Serratus anterior muscle with common trigger point. Image based on web open-source material: https://www.quora.com/What-causes-side-stitch-while-running-and-what-are-good-ways-to-deal-with-this-pain
General and musculoskeletal physical exam findings in a patient with a serratus anterior trigger point may include reduced chest wall expansion, rounded shoulder posture, and limited scapular adduction with disruption of scapulohumeral rhythm. The palpatory portion of the examination for TPs is performed using either the flat technique in which the taut band of the trigger point is compressed between the examiner’s finger and underlying bone or the pincer technique in which the affected tissue is held between the clinician’s finger and thumb. The minimum criteria for identification of an active trigger point are the presence of a taut band with exquisite spot tenderness and patient-recognized pain . Such findings are expected along the upper two-thirds of the midaxillary line around the fifth or sixth rib with referred pain expected in the distribution previously described when the TP is in the serratus anterior muscle.
44.2.3 Diagnostic Studies
There is no specific laboratory test, imaging study, or intervention for diagnosing trigger points, although the use of ultrasonography, electromyography, thermography, and muscle biopsy have been studied as potential diagnostic tools. The diagnosis relies on careful palpation, but there remain no research-validated diagnostic criteria . Depending on the study, the most reliable physical exam indicators are presence of a taut band associated with tenderness or presence of a jump sign and pain referral patterns [6, 7].
Initial treatments for trigger points include prescription of oral nonsteroidal anti-inflammatory medications for improved analgesia, and activity modification to eliminate chronic overuse or stress in the affected muscle. Spray and stretch techniques are commonly employed to inactivate trigger points, relieve muscle spasm, and reduce referred pain . This technique involves spraying either dichlorodifluoromethane-trichloromonofluoromethane or ethyl chloride spray topically to produce temporary anesthesia, which then allows the muscle to be passively stretched to interrupt the chronic contraction and break the vicious cycle perpetuating the TP. For spray and stretch of the serratus anterior, the patient lies on the uninvolved side with the back to the clinician and the upper arm extended. This initiates a stretch of the muscle which can be further increased by the clinician placing the scapula in greater adduction and by the patient taking a deep breath to enlarge the lower rib cage . One effective self-stretch of the serratus anterior requires the patient to sit sideways on a chair with the affected side toward the backrest with the arm on the affected side positioned over the backrest. The patient then rotates the upper trunk in the opposite direction toward the front of the chair . The ultimate goal of such manual methods is to train the patient to effectively self-manage their pain .
Alternatively, or if failure with manual techniques occurs, a more invasive approach utilizing trigger point injection (TPI) can provide prompt symptomatic relief. Contraindications to TPI include anticoagulation or bleeding disorders, local or systemic infection, allergy to anesthetic agents, acute muscle trauma, or extreme fear of needles [1, 10]. The patient should be positioned in a comfortable position, preferably recumbent to minimize muscle tension at the site of injection and protect against injury from fall should the patient have a vasovagal reaction. For serratus anterior injection, this is the same position as for spray and stretch with the patient side lying with the unaffected side on the examination table and the arm extended posteriorly. Typically a 22-gauge, 1.5-in. needle is sufficient to reach the trigger point. Most often, a solution of 1% lidocaine is injected, but other substances such as diclofenac, botulinum toxin type A, and corticosteroids have been used, but are associated with myotoxicity [1, 11]. First, the trigger point is identified and prepped to establish a sterile field. The practitioner then inserts the needle 1–2 cm away from the TP and advances it at an angle of 30° to the skin. Proper technique when injecting muscles of the chest wall requires fixing the TP against the rib between two fingers and directing the needle tip directly toward the rib to avoid deeper than intended penetration through the intercostal space resulting in a pneumothorax. To confirm that the needle has not entered a blood vessel or lung, negative pressure should be applied to the syringe while observing for withdrawal of blood or air. Once satisfied, a small amount of injectate is delivered. Then, the needle is withdrawn to the level of the subcutaneous tissue and redirected to a different region of the TP. This process is repeated superiorly, inferiorly, laterally, and medially until the local twitch response is no longer elicited or resisting muscle tautness is no longer perceived . Stretching the affected muscle group immediately after injection can help increase the efficacy of TPIs.
44.2.5 Complications of Treatment
Potential complications of TPI include vasovagal syncope, skin infection, needle breakage, hematoma formation, and pneumothorax. Although rare, the consequences of a pneumothorax can be devastating if not identified and treated in a timely fashion.
A pneumothorax may occur spontaneously, often in cases of underlying lung pathology such as chronic obstructive pulmonary disease, tuberculosis, cystic fibrosis or severe asthma, or due to trauma. Traumatic causes may either be iatrogenic (as in this case) or non-iatrogenic such as with penetrating chest trauma, rib fractures, and barotrauma during flight or while diving. Other common iatrogenic causes of pneumothorax include thoracentesis, transthoracic needle biopsy, central venous subclavian vein catheterization, transbronchial lung biopsy, intercostal nerve block, suprascapular nerve block, nasogastric tube placement, cardiopulmonary resuscitation, and positive pressure ventilation [12–15].