Maggie E. Horn

Self-reported pain and disability outcomes from an endogenous model of muscular back pain

BackgroundOur purpose was to develop an induced musculoskeletal pain model of acute low back pain and examine the relationship among pain, disability and fear in this model.MethodsDelayed onset muscle soreness was induced in 52 healthy volunteers (23 women, 17 men; average age 22.4 years; average BMI 24.3) using fatiguing trunk extension exercise. Measures of pain intensity, unpleasantness, and location, and disability, were tracked for one week after exercise.ResultsPain intensity ranged from 0 to 68 with 57.5% of participants reporting peak pain at 24 hours and 32.5% reporting this at 48 hours. The majority of participants reported pain in the low back with 33% also reporting pain in the legs. The ratio of unpleasantness to intensity indicated that the sensation was considered more unpleasant than intense. Statistical differences were noted in levels of reported disability between participants with and without leg pain.Pain intensity at 24 hours was correlated with pain unpleasantness, pain area and disability. Also, fear of pain was associated with pain intensity and unpleasantness. Disability was predicted by sex, presence of leg pain, and pain intensity; however, the largest amount of variance was explained by pain intensity (27% of a total 40%). The second model, predicting pain intensity only included fear of pain and explained less than 10% of the variance in pain intensity.ConclusionsOur results demonstrate a significant association between pain and disability in this model in young adults. However, the model is most applicable to patients with lower levels of pain and disability. Future work should include older adults to improve the external validity of this model.

Fear of Severe Pain Mediates Sex Differences in Pain Sensitivity Responses to Thermal Stimuli

The purpose of this paper was to examine the relationship of sex and pain-related fear in pain intensity reports to thermal stimuli and whether sex differences in reported pain intensity were mediated by pain-related fear. 177 participants, 124 female (23.5 ± 4.5 years old), filled out a demographic and fear of pain questionnaire (FPQ-III). Experimental pain testing was performed using thermal stimuli applied to the lower extremity. Participants rated the intensity of pain using the numerical pain rating scale (NPRS). Independent t-tests, Sobels test, and linear regression models were performed to examine the relationships between sex, fear of pain, and pain sensitivity. We found significant sex differences for thermal pain threshold temperatures (t = 2.04,  P = 0.04) and suprathreshold pain ratings for 49°C (t = −2.12,  P = 0.04) and 51°C (t = −2.36,  P = 0.02). FPQ-severe score mediated the effect of suprathreshold pain ratings of 49° (t = 2.00,  P = 0.05), 51° (t = 2.07,  P = 0.04), and pain threshold temperatures (t = −2.12,  P = 0.03). There are differences in the pain sensitivity between sexes, but this difference may be mediated by baseline psychosocial factors such as fear of pain.

Exercise-induced pain intensity predicted by pre-exercise fear of pain and pain sensitivity

ObjectivesOur primary goals were to determine whether preexisting fear of pain and pain sensitivity contributed to post-exercise pain intensity. MethodsDelayed-onset muscle pain was induced in the trunk extensors of 60 healthy volunteers using an exercise paradigm. Levels of fear of pain and experimental pain sensitivity were measured before exercise. Pain intensity in the low back was collected at 24 and 48 hours post-exercise. Participants were grouped based on pain intensity. Group membership was used as the dependent variable in separate regression models for 24 and 48 hours. Predictor variables included fear, pain sensitivity, torque lost during the exercise protocol, and demographic variables. ResultsThe final models predicting whether a participant reported clinically meaningful pain intensity at 24 hours only included baseline fear of pain at each level of pain intensity tested. The final model at 48 hours included average baseline pain sensitivity and the loss of muscle performance during the exercise protocol for 1 level of pain intensity tested (greater than 35 mm of 100 mm). DiscussionCombined, these findings suggest that the initial reports of pain after injury may be more strongly influenced by fear whereas the inflammatory process and pain sensitivity may play a larger role for later pain intensity reports.

Effect of a single session of muscle-biased therapy on pain sensitivity: A systematic review and meta-analysis of randomized controlled trials

