Comparing Deep and Superficial Dry Needling for Neck Pain: An Ultrasound and EMG Study

The musculoskeletal system, the largest in the human body, is highly susceptible to pain, affecting up to 80% of individuals (Bourgaize et al., 2018; Weller et al., 2018). Among these disorders, myofascial pain syndrome (MPS) is one of the most prevalent and costly conditions, affecting approximately 85% of the general population at least once in their lifetime (Pal et al., 2014). The economic burden of MPS is substantial, with estimated costs of 522 million dollars in Canada and around 57.51 million dollars in the United States (Berger et al., 2007). MPS was described by Simons and Travell (1983) as a regional pain condition associated with one or more myofascial trigger points (MTrPs)-hyperirritable nodules in taut muscle bands (Barbero et al., 2019). These trigger points may result from trauma or repetitive strain, producing an energy crisis characterized by motor endplate dysfunction, sustained contraction, and local hypoxia (Zhang et al., 2020).

The upper back region is the most frequent site of MTrPs; 65% occur in the levator scapulae and trapezius muscles, and 50% in the suboccipital muscles (Lluch et al., 2015). Notably, 38.8% of individuals with neck pain have MTrPs in the upper trapezius (Cohen & Hooten, 2017). Electromyography (EMG) studies revealed that MTrPs exhibit higher amplitude and longer duration of motor unit potentials compared with normal muscle (Audette et al., 2004; Wytrążek et al., 2011). Ultrasonographic investigations found band-like hypoechoic regions, reduced entropy, and increased stiffness in active MTrPs (Ballyns et al., 2012; Turo et al., 2013; Adigozali et al., 2017; Ball et al., 2022). Doppler ultrasound studies demonstrated increased retrograde diastolic blood flow, indicating altered local circulation (Sikdar et al., 2010; Ballyns et al., 2011). In addition, microdialysis research revealed lower pH and elevated levels of substance P and calcitonin gene-related peptide in active MTrPs, reflecting a pro-inflammatory biochemical milieu (Shah et al., 2005; Shah et al., 2008; Gerdle et al., 2014).

Among treatment modalities, dry needling (DN)-introduced by Lewit (1979)-is one of the most widely used. Two main approaches exist: superficial DN, involving shallow insertion without reaching the MTrP (Baldry, 2002; Legge, 2014), and deep DN, in which the needle penetrates into the muscle to mechanically deactivate the MTrP (Griswold et al., 2019). Superficial DN is thought to activate Aδ nerve fibers that inhibit nociceptive transmission (Bowsher, 1998; Karavis, 1997; Baldry, 2002), whereas deep DN may disrupt dysfunctional endplates, normalize acetylcholine activity, and improve blood flow and oxygenation (Fernández-de-Las-Peñas & Nijs, 2019; Cagnie et al., 2012).

Although both techniques reduce pain and disability effectively (Sedighi et al., 2017; Sarrafzadeh et al., 2018; Ezzati et al., 2019; Griswold et al., 2019; Hoseininejad et al., 2023), no studies have compared their effects on ultrasound-measured muscle properties and electromyographic activity. Therefore, the present study aims to compare deep versus superficial dry needling on the ultrasound and EMG characteristics of MTrPs in the upper trapezius among patients with neck pain.

Objective: