The shoulder is a ‘ball and socket’ joint made of two bones, the humerus, or arm bone, and the scapula or shoulder blade. Unlike the hip ball and socket joint, the shoulder joint is further complicated by the scapula moving on the chest wall and also being attached to the collar bone via the acromioclavicular (AC) joint. The surfaces of the bones that move against each other are covered by a layer of tissue called articular cartilage, or the joint surface. In healthy joints this is smooth and the surfaces move freely against each other. In damaged or arthritic joints this layer may be rough or patchy and this can cause pain, swelling and feelings of instability.
The shoulder joint has a very wide and free range of motion which is important to allow us to get our hands to where we need them to do work. For this reason, the ‘socket’ of the joint (the glenoid) is small and shallow and only about a quarter of the surface area of the ‘ball’ (humeral head). This does give a great range of movement but is not particularly stable. To account for this, there are many important ligaments, extra cartilages, a strong joint capsule and special muscle groups that are very important for the shoulder to function properly. Unfortunately, this complexity also results in many shoulder conditions.
Common Shoulder Conditions
Rotator Cuff Disease. The rotator cuff is the name given to a special group of muscles that surround the ball and socket component of the shoulder joint. It is important for fine control of shoulder function. The muscles work together to produce the desired movement. Sometimes this co-ordination becomes impaired and results in problems. These can include fraying or frank tearing of the rotator cuff itself or inflammation with or without calcification. Rotator cuff disease is very common and gets more common as you get older. A vast majority of the time it can be treated without surgery if the patient presents early enough, with a combination of physiotherapy, exercises taping and sometimes steroid injections. However, in an active patient that has torn their cuff completely, early presentation and surgery gets better results and can prevent arthritis in the future.
Shoulder Dislocation. The shoulder joint is well known to be prone to dislocation. This is in part due to its anatomy with a shallow socket. In younger people, first dislocations will often be managed without surgery but the risk of re-dislocation is high. In these circumstances, stabilisation surgery may need to be performed. In older patients, the risk of re-dislocation is lower.
Acromioclavicular Joint Damage. The acromioclavicular joint is commonly damaged in sporting injuries, resulting in various grades of dislocation. The classic ‘spear tackle’ landing onto the point of the shoulder will cause these. The vast majority of these will be able to be managed without surgery. In certain circumstances, surgery is required and reconstructions can be performed. The operations for this have improved significantly in the past few years with far better outcomes than previously.
Frozen shoulder is a peculiar condition and we are still not sure of the cause. In this condition, the shoulder initially becomes painful, even at rest. It goes on to become painful and stiff and then slowly the pain resolves and the stiffness remains. Eventually, the stiffness will go. There does not have to be any history of injury or other condition. It is more common in diabetics, people who have had open-heart surgery and sometimes after surgery. The time for it to run its course is quite variable, often quoted from 3 months to 3 years. Physiotherapy will often make it worse. Surgery is usually not indicated. Sometimes if the joint is just stiff and no longer painful, resolution can be hastened by putting the patient to sleep with a brief anaesthetic and moving the arm around whist they are under. This breaks up the joint adhesions and makes it easier for the patient to move the arm.