Muscle:Intercostal Muscles

Intercostal muscles occupy the spaces between adjacent ribs and serve dual roles in respiration and postural stabilisation of the thoracic spine. Because their trigger points (TrPs) produce chest pain that worsens with breathing, coughing, and sneezing, they are frequently misattributed to cardiac or pleuropulmonary pathology. When intercostal TrPs are active, even quiet breathing can become painful, and the resulting voluntary breath-restriction may itself perpetuate the TrPs.

The intercostals are uniquely well suited to thoracic rotation — a function that is often overlooked clinically. Respiratory demand takes precedence over postural activity, but when the two functions are compatible they reinforce one another; when they conflict, respiration inhibits rotation. This means that restricted rotation of the thoracic spine is a cardinal sign of intercostal TrP involvement, not merely a musculoskeletal coincidence.

Anatomy

There are eleven external and eleven internal intercostal muscles on each side. The external and internal layers cross each other at nearly a right angle — a crisscross arrangement analogous to the external and internal abdominal obliques, and mechanically similar to the successive plies of an automobile tyre.

External intercostal muscles — fibres run obliquely inferomedially when viewed from the front, and obliquely inferolaterally when viewed from behind. They do not extend quite the full length of each intercostal space, reaching only to the costal cartilage anteriorly (except between the lowest ribs). Anteriorly, the external intercostal is replaced by the external intercostal membrane, which reaches to the sternum.

Internal intercostal muscles — fibres run in the reverse direction to the external fibres. They extend anteriorly from near the sternum but are incomplete posteriorly, represented medially only by the internal intercostal membrane. The internal intercostal muscles are absent medial to the angle of the ribs posteriorly.

Innermost intercostal muscles (subcostalis) — variant deep fibres with a nearly identical direction to the internal intercostals. The neurovascular bundle (intercostal nerve, artery, and vein) runs between the internal and innermost layers, protected by a slight overhang of the inferior margin of the more cephalad rib.

Parasternal (intercartilaginous) internal intercostals — fibres attaching to the cartilaginous part of the ribs anteriorly. These have a distinctly different function from the interosseous internal intercostal muscles: they are muscles of inhalation, not exhalation.

Each muscle spans the distance between two ribs (or costal cartilages).

Primary functions: Respiration (see Muscle:Diaphragm for overall mechanics) and thoracic rotation. External intercostals on the left side and internal intercostals on the right side both rotate the trunk to the right; the reverse combination rotates the trunk to the left.

Innervation: Each intercostal muscle is supplied by several branches of the corresponding intercostal nerve — a classic example of segmental innervation.

Referred Pain Patterns

TrPs in intercostal muscles refer pain locally in the region of the TrP and tend to refer pain along that interspace toward the front, away from the vertebral column, rather than toward the back. The more posteriorly the TrP is located, the stronger its tendency to refer pain toward the front. More severe TrPs may refer pain that includes interspaces above and below the TrP.

Intercostal TrP pain is:

• Aching, localised to a rib interspace
• Aggravated by deep inhalation, coughing, or sneezing
• Increased with thoracic side-bending away from the affected side
• Somewhat relieved by bending toward the painful (TrP) side

Cardiac arrhythmia — including auricular fibrillation — may depend on an arrhythmia TrP sometimes located in intercostal muscles on the right side. When this occurs, cardiac arrhythmia is one symptom of intercostal TrPs.

Activation and Perpetuating Factors

• Trauma: Gross or local impact trauma to the chest wall; rib fracture
• Surgery: Chest surgery, including use of chest retractors during thoracotomy (a significant cause of painful intercostal TrP clusters); open heart surgery via sternal incision is more likely to cause pectoralis major and minor TrPs than anterior intercostal TrPs
• Excessive coughing: Repeated coughing induces enthesopathy at muscle attachments and activates TrPs, especially in expiratory muscles. A coughing spell can be excruciating. Chronic cough perpetuates both intercostal and diaphragmatic TrPs
• Herpes zoster: Patients with herpes zoster are prone to developing intercostal TrPs that contribute significantly to pain and are treatable. The neurogenic pain of herpes is typically a shooting pain responsive to Tegretol, while TrP pain is a localised ache that persists despite Tegretol but responds to TrP therapy
• Intrathoracic lesions: Pneumothorax, pyothorax, and pleural effusion secondary to tumour — associated TrPs are likely to involve the last three intercostal muscles and produce posterolateral low chest pain
• Paradoxical breathing: A chronic perpetuating pattern — see Corrective Actions below
• Postural factors: Head-forward, slumped posture; restriction of rib mobility from any cause

Clinical Examination

Postural Assessment

Inspect the chest for symmetry of expansion during respiration. Assess for paradoxical breathing — abdominal paradox (abdominal wall moves inward rather than outward during inhalation) is a serious perpetuating factor for all respiratory muscle TrPs.

