AC Joint Degeneration most commonly affects middle-aged and older adults. However, the condition can also occur in younger adults, particularly those who participate in contact sports or other activities that put repetitive stress on the shoulder. In this article we will explore AC Joint Degeneration, what causes deterioration of the acromioclavicular joint and what treatment options are available.

What is the AC Joint?

What we often refer to as our shoulder is actually a complex of four separate joints. The Acromioclavicular Joint or AC Joint is formed where the outer end of the collarbone or clavicle meets the acromion, a bony process on the scapula bone. The AC Joint attaches the scapula to the clavicle and is therefore the primary connection that suspends the upper limb from the trunk.

Several strong ligaments surround the AC Joint and work together to provide stability and maintain the alignment of the joint. The bony surfaces of the distal clavicle and the acromion are lined with joint cartilage and the joint capsule contains joint fluid to keep things moving smoothly. Some people have a small joint disc made up of fibrocartilage, similar to the meniscus found in the knee joint.

What is the function of the AC Joint?

The AC Joint is not as highly mobile as the Glenohumeral Joint (the ball and socket joint we often refer to as the shoulder) but it serves a few important functions:

1. It allows the scapula to rotate and tip on the thorax.
2. It allows for transmission of forces from the upper limb to the clavicle.

The AC Joint is hard at work whenever you move your upper limb through its range of motion, think of throwing, serving in tennis, push-ups and any other demanding movement of the arm and shoulder.

What causes AC joint degeneration?

The AC Joint is relatively small, but it still needs to deal with significant forces. In other words, we subject our AC Joints to large forces per unit area compared to our other joints. Unfortunately, this means that the AC Joint is extremely susceptible to trauma (often because of sporting injuries) and degenerative change. 

Primary osteoarthritis refers to joint degeneration that occurs with no underlying cause. It develops because of constant stress on the joint over a period of many years, often in people who perform repeated overhead lifting activities. Degenerative change refers to the gradual thinning and destruction of the joint cartilage to where the joint becomes osteoarthritic and painful. Degenerative change can occur as early as the 2nd decade but is very common and almost universal by the 6th decade.

Secondary osteoarthritis occurs because of a traumatic injury or an underlying inflammatory condition like rheumatoid arthritis. In a traumatic injury, a sudden abnormal force separates or dislocates the joint. Besides being extremely painful, these injuries raise the risk for later degenerative change. 

What are the symptoms of AC joint degeneration?

The primary symptom of AC Joint degeneration is pain. The pain is often felt at the top of the shoulder and provoked by overhead movements or sleeping on the affected shoulder. Sometimes there is some swelling or redness on top of the shoulder. Popping, clicking, or grinding sensations may be felt as the damaged cartilage surfaces move against one another. The AC Joint may be tender to the touch and even feel a little warmer than the surrounding area.

Your sports physician will make the diagnosis by performing a clinical examination and perhaps ordering imaging tests such as x-rays, ultrasound scans, or even an MRI.

How is AC joint degeneration treated?

Physiotherapy and activity modification

Physiotherapy is essential to manage pain, maintain the joint range of motion, strengthen stabilising muscles, and correct postural issues. Physiotherapy may include manual therapy, electro-modalities and exercise prescription.

Activity modification helps to avoid stressing the joint further and worsening the symptoms. Your physio will advise you to avoid push-ups, dips, flies, bench-press, and any repetitive overhead activities.

Oral analgesia

Pain-killing medications like non-steroidal anti-inflammatory drugs (NSAIDs) can diminish the pain from ACJ degeneration but have side-effects to consider.

Local corticosteroid injection

Your doctor will inject a mix of cortisone and local anaesthetic directly into the joint, usually under the guidance of an ultrasound scan. Corticosteroid injections can provide good pain relief but are ineffective in the long term. The pain usually comes back over a period of weeks to months.

Surgery

Surgical treatment is reserved for those severe cases that do not respond to at least six months of conservative treatment. Surgery can be done as an open or arthroscopic procedure (“keyhole surgery”). Arthroscopic procedures are generally associated with less pain and a faster return to function. 

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What is the AC Joint?

The Acromion-Clavicular Joint (AC Joint) is the joint between the bony tip of the shoulder (acromion) and the collar bone (clavicle). The Acromion-clavicular joint is one of the synovial articulations of the shoulder complex which connects the axial to the appendicular skeleton.

