Injection in the Cervical Facet Joint for Shoulder Pain With Myofascial Trigger Points in the Upper Trapezius Muscle

Shoulder/Elbow

By Chien-Tsung Tsai, MD, MSc; Lin-Fen Hsieh, MD; Ta-Shen Kuan, MD, MS; Mu-Jung Kao, MD; Chang-Zern Hong, MD
ORTHOPEDICS 2009; 32:557

Abstract

The goal of this double-blinded, randomized, controlled study was to confirm the effectiveness of the cervical facet joint injection in treating shoulder pain with the myofascial trigger point in the upper trapezius muscle secondary to cervical facet lesion. Eighty-nine patients with chronic unilateral shoulder pain due to myofascial trigger points in the upper trapezius muscle received an injection to the C4-5 facet joint in the experimental group and to the corresponding unilateral multifidi muscle in the control group. Subjective pain intensity and pressure pain threshold of the myofascial trigger point were assessed, and the prevalence of endplate noise in the myofascial trigger point region was measured in 28 patients before, immediately after, and 1 month after the injection.

Half of the patients in the experimental group, but none of the control patients, reported being completely pain free 1 month after the injection. Both the decrease in the pain intensity and the increase in pressure pain threshold were significantly more in the experimental group than in the control group either immediately or 1 month after the injection. There was no significant difference in the change of endplate noise prevalence between the 2 groups.

This study demonstrates that intra-articular or peri-articular injection into the cervical facet joint region can effectively inactivate the upper trapezius myofascial trigger point secondary to the facet lesion.

Shoulder pain in the upper trapezius region is a frequent complaint in clinical practice.¹ In most cases, >1 myofascial trigger points can be identified in the upper trapezius muscles, and inactivation of the myofascial trigger points may provide complete relief of shoulder pain.¹

A myofascial trigger point is the most sensitive spot in a taut band of skeletal muscle.¹ Nearly every normal adult has latent myofascial trigger points that are tender but not spontaneously painful. A non-painful latent myofascial trigger point can become an active painful myofascial trigger point in response to a soft tissue lesion near or remote to it via central sensitization (increase of the sensitivity in the central pain pathway of this myofascial trigger point, elicited by the irritable impulse from another source).^2-4 An active myofascial trigger point is painful spontaneously or during movement.¹ There are many sensitive loci (probably sensitized nociceptors) in a myofascial trigger point region.^2,4,5

Endplate noise can be recorded from a myofascial trigger point region more frequently than from a non-myofascial trigger point site.^6,7 Endpoint noise is non-propagated potentials due to excessive leakage of acetylcholine in a dysfunctional endplate associated with myofascial trigger point.^6,7 It has been demonstrated that the irritability of a myofascial trigger point is inversely proportionate to the pressure pain threshold^8,9 and directly proportionate to the prevalence of endplate noise in that myofascial trigger point region.¹⁰ A painful myofascial trigger point of the upper trapezius can be inactivated immediately after a myofascial trigger point injection; however, the pain frequently recurs a few weeks after the injection if the underlying lesion that causes the activation of the myofascial trigger point is not eliminated.

It has been suggested that a facet joint lesion of the cervical spine, especially at the C4-5 or C5-6 level, is one of the important causes of shoulder and/or scapular pain.^11-13 Previous studies have indicated that the pain from the C4-5 facet joint may refer or traverse to the shoulder region.^14-16 In many cases, the pain of the myofascial trigger point in the upper trapezius muscle can be elicited or aggravated by rotating the neck to the painful side, followed by extending the neck backward (stimulation to the ipsilateral cervical facet joints, mainly at the C4-5 and C5-6 levels).^11,12,14,17 An injection to the C4-5 and/or C5-6 facet joints can provide long-term relief of shoulder pain.^11,12 Cervical facet joint injection, either intra-articularly or peri-articularly, has been applied in treating pain in the neck region, and sometimes the shoulder pain referred from a facet joint if the pain is caused by a facet joint lesion, but the effectiveness is still controversial.^18-20 Therefore, this double-blinded, controlled study was designed to assess the effectiveness of the cervical facet joint injection in treating shoulder pain of facet joint origin.

