PAIN MEDICINE Volume * • Number * • 2009

A New Muscle Pain Detection Device to Diagnose Muscles as a Source of Back and/or Neck Pain Corey Hunter, MD,* Michel Dubois, MD,† Shengping Zou, MD,† William Oswald, PT,‡ Kathleen Coakley,§ Mourad Shehebar,¶ and Ann Marie Conlon, RN† *Department of Physical Medicine and Rehabilitation, New York University Langone Medical Center—Rusk Institute of Rehabilitation Medicine; †Pain Management Center, New York University Langone Medical Center; ‡Department of Physical Therapy, New York University Medical Center; §Touro College of Osteopathic Medicine, New York; ¶School of Medicine, George Washington University, Washington, DC, USA


Background. Trigger point (TrPs) identification has become the mainstay of diagnosis for the treatment of Myofascial Pain Syndrome; however, manual pressure (MP) to identify TrPs by determining low-pressure pain threshold has low interrater reliability and may lack validity since it is done on inactive muscles. To elicit contractions and mimic an active muscle or movement that “causes” pain, a Muscle Pain Detection Device (MPDD) has been developed. A selected muscle is stimulated and painful muscles are precisely detected, allowing distinctions between primary and referred muscle pain as well as distinguishing other functional muscle pain thought to cause MPS. Methods. An IRB approved randomized controlled study is presented of MP (20 patients) control vs MPDD (20 patients) to identify which muscle(s) was the source of pain in subjects presenting to the NYU Pain Management Center with a minimum 3 months history of back pain. Patients were unaware of their diagnostic method. Subjects were injected in 1–3 sites identified via MP or MPDD by a separate, blinded physician. Prior to, and following treatment at one week and one month, the patients were administered Oswestry and visual analog scale pain questionnaires by a blinded evaluator, and their range of motion was measured by a blinded physical therapist. Results. The MPDD group reported significantly larger improvements in pain, mood and Oswestry scores compared with the control (P < 0.05). Moreover, the MPDD group reported 82.5% pain relief at 1 month, compared with 53.2% in the control (P < 0.001). The range of motion measurements failed to reveal any significant difference between the groups. Conclusions. Using the MPDD appears to be more valid and potentially more reliable than palpation to identify muscles causing regional pain that could benefit from injections.

Key Words. Myofascial; Muscle; Trigger Point Injections; Neck (Pain); Low Back Pain

Reprint requests to: Michel Dubois, MD, New York University Langone Medical Center—Pain Management Center, Department of Anesthesiology, 317 East 34th Street, Suite 902, New York, NY 10016, USA. Tel: 212-201-1004; Fax: 212-685-5365; E-mail: [email protected]

prevalence, there is no generally accepted method for the diagnosis of muscles as a pain source or an inclusion of muscle evaluation/treatment in any of the proposed guidelines [2,3] for common pain syndromes such as low back and neck pain [4]. One reason is the difficulty in accurately and reliably identifying trigger points (TrPs), the putative source of pain most mentioned in studies of clinical muscle pain [5]. While there are numerous criteria characteristic of a TrP, the community standard for determining if a muscle contains TrPs, and is the cause of

© American Academy of Pain Medicine 1526-2375/09/$15.00/** **–**




s muscles account for greater than 50% of the body by weight, it is not surprising that nearly 70% of the cases diagnosed as nonspecific or idiopathic back pain are assumed to be the result of soft tissue sprains and strains [1]. Despite this


Hunter et al.

regional pain, is palpation with pressure strong enough to elicit pain [6]. Manual pressure (MP), to identify TrPs by finding diminished pressure pain threshold has low interrater reliability [5,7–10] and may lack validity since it is done on inactive muscles. Moreover, it has been demonstrated that TrP palpation is not reliable for detecting taut bands and local twitch response, and only marginally reliable for referred pain even after intense training [5,6]. A Muscle Pain Detection Device (MPDD), a product of Spoc (Stamford, CT), a medical device corporation that was formed by Stevens Institute of Technology, has been developed to elicit contractions in the muscle that is thought to cause the pain. Most patients who complain of muscle related pain report that it is worst with activity, not at rest. When the MPDD produces pain in a selected muscle, it is speculated that this identified muscle is the source of pain. The actual etiology of the pain could be tension, weakness, stiffness, spasm, or TrPs; all of which are thought to cause myofascial pain syndrome [11]. The MPDD may possibly provide a more valid and reliable tool to assess muscle pain than MP alone (Figure 1).

