Another source for shoulder pain: Could it be the AC joint?

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 (Ac) joint.

Anatomy

The clavicle (collar bone) has 2 joints a medial (to sternum) and lateral end (to the acromion of the scapula-shoulder). The Ac joint refers to the lateral articulation with the acromion of the scapula. The joint is stabilised via the acromioclavicular, coracoacromial and coracoclavicular ligaments and the upper and middle fibers of trapezius muscles aswell as well as the deltoids.

Anatomy: Image from Orthoinfo.aaos.org
click for larger view

Injuries
Ac joint dysfunction is a result of a sprain, dislocation, fracture or osteoarthritis at this joint

Dislocation and sprain
The Ac joint is usually injured by a direct fall onto the top of the shoulder, cycling injuries, or associated with over head throwing (Javelin) athletes. The shoulder blade (scapula) is forced downwards and the clavicle (collarbone) appears prominent. The degree of injury at the joint is classified by the separation of 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 is 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 thr clavicle that is required to achieve end range forward flexion (overhead ROM). Pain will occur as a result of over stretched/ ruptured ligamemts (depending on the severity) and a stretched joint capsule. As a protective mechanism, pain tends to lead to altered postures which may comtribute to neck pain and altered muscles activity of muscles that attach to the clavicle; such as the pecs, trapezius and  sternocleidomastoid.

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

Arthritis
The incidence of arthritis at this joint has been shown to be about 50% in MRI studies of elderly populations, however these people may be asymptomatic.
Just like any arthritis this refers to 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, as well as 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
Arthritis
Pain and stiffness of the joint is a 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.

Dislocation and sprain

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 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. Similar to arthhiritis the individual will report pain on moving the shoulder, especially with overhead activities and across your body motion.

Treatment

Acute injuries will respond to ice therapy, anti-inflammatory medications and a sling is 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 (clavicle) at painful ranges is also a common intervention used by physiotherapist to restore normal and pain free alignment.

If your not too sure whats causing your shoulder to hurt- book in to see a therapist for a shoulder assessment and treatment.

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