Muscle:Diaphragm

The diaphragm is the primary muscle of inhalation in humans, generating 70–80% of the inhalation force during quiet breathing. Its trigger points (TrPs) produce referred pain in two distinct patterns depending on whether the central dome or the peripheral costal fibres are involved — a distinction that reflects the dual innervation of the muscle. Diaphragmatic TrPs are a clinically underrecognised cause of persistent chest pain, dyspnoea, and the "stitch in the side" experienced during vigorous exercise.

Because the diaphragm is inaccessible to direct manual palpation, its TrPs are identified by clinical history, motion testing, and response to indirect release techniques rather than by direct trigger point localisation. Presumptive diagnoses of diaphragmatic spasm, undiagnosed atypical chest pain, and negative studies for peptic ulcer or gallbladder disease should all include diaphragmatic TrPs in the differential diagnosis.

Anatomy

The diaphragm is a dome-shaped musculofibrous structure that separates the thoracic and abdominal cavities. The dome of the diaphragm is a central tendon surrounded by muscle fibres that form an extended "skirt" attaching peripherally to the circumference of the inferior thoracic outlet.

The muscle is divided into three portions by attachment:

• Sternal portion — anteriorly, attaches to the xiphoid process
• Costal portion — laterally, attaches to the costal margin (ribs 7–12)
• Lumbar (crural) portion — posteriorly, attaches by two muscular crura to the bodies of the upper lumbar vertebrae; also attaches to two bilateral arcuate ligaments spanning from the vertebral transverse processes to the 12th rib

The diaphragm is penetrated by the aorta, vena cava, and oesophagus. The arcuate ligaments provide passage posteriorly for the psoas major and quadratus lumborum muscles.

Primary function: Inhalation. Contraction of the diaphragm depresses the dome (piston-like motion), increasing the vertical diameter of the thoracic cavity and reducing intrathoracic pressure, drawing air into the lungs. The diaphragm also elevates and spreads the lower costal margin when support and resistance are supplied to the central tendon by the abdominal contents.

Motor innervation: Exclusively via the phrenic nerves, which originate in the third, fourth, and fifth cervical segments (C3–C5).

Sensory innervation: Dual — the central dome is supplied by the phrenic nerve (C3–C5); the peripheral costal fibres are supplied by the lower six intercostal nerves (T7–T12). This difference in innervation explains the two distinct referred pain patterns.

Fibre types: Approximately 42% type I (slow twitch, oxidative) and 58% type II (fast twitch) fibres. The diaphragm has practically no muscle spindles, unlike the intercostal muscles.

Referred Pain Patterns

Central Dome (Phrenic Innervation)

Stimulation of the central (peritoneal/caudal) surface of the diaphragm refers pain to the upper border of the ipsilateral shoulder, in the region of the anterior border of the upper trapezius muscle, about halfway between the acromion and the base of the neck. This pattern is mediated by the phrenic nerve (C3–C5) and follows the same pathway as referred pain from diaphragmatic irritation of any cause (e.g., subphrenic abscess, haemoperitoneum). Pain intensity from central dome stimulation is sharply localised.

Peripheral Costal Fibres (Intercostal Innervation)

Stimulation of the peripheral margin of the diaphragm refers a diffuse aching pain to the region of the adjacent costal margin. The patient typically indicates the area with a hand placed transversely over the lower ribs and over the right hypochondrium.

The difference in quality and location of pain referred from the central compared to the peripheral parts of the diaphragm reflects the marked differences in their innervation and in the spatial resolution of the tendon and muscle nociceptors.

Exercise-related "Stitch in the Side"

During vigorous exercise, diaphragmatic TrPs can produce the pain commonly described as a stitch in the side — a deep anterolateral pain felt in the region of the lower border of the rib cage. The pain tends to be aggravated by continued exercise and relieved by rest. Patients with diaphragmatic TrPs are prone to develop this pain at the end of a full exhalation, when the diaphragm fibres are most stretched.