Materials and Methods

General Design

Patients with unilateral shoulder pain with active myofascial trigger points in the upper trapezius muscle and who met the criteria (listed in the next section) were recruited for this study. Intra-articular or peri-articular injections to the involved C4-5 facet joint were given to patients in the experimental group, and local injections to the multifidus muscle in the painful side at the same vertebral level were given to patients in the control group. The subjective pain intensity, the pressure pain threshold, and the prevalence of endplate noise in the myofascial trigger point region of the upper trapezius were measured before, immediately after, and 1 month after the injection. Since neither the patients nor the examiners doing outcome assessments were aware of group assignment, the study was considered double-blinded.

Patients

Patients with unilateral shoulder pain were recruited for the study. Inclusion criteria included: (1) having chronic pain in the shoulder region for >3 months with poor responses to any previous treatment; (2) having no previous cervical facet joint injection; (3) having a myofascial trigger point in the ipsilateral upper trapezius muscle; (4) having positive provoking tests (both facet irritation tests and facet compression tests) to irritate the ipsilateral C4-5 facet joint to reproduce or aggravate the patient’s complaint; (5) having no treatment for such pain other than physical therapy and/or oral nonsteroid analgesics within 1 month prior to the study; (6) having no contraindication for needling of the neck, such as bleeding tendency, local infection in the neck region, serious medical problems, recent neck or upper back trauma (within 1 month), or pregnancy; (7) having no condition such as cognitive deficit or substance abuse (including alcohol) that may interfere with the assessment of pain intensity or pain threshold; (8) having no thick subcutaneous fat in the neck (so that the facet joint could be palpated); (9) having no neurological deficit in the upper limbs based on neurological examination and electrodiagnostic tests; (10) having no destructive lesion, severe sclerotic lesion, or disk herniation with cervical spinal cord compression on radiographs or magnetic resonance imaging (MRI); and (11) having had no previous surgery to the neck region. After signing the approved consent form, which was approved by the Institutional Review Board, the selected patients were randomly divided into 2 groups: experimental and control.

Identification of Myofascial Trigger Point

Diagnosis of a myofascial trigger point is based on the most sensitive, tender spot in a palpable taut band and on recognized pain when the sensitive spot is compressed.^21,22

Provoking Tests for Diagnosis of Facet Joint Lesion

Cervical facet irritation test. When the patient turned his or her head to the side with pain, followed by extension of the neck, pain in the upper trapezius myofascial trigger point was aggravated. This was considered a positive facet sign. To increase the degree of irritation to the C4-5 facet, the examiner’s index finger was placed just below the C4-5 facet joint before the rotation–extension movement of the neck. If the pain got stronger, this was considered a positive C4-5 facet sign.

Cervical facet compression test. When the ipsilateral C4-5 facet joint was compressed with the examiner’s finger, pain in the myofascial trigger point of upper trapezius could be aggravated. This was considered a positive facet compression test. The ipsilateral C5-6 facet joint was also compressed. If the shoulder pain elicited by C5-6 facet compression was stronger than that elicited by C4-5 facet compression, the patient was excluded from this study.

Identification of C4-5 facet joint by palpation. The patient was in a side-lying position (lateral decubitus) with a pillow to support the head and neck on the nonpainful side (Figure 1). The pressure between the pillow and the supporting surface of the neck and head was as evenly distributed as possible. The neck was in the neutral position from the C5 to C7 levels, but slightly bending to the nonpainful side (downward) from the C4 up to the C2 level. In this way, a mild convex curve in the symptomatic side could be noticed. Then the physician who gave the facet injection put the index finger of his nondominant hand on the clavicle head of the sternocleidomastoid muscle at the C4-5 level, and then slid it backward slowly and deeply (to separate the scalenus medius muscle anteriorly and the levator scapulae muscle posteriorly) until the transverse process could be palpated. Then his finger was moved in a longitudinal direction (up and down) to feel the most prominent site (facet joint). In this way, the lowest level of facet joint that could be palpated was the C5-6 facet, and the C4-5 facet was 1 level above.

Figure 1: Positioning for cervical facet joint injection.

