AC joint dysfunction: Another source for shoulder pain

Rotator cuff tears, frozen shoulder and impingement are all very common and well-known conditions that may produce dysfunction at the shoulder. Less common but still potentially problematic and therefore; another important consideration when determining the source of shoulder pain is the Acromion clavicular also known as AC joint dysfunction.

Anatomy of the shoulder joint

The clavicle (collar bone) has 2 joints, firstly a medial (to sternum) and secondly, lateral end (to the acromion of the scapula-shoulder). The Ac joint dysfunction refers to the lateral articulation with the acromion of the scapula.

The joint stabilised via the acromioclavicular, coracoacromial/ coracoclavicular ligaments; the upper and middle fibres of trapezius muscles as well as the deltoids.

(Acromion Clavicle) AC Joint Dysfunction
(Acromion Clavicle) AC Joint Dysfunction

Injuries of the shoulder joint

(Acromion clavicular) AC joint dysfunction is a result of a sprain, dislocation, fracture or osteoarthritis at this joint

Dislocation and sprain

The AC joint dysfunction usually injured by a direct fall onto the top of the shoulder; cycling injuries, or associated with overhead throwing (Javelin) athletes.

The shoulder blade (scapula) forced downwards and the clavicle (collarbone) appears prominent. The degree of injury at the joint is classified by separating the joint and damage to ligaments supporting it.

A sprain suggests ligament injury whereas a dislocation refers; to the clavicle moving upwards and backwards out of its normal alignment. The degree of this separation; between the clavicle and acromion graded on a 6 point scale, with grade 3-4 or higher requiring surgery.

The altered position of the clavicle disrupts the normal rotation action of the clavicle that required to achieve end-range forward flexion (overhead ROM). The pain will occur as a result of overstretched/ ruptured ligaments (depending on the severity) and a stretched joint capsule.

As a protective mechanism, pain tends to lead to altered postures which may contribute to neck pain and altered muscles activity of muscles that attach to the clavicle; such as the pecs, trapezius and sternocleidomastoid.

Fracture of the collar bone

The fracture may occur at the distal end of the clavicle following contact sports injuries, bicycle and car accidents.

Arthritis of the (Acromion Clavicular) AC joint dysfunction

The incidence of arthritis at this joint has shown to be about 50% in MRI studies of elderly populations, however, these people may be asymptomatic.

Just like any arthritis, this refers to the degeneration of the cartilage at the ends of the clavicle and acromion. Normal day-to-day activities that require repetitive arm motion can cause cartilage loss (primary osteoarthritis). In addition, arthritis may be due to cartilage degeneration after an injury to the joint (post-traumatic arthritis).

Regardless of the cause, predominately the normally smooth cartilage and the meniscus between the bones breakdown leading to pain; due to increased friction and thus creating an inflammatory response at the joint.

Signs and Symptoms of (Acromion clavicular) AC Joint Dysfunction


Pain and stiffness of the joints are common symptoms as is catching and “clicking” at the shoulder. Usually, these complaints are worst with overhead activity or with positioning the arm across the body. These are both common positions of the arm- from daily activities such as brushing your hair or reaching your back pocket, putting a shirt on, to sports activities such as a golf swing.


Pain initially may be widespread throughout the shoulder until the acute phase resolves, following this stage the person will demonstrate specific tenderness at the site of the end of the clavicle.

Swelling and depending on the extent of the injury a step-deformity may be visible. This is an obvious lump where the joint has been disrupted (as in the case of a dislocation) and is seen in more severe injuries.

Similarly, with arthritis; the individual will report pain on moving the shoulder, especially with overhead activities and across your body motion.

Treatment of (Acromion Clavicular) AC Joint Dysfunction Dysfunction

Acute injuries will respond to ice therapy, anti-inflammatory medications and a sling are often used.

Electrotherapy could be utilised to prevent the formation of scar tissue in the ligament and promote healing and decrease swelling.

Exercise therapy to restore strength and range of motion of both the neck and shoulder is vital.

Strengthening exercises include lateral rotator work, as well as shoulder blade pinching exercises. Taping can be applied to offload and realign the AC joint.

Mobilisation of the AC joint dysfunction(clavicle) and painful ranges are common interventions used by physiotherapists to restore normal and pain-free alignment.

In essence, if you are not too sure what’s causing your shoulder to hurt- book in to see a therapist for a shoulder assessment and treatment.


Experiencing neck pain? Find out more about neck pain relief and how Core Concepts Physiotherapy Singapore can help resolve your pain.