Mechanosensitive afferent units in the lumbar posterior longitudinal ligament

Mechanisms behind the Development of Chronic Low Back Pain and Its Neurodegenerative Features

Chronic back pain is complex and there is no guarantee that treating its potential causes will cause the pain to go away. Therefore, rather than attempting to "cure" chronic pain, many clinicians, caregivers and researchers aim to help educate patients about their pain and try to help them live a better quality of life despite their condition. A systematic review has demonstrated that patient education has a large effect on pain and pain related disability when done in conjunction with treatments. Therefore, understanding and updating our current state of knowledge of the pathophysiology of back pain is important in educating patients as well as guiding the development of novel therapeutics. Growing evidence suggests that back pain causes morphological changes in the central nervous system and that these changes have significant overlap with those seen in common neurodegenerative disorders. These similarities in mechanisms may explain the associations between chronic low back pain and cognitive decline and brain fog. The neurodegenerative underpinnings of chronic low back pain demonstrate a new layer of understanding for this condition, which may help inspire new strategies in pain education and management, as well as potentially improve current treatment.

Does discectomy improve low back pain as well as radiating pain in patients with lumbar herniated intervertebral disc (HIVD)?

Most postoperative patients with herniated lumbar disc complained of lower leg radiating pain (LRP), referred buttock pain (RBP), and low back pain (LBP). When discectomy is performed, improvement in LRP is observed due to spinal nerve irritation. However, long-term LBP due to degenerative changes in the disc may occur postoperatively. In addition, limited research has been reported on the short-term (within 1 year) improvement in LBP after discectomy. This study aimed to evaluate the effectiveness of discectomy in reducing LBP within 1 year postoperatively.Among the 183 patients who underwent discectomy performed by a single surgeon from January 2010 to December 2016, 106 who met the inclusion and exclusion criteria were enrolled. In the 106 patients who underwent lumbar discectomy, 3 types of spine-related pain were pre-operatively assessed and 3, 6, and 12 months postoperatively. Functional outcomes were evaluated, and quality of life was assessed 12 months postoperatively by using the Short-Form 36 questionnaire, which was subdivided into mental and physical components.LBP showed both statistical and clinical improvement within the first 3 months postoperatively, but the improvement was not observed until 12 months postoperatively. RBP and LRP showed both statistical and clinical improvement within the first 3 months and further consistently showed statistical improvement. LBP improved clinically only until 3 months postoperatively regardless of the type of herniation.LBP showed improvement within the first 3 months postoperatively and plateaued afterward, and RBP and radiculopathy showed consistent improvement until 12 months postoperatively. This may explain why patients from 12-month follow-up showed improvement in RBP and radiculopathy but not LBP.

Analysis of chronic low back pain with magnetic resonance imaging T2 mapping of lumbar intervertebral disc

BACKGROUND

Magnetic resonance imaging (MRI) T2 mapping utilizes the T2 values for quantification of moisture content and collagen sequence breakdown. Recently, attempts at quantification of lumbar disc degeneration through MRI T2 mapping have been reported. We conducted an analysis of the relationship between T2 values of degenerated intervertebral discs (IVD) and chronic low back pain (CLBP).

METHODS

The subjects who had CLBP comprised 28 patients (15 male, 13 female; mean age 48.9 ± 9.6 years; range 22-60 years). All subjects underwent MRI and filled out the low back pain visual analog scale (VAS) and Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ). The disc was divided into the anterior annulus fibrosus (AF), the nucleus pulposus (NP), and the posterior AF, and each T2 value was measured. This study involved 25 asymptomatic control participants matched with the CLBP group subjects for gender and age (13 male, 12 female; mean age 43.8 ± 14.5 years; range 23-60 years). These subjects had no low back pain, and constituted the control group.

RESULTS

T2 values for IVD tended to be lower in the CLBP group than in the control group, and these values were significantly different within the posterior AF. The correlation coefficients between the VAS scores and T2 values of anterior AF, NP and posterior AF were r = 0.30, -0.15 and -0.50. The correlation coefficient between the JOABPEQ scores (low back pain) and T2 values of anterior AF, NP and posterior AF were r = -0.0041, 0.11 and 0.42. Similarly, the JOABPEQ scores (lumbar function) were r = -0.22, -0.12 and 0.57.

CONCLUSIONS

The results indicated a correlation between posterior AF degeneration and CLBP. This study suggests that MRI T2 mapping could be used as a quantitative method for diagnosing discogenic pain.

