Cluster analysis of pressure pain threshold maps from the trapezius muscle

Eccentric Exercise Reduces Upper Trapezius Muscle Stiffness Assessed by Shear Wave Elastography and Myotonometry

In this study, we tested the hypotheses that unaccustomed eccentric exercise (ECC) would reduce the elastic modulus and dynamic stiffness of the upper trapezius muscle and that these changes would correlate with increases in muscle thickness, reflecting muscle edema. Shear wave elastography was used to measure elastic modulus, dynamic stiffness was assessed using myotonometry, and muscle thickness was measured using ultrasonography. All measurements were performed at four locations over the upper trapezius before and 24 h after a single bout of ECC. Fourteen healthy participants (11 males and 3 females; 23.2 ± 3.0 years; height 175.1 ± 10.4 cm; body mass 73.8 ± 11.3 kg) took part in the study. Overall, ECC resulted in decreased elastic modulus (from 45.8 ± 1.6 to 39.4 ± 1.2 kPa, p < 0.01) and dynamic muscle stiffness (from 369.0 ± 7.3 to 302.6 ± 6.0 N/m, p < 0.01). Additionally, ECC resulted in increased muscle thickness (from 6.9 ± 0.4 to 7.3 ± 0.4 mm, p < 0.01). Spatial changes (across the four locations) were found for elastic modulus, stiffness and thickness. No significant correlations were found between changes in measures of muscle stiffness, or between changes in stiffness and changes in thickness. In conclusion, the present pilot study showed that ECC altered biomechanical muscle properties, reflected by decreased elastic modulus and dynamic muscle stiffness 24 h after ECC.

Topographic mapping of pain sensitivity of the lower back – a comparison of healthy controls and patients with chronic non-specific low back pain

Background and aims

The choice of testing site for quantitative sensory testing (QST) of pain sensitivity is important and previous studies have demonstrated patterns in pain sensitivity within discrete areas in different body regions. Some areas are characterized by a relatively high degree of spatial pain discrimination and recognizable patterns of pain referral, whilst others are not. The lumbar region is likely to have relatively low pain acuity and overlapping of pain referral. The current study was conducted to determine whether patterns of pain sensitivity (detection thresholds) could be identified in the lower back, whether differences in such patterns exist between different groups and whether such patterns could help identify a clinical source of pain and localized increased pain sensitivity.

Methods

Twenty-one patients with non-specific chronic low back pain and 21 healthy controls were tested for pressure and heat pain thresholds on 30 pre-defined locations over the mid and lower back. Topographical maps of mean pain thresholds and variability were produced, inspected visually and analyzed statistically. Between group differences in pain threshold were analyzed statistically as an indicator of widespread increased pain sensitivity. Evidence of segmental increased pain sensitivity was examined by group statistical comparison of mid-line lower range.

Results

A clear pattern of higher pain thresholds in the mid-line was evident in both groups and for both pain modalities. No discernible patterns were evident for variability within groups, but marked differences were seen between groups: variability for pressure pain thresholds appeared similar between groups, however for heat pain threshold, variability was uniformly low in the control group and uniformly high in the patient group. A highly significant (p<0.0001) difference in pain thresholds for pressure and heat was found with patients exhibiting lower thresholds than controls. No between group difference was found for mid-line lower range for either modality (p>0.05).

Conclusions

The current study supports previous findings of widespread, increased pain sensitivity in chronic non-specific low-back pain patients. It also indicates that there are discernible and similar topographical patterns of pain sensitivity in the dorsal area in both groups, but that this pattern is related to the lateral position of the test site and not the segmental level. Specific segments with increased pain sensitivity could not be identified in the patient group, which casts doubt on the utility of pressure and heat pain thresholds as indicators of the clinical source of spinal pain – at least in a population of chronic non-specific low-back pain.

Implications

In a cohort of chronic non-specific low-back pain patients and with the chosen methodology, topographical QST mapping in the lumbar region does not appear useful for identifying the spinal segment responsible for clinical pain, but it does demonstrate widespread group differences in pain sensitivity.

Spotlight on topographical pressure pain sensitivity maps: a review

Mechanical hyperalgesia defined as decreased pressure pain thresholds (PPTs) is commonly associated with pain. In this narrative review, we report the current state of the art within topographical pressure sensitivity maps. Such maps are based on multiple PPT assessments. The PPTs are assessed by an a priori defined grid with special focus on both spatial and temporal summation issues. The grid covers the muscle or the body region of interest using absolute or relative values determined from anatomical landmarks or anthropometric values. The collected PPTs are interpolated by Shepard or Franke and Nielson interpolation methods to create topographical pressure sensitivity maps. This new imaging technique has proven to be valuable in various disciplines including exercise physiology, neurology, physical therapy, occupational medicine, oncology, orthopedics, and sport sciences. The reviewed papers have targeted different body regions like the scalp, low back, neck-shoulder, and upper and lower extremities. The maps have delineated spatial heterogeneity in the pressure pain sensitivity underlining the different extents of pressure pain hyperalgesia in both experimentally induced and disease-associated pain conditions. Furthermore, various intervention studies have proven the utility of topographical pressure pain sensitivity maps. Topographical pressure pain sensitivity maps have contributed to revealing the efficacy of therapeutic, ergonomic, or training interventions that aim at reducing pain.

