Shoulder arthrocentesis can be performed either diagnostically (to identify the etiology of acute arthritis) or therapeutically (to drain an effusion). With the same technique, the joint can be injected therapeutically with corticosteroids, anesthetics, or both.
Aspiration of the glenohumeral joint can be accomplished via either an anterior or a posterior approach. The posterior approach allows the patient to be blinded from the procedure, and it mimics the approach used in arthroscopy of the joint.
Diagnostically, shoulder arthrocentesis is indicated in patients with shoulder pain for injection of anesthetic (with or without corticosteroid) with the aim of determining whether the glenohumeral joint is the source of the patient's pain. By permitting joint aspiration, arthrocentesis aids in the diagnosis of the underlying pathologic process through synovial fluid analysis. [1, 2]
Therapeutically, shoulder arthrocentesis is indicated for providing pain relief and functional improvement in patients who have glenohumeral osteoarthritis, rheumatoid arthritis, or adhesive capsulitis  (this may be performed through drainage of an effusion, septic joint, or hemarthrosis or through instillation of medication).
Bacteremia, cellulitis of overlying skin, and adjacent osteomyelitis are often considered absolute contraindications for shoulder arthrocentesis because of the potential risk of seeding the joint with bacteria. In these situations, the procedure should be performed only if the clinician strongly suspects septic arthritis as the cause of overlying inflammatory changes, and then only after consultation with an orthopedist.
Relative contraindications include glenohumeral joint infection, chronic infection distant to the injection site, allergy to the injectate, diabetes mellitus, and uncontrolled coagulopathy.
The practitioner performing the procedure should be familiar with the anatomy of the glenohumeral joint and the surrounding structures so as to minimize the risk of complications.
The glenohumeral joint of the shoulder is formed by the humeral head and the glenoid fossa of the scapula. It is bounded by the acromion. The subdeltoid bursa lies under the deltoid muscle and covers the lateral and superior aspect of the proximal humerus. The neurovascular bundle lies medially in the axilla.
Three glenohumeral ligaments exist, as follows:
Superior glenohumeral ligament (SGHL)
Middle glenohumeral ligament (MGHL)
Inferior glenohumeral ligament (IGHL)
The SGHL has a variable origin and inserts on the humerus near the lesser tubercle; it resists inferior translation of the humeral head in the adducted shoulder. The MGHL originates from the labrum and inserts on the humerus medial to the lesser tubercle; it resists inferior translation in the adducted and externally rotated shoulder. The IGHL originates from the labrum and the adjacent glenoid neck and inserts on the anatomic neck of the humerus; it resists humeral head anterior and posterior translation. (See Shoulder Joint Anatomy.)