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Shoulder Impingement Syndrome

  • Shoulder pain with overhead activities is a common musculoskeletal complaint.
  • Impingement syndrome:
    • Inflammatory condition of the soft tissues of the subacromial space
    • Most common cause of presentation for shoulder complaints to a physician’s office (>50% of all shoulder complaints)
  • Represents a continuum, progressing from acute bursitis, to chronic bursitis, to partial-thickness tears of the rotator cuff, to full-thickness rotator cuff tears, to rotator cuff arthropathy with degenerative changes
  • The subacromial space is defined as the humeral head inferiorly, the anterior edge and undersurface of the anterior 1/3 of the acromion, and the coracoacromial ligament and AC joint superiorly.
  • The soft tissues of the subacromial space include the subacromial bursa, supraspinatus and infraspinatus tendons, tendon of the long head of the biceps, and capsule of shoulder, all of which are susceptible to inflammation.
  • External impingement:
    • The most common type of impingement
    • With overhead elevation of the arm, the rotator cuff impinges on the coracoacromial arch.
  • Neer classification:
    • Stage I:
      • Acute inflammation, edema, and hemorrhage
      • Usually reversible with nonoperative treatment
    • Stage II:
      • Continuum from stage I
      • Progression of rotator cuff abnormalities to fibrosis and tendinitis
      • Less likely than stage I impingement to respond to nonoperative management
    • Stage III:
      • Rotator cuff tears and changes to the coracoacromial arch
      • Spurs form along the anterior-inferior acromion (hooked acromion)
  • Internal impingement:
    • Occurs primarily in overhead and throwing athletes
    • The posterior supraspinatus and infraspinatus tendons are pinched between the humeral head and posterior glenoid during maximum abduction and external rotation, as seen in throwing.
  • Secondary impingement: Dynamic impingement, seen with scapular muscle fatigue, occult shoulder instability, and rotator cuff dysfunction (Improper shoulder mechanics leads to dynamic impingement of an intact rotator cuff under an otherwise normal coracoacromial arch.)
  • Synonyms: Subacromial bursitis, Subacromial impingement, Rotator cuff tendinitis
General Prevention
Proper overhead mechanics
  • Common after the age of 50 years
  • Equally as common in males as in females
  • May occur at any age
  • Increasing incidence with increasing age, likely secondary to degenerative changes in the rotator cuff
  • Bone spurring of the acromion, which is associated with impingement syndrome, is 4 times more likely in patients >50 years old.
  • Internal impingement and secondary impingement from glenohumeral instability can cause shoulder pain in the younger patient (<40 years old), especially in overhead athletes (pitchers, tennis players, swimmers, etc.).
Very common
Risk Factors
  • Increasing age (>50 years)
  • Overhead athletics and occupations
  • Instability
  • Hooked acromion
  • Os acromiale (failure of the acromion to fuse after birth)
  • Trauma
No known inheritance patterns
  • The pinching of the subacromial soft tissues between the humeral head and coracoacromial arch is the primary cause of the inflammation.
    • Commonly seen in patients with a type III hooked acromion
    • In addition to a congenital type III hooked acromion, the hook may be secondary to calcification at the coracoacromial ligament from repetitive impingement.
    • Mild glenohumeral instability (acquired or congenital) can predispose patients to secondary and internal impingement.
    • Overhead activities: Athletics and occupations that require overhead activities (electricians, builders, shelf stockers, etc.)
    • Rotator cuff dysfunction or weak cuff muscles allow superior migration of the humeral head, narrowing the subacromial space with overhead activities.
Associated Conditions
  • Rotator cuff tears (partial thickness and the continuum to full thickness)
  • Calcific tendinitis:
    • Calcification in rotator cuff tendons from unknown cause
    • Typically undergoes spontaneous resorption and healing with time
    • Acutely painful during calcium resorption
  • Biceps tendinitis:
    • Inflammation of the tendon of the long head on the biceps
    • Incidence increases with rotator cuff disease.
  • AC arthritis:
    • Pain at the AC joint
  • Adhesive capsulitis:
    • Stiff shoulder secondary to capsular fibrosis
  • Labral tears:
    • SLAP tears are common in overhead athletes with internal impingement and in patients with rotator cuff tears
Signs and Symptoms
Pain with overhead activity of the arm
History of pain with overhead activities (combing hair, putting dishes away, etc.)
Physical Exam
  • Tenderness to palpation over anterior and lateral acromion and rotator cuff
  • Positive Hawkins sign: Pain with passive flexion and internal rotation
  • Positive Neer sign: Pain with passive flexion of shoulder while scapula is stabilized
  • Painful arc: Arc where pain occurs with active abduction
  • Decreased active and passive forward flexion and abduction secondary to pain
  • Pain with infraspinatus and supraspinatus muscle testing
  • Impingement test:
    • Inject 10 mL of 1% lidocaine into the subacromial space with sterile technique.
