Steffan Wittrup Christensen

Digital Pain Drawings: Assessing Touch-screen Technology and 3D Body Schemas.

Objectives:To assess the consistency and level of agreement between pain drawings collected on (1) paper and a personal computer tablet; and (2) between a 2-dimensional (2D) line drawing and 3-dimensional (3D) body schema. Materials and Methods:Pain-free participants (N=24) recreated a premarked “pain” area from a 2D line drawing displayed on paper onto paper or tablet, and individuals with chronic neck pain (N=29) expressed their current pain on paper and tablet. A heterogeneous group (N=26) was recruited from cross-disciplinary pain clinic and expressed their pain on a 2D line drawing and a 3D body schema, as displayed on a tablet, and then completed an user-experience questionnaire. Results:Pain drawings showed moderate to high level of consistency and a high level of agreement for paper and tablet and between 2D line drawing and 3D body schema. A fixed bias (−1.0042, P<0.001) revealed that pain areas were drawn slightly smaller on paper than on tablet, and larger on the 2D than the 3D body schema (−0.6371, P=0.003), as recorded on a tablet. Over one-third of individuals with chronic pain preferred and/or believed that the 3D body schema enabled a more accurate record; 12 believed they were equal, and 3 preferred the 2D line drawing. Discussion:Pain drawings recorded with touch-screen technology provide equal reliability to paper but the size of the drawing slightly differs between the platforms. Although, 2D line drawings and 3D body schemas were similar in terms of consistency and reliability, it remains to be confirmed whether 3D body schemas increase the accuracy and precision of pain drawings.

Reorganised motor control strategies of trunk muscles due to acute low back pain

This study assessed how the low back motor control strategies were affected by experimental pain. In twelve volunteers the right m. longissimus was injected by hypertonic and isotonic (control) saline. The pain intensity was assessed on a visual analog scale (VAS). Subjects were seated on a custom-designed chair including a 3-dimensional force sensor adjusted to the segmental height of T1. Electromyography (EMG) was recorded bilaterally from longissimus, multifidus, rectus abdominis, and external oblique muscles. Isometric trunk extensions were performed before, during, and after the saline injections at 5%, 10%, and 20% of maximum voluntary contraction force. Visual feedback of the extension force was provided whereas the tangential force components were recorded. Compared with isotonic saline, VAS scores were higher following hypertonic saline injections (P<.01). Experimental low back pain reduced the EMG activity bilaterally of the rectus abdominis muscles during contractions at 10% and 20% MVC (P<.01) although force accuracy and tangential force variability was not affected. Increased variability in the tangential force composition was found during pain compared with the non-painful condition (P<.05). The immediate adaptation to pain was sufficient to maintain the quality of the task performance; however the long-term consequence of such adaptation is unknown and may overload other structures.

Modulation of motor variability related to experimental muscle pain during elbow-flexion contractions

Experimental muscle pain typically reorganizes the motor control. The pain effects may decrease when the three-dimensional force components are voluntarily adjusted, but it is not known if this could have negative consequences on other structures of the motor system. The present study assessed the effects of acute pain on the force variability during sustained elbow flexion when controlling task-related (one-dimensional) and all (three-dimensional) contraction force components via visual feedback. Experimental muscle pain was induced by bolus injection of hypertonic saline into m. biceps brachii, and isotonic saline was used as control. Twelve subjects performed sustained elbow flexion at different levels of the maximal voluntary contraction (5-30% MVC) before, during, and after the injections. Three-dimensional force components were measured simultaneously with surface electromyography (EMG) from elbow flexors and auxiliary muscles. Results showed that force variability was increased during pain compared to baseline for contractions using one-dimensional feedback (P<.05), but no significant differences were found for three-dimensional feedback. During painful contractions (1) EMG activity from m. trapezius was increased during contractions using both one-dimensional and three-dimensional feedback (P<.05), and (2) the complexity of EMG from m. triceps brachii and m. deltoid was higher for the three-dimensional feedback (P<.05). In conclusion, the three-dimensional feedback reduced the pain-related functional distortion at the cost of a more complex control of synergistic muscles.

