Spine loading characteristics of patients with low back pain compared with asymptomatic individuals.

STUDY DESIGN: Patients with low back pain and asymptomatic individuals were evaluated while performing controlled and free-dynamic lifting tasks in a laboratory setting. OBJECTIVE: To evaluate how low back pain influences spine loading during lifting tasks. SUMMARY OF BACKGROUND DATA: An important, yet unresolved, issue associated with low back pain is whether patients with low back pain experience spine loading that differs from that of individuals who are asymptomatic for low back pain. This is important to understand because excessive spine loading is suspected of accelerating disc degeneration in those whose spines are damaged already. METHODS: In this study, 22 patients with low back pain and 22 asymptomatic individuals performed controlled and free-dynamic exertions. Trunk muscle activity, trunk kinematics, and trunk kinetics were used to evaluate three- dimensional spine loading using an electromyography- assisted model in conjunction with a new electromyographic calibration procedure. RESULTS: Patients with low back pain experienced 26% greater spine compression and 75% greater lateral shear (normalized to moment) than the asymptomatic group during the controlled exertions. The increased spine loading resulted from muscle coactivation. When permitted to move freely, the patients with low back pain compensated kinematically in an attempt to minimize external moment exposure. Increased muscle coactivation and greater body mass resulted in significantly increased absolute spine loading for the patients with low back pain, especially when lifting from low vertical heights. CONCLUSIONS: The findings suggest a significant mechanical spine loading cost is associated with low back pain resulting from trunk muscle coactivation. This loading is further exacerbated by the increases in body weight that often accompany low back pain. Patient weight control and proper workplace design can minimize the additional spine loading associated with low back pain.     

Corticospinal excitability in patients with chronic low back pain

OBJECTIVE: This study was designed to investigate corticospinal excitability of lumbar muscles using transcranial magnetic stimulation (TMS) in patients with chronic low back pain and correlate this with self-rated measures of disability and pain. METHODS: Twenty-four patients with chronic low back pain and 11 healthy control subjects were used in this study. TMS was delivered through an angled double-cone coil, with its cross-over on the vertex and a posterior-to-anterior current flow in the brain. Electromyographic (EMG) recordings were made from erector spinae (ES) muscles at the fourth lumbar level. Motor cortical excitability was assessed using motor threshold (MTh) for motor evoked potentials (MEPs) and threshold for silent period (SP) during facilitation of the back muscles. Latency, duration, and area of MEPs and SPs were also measured. RESULTS: The latency, duration, and size of MEPs and SPs did not differ between the left and right ES muscles in either the patients or the control subjects and also did not differ between the patients and the control subjects. However, there was a significantly higher MTh and threshold for the SP in the patients as compared with the control subjects; the full significance of this requires further investigation. Interestingly, there was a positive correlation between the self-rated measure of disability (the Oswestry Disability Index score) and both the MTh and the threshold for the SP in the patients. There was also a positive correlation between the self-rated index of back pain and the threshold for the SP in the patients. This finding of an association between clinical and neurophysiologic measures reinforces the need for further research to establish the clinical relevance of these rises in MTh and SP threshold. CONCLUSIONS: In summary, this study has revealed that corticospinal excitability, driving ES muscles close to the site of pain, is lowered in patients with chronic low back pain.     

Outcome research in patients with chronic low back pain

Outcome research in chronic low-back pain is entering a new phase. In the past several years, several outcome measures have been evaluated for their psychometric properties, and databases for patients with low-back pain exist for some of them. A set of recommended and standardized outcome measures and questionnaires is now available for the different outcome domains. The use of computerized versions of these questionnaires will allow simplified data collection and analyses, which will not only help to formulate a more uniform design of research trials, but can be useful for clinicians interested in documenting multi-dimensional outcomes in their patient population.     

