Great potential of ultrasound elastography for the assessment of the masseter muscle in patients with temporomandibular disorders. A systematic review

Ultrasonographic characteristics of myogenous temporomandibular disorders: A scoping review

OBJECTIVE

To identify the available evidence on the ultrasonographic characteristics of masticatory muscles in subjects with myogenous TMD, as well as the potential use of ultrasonography as a diagnostic and treatment assessment outcomes tool.

METHOD

An electronic search of the PubMed, Web of Science and Scopus databases was performed using the following terms: 'ultrasonography', 'ultrasound', 'masseter', 'temporal', 'masticatory muscles', 'temporomandibular disorders', 'temporomandibular joint disorders'. Full-text articles were obtained from the records after applying the inclusion/exclusion criteria.

RESULTS

Thirteen articles were included for analysis: one comparative cross-sectional study, five case-control studies, six clinical trials and one randomised clinical trial. Main ultrasonographic characteristic assessed were local cross-sectional dimension and intramuscular ultrasonographic appearance. Retrieved studies reported the use ultrasonography for diagnosis or treatment assessment purposes showing heterogeneous results. For diagnosis purposes, the results of local cross-sectional dimension are not consistent; therefore, its diagnostic value for myogenous TMD diagnosis is weak. However, more homogeneous results were observed for intramuscular ultrasonographic appearance showing a higher prevalence of type-II pattern in myogenous TMD subjects than non-TMD subjects. On the other hand, for treatment assessment purposes, muscles were observed thinner after treatment compared to pre-treatment. Also, results of intramuscular ultrasonographic appearance show disappearance or reduction of anechoic areas, higher prevalence of type-II pattern and significant distinction of echogenic bands were observed after treating TMD subjects.

CONCLUSION

Ultrasonography cannot be considered as a diagnostic instrument, but maybe as a complementary tool for treatment assessment of myogenous TMD subjects, even though future research is required to confirm its utility.

Is musculoskeletal pain associated with increased muscle stiffness? Evidence map and critical appraisal of muscle measurements using shear wave elastography

INTRODUCTION AND AIMS

Approximately 21% of the world's population suffers from musculoskeletal conditions, often associated with sensations of stiff muscles. Targeted therapy requires knowing whether typically involved muscles are objectively stiffer compared to asymptomatic individuals. Muscle stiffness is quantified using ultrasound shear wave elastography (SWE). Publications on SWE-based comparisons of muscle stiffness between individuals with and without musculoskeletal pain are increasing rapidly. This work reviewed and mapped the existing evidence regarding objectively measured muscle stiffness in musculoskeletal pain conditions and surveyed current methods of applying SWE to measure muscle stiffness.

METHODS

A systematic search was conducted in PubMed and CINAHL using the keywords "muscle stiffness", "shear wave elastography", "pain", "asymptomatic controls" and synonyms. The search was supplemented by a hand search using Google Scholar. Included articles were critically appraised with the AXIS tool, supplemented by items related to SWE methods. Results were visually mapped and narratively described.

RESULTS

Thirty of 137 identified articles were included. High-quality evidence was missing. The results comprise studies reporting lower stiffness in symptomatic participants, no differences between groups and higher stiffness in symptomatic individuals. Results differed between pain conditions and muscles, and also between studies that examined the same muscle(s) and pathology. The methods of the application of SWE were inconsistent and the reporting was often incomplete.

CONCLUSIONS

Existing evidence regarding the objective stiffness of muscles in musculoskeletal pain conditions is conflicting. Methodological differences may explain most of the inconsistencies between findings. Methodological standards for SWE measurements of muscles are urgently required.