The synovial joint is formed between the convex lateral clavicular and medial concave acromial ends.

A fibrocartilaginous disc similar to the knee’s meniscus sits between the articulating surfaces. Degeneration of this disc occurs with increasing age and activity and is thought to contribute to pain and disability in the elderly and overhead athletes.

The AC joint has four planes of movement: anterior-posterior and superior-inferior.

The capsule surrounding the joint,  the condensed acromioclavicular ligaments, and the coracoclavicular ligament complex is the restraint that keeps the joint in position and protects it from its dislocation.

AC joint injuries account for 9 to 12% of all shoulder injuries, both traumatic and degenerative injuries. 

Traumatic AC injuries are mostly seen in people aged in the twenties whereas Degenerative AC Injuries are more prevalent in people in their fifties. The AC joint sprains which can be due to direct or indirect force are high in collision and combat sports like hockey, American football, rugby, and karate.

How to find the AC Joint?

The joint can be found by running your fingers along the clavicle, also known as the collar bone, towards the shoulder. At the point where the clavicle ends, depression can be sensed between the clavicle and an overriding acromion. This joint space is the AC joint space. 

Can AC joint injury cause neck pain?

Yes, AC joint injuries can cause neck pain. The stability of the AC joint is provided by trapezius and deltoid muscles dynamically. They help in maintaining the joint position during movements of the arm. Hence any injury to the joint can cause a protective spasm in the upper trapezius and muscles surrounding the joint to guard the joint against further injury. Even some of the experimental pain studies have reproduced pain in the trapezius – supraspinatus, anterolateral neck region, and deltoid region by injecting saline in the AC joint. 

AC joint can cause referred pain in the neck region, for which the joint needs to be tested clinical-radiologically, with good attention given to the mechanism of injury.

How do you treat an injured AC joint?

An injured AC joint is treated according to the mechanism of injury. A degenerative or a micro traumatic AC joint is de-loaded by activity modification or restriction, icing, and taping. The scapular muscles are strengthened statically and dynamically and flexibility is restored to normal length.

An acutely sprained AC joint is generally treated with rest and immobilisation in a sling. Mobility, motor control, and strength are built gradually as the pain settles down and movement becomes easier.

How long does the AC joint take to heal?

The healing of the AC joint depends upon the number of structures injured, the mechanism of injury, the intensity of the traumatic force, the age of the patient, and his/her occupational demands. 

A degenerative joint disorder generally requires three to seven days of sling immobilisation with anti-inflammatories, physical therapy focuses on scapular control and flexibility, followed by activity modifications and strengthening. In some cases, intra-articular injections are also helpful in controlling inflammation. 

Acute AC joint sprains are classified according to Rockwood classification, depending upon the ligaments and trapezius – deltoid fascia involved. Type 1 and 2 injuries are mild sprains without any separation of the joint surfaces. These injuries are treated non-operatively with rest, immobilisation in a sling a gradual physiotherapy program focussing on building strength and scapular kinematics. Depending upon the extent of the injury and other comorbidities it might take 3 to 12 weeks of rehabilitation to heal an AC joint injury.

With respect to athletic injuries, especially in collision sports the player position, injury time compared to the athletic season, and throwing demands are taken into consideration to make treatment decisions. Athletes predisposed to further AC joint injuries are predominantly treated conservatively. Type 3 injuries can be treated both operatively and non-operatively depending upon the case and the structures involved.

Does AC joint separation need surgery?

Most AC joint separations are Types I- III and do not require surgery. Type IV – VI AC joint separations require surgery and can occur in high-impact traumas such as car crashes. These injuries have a high risk of instability of the shoulder joint and are treated surgically with one of  4 types of procedures as follows:

1. Primary repair of AC joint with pins, needles, or rods
2. Distal clavicle resection and reconstruction of soft tissues(Weaver Dunn Procedure).
3. Anatomic coracoclavicular reconstruction
4. Arthroscopic fixation with sutures

 The post-operative rehabilitation is gradual and might take 6 to 12 months for a full recovery and return to sport depending upon the structures involved and the surgical procedures used, with arthroscopic procedures requiring less time compared to the open ones.

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