We postulate that MP to identify a muscular source of regional pain is an imprecise process as it is done on a sedentary/resting muscle and only identifies a low-pressure pain threshold. The MPDD actually stimulates the muscle to contract, as in vivo, deforming the TrPs and stimulating the density of muscle nociceptors found in the bony tendon attachments [12]. This study evaluated the accuracy of the MPDD vs MP in determining which muscle(s) causes pain in a region of the body of which the patient complains. Our objective was to evaluate the comparative effectiveness of the MPDD vs MP based on the outcome of standardized injections to muscles identified by each respective technique.

Materials and Methods

Device Description The MPDD is a device that uses an interferential current produced through an aluminum head that moves easily over the skin and causes the stimulated muscle to contract. This allows the examiner to run the current along the entirety of the suspected muscle, from origin to insertion, to see if

Figure 1 Flowchart.

New Muscle Pain Detection Device pain is consistently produced. When used on an unaffected or “normal” muscle, the patient will simply experience an involuntary, painless contraction of the muscle. The MPDD is preset for pulse frequency and width and can only be adjusted for signal strength. Each subject may vary in his or her muscle response to an electrical stimulus, in part due to body habitus; therefore, each subject will be tested with a signal strength determined by their response (visible, painless contraction) to the stimulation (generally between 12 and 20 mA) of an uninvolved nonpainful muscle, usually the Trapezius.

Study Design This is an Institutional Review Board-approved, randomized controlled study of 40 patients (20 MPDD and 20 MP) presenting to the New York University Langone Medical Center, Pain Management Center with chronic low back or neck pain. Screening Forty-five patients suffering from back and/or neck pain and seeking treatment were considered potential candidates. The inclusion and exclusion criteria were reviewed to confirm candidacy, (see Table 1). If patients were considered to be good candidates based on the initial interview, the study Table 1

Subject selection

Inclusion Criteria

Exclusion Criteria

20–70 years of age

Severe systemic musculoskeletal disease or advanced degenerative joint disease resulting in extremely limited range of motion Any contraindications to trigger point injections (including, but not limited to: bleeding disorders and allergy to Lidocaine Any skin or nearby tissue conditions (i.e., inflammation, rash, tumors.)

History of at least 3 months of back and/or neck pain Willing to comply with the study procedures Able to provide written consent

Able to demonstrate understanding of the risks and the device

History of severe psychiatric or neurological disease that could compromise assessment and data collection History of any systemic disease that could potentially risk participation in the study History of substance abuse Pacemaker or defibrillator implanted Participation in an investigation trial within 30 days prior to the screening visit Current involvement in any other pain intervention treatment (i.e., physical therapy, chiropractic treatment, acupuncture)

3 and its purpose were explained. All potential benefits and risks were carefully described prior to signing the consent. If the patients met all of the inclusion criteria and none of the exclusion criteria, the patient was accepted into the study and randomized to one of the two diagnostic groups. The patients were given a Memorial Pain Assessment Card and an Oswestry Disability Questionnaire to fill out.

Pretreatment Functional Assessment Patients were assessed for their range of motion (ROM) by a physical therapist blinded to the randomization. Patients were measured in either the lumbar or cervical region depending upon the location of their complaint. Measurements included flexion, extension, and lateral flexion. Rotation was also measured for cases involving cervical complaints. Randomization and Examination The randomization sequence for the method of examination utilized, MP vs MPDD, was designed by an independent study coordinator, who had no interaction with the subjects. The sequence of randomization was created at the beginning of the study and was designed to have 20 patients enrolled in each group, 40 overall. The sequence was numbered 1–40 and each number would correspond the patient in order of their recruitment to the study. For example, if the prearranged sequence were randomized to be 1) MP, 2) MPDD, and 3) MPDD, the first patient recruited would end up in the MP group, the second in the MPDD group and the third in the MPDD. If a patient was excluded, the study coordinator recorded the method of intended group assignment. As each patient was excluded, his/her intended assignment was then re-inserted into the remainder of the sequence at a random location by the study coordinator, unknown to the examiner. For example, if a subject was intended to be MP and was subsequently excluded, an additional MP assignment was inserted randomly at some point in the remaining, unrevealed sequence. All patients were examined by the Principal Investigator (PI). Upon completion of the aforementioned screening and assessments, the PI would examine the patient utilizing MP and record the muscles identified. At this point, the group assignment of MP vs MPDD was revealed. The randomization was revealed only to the PI and would remain blinded from all other clinicians and study participants for the remainder of the

