Muscle:Serratus Posterior

Serratus Posterior Superior and Serratus Posterior Inferior are two thin, quadrilateral muscles of the posterior thorax that serve opposite respiratory functions — the superior assists inhalation, the inferior assists exhalation and rib stabilisation. Both lie deep to the more superficial back muscles (trapezius, rhomboids, latissimus dorsi) and are therefore palpated through overlying layers. Neither causes nerve entrapment. Their trigger points (TrPs) are clinically important primarily because the referred pain patterns mimic serious conditions including cervical radiculopathy (superior) and renal disease (inferior), leading to diagnostic confusion and unnecessary investigation.

Anatomy

Serratus Posterior Superior

• Origin: Dorsal midline fascia from C6 through T2 (or T3)
• Insertion: Cranial borders of ribs 2–5, by four digitations; number of digitations is variable
• Fibre orientation: Approximately 45° to horizontal, inclined inferolaterally
• Layering: Lies immediately beneath the rhomboids; both rhomboid and serratus posterior superior lie beneath the trapezius. The iliocostalis and longissimus thoracis lie deep to its paraspinal portion.
• Innervation: Anterior primary divisions of spinal nerves T1–T4
• Function: Elevates ribs 2–5 to expand the chest during inhalation; acts synergistically with the diaphragm, intercostals, levator costae, and scalenes

Serratus Posterior Inferior

• Origin: Aponeurosis from spinous processes of T11–L2
• Insertion: Inferior borders of ribs 9–12, just medial to their angles, by four digitations; digitations to ribs 9 and 12 are sometimes absent; rarely the entire muscle is absent
• Layering: Lies beneath the latissimus dorsi
• Innervation: Anterior primary divisions of thoracic spinal nerves T9–T12 (not posterior divisions — important: it is not a paraspinal muscle)
• Function: Depresses the lower ribs; stabilises ribs 9–12 against the upward pull of the diaphragm during inhalation; unilateral contraction contributes to trunk rotation; bilateral contraction extends the lower thorax. EMG studies have not confirmed a clear respiratory function — the stabilisation role is the most clinically accepted.
• Functional unit: Acts synergistically with iliocostalis and longissimus thoracis of the same side for rotation and extension; acts with quadratus lumborum as an accessory exhalation muscle

Referred Pain Patterns

Superior: Referred Pain

The dominant TrPs in the serratus posterior superior are attachment TrPs (ATrPs) at the rib insertions, accessed only when the scapula is fully abducted.

Essential zone (bold — must be present):

• Deep ache under the upper portion of the scapula — perceived as deeper than middle trapezius TrP5 pain; the patient typically reaches back with the opposite arm but cannot touch the area because the scapula covers it
• Posterior border of the deltoid and long head of triceps brachii

Spillover zone (may be present):

• Entire triceps region with accent at the olecranon process of the elbow
• Ulnar side of the forearm, hand, and all of the little finger (5th digit)
• Pectoral region anteriorly (occasionally)

Referred neurological phenomena:

• Referred numbness into the C8–T1 distribution of the hand — this is referred sensation, not a true neurological deficit; no objective motor or reflex deficit is present

Inferior: Referred Pain

Essential zone:

• Diffuse aching discomfort over and around the muscle itself — lower thoracic region, spreading across the back and over the lower ribs
• Pain is relatively local compared to the superior muscle

Spillover zone:

• Occasionally perceived as extending through the chest anteriorly

Character: An annoying, persistent ache rather than a severely threatening pain. Patients often recognise the pain as muscular in origin. Squirming and stretching provide some transient relief.

Note: Maximal deep inhalation and coughing do not typically provoke pain from serratus posterior inferior TrPs — this distinguishes it from serratus anterior, quadratus lumborum, and deep abdominal wall TrPs, which are provoked by these manoeuvres.

