|ECR 2018 / C-0814|
|Myofascial pain: ultrasound amplitude > width of the masseter muscle|
Methods and materials
The study was carried out in the Department of Stomatology and Maxillofacial Surgery of Valencia University General Hospital (Valencia, Spain), following approval by the local Clinical Research Ethics Committee. A case-control design was used. A total of 31 subjects diagnosed with myofascial pain of the masticatory muscles were included between October 2014 and January 2016, based on the following inclusion/exclusion criteria:
- A diagnosis of myofascial pain (according to the Research Diagnostic Criteria for Temporomandibular Disorders [RDC/TMD]), (5) with involvement of at least one of the two MMs at some of the three diagnostic points (muscle origin, body or insertion).
A minimum evolution of three months from pain onset.
At least one occlusal contact in each posterior segment (premolars and molars).
Subjects with a history of major surgery and/or radiotherapy in the maxillofacial region.
Minor surgery in the maxillofacial region during the previous three months.
Organic disease of either MM (cysts, tumors, infections) detected during the magnetic resonance imaging (MRI) and/or ultrasound explorations.
Systemic muscle disease.
Subjects under 18 years of age.
A total of 35 controls were selected from among subjects with TMD but without a diagnosis of myofascial pain in the orofacial region.
After signing of the informed consent document, ultrasound was used to explore both temporomandibular joints (TMJs) and the masticatory muscles (masseter and temporal muscles) in all the MFP-subjects and controls. All the explorations were made by the same operator (PM) specialized in musculoskeletal ultrasound and blinded to the clinical diagnosis. An Aplio 500 Premium® ultrasound system with a linear probe operating in the range of 5-14 MHz was used (ToshibaTM, Otarawa, Japan).
With the subject in dorsal decubitus, the ultrasound probe was positioned perpendicular to the anterior margin of the MM and external surface of the mandibular ramus, between 2-2.5 cm above the lower mandibular margin. The subject was instructed to establish contact with the teeth of both arches, though without applying pressure (UOC). Then the maximum transverse width of both MMs from the internal band of the epimysium (external surface of the ascending mandibular ramus) to the external fascia at the intermediate point between the origin and insertion of the muscle was measured (Fig. 1). The subject was then instructed to occlude the teeth with maximum force, and again the width of both MMs likewise at the intermediate point between the origin and insertion of the muscle was measured (Fig. 2).
Comparison was made of the MM width of the MFP-subjects and controls under both UOC and at maximum contraction, followed by comparison of the increase in muscle width (amplitude) at maximum contraction both in absolute terms (width at maximum contraction minus UOC width) and as relative values (width at maximum contraction / UOC width). Case-control comparisons were made using single-factor analysis of variance (ANOVA) for variables with a normal distribution, and the Mann-Whitney U-test for variables with a non-normal distribution. Normal data distribution was assessed using the Shapiro-Wilk test. Linear correlations were used to analyze the influence of MFP-subject age and the duration of the disorder upon the main study variables. A statistical significance level of p<.05 was used in all cases.
Repeat measurements on the ultrasound images of 10 MFP subjects and 10 controls were carried out between 2-3 months after the first exploration, with calculation of the intraclass correlation coefficient. Values less than 0.4 being assumed to imply study suspension.(6)
The statistical analysis was performed using the SPSS version 22.0 statistical package for Microsoft Windows (IBM Corp., Armonk, NY, USA).
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