Muscle:Infraspinatus

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Infraspinatus is a broad, superficial muscle of the posterior scapula and one of the four rotator cuff muscles. It is the principal myofascial source of deep anterior shoulder joint pain — a presentation so characteristic that Travell & Simons designated it the "Shoulder Joint Pain" muscle. When trigger points (TrPs) are active, referred pain concentrates deeply in the front of the shoulder and radiates down the anterolateral arm and forearm, often preventing sleep in any position and making behind-the-back movements impossible. The infraspinatus is among the most frequently involved muscles in shoulder-girdle pain; in clinical series it accounts for referred shoulder pain in approximately 31% of patients — second in frequency only to the levator scapulae.

Anatomy

The infraspinatus attaches medially to the medial two-thirds of the infraspinous fossa of the scapula and to the adjacent deep fascia. Laterally, it inserts into the posterior aspect (middle facet) of the greater tubercle of the humerus, with the tendon blending superiorly and posteriorly into the shoulder joint capsule.

The upper medial portion of the muscle is covered by the lower trapezius.

Primary actions:

  • Lateral rotation of the arm at the glenohumeral joint (in any position of the arm)
  • Stabilisation of the humeral head in the glenoid cavity during arm movements
  • EMG activity increases linearly with increasing abduction; also active during flexion with a marked increase at approximately 140°

Innervation: Suprascapular nerve (C5, C6), via the upper trunk of the brachial plexus. The suprascapular nerve passes through the scapular notch under the superior transverse ligament, innervates the supraspinatus, then swings around the lateral border of the spine of the scapula to innervate the infraspinatus. It is subject to entrapment both at the scapular notch and at the spinoglenoid notch.

Functional synergists:

  • Lateral rotation of the arm: teres minor, posterior deltoid
  • Humeral head stabilisation: supraspinatus and other rotator cuff muscles

Functional antagonists:

  • Medial rotation: subscapularis, pectoralis major, anterior deltoid

Referred Pain Patterns

The essential and spillover pain zones of the infraspinatus are clinically important because they are frequently mistaken for primary shoulder joint pathology or radiculopathy.

Essential pain zone (present in nearly all patients with active TrPs):

  • Deeply within the anterior shoulder joint and anterior deltoid region — the patient characteristically covers the front of the shoulder with the hand to indicate the most painful area
  • The pain is felt inside the joint, not on the surface

Spillover pain zones (present in a proportion of patients):

  • Anterolateral aspect of the arm — 46% of patients in a series of 193
  • Lateral forearm — 21%
  • Radial side of the hand — 13%
  • Suboccipital and upper posterior cervical region — 14%
  • Occasionally to the fingers

Additional trigger area (vertebral border): A separate trigger area of spot tenderness may occur near the vertebral border of the scapula at the musculotendinous junction region (Fig. 22.1B). This refers pain to the adjacent interscapular rhomboid region — a pattern difficult to distinguish from trapezius TrP₄ pain, and most likely represents enthesopathy secondary to the primary infraspinatus TrPs.

Activation and Perpetuating Factors

Infraspinatus TrPs are characteristically activated by acute overload rather than sustained overload, distinguishing them from the supraspinatus which is more vulnerable to chronic repetitive strain:

  • Reaching out and backward to a bedside stand — particularly during illness when muscles are "below par"
  • Grabbing behind for support to regain balance (e.g. grasping a railing when slipping on stairs)
  • Twisting the arm that holds a ski pole during a fall
  • Excessive poling when skiing
  • Delivering a particularly hard tennis serve when off balance
  • An experienced skater dragging a novice by the arm for a prolonged period

The onset of shoulder pain is typically within a few hours of the initiating event. The patient can usually identify exactly what happened and when.

Motor vehicle accidents activate infraspinatus TrPs in approximately 20–30% of patients regardless of the direction of impact — slightly less commonly than the supraspinatus, but still a significant post-accident finding.

Repeated reaching backward — such as regularly rolling hair onto night curlers or reaching back to a bedside table — perpetuates TrPs once activated.

Clinical Examination

Subjective Presentation

The subjective profile of infraspinatus TrP pain has several features that are clinically characteristic and help distinguish it from other sources of shoulder pain.