Narrow rib interspaces are visible evidence of tense intercostal muscles and restricted excursion on the affected side. Thoracic side-bending toward the side opposite the TrPs tends to be painful.

The patient with intercostal TrPs is unable to raise the arm straight up on the affected side without pain, because full arm elevation opens the intercostal spaces on that side and stretches fascial tissues over the chest wall.

Range of Motion Assessment

• Rotation of the thoracic spine — restricted in one or both directions by intercostal TrPs
• Deep inhalation — painful; vital capacity is likely reduced because TrPs painfully restrict deep inhalation or full exhalation
• Full exhalation — test separately; painful full exhalation suggests diaphragmatic TrP involvement (see Muscle:Diaphragm)

Trigger Point Examination

Begin by examining the rib cage for abnormally narrow rib interspaces that indicate tense intercostal muscles. The patient typically describes pain along a narrowed interspace if active intercostal TrPs are responsible.

Run the palpating finger between the ribs for the full length of the suspected segment. Intercostal TrPs are usually located anterolaterally or posterolaterally, and less commonly in the extreme anterior and posterior portions of the muscle.

Parasternal internal intercostal muscles: These should be carefully investigated in cases of suspected costochondritis and Tietze syndrome, as TrPs in these muscles may be responsible for these syndromes.

Hiccup TrP: A TrP located posteriorly between ribs 4 and 5, close to the rhomboid minor muscle, has been observed to initiate a hiccup when pressed before TrP injection, but not following injection.

Differential Diagnosis

Condition	Distinguishing features
Lower rib articular dysfunction	Best treated by inactivating TrPs, rib-mobilising muscle stretch, or indirect (functional) techniques; TrPs should be included as another cause of the symptoms
Intercostal muscle spasm	Muscle tension caused by TrPs is commonly mistaken for spasm; Blumer considered intercostal muscle spasm one of the most common, generally unrecognised, benign causes of chest pain
Costochondritis / Tietze syndrome	May be caused by TrPs in the parasternal internal intercostal muscles; Calabro et al. clearly differentiated these two conditions
Fibromyalgia	When intercostal pain is widespread (multiple bilateral TrPs), fibromyalgia should be considered; unilateral intercostal TrPs are more typical of myofascial pain
Cardiac arrhythmia	An arrhythmia TrP in the right intercostal muscles may produce or mimic cardiac arrhythmia
Myocardial infarction, tumour, pleural effusion, pyothorax	Must be ruled out; if intercostal TrPs respond poorly to treatment, imaging of the chest and search for other conditions is strongly indicated
Herpes zoster	Intercostal TrPs commonly develop in conjunction with herpes zoster; TrP pain is a localised ache that persists despite antineuralgic therapy but responds to TrP treatment
Thoracic radiculopathy	Should be included in the differential diagnosis
Peptic ulcer / gallbladder disease	Presumptive diagnoses of atypical chest pain with negative studies should include myofascial TrPs in the differential diagnosis

Treatment

Trigger Point Release — Upper Thorax

For TrPs in intercostal muscles of the upper thorax (ribs 2–5):

1. Patient lies supine
2. The clinician places one hand medial to the vertebral border of the scapula, contacting the appropriate affected ribs posteriorly, and applies pressure in a cephalad direction with the fingers
3. The other hand is positioned anteriorly over the affected ribs, applying downward pressure that resists rib elevation when the patient inhales
4. During the exhalation phase, the clinician assists rib depression, utilising respiration to augment release of the tense intercostal muscles
5. An alternate position has the patient's arm in elevation

Direct techniques (TrP pressure release, deep stripping massage) are effective for essentially all intercostal muscles. Spray and stretch — vapocoolant spray applied over the involved muscles, fully covering the TrP area and the entire zone of pain and tenderness — followed by stretch using postisometric relaxation enhanced by coordinated respiration, is also effective.