Predictors of isokinetic back muscle strength in patients with low back pain

STUDY DESIGN: Testing for trunk muscle strength was performed on 105 patients with chronic low back pain. OBJECTIVES: To investigate prediction of isokinetic back muscle strength in patients with low back pain. SUMMARY OF BACKGROUND DATA: The clinical evaluation of patients with chronic low back pain often in difficult because of discrepancy between disability and impairment. The isokinetic trunk device was developed as a tool for objective assessment of back muscle strength. However, the performance of patients depends on radiologic abnormalities of the spine, conditions of the back muscles, and various psychosocial factors. Studies are warranted that address how these variables influence back muscle strength. METHODS: The patients with chronic low back pain were tested by an isokinetic trunk muscle strength test (Cybex TEF, Ronkonkoma, NY). In addition, the following variables were recorded: gender, age, body mass index, emotional distress, pain on exertion, self-efficacy for pain, degenerative changes of the lumbar spine, cross-sectional area, and density of the erector spinae muscles. The three latter variables were estimated by computed tomography scans. The sum of the total work performed during isokinetic extension strength test was the dependent variable in a multiple regression analysis, and anthropometric, demographic, psychological, and radiologic factors were independent variables. RESULTS: Gender, cross-sectional muscle area, and pain on exertion were the most powerful predictors of isokinetic back muscle strength. The final regression model, which included these variables, could account for approximately 40% of the variability in back muscle strength. CONCLUSION: For assessing the results of an isokinetic trunk muscle strength test, cross-sectional muscle area, gender, and pain on exertion should be taken into account.     

Axial loading during MRI reveals deviant characteristics within posterior IVD regions between low back pain patients and controls

Purpose

To investigate differences in functional intervertebral disk (IVD) characteristics between low back pain (LBP) patients and controls using T2-mapping with axial loading during MRI (alMRI).

Methods

In total, 120 IVDs in 24 LBP patients (mean age 39 years, range 25–69) were examined with T2-mapping without loading of the spine (uMRI) and with alMRI (DynaWell^® loading device) and compared with 60 IVDs in 12 controls (mean age 38 years, range 25–63). The IVD T2-value was acquired after 20-min loading in five regions of interests (ROI), ROI1-5 from anterior to posterior. T2-values were compared between loading states and cohorts with adjustment for Pfirrmann grade.

Results

In LBP patients, mean T2-value of the entire IVD was 64 ms for uMRI and 66 ms for alMRI (p?=?0.03) and, in controls, 65 ms and 65 ms (p?=?0.5). Load-induced T2-differences (alMRI–uMRI) were seen in all ROIs in both patients (0.001?>?p?<?0.005) and controls (0.0001?>?p?<?0.03). In patients, alMRI induced an increase in T2-value for ROI1-3 (23%, 18% and 5%) and a decrease for ROI4 (3%) and ROI5 (24%). More pronounced load-induced decrease was detected in ROI4 in controls (9%/p?=?0.03), while a higher absolute T2-value was found for ROI5 during alMRI in patients (38 ms) compared to controls (33 ms) (p?=?0.04).

Conclusion

The alMRI-induced differences in T2-value in ROI4 and ROI5 between patients and controls most probably indicate biomechanical impairment in the posterior IVD regions. Hence, alMRI combined with T2-mapping offers an objective and clinical feasible tool for biomechanical IVD characterization that may deepen the knowledge regarding how LBP is related to altered IVD matrix composition.

Graphical abstract

These slides can be retrieved under Electronic Supplementary Material.

Open image in new window

     

Muscle response pattern to sudden trunk loading in healthy individuals and in patients with chronic low back pain