Activation and Perpetuating Factors

Superior Activation

Respiratory overload — the primary mechanism:

• Prolonged or repeated coughing (pneumonia, asthma, chronic emphysema)
• Paradoxical breathing — diaphragm and abdominal muscles working out of phase, which reduces tidal volume and forces the accessory inspiratory muscles to compensate; see Assessment and Perpetuating Factors

Postural and mechanical overload:

• Sitting for long periods writing at a high desk with shoulders elevated and rotated forward
• Repeatedly reaching to the rear of a high work surface (e.g. laboratory technicians)
• Scoliosis — protrusion of the thorax against the scapula
• Side-lying on the ipsilateral side — the scapula presses against the attachment TrPs
• Reaching forward with outstretched hands

Inferior Activation

• Acute back strain — the primary trigger; typically occurs during combined lifting, turning, and reaching
• Standing on a ladder with the back hyperextended to reach overhead
• Paradoxical breathing
• Lower limb length discrepancy (perpetuating factor — maintains chronic postural strain)

Clinical Examination

Superior: Trigger Point Examination

Critical prerequisite: The scapula must be fully abducted to access the TrPs. In the resting position, the ATrPs are entirely covered by the scapula and are not palpable.

Patient positioning:

• Seated, leaning slightly forward with the arm hanging forward and down on the side to be examined, OR
• With the homolateral hand placed in the opposite axilla — this fully abducts the scapula, making the ATrPs accessible

Palpation technique:

• The serratus posterior superior is palpated through the overlying trapezius and rhomboid muscles — a taut band is therefore unlikely to be palpable through two muscle layers
• A TrP is identified as a spot of exquisite deep tenderness when palpated against an underlying rib
• Snapping palpation of the overlying trapezius may produce local twitch responses in the superficial horizontal trapezius fibres — these are distinguished by their horizontal fibre direction from the deeper obliquely oriented serratus and rhomboid fibres
• Confirmatory sign: Pressure on either a central TrP or ATrP reproduces the patient's familiar referred pain pattern — this is the key diagnostic confirmation

Scapula position:

• In normal rest position: ATrP is inaccessible (covered by scapula)
• With scapula abducted: ATrP accessible, palpated against rib

Inferior: Trigger Point Examination

Palpation technique:

• Flat palpation across the direction of the muscle fibres
• Central TrPs (CTrPs) — midfibre spot tenderness is usually identifiable
• ATrPs — exquisite tenderness at the lateral rib attachments is typically the more readily located finding
• A nodule in a taut band may be difficult to palpate through or distinguish from the overlying latissimus dorsi muscle
• Local twitch responses are difficult to elicit and detect by palpation, but may be felt during TrP injection

Movement restriction:

• Patients may have slight restriction of thoracolumbar flexion and spinal extension
• May be limited in rotating the torso away from the painful side

Provocative manoeuvres:

• Maximal inhalation and coughing typically do not reproduce pain (distinguishing feature — see Referred Pain Patterns above)
• Deep inhalation and coughing provoke pain from serratus anterior, quadratus lumborum, and deep abdominal wall muscles — use this distinction when differentiating

Associated articular dysfunction:

• The most common articular dysfunction associated with serratus posterior inferior TrPs is a simple neutral dysfunction extending from T10 to L2
• Occasionally a concurrent depression or "exhalation" dysfunction of the lower four ribs is found

Differential Diagnosis

Superior Differential

The referred pain and numbness pattern of the serratus posterior superior is the most common myofascial mimic of C8–T1 radiculopathy in clinical practice.

Condition	Must-have distinguishing features	Serratus posterior superior TrP features
C7–C8 radiculopathy	Objective neurological deficit (motor weakness, reflex change, positive Spurling's, dermatomal sensory loss on examination)	No primary neurological deficit; TrP tenderness, palpable bands, and referred pain evoked by muscle pressure are absent in true radiculopathy
Thoracic outlet syndrome	Positive vascular and neural provocative tests; see Differential:ThoracicOutletSyndrome	No vascular signs; no objective motor deficit
Ulnar neuropathy	Objective weakness and wasting of intrinsic hand muscles (C8–T1); positive elbow/wrist compression tests; reduced nerve conduction velocity	Referred numbness only — no weakness, no wasting, normal nerve conduction
Olecranon bursitis	Localised swelling and fluctuance at the olecranon; positive bursal compression; no referred scapular pain	No bursal swelling; pain extends from scapula to elbow, not isolated to olecranon
Scapulocostal syndrome	Enthesopathy at the lateral rib attachments — the serratus posterior superior TrP pattern overlaps considerably; may represent the same pathophysiology	ATrPs in the serratus posterior superior cause enthesopathy at the same lateral digitation attachments to the ribs

