Thorvaldur Skuli Palsson

Experimental pelvic pain facilitates pain provocation tests and causes regional hyperalgesia

TOC summary An experimental pain model indicates that the superficial ligamentous structures of the sacroiliac joint are a possible source of symptoms in pelvic girdle pain. ABSTRACT The extra‐articular sacroiliac joint (SIJ) structure is a potential source for low back and pelvic pain. This study hypothesised that experimental pain induced in a superficial pelvic ligament causes (1) hyperalgesia to pressure, (2) distinct pain referral, and (3) an increased frequency of positive pain provocation tests of the SIJ complex. Thirty healthy subjects (15 females) participated in this study designed as a randomised crossover trial. Pain was induced in the long posterior sacroiliac ligament by injection of hypertonic saline, with the contralateral ligament injected with isotonic saline as control. Pain intensity was assessed on an electronic visual analogue scale (VAS). Pressure pain thresholds (PPTs) and pain provocation tests were assessed on 3 occasions: at baseline, after injection, and when pain had subsided. PPT sites were located bilaterally at the injection site, lateral to spinous processes of S2 and L5, and at the gluteus medius and gastrocnemius muscles. Hypertonic saline caused significantly higher VAS scores and more extended pain referral than isotonic saline (P < 0.001). PPTs at the injection site and lateral to S2 were significantly reduced after hypertonic saline compared with baseline and isotonic saline (P < 0.002). Significantly more subjects had positive pain provocation tests after hypertonic (67% of subjects) compared with isotonic saline (20%; P < 0.001). These data demonstrate that the extra‐articular SIJ structure accommodates nociceptors that are capable of inducing pain referral and regional hyperalgesia sensitive to manual pain provocation tests similar to what previously have been found in pelvic girdle pain patients.

Experimental pelvic pain impairs the performance during the active straight leg raise test and causes excessive muscle stabilization

Objectives:The active straight leg raise (ASLR) test is widely used clinically to assess severity of lumbopelvic pain due to decreased stability of the sacroiliac joint (SIJ). This study aimed to bypass the influence of decreased SIJ stability on the ASLR test by investigating the effect of experimental pelvic pain and hyperalgesia on the outcome of the ASLR test. Methods:Thirty-four healthy participants took part in this randomized crossover study. Pelvic pain was induced by injecting hypertonic saline into the long posterior sacroiliac ligament. Isotonic saline was injected on the contralateral side as control. Pain intensity was assessed on an electronic visual analogue scale. The Likert scores of difficulty performing the ASLR test and simultaneous electromyography of trunk and thigh muscles were recorded before, during, and postpain. Pressure pain thresholds were assessed bilaterally in the pelvic area and lower limb. Results:Compared with the control condition and baseline, hypertonic saline injections caused (P<0.05): (1) higher visual analogue scale scores of the pain intensity; (2) reduced pressure pain thresholds at the injection site and lateral to S2; (3) increased difficulty in performing the ASLR rated on the Likert scale; and (4) bilateral increase in the electromyography activity of stabilizing trunk and thigh muscles during pain. Discussion:These data demonstrate that pain and hyperalgesia in conditions unaffected by biomechanical SIJ impairments change the outcome of the ASLR test toward what is seen in clinical lumbopelvic pain. This may implicate pain-related changes in motor control strategies potentially relevant for the transition from acute into chronic pain.

Resisted adduction in hip neutral is a superior provocation test to assess adductor longus pain: An experimental pain study.

The criterion of long‐standing groin pain diagnoses in athletes usually relies on palpation and clinical tests. An experimental pain model was developed to examine the clinical tests under standardized conditions. Pain was induced by hypertonic saline injected into the proximal adductor longus (AL) tendon or rectus femoris (RF) tendon in 15 healthy male participants. Isotonic saline was injected contralaterally as a control. Pain intensity was assessed on a visual analog scale (VAS). Resisted hip adduction at three different angles and trunk flexion were completed before, during, and after injections. Pain provocation in the presence of experimental pain was recorded as a true positive compared with pain provocation in the non‐pain conditions. Similar peak VAS scores were found after hypertonic saline injections into the AL and RF and both induced higher VAS scores than isotonic saline (P < 0.01). Adduction at 0° had the greatest positive likelihood ratio (+LR = 2.8, 95%CI: 1.09–7.32) with 45° (−LR = 0.0, 95%CI: 0.00–1.90) and 90° (−LR = 0.0, 95%CI: 0.00–0.94) having the lowest negative LR. This study indicates that the 0° hip adduction test resisted at the ankles optimizes the diagnostic procedure without compromising diagnostic capacity to identify experimental groin pain. Validation in clinical populations is warranted.

