Acromioclavicular Joint Injection

Acute or chronic capsulitis

Causes and findings:
• Trauma or occasionally prolonged overuse in a degenerative shoulder
• Pain at point of shoulder: occasionally a bump of bone or swelling is seen
• Painful: end-range of all passive movements, especially full passive horizontal adduction (scarf test)
• Occasionally painful: arc on active elevation especially towards end of range

Equipment:
Syringe - 1ml
Needle - 25G 0.5 inches (16mm) orange
Kenalog 40 - 10 mg
Lidocaine - 0.75 ml 2%
Total volume - 1ml

Anatomy:
The acromioclavicular joint line runs in the sagittal plane about a thumb's width medial to the lateral edge of the acromion. The joint plane runs obliquely medially from superior to inferior and usually contains a small meniscus. Often a small step can be palpated where the acromion abuts against the clavicle, or a small V-shaped gap felt at the anterior joint margin. Passively gliding the acromion downwards on the clavicle may help in finding the joint line.

Technique:
• Patient sits supported with arm hanging by side to slightly separate the joint surfaces
• Identify lateral edge of acromion. Move medially about a thumb's width and mark mid-point of joint line
• Insert needle angling medially about 30° from the vertical and pass through capsule
• Inject solution as a bolus

Aftercare:
The patient should rest the shoulder for a week then begin gentle mobilizing exercises. Acutely inflamed joints are helped by the application of ice, taping to stabilize the joint and by oral pain killers.

Comments:
Occasionally the joint is difficult to enter; it is normally a narrow space and degenerative changes make it more so. Traction on the arm can open up the joint space and peppering of the capsule with the solution will anaesthetize it while feeling for the joint space with the needle. This will avoid giving unnecessary pain.

Alternative approach:
The joint can also be injected anteriorly and horizontally at the V-shaped gap if the superior approach is difficult. The unstable or repeatedly subluxing joint can be helped by sclerosing injections or possibly surgery.