Key clinical rule: A true radiculopathy does not cause TrP tenderness, palpable bands, or referred pain evoked by pressure applied to the muscle. When all three are present, the diagnosis is myofascial — not radiculopathy.

Articular dysfunction: Associated dysfunction typically occurs at the T1 level. There is usually exquisite tenderness over the spinous process of T1, and on inspection the presentation is one of regional extension of the upper thoracic spine with inability to flex forward across the involved segments.

Scalene TrPs: The TrPs in the serratus posterior superior lie within the pain reference zone of the synergistic scalene muscles. Scalene TrPs may mimic, in part, the pain pattern of the serratus posterior superior. Always examine the neck for scalene TrPs if a serratus posterior superior TrP is found.

Inferior Differential

Condition	Must-have distinguishing features
Renal disease (caliectasis, pyelonephritis, ureteral reflux)	Urinalysis abnormalities; renal tenderness on percussion (costovertebral angle); systemic features; imaging findings
Lower thoracic radiculopathy	Objective dermatomal sensory change; positive nerve root provocation; imaging correlation
Articular dysfunction T10–L2	Segmental joint tenderness; restricted intersegmental movement; may coexist with TrPs

Note on symptom sequence: The serratus posterior inferior TrP ache is characteristically noticed only after successful treatment of TrPs in the adjacent major back muscles (iliocostalis, longissimus thoracis). If a patient reports a residual nagging lower thoracic ache after paraspinal treatment, suspect this muscle.

Treatment

Superior Treatment

Trigger point release:

Spray and stretch technique (Fig. 47.5 in T&S):

1. Patient seated with upper thoracic spine flexed and arm supported in a forward position to swing the scapula laterally (abducted)
2. Apply vapocoolant spray (or ice strokes) in slow parallel sweeps laterally downward over the muscle fibres, then outward over the shoulder and down the arm to cover the 5th digit — cover the full referred pain pattern
3. Manual release using postisometric relaxation: have the patient look up to one side and breathe in; as the patient looks down and slowly breathes out, the operator takes up slack in the muscle. One hand stabilises the spinous processes; the other applies light steady pressure downward and laterally directly on the rib cage medial to the scapula.

Trigger point pressure release:

• Effective for central TrPs that lie directly over a rib
• Most effective when the muscle is on moderate (non-painful) stretch
• The position of placing the arm across the chest with the hand in the opposite axilla is useful for examination but should not be used for treatment — this position tends to elevate, rather than lower, the rib cage and prevents full relaxation of the chest musculature

TrP injection: See Concept:Trigger_Point_Injection.

• Significant pneumothorax risk — must be performed with precautions and adequate skill
• Patient lies on the opposite side with scapula fully abducted
• TrP is precisely located and fixed with fingers against the underlying rib
• Needle directed nearly tangent to the skin and at all times toward a rib — never toward an intercostal space
• The Hong method of syringe grip is recommended
• Following injection: patient flexes upper thorax forward during inhalation and takes three slow full-range breaths; spray and stretch repeated; moist heat applied

Home programme:

• Supine over a tennis ball placed under the interscapular region, with the scapula sufficiently abducted — allows self-applied TrP pressure release
• A companion may be taught to apply TrP pressure release

Inferior Treatment

Trigger point release:

Manual release with respiratory augmentation (Fig. 47.9 in T&S):

1. Patient side-lying on the opposite side with the ipsilateral arm elevated overhead (this pulls the rib cage upward and rotates the torso to take up slack)
2. Preliminary application of serial sweeps of vapocoolant spray in the direction of the muscle fibres, covering the entire muscle and pain zone
3. Release begins: patient looks up to the affected side and breathes in
4. As the patient looks down, slowly breathes out, and reaches toward the floor with the elevated arm, the operator takes up slack
5. One hand stabilises the lower thoracic and upper lumbar spinous processes; the other applies light steady pressure upward and laterally directly on the lower rib cage
6. During the stretch phase, the operator may place one finger directly on the TrP and apply light pressure release simultaneously

TrP pressure release: Responds well; see Concept:Apropos_Treatment.