Background Muscle-biased therapies (MBT) are commonly used to treat pain, yet several reviews suggest evidence for the clinical effectiveness of these therapies is lacking. Inadequate treatment parameters have been suggested to account for inconsistent effects across studies. Pain sensitivity may serve as an intermediate physiologic endpoint helping to establish optimal MBT treatment parameters. The purpose of this review was to summarize the current literature investigating the short-term effect of a single dose of MBT on pain sensitivity in both healthy and clinical populations, with particular attention to specific MBT parameters of intensity and duration. Methods A systematic search for articles meeting our prespecified criteria was conducted using Cumulative Index to Nursing and Allied Health Literature (CINAHL) and MEDLINE from the inception of each database until July 2012, in accordance with guidelines from the Preferred Reporting Items for Systematic reviews and Meta-Analysis. Relevant characteristics from studies included type, intensity, and duration of MBT and whether short-term changes in pain sensitivity and clinical pain were noted with MBT application. Study results were pooled using a random-effects model to estimate the overall effect size of a single dose of MBT on pain sensitivity as well as the effect of MBT, dependent on comparison group and population type. Results Reports from 24 randomized controlled trials (23 articles) were included, representing 36 MBT treatment arms and 29 comparative groups, where 10 groups received active agents, 11 received sham/inert treatments, and eight received no treatment. MBT demonstrated a favorable and consistent ability to modulate pain sensitivity. Short-term modulation of pain sensitivity was associated with short-term beneficial effects on clinical pain. Intensity of MBT, but not duration, was linked with change in pain sensitivity. A meta-analysis was conducted on 17 studies that assessed the effect of MBT on pressure pain thresholds. The results suggest that MBT had a favorable effect on pressure pain thresholds when compared with no-treatment and sham/inert groups, and effects comparable with those of other active treatments. Conclusion The evidence supports the use of pain sensitivity measures by future research to help elucidate optimal therapeutic parameters for MBT as an intermediate physiologic marker.

Magnitude of spinal muscle damage is not statistically associated with exercise-induced low back pain intensity

BACKGROUND CONTEXT Findings on imaging of noncontractile anatomic abnormalities and the intensity of low back pain have weak associations because of false-positive rates among asymptomatic individuals. This association might be stronger for contractile tissues. PURPOSE The purpose of this study was to examine the relationship between location and reports of pain intensity in the low back and exercise-induced muscle damage to the lumbar paraspinal muscles. STUDY DESIGN Nondiagnostic observational study in a laboratory setting. METHODS Delayed onset muscle soreness was induced in the low back of healthy pain-free volunteers. Measures of pain intensity (100-mm visual analog scale [VAS]) and location (area on the pain diagram) were taken before and 48 hours after exercise. Muscle damage was quantified using mechanical pain thresholds, motor performance deficits, and transverse relaxation time (T2)-weighted magnetic resonance imaging (MRI). Changes pre- to postexercise in signal intensity on T2-weighted imaging within the erector spinae, pain intensity, pain area, mechanical pain threshold, and isometric torque were assessed using paired t tests. Bivariate correlations were conducted to assess associations among muscle damage, pain intensity, and pain drawing area. RESULTS Twenty participants volunteered (11 women; average age, 22.3 years; average body mass index, 23.5) for study participation. Reports of pain intensity at 48 hours ranged from 0 to 59 mm on the VAS. Muscle damage was confirmed by reductions in mechanical threshold (p=.011) and motor performance (p<.001) and by changes in T2-weighted MRI (p=.007). This study was powered to find an association of at least r=0.5 to be statistically significant. Correlations of continuous variables revealed no significant correlations between pain intensity and measures of muscle damage (ranging between -0.075 and 0.151). There was a significant association between the remaining torque deficit at 48 hours and pain area. CONCLUSIONS The results of this study indicate that there was no association between the magnitude of muscle damage in the lumbar erector spinae and reported pain intensity in the low back. In future studies, larger cohorts may report statistically significant associations, but our data suggest that there will be low magnitude potentially indicating limited clinical relevance.

Investigating dynamic pain sensitivity in the context of the fear-avoidance model.

Although nearly everyone at some point in their lives experiences back pain; the amount of interference with routine activity varies significantly. The fear‐avoidance (FA) model of chronic pain explains how psychological variables, such as fear, act as mediating factors influencing the relationship between clinical pain intensity and the amount of interference with daily activities. What remains less clear is how other mediating factors fit within this model. The primary objective of this report was to examine the extent to which a dynamic measure of pain sensitivity provides additional information within the context of the FA model.

Implications of practice setting on clinical outcomes and efficiency of care in the delivery of physical therapy services.

STUDY DESIGN Retrospective analysis of episodes of care. OBJECTIVE To assess the implications of practice setting (hospital outpatient settings versus private practice) on clinical outcomes and efficiency of care in the delivery of physical therapy services. BACKGROUND Many patients with musculoskeletal conditions benefit from care provided by physical therapists. The majority of physical therapists deliver services in either a private practice setting or in a hospital outpatient setting. There have not been any recent studies comparing whether clinical outcomes or efficiency of care differ based on practice setting. METHODS Practices that use the Focus On Therapeutic Outcomes, Inc system were surveyed to determine the specific type of setting in which outcomes were collected in patients with musculoskeletal impairments. Patient outcome data over 12 months (2011-2012) were extracted from the database and analyzed to identify differences in the functional status achieved and the efficiency of the care delivery process between private practices and hospital outpatient settings. RESULTS The data suggest that patients experience more efficient care when receiving physical therapy in hospital outpatient settings compared to private practice settings, as demonstrated by 3.1 points of greater improvement in functional status over 2.9 fewer physical therapy visits. However, the difference in improvement between settings is less than the minimum clinically important difference of 9 points in functional status outcome score. CONCLUSION In this cohort, our data suggest that more efficient care was delivered in the hospital outpatient setting compared to the private practice setting. However, we cannot conclude that care delivered in the hospital setting is more cost-effective, because it is possible that any difference in efficiency of care favoring the hospital outpatient setting is more than offset by higher costs of care.