Explorative study using ultrasound time-harmonic elastography for stiffness-based quantification of skeletal muscle function

Time-harmonic elastography (THE) is an emerging ultrasound imaging technique that allows full-field mapping of the stiffness of deep biological tissues. THE's unique ability to rapidly capture stiffness in multiple tissues has never been applied for imaging skeletal muscle. Therefore, we addressed the lack of data on temporal changes in skeletal muscle stiffness while simultaneously covering stiffness of different muscles. Acquiring repeated THE scans every five seconds we quantified shear-wave speed (SWS) as a marker of stiffness of the long head (LHB) and short head (SHB) of biceps brachii and of the brachialis muscle (B) in ten healthy volunteers. SWS was continuously acquired during a 3-min isometric preloading phase, a 3-min loading phase with different weights (4, 8, and 12 kg), and a 9-min postloading phase. In addition, we analyzed temporal SWS standard deviation (SD) as a marker of muscle contraction regulation. Our results (median [min, max]) showed both SWS at preloading (LHB: 1.04 [0.94, 1.12] m/s, SHB: 0.86 [0.78, 0.94] m/s, B: 0.96 [0.87, 1.09] m/s, p < 0.001) and the increase in SWS with loading weight to be muscle-specific (LHB: 0.010 [0.002, 0.019] m/s/kg, SHB: 0.022 [0.017, 0.042] m/s/kg, B: 0.039 [0.019, 0.062] m/s/kg, p < 0.001). Additionally, SWS during loading increased continuously over time by 0.022 [0.004, 0.051] m/s/min (p < 0.01). Using an exponential decay model, we found an average relaxation time of 27 seconds during postloading. Analogously, SWS SD at preloading was also muscle-specific (LHB: 0.018 [0.011, 0.029] m/s, SHB: 0.021 [0.015, 0.027] m/s, B: 0.024 [0.018, 0.037] m/s, p < 0.05) and increased by 0.005 [0.003, 0.008] m/s/kg (p < 0.01) with loading. SWS SD did not change over loading time and decreased immediately in the postloading phase. Taken together, THE of skeletal muscle is a promising imaging technique for in vivo quantification of stiffness and stiffness changes in multiple muscle groups within seconds. Both the magnitude of stiffness changes and their temporal variation during isometric exercise may reflect the functional status of skeletal muscle and provide additional information to the morphological measures obtained by conventional imaging modalities.

Quantitative and qualitative evaluation of the masseter muscle by ultrasonography and correlation with whole body health status

[Purpose] Ultrasonography can be used to non-invasively analyze any cross-section of the human body and to measure tissue elasticity, thickness, and brightness. This study was performed to examine the quantitative and qualitative changes in the masseter muscle at rest and at maximal occlusion, and to evaluate the relationship between these changes and the general health of the individual. [Participants and Methods] The study cohort comprised 30 healthy adults. Correlations between basic participant information (sex, age, height, body weight, body mass index, body fat, maximum bite force, handgrip strength, and tongue pressure) and masseter muscle ultrasonographic data were examined. [Results] Masseter muscle thickness was significantly greater in males than in females. Body weight and body mass index correlated positively with masseter muscle thickness. Body mass index and body fat percentage correlated positively with masseter muscle brightness. Tongue pressure correlated positively with handgrip strength. [Conclusion] Our analyses of muscle thickness and brightness suggest that ultrasonography may be useful in evaluating masseter muscle quantity and quality, and that the condition of the masseter muscle may correlate with the overall health status of the individual.

Determination of masseter and temporal muscle thickness by ultrasound and muscle hardness by shear wave elastography in healthy adults as reference values

OBJECTIVES

The purpose of this study is to prospectively investigate the reference values of masseter and temporal muscle thicknesses by ultrasonography and muscle hardness values by shear wave elastography in healthy adults.

METHODS

The sample of the study consisted of a total of 160 healthy individuals aged between 18 and 59, including 80 women and 80 men. By examining the right and left sides of each participant, thickness and hardness values were obtained for 320 masseter muscles and 320 temporal muscles in total.

RESULTS

The mean masseter muscle thickness was found to be 1.09 cm at rest and 1.40 cm in contraction. The mean temporal muscle thickness was found to be 0.88 cm at rest and 0.98 cm in contraction. The thickness values of the masseter and temporal muscles were significantly greater in the male participants than in the female participants (P < .001). While there were significant differences between the right and left masseter muscle thickness values at rest and in contraction, the values of the temporal muscles did not show a significant difference between the sides. While the resting hardness (rSWE) of the masseter muscle was transversally 6.91 kPa and longitudinally 8.49 kPa, these values in contraction (cSWE) were found, respectively, 31.40 and 35.65 kPa. The median temporal muscle hardness values were 8.84 kPa at rest and 20.43 kPa in contraction. Masseter and temporal muscle hardness values at rest and in contraction were significantly higher among the male participants compared to the female participants (P < .001).