Injections

For all patients in both groups, a solution containing 1.0 mL of triamcinolone (40 mg/mL) and 1.0 mL of 1% lidocaine was prepared for injection. A 3-mL syringe and a #27 needle (diameter 0.4 mm) with a length of 1.25 inches were used for injection.

Cervical facet joint injection for the experimental group. When the C4-5 facet joint was identified, the index finger of the physician’s nondominant hand would remain unmoved to guide the needle (Figure 2). After sterilization, the needle penetrated the skin at a site 1 to 2 mm above the C4-5 facet joint at an angle aimed toward the C4-5 facet joint. The syringe was held gently with the thumb and long finger of the physician’s dominant hand, similar to Hong’s technique for myofascial trigger point injection.¹ The index finger was on the non-needle end of the syringe to withdraw and push the solution (Figure 3). The needle was moved slowly toward the C4-5 facet joint until it encountered the bone. Then the needle was pulled out slightly (approximately 1 mm) and reinserted in any direction (but avoiding the anterior direction beyond the facet margin) to another point approximately 0.5 to 1.0 mm from the last insertion site. This procedure was repeated continuously in a sequence to map the depth of the structures at and near the facet joint.

Figure 2: Posteroanterior (left) and lateral (right) views of palpation and injection of the facet joint and the location of the needle tip.

Figure 3: Control of the syringe: withdrawal (left) and injection (right).

When a narrow dip (facet joint or near facet joint) could be felt, the solution in the syringe was pushed into this space. In our clinical experience, approximately 0.5 to 1.0 mL of solution can be injected into the facet joint with no significant resistance. If the solution could not be pushed out from the syringe due to a strong resistance, this procedure was repeated until the solution could be injected without resistance. However, if the dip space (facet joint) could not be identified in 10 attempts of needle placement, the solution was injected into the most prominent portion of the palpable facet region. This would be a peri-articular injection. In many cases, the patient reported a sharp pain sensation when the needle encountered the facet joint. This technique requires delicate feeling on the accurate location of the needle tip via the sensation of the thumb and index finger that held the syringe. The remaining solution was discarded after injection.

In a pilot (unreported) study by our group, C4-5 facet joints of 8 patients were injected by 1 physiatrist using this palpation technique, and also under simultaneous fluoroscopic observation by an experienced radiologist. In all cases, the accurate location of the needle tip had also been confirmed by this radiologist once the physiatrist reported an accurate position of the needle tip.

Cervical deep paraspinal muscle injection for the control group. To avoid injection at the facet joint, the ipsilateral C4-5 facet joint was identified and compressed with the index finger of the physician’s nondominant hand during the whole procedure. Similar to facet joint injection, the index finger remained unmoved to guide the needle. After sterilization, the needle penetrated the skin at a site approximately 2 to 3 mm above the C4-5 facet joint. Then the needle was moved in a direction at least 3 mm away from the C4-5 facet joint. When the needle tip reached a depth closed to the bone, 1.0 mL of the solution was injected into the multifidus muscle. The needle was moved in and out 3 to 5 times before being withdrawn from the skin. The remaining solution was discarded after injection.

Post-injection care. Immediately after the injection, the injected region including the facet joint and the site of needle penetration was compressed firmly to avoid post-injection bleeding, the major cause of post-injection soreness,^5,23 for at least 3 minutes. The patient was allowed to take non-steroid analgesic medicine for post-injection pain or any residual myofascial pain as necessary.

Assessments

Subjective assessment of pain intensity. Pain intensity was subjectively reported by the patient using a numerical pain scale from 0 to 10, with 0 representing no pain and 10 representing the worst imaginable pain. The patient was also informed that a value of pain intensity <5>

Assessment of the pressure pain threshold. The pressure pain threshold measurement procedure recommended by Fischer^24,25 was used in this study. The patient was in a comfortable sitting position and encouraged to maintain complete relaxation. The procedure was explained to the patient clearly, then the identified myofascial trigger point of the upper trapezius muscle was marked so that the 3 consecutive measurements could be performed over the same area. A pressure algometer was used to measure the pressure pain threshold. This pressure algometer was applied on this marked area with the metal rod perpendicular to the surface of the skin. The pressure of compression was increased gradually at a speed approximately 1 kg/sec. The patient was asked to report any distinct increase of pain or discomfort. The compression stopped as soon as the patient reported pain, and the reading on the algometer was recorded as a pressure pain threshold value. The patient was asked to remember this level of pain or discomfort at that point and to apply the same criterion for the next measurement.