STUDY DESIGN: A quick-release method in four directions of isometric trunk exertions was used to study the muscle response patterns in 17 patients with chronic low back pain and 17 matched control subjects. OBJECTIVES: It was hypothesized that patients with low back pain would react to sudden load release with a delayed muscle response and would exhibit altered muscle recruitment patterns. SUMMARY OF BACKGROUND DATA: A delay in erector spinae reaction time after sudden loading has been observed in patients with low back pain. Muscle recruitment and timing pattern play an important role in maintaining lumbar spine stability. METHODS: Subjects were placed in a semiseated position in an apparatus that provided stable fixation of the pelvis. They exerted isometric contractions in trunk flexion, extension, and lateral bending. Each subject performed three trials at two constant force levels. The resisted force was suddenly released with an electromagnet and electromyogram signals from 12 trunk muscles were recorded. The time delay between the magnet release and the shut-off or switch-on of muscle activity (reaction time) was compared between two groups of subjects using two-factor analysis of variance. RESULTS: The number of reacting muscles and reaction times averaged over all trials and directions showed the following results: For healthy control subjects a shut-off of agonistic muscles (with a reaction time of 53 msec) occurred before the switch-on of antagonistic muscles (with a reaction time of 70 msec). Patients exhibited a pattern of co-contraction, with agonists remaining active (3.4 out of 6 muscles switched off) while antagonists switched on (5.3 out of 6 muscles). Patients also had longer muscle reaction times for muscles shutting off (70 msec) and switching on (83 msec) and furthermore, their individual muscle reaction times showed greater variability. CONCLUSIONS: Patients with low back pain, in contrast to healthy control subjects, demonstrated a significantly different muscle response pattern in response to sudden load release. These differences may either constitute a predisposing factor to low back injuries or a compensation mechanism to stabilize the lumbar spine.     

Nerve root injuries in patients with chronic low back pain

In conclusion, the nerve roots and the DRG play an important role in the pain mechanisms of patients suffering from chronic low back pain. Signs of demyelination and increased sensitization for stimuli occurs after a direct nerve root trauma, and the plasticity for the DRG also may change the response to a given peripheral stimuli when repeated frequently over a long period of time. The regeneration mechanisms of spinal nerve roots and DRG regarding function are slow, and the final grade of recurrence depends on the degree of injury. The limited regeneration mechanisms for nerve injury and the fact that "established chronic pain centers" are hard to influence after a long pain history favor an aggressive strategy for pain management. Today, a number of treatment strategies exist for chronic low back pain patients (with or without a diagnosed nerve root injury). These strategies include physiotherapy, nonsteroid anti-inflammatory drugs (NSAIDs), steroids, analgesics of different types and administration routes, surgery, and other sorts of invasive treatments. Further knowledge about the nerve root, DRG, and the rest of the nervous system in these patients is necessary; for understanding how and when to treat patients with chronic low back pain, we need to understand more about what we are trying to treat.     

Lumbar spine kinesthesia in patients with low back pain.

STUDY DESIGN: Single-group, posttest only, using a sample of convenience. OBJECTIVE: To measure the repositioning error of subjects with low back pain for lumbar sagittal movement using a simple kinesthetic test previously described. BACKGROUND: Patients with low back pain are commonly observed to have difficulty in adopting a mid or neutral position of the lumbar spine. METHODS AND MEASUREMENTS: Twenty subjects with low back pain were required to reproduce an upright neutral posture of the lumbar spine following movement into flexion in a sitting position. Trunk positioning accuracy was measured with an electromagnetic tracking device. RESULTS: The mean absolute value of the repositioning error in the sagittal plane was 2.25 degrees +/-0.88 degrees on day 1 and 2.32 degrees +/-1.62 degrees on day 2. The performance of patients with low back pain was similar to that of asymptomatic patients in a previous study, although subjects with low back pain overshot the neutral position more frequently (79%) than did nonimpaired subjects (50%). CONCLUSIONS: Subjects with low back pain may have attempted to use extra mechanoreceptive cues to compensate for some kinesthetic deficit. Nevertheless, the kinesthetic test used was not sensitive enough to detect any repositioning deficits, and reasons for this are explored.     