Disturbance and recovery of trunk mechanical and neuromuscular behaviors following repeated static trunk flexion: influences of duration and duty cycle on creep-induced effects

Occupations involving frequent trunk flexion are associated with a higher incidence of low back pain. To investigate the effects of repeated static flexion on trunk behaviors, 12 participants completed six combinations of three static flexion durations (1, 2, and 4 min), and two flexion duty cycles (33% and 50%). Trunk mechanical and neuromuscular behaviors were obtained pre- and post-exposure and during recovery using sudden perturbations. A longer duration of static flexion and a higher duty cycle increased the magnitude of decrements in intrinsic stiffness. Increasing duty cycle caused larger decreases in reflexive muscle responses, and females had substantially larger decreases in reflexive responses following exposure. Patterns of recovery for intrinsic trunk stiffness and reflexive responses were consistent across conditions and genders, and none of these measures returned to pre-exposure values after 20 min of recovery. Reflexive responses may not provide a compensatory mechanism to offset decreases in intrinsic trunk stiffness following repetitive static trunk flexion. A prolonged recovery duration may lead to trunk instability and a higher risk of low back injury.

Outcome predictors of percutaneous endoscopic lumbar discectomy and thermal annuloplasty for discogenic low back pain

PURPOSE

Endoscopic discectomy with annuloplasty is considered as a novel minimally invasive technique for treating chronic discogenic low back pain (DLBP). The purpose of this study was to evaluate the outcome predictors and to describe technical aspects for endoscopic solutions against DLBP.

MATERIALS AND METHODS

We performed a prospective study of 87 patients who underwent percutaneous endoscopic lumbar discectomy and thermal annuloplasty (PELDTA) for DLBP. The inclusion criteria were disc degenerations with annular tear confirmed by imaging studies and discography. Clinical outcomes were assessed using the visual analog scale (VAS), the Oswestry disability index (ODI), and the modified MacNab criteria. The univariate and multivariate analyses were performed to evaluate the outcome predictors.

RESULTS

The 2-year follow-up rate was 90.8% (79 of 87 patients). The VAS and ODI scores at postoperative 6 months and 2 years were significantly improved (p < 0.001). Based on the modified MacNab criteria, the global outcomes were excellent in 39 out of 79 patients (49.4%), good in 17 patients (21.5%), fair in 10 patients (12.7%), and poor in 13 patients (16.5%). Therefore, the percentage of symptomatic improvement was 83.5% and the success rate (excellent or good) was 70.9%. In the univariate and multivariate analyses, the presence of concurrent disc herniation with DLBP was the most significant predictor (OR = 3.207, 95% CI 1.02-10.06, p = 0.046).

CONCLUSIONS

PELDTA may be effective for patients with chronic DLBP in selected cases. Central disc herniation causing DLBP was the most important predictor for clinical success.

Use of Temporary Implantable Biomaterials to Reduce Leg Pain and Back Pain in Patients with Sciatica and Lumbar Disc Herniation

The principle etiology of leg pain (sciatica) from lumbar disc herniation is mechanical compression of the nerve root. Sciatica is reduced by decompression of the herniated disc, i.e., removing mechanical compression of the nerve root. Decompression surgery typically reduces sciatica more than lumbar back pain (LBP). Decompression surgery reduces mechanical compression of the nerve root. However, decompression surgery does not directly reduce sensitization of the sensory nerves in the epidural space and disc. In addition, sensory nerves in the annulus fibrosus and epidural space are not protected from topical interaction with pain mediators induced by decompression surgery. The secondary etiology of sciatica from lumbar disc herniation is sensitization of the nerve root. Sensitization of the nerve root results from a) mechanical compression, b) exposure to cellular pain mediators, and/or c) exposure to biochemical pain mediators. Although decompression surgery reduces nerve root compression, sensory nerve sensitization often persists. These observations are consistent with continued exposure of tissue in the epidural space, including the nerve root, to increased cellular and biochemical pain mediators following surgery. A potential contributor to lumbar back pain (LBP) is stimulation of sensory nerves in the annulus fibrosus by a) cellular pain mediators and/or b) biochemical pain mediators that accompany annular tears or disruption. Sensory fibers located in the outer one-third of the annulus fibrosus increase in number and depth as a result of disc herniation. The nucleus pulposus is comprised of material that can produce an autoimmune stimulation of the sensory nerves located in the annulus and epidural space leading to LBP. The sensory nerves of the annulus fibrosus and epidural space may be sensitized by topical exposure to cellular and biochemical pain mediators induced by lumbar surgery. Annulotomy or annular rupture allows the nucleus pulposus topical access to sensory nerve fibers, thereby leading to LBP. Coverage of the annulus and adjacent structures in the epidural space by absorbable viscoelastic gels appears to reduce LBP following surgery by protecting sensory fibers from cellular and biochemical pain mediators.