4 study. The subjects were not aware which examination technique was considered experimental or control. If the patient were assigned to the control group, the findings recorded with MP prior to revealing the group assignment would be used. If the clinical findings with MP revealed that 1–3 muscles required injections, the patient would continue to the treatment phase and receive the injections according to the protocol described below. If no muscles were identified, it was assumed the patient’s pain was not muscle related and therefore excluded from the study. Should four or more muscles be identified, these subjects were not allowed to participate in the study because they would have required more treatment than the protocol could provide. However, they did receive treatment according to existing standards of care at the NYU Pain Management Center. At this point the exam would end and the patient would proceed to the injection phase. If the assignment revealed MPDD, the patient would now be examined with the MPDD and evaluated based on the criteria mentioned below. Using the sites of a positive identification with MP, MPDD would then be used and the muscle site to be injected would be determined by the results of the MPDD evaluation and not the MP evaluation. Use of the MPDD can elicit three diagnostic outcomes, which are based on the clinical observations and functional classifications of muscle pain by Dr. Hans Kraus [11]. 1. No pain: The muscle(s) being stimulated are not experienced as painful by the patient. The conclusion is that the contraction of the muscle(s) does not produce pain and therefore muscle(s) are not a contributing source of the pain syndrome of which the patient complains. 2. Pain with stimulation that disappears with continued or repeated stimulation: In this case the pain is determined to be the result of pain from tension, stiffness, or spasm. All of these are considered reversible pain producing functional changes in muscle(s), demonstrated by stimulating the muscle(s) to the production of pain and then having the pain disappear. Conservative methods such as electrical stimulation, massage or exercise, may all suffice to eliminate the pain originating in that particular muscle identified by MPDD. 3. Pain that persists with continuous or repeated stimulation. Should the patient continue to have pain with repeated stimulation, it is sur-

Hunter et al. mised that continued use of this muscle (either artificially with electrical stimulation or through voluntary activity) would produce pain, because there are histological changes such as trigger points, within the muscle, that produce painful contractions. Subjects with pain that persisted with continuous or repeated stimulation occurring in 1–3 muscles were considered as the Study Group subjects and were injected according to the protocol described below. Subjects found to have four or more muscles with trigger points were not allowed to participate in the study because they would have required more treatment than the protocol could provide. However, they did receive treatment according to existing standards of care at the NYU Pain Management Center.

Injection Patients in the MPDD group with outcome no. 3 and MP group with 1–3 muscles identified would advance to the injection phase. A blinded physician who was only aware of what muscles to inject, not the method used to diagnose, performed the injections. The technique outlined by Travell and Simons was used as the basis for the injection protocol [13]. Two cc of 1% lidocaine were injected via a 25-gauge needle into each muscle identified in a starburst pattern to maximize the area treated. Post-Treatment Functional Assessment One week after the injection(s), the treating physician performed a physical assessment, interviewed the patient for any complications as a result of the device and or injection(s), any changes in pain medication, and administered another Memorial Pain Assessment Card (which now included perceived pain relief) and an Oswestry Disability Questionnaire. The physical therapist re-assessed the range of motion, still unaware of the diagnostic group. Long-Term Follow-up Assessment One month after the injection(s), the subject returned for another physical assessment and interview with the investigator, exam by the physical therapist for range of motion, and was given another Memorial Pain Assessment Card (that included perceived pain relief and satisfaction in the study) and an Oswestry Disability Questionnaire. Data Analysis The Memorial Pain Assessment Card utilized a visual analog scale (VAS) for mood, pain, pain


New Muscle Pain Detection Device

Figure 2 Self-reported verbal pain assessment. (0—No pain, 1—Just noticeable, 2—Weak, 3—Mild, 4—Moderate, 5—Strong, 6—Severe, 7—Excruciating.) All P values were calculated using Mann–Whitney U-test evaluating changes from baseline in each group. *P ⱕ 0.05; **P ⱕ 0.001.

relief, and study satisfaction. The patient was asked to record their answers along a 10 cm line. The position of the “x” was measured and the changes in the distance were used as the basis for analysis. The Memorial Pain Assessment Card also contained a verbal rating scale (VRS) for pain intensity, which we termed the “Verbal Pain Assessment” (Figure 2). The choices were: no pain, just noticeable, weak, mild, moderate, strong, severe, and excruciating, in a random assortment and the subjects were asked to circle the word that best described the severity of their pain. For analytical purposes, each word was assigned a value from 0–7, with “No Pain” being zero to “Excruciating” being seven. The Oswestry Disability Questionnaire was scored according to standard guidelines. The range of motion values provided by the physical therapist were recorded in degrees. The Oswestry Disability Questionnaire, VAS and VRS pain scores were analyzed for statistically significant improvements using the Mann– Whitney U-test to account for skewness. These criteria were also analyzed for statistical significance of interval change using a paired t-test. The perceived pain relief and overall satisfaction in the study were analyzed for statistical significance using a student t-test. Finally, the range of motion scores were analyzed using the Mann–Whitney U-test to also account for skewness. P values ⱕ0.05 were deemed statistically significant. Results