Prevalence of sleep disturbance in patients with low back pain

Low back pain (LBP) is a common health condition that is often associated with disability, psychological distress and work loss. Worldwide, billions of dollars are expended each year trying to manage LBP, often with limited success. Recently, some researchers have reported that LBP patients also report sleep disturbance as a result of their LBP. However, as most of this evidence was obtained from highly selected groups of patients or from studies with small samples, high quality data on prevalence of sleep disturbance for patients with LBP are lacking. It is also unclear whether sleep disturbance is more likely to be reported by patients with recent-onset LBP than by patients with persistent LBP. Finally, it is not known whether high pain intensity, the most relevant condition-specific variable, is associated with higher rates of reported sleep disturbance. The present study aimed to determine the prevalence of reported sleep disturbance in patients with LBP. In addition, we aimed to determine whether sleep disturbance was associated with the duration of back pain symptoms and whether pain intensity was associated with reported sleep disturbance. Data from 1,941 patients obtained from 13 studies conducted by the authors or their colleagues between 2001 and 2009 were used to determine the prevalence of sleep disturbance. Logistic regression analyses explored associations between sleep disturbance, the duration of low back symptoms and pain intensity. The estimated prevalence of sleep disturbance was 58.7% (95% CI 56.4–60.7%). Sleep disturbance was found to be dependent on pain intensity, where each increase by one point on a ten-point visual analogue scale (VAS) was associated with a 10% increase in the likelihood of reporting sleep disturbance. Our findings indicate that sleep disturbance is common in patients with LBP. In addition, we found that the intensity of back pain was only weakly associated with sleep disturbance, suggesting that other factors contribute to sleep problems for LBP patients.     

Limited clinical utility of pain drawing in assessing patients with low back pain

OBJECTIVE: The aim of this study was to assess the use of pain drawing by studying its ability to identify patients with low back pain and abnormal psychological profile. The intraevaluator repeatability of the penalty point method of scoring of pain drawing was also evaluated. METHODS: A total of 331 consecutive patients with low back pain were prospectively recruited. The psychologic profile was assessed using the Hospital Anxiety and Depression Scale. The pain drawings were scored with the penalty point method. The ability of pain drawing to identify patients with significant anxiety and depression was assessed by calculating the sensitivity, specificity, and positive predictive value. The intraevaluator repeatability was calculated for scoring done at an interval of 1 month using the kappa statistic. RESULTS: There were statistically significant differences in the anxiety and depression scores in patients with normal (n = 200) and abnormal (n = 131) pain drawing (anxiety: 9 +/- 4 vs 10.3 +/- 3.7; depression: 8.1 +/- 3.5 vs 8.8 +/- 3.6; P < 0.005). The pain drawing had a low sensitivity for detecting patients with any degree of anxiety (43%) or depression (40%). The positive predictive value of pain drawing for anxiety and depression was 78% and 69%, respectively. The kappa value for intraobserver assessment was 0.6 (P < 0.05). CONCLUSION: Though there are differences in anxiety and depression scores in patients with normal and abnormal pain drawing, the performance characteristics of pain drawing are less than acceptable and therefore limit its use in clinical practice.     

Effects of volitional spine stabilization on lifting task in recurrent low back pain population

Purpose

To examine the influence of volitional preemptive abdominal contraction (VPAC) and recurrent low back pain (rLBP) on trunk mechanics and neuromuscular control during a symmetric lifting task.

Methods

A 2 × 2 crossover mixed design was used to examine the effects of VPAC and group. Thirty-seven healthy individuals and 32 rLBP individuals performed symmetric box lifting trials with and without VPAC to a 1-m height table 3D trunk, pelvis, and hip joint angle and electromyographic magnitude variables were obtained. Selected variables were analyzed using ANOVA.

Results

The VPAC induced differences in joint kinematics and muscle activity in rLBP and healthy subjects during symmetric lifting. A significant two-way interaction effect was observed for the semitendinosus activity. The VPAC increased external oblique muscle activity, reduced erector spinae and multifidus muscles activity, and induced greater trunk flexion angle, greater trunk side flexion angle, and greater hip flexion angle, and decreased pelvis obliquity angle in both groups. In addition, the rLBP subjects presented with a reduced external oblique and gluteus maximus muscle activity, greater erector spinae and multifidus muscles activity, and greater pelvis posterior tilt angle.

Conclusions

Our results provide evidence that a VPAC strategy performed during symmetric lifting may potentially reduce exposure to biomechanical factors that can contribute to lumbar spine injury. The hamstring muscles may play an important role in achieving pelvic balance during the lifting maneuver. Incorporating the VPAC during dynamic stressful activities appears to help improve sensorimotor control and facilitate positioning of the lower extremities and the pelvis, while protecting the lumbar spine.