What is different about spinal pain?

Masticatory Myofascial Pain Syndrome: Implications for Endodontists

INTRODUCTION

Masticatory myofascial pain syndrome can present similarly to other dental conditions in odontogenetic structures. Endodontists should be familiar with the symptomology and pathophysiology of masticatory myofascial pain syndrome to avoid misdiagnosis, incorrect treatment, and medicolegal repercussions. The aim of this review was to provide a foundational summary for endodontists to identify and correctly manage masticatory myofascial pain syndrome.

METHODS

A narrative review of the literature was performed through a MEDLINE search and a hand search of the major myofascial pain textbooks.

RESULTS

Masticatory myofascial pain syndrome is a musculoligamentous syndrome that can present similarly to odontogenic pain or refer pain to the eyebrows, ears, temporomandibular joints, maxillary sinus, tongue, and hard palate. Currently, the most comprehensive pathophysiology theory describing masticatory myofascial pain syndrome is the expanded integrated hypothesis. The most widely accepted diagnostic guidelines for masticatory myofascial pain syndrome are the Diagnostic Criteria for Temporomandibular Disorders; however, their diagnostic capability is limited. There is no hierarchy of treatment methods because each patient requires a tailored and multidisciplinary management aimed at regaining the muscle's range of motion, deactivating the myofascial trigger points, and maintaining pain relief.

CONCLUSIONS

The pain patterns for masticatory myofascial pain syndrome are well-known; however, there is a lack of consensus on the most proper method of trigger point diagnosis or pain quantification. The diagnostic strategies for masticatory myofascial pain syndrome vary, and the diagnostic aids are not well developed.

Exploring the effect of capsaicin-induced central sensitization on the upper limb nociceptive withdrawal reflex threshold

The nociceptive withdrawal reflex (NWR) threshold is commonly employed in the lower limb to assess clinical and experimentally induced pain. However, no studies to date have investigated changes in spinal nociception in the upper limb, via the NWR threshold, following experimentally induced central sensitization (CS). We tested the hypothesis that experimentally induced CS of the C5-C6 spinal segment significantly reduces NWR thresholds in muscles of the upper limb. Upper limb NWR thresholds from 20 young, healthy adults were assessed by applying noxious electrical stimuli to the right index finger and recording muscle activity from the biceps brachii (BI), triceps brachii (TRI), flexor carpi ulnaris (WF), and extensor carpi radialis longus (WE) muscles via surface electromyography. Topical cream (either 0.075% capsaicin, or control) was applied to the C5-C6 dermatome of the lateral forearm (50 cm²). NWR thresholds were compared at baseline, and four 10-min intervals after topical application. WF muscle NWR thresholds were significantly reduced in the capsaicin session compared to control, while TRI muscle NWR thresholds were significantly reduced 40 min after capsaicin application only (p < 0.05). There were no significant differences for BI or WE muscle NWR thresholds. We observed poor to moderate test-retest reliability for all upper limb NWR thresholds, a key contributor to the selective reduction in NWR thresholds among muscles. Accordingly, while our findings demonstrate some comparability to previously reported lower limb NWR studies, we concurrently report limitations of the upper limb NWR technique. Further exploration of optimal parameters for upper limb NWR acquisition is needed.

Prevalence and Factors Associated with Back Pain among Patients Undergoing Spinal Anesthesia at the University of Gondar Comprehensive and Specialized Hospital, North West Ethiopia: An Institutional Based Cross-Sectional Study

BACKGROUND

Back pain is often reported as a common complaint after surgery. Many studies showed that the prevalence of back pain after spinal anesthesia is high and its magnitude is considerable in developing countries. It is highly related to reduced quality of life, loss of work productivity, burden of health care costs, and satisfaction regarding health care service; therefore, measures should be taken to reduce or prevented postspinal back. The aim of this cross-sectional study was to assess the prevalence and factors associated with back pain among patients undergoing spinal anesthesia at the University of Gondar Comprehensive and Specialized Hospital, Northwest Ethiopia. Methodology. An institutional based cross-sectional study was conducted from March to May 2020. A total of 215 participants were enrolled in this study. A convenience sampling technique was used to get the study participants. Both univariable and multivariable logistic regression were used to identify factors associated with postspinal back pain. Variables with a p value less than <0.2 in the bivariable analysis were fitted into the multivariable analysis. In the multivariable analysis, a variable with a p value of <0.05 was considered statistically significant.