Three repetitive measurements at an interval of 30 to 60 seconds were performed at each site. The average values of the 3 pressure pain threshold readings were used for data analysis. Three well-trained examiners (C.T., T.K.) performed this measurement. The same patient was examined and measured by the same examiner for all measurements at different times. The examiners were blinded regarding whether the patients were in the experimental or control group.

Assessment of the prevalence of endplate noise in the trigger point region. A 4-channel electromyography machine was used to record the electrical activity in the myofascial trigger point region with disposable monopolar Teflon-coated electromyography needle electrodes. The first channel recorded the electrical activity from the active electrode (experimental needle electrode) in the myofascial trigger point region. The reference needle electrode was placed in a site approximately 3 to 4 cm from the myofascial trigger point. The second channel recorded the electrical activity from the control site. For the control recordings, the active recording electrode was place in a non-myofascial trigger point region outside the endplate zone. The reference electrode was connected to the reference electrode of the first channel through a bridge connector to form a common reference electrode. A ground electrode was placed on the skin near the recording sites. For both channels, the sensitivity of recording was set at 20 µV per vertical division, and the spread speed was set at 10 milliseconds per horizontal division. The high frequency filter was set at 10 kHz and the low frequency filter at 20 Hz.

The procedure to assess the endplate noise prevalence was similar to that used in previous studies.^6,7 The active recording needle electrode was inserted progressively into the myofascial trigger point region. The needle was advanced gently and slowly through the least possible distance (usually 1 to 2 mm) by simultaneously rotating the needle to facilitate smooth entry through the tissue. After 5 thrusts (advancements of the needle in 1 track), the needle was pulled out to the original insertion depth and reinserted in a slightly different direction (a near track). This procedure was repeated again to explore a total of 25 thrusts (5 thrusts/insertions × 5 insertions). All occurrences of endplate noise were recorded. Three well-trained examiners performed this measurement. The same patient was examined and measured by the same examiner for all measurements at different times. The examiners were blinded regarding whether the patients were in the experimental or control group.

Statistical Methods

The mean and standard deviation of the values measured for pain intensity, pressure pain threshold, and endplate noise prevalence were calculated. An analysis of variance was used to assess the differences among the data before, immediately after, and 1 month after injection, and also the differences between the 2 groups. The changes in pain intensity, pressure pain threshold, and endplate noise prevalence after injection were further normalized as follows: percentage of changes=[(post-treatment data–pre-treatment data)/pre-treatment data]×100%. After data normalization, the differences in the changes of pain intensity, pressure pain threshold, and endplate noise between the 2 groups were compared with a Student t test. For all statistical analysis, the confidence interval was set at 95% (P<.05).

Results

Eighty-nine patients met the inclusion criteria, signed the consent forms approved by the Institutional Review Board, and completed the whole course of the 1-month study. As shown in Table 1, the experimental group consisted of 46 patients and the control group consisted of 43 patients. There were no statistical differences in the mean age, mean duration of onset, and causes of shoulder pain between the 2 groups.

Changes in Subjective Pain Intensity in the Experimental Group

As listed in Table 2, 12 patients in the experimental group reported being pain free immediately after the injection. Only 1 of these 12 patients had pain intensity increase to 1 on the 10-point scale 1 month later, and the rest remained pain free. Besides these 12 pain-free patients, an additional 12 patients reported being pain free 1 month after the injection. Half of the patients in the experimental group were pain free 1 month after the injection, and only 9% of patients still had intolerable pain (pain intensity >5).

Changes in Subjective Pain Intensity in the Control Group

No patients in the control group reported being pain free either immediately after or 1 month after the injection (Table 2). In fact, the majority of patients in the control group reported pain (pain intensity >5).

Comparison of Changes in Subjective Pain Intensity Between the Two Groups

Table 3 shows the comparison of changes in pain intensity between the 2 groups before and after the injection. In the experimental and control groups, there was a significant decrease in pain intensity immediately after and 1 month after the injection (P<.05). However, in comparing the difference in the percentage of change (decrease in pain intensity) between the experimental and control groups, the mean pain intensity reduced significantly more (P<.05) in the experimental group than the control group, both immediately after and 1 month after the injection.

