Treatment of myofascial pain syndrome with lidocaine injection and physical therapy, alone or in combination: a single blind, randomized, controlled clinical trial

Myofascial pain syndrome (MPS) is a major cause of chronic musculoskeletal pain and is characterized by the presence of hypersensitive areas and myofascial trigger points (MTrPs) in a muscle or its fascia that, when palpated, may trigger a characteristic referred pain, tenderness and autonomic phenomena [1].

The prevalence of MPS varies from 21 % in orthopedic clinics to 30 % in general practice, and between 55 and 95 % in specialized pain management centers [2, 3]. Some studies suggest that latent MTrPs may be present in between 45 and 55 % of the muscles of the shoulder girdle and between 5 and 55 % of the muscles of the pelvic girdle of asymptomatic young adults [4]. Myofascial pain syndrome can be acute or chronic and primary or secondary. MPS may be associated with radiculopathy, nerve entrapments, metabolic and nutritional disorders, biomechanical imbalance, and/or physical deconditioning [5].

The concept of MTrPs can be considered to be controversial because some researchers argue that the key phenomenon of muscle tenderness demands a robust plausible explanation based on neurobiology [6]. In response, other researchers purport this argument is not sufficient to invalidate the integrated trigger point hypothesis [7]. They insist that numerous physiological mechanisms have been proposed. The integrated trigger point hypothesis is the most accepted physiological model to explain these phenomena. This model explains how abnormal depolarization of the post-junctional membrane of motor endplates causes a localized hypoxic energy crisis associated with sensory and autonomic reflex arcs that are sustained by complex sensitization mechanisms [8, 9]. Biochemical abnormalities have been described to explain this neuromuscular dysfunction consisting of motor and sensory abnormalities involving both the peripheral and central nervous system [10, 11]. A more recent hypothesis suggests that MTrPs are caused by a nociception-induced central nervous system disorder which is centrally maintained by α-motoneuron plateau depolarization, but unfortunately experimental evidence for this hypothesis is still lacking [12, 13]. Furthermore, it is possible that some of the mechanisms proposed to explain chronic non-specific low back pain could be considered to apply to chronic myofascial pain in the cervical region [14]. For example, psychosocial factors may make acute pain become chronic and, indeed, patients with MPS have been found to have higher rates of anxiety and depression [15].

The diagnosis of MPS can also be considered controversial. Some researchers suggest that focal areas of muscle pain defined as associated with MTrPs cannot be reliably identified. Although inter-observer variability does exist, research shows that, after implementing a training program to ensure systematic physical examinations, an appropriate percentage of agreement between different examiners can be achieved, especially when palpating the trapezius, gluteus maximus and quadratus lumborum trigger points [16‐18]. Various methods have been utilized to achieve better reproducibility of the diagnosis of MPS. For instance, Simons and Travell’s method takes into account the existence of MTrPs during muscle palpation, a characteristic pattern of referred pain, the display of local response contractions or twitches, and joint mobility restriction in compromised muscles. Functional limitation is evaluated by means of specific movements such as the hand-back (patient’s ability to touch the lower angle of the contralateral scapula) and the hand-mouth (patient’s ability to exceed the contralateral labial commissure when passing the hand behind the head) maneuvers [1, 19].

There are many different treatments for MPS. Non-invasive treatments include therapeutic exercise, ultrasound, and massage and stretching the affected muscle with aerosolized fluoromethane. A systematic review of 21 randomized controlled trials (RCTs) [20] showed moderate quality evidence according to the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) system [21] that stretching and strengthening are effective for improving pain, function, and perception of improvement in chronic neck pain in the early and intermediate follow-up periods. In another systematic review of 26 RCTs, exercise proved to be effective for improving pain and function in rotator cuff disease [22]. A meta-analysis synthesizing the evidence from 12 studies indicated that high-quality therapeutic massage was effective for neck and shoulder pain, but did not improve function [23]. No interventions have demonstrated the effectiveness of capsaicin patches [24], except those with lidocaine, which improved pain over a 1-month period [25].