Sensitization and Serological Biomarkers in Knee Osteoarthritis Patients With Different Degrees of Synovitis

OBJECTIVE

Synovitis is a frequent condition in knee osteoarthritis (KOA) and has been associated with pain. This study investigated the links between the pressure hyperalgesia, the clinical pain, the degree of the synovitis, inflammatory biomarkers, and tissue-specific biomarkers in KOA patients.

MATERIALS AND METHODS

Fifty-eight KOA patients and 33 pain-free controls participated in this study. The patients were magnetic resonance imaging scanned, and the Boston-Leeds OA Knee Score (BLOKS, 0 to 3) was used to assess the degree of synovitis. The maximal knee pain intensity over the last 24 hours was scored on a visual analog scale (VAS). The pressure pain thresholds (PPTs) were assessed over the KOA-affected knee. Serological biomarkers were measured in fasting serum: high-sensitive C-reactive protein, matrix metalloproteinase-mediated degradation of CRP, and matrix metalloproteinase-mediated collagen type I, II, and III degradation (C1M [connective tissue], C2M [cartilage], C3M [synovial membrane]).

RESULTS

Compared with controls, the KOA patients showed increased levels of C1M (P<0.02), C2M (P<0.001), and high-sensitive C-reactive protein (P<0.02), decreased level of C3M (P<0.03), and reduced PPTs (P<0.03). Patients with no (BLOKS 0) and moderate to severe (BLOKS 2&3) synovitis had significantly lower PPTs compared with mild synovitis (BLOKS 1). Significantly negative correlations were found between VAS and PPTs. No correlations were found between BLOKS and the VAS, PPT, or biomarkers.

DISCUSSION

Patients without and with moderate to severe synovitis demonstrated local pressure hyperalgesia and increased degrees of: (1) systemic inflammation, (2) connective tissue degradation, (3) cartilage degradation, and (4) decreased synovial membrane degradation as compared with controls.

Pressure Pain Sensitivity Maps of the Neck-Shoulder Region in Breast Cancer Survivors

OBJECTIVE

The aim of the present study was to report pressure pain sensitivity topographical maps of the frontal and dorsal parts of the shoulder region, and locate the pressure pain sensitive areas in breast cancer survivors compared with matched healthy control subjects.

METHODS

Twenty-two breast cancer survivors (BCS) and 22 matched control subjects participated. A numeric pain rating scale of the neck-shoulder area and pressure pain thresholds (PPTs) was assessed bilaterally over 28 points in the frontal and dorsal neck-shoulder area. Topographical pain sensitivity maps of the upper trapezius, pectoral, and anterior deltoid areas were computed.

RESULTS

A three-way analysis of variance was carried out to evaluate the differences in PPTs. The BCS reported spontaneous neck pain (mean ± SD 3.6 ± 2.8), pain in the affected shoulder (4.3 ± 2.7), and pain in the non-affected shoulder (0.9 ± 1.8). Additionally, the BCS exhibited bilaterally lower PPTs in all the measurement points as compared with the control subjects (P < 0.05). The PPTs were lower at the superior part of the trapezius muscle (P < 0.001), the musculotendinous insertion, the anterior part of the deltoid muscle (P < 0.001), and the tendon of the pectoral muscle (P < 0.001) as compared with the control subjects.

CONCLUSIONS

The results suggest the sensitization processes in the BCS and give preliminary evidence to most sensitive areas in the superior part of the upper trapezius and musculotendinous insertion of the pectoral muscle.

Basic aspects of musculoskeletal pain: from acute to chronic pain

The transition from acute to chronic musculoskeletal pain is not well understood. To understand this transition, it is important to know how peripheral and central sensitization are manifested and how they can be assessed. A variety of human pain biomarkers have been developed to quantify localized and widespread musculoskeletal pain. In addition, human surrogate models may be used to induce sensitization in otherwise healthy volunteers. Pain can arise from different musculoskeletal structures (e.g. muscles, joints, ligaments, or tendons), and differentiating the origin of pain from those different structures is a challenge. Tissue specific pain biomarkers can be used to tease these different aspects. Chronic musculoskeletal pain patients in general show signs of local/central sensitization and spread of pain to degrees which correlate to pain intensity and duration. From a management perspective, it is therefore highly important to reduce pain intensity and try to minimize the duration of pain.