Introduction
One frequent muscular impairment observed in individuals with chronic pain is myofascial pain syndrome (MPS), characterized by the presence of myofascial trigger points (MTrPs). A MTrP is defined as a hyperirritable spot in a taut band of a skeletal muscle which is painful on stimulation (e.g., palpation, stretch, contraction, or needling), elicits referred pain, and induces motor or autonomic disturbances1. Active MTrPs are those which pain referral reproduces the symptoms of the patient, whereas latent MTrPs are those which referred pain does not reproduce the symptoms of the patient1.
Myofascial trigger points have been found to be highly prevalent in spinal pain disorders2. Simons et al.1 suggest that one relevant muscle for the development of thoracic spine pain is the rhomboid muscle. In fact, patients with cervical radiculopathy show a prevalence of 10.2% of active MTrPs in the rhomboid musculature3. In addition, up to 75% of patients with thoracic pain also exhibit active MTrPs in the rhomboid4.
The rhomboid major is a quadrangular muscle located in the thoracic spine innervated by the dorsal scapular nerve which contributes to the positioning and motion of the scapula. The rhomboid major muscle originates from the supraspinous ligament and the spinous processes of T2-T5 vertebrae and inserts into the line between the scapular spine root and the inferior angle on the medial margin of the scapular spine5. It lies superficial to the posterosuperior serratus (immediately superficial to the ribs) and deeper to the middle trapezius muscle.
Manual therapy and dry needling are the most common therapeutic interventions applied for the management of MTrPs. Dry needling consists of the insertion of a solid filament needle into the muscle targeting a potential MTrP and has received increasing attention in the literature in the last years6. Since dry needling is an invasive technique, improving its safety is crucial7.
Despite the fact that dry needling is declared as a safe intervention safety, several adverse events have been described in the literature. It has been reported that the most common adverse events associated to dry needling can be considered minor and include bruising, bleeding, pain during treatment and pain after treatment8,9. Nevertheless, serious adverse events cannot be excluded, Brady et al.8 gave an estimated risk rate of ≤ 0.04% for significant adverse events. Pneumothorax is one of the most serious adverse events occurring when dry needling the thorax or rib cage and resulting from an improper needle insertion into the pleural space during the technique. In fact, several case reports describing iatrogenic pneumothorax after the application of dry needling into posterior thoracic muscles are described10.
Due to the anatomical location of the rhomboid musculature, a correct safety and prevention is needed due to the severity of this complication. In fact, different strategies have been proposed to ensure patient’s safety and decrease relative risk during invasive procedures. Cushman et al have suggested palpation of the ribs before dry needling could prevent pneumothorax; however, these authors reported poor accuracy in subjects with larger muscle thickness and higher body mass index11. As conclusion of their study, they recommended the use of ultrasound evaluation during or before dry needling to ensure the correct needle length. Folli et al. recently reported, as assessed with ultrasound imaging, a mean thickness of the major rhomboid muscle of 16.3mm (males muscle thickness: 25.4mm; women muscle thickness: 20.4mm)12. However, the routinely use of ultrasound in clinical practice is not always possible due to its high economic costs.
Seol et al.13 provided tentative needle lengths and safe margins based on the Body Mass Index of subjects based on a 3-group classification (BMI>25; 23<BMI<25; and BMI<23). A similar procedure including more potential predictors (e.g. age, thorax circumference, respiratory moment, gender) could help clinicians to determine the depth of the pleura and rhomboid major muscle, and, hence, determining the appropriate length of the needle. Therefore, the aim of this study was to evaluate if anthropometric features can predict rhomboid major muscle and pleura depth, as assessed with ultrasound imaging, in a sample of healthy subjects. Our hypothesis is that a prediction model based on age, height, weight, respiratory moment, thorax circumference, BMI and gender could assist during the application of dry needling into the rhomboid musculature.