Cardinal subjective features:

Feature Detail
Pain location Deeply inside the front of the shoulder joint; the patient covers the anterior deltoid and shoulder with the hand
Quality Deep, aching, inside the joint — not superficial or sharp
Sleep disturbance Cannot lie on the painful side (weight of thorax compresses TrPs); cannot lie on the pain-free side (arm falls forward and painfully stretches the infraspinatus); severely active TrPs may force the patient to sleep sitting upright in a chair or on a sofa
Functional complaints Cannot reach behind to the back trouser pocket; cannot fasten a brassiere behind the back; cannot zip up the back of a dress; must put the sore arm into a coat sleeve first (not last); cannot reach back to a bedside stand; difficulty combing hair or brushing teeth
Onset pattern Typically acute — patient can usually identify the exact incident and time of onset
Arm pain May radiate down the anterolateral arm to the lateral forearm and radial hand — easily mistaken for C5–C6 radiculopathy
Additional features Shoulder-girdle fatigue, grip weakness, and hyperhidrosis in the referred pain zone (Sola and Williams)

Features that distinguish infraspinatus from the principal differential muscles:

Feature Infraspinatus Supraspinatus Subscapularis Deltoid
Primary pain location Deep inside anterior shoulder joint Lateral shoulder and upper arm Posterior shoulder, wrist (posterior band) Over the deltoid region at the site of TrPs
Arm/forearm radiation Anterolateral arm → lateral forearm → radial hand Lateral arm to elbow level Posterior shoulder, dorsum of wrist Anterolateral arm (weak referral; not to hand)
Sleep position problem Cannot sleep on either side Cannot sleep on affected side Cannot sleep; severe restriction of all rotation Less prominent sleep disturbance
Behind-the-back movement Severely restricted (cannot reach pocket or brassiere hooks) Restricted overhead; less affected behind back May allow further behind-the-back reach passively Not specifically restricted
Onset pattern Acute overload; patient recalls specific incident Often chronic/repetitive overload Commonly chronic; often with frozen shoulder presentation Acute or repetitive direct loading
Rotation restriction Lateral rotation restricted; Hand-to-shoulder Blade Test positive Abduction arc restricted; painful arc Medial rotation restricted; lateral rotation severely restricted Minimal rotation restriction

Active Range of Motion

Hand-to-shoulder Blade Test — this is the most specific movement screen for infraspinatus TrP restriction.

Procedure:

  1. The patient places the hand behind the back and reaches as far up toward the opposite scapula as possible
  2. Normally, fingertips should reach at least to the spine of the scapula
  3. This test stretches the abductors and lateral rotators (including the infraspinatus) and contracts the subscapularis and latissimus dorsi in the shortened position

Interpretation:

  • Infraspinatus TrPs: fingers may barely reach the hip pocket — restriction is similar whether performed actively or passively (the muscle is short and cannot lengthen)
  • Subscapularis TrPs: fingers may reach the spinal column or beyond when done passively (the infraspinatus is not the limiting factor), but active performance is restricted because the subscapularis contracts in the shortened position
  • If this test remains restricted after injection therapy, check for TrPs in the forearm supinator muscle — the test can be restricted when the forearm does not pronate fully

Mouth Wrap-around Test — useful as a broader shoulder-girdle screen (see Muscle:Levator_Scapulae for full description). With infraspinatus TrPs, restriction of this test results from the strongly contracted and shortened infraspinatus and middle deltoid causing pain; the pain is in the immediate vicinity of the TrPs. Distinguish from:

  • Subscapularis TrPs — which refer pain behind the shoulder and to the wrist when passively stretched during this test
  • Levator scapulae TrPs — which restrict the test primarily through lack of head/neck rotation

Shoulder abduction: Pain is severe and motion is exhibited through a limited arc when a rotator cuff lesion is responsible — distinguishing rotator cuff pathology from infraspinatus TrPs in which the arc may be fuller.

Infraspinatus Trigger Point Examination

The infraspinatus frequently harbours multiple TrPs. Three common TrP locations are found by flat palpation; no clinically meaningful distinction in pain patterns arises from each:

  1. Upper medial TrP — the most common location; caudal to the junction of the medial quarter and adjacent quarter of the scapular spine length. This is the primary TrP region.
  2. Upper lateral TrP — caudal to the midpoint of the scapular spine; may extend as far lateral as the lateral border of the scapula.
  3. Vertebral border trigger area — near the musculotendinous junction at the medial border of the scapula; represents enthesopathy rather than a primary TrP; refers pain into the adjacent interscapular rhomboid region.

