Background: An increasing number of people suffer from neck pain due to life style and prolonged
use of computers. Research has revealed that myofascial trigger points (MTrPs) and the intramuscular
innervation zone (IZ) are involved in neck pain. MTrPs are induced mainly by IZ dysfunction of the
affected skeletal muscle and the 2 do not overlap in location. The question is whether injection
treatment in MTrPs or in the IZ is more effective to relieve MTrPs-associated pains. The precise location
and body-surface map of the intramuscular IZ in the trapezius muscle and a clinical injection study in
the IZ may provide a useful answer to the question.
Objectives: This study aimed to investigate the efficacy of lidocaine injection in the intramuscular
IZ for the treatment of chronic neck pain caused by MTrPs in the trapezius muscle.
Study Design: Prospective observational study, approved by the local research ethics.
Setting: University hospital, departments of Anesthesiology and Anatomy.
Methods: First, for the determination of IZ distribution and body-surface mapping, a modified
intramuscular Sihler’s neural staining technique was applied to elucidate nerve distribution patterns
of the trapezius muscle. Then, 120 patients with myofascial pain syndrome (MPS) of the trapezius
muscle were randomly divided into 5 groups for analysis. Group 1 (n = 24) received injections of
saline (0.9% NaCl) at the MTrPs. Group 2 (n = 24) received injections of 0.5% lidocaine at the MTrPs.
Group 3 (n = 24) received injections of saline (0.9% NaCl) at the mid-upper trapezius (Point E). Group
4 (n = 24) received injections of 0.5% lidocaine at Point E. Group 5 (n = 24) received a combined
injection of 0.5% lidocaine treatment at both Point E and the lower trapezius (Point F). The injection
dose was 4 mL at each injection site. All patients received injections once a week for 4 weeks. The
visual analogue scale (VAS) and the frequency of painful days per month (FPD) were obtained before
treatment and at 2, 4, and 6 months after treatment.
Results: The intramuscular terminal nerve branches presented a “dendritic” distribution in the
trapezius muscle and were connected with each other to form an S-shaped IZ belt in the middle
of the muscle belly. Compared with the MTrP injection group, lidocaine-injection therapy in the IZ
significantly reduced the degree and frequency of neck pain in patients at 6 months after treatment,
especially the combined lidocaine-injection therapy in the IZ of both the mid-upper trapezius and the
lower trapezius are more effective (all P < 0.05).
Conclusions: This study confirms that lidocaine-injection therapy in the IZ significantly reduces
the degree and frequency of neck pain in patients at 6 months after treatment. The combined
lidocaine-injection therapy in the IZ of both the mid-upper trapezius and the lower trapezius is more
effective. In addition, this study establishes a clear distribution map of intramuscular nerves that will
be conducive to the future use of chemical blockers and electrical stimulation in the nervous system
in treating MPS of the trapezius muscle.
Limitations: The small number of patients and the short duration of follow-up.
Key words: Neck pain, intramuscular innervation zone, myofascial trigger points, lidocaine
Effects of Radial Extracorporeal Shockwave Therapy Versus 1% Lidocaine Injection for Myofascial Trigger Points Measured with Elastic Index