Invasive treatments have also been used to treat MPS, including dry-needling or medications, such as local anesthetics, corticosteroids, or botulinum toxin [5]. Dry needling has proven effective, with improvement depending on the technique used [26]. Lidocaine and bupivacaine injections were found to be more effective than placebo injections for improving pain [25, 26], with the needle size used (21, 23, and 25 gauge) unrelated to treatment effectiveness [27]. Studies of non-steroidal anti-inflammatory drugs (NSAIDs), psychotropic medications, steroid injections, and muscle relaxants have been conducted with limited evidence and unclear benefits [28, 29].

Data was analyzed from 127 patients: 43 patients in the PT + LI group, 41 in the PT group, and 43 in the LI group. See the flowchart in Fig. 1.

A total of 92 % the of participants received public health care assistance and 10 % had hypertension. These proportions were similar among groups. Additional baseline characteristics of the three groups are shown in Table 1. Groups were similar in socio-demographic and clinical characteristics - 96 % had active trigger points and 4 % latent MTrPs at the time of examination, and 65 % of these experienced a characteristic pattern of referred pain. A significantly larger proportion of the PT group (83.7 %) had referred pain compared to the other two groups (53 % each one; p < 0.01). Functional limitations presented by the patients were as follows: 15 % could not lower horizontal objects, 14 % had difficulty combing their hair, 9 % had difficulty dressing, and 6.5 % had difficulty bathing. These proportions of patients experiencing functional limitations were similar across the three groups.

In terms of the limitation in range of motion, the head tilt to the left was the most limited (31 %) followed by the right slant (27 %), rotations to the left (19 %) and right (14 %), flexion (7.3 %) and finally extension (5.6 %). There were no significant differences between the groups in range of motion.

In this study, the efficacy and safety of two interventions, PT and LI, were compared, alone vs. in combination, in male and female patients over 18 years of age with shoulder or neck pain of more than 6 weeks duration and MTrPs of the trapezius, infraspinatus, and/or levator scapulae (cervical portion). There were no statistically significant differences between the combination group and the individual treatment alone groups in VAS pain ratings, PHQ-9 depression scores, or SF-36 QoL domains at neither 1 nor 3 months.

There are no studies in the literature that evaluate head-to-head whether lidocaine injection into MTrPs combined with a PT program might be more effective than each separate treatment alone in improving pain, function, and quality of life in patients with MPS of the shoulder girdle and cervical region. However, in a recent Cochrane review of treatments for chronic neck pain, moderate quality evidence supports cervico-scapulothoracic and upper extremity strength and endurance exercises and combined cervical, shoulder and scapulothoracic strengthening and stretching exercises to improve pain and function [36]. The present study’s PT treatment incorporated similar PT exercises, without homework exercises, and included patients with MTrPs in the infraspinatus muscle as well. In this study, PT alone and in combination with LI showed better right, but not left limb hand-back maneuver functioning compared to LI injection alone. Several studies have documented the effectiveness of PT exercises on myofascial pain. For instance, an RCT of patients with MTrPs in the upper trapezius found that employing different manual techniques (such as ischemic compression, stretching after ischemic compression, and passive stretching) resulted in improved range of motion and pain sensitivity; outcomes in this study were measured only at 24 h and 1 week, and other functional outcomes were not evaluated [37]. In this study, PT treatment involved the use of hot packs and ultrasound, manual compression, deep stroking or strumming, and muscle-stretching and strengthening exercises. These techniques were focused on the cervical and shoulder girdle and specifically the trapezius, infraspinatus, and the levator scapulae muscles. Furthermore, the current study assessed longer term outcomes at 1 and 3 months post-treatment, and the groups receiving PT had significantly better right upper limb hand-back maneuver function. However, left upper limb function was not significantly different between groups, so additional research on the value of PT focused on these muscles in this patient group may be warranted. Another study in patients with shoulder pain of more than 6 months with a MTrP average pain rating of 7.4 (3.6) showed that a comprehensive PT treatment once a week with manual TP compression, stretching, cold application, and instructions for home exercises was more effective than doing nothing to improve the function; this improvement was demonstrated on the DASH (Disabilities of the Arm, Shoulder, and Hand) and on pain measured via the VAS at the time of the evaluation and in the final 7 days of treatment [29]. The present study PT treatment incorporated similar PT exercises and also included patients with MTrPs in the shoulder (infraspinatus muscle) but we did not use the DASH Scale to measure function.