Palpation technique:

  • Patient seated with slight tension placed on the muscle by bringing the hand and arm across the front of the chest to grasp the far armrest of the chair, or lying on the pain-free side
  • Flat palpation is the appropriate technique — pincer palpation is not applicable to this broad flat muscle
  • Firm taut bands may be more difficult to identify than expected; the overlying skin is often thick and indurated by associated panniculosis
  • Local twitch responses (LTRs) are moderately difficult to elicit manually in this muscle — more difficult than in most muscles — and agreement on their presence is poorer than for spot tenderness and taut band
  • When an LTR is observed, it is a strongly confirmatory finding and especially valuable during needling
  • Referred pain can usually be evoked or aggravated by sustained pressure on an active TrP

Clinical significance of LTR difficulty: Learning to palpate taut bands reliably is the essential first step to TrP recognition; the LTR should be sought but its absence does not exclude a TrP.

Screening Tests

Mouth Wrap-around Test

See Mouth Wrap-around Test for full procedure. Pain during this test in the immediate vicinity of the infraspinatus TrPs is caused by strong contraction of the infraspinatus and middle deltoid in the shortened position.

Hand-to-shoulder Blade Test

This is described in full in the Active Range of Motion section above and is the definitive screening test for infraspinatus TrP restriction.

Differential Diagnosis

Suprascapular Nerve Entrapment

Both suprascapular nerve entrapment and infraspinatus TrPs can cause shoulder pain. Entrapment is distinguished by:

  • Prolonged nerve conduction latency on electrodiagnostic testing
  • Muscular atrophy of the infraspinatus
  • Entrapment at the scapular notch involves both supraspinatus and infraspinatus; entrapment at the spinoglenoid notch involves the infraspinatus only
  • MRI or ultrasound may reveal a structural abnormality (e.g. ganglion at the spinoglenoid notch)

Rotator Cuff Lesions

With rotator cuff pathology, pain is severe and exhibited through a limited arc of motion — a pattern distinct from TrP-related restriction. If rotator cuff damage is suspected, the infraspinatus should not be stretched; non-stretching treatment methods are used until structural integrity is confirmed (see Treatment below).

Bicipital Tendinitis

Patients diagnosed with bicipital tendinitis who have failed multiple treatments are likely harbouring unidentified TrPs in the infraspinatus or biceps brachii responsible for the anterior shoulder pain. The biceps brachii refers pain to the anterior shoulder and biceps region, closely mimicking bicipital tendinitis.

C5–C6 Radiculopathy

Infraspinatus TrPs refer pain in the C5, C6, and C7 distributions, which can cause diagnostic confusion with radiculopathy from intervertebral disc disease. Neurological deficits (dermatomal sensory loss, reflex change, myotomal weakness) and electrodiagnostic findings are required to confirm radiculopathy and must be considered alongside the pain distribution.

Glenohumeral Joint Arthritis

Referred pain from infraspinatus TrPs closely mimics pain arising from arthritis of the glenohumeral joint itself. The absence of radiological joint changes and the response to TrP treatment distinguish the two; both conditions may coexist.

Scapulohumeral Syndrome

As defined by Long, the scapulohumeral syndrome — which also may include pain from pectoralis major, pectoralis minor, and the long head of biceps brachii — may be due to active infraspinatus TrPs. All contributing muscles should be assessed.

Pseudo-TOS / Myofascial Pseudothoracic Outlet Syndrome

When the infraspinatus TrPs coexist with active TrPs in the pectoralis major, latissimus dorsi, teres major, and subscapularis (the "quadrad" of pseudo-TOS), the patient may present with a complex shoulder and arm pain syndrome mimicking multilevel cervical radiculopathy, bursitis, or thoracic outlet syndrome. All four muscles should be assessed when infraspinatus TrPs are active and the presentation is complex.

Treatment

Important Precaution

If there is any suspicion of rotator cuff damage, the infraspinatus must not be stretched. In this situation, treatment is limited to non-stretching methods: trigger point pressure release, deep massage to the taut band, gentle hold-relax techniques without range of movement, indirect techniques, and/or injection. Vapocoolant or icing may precede any of these.

When joint play is restricted in the shoulder complex (acromioclavicular and sternoclavicular articulations) or the elbow, joint mobility should be restored before or alongside TrP treatment.