Activation and Perpetuating Factors

• Vigorous or prolonged exercise: Rapid walking, running, sustained aerobic activity
• Persistent cough: A coughing spell can be excruciating when diaphragmatic TrPs are present; enthesopathy develops at the attachments of the expiratory muscles. Chronic cough perpetuates both diaphragmatic and intercostal TrPs
• Surgery: Gastrectomy and other abdominal or thoracic procedures
• Emotional stress: Psychic distress can precipitate diaphragmatic spasm and eliminate diaphragmatic function, blocking both the pump-handle and bucket-handle movements of the thorax. Increased diaphragmatic muscle tension caused by TrPs would produce the same effect and would also be aggravated by emotional stress
• Paradoxical breathing: A fundamental perpetuating pattern that must be corrected for lasting relief — see Corrective Actions below
• Hyperinflation of the lungs: As in obstructive lung disease; places the diaphragm at a serious disadvantage and can reverse its effect on the costal margin

Clinical Examination

Postural Assessment

Assess for head-forward, slumped posture, which restricts normal diaphragmatic excursion. Check for paradoxical breathing — the hallmark perpetuating sign that demands priority correction. When paradoxical breathing is present, priority should be given to effective correction of this abnormal breathing pattern, both during initial therapy and at follow-up visits.

Respiratory Motion Testing

Full exhalation test: Pain from diaphragmatic TrPs tends to be most intense at the end of a full exhalation when the diaphragm fibres are maximally stretched. Assess for painful full exhalation (diaphragmatic TrPs) and compare with painful deep inhalation (intercostal TrPs).

Augmented stretch test: To increase the sensitivity of testing, the patient can increase stretch tension on the diaphragm near full exhalation by vigorous contraction of the abdominal muscles. If the abdominal musculature is weak, the patient can apply external pressure to the abdomen to increase intra-abdominal pressure, forcing the diaphragm upward. This manoeuvre must be performed during continued exhalation to keep the glottis open. Vigorous coughing at nearly complete exhalation can also induce pain from diaphragmatic TrPs.

Trigger Point Examination

The mid-fibre central TrPs of the diaphragm are not directly accessible to palpation, as they are located inside the thoracic cage.

Attachment TrPs at the costal portion of the diaphragm are detectable just inside the lower border of the thoracic cage. Tenderness in this region could originate in the diaphragm, the external oblique, internal oblique, or transversus abdominis muscles — careful examination is required to distinguish these.

Distinguishing diaphragmatic from abdominal TrP tenderness: Test whether pain and tenderness are increased by stretching the abdominal muscles (protruding the abdomen) or by stretching the diaphragm (compressing the abdomen near full exhalation). Pain on full inhalation (abdomen protruded, transversus stretched) is more likely from transversus TrPs; pain on full exhalation (abdomen pulled in, diaphragm stretched) is more likely from diaphragmatic TrPs.

Differential Diagnosis

Condition	Distinguishing features
Diaphragmatic spasm	Muscle tension and pain in the absence of true spasm are cardinal features of TrPs; "diaphragmatic spasm" may in many cases represent TrP-generated muscle tension without EMG-confirmed spasm
Peptic ulcer	Negative upper GI studies with persistent symptoms should prompt consideration of diaphragmatic TrPs
Gastroesophageal reflux	Diaphragmatic TrPs should be included in the differential when reflux symptoms are atypical or treatment-resistant
Gallbladder disease	Atypical right-sided chest or upper abdominal pain with negative studies; right-side unilateral diaphragmatic TrPs characteristically refer pain in or near the right hypochondrial region
Atypical chest pain / precordial catch / xiphoidalgia / slipping rib syndrome	Atypical chest pain in the lower sternal area has been shown to be due to a TrP in the diaphragm muscle in at least one characteristic case
Subphrenic or intraperitoneal irritation	Pain referred to the shoulder via the phrenic nerve mimics central dome diaphragmatic TrP referral — distinguish by clinical context (fever, peritoneal signs)
Rectus abdominis TrPs	Diaphragmatic TrPs can be satellites to TrPs in the upper portion of the rectus abdominis on the same side
Transversus abdominis TrPs	Pain on full inhalation (abdomen protruded) is more likely from transversus TrPs; pain on full exhalation is more likely diaphragmatic

Treatment

Diaphragm Release — Indirect Manual Technique

The diaphragm is inaccessible to direct manual therapy techniques such as direct TrP pressure release. However, the costal attachment TrPs can be released by the following technique:

