGN

To investigate the effects of phospholipase A2 on the neurophysiology and histology of rat lumbar spinal nerves and the corresponding behavioral changes.

OBJECTIVES

To study possible mechanisms of sciatica.

SUMMARY OF BACKGROUND DATA

The pathophysiology of sciatica is uncertain, although mechanical, chemical, and ischemic factors have been proposed.

METHODS

Phospholipase A2 was injected into the rat L4-L5 epidural space, and the rats were observed for 3 or 21 days. Behavioral studies were conducted daily during the survival period. On the 3rd or 21st day, extracellular nerve recordings were made from dorsal roots, to determine discharge properties and mechanical sensitivity. The nerve roots were then sectioned for a light-microscopic examination.

RESULTS

Motor weakness of hind limbs and altered sensation were observed. In the 3-day phospholipase A2 groups, squeezing the dorsal roots at the L4-L5 disc level (force = 0.8 g) evoked sustained ectopic discharge that lasted approximately 8 minutes. Squeezing the roots distal to the L4-L5 area did not result in sustained discharges. In sham, control, and 21-day phospholipase A2 groups, squeezing the dorsal roots elicited only a transient firing that lasted approximately 0.1 second. Loss of myelin was seen in the nerve root cross sections in the 3-day group, and remyelination was observed in the 21-day group. No abnormality was found in the control groups.

CONCLUSIONS

Based on these studies, it is hypothesized that phospholipase A2 causes demyelination that results in hypersensitive regions where ectopic discharge may be elicited by mechanical stimulation. These ectopic discharges may be a source of sciatica. We believe that, as long as these irritating factors are present, the hypersensitive nerve root nerve will continue to fire, and sciatic pain will persist.

Identification of the location, extent, and pathway of sensory neurologic feedback after mechanical stimulation of a lateral spinal ligament in chickens

STUDY DESIGN

This study traced the location, extent, and pathway of sensory feedback after the mechanical stretching of a lateral spinal ligament in young chickens. The pathway was traced by locating the sites of Fos protein production in neuronal cell bodies at various sites in the nervous system.

OBJECTIVES

To trace the location, extent, and pathway of sensory feedback after the mechanical stretching of a lateral spinal ligament in young chickens.

SUMMARY OF BACKGROUND DATA

The innervation of ligaments is thought to form part of a protective feedback mechanism to provide stability for joints. The precise pathway and extent of the feedback for spinal ligaments is currently unknown. Such information would provide a clear focus for future studies, especially for diseases such as scoliosis where it has been suggested that there is abnormality in perception of sensory feedback.

METHODS

The intertransverse ligament on the right side at T3-T4 in 4-week-old chickens was exposed by blunt dissection. After Fos production resulting from the surgery had been stopped, the ligament was stretched mechanically and repeatedly for 60 minutes using a 300-g weight. Various areas of the nervous system then were sectioned and processed immunohistochemically to identify areas of Fos production in nerve cell bodies. The presence of Fos indicated neurons that had been stimulated by the stretching the ligament, including interneurons along the feedback pathway.

RESULTS

Fos protein was identified in nerve cell bodies in the dorsal root ganglia and intermediate gray matter of the spinal cord at the level of stimulation as well as at several spinal cord levels above and below the site of stimulation. Identification was made on the ipsilateral and the contralateral sides, although the extent of Fos production was less on the contralateral side. Fos presence also was identified in sympathetic ganglia at these sites. Nerve cell bodies in the combined nucleus cuneatus and gracilis in the medulla oblongata, the vestibular nuclei, and the thalamus also contained Fos-positive particles.

CONCLUSIONS

Stretching a single lateral ligament of the spine produces a barrage of sensory feedback from several spinal cord levels on both sides of the spinal cord. This sensory information also is transferred to higher levels in the brain, including the nucleus gracilis and cuneatus, the vestibular nuclei, and the thalamus. These sites of Fos production suggest the locations of pathways for this sensory information, which include the dorsal columns and the spinocerebellar tracts. The information obtained from this study provides a clear focus for future studies in this area, particularly for diseases such as scoliosis where it is thought that incorrect perception of sensory information from the ligaments might be a major contributing factor.

Lumbar facet pain: biomechanics, neuroanatomy and neurophysiology

Idiopathic low back pain has confounded health care practitioners for decades. Although there has been much advance in the understanding of the biomechanics of the lumbar spine over the past 25 years, the cellular and neural mechanisms that lead to facet pain are not well understood. An extensive series of experiments was undertaken to help elucidate these mechanisms and gain a better understanding of lumbar facet pain. Biomechanic and neuroanatomic studies were performed in human cadaveric facet joints and neurophysiologic studies were performed in New Zealand White rabbits. These studies provide the following evidence to help explain the mechanisms of lumbar facet pain: (1) The facet joint can carry a significant amount of the total compressive load on the spine when the human spine is hyperextended. (2) Extensive stretch of the human facet joint capsule occurs when the spine is in the physiologic range of extreme extension. (3) An extensive distribution of small nerve fibers and free and encapsulated nerve endings exists in the lumbar facet joint capsule, including nerves containing substance P, a putative neuromodulator of pain. (4) Low and high threshold mechanoreceptors fire when the facet joint capsule is stretched or is subject to localized compressive forces. (5) Sensitization and excitation of nerves in facet joint and surrounding muscle occur when the joint is inflamed or exposed to certain chemicals that are released during injury and inflammation. (6) Marked reduction in nerve activity occurs in facet tissue injected with hydrocortisone and lidocaine. Thus, the facet joint is a heavily innervated area that is subject to high stress and strain. The resulting tissue damage or inflammation is likely to cause release of chemicals irritating to the nerve endings in these joints, resulting in low back pain.

Effects of a carrageenan-induced inflammation in rabbit lumbar facet joint capsule and adjacent tissues

The effects of experimentally induced inflammation of the lumbar facet joint capsule and adjacent tissues were investigated electrophysiologically and histologically. Type II carrageenan was injected into the receptive fields innervated by identified mechanosensitive afferent units. The multi-unit spontaneous background discharge rate showed increases that consisted of two phases over a time period of 150 min: the first phase (0-30 min) and the second phase (45-150 min). The time course of single units, identified as groups II, III and IV, and silent units, was also investigated. The silent unit discharge rates displayed a gradual increase in the first 15 min and persisted beyond 75 min. Histological examination revealed inflammatory changes in carrageenan injected tissues. In contrast, in isotonic saline injected control experiments there were no changes observed in the electrophysiological or histological studies. This study shows the effects of inflammation in rabbit lumbar facet joint capsule and adjacent tissues. The electrophysiological results show that inflammation of the facet joint and deep back muscles causes (1) increases in multi-unit discharge rate, (2) sensitization to mechanical stimuli and (3) recruitment of previously silent units. Inflammatory changes were also demonstrated histologically.