Changes in Pressure Pain Threshold

The mean values of pressure pain threshold in both the experimental and control groups before and after the injection are listed in Table 4. There was a significant increase in pressure pain threshold in the experimental group (P<.05) but not in the control group (P>.05) either immediately after or 1 month after the injection. Comparing the difference in the percentage of change (increase in pressure pain threshold) between the experimental and control groups, the mean pressure pain threshold increased significantly more (P<.05) in the experimental group than the control group, both immediately after and 1 month after the injection.

Changes in Prevalence of Endplate Noise

The mean values of endplate noise prevalence in both groups before and after the injection are listed in Table 5. There was a significant decrease in endplate noise prevalence in the experimental group (P<.05), but not in the control group (P>.05) immediately after the injection. However, 1 month after the injection there was no significant change in endplate noise prevalence compared to the value before the injection in either the experimental or the control group. There was no significant difference in the percentage of changes in endplate noise prevalence between the experimental and the control groups either immediately after or 1 month after the injection (P>.05).

Comparison Between Intra-articular and Peri-articular Injections in the Experimental Group

In the experimental group, 6 patients (3 men and 3 women, average age 48.0±11.4 years) who also had degenerative facet joints were injected peri-articularly rather than intra-articularly. They all reported a significant improvement, with pain intensity <3>

Adverse Effects

Only patients with poor responses to the injection required nonsteroid analgesic medicine. No significant adverse effects other than post-injection soreness for a few hours were observed in all patients.

Discussion

This study demonstrates the short-term therapeutic effectiveness of C4-5 facet joint injection in treating ipsilateral shoulder pain with myofascial trigger points in the upper trapezius muscle secondary to cervical facet lesion. The effect lasted for at least 1 month.

Possible Mechanism of Shoulder Pain Relief After Cervical Facet Joint Injection

The mechanism of cervical facet injection for pain relief is unclear.¹⁹ The cervical facet joint is innervated by the medial branch of posterior rami of the cervical root.²⁶ There are nociceptors in the cervical facet joint capsules,^27,28 especially in the posterolateral capsules.²⁸ When the facet joint is injured or inflamed, the facet nociceptors may transmit the nociceptive information to the brain via the spinal cord. In the spinal cord, the sensory impulse may also transmit to other dorsal horn neurons of other receptive fields. Similar to the mechanism of referred muscle pain suggested by Mense,^29-31 it may also cause referred pain in other sites, such as the shoulder. Therefore, the upper trapezius myofascial trigger point can be activated via central sensitization. This is the probable mechanism of the referred shoulder pain from a C4-5 facet joint lesion.

Evidence exists of the association between active myofascial trigger points and lesions of non-muscular origin, such as osteoarthritis of knee,³² cervical disk lesion,³³ or cervical facet lesion.¹³ Chiropractic adjustment³⁴ or local injection¹¹ of the cervical facet joint could inactivate the myofascial trigger points. Bogduk and Simons¹³ have suggested that facet nociceptors and myofascial trigger point nociceptors may be connected in the spinal cord and may use the same nociceptive pathway to the higher center. Therefore, when the pain in the facet joint is suppressed, the pain due to myofascial trigger point can also be controlled, and vice versa. However, we found no case in the literature of cervical facet joint pain completely controlled with a myofascial trigger point injection of the upper trapezius muscle. Furthermore, if the pain in the upper trapezius myofascial trigger point is not elicited by the cervical facet lesion, the pain relief in the myofascial trigger point region should not last long after the facet joint injection. In fact, long-term relief of a myofascial trigger point pain could be observed in this study (longer than 1 month) and in a previous case report (longer than 1 year).¹¹

During physical examination, provoking tests to irritate the related level of the facet joint can elicit pain in the myofascial trigger point region, but stimulation of the associated myofascial trigger point can rarely induce pain in the correlated facet joint. Therefore, facet dysfunction may be one of the important causes to activate remote myofascial trigger points. This study has further supported the importance of treating the underlying etiological lesion for long-term relief of myofascial pain due to myofascial trigger points.^3,12