CONCLUSION

In this study, reference values for the thickness and hardness of the masseter and temporal muscles are reported. Knowing these values will make it easier to assess pain in the masseter and temporal muscles and determine the diagnosis and prognosis of masticatory muscle pathologies by allowing the morphological and functional assessments of these muscles, and it will identify ranges for reference parameters.

Dynamic Quantitative Imaging of the Masseter Muscles in Bruxism Patients with Myofascial Pain: Could It Be an Objective Biomarker?

We aimed to investigate whether the collaboration of shear wave elastosonography (SWE) and B-mode ultrasonography (US) could be offered as diagnostic tools to assess the presence, severity, and progress of bruxism, as well as a biomarker for the effectiveness of treatment in daily clinical practice. The study was designed as a quantitative evaluation of the masseter muscles (MMs) of the clinically diagnosed bruxism patients suffering from myofascial pain and MMs of the healthy individuals. Clinical examinations were made according to the diagnostic criteria for temporomandibular disorders (DC/TMD), and pain was assessed using a visual analog scale (VAS). Painful MMs with VAS scores ≥ 4 were assigned to Group A, and healthy MMs were assigned to Group B. Also, the MMs of the painful bruxers were analyzed based on wearing occlusal splints. Group A was divided into two subgroups as splint users (Group AI) and non-users (Group AII). All the participants were scanned with dynamic US and SWE to quantify the size and stiffness of the MMs. Measurements of each muscle pair while the jaw is in a resting position (relaxation) and clenching position (contraction) were recorded. The significant differences in stiffness and thickness became visible in the relaxation state. Bruxism patients with myofascial pain had significantly harder and thinner MMs than healthy individuals. During the relaxation, the mean thickness and elasticity values were 9.17 ± 0.40 mm and 39.13 ± 4.52 kPa for Group A and 10.38 ± 0.27 and 27.73 ± 1.92 for Group B, respectively. Also, stiffer MMs were measured in Group AII (38.16 ± 3.61 kPa) than in Group AI (26.91 ± 2.13 kPa). In conclusion, the combination of SWE and US using a dynamic examination technique has the potential to be a valuable tool for the management of bruxism patients suffering from myofascial pain.

Assessing thickness and stiffness of superficial/deep masticatory muscles in orofacial pain: an ultrasound and shear wave elastography study

INTRODUCTION

Sonoelastography has been increasingly used for non-invasive evaluation of the mechanical features of human tissues. The interplay between orofacial pain and regional muscle activity appears clinically paramount, although only few imaging studies have investigated this association. Using shear wave sonoelastography (SWS), this study ascertained whether orofacial pain induced alterations in the stiffness of superficial and deep masticatory muscles.

METHODS

All participants were systematically evaluated for oral/facial-related conditions, including the area and intensity of pain. SWS was applied to measure the stiffness of the bilateral masseter, temporalis, and lateral pterygoid muscles. The association between orofacial pain and muscle stiffness/thickness was investigated using a generalized estimating equation for adjusting the influence of age, sex, laterality, and body mass index on muscle thickness/stiffness.

RESULTS

A total of 98 participants were included in the present study: 48 asymptomatic controls, 13 patients with unilateral pain, and 37 patients with bilateral orofacial pain. The reliability, quantified by the intraclass correlation coefficient for muscle stiffness measurement, ranged from 0.745 to 0.893. Orofacial pain at the individual muscle level was significantly associated with masseter muscle stiffness. A trend of increased stiffness (p = 0.06) was also observed in relation to the painful side of the temporalis muscle. No significant correlation was identified between the numeric rating scales for pain and stiffness measurements.

CONCLUSIONS

SWS provides reliable stiffness measurements for the superficial and deep masticatory muscles. The ipsilateral masseter and temporalis muscles might be stiffer than those on the side without orofacial pain. Future studies using the present sonoelasotography protocol can be designed to investigate the stiffness changes in the target muscles after interventions.

