What is the AC or Acromio-Clavicular Joint?
The Acromio-Clavicular joint is a small joint between the outer end of the clavicle and the acromial process of the scapula. Its full name is commonly abbreviated as the AC Joint. Although a small amount of movement occurs at the AC Joint it’s more important role is to help stabilise the scapula or shoulder blade on the chest wall. This in turn helps to provide a stable foundation for the entire shoulder joint.
What is AC Joint Arthritis?
AC joint arthritis is a term which refers to any condition where the cartilage on the end of the clavicle and the adjoining surface of the acromion is damaged or worn. Wearing of the joint cartilage may occur gradually over many years due to the physical loads placed on the AC Joint in everyday life. This is referred to as Osteoarthritis. Some inflammatory arthritic conditions such as Rheumatoid Arthritis may also damage the AC Joint.
The AC Joint may be injured by a fall on to the shoulder or any form of direct impact that compresses the joint surfaces. A fracture at the outer end of the clavicle may also damage the joint cartilage. This can set the scene for the later development of AC Joint Arthritis.
It may also be damaged by less forceful repetitive loads on the joint such as heavy overhead weight lifting in the gym. Bench pressing in particular applies great loads on the AC Joint. This particular exercise may result in a particular form of AC Joint Arthritis. It is theorised that stress fractures at the outer ender of the clavicle may result in gradual collapse of the supporting bony under the joint cartilage. This condition is referred to as Osteolysis of the clavicle
What are the Symptoms of AC Joint Arthritis?
Regardless of the underlying cause of the arthritis the condition presents with pain. There can be a localised sharp pain in the region of the AC Joint. This pain typically occurs when the arm is lifted in front and taken across the body. Sometimes the pain is more in the form of an ache, often in the back of the shoulder or upper arm. Lying on the shoulder compresses the worn AC Joint and may cause sleep disturbance.
Diagnosis of AC Joint Arthritis
The symptoms and clinical examination findings may be characteristic. Mr Lyons may apply compressive forces on the joint to see if your pain is reproduced.
X-rays will show reduction of the joint space and irregularity of the joint surfaces. MRI scans will show similar changes. It may also demonstrate inflammation and excess fluid in the joint. Although X-rays may show arthritic wear in the AC Joint the wear may not necessarily explain your pain. In cases of uncertainty Mr Lyons may suggest an ultrasound guided injection of local anaesthetic and cortisone in to the joint. If the injection provides at least temporary pain relief it will help to confirm that the AC Joint is the problem.
Treatment of AC Joint Arthritis
A trial of anti-inflammatory medication or an ultrasound guided cortisone injection may be helpful if symptoms are of recent onset. Chronic symptoms, especially nocturnal pain, may require a surgery. Patients undergoing rotator cuff surgery may also have a component of AC Joint Arthritis. If so, the AC Joint can also be addressed at the time of the rotator cuff surgery.
The surgery involves the removal of approximately 1.5cm of bone from the outer end of the clavicle and removal of the inflamed joint lining or synovectomy. This surgical procedure is commonly referred to as an Excisional Arthroplasty of the AC Joint. It prevents contact between the worn AC Joint surfaces. It is generally very reliable in restoring normal shoulder comfort and function. The surgery can be performed using either open or arthroscopic surgical techniques depending upon the technicalities of the surgery.
AC Joint Arthritis – Bone to Bone Contact
Division and Removal of Outer Clavicle