1. Patient is supine; the clinician stands at the patient's side opposite the muscle to be released (e.g., at the patient's right side for release of the left part of the diaphragm)
2. Both hands are placed anteriorly at the lower border of the patient's rib cage
3. The patient is instructed to breathe in normally and then breathe out slowly
4. During exhalation, the clinician's thumbs follow the diaphragm in and under the ribs, then lift the rib cage anteriorly — this is the actual release phase
5. Additional release occurs on subsequent respiratory cycles
6. This procedure is also helpful for releasing lower intercostal muscle trigger points

Postisometric relaxation variation: One hand is placed on the epigastrium and the other under the upper lumbar spine. The operator gently assists exhalation with pressure applied between the hands, asks the patient to hold the exhalation for several seconds, then gently resists inhalation. This encourages successively smaller lung volumes with each breath, producing progressive lengthening of diaphragm fibres.

Vapocoolant spray applied to cover the margin of the lower rib cage where the costal diaphragm fibres attach can precede the manual release technique.

Self-Release of Diaphragm (Patient Home Technique)

1. Patient lies supine with hips and knees flexed to relax the abdominal musculature
2. The patient hooks his or her fingers under the lower ribs of the affected side and then inhales deeply in a slow, relaxed manner
3. During slow exhalation, the patient's fingers follow the diaphragm in and under the ribs, then apply upward traction on the ribs for the actual release
4. This self-stretch procedure also helps to release lower intercostal muscle trigger points

Gravity-assisted stretch: In the head-down position, gravity pushes the abdominal contents toward the chest, producing a gravity-assisted stretch of the diaphragm that is enhanced during full exhalation. Increasing intra-abdominal pressure by voluntary contraction of the abdominal muscles, application of hand or arm pressure to the abdomen, or bending the body forward on exhalation can provide additional stretch.

Maximum elevation of the diaphragm is achieved in the supine position by letting the breath out completely and then contracting the abdominal muscles, placing the diaphragm on maximum passive stretch with some additional help from reciprocal inhibition.

Trigger Point Injection

Needle penetration in the diaphragm region is hazardous due to the great danger of producing a pneumothorax. Injection of the diaphragm is usually unnecessary, extremely dangerous, requires an unusual combination of skills, and is probably not very effective because only attachment TrPs are within reach.

If subcostal tenderness is clearly not from abdominal TrPs and mobilisation manoeuvres are not helpful, then one who is sufficiently skilled and properly equipped can consider injection of attachment TrPs of the diaphragm at the costal margin. The technique is similar to that used for needle EMG recordings of diaphragm motor unit activity.

Important: Injection techniques can only reach attachment TrPs. The endplate zone where the central TrPs are located is a horseshoe-shaped line running midway between the peripheral end of each fibre and its attachment onto the central tendon. Subcostal injection of Botulinum Toxin A would therefore be essentially useless and is seriously hazardous.

Corrective Actions

For lasting relief of diaphragmatic TrPs, the patient must be instructed to correct paradoxical breathing. It is important for full recovery of normal function to retrain these patients to use normal coordinated respiration.

• Restore normal breathing pattern: Training is usually effective when a skilled clinician combines tactile monitoring with appropriate verbal feedback. The clinician should help the patient become aware of normal lateral lower rib movements
• Erect posture: Head-forward, slumped posture needs to be corrected
• Control chronic cough: When a patient has a chronic cough, it must be controlled before lasting relief from TrPs in respiratory muscles can be obtained

Satellite Trigger Points

• Intercostal Muscles — commonly co-active; chronic cough and paradoxical breathing perpetuate TrPs in both muscles
• Rectus Abdominis — diaphragmatic TrPs can be satellites to TrPs in the upper portion of the rectus abdominis on the same side
• Scalene (Anterior) — primary muscle of inhalation; co-active with diaphragm

Related Pages

• Muscle:Intercostal_Muscles — co-active with diaphragm; intercostal TrPs produce pain worsened by deep inhalation
• Muscle:Rectus_Abdominis — key satellite relationship
• Muscle:Scalene/Anterior, Muscle:Scalene/Middle, Muscle:Scalene/Posterior — primary inspiratory muscles; must be assessed alongside diaphragmatic TrPs
• Muscle:Abdominal_Oblique — primary muscles of exhalation; commonly co-active with diaphragmatic TrPs
• Pain:Chest — diagnostic algorithm including diaphragmatic TrPs as a cause of chest pain
• Pain:Shoulder — central dome TrP referral to the ipsilateral shoulder

References

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