Measuring Shear Wave Velocity in Adult Skeletal Muscle with Ultrasound 2-D Shear Wave Elastography: A Scoping Review

Ultrasound 2-D shear wave elastography (US 2D-SWE) is a non-invasive, cost-effective tool for quantifying tissue stiffness. Amidst growing interest in US 2D-SWE for musculoskeletal research, it has been recommended that shear wave velocity (SWV) should be reported instead of elastic moduli to avoid introducing unwanted error into the data. This scoping review examined the evolving use of US 2D-SWE to measure SWV in skeletal muscle and identified strengths and weaknesses to guide future research. We searched electronic databases and key review reference lists to identify articles published between January 2000 and May 2021. Two reviewers assessed the eligibility of records during title/abstract and full-text screening, and one reviewer extracted and coded the data. Sixty-six studies met the eligibility criteria, of which 58 were published in 2017 or later. We found a striking lack of consensus regarding the effects of age and sex on skeletal muscle SWV, and widely variable reliability values. Substantial differences in methodology between studies suggest a pressing need for developing standardized, validated scanning protocols. This scoping review illustrates the breadth of application for US 2D-SWE in musculoskeletal research, and the data synthesis exposed several notable inconsistencies and gaps in current literature that warrant consideration in future studies.

Shear Wave Elastography in Bruxism-Not Yet Ready for Clinical Routine

Ultrasound shear wave elastography (SWE) is an emerging modality for the estimation of stiffness, but it has not been studied in relation to common disorders with altered stiffness, such as bruxism, which affects almost one-third of adults. Because this condition could lead to an increased stiffness of masticatory muscles, we investigated SWE in bruxism according to a proof-of-principle and feasibility study with 10 patients with known bruxism and an age- and gender-matched control group. SWE of the left and right masseter muscles was estimated under three conditions: relaxed jaw, 50% of the subjective maximal bite force, and maximal jaw opening. Rejecting the null hypothesis, SWE was significantly increased during relaxed jaw (bruxism 1.92 m/s ± 0.44; controls 1.66 m/s ± 0.24), whereas for maximal mouth opening, the result was vice versa increased with 2.89 m/s ± 0.93 for bruxism patients compared with 3.53 m/s ± 0.95 in the healthy control, which could be due to limited jaw movement in chronic bruxism patients (bruxism 4.46 m/s ± 1.17; controls 5.23 m/s ± 0.43). We show that SWE in bruxism is feasible and could be of potential use for diagnostics and monitoring, though we also highlight important limitations and necessary methodological considerations for future studies.

Botox Therapy for Hypertrophy of the Masseter Muscle Causes a Compensatory Increase of Stiffness of Other Muscles of Masticatory Apparatus

Little is known about the nature of masseter muscle hypertrophy. We investigated the masseter muscle stiffness change after a single intra-masseteric session of Botox injections in people with benign bilateral masseter hypertrophy and the effect of the treatment on the stiffness of the temporalis muscle. Stiffness of the muscles was measured with shear-wave elastography at baseline and 3 weeks after Botox injections in 22 otherwise healthy people. Before the treatment, the stiffness of the masseter was lower than of the temporalis muscle (10.18 ± 1.67 kPa vs. 11.59 ± 1.54 kPa; p = 0.002). After the treatment, this difference increased (6.38 ± 1.34 vs. 13.10 ± 1.92; p < 0.0001). The drop in the stiffness of the masseter muscle was symmetrical (left side by 3.78 kPa; right side by 3.83 kPa). No differences between the left and right sides of the face in terms of muscle stiffness were observed. The study shows that Botox injections reduce stiffness of the masticatory muscles which, in turn, increases the stiffness of the temporalis muscles. Due to the knock-on effect of the change in the masseter function on the other masticatory muscles, simultaneous evaluation and treatment of the temporalis muscle may be required to ensure the desired functional and cosmetic effect.

Assessment of the masseter stiffness in patients during conservative therapy for masticatory muscle disorders with shear wave elastography

Background

The complex structure of the stomatognathic system plays a vital role in chewing, digestion, speaking, breathing, facial expression and swallowing. Its complexity is the primary reason for creating multidisciplinary teams to manage temporomandibular disorders (TMD). We aimed to assess the masseter stiffness in patients undergoing conservative therapy for masticatory muscle disorders and evaluate the efficacy of manual therapy and stabilization occlusal splint in the treatment of masticatory muscle disorders.

