Shoulder Impingement Syndrome (Subacromial Pain Syndrome)

Notes

Musculoskeletal Injuries (Acute and Overuse) | Sports Medicine | Upper Limb

Overview

Shoulder impingement syndrome, now more commonly referred to as subacromial pain syndrome (SAPS), is one of the most frequent causes of shoulder pain. It accounts for ~40–65% of shoulder complaints in primary care and sports medicine settings. It occurs due to mechanical compression of the rotator cuff tendons (most commonly supraspinatus) and subacromial bursa beneath the coracoacromial arch, especially during arm elevation. Repetitive overhead activity, structural narrowing, or rotator cuff dysfunction all contribute.

Definition

Subacromial space: Anatomical area between the humeral head and coracoacromial arch.
Rotator cuff: Group of four muscles stabilising the glenohumeral joint (SITS – supraspinatus, infraspinatus, teres minor, subscapularis).
Bursitis: inflammation or irritation of a bursa, which is a small, fluid-filled sac that acts as a cushion between bones, tendons, and muscles near joints.
Neer sign: Pain with passive forward flexion of the arm while stabilising the scapula (suggests impingement).

Anatomy & Physiology

Subacromial space contents: Supraspinatus tendon, long head of biceps tendon, subacromial bursa.
Normal physiology: During abduction/flexion, humeral head depresses, allowing tendons to glide beneath acromion.
Pathology: Weakness of cuff or narrowing of subacromial space → compression/irritation → inflammation and pain.

Supraspinatus is the most commonly affected tendon.

Aetiology and Risk Factors

Aetiology

Primary (structural):
- Acromial shape (hooked acromion type III).
- Subacromial osteophytes.
- Thickened coracoacromial ligament.
Secondary (functional):
- Rotator cuff weakness/imbalance.
- Glenohumeral instability.
- Scapular dyskinesis.

Risk Factors

Repetitive overhead activity (e.g., throwing, swimming, painting).
Age >40 years (degenerative).
Poor posture (rounded shoulders, kyphosis).
Occupations involving lifting or overhead work.

Pathophysiology

Narrowing of subacromial space (structural or functional).
Supraspinatus tendon and subacromial bursa compressed during abduction/flexion.
Repetitive microtrauma → tendon inflammation and bursitis.
Progression to cuff degeneration/partial tear if untreated.

Repetitive overhead movement → tendon squeezed → pain → cuff tear.

Clinical Manifestations

Insidious, activity-related shoulder pain.
Pain localised to anterolateral shoulder, worse with overhead activity and at night (especially lying on shoulder).
Painful arc: pain between 60–120° of abduction.
Weakness (later stages with cuff involvement).
Limited range of motion (ROM).

Exam findings:

Neer’s test: Pain with passive forward flexion.
Hawkins–Kennedy test: Pain with forward flexion and internal rotation.
Jobe’s (empty can) test: Supraspinatus weakness/pain.

Impingement Triad: Painful arc (60–120° abduction), Positive Neer’s test, Positive Hawkins–Kennedy test.

Diagnosis

Clinical diagnosis primarily.
X-ray: May show acromial spur or subacromial narrowing.
Ultrasound: Rotator cuff/bursa inflammation.
MRI: Best for cuff pathology/tears.

Differential Diagnosis

Condition	Differentiating Features
Rotator cuff tear	More weakness, positive drop-arm test
Adhesive capsulitis	Global stiffness, painful passive ROM
Glenohumeral arthritis	Older patients, radiographic joint changes
AC joint arthritis	Localised AC joint tenderness, cross-body adduction pain

Treatment

Conservative (first-line):
- Activity modification (avoid overhead/repetitive use).
- NSAIDs, ice, physiotherapy (strengthen rotator cuff/scapular stabilisers, posture correction)
- Subacromial corticosteroid injections for persistent pain.
Surgical:
- Arthroscopic subacromial decompression or acromioplasty if conservative measures fail >6 months.
- Repair if associated rotator cuff tear.

90% respond to conservative therapy; surgery for refractory cases.

Complications & Prognosis

Progression to rotator cuff tears (partial/full).
Chronic shoulder pain and dysfunction.
Subacromial bursitis.
Prognosis: Good with early management; chronic untreated cases → cuff degeneration.

Failure to treat early can convert a reversible condition into a degenerative cuff tear.

References

van der Windt DA, Koes BW, de Jong BA, Bouter LM. Shoulder disorders in general practice: incidence, patient characteristics, and management. Ann Rheum Dis. 1995;54(12):959–64.
Neer CS. Impingement lesions. Clin Orthop Relat Res. 1983;(173):70–7.
Michener LA, McClure PW, Karduna AR. Anatomical and biomechanical mechanisms of subacromial impingement syndrome. Clin Biomech. 2003;18(5):369–79.
Henkus HE, Cobben LP, Coerkamp EG, Nelissen RG, van Arkel ER. The accuracy of subacromial impingement tests. J Bone Joint Surg Br. 2006;88(4):566–72.
Hanratty CE, McVeigh JG, Kerr DP, Basford JR, Finch MB, Pendleton A. The effectiveness of physiotherapy exercises in subacromial impingement syndrome: systematic review and meta-analysis. Semin Arthritis Rheum. 2012;42(3):297–316.