TrP injection: See Concept:Trigger_Point_Injection.

• Recommended only for those experienced in TrP injection
• Patient side-lying; needle angled toward ribs 9–12 depending on the digitation involved
• Penetration between ribs must be avoided — pneumothorax risk
• Injection characteristically elicits palpable local twitch responses and affords prompt relief
• After injection: stretch and spray, moist heat applied

Patient Education

Breathing pattern correction (both muscles):

• Coordinated chest and abdominal breathing must be established; paradoxical breathing perpetuates both superior and inferior TrPs
• See Concept:Perpetuating_Factors for breathing normalisation protocol

Posture (both muscles):

• Normal lumbar lordosis must be maintained both standing and sitting
• When seated: an appropriately sized lumbar pillow in the small of the back, then lean back so the pillow maintains both lumbar and thoracic curves without muscle strain
• Standing: normal lordotic lumbar curve

Scoliosis and leg length (inferior):

• Lifts to correct compensatory scoliosis caused by a small hemipelvis when sitting, or by a lower limb length discrepancy when standing — see Concept:Perpetuating_Factors

Seating:

• Chairs that fit with adequate lumbar support
• Desk height appropriate — avoid sustained shoulder elevation

Sleep:

• Firm mattress — a mattress that sags perpetuates inferior TrPs

Satellite Trigger Points

Satellites of Serratus Posterior Superior

Scalenes → Serratus posterior superior (key satellite relationship):

• Key TrPs in the scalene muscles can induce satellite TrPs in the serratus posterior superior
• The reverse direction also occurs — serratus posterior superior TrPs can be the primary driver activating scalene satellites
• The neck must always be examined for scalene TrPs when a serratus posterior superior TrP is found

Also examine:

• Rhomboids — overlying muscle; associated TrPs common
• Iliocostalis thoracis — nearby; associated TrPs
• Longissimus thoracis — nearby; associated TrPs
• Multifidi — nearby; associated TrPs

Satellites of Serratus Posterior Inferior

Primary associated muscles:

• Iliocostalis lumborum — adjacent; TrPs develop concurrently with overload strain
• Longissimus thoracis — adjacent; TrPs develop concurrently

Clinical note: The inferior serratus TrP ache is characteristically a residual finding after treatment of the major paraspinal TrPs. Treat the paraspinal muscles first; address the serratus posterior inferior if the lower thoracic ache persists.

Related Pages

• Muscle:Scalene — key satellite relationship with serratus posterior superior; always examine the neck
• Muscle:Rhomboids — overlying the serratus posterior superior; frequently co-involved
• Muscle:Iliocostalis_Thoracis — adjacent to both muscles; concurrent TrPs common
• Muscle:Longissimus_Thoracis — adjacent to both muscles; concurrent TrPs common
• Muscle:Multifidi — nearby; associated TrPs
• Muscle:Iliocostalis_Lumborum — adjacent to serratus posterior inferior
• Muscle:Quadratus_Lumborum — functional unit partner for exhalation; distinguish referred pain
• Muscle:Serratus_Anterior — distinguish by cough/inhalation provocation
• Differential:ThoracicOutletSyndrome — in the differential for serratus posterior superior
• Concept:Trigger_Point_Injection — injection technique including pneumothorax precautions
• Concept:Apropos_Treatment — TrP pressure release and spray and stretch
• Concept:Perpetuating_Factors — paradoxical breathing, leg length discrepancy, scoliosis

References

• Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 1: The Upper Half of Body. 2nd ed. Baltimore: Williams & Wilkins; 1999. Chapter 47.