Relationship of Intersession Variation in Negative Pain-Related Affect and Responses to Thermally-Evoked Pain

UNLABELLED The purpose of this study was to determine whether session-specific measures of negative pain-related affect would account for longitudinal variability in the ratings of the evoked thermal pain. Pain-free subjects rated pain evoked on the posterior leg using thermal stimuli of 45 degrees , 47 degrees , 49 degrees , and 51 degrees C on 3 occasions, each separated by 2 weeks. Session-specific negative pain-related affect measures were also collected. Ratings of pain decreased significantly with repeated testing, demonstrating a systematic change in rating from the first to second sessions that ranged from a mean of 5.3 at 47 degrees C to 9.1 at 49 degrees C. In addition, large random variation occurred across all sessions, resulting in minimal detectable change ranging from 14 to 27. The least variability occurred when a mean rating of the 4 temperatures was used. Session-specific measures of pain-related affect decreased with repeated testing; however, the significant between-subject variability in both rating of pain and pain-related affect were not related to each other. No associations were identified between psychological measures and variability in rating of evoked pain. Future studies of the variability in ratings should consider other factors such as attentional focus. PERSPECTIVE The individual variability in thermal rating was not explained by individual variation in session-specific measures of negative pain-related affect. The results of this study support the use of repeated baseline measures of thermal stimuli when feasible. When this is not possible, the variability in ratings of thermal stimuli over multiple sessions is reduced when the mean of multiple temperatures is used.

Flexion Relaxation Ratio Not Responsive to Acutely Induced Low Back Pain from a Delayed Onset Muscle Soreness Protocol

Background. The flexion relaxation ratio (FRR) has been suggested as a measure of muscular performance in patients with low back pain (LBP). The purpose of this study was to investigate whether the FRR was responsive to acute LBP produced from a delayed onset muscle soreness (DOMS) protocol. Methods. Fifty-one pain-free volunteers performed DOMS to induce LBP. Current pain intensity, trunk flexion range of motion (ROM), and passive straight leg raise (SLR) were measured at baseline, 24 and 48 hours after DOMS. Participants were categorized into pain groups based on reported current pain intensity. Changes in FRR, trunk flexion ROM, and SLR ROM were examined using two-way repeated measures analysis of variance. Results. Pain group was not found to have a significant effect on FRR (F 1,29 = 0.054, P = 0.818), nor were there any two-way interactions for changes in FRR. The pain group had decreased trunk flexion ROM compared to the minimal pain group (F 1,38 = 7.21, P = 0.011), but no decreases in SLR ROM (F 1,38 = 3.51, P = 0.057) over time. Interpretation. There were no differences in FRR based on reported pain intensity of LBP from a DOMS protocol. The responsiveness of FRR might be limited in patients with acute onset LBP of muscular origin.

Influence of Initial Provider on Health Care Utilization in Patients Seeking Care for Neck Pain

Objective To examine patients seeking care for neck pain to determine associations between the type of provider initially consulted and 1-year health care utilization. Patients and Methods A retrospective cohort of 1702 patients (69.25% women, average age, 45.32±14.75 years) with a new episode of neck pain who consulted a primary care provider, physical therapist (PT), chiropractor (DC), or specialist from January 1, 2012, to June 30, 2013, was analyzed. Descriptive statistics were calculated for each group, and subsequent 1-year health care utilization of imaging, opioids, surgery, and injections was compared between groups. Results Compared with initial primary care provider consultation, patients consulting with a DC or PT had decreased odds of being prescribed opioids within 1 year from the index visit (DC: adjusted odds ratio [aOR], 0.54; 95% CI, 0.39-0.76; PT: aOR, 0.59; 95% CI, 0.44-0.78). Patients consulting with a DC additionally demonstrated decreased odds of advanced imaging (aOR, 0.43; 95% CI, 0.15-0.76) and injections (aOR, 0.34; 95% CI, 0.19-0.56). Initiating care with a specialist or PT increased the odds of advanced imaging (specialist: aOR, 2.96; 95% CI, 2.01-4.38; PT: aOR, 1.57; 95% CI, 1.01-2.46), but only initiating care with a specialist increased the odds of injections (aOR, 3.21; 95% CI, 2.31-4.47). Conclusion Initially consulting with a nonpharmacological provider may decrease opioid exposure (PT and DC) over the next year and also decrease advanced imaging and injections (DC only). These data provide an initial indication of how following recent practice guidelines may influence health care utilization in patients with a new episode of neck pain.