The effect of experimental neck pain on pressure pain sensitivity and axioscapular motor control

UNLABELLED Clinical neck pain affects pain sensitivity and coordination of neck muscles, but the impact on the shoulder muscles is unclear. This study investigated the effect of experimental neck pain on the activity of the axioscapular muscles during arm movements and changes in pain sensitivity. Experimental neck pain was induced in 24 healthy volunteers by injecting hypertonic saline into the splenius capitis. Isotonic saline was injected as control. Before, during, and after injections, electromyography was recorded bilaterally from 8 muscles during standardized arm movements (140° scapular plane elevation), and the root mean square amplitude was extracted. Likewise, pressure pain thresholds were assessed bilaterally on 3 sites. The root mean square electromyography was decreased for the ipsilateral upper trapezius (P < .01) and increased for the ipsilateral middle deltoid (P < .03) during upward movements. The root mean square electromyography was reduced for the ipsilateral upper trapezius (P < .01) during downward movement, whereas an increase was recorded in the contralateral external oblique (P < .02). At the injection site, the pressure pain threshold increased during pain compared with the post condition (5 minutes after potential pain had subsided; P < .03). In this study, trunk and axioscapular muscle activities were reorganized in response to localized and referred pain evoked by hypertonic saline injection into an intrinsic neck muscle with no direct attachments to the trunk or shoulder girdle. PERSPECTIVE Reorganized activity of the axioscapular muscles has been shown previously in neck pain patients and is believed to happen during the transition from acute to chronic pain. The present study demonstrates for the first time that such reorganization may happen acutely, adding to our understanding of the effects of acute neck pain.

Movement Evoked Pain and Mechanical Hyperalgesia after Intramuscular Injection of Nerve Growth Factor: A Model of Sustained Elbow Pain

OBJECTIVE Lateral epicondylalgia presents as lateral elbow pain provoked by upper limb tasks. An experimental model of elbow pain provoked by movement/muscle contraction and maintained over several days is required to better understand the mechanisms underlying sustained elbow pain. This study investigated the time course and pain location induced by nerve growth factor (NGF) injection into a wrist extensor muscle, and whether movement and muscle contraction/stretch provoked pain. METHODS On Day 0 twenty-six painfree volunteers were injected with NGF (N = 13) or isotonic saline (randomized) into the extensor carpi radialis brevis (ECRB) muscle of the dominant arm. On Day 2 pain was induced in all participants by hypertonic saline injection into ECRB. A Likert scale and patient-rated tennis elbow evaluation (PRTEE) was used to assess pain and functional limitation (Days 0-10). Pain intensity during contraction/stretch of ECRB, and pressure pain thresholds (PPTs) were recorded before and after injections on Days 0 and 2, and Days 4 and 10. RESULTS Compared with isotonic saline, NGF evoked: i) greater Likert pain ratings from 12 hours post-injection until Day 6, ii) greater PRTEE scores on Days 2 and 4, iii) greater pain during ECRB contraction/stretch on Day 2, and iv) lower PPTs on Day 4. CONCLUSIONS This article presents a novel experimental human pain model suitable to study the sustained effects of lateral elbow pain on sensorimotor function and to probe the mechanisms underlying persistent musculoskeletal pain.

