Rotator Cuff Impingement

Rotator cuff impingement, also called subacromial impingement syndrome, is one of the most common causes of shoulder pain, accounting for up to 65% of all shoulder consultations. It occurs when the rotator cuff tendons and subacromial bursa are repeatedly compressed between the humeral head and the bony arch above them during arm elevation.

Between the top of the humeral head and the underside of the acromion lies the subacromial space, normally 9-10 mm wide. Through this narrow passage run the supraspinatus tendon, the subacromial bursa (a fluid-filled cushion that reduces friction), and the long head of the biceps tendon. When this space narrows, due to acromial shape, posture, muscle imbalance, or tissue swelling, the contents are pinched during arm elevation, producing pain and, over time, progressive tendon damage.

What is the Subacromial Space?

Normal subacromial space

Space ~9-10 mm. Supraspinatus tendon passes freely beneath the acromion during arm elevation. Bursa is thin and uncompressed. No pain on lifting the arm.

Impinged subacromial space

Space reduced to <6 mm. Tendon and bursa are compressed during elevation. Bursa becomes inflamed and thickened, further narrowing the space in a worsening cycle. Painful arc 60-120°.

Types of Impingement

Primary (external) - 95%

Mechanical compression beneath the coracoacromial arch. Caused by a hooked acromion , AC joint osteophytes, or thickening of the coracoacromial ligament. More common in patients over 40.

Secondary (internal)

Dynamic narrowing due to rotator cuff weakness or poor scapular control. The cuff fails to depress the humeral head during elevation, causing superior migration. Common in young overhead athletes.

Posterior internal

The posterior cuff and labrum are pinched between the humeral head and posterior glenoid rim during the late cocking phase of throwing. Produces posterior shoulder pain during overhead sport.

Subcoracoid

Compression of the subscapularis tendon between the coracoid process and the lesser tuberosity during internal rotation and forward flexion. Less common but increasingly recognised.

Neer’s Stages of Disease Progression

Neer described three progressive stages of impingement, understanding which stage you are in guides both your prognosis and treatment approach.

Stage II: Fibrosis

Age 25-40. The bursa becomes fibrotic and the tendon thickens in response to repeated mechanical trauma. The enlarged tendon further narrows the subacromial space, a self-perpetuating cycle. Less reversible without treatment.

Stage III: Structural damage

Typically over 40. Chronic impingement causes partial or full-thickness supraspinatus tearing, most often at the 'critical zone', 1 cm from its insertion. Bone spur formation at the undersurface of the acromion.

Stage I: Reversible

Patients typically under 25. Oedema and minor bleeding within the bursa and tendon from acute overuse. Fully reversible with rest and rehabilitation. No structural tendon damage at this stage.

The Painful Arc: Understanding your pain

The hallmark of impingement is pain that occurs in a specific arc of elevation, not throughout the full range of movement. This is because compression of the supraspinatus tendon beneath the acromion peaks in the mid-range of arm elevation.

60° - 120° (the painful arc)

Maximum subacromial compression. The greater tuberosity sweeps beneath the acromion, compressing the bursa and tendon. Pain is often worse when lowering the arm back down through this zone than when raising it.

Above 120° (above the arc)

The greater tuberosity moves posterior to the acromion and compression reduces. Many patients find full overhead reach less painful than the mid-range, distinguishing impingement from frozen shoulder where all ranges are restricted.

0° - 60° (below the arc)

The supraspinatus tendon is not yet being compressed beneath the acromion. This range is typically comfortable or mildly uncomfortable. Most patients can perform everyday low-level tasks within this range.

Causes and Risk Factors

Acromial spur

A downward hook on the front of the acromion reduces the subacromial outlet structurally. Found in up to 70% of patients with chronic impingement, a key target for surgical acromioplasty.

Rotator cuff weakness

Weak cuff muscles, particularly the lower cuff, allow the humeral head to migrate superiorly during elevation, dynamically narrowing the space with every arm movement.

Scapular dyskinesis

Abnormal shoulder blade movement or tilting reduces the subacromial space during arm elevation and is a major contributor to secondary impingement in younger patients.

AC joint osteophytes

Arthritic bone spurs growing downward from the acromioclavicular joint directly encroach on the subacromial space from above and may require surgical removal.