    • Wait 5-10 minutes and repeat the shoulder examination.
    • Positive test: Improvement in symptoms
  • AP or 30° caudad angled AP view (Grashey view):
    • Subacromial sclerosis (eyebrow sign)
    • Greater tuberosity cyst
    • Superior migration of humeral head
  • Supraspinatus outlet views:
    • Acromial morphology (hooked acromion)
  • MRI:
    • Helpful in delineating injury to rotator cuff
Pathological Findings
  • Degenerative changes in rotator cuff tendons
  • Inflammation and fibrosis of the subacromial bursa
Differential Diagnosis
  • Rotator cuff tears:
    • May be partial or full thickness
    • Weakness and pain with supraspinatus and infraspinatus muscle testing
    • Drop arm test: Inability to hold arm abducted
    • MRI >1.5 tesla magnetic and shoulder coil is the best diagnostic test.
  • Calcific tendinitis: Calcification of cuff tendons seen on radiographs
  • Biceps tendinitis:
    • Tender to palpation along the biceps tendon
    • Positive Speed (resisted shoulder flexion with palm up) and Yergason (pain with resisted supination) tests
  • Cervical spine:
    • Any pain that is distal to elbow should raise concern for a cervical spine cause.
    • Always perform a thorough neurovascular examination.
    • Cervical spine imaging
  • AC arthritis:
    • Localized pain at AC joint
    • Pain with passive cross-body arm adduction
    • Degenerative changes seen on radiographs
    • Pain improved with injection of lidocaine into the AC joint
  • Glenohumeral instability:
    • Apprehension and relocation tests
    • Sulcus sign (passive inferior subluxation of humeral head)
  • Glenohumeral arthritis:
    • Decreased active and passive ROM with crepitance and pain
    • Degenerative changes in glenoid and humeral head on radiographs
  • Adhesive capsulitis:
    • Decreased ROM, especially external rotation
    • Decreased ROM (active, passive)
    • Pain at extremes of motion
  • SLAP lesion:
    • Tear at superior labrum at insertion of biceps tendon
    • Positive O’Brien test
    • MRA is the best diagnostic test.
General Measures
Initial nonoperative management trial before surgical intervention is successful in ~70%.
No shoulder abduction or flexion >60° during early inflammatory stage
Special Therapy
Physical Therapy
  • Improves ROM, particularly internal rotation
  • Rotator cuff program
  • Strengthening:
    • Work in pain-free ROM
    • Scapular stabilizers
    • Rotator cuff muscles
    • Help keep humeral head within glenoid
  • Ice, ultrasound, electrical stimulation
First Line
Second Line
Subacromial corticosteroid injections
  • Indicated if symptoms continue after 6 months of a well-designed and monitored nonoperative regimen
  • Open or arthroscopic acromioplasty and subacromial decompression:
    • Successful in ~75-90% of cases
    • Currently, an arthroscopic procedure is the most common technique:
      • Remove inflamed subacromial bursa.
      • Resect undersurface of acromion and acromial hook.
      • Can resect distal clavicle for AC arthritis
      • Affords visualization of the glenohumeral joint to determine if additional intervention is needed
    • Open acromioplasty:
      • Less commonly used, unless used with an open rotator cuff repair
      • If the deltoid attachment is mobilized, care must be taken to repair it adequately
    • Early ROM is critical for avoiding a stiff shoulder.
  • Success rate with nonoperative treatment: ~70%
  • Success rate of acromioplasty in those for whom nonoperative treatment fails: ~75-90%
  • Surgical:
    • Failure to resolve symptoms:
      • Inadequate resection of acromion
      • Incorrect diagnosis: AC arthritis, glenohumeral arthritis
    • Stiff shoulder:
      • Postoperative adhesions
      • Inadequate postoperative arm mobilization
    • Infection
    • Hematoma
  • Progression of impingement:
    • Rotator cuff tear
    • Cuff arthropathy
    • Tearing of proximal tendon of long head of the biceps (Popeye arm)
Patient Monitoring
Close outpatient follow-up to monitor ROM
726.2 Impingement syndrome, shoulder
Patient Teaching
Proper overhead technique
Q: Does shoulder impingement require surgery?
A: No. Most impingement symptoms improve with a good rotator cuff rehabilitation program. Subacromial decompression to relieve impingement is recommended only for shoulders unresponsive to 6 months of physical therapy.
Q: What are some of the causes of shoulder impingement in patients <40 years old?
A: Common causes in a young patient are occult instability, rotator cuff dysfunction, and os acromiale.

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