Acromio-clavicular joint

Introduction
The AC-joint is a tight joint between the clavicle and the shoulder roof (acromion), hence its full name of acromioclavicular joint.

In addition to tight ligaments, the joint consists of a disc of fibrous cartilage. Damage to the AC-joint frequently arises through accidents involving direct contusion of the shoulder, occurring for instance, among cyclists and hockey players. Depending on the number of torn ligaments, greater or lesser displacement of the joint occurs and can be divided into 5 grades. To reach a decision on whether to proceed with surgical or conservative treatment, it is necessary to carefully weigh up the type of injury and the needs of the patient. Injuries of grade I or II (according to Rockwood) can usually be managed conservatively, whereas grades IV and V should be operated on, and the management of the common grade III injury should be decided on a case-to-case basis. In addition to accidental damage, joint destruction (arthritis) is commonly seen at the AC-joint and can be the cause of persistent shoulder pain.

Surgical procedure
If an injury of the AC joint requires surgery, an appropriate procedure (screw, loop of strong threads, etc) restores the anatomical relationship between the acromion and clavicle until the ligaments heal. As the cartilage disc is often irreversibly damaged and torn up, the joint may in due course become painful and arthritic even when the joint is correctly repositioned. In the case of older injuries, it must be decided if a clearing-out of the AC joint (which can be readily achieved by arthroscopy) is sufficient or if additional ligament reconstruction, using the semitendinosus tendon from the thigh is required.

Follow-up
With a surgical reconstruction of the AC-joint, you should, as always, proceed according to the surgeon’s directions. As a rule, the arm should be largely rested with a shoulder bandage for the first four weeks. In the subsequent four weeks, the shoulder should be mobilised as far as the horizontal without load-bearing. If a screw has been placed, this can be removed after 3 months, and complete mobilisation and strengthening of the shoulder is then possible.

However, when the AC joint has only been cleared out arthroscopically, the shoulder can be immediately mobilized – actively and passively – and strengthened, as soon as the initial pain has passed.

Prognosis
In the majority of cases you can rely on the operation to be successful. There is no functional impairment resulting from the removal of a piece of bone from the distal extremity of the clavicle. It is important to avoid painful contact between the two bony structures and to restore sufficient stability between clavicle and coracoid process of the scapula with an appropriate reconstructive procedure.