Do Australian Football players have sensitive groins? Players with current groin pain exhibit mechanical hyperalgesia of the adductor tendon

OBJECTIVES This is the first study to evaluate the mechanical sensitivity, clinical classifications and prevalence of groin pain in Australian football players. DESIGN Case-control. METHODS Professional (n=66) and semi-professional (n=9) Australian football players with and without current or previous groin injuries were recruited. Diagnoses were mapped to the Doha Agreement taxonomy. Point and career prevalence of groin pain was calculated. Pressure pain thresholds (PPTs) were assessed at regional and distant sites using handheld pressure algometry across four sites bilaterally (adductor longus tendon, pubic bone, rectus femoris, tibialis anterior muscle). To assess the relationship between current groin pain and fixed effects of hyperalgesia of each site and a history of groin pain, a mixed-effect logistic regression model was utilised. Receiver Operator Characteristic (ROC) curve were determined for the model. RESULTS Point prevalence of groin pain in the preseason was 21.9% with a career prevalence of 44.8%. Adductor-related groin pain was the most prevalent classification in the pre-season period. Hyperalgesia was observed in the adductor longus tendon site in athletes with current groin pain (OR=16.27, 95% CI 1.86 to 142.02). The ROC area under the curve of the regression model was fair (AUC=0.76, 95% CI 0.54 to 0.83). CONCLUSIONS Prevalence data indicates that groin pain is a larger issue than published incidence rates imply. Adductor-related groin pain is the most common diagnosis in pre-season in this population. This study has shown that hyperalgesia exists in Australian football players experiencing groin pain indicating the value of assessing mechanical pain sensitivity as a component of the clinical assessment.

Pregnancy Is Characterized by Widespread Deep-Tissue Hypersensitivity Independent of Lumbopelvic Pain Intensity, a Facilitated Response to Manual Orthopedic Tests, and Poorer Self-Reported Health

UNLABELLED Lumbopelvic pain is common in pregnancy but the sensitization factors underlying the condition are largely unknown. This study characterized the somatosensory profile of pregnant and nonpregnant women and the relationship between pain, hypersensitivity, and commonly used manual clinical tests. Thirty-nine pregnant and 22 nonpregnant women were included. Although lumbopelvic pain was not an inclusion criterion, the pregnant women were divided into low- and high-pain groups following data collection. The sensitivity to light brush, pin-prick, and pressure pain was assessed bilaterally at 3 sites in the lumbopelvic region, at the shoulder, and in the lower leg. Responses to the active straight leg raise test and pain provocation tests of the sacroiliac joint were recorded. Participants completed questionnaires addressing emotional and physical well-being and rated disability using the Pelvic Girdle Questionnaire. Compared with controls, the high-pain group rated the active straight leg raise test as more difficult (P < .05), and both pain groups had more positive pain provocation tests (P < .05). The pregnant groups demonstrated significantly lower pressure pain thresholds at most assessment sites compared with controls (P < .05), but self-reported disability and pain were not correlated with pressure pain thresholds within pregnant participants. The high-pain group reported worse emotional health and poorer sleep quality than controls (P < .05). PERSPECTIVE This article presents the somatosensory profile of a healthy pregnant cohort. The results indicate that pain sensitivity increases during pregnancy possibly owing to the physical changes the body undergoes during pregnancy but also owing to changes in emotional health. This should be accounted for in clinical management of pregnant women with lumbopelvic pain.

Pressure-induced referred pain is expanded by persistent soreness

Abstract Several chronic pain conditions are accompanied with enlarged referred pain areas. This study investigated a novel method for assessing referred pain. In 20 healthy subjects, pressure pain thresholds (PPTs) were recorded and pressure stimuli (120% PPT) were applied bilaterally for 5 and 60 seconds at the infraspinatus muscle to induce local and referred pain. Moreover, PPTs were measured bilaterally at the shoulder, neck, and leg before, during, and after hypertonic saline–induced referred pain in the dominant infraspinatus muscle. The pressure and saline-induced pain areas were assessed on drawings. Subsequently, delayed onset muscle soreness was induced using eccentric exercise of the dominant infraspinatus muscle. The day-1 assessments were repeated the following day (day 2). Suprathreshold pressure stimulations and saline injections into the infraspinatus muscle caused referred pain to the frontal aspect of the shoulder/arm in all subjects. The 60-second pressure stimulation caused larger referred pain areas compared with the 5-second stimulation (P < 0.01). Compared with pressure stimulation, the saline-induced referred pain area was larger (P < 0.02). After saline-induced pain, the PPTs at the infraspinatus and supraspinatus muscles were reduced (P < 0.05), and the 5-second pressure-induced referred pain area was larger than baseline. Pressure pain thresholds at the infraspinatus and supraspinatus muscles were reduced at day 2 in the delayed onset muscle soreness side (P < 0.05). Compared with day 1, larger pressure and saline-induced referred pain areas were observed on day 2 (P < 0.05). Referred pain to the shoulder/arm was consistently induced and enlarged after 1 day of muscle soreness, indicating that the referred pain area may be a sensitive biomarker for sensitization of the pain system.