Overhead activities

Repeated overhead sport (swimming, tennis, throwing, volleyball) or occupation (painting, plastering, warehousing) increases the cumulative compression load through the subacromial space.

Postural factors

Rounded shoulders, forward head posture, and a kyphotic thoracic spine all alter scapular resting position, reducing the effective subacromial outlet even at rest.

Symptoms

  • Painful arc between 60° and 120° of arm elevation - often described as a catching or pinching sensation

  • Night pain - aching when lying on the affected shoulder, disrupting sleep

  • Difficulty and pain reaching overhead, behind the head, or across the body to the opposite shoulder

  • Weakness lifting the arm - partly from pain inhibition, partly from underlying tendon damage

  • Pain with activities such as reaching into overhead cupboards, hanging washing, or serving in tennis

⚠ Impingement is a diagnosis of exclusion. Your surgeon will assess for rotator cuff tears, AC joint pathology, frozen shoulder, shoulder instability, calcific tendinitis, and cervical spine referral, all of which can produce similar symptoms. Do not assume a self-diagnosis of impingement without formal examination and appropriate imaging.

Examination includes Neer's impingement sign (pain on passive forward flexion with the arm internally rotated) and the Hawkins-Kennedy test (pain on internal rotation in 90° of forward flexion). A diagnostic subacromial injection of local anaesthetic, which abolishes symptoms if truly subacromial in origin, confirms the diagnosis. X-rays assess acromial morphology (Type I flat, Type II curved, Type III hooked) and AC joint osteophytes. Ultrasound identifies bursitis, tendon thickening, and dynamic impingement. MRI is arranged when an associated rotator cuff tear is suspected, which changes the surgical plan.

How is it diagnosed?

Treatment - Stepwise Approach

The vast majority of patients with impingement recover fully with non-surgical treatment. Surgery is reserved for the minority in whom conservative measures fail after a thorough attempt.

Activity modification and relative rest

Avoid provocative overhead activities and positions that compress the subacromial space during the acute phase. This reduces bursitis and allows the tendon to settle. Complete rest is not recommended, a graduated return to activity is planned alongside rehabilitation.

1

Physiotherapy - the cornerstone of treatment

A structured programme targeting rotator cuff strengthening (particularly the inferior cuff to actively depress the humeral head during elevation), scapular stabilisation exercises, and postural correction. This is the single most effective long-term intervention for impingement. Most patients who complete a dedicated programme achieve excellent results without needing surgery.

2

NSAIDs and analgesia

A short course (2–4 weeks) of non-steroidal anti-inflammatory medication reduces bursitis and tendon swelling, making it easier to engage with physiotherapy. More effective when taken regularly at a consistent dose rather than on an as-needed basis only when pain is severe.

3

Subacromial corticosteroid injection

A steroid injection directly into the subacromial bursa provides significant pain relief for 6-12 weeks, particularly useful during acute flares and for enabling physiotherapy participation. The injection treats the bursitis and pain but does not correct the underlying mechanical cause. Rehabilitation must continue alongside it.

4

Ultrasound-guided injection or barbotage

Image guidance ensures accurate placement of the steroid into the subacromial space - particularly useful if a previous blind injection provided inadequate relief. For calcific tendinitis, needling and lavage (barbotage) under ultrasound guidance breaks up and aspirates the calcium deposit under local anaesthetic.

5

Arthroscopic subacromial decompression (ASD)

Keyhole surgery to remove the inflamed bursa (bursectomy), smooth the undersurface of the acromion (acromioplasty), and release the coracoacromial ligament. Reserved for patients who have completed at least 3-6 months of supervised physiotherapy without adequate improvement. Around 80-85% of patients achieve lasting pain relief. Any associated rotator cuff tear identified at arthroscopy can be repaired in the same procedure.

6

Special Case: Calcific Tendinitis

In some patients, calcium deposits form within the supraspinatus tendon - a condition called calcific tendinitis. This typically follows a natural history of three phases:

Formative phase

Calcium is deposited in the tendon in a solid, chalky form. Often asymptomatic or mildly uncomfortable at this stage.

Resting phase

Calcium is solid and stable. Pain is variable - some patients have significant discomfort, others are unaware of the deposit.

Resorptive phase

The calcium transforms from solid chalk to a toothpaste-like consistency as the body's inflammatory cells attempt to remove it. This phase can produce one of the most acutely painful shoulder presentations seen in clinic - severe pain at rest, at night, and with any movement.