Trigger Point Release — Lower Thorax

For TrPs in lower intercostal muscles (ribs 11 and 12):

1. Patient lies supine with the arm on the affected side positioned upward and reaching over the head
2. One hand of the clinician spans the lateral aspect of the patient's lower ribs; the other hand is placed in the patient's axillary region for stabilisation
3. The patient takes a deep breath; during exhalation, the clinician applies gentle downward (caudally directed) pressure on the patient's lower ribs
4. As the patient inhales, the examiner resists elevation of the lower ribs; as the patient exhales, the examiner's downward pressure facilitates depression and release of the lower ribs
5. The patient is instructed to reach overhead toward the opposite shoulder during exhalation, which accentuates the stretch of both the intercostal muscles and the latissimus dorsi
6. The stretch cycle is repeated until release is satisfactory

This technique is sometimes called "lower rib release" and can also be used to release TrP tension in the latissimus dorsi muscle.

Trigger Point Injection

Injection of intercostal muscles can be effective with proper precautions to prevent pneumothorax, but should be attempted only by those who have already become very skilful in the injection of TrPs. Injection should NOT be considered until non-invasive techniques have been exhaustively explored and proven unsuccessful, and until perpetuating factors including chronic cough have been corrected.

Hong technique (recommended): The syringe is held with the wrist and ulnar side of the injecting hand resting solidly on the patient's rib cage, so that any unexpected movement by the patient would move that hand with the body, preventing unintended advancement of the needle into the pleura.

Key procedural points:

• Patient placed in supine or sidelying position; pillows ensure comfort
• Guide hand placed on the chest wall with two fingers straddling the TrP on adjacent ribs
• 27-gauge needle on a 5 ml syringe loaded with 0.5% procaine or lidocaine
• Needle angled close to the chest wall, no more than 45° from the skin surface
• Do not proceed beyond a second barrier of fascial resistance (usually less than 5 mm beyond the first barrier)
• Monitor for local twitch response to confirm effectiveness

If the lung is penetrated (pneumothorax), the patient typically notices a salty taste in the mouth, is likely to cough, and may become short of breath. Auscultation reveals a lack of breath sounds on the injected side. This requires emergency medical treatment.

Corrective Actions

For lasting relief, the patient must be instructed to correct paradoxical breathing, which is very common in this group and can be responsible for TrPs. Lasting relief cannot be realised until normal coordinated respiration has been restored.

• Restore normal breathing pattern: The patient should learn to use normal coordinated respiration with attention to normal lateral lower rib movements
• Erect posture: Head-forward, slumped posture must be corrected
• Avoid unnecessary chest binders: Intercostal TrPs are aggravated and perpetuated by restriction of rib movement. If a chest binder is required, it should be removed for 5 minutes approximately every 3 hours to reestablish intercostal muscle function
• Control chronic cough: The source of the cough must be controlled before lasting relief is possible

Satellite Trigger Points

• Diaphragm — TrPs in both the diaphragm and intercostals are commonly co-active; chronic cough and paradoxical breathing perpetuate both
• Pectoralis Major — the arrhythmia TrP near the right intercostal region
• Serratus Anterior — spot tenderness where serratus anterior attaches to ribs may represent enthesopathy secondary to serratus TrPs rather than primary intercostal TrPs
• Latissimus Dorsi — lower rib release technique also releases latissimus TrP tension

Related Pages

• Muscle:Diaphragm — co-active with intercostals; diaphragmatic TrPs produce referred pain to shoulder and costal margin
• Muscle:Pectoralis_Major — overlapping chest pain zone; arrhythmia TrP
• Muscle:Serratus_Anterior — related TrPs at rib attachments
• Muscle:Scalene/Anterior, Muscle:Scalene/Middle, Muscle:Scalene/Posterior — primary muscles of inhalation; co-active with upper intercostals
• Muscle:Abdominal_Oblique — antagonists during exhalation; crisscross anatomy analogous to intercostals

References

• Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 2: The Lower Extremities. Baltimore: Williams & Wilkins; 1992. Chapter 45.