In order to get the 40 enrolled patients (20 in each group), 45 patients were initially approached for

the study. Among 24 patients assigned to the MPDD group, four needed to be excluded: one had no muscles suitable for injection identified by the device (outcome no. 2), and another three left the study by their own choice. In the MP group, one patient was assessed and injected prior to the Pretreatment Functional Assessment, thus excluded from further study, leaving 20 valid patients in that group. There were no complications experienced in any patients in either group over the course of the study. Patients who completed the study made all scheduled follow-ups except two (1 MPDD and 1 MP). These patients missed the 1-week follow-up, however they were available for a phone interview and were faxed the Memorial Pain Assessment Card and Oswestry Disability Questionnaire. The forms were returned at the 1-month follow-up visit. The examination for muscles that would benefit from injection revealed 45 muscles with MP (mean per patient 2.25 and SD 1.11) and 46 muscles (mean 2.3 and SD 0.8) with the device in the MPDD group. Of the 45 muscles found by MP, 11 (24%) had no pain with the MPDD and in 19 (42%), the pain disappeared within 1 minute of continuous stimulation; 15 (33%) were confirmed by the MPDD as injectable sites. There were 31 muscles recorded in the MPDD group that were not identified by MP (Table 2). In the MP group, 41 total muscles were identified for injection. The mean number of muscles found by MP did not differ between the patients assigned to MPDD and the MP controls (P = 0.513).

Pain, Pain Relief, Mood, Oswestry, and Satisfaction in the Study Despite the randomization, there was a group difference observed in the verbal pain assessment and VAS pain scores at the screening with the MPDD group having higher values for baseline pain (P < 0.002); however, there was no significant difTable 2

Characteristics of groups

Sex Male Female Mean age (SD) Mean duration of pain in years (SD) Mean N of muscles found by MP (SD)




7 13 48.3 (13) 5.86 (8.6)

7 13 53.8 (11.8) 6.4 (6.81)




MPDD = Muscle pain detection device; MP = manual pressure.

0.168 0.83 0.513

6 Table 3

Hunter et al. Mean scores at screening

Self-reported verbal pain assessment (SD) Self-reported VAS pain score (SD) Self-reported mood score (SD) Oswestry disability score (SD) ROM—Flexion (SD) ROM—Extension (SD) ROM—Left lateral flexion (SD) ROM—Right lateral flexion (SD)



P value

4.85 67.1 59.9 41.9 59.4 17.4 17.7 19

3.8 45.2 59.6 38.7 52.5 27.8 24.5 23.8

0.002 0.002 0.963 0.559 0.289 0.075 0.03 0.121

(1.03) (19.42) (22.55) (19.34) (22.22) (11.03) (6.22) (5.62)

(0.95) (22.4) (23.65) (14.42) (18.1) (21.67) (11.65) (10.71)

P-values calculated using two sample t-test. ROM = range of motion; MPDD = muscle pain detection device; VAS = visual analog score.

ference observed in mood or the Oswestry Disability Questionnaire at the screening—(Table 3). The MPDD group reported significantly greater improvements in pain (verbal [both time points] and VAS [1 month; Figure 3]), mood (both; Figure 4) and Oswestry Disability scores (1 month; Figure 5) when compared to the control group—(Tables 3 and 4). When asked to account on their perceived pain relief, the patients

Table 4 Memorial pain card assessment: mean changes from baseline Screening to 1 Week

Screening to 1 Month

Self-reported verbal pain assessment—mean change MPDD (SD) -2.35 (1.84) -3.1 (2.02) Control (SD) -0.85 (1.5) -0.05 (1.43) P value 0.0123 0.0001 Self-reported VAS pain score—mean change MPDD (SD) -35.06 (34.8) Control (SD) -12.75 (35.78) P value 0.659 Self-reported mood score—mean change MPDD (SD) 23.57 (26.67) Control (SD) 4.85 (24.45) P value 0.0468 Oswestry disability score—mean change MPDD (SD) -12.15 (14.71) Control (SD) -13.295 (18.35) P value 1.0

-42.86 (30.93) 5.8 (27.03)