The painful arc: when raising the arm becomes a problem

Pain when raising the arm between 60° and 120° — the so-called painful arc — is one of the most recognizable clinical signs of shoulder impingement syndrome. The motion of pulling a shirt on overhead, reaching for something on a high shelf, or fastening a seatbelt triggers a sharp jab on the anterior or lateral aspect of the shoulder. The mechanism: the tendon of the supraspinatus muscle becomes trapped between the head of the humerus and the acromion during this arc of motion.

But impingement syndrome is rarely purely structural. In most cases, active trigger points in the supraspinatus and infraspinatus increase tendon tension, reduce the subacromial space, and perpetuate the pain cycle — even when there is no significant tendon injury on MRI. The infraspinatus, in particular, refers pain to the anterior aspect of the shoulder and upper arm, mimicking impingement pain and causing diagnostic confusion.

Prevalence and impact

frequent
AMONG SHOULDER PAIN CAUSES
impingement syndrome is among the most common musculoskeletal diagnoses of the shoulder in adults; exact prevalences vary across series
~1 in 3
ADULTS OVER 60
has some degree of rotator cuff injury in population studies — often asymptomatic
favorable response
IN CLINICAL STUDIES
reported with acupuncture and electroacupuncture in some studies, with effects comparable to other conservative interventions on certain outcomes; specific figures vary by protocol
6–12
WEEKS
is the time frequently described for recovery with appropriate conservative treatment; some patients respond faster, others require longer periods

From muscular tension to pinching: the complete mechanism

  1. Posture with anteriorly projected shoulders

    Computer work, smartphones, and prolonged driving keep the shoulders in protraction. The supraspinatus chronically works at a mechanical disadvantage.

  2. Trigger points in the cuff

    Supraspinatus and infraspinatus develop trigger points that shorten the muscle belly and increase tendinous tension, reducing available subacromial space.

  3. Painful arc between 60° and 120°

    In abduction between 60° and 120°, the tendon thickened by the trigger point impacts against the acromion and the coracoacromial ligament — generating the typical sharp pain.

  4. Secondary inflammation of the bursa

    Repeated impingement inflames the subacromial bursa, which in turn further compresses the tendon — creating a vicious cycle of inflammation, thickening, and renewed impingement.

  5. Electroacupuncture in the cuff

    Needling of the supraspinatus (upper border of the scapula) and infraspinatus (infraspinous fossa) can reduce trigger point activity, decrease local muscular tone, and favor functional gain in subacromial space in selected cases.

Recognizing the shoulder impingement pattern

Critérios clínicos
08 itens

Impingement syndrome \u2014 typical clinical presentation

  1. 01

    Sharp pain or jab when raising the arm between 60° and 120° (painful arc)

  2. 02

    Pain when pulling a shirt on overhead or reaching for objects on high shelves

  3. 03

    Pain on the anterior or lateral aspect of the shoulder, possibly radiating to the upper arm

  4. 04

    Worsens when lying on the affected shoulder

  5. 05

    Pain when crossing the arm in front of the chest (Hawkins maneuver)

  6. 06

    Relative weakness in shoulder abduction — a "heavy arm" sensation

  7. 07

    Clicking in the shoulder during movement (subacromial crepitus)

  8. 08

    Absence of pain below the elbow (distinction from cervical radiculopathy)

Protocol with electroacupuncture

Clinical diagnosis
1st visit

Neer, Hawkins-Kennedy, and painful arc tests. Assessment of cuff strength (external rotators and abductors). Palpation of the supraspinous and infraspinous fossae. Exclusion of complete tear.

Acute phase
Sessions 1–3

Dry needling of the supraspinatus (upper border of the scapular spine) and infraspinatus, in line with protocols described in the myofascial pain literature. Acupuncture at LI-15, SI-9, SI-10, TE-14, and distal points for pain modulation — complementary to, not a substitute for, medications prescribed by the physician when indicated.

Electroacupuncture
Sessions 4–7

Electroacupuncture 2–4 Hz at the local cuff points for neuromodulation and increased tendinous blood flow. Subscapularis and pectoralis minor included if there is shoulder protraction.

Functional rehabilitation
Sessions 8–10

Medical prescription of strengthening exercises for external rotators and scapular stabilizers. Postural correction. Discharge or monthly maintenance according to progress.

Myths and facts about shoulder pain

Myth vs. Fact

MYTH

If it hurts to raise the arm, surgery is required

FACT

A large share of impingement syndrome cases improve with conservative treatment in 6–12 weeks, without immediate need for surgery. Surgery is usually reserved for complete cuff tears with functional deficit or for cases of failure of conservative treatment after 3–6 months — the indication is individual.

MYTH

A calcification in the tendon means the pain will never go away

FACT

Tendinous calcifications are frequently asymptomatic. When symptomatic, they respond well to medical acupuncture and, in selected cases, to ultrasound-guided percutaneous lavage. Surgery is rarely necessary.

MYTH

Corticosteroid injection is the best treatment for impingement

FACT

Corticosteroid injections may offer rapid relief, but the effect tends to be transient (from weeks to a few months) and repeated injections have been associated with deleterious effects on the tendon. Comparative studies suggest that medical acupuncture may produce comparable effects on certain medium-term outcomes, with a different risk profile for tendon integrity.

Clinical pearl: differentiating impingement from pure trigger point

Frequently asked questions

FREQUENTLY ASKED QUESTIONS · 03

Frequently Asked Questions

It depends on the exercise. Bench press, overhead press, and lateral raises with load should be avoided or replaced with variations that do not generate subacromial impingement (such as rows and pull-downs at a favorable angle). The medical acupuncturist provides specific guidance on which movements to allow and which to adapt during treatment.

Electroacupuncture produces a tingling sensation or light pulsing in the treated muscles — comfortable for most patients. The intensity is always adjusted individually. Few patients describe the sensation as uncomfortable, and the intensity is reduced immediately if needed.

After shoulder surgery (cuff repair, for example), medical acupuncture is usually started from the 4th–6th postoperative week, always in agreement with the responsible surgeon. It is proposed that postoperative needling may help in pain modulation and the rehabilitation process — the molecular mechanisms (local growth factors, inflammatory modulation) remain under investigation.