This study also demonstrated immediate pain relief after the facet injection. Theoretically, the anti-inflammatory effect from a local steroid injection is not an immediate process. The immediate pain relief may be related to hyperstimulation analgesia from the needle stimulation, similar to myofascial trigger point injection or acupuncture.^3,12,35 Strong stimuli to nociceptors may elicit strong neural impulses to the spinal cord interneurons, including the hypothetic myofascial trigger point circuit of a myofascial trigger point,^3,12 to inhibit the cycle of pain and thus provide immediate pain relief. Therefore, in addition to the anti-inflammatory effect, a local steroid injection may also provide a hyperstimulation analgesic effect.

Changes in Pressure Pain Threshold and Endplate Noise Prevalence

In this study, improvement in the myofascial trigger point irritability estimated with pressure pain threshold was significantly more in the experimental group than in the control group. However, the change in endplate noise prevalence was only temporary. It is likely that the mechanism of pain relief after the facet injection is a central (spinal cord level) desensitization process with little, if any, influence on the myofascial trigger point itself. Therefore, after the facet joint injection, the irritability of myofascial trigger point measured peripherally with endplate noise prevalence is still high, although the pain sensation is reduced via the central desensitization. However, the assessment of pressure pain threshold depends on a subjective report of pain and can be influenced by the central desensitization process.

Technique Issues

The facet joint injection technique in this study could be blinded visually, but was not blinded for the identification of the facet joint by palpation (tactile sensory feedback). Using this technique, we injected the facet joint from lateral and posterior approaches. In an animal study, it was found that more nociceptors could be identified in the dorsolateral aspect of the cervical facet joint than other sites.²⁸ This technique is less time consuming, results in less radiation exposure, and is less expensive.

By using the compression/palpation technique (Figure 3), a shorter needle can be used, and thus less tissue destruction would be expected. No serious side effects (such as an injection into the spinal cord or the vertebral artery) would be expected if the procedure were performed carefully. One important concern is that multiple insertions of the needle may cause extensive tissue damage; however, if the side movement of the needle can be avoided, tissue damage can be minimized. In fact, even under the guidance of fluoroscopy^18,19 or ultrasound,³⁶ the chance of one-time insertion into the facet joint is also not high. In our practice, we could usually reach the facet joint with fewer than 5 needle insertions, and sometimes with 1 insertion. Post-injection soreness was mild and temporary (<12>3 minutes.

The major problem with this technique is the requirement of a high skill of palpation on the facet joint. Not every physician is well trained in this technique. Another problem is the difficulty in palpation on the neck of a patient with thick subcutaneous fat. Such patients would be excluded from receiving an injection with this technique.

Conclusion

This study demonstrates that a facet joint injection, either intra-articularly or peri-articularly, at the C4-5 level using a careful palpation technique may effectively suppress shoulder pain with upper trapezius myofascial trigger points due to facet lesion immediately after the injection and possibly for 1 month afterward. The study also supports the hypothesis that the myofascial trigger point in the upper trapezius muscle can be caused by a cervical facet lesion at the C4-5 level.

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Authors

Dr Tsai is from the Department of Rehabilitation Medicine, Da Chien General Hospital, Miao-Li City, Dr Hsieh is Department of Physical Medicine and Rehabilitation, Shin Kong Wu Ho-Su Memorial Hospital School of Medicine, Fu Jen Catholic University, Taipei, Dr Kuan is from the Department of Physical Medicine and Rehabilitation, College of Medicine, National Cheng-Kung University, Tainan, Dr Kao is from the Department of Rehabilitation Medicine, Taipei City Hospital, Taipei, and Dr Hong is from the Department of Physical Therapy, Hung-Kuang University, Sha Lu, Taichung, Taiwan.

Drs Tsai, Hsieh, Kuan, Kao, and Hong have no relevant financial relationships to disclose.

Correspondence should be addressed to: Chang-Zern Hong, MD, Department of Physical Therapy, Hung-Kuang University, 34 Chung-Chie Rd, Sha Lu, Taichung 433, Taiwan.

DOI: 10.3928/01477447-20090624-04