Movement Does Not Promote Recovery of Motor Output Following Acute Experimental Muscle Pain

Objective To examine the effect of motor activity on the magnitude and duration of altered corticomotor output following experimental muscle pain. Design Experimental, pre-post test. Setting University laboratory. Subjects Twenty healthy individuals. Methods Participants were randomly allocated to a Rest or Movement group. The Rest group sat quietly without moving for the duration of the experiment. The Movement group repeated a unimanual pattern of five sequential keystrokes as quickly and as accurately as possible immediately following the resolution of pain. Pain was induced into the right extensor carpi radialis brevis muscle by a bolus injection of 0.5 mL hypertonic saline. Corticomotor output was assessed as motor evoked potentials in response to transcranial magnetic stimulation before, immediately after, and at 10, 20, and 30 minutes following pain resolution. Pain intensity was recorded every 30 seconds using an 11-point numerical rating scale. Results There was no difference in peak pain intensity (P < 0.09) or duration (P < 0.2) between groups. Corticomotor output was reduced in both groups (P < 0.002) at 10 minutes (P < 0.002), 20 minutes (P < 0.02), and 30 minutes (P < 0.037) following the resolution of pain relative to baseline. There was no difference between groups at any time point. Conclusions Performance of motor activity immediately following the resolution of acute muscle pain did not alter the magnitude or duration of corticomotor depression. Understanding corticomotor depression in the postpain period and what factors promote recovery has relevance for clinical pain syndromes where ongoing motor dysfunction, in the absence of pain, may predispose to symptom persistence or recurrence.

Commentary: Trunk Muscle Activity during Drop Jump Performance in Adolescent Athletes with Back Pain

It was with great interest we read the recently published article “Trunk Muscle Activity during Drop Jump Performance in Adolescent Athletes with Back Pain.” Investigating back pain (BP) in adolescents is commendable as there is growing evidence that for many, an experience of BP as early as 14 years of age may relate to ongoing pain in adulthood (Coenen et al., 2017). Indeed, the conventional narrative is changing as individual physical factors such as posture, use of schoolbags, and hypermobility are only weakly associated with adolescent BP. Rather, factors which predict BP at a young age are considered to be multi-dimensional and include gender, negative BP beliefs and poor mental health (O’Sullivan et al., 2017; Smith et al., 2017). Mueller et al. (2017) have focused on a single physical factor (trunk muscle activation patterns) drawing inferences regarding BP prevention and treatment. This article prompts consideration of three essential aspects regarding research design and interpretation of findings:

Smartphone-based accelerometry is a valid tool for measuring dynamic changes in knee extension range of motion

INTRODUCTION Measurement of static joint range of motion is used extensively in orthopaedic and rehabilitative communities to benchmark treatment efficacy. Static measures are, however, insufficient in providing detailed information about patient impairments. Dynamic range of motion measures could provide more detailed information about patient impairments thus leading to better clinical assessments. Reliable and valid methods are available, but due to limitations in the present technology, dynamic measures are seldom performed in clinical settings. The objective of this study was to determine the validity of smartphone-based accelerometry measuring the dynamic range of motion of the knee joint during a passively executed extension movement. MATERIALS AND METHODS Dynamic knee extension range of motion was examined three consecutive times in twenty-one healthy male subjects utilising an isokinetic dynamometer to generate passively the extension motion. Measurements of joint angles in dynamic knee extension were performed using two methods: (i) isokinetic dynamometer (gold-standard method, Biodex System 4 Pro) and (ii) smartphone (iPhone 6, attached to the tibia) accelerometry data. RESULTS Tests of validity showed excellent correlation (rs=0.899) between methods, with a low standard error of measurement of 0.62deg. and limits of agreement ranging from -9.1 to 8.8deg. Interclass correlation coefficients showed excellent between-measures reliability (ICC>0.862) for both methods. CONCLUSIONS Smartphone-based accelerometry is a valid tool for measuring the range of motion at the knee joint during dynamic extension movements. This method enables the clinician to carry out simple, low cost, and valid clinical measurements of dynamic knee extension range of motion.

Experimental pain in the groin may refer into the lower abdomen: Implications to clinical assessments

OBJECTIVES To investigate the effects of experimental adductor pain on the pain referral pattern, mechanical sensitivity and muscle activity during common clinical tests. DESIGN Repeated-measures design. METHODS In two separate sessions, 15 healthy males received a hypertonic (painful) and isotonic (control) saline injection to either the adductor longus (AL) tendon to produce experimental groin pain or into the rectus femoris (RF) tendon as a painful control. Pain intensity was recorded on a visual analogue scale (VAS) with pain distribution indicated on body maps. Pressure pain thresholds (PPT) were assessed bilaterally in the groin area. Electromyography (EMG) of relevant muscles was recorded during six provocation tests. PPT and EMG assessment were measured before, during and after experimental pain. RESULTS Hypertonic saline induced higher VAS scores than isotonic saline (p<0.001), and a local pain distribution in 80% of participants. A proximal pain referral to the lower abdominal region in 33% (AL) and 7% (RF) of participants. Experimental pain (AL and RF) did not significantly alter PPT values or the EMG amplitude in groin or trunk muscles during provocation tests when forces were matched with baseline. CONCLUSIONS This study demonstrates that AL tendon pain was distributed locally in the majority of participants but may refer to the lower abdomen. Experimental adductor pain did not significantly alter the mechanical sensitivity or muscle activity patterns.