Methods

This uncontrolled prospective cohort study included 35 patients with masticatory muscle disorders. The study lasted for eight weeks. The patients were treated with manual therapy and stabilization occlusal splint and evaluated using shear wave elastography of the masseter muscles and patient-reported outcome measures (PROMs) to assess pain, anxiety, quality of sleep, satisfaction with life and perceived stress.

Results

After the treatment, the stiffness of both masseter muscles decreased significantly (by 4.21 kPa). The patients reported a significant reduction in pain. At baseline, the median scores ranged from 5 to 8; after treatment, they ranged from 0 to 1 (p < 0.0001). The patients also reported significant improvement in terms of all patient-reported outcome measures. The reduction in stiffness corresponded to the improvement in pain and PROMs, as shown by correlations which were insignificant for all measures.

Conclusions

Conservative therapy of masticatory muscle disorders involving manual therapy and stabilization occlusal splint is effective. It reduces the masseter stiffness as objectively shown in shear wave elastography and improves subjective PROMs scores, including numerical pain assessment and selected questionnaires. Shear wave elastography has the potential for broad application in clinical practice to monitor masticatory muscle disorders treatment effects due to its objectivity and non-invasive character. Further research is recommended on larger patient populations and longer follow-up.

Trial registration

The study was registered at clinicaltrials.gov (NCT03844854). First posted date: 19/02/2019.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05392-9.

[Feeling stiff…but what does it mean objectively? : Can you measure muscle tension?]

Almost everyone is familiar with "tense muscles", but what is muscle tension physiologically behind? Are tense muscles more active; do they have problems relaxing? Are they harder or stiffer than asymptomatic muscles? In this work, current evidence regarding the activity and stiffness of tense neck muscles is presented. Further, measurement methods and their limitations are explained. These limitations reveal the shortcomings of the current knowledge and the need for further research. Finally, a recently funded research project on the measurement of tense muscles is presented.

Stiffness of the Masseter Muscle in Children-Establishing the Reference Values in the Pediatric Population Using Shear-Wave Elastography

In children, the quality and muscle function are altered in many pathologic conditions, including temporomandibular disorders. Although several methods have been used to evaluate muscle tonus, none became a golden standard. Moreover, the masseter muscle characteristics in children have not been investigated to date. This study aimed to measure the stiffness of the masseter muscle using shear-wave elastography in healthy children. We enrolled 30 healthy children (mean age 10.87 ± 3.38 years). The stiffness of masseter muscles was measured with shear wave elastography. Stiffness for the total sample was 6.37 ± 0.77 kPa. A comparison of the measurements did not show significant differences between the right and the left masseter muscles (left—6.47 ± 0.78 kPa; right—6.24 ± 0.76 kPa; p = 0.3546). A significant difference was seen between boys and girls (boys—5.94 ± 0.50 kPa; girls—6.63 ± 0.80; p = 0.0006). Shear-wave elastography is a promising diagnostic tool. It may help to detect changes in the stiffness of the masseter muscle and draw attention to pathological processes within the jaw muscles. Directions for further research shall include determining stiffness values in pathological conditions and the impact of biological and functional factors on the stiffness of the masseter muscle.

Intramuscular Injections and Dry Needling within Masticatory Muscles in Management of Myofascial Pain. Systematic Review of Clinical Trials

Background: Myofascial pain is an important cause of disability among the whole population, and it is a common symptom of temporomandibular joint disorders (TMDs). Its management techniques vary widely; however, in recent years, there has been a growing interest especially in needling therapies within masticatory muscles, due to their simplicity and effectiveness in pain reduction. Methods: The construction of the following study is based on PICOS and PRISMA protocols. A systematic literature search was conducted based on the PubMed and BASE search engines. Searching the abovementioned databases yielded a total of 367 articles. The screening procedure and analysis of full texts resulted in the inclusion of 28 articles for detailed analysis. Results: According to analyzed data, clinicians manage myofascial pain either with wet or dry needling therapies. The most thoroughly studied approach that prevails significantly within the clinical trials is injecting the botulinum toxin into the masseter and temporalis. Other common methods are the application of local anesthetics or dry needling; however, we notice the introduction of entirely new substances, such as platelet-rich plasma or collagen. In the analyzed articles, the target muscles for the needling therapies are most commonly localized by manual palpation although there are a variety of navigational support systems described: EMG, MRI or EIP electrotherapy equipment, which often aid the access to located deeper lateral and medial pterygoid muscle. Conclusions: Needling therapies within masticatory muscles provide satisfactory effects while being simple, safe and accessible procedures although there still is a need for high quality clinical trials investigating especially injections of non-Botox substances and needling within lateral and medial pterygoid muscles.