RESULTS

The overall prevalence of postspinal back pain was 40.5% (95% CI: 34.0, 47.4). Being overweight (AOR = 3.8; 95% CI: 1.47, 9.96) and obese (AOR = 4.9; 95% CI: 1.19, 20.4), using big spinal needles (AOR = 5.9; 95% CI: 1.04, 33.4), two attempts of lumbar puncture (AOR = 5.5; 95% CI: 1.74, 17.59), more than three attempts of lumbar puncture (AOR = 4.9; 95% CI: 1.63, 15.2), and the number of bone contacts during spinal anesthesia procedure (AOR = 3.1; 95% CI: 1.14, 8.45) were positively associated with postspinal back pain. Conclusion and Recommendation. The overall incidence of back pain is high. Body mass index, size of spinal needle, number of attempts, and number of bone contacts are significantly associated with the incidence of back pain following spinal anesthesia. Thus, it is better to minimize the number of lumbar puncture attempts and bone contacts during spinal anesthesia to reduce postspinal back pain. In addition, using smaller size spinal needle is a good choice.

The Pathways and Processes Underlying Spinal Transmission of Low Back Pain: Observations From Dorsal Root Ganglion Stimulation Treatment

BACKGROUND

Dorsal root ganglion stimulation (DRG-S) is a novel approach to treat chronic pain. Lead placement at L2 has been reported to be an effective treatment for axial low back pain (LBP) primarily of discogenic etiology. We have recently shown, in a diverse cohort including cases of multilevel instrumentation following extensive prior back surgeries, that DRG-S lead placement at T12 is another promising target. Local effects at the T12 DRG, alone, are insufficient to explain these results.

MATERIALS AND METHODS

We performed a literature review to explore the mechanisms of LBP relief with T12 DRG-S.

FINDINGS

Branches of individual spinal nerve roots innervate facet joints and posterior spinal structures, while the discs and anterior vertebrae are carried via L2, and converge in the dorsal horn (DH) of the spinal cord at T8-T9. The T12 nerve root contains cutaneous afferents from the low back and enters the DH of the spinal cord at T10. Low back Aδ and C-fibers then ascend via Lissauer's tract (LT) to T8-T9, converging with other low back afferents. DRG-S at T12, then, results in inhibition of the converged low back fibers via endorphin-mediated and GABAergic frequency-dependent mechanisms. Therefore, T12 lead placement may be the optimal location for DRG-S to treat LBP.

Subcutaneous accessory pain system (SAPS): A novel pain pathway for myofascial trigger points

Despite the accumulating neuro-physiological evidence of myofascial pain, many clinicians are skeptical about its existence as a separate disease entity. No single theory can fully explain the four cardinal features of MPS; taut bands, local tenderness, local twitching and the characteristic pattern of referred pain. Bridging the gap between basic and clinical knowledge mandates coupling the local trigger point changes with the clinically seen distant somatically innervated referred pain. The main question addressed by the present theory is why do trigger points behave differently in comparison to the surrounding muscle tissue and are trigger points the primary problem or secondary to a primary pathology. We propose that trigger points have an extra-innervation system that connect them with other spinal structures such as the facet, the annulus and other trigger points with a role for the subcutaneous fascia as part of trigger points pathogenesis or passage for the extra-innervation. The extra-innervation system is Subcutaneous accessory pain system (SAPS). The novel SAPS system connecting trigger points to the spinal segments via dorsal rami is presented. Individuals with this accessory pathway are prone to myofascial pain, trigger point activation and segmental referred somatic pain similar to other axial spinal structures. Despite the high prevalence of myofascial pain, the mechanism is not universally agreed upon. Why do the trigger points act differently from surrounding muscle tissue and are almost constant in location in different individuals is controversial. Why does myofascial pain and its two components, trigger points and referred pain, exist or are more prevalent in some individuals than in others is unexplained. The correlation between axial spinal structures pathology and the trigger points is not explored well. The existing theories about trigger point formation and referred pain is scientifically credible for each separate component and the SAPS novel system can provide the link between the two.