Trigger Point Release

Spray and stretch — three effective positions:

  1. Hand-to-shoulder Blade position (seated): Patient places the hand behind the thorax (as in the Hand-to-shoulder Blade Test). Vapocoolant spray is applied in slow parallel sweeps from medial to lateral over the muscle, covering the shoulder pain pattern and continuing down the arm to the fingertips and over the thumb. Separate sweeps are directed upward over the posterior cervical pain reference zone.
  1. Arm across chest (seated): Patient brings the involved arm in full horizontal adduction across the front of the chest. The patient's active effort to reach across while the operator stabilises the scapula reciprocally inhibits the infraspinatus and allows it to lengthen. Ice is applied in the same medial-to-lateral direction.
  1. Hand behind ipsilateral pelvis (sidelying): Patient lies on the pain-free side with the hand of the involved limb placed behind the ipsilateral pelvis, medially rotating the arm. The operator stabilises the scapula; the patient takes up slack by letting the humerus and elbow drop forward (increasing medial rotation). Vapocoolant spray is applied.

After spray and stretch:

  • Stretch and spray the antagonistic anterior deltoid and pectoralis major — these can experience immediate or delayed shortening and latent TrP activation in response to the infraspinatus release
  • Active range of motion of involved muscles
  • Moist heat application

Postisometric relaxation (effective alternative): Patient lies supine with the affected arm abducted and the elbow extended over the edge of the table, flexed 90°. As the patient takes slow deep breaths and relaxes on exhalation, gravity medially rotates the arm and takes up slack in the lateral rotators. The patient can augment this with voluntary effort to lower the hand (increasing medial rotation) via reciprocal inhibition. This position may also be used for patient self-treatment.

Trigger Point Injection

Patient lies on the pain-free side. The arm is abducted and flexed to approximately 45° and the elbow rests on a pillow placed against the chest.

The TrP is located and pinned between two fingers against the scapula. A 3.8 cm (1.5 in) needle is probed until a local twitch response, a local pain response, and usually the referred pain pattern are elicited. Procaine solution is injected while exploring the area to reach any remaining TrPs. Alternatively, dry needling with an acupuncture needle may be used, rapidly needling the TrP region until no further LTRs are elicited — equally effective as injection but produces more post-injection soreness.

Injection is always performed with the patient recumbent — never seated — to minimise psychogenic syncope and the risk of falling if the patient faints.

Safety note: Portions of the infraspinous fossa can be paper-thin. The needle must not be advanced expecting scapular bone at depth if resistance is unexpectedly absent — a fibrous membrane may be present and penetration risks pneumothorax. Be sensitive to the resistance encountered at depth.

After injection: stretch and spray, moist heat, active range of motion.

Self-Treatment

  • Tennis ball / Theracane® compression: The patient lies supine on a tennis ball placed directly under a tender spot in the infraspinatus. Body weight is used to maintain increasing pressure for 1–2 minutes. Repeated daily or every second day until TrP tenderness resolves.
  • Self-stretch under warm shower: The affected arm is pulled across the body — first in front (position B) and then posteriorly behind the back (position A). Warm water is directed on the infraspinatus and associated muscles.
  • Bedside table repositioning: The bedside table should be moved toward the foot of the bed, or the unaffected arm should be used to reach across — eliminating the habitual backward-reaching overload.

Patient Education

Sleep Positioning

Correct sleep positioning is critical because infraspinatus TrPs are uniquely problematic in any recumbent position:

  • Painful side down: The weight of the thorax compresses and stimulates the infraspinatus TrPs — avoid.
  • Pain-free side down: The uppermost (affected) arm falls forward and painfully stretches the infraspinatus — a pillow under the uppermost elbow and forearm prevents this stretch and is the recommended sleep position (see Figure 22.6A of the source text).
  • Severely active TrPs: The patient may only be able to sleep propped upright in a chair or sofa. This should resolve with successful TrP treatment.

Apply a hot pack to the muscle for 15–20 minutes on retiring to reduce TrP irritability. Do not fall asleep with a heating pad on a high setting — severe burns can result.

Activity Modification

Avoid habitual sustained or repetitive backward-reaching movements:

  • Move the bedside table toward the foot of the bed or use the unaffected arm
  • Avoid regular hair-rolling on night curlers with the affected arm
  • Avoid reaching across to the opposite seat back in a car

Satellite Trigger Points

Three families of associated muscles may develop active TrPs in relation to infraspinatus TrPs. Any given patient typically exhibits involvement of only one family:

Family 1 — Pain reference zone satellite:

  • Muscle:Deltoid (anterior) — lies in the essential pain reference zone of the infraspinatus; frequently develops satellite TrPs in response to prolonged infraspinatus activation

Family 2 — Synergistic elevation team:

Family 3 — Counter-rotation antagonists:

Also assess:

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 22.
  • Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 1. 2nd ed. Chapter 18 (Overview of the Upper Back, Shoulder, and Arm Region).
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