Blood flow after contraction and cuff occlusion is reduced in subjects with muscle soreness after eccentric exercise

Delayed onset muscle soreness (DOMS) occurs within 1‐2 days after eccentric exercise, but the mechanism mediating hypersensitivity is unclear. This study hypothesized that eccentric exercise reduces the blood flow response following muscle contractions and cuff occlusion, which may result in accumulated algesic substances being a part of the sensitization in DOMS. Twelve healthy subjects (five women) performed dorsiflexion exercise (five sets of 10 repeated eccentric contractions) in one leg, while the contralateral leg was the control. The maximal voluntary contraction (MVC) of the tibialis anterior muscle was recorded. Blood flow was assessed by ultrasound Doppler on the anterior tibialis artery (ATA) and within the anterior tibialis muscle tissue before and immediately after 1‐second MVC, 5‐seconds MVC, and 5‐minutes thigh cuff occlusion. Pressure pain thresholds (PPTs) were recorded on the tibialis anterior muscle. All measures were done bilaterally at day 0 (pre‐exercise), day 2, and day 6 (post‐exercise). Subjects scored the muscle soreness on a Likert scale for 6 days. Eccentric exercise increased Likert scores at day 1 and day 2 compared with day 0 (P<.001). Compared with pre‐exercise (day 0), reduced PPT (~25%, P<.002), MVC (~22%, P<.002), ATA diameter (~8%, P<.002), ATA post‐contraction/occlusion blood flow (~16%, P<.04), and intramuscular peak blood flow (~23%, P<.03) were found in the DOMS leg on day 2 but not in the control leg. These results showed that eccentric contractions decreased vessel diameter, impaired the blood flow response, and promoted hyperalgesia. Thus, the results suggest that the blood flow reduction may be involved in the increased pain response after eccentric exercise.

Altered pain sensitivity and axioscapular muscle activity in neck pain patients compared with healthy controls

Previous studies have indicated that neck pain patients feel increased symptoms following upper limb activities, and altered axioscapular muscle function has been proposed as a contributing factor.

Bilateral experimental neck pain reorganize axioscapular muscle coordination and pain sensitivity

Neck pain is a large clinical problem where reorganized trunk and axioscapular muscle activities have been hypothesised contributing to pain persistence and pain hypersensitivity. This study investigated the effects of bilateral experimental neck pain on trunk and axioscapular muscle function and pain sensitivity.

Agreement between physiotherapists rating scapular posture in multiple planes in patients with neck pain: Reliability study

OBJECTIVE Evaluation of scapular posture is an integral component of the clinical assessment of painful neck disorders. The aim of this study was to evaluate agreement between therapist judgements of scapula posture in multiple biomechanical planes in individuals with neck pain. DESIGN Inter-therapist reliability study. SETTING Research laboratory. PARTICIPANTS Fifteen participants with chronic neck pain. MAIN OUTCOME MEASURES Four physiotherapists recorded ratings of scapular orientation (relative to the thorax) in five different scapula postural planes (plane of scapula, sagittal plane, transverse plane, horizontal plane, and vertical plane) under four test conditions (at rest, and during three isometric shoulder conditions) in all participants. Inter-therapist reliability was expressed using both generalized and paired kappa coefficient. RESULTS Following adjustment for expected agreement and the high prevalence of neutral ratings (81%), on average both the generalised kappa (0.37) as well as Cohens Kappa for the two therapist pairs (0.45 and 0.42) demonstrated only slight to moderate inter-therapist reliability. CONCLUSIONS The findings suggest that ratings of scapular posture in individuals with neck pain by visual inspection has only slight to moderate reliability and should only be used in conjunction with other clinical tests when judging scapula function in these patients.

Neck pain – Sensory and motor effects during shoulder movements

The current work explored the relationship between neck pain, pain sensitivity and axioscapular motor control, during acute and ongoing neck pain. To examine the effect of acute neck pain in healthy participants, experimental neck pain was induced by injecting hypertonic saline into the splenius capitis muscle, either unilaterally (Study I) or bilaterally (Study II). To investigate the effect of ongoing neck pain, two patient populations, insidious onset of neck pain (IONP) and whiplash associated disorder (WAD), were recruited (Study III). In all three studies, pressure pain thresholds (PPT) were used to determine pain sensitivity while electromyography recordings from both axioscapular and trunk muscles, during a standardized arm movement, was used to examine muscle activity.