AC Joint - collar bone

What is the Acromioclavicular Joint?

The acromioclavicular joint (AC Joint) or outer collar bone joint can be easily felt on the top of the shoulder, sometimes referred to as the knuckle of the shoulder. It is the joint between the outer end of the collar bone and the shouldewr blade as it curves on top of the shoulder joint. It is a very small joint, but can be a source of pain due to inflammation or arthritis.

Why does the joint become painful?

Inflammation due to over use or osteoarthritis are the two common causes.

Inflammation due to over use or injury occurs mainly in adults over 30, it can be related to heavy lifting and bodybuilding. People with AC joint pain usually point with one finger to the pain being on top of the joint. The pain occurs on overhead movements and movement across the chest.

Osteoarthritis cause similar pain but there may not be any injury or precipitating factors. Osteoarthritis of the AC joint makes the joint more prominent and bigger. This bigger joint may rub againt the rotator cuff tendons as they pass under the joint and cause pain similar to impingement over the outer aspect of the shoulder.

What's the difference between inflammation in the joint and arthritis?

All joints of the body have a sensitive lining on the inside of the capsule of the joint. This produces fluid which lubricates the joint and nourishes the articular cartilage (gristle). This lining can be injured or irritated by wear particles from the gristle surface. Once inflammed the lining will produce more fluid, the lining will swell itself and the lining releases chemicals into the joint which produce pain.Pain is also caused by the fluid distending the joint. The body produces its own pain killers, steroids and anti-inflammatories to reverse the inflammation.

In arthritis the articular cartilage is worn away to expose the underlying bone. Inflammation may still occur as the remains of the articular cartilage are worn off and irritate the lining of the joint. Pain may also arise as the bones on either side of an arthritic joint rub on each other. Not all arthritic joints produce pain and arthritis of some degree in the AC joint is almost universal over the age of 60, so its almost a natural ageing process like "wrinkles".

How is the diagnosis made?

Your doctor will examine you and an X-rays, bone scan or an MRI scan may be used to confirm the diagnosis.

What's the Treatment?

Initially rest and anti-inflammatories may be tried to settle the pain.  A steroid injection may help to confirm the diagnosis and treat the condition in the early stages. Surgical excision of the worn ends of the joint either by a key hole or an open operation is usually curative.

This operation is done through two or three, 0.5 cm puncture wounds under a general anaesthetic. Most people would go home the same day and wear a sling for a few days until the shoulder is comfortable. The pain of the operation settles in 2-3 weeks and the original pain settles over a period of 3 months. All pain free activities are allowed once the sling comes off. Any painful activity is to be avoided until the pain related to that activity settles. In general, anything you could do just before the operation, you can do within 3 weeks after the operation and all normal activities will be possible between 3 & 6 months after surgery.

Dislocation of the AC Joint

Dislocation of the AC joint is a common sports injury. The injury occurs following a fall on to the tip of the shoulder. The dislocation maybe partial (subluxation) or total. At the time of the injury the shoulder is painful and movement is limited. The end of the clavicle or collar bone is prominent but this is because the rest of the shoulder is dropped.

Within a few days the pain and bruising settles and the movement slowly returns.

How is the Diagnosis made?

The diagnosis is confirmed by X-rays. The degree of dislocation, partial or total can be diagnosed by special weight bearing X rays.

What's the definitive treatment?

Partial separation of the AC joint is usually treated in a sling until the shoulder is comfortable. 75% of the time, this leaves you with a pain free shoulder and a slightly prominent end of the collar bone. If the AC joint continues to be painful, treatment similar to that described for arthritis above can be considered. 

Complete separation of the AC joint can be treated in a sling as well. However, you may complain of weakness and clicking in the shoulder. This maybe a concern if you are an overhead athlete such as a racket player, rock climber, basketball player etc.. You may also find the deformity unacceptable.

The alternative treatment for complete separation of the AC joint is reconstruction of the ligament that stabilises the joint. This is normally an open operation and requires immobilisation in a sling for 6 weeks afterwards. This operation can be performed at the time of the initial injury or at any time after that. Occasionally, it is possible to reconsruct this joint with a keyhole operation.

What is the sterno-clavicular joint and what can go wrong with it ?

The sterno-clavicular joint (SC joint) is the joint between the inner aspect of the collar bone and the chest bone.

In young people, the SC joint may dislocate (complete separation) after an injury or more commonly subluxate (partial separation) without an injury. The long term consequenses of this condition are mild and surgery is best avoided.

In older people, the SC joint may become arthritic. Treatment for arthritis of the SC joint is similar to that of the AC joint.

Rarely arthritis and inflammation may affect the inner end of the collar bone (sternoclavicular joint) producing local swelling and pain. Movements as above maybe similarly affected. The treatment is similar to treatment of the commoner AC Joint inflammation and arthritis.

I fractured my collar bone, whats the best treatment ?

Fractures of the collar bone can affect the inner third, middle third or outer third of the bone. Fractures of the middle third are the most common (in fact this is the most commonly fractured bone in the body). Fractures of the outer third are relatively common, but fractures of the inner third are rare.

Most of these fractures can be treated in a sling. They tend to heal most of the time but may leave you with a prominent lump if the fracture was displaced. The chances of the fracture not healing is about 5% for the middle third and 33% for the outer third.

Displaced fractures and fractures of more than two pieces are less likely to heal and your doctor may discuss operative treatment of these fractures with you. Most of the time surgery is needed only when the fracture has failed to heal or healed with a significant deformity.

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