Massage, another technique incorporated into the PT treatment group of the present study, has been shown to be effective in reducing pain compared with inactive therapies, such as usual care; however, massage alone has not been found to be more effective than active therapies, such as exercise [23]. In one study, massage was effective for the relief of subacute and chronic neck pain, but only in the short term [38]. In the present study, massage was used, but only in combination with other PT techniques, i.e., muscles involved were stretched and strengthened, thus further study that isolates the effects of massage alone on function or other outcomes may prove valuable.

Regarding lidocaine injections, in this study, using lidocaine injections alone was found to be similarly effective to lidocaine plus physical therapy. Similarly, in an RCT conducted with a smaller sample size of 80 patients, both dry needling and an injection of lidocaine improved pain ratings, but there were no differences between the groups [39]. In the present study, lidocaine was injected only one time and it is possible that multiple injections over time might lead to more improvement. One study showed that, compared to placebo, a series of 5 lidocaine injections on alternating days to the pericranial muscles significantly reduced both the frequency and severity of pain at 2, 4 and 6 months post treatment in MPS patients. [40] Additional RCTs examining the intensity and frequency of the proposed interventions, either alone or in combination, may help guide clinicians in their treatment strategies.

In a systematic review of needling therapies in the management of MTrP pain, the effect of MTrP injections was independent of the injected substance, which in most studies was an anesthetic such as lidocaine, bupivacaine, or procaine. No trials were of sufficient quality or design to test the efficacy of any needling technique beyond placebo in the treatment of myofascial pain. In another systematic review with meta-analysis, there was no significant difference between dry needling and lidocaine in the management of MTrPs in the neck and shoulder region. The quality of evidence for the studies was limited [41].

In another study, TrP pain pressure values were significantly higher in lidocaine group than dry needle and pain scores were significantly lower than in both the botulinum toxin type A (BTX-A) and dry needle groups. The Canadian Agency for Drugs and Technologies for Health (CADTH) conducted a Rapid Response and synthesized evidence from identified one systematic review and five RCTs. They concluded that evidence cannot support the use of botulinum toxin type A (BoNTA) injection in MTrPs for myofascial pain, given that four out of five included trials reported that BoNTA had no statistically significant effect on pain. Therefore, BoNTA was not considered to be effective for the treatment of MPS [42]. In summary, there are few outcome studies of good quality and, although some studies showed reduction in pain scores and pressure pain thresholds, the literature has neither convincingly supported nor refuted the effectiveness of some invasive and non-invasive modalities beyond placebo [13].

Myofascial pain is often chronic and treatment with any of the interventions studied produced similar outcomes, except for a slight advantage of those receiving interventions with PT showing better right limb hand-back maneuvering function compared to the LI only group. These findings suggest that PT treatment involving the use of hot packs and ultrasound, manual compression, deep stroking or strumming, and muscle-stretching and strengthening exercises could play a role in improving upper limb function, although more research is needed. Lidocaine injections, which produced similar outcomes in the MPS patients studied, are an inexpensive treatment even in repeated over time. Other studies have found that botulinum toxin is no more effective than injections with local anesthetic and is more expensive [42, 45‐47]. Future research should examine more specific PT treatments at varying time intervals, conduct longitudinal assessment of more comprehensive longer-term outcomes, assess and control for contextual factors like the patient’s occupation, and incorporate additional outcomes such as relapses and disability.