Treatment for symptomatic calcific tendinitis includes ultrasound-guided needling and lavage (barbotage) - the calcific deposit is needled, broken up, and aspirated under local anaesthetic with image guidance. Most cases resolve completely with this technique within 1-3 months. Surgery to remove the deposit is rarely needed.

Evidence: Surgery vs Physiotherapy

The UK CSAW trial (2017, Lancet) compared arthroscopic subacromial decompression, diagnostic arthroscopy alone, and supervised physiotherapy alone for subacromial impingement. At 12 months, all three groups showed similar functional improvement, with no statistically significant benefit of decompression over physiotherapy. This reinforces that supervised physiotherapy is the priority intervention. Surgery adds most value when genuine structural pathology (hooked acromion, AC osteophytes, significant bursitis) persists after completing a full rehabilitation programme.

Recovery After Arthroscopic Subacromial Decompression

  • Day-case procedure performed under general anaesthesia (40-60 minutes). Two or three small portal wounds with dressings. Arm in a sling for comfort only, not structural protection. Active range-of-movement exercises begin immediately. Most patients notice a dramatic improvement in pain within the first few days after surgery.

  • Sutures or dressings removed at 10-14 days. Sling discarded by day 5-7. Physiotherapy begins with focus on regaining full range of movement. Most patients return to desk work and driving within 1-2 weeks.

  • Progressive rotator cuff and scapular strengthening. Driving typically resumes at 3 weeks. Return to light manual work around 4-6 weeks. Overhead activities cautiously reintroduced.

  • Return to overhead sport, heavy manual activities, and full occupational demands. Full recovery expected by 3-4 months for isolated ASD without a rotator cuff repair. Physiotherapy continues to address underlying biomechanical contributors and prevent recurrence.

FREQUENTLY ASKED QUESTIONS

  • No, but they are closely related. Impingement is a mechanical process of compression; a rotator cuff tear is the structural damage that can result from chronic, unresolved impingement. Many patients have impingement without any tendon tear, and the pain can be just as significant. Conversely, a significant rotator cuff tear causes the humeral head to migrate upward, itself causing secondary impingement. Your MRI or ultrasound scan will clarify whether a tear is present and guide the appropriate treatment.

  • With a structured physiotherapy programme, most patients see significant improvement within 6-12 weeks and full recovery within 3-6 months. Those with more chronic changes, underlying acromial spurs, or associated calcific deposits may take longer. It is important to complete the full course of rehabilitation, symptoms that settle quickly often return if the underlying muscle imbalances and postural contributors are not fully corrected.

  • Around 70-80% of patients with impingement recover fully without surgery when they commit to a proper physiotherapy programme. Surgery is most appropriate when there is a structural mechanical cause (hooked acromion, AC joint osteophyte) that will not respond to rehabilitation alone, or when symptoms remain disabling after 3-6 months of supervised physiotherapy. Your surgeon will discuss whether surgery is appropriate for your specific anatomy and circumstances.

  • Yes, with the right guidance. Avoiding overhead activities and heavy loading during the acute phase is sensible, but complete rest is counterproductive. Your physiotherapist will guide you through exercises that strengthen the rotator cuff and scapular muscles without provoking the impingement zone. Swimming (avoiding overhead strokes initially), walking, and cycling are generally well tolerated. The goal is to load the tendons at a level that promotes healing without causing a flare.

  • After a successful acromioplasty, structural recurrence is uncommon, the acromion does not re-grow a spur. However, if the underlying muscle imbalances, postural habits, and biomechanical contributors to impingement are not addressed through rehabilitation, symptoms can return even without a structural spur. This is why physiotherapy after surgery is just as important as before it.

  • Calcific tendinitis is a distinct condition where calcium crystals are deposited within the tendon substance itself, most commonly the supraspinatus. It can occur alongside impingement or independently. During the resorptive phase, when the body attempts to dissolve the calcium, it can cause extremely severe pain, often described as the worst pain patients have experienced. Ultrasound-guided needling and lavage (barbotage) is highly effective and produces complete resolution in most cases.

This guide is intended for patient education purposes and does not replace a formal surgical consultation. Treatment decisions are always individualised based on your specific history, examination findings, and imaging. Please discuss your symptoms and management plan directly with your orthopaedic surgeon.