Short rest between cyclic flexion periods is a risk factor for a lumbar disorder

BACKGROUND

The epidemiology identifies cyclic lumbar loading as a risk factor for cumulative trauma disorder. Experimental biomechanical and physiological confirmation is lacking. The objective of this study was to asses the impact of different rest durations applied between periods of cyclic loading on the development of an acute lumbar disorder which, if continued to be subjected to loading, may develop into a cumulative disorder.

METHODS

Three groups of in vivo feline preparations were subjected to six sequential 10 min loading periods of cyclic lumbar flexion at 40 N with a frequency of 0.25 Hz applied to the L-4/5 level. The rest durations varied from 5 min in the first group, to 10 min in the second and to 20 min in the third. Reflexive EMG from the multifidi and lumbar displacement were used to identify significant (P<0.001) effects of time and rest duration for post-load EMG and displacement. Single-cycle test were performed hourly for 7 h post-loading to assess recovery. A model developed earlier was applied to represent the experimental data.

FINDINGS

The groups allowed 5 and 10 min rest exhibited an acute neuromuscular disorder expressed by a significant (P<0.001) delayed hyperexcitability 2-3 h into the 7 h recovery period with the intensity of the hyperexcitability significantly higher (P<0.001) for the group allowed only 5 min rest. The group allowed 20 min rest had a slow, uneventful recovery, free of delayed hyperexcitability.

INTERPRETATIONS

Occupational and sports activities requiring repetitive (cyclic) loading of the lumbar spine may be a risk factor for the development of a cumulative lumbar disorder and may require sufficient rest, as much as twice as long as the loading period, for prevention. Comparison to similar data for static lumbar loading shows that cyclic loading is more deleterious than static loading, requiring more rest to offset the negative effect of the repeated acts of stretch.

A hypothesis of chronic back pain: ligament subfailure injuries lead to muscle control dysfunction

Clinical reports and research studies have documented the behavior of chronic low back and neck pain patients. A few hypotheses have attempted to explain these varied clinical and research findings. A new hypothesis, based upon the concept that subfailure injuries of ligaments (spinal ligaments, disc annulus and facet capsules) may cause chronic back pain due to muscle control dysfunction, is presented. The hypothesis has the following sequential steps. Single trauma or cumulative microtrauma causes subfailure injuries of the ligaments and embedded mechanoreceptors. The injured mechanoreceptors generate corrupted transducer signals, which lead to corrupted muscle response pattern produced by the neuromuscular control unit. Muscle coordination and individual muscle force characteristics, i.e. onset, magnitude, and shut-off, are disrupted. This results in abnormal stresses and strains in the ligaments, mechanoreceptors and muscles, and excessive loading of the facet joints. Due to inherently poor healing of spinal ligaments, accelerated degeneration of disc and facet joints may occur. The abnormal conditions may persist, and, over time, may lead to chronic back pain via inflammation of neural tissues. The hypothesis explains many of the clinical observations and research findings about the back pain patients. The hypothesis may help in a better understanding of chronic low back and neck pain patients, and in improved clinical management.

The anatomic and physiologic basis of local, referred and radiating lumbosacral pain syndromes related to disease of the spine

Conscious perception and unconscious effects originating from the vertebral column and its neural structures, although complex, have definite pathways represented in a network of peripheral and central nervous system (CNS) ramifications. These neural relationships consequently result in superimposed focal and diffuse, local and remote conscious perceptions and unconscious effects. Any one or combination of somatic and autonomic signs and symptoms may potentially be observed in a particular patient. This variety and inconsistency may mislead or confuse both the patient and the physician. A clear understanding of the basic anatomic and physiologic concepts underlying this complexity should accompany clinical considerations of the potential significance of spondylogenic and neurogenic syndromes in any disease process affecting the spine.

Low back pain: pathophysiology and management

Basic research is advancing the understanding of the pathogenesis and management of low back pain at the molecular and genetic levels. Frequently, low back pain is caused by disorders of the intervertebral disk. Cytokines such as matrix metalloproteinases, phospholipase A2, nitric oxide, and tumor necrosis factor-alpha are thought to contribute to the development of low back pain. Drugs are being developed to modulate these chemical mediators. Recent research using growth factors to promote chondrocyte regeneration appears to be promising. Advances in gene therapy to both prevent disk degeneration and regenerate the disk eventually may have clinical application.