Coexistent lumbar spine disorders have a crucial impact on the clinical outcome after total hip replacement

BACKGROUND

Degenerative hip and spine disease are known to frequently coexist. Lumbar spine disorders (LSDs), as opposed to other patient-related factors, are disregarded in the assessment of the clinical outcome after total hip replacement (THR). This prospective study investigates the influence of LSDs on the pre- and postoperative health-related quality of life and functional outcome of patients undergoing THR.

METHODS

According to clearly defined criteria, 42 patients scheduled for cementless THR were assigned either to the LSD (13 patients with LSDs) or non-LSD group (29 patients without LSDs). A clinical assessment was performed preoperatively as well as 12, 24 and 60 months postoperatively using the Harris hip score (HHS), the Western Ontario and McMaster University osteoarthritis index (WOMAC) and the 36-item short form health survey (SF-36).

RESULTS

The statistical analysis comparing the pre- and postoperative status within both groups showed an ongoing improvement of mean HHS and WOMAC after THR. The non-LSD group had a significantly higher postoperative HHS and WOMAC after 12, 24 and 60 months as well as SF-36 after 24 and 60 months. The LSD group improved significantly in the HHS at 24 and 60 months and the WOMAC at 12, 24 and 60 months postoperatively, whereas the SF-36 improvement was not significant. Comparison of preoperative data in both groups revealed a significantly higher SF-36 in the non-LSD group but no difference between the HHS and WOMAC. At each postoperative assessment, the HHS, WOMAC and SF-36, including its physical and mental health sum scores, were significantly higher in the non-LSD group, except for the WOMAC after 60 months.

CONCLUSION

Owing to their crucial impact on hip function scores and health-related quality of life, it is recommended to consider LSDs preoperatively in studies dealing with the clinical outcome after THR.

Contrasting alterations to synaptic and intrinsic properties in upper-cervical superficial dorsal horn neurons following acute neck muscle inflammation

Background

Acute and chronic pain in axial structures, like the back and neck, are difficult to treat, and have incidence as high as 15%. Surprisingly, most preclinical work on pain mechanisms focuses on cutaneous structures in the limbs and animal models of axial pain are not widely available. Accordingly, we developed a mouse model of acute cervical muscle inflammation and assessed the functional properties of superficial dorsal horn (SDH) neurons.

Results

Male C57/Bl6 mice (P24-P40) were deeply anaesthetised (urethane 2.2 g/kg i.p) and the rectus capitis major muscle (RCM) injected with 40 μl of 2% carrageenan. Sham animals received vehicle injection and controls remained anaesthetised for 2 hrs. Mice in each group were sacrificed at 2 hrs for analysis. c-Fos staining was used to determine the location of activated neurons. c-Fos labelling in carrageenan-injected mice was concentrated within ipsilateral (87% and 63% of labelled neurons in C1 and C2 segments, respectively) and contralateral laminae I - II with some expression in lateral lamina V. c-Fos expression remained below detectable levels in control and sham animals. In additional experiments, whole cell recordings were obtained from visualised SDH neurons in transverse slices in the ipsilateral C1 and C2 spinal segments. Resting membrane potential and input resistance were not altered. Mean spontaneous EPSC amplitude was reduced by ~20% in neurons from carrageenan-injected mice versus control and sham animals (20.63 ± 1.05 vs. 24.64 ± 0.91 and 25.87 ± 1.32 pA, respectively). The amplitude (238 ± 33 vs. 494 ± 96 and 593 ± 167 pA) and inactivation time constant (12.9 ± 1.5 vs. 22.1 ± 3.6 and 15.3 ± 1.4 ms) of the rapid A type potassium current (I_Ar), the dominant subthreshold current in SDH neurons, were reduced in carrageenan-injected mice.

Conclusions

Excitatory synaptic drive onto, and important intrinsic properties (i.e., I_Ar) within SDH neurons are reduced two hours after acute muscle inflammation. We propose this time point represents an important transition period between peripheral and central sensitisation with reduced excitatory drive providing an initial neuroprotective mechanism during the early stages of the progression towards central sensitisation.