Determination of Reference Values of the Masseter Muscle Stiffness in Healthy Adults Using Shear Wave Elastography

Shear wave elastography (SWE) is an objective and reliable method for the assessment of muscles and internal organs. Every organ exhibits its own stiffness characteristics and hence requires individual reference values. We aimed to determine the reference values of stiffness of the masseter muscle in healthy adult individuals using SWE. We analyzed the data of 140 participants (74 men, 66 women) with a median age of 50 years. The overall mean elasticity was 10.67 ± 1.77 kPa. The average values were lower by 2.25 kPa (9.15%) in women compared to men (9.48 ± 1.47 kPa vs. 11.73 ± 1.27 kPa; p < 0.0001). The values of stiffness increased with age, with a correlation coefficient of about 0.35 and a p < 0.0001. Age was a significant influencing factor of masseter muscle stiffness. The left and right masseters had similar stiffness. We conclude that stiffness values are significantly lower in women than in men with a difference of 9%. Age significantly influences the stiffness of masseter muscle, and the values of stiffness increase significantly with age, particularly in men. However, further studies are required to determine the precise ranges of stiffness accounting for age and sex in healthy subjects and people with disorders and conditions of the masticatory system.

Monitoring of Changes in Masticatory Muscle Stiffness after Gum Chewing Using Shear Wave Elastography

This study aimed to investigate if intensive exercise affects the stiffness of the masticatory muscles measured with shear-wave elastography. The study included a cohort of healthy adults (n = 40) aged 40 ± 11 years. In each individual, the stiffness of both the masseter and temporalis muscle was examined three times: at baseline, after 10 min of intensive exercise (chewing gum), and after 10 min of relaxation. Stiffness values (median (IQR)) of both the masseter and temporalis muscle were the lowest at the baseline (11.35 (9.7–12.65) and 10.1 (9.1–10.95)), increased significantly after the exercise (12.5 (11.1–13.25) and 10.3 (10.2–10.52)) and then dropped significantly after 10 min of relaxing (11.75 (9.95–12.6) and 10.2 (9.65–11.9)). The stiffness of the temporalis muscle was significantly lower than that of the masseter muscle. The values of the stiffness of the masseters correlated significantly with the values of the stiffness of the temporalis muscles. Shear wave elastography proved to be a sensitive method for showing changes in the stiffness of the muscles involved in the mastication occurring as a response to the effort, which increased the muscle stiffness. Further research is needed to broaden knowledge on the impact of eating habits and the occurrence of parafunctions on the development of temporomandibular disorders and the condition of masticatory muscles.

Potential of Using Shear Wave Elastography in the Clinical Evaluation and Monitoring of Changes in Masseter Muscle Stiffness

The study aimed to evaluate masseter muscle stiffness in adult healthy volunteers referred to a massage treatment and also to investigate whether shear-wave elastography can be used to monitor the effect of massage on the masseter muscle. The study included 21 healthy volunteers, who were subjected to a 30-minute massage of the masseter muscle. Muscle stiffness was measured by shear-wave elastography before and directly after the massage. Pain during the massage was assessed using the visual analogue scale (VAS). The data of 20 patients (one excluded due to severe pain) with a median age of 34.5 years were analysed. The stiffness values were 11.46 ± 1.55 kPa before and 8.97 ± 0.96 kPa after the massage (p < 0.0001). The mean drop was 2.49 ± 1.09 kPa. The greatest decrease was observed in people with higher elasticity values before the massage (r = 0.79; p < 0.0001). The median intensity of pain was 7.2 (range: 6–9.5). We concluded that shear-wave elastography is a sensitive tool to monitor changes in the stiffness of the masseter muscle.