Figure 1
I thought I would take this opportunity to describe some of the recent innovations in shoulder arthroplasty. Good results are now the norm for patients undergoing shoulder replacement surgery as shown in several National Joint Registries. Despite this, I still have patients in my rooms who tell me that doctors have told them there is no point having a shoulder replacement as they don’t work. Hip and knee replacements have had excellent success. They are relatively simple joints and the joint surfaces are highly congruent. In this circumstance, replacing the joint with two appropriately matching surfaces usually produces a satisfactory outcome. In the shoulder joint matters are more complex. There is a relative mismatch in size between the small glenoid fossa and the much larger humeral head. There is no inherent stability between the joint surfaces. Instead, the function of the shoulder joint depends vitally on a complex group of muscles and tendons called the rotator cuff and it is this that controls movement and stability. Shoulder replacement is usually successful but in poor outcomes this is usually related to poor function of the rotator cuff.Thus in evaluating a patient with shoulder joint degeneration the surgeon must specifically assess the integrity and function of the rotator cuff along with range of movement. This may be done simply by examining the rotator cuff. An xray showing a healthy subacromial space is helpful . If there are doubts then either ultrasound or MRI will confirm any damage to the tendons. Figure 1 shows a patient with advanced gleno-humeral degenerative changes. There is loss of joint space but no collapse of the humeral head or glenoid fossa. There is conservation of the sub-acromial space which still measures approximately 1cm. Examination of the patient revealed very poor range of movement but rotator cuff power was felt to be normal and its integrity was confirmed by ultrasound.
Figure 2
This patient underwent the simplest of shoulder replacements, a resurfacing hemiarthroplasty with good result.(Fig 2) In this procedure an approach to the joint is made through the subscapularis tendon and a new metal surface is applied to the existing humeral head. The surgeon goes to great lengths to free up and mobilise the rotator cuff tendons which are often significantly scarred. At the end of the procedure the subscapularis tendon is repaired and it is for this reason that the patient needs to protect the shoulder in a sling for 3 weeks.
Figure 3
Total shoulder replacement is also an option particularly if there is significant damage to the glenoid fossa. In this procedure the existing head is usually removed to gain sufficient access to the glenoid fossa to allow replacement of this surface. The humeral head is then replaced using a stemmed prosthesis in a manner very similar to conventional hip replacement. (Fig 3) There is recent research that suggests the best results are obtained with total shoulder replacement. However the complication rate is higher for totals and these complications are often difficult to manage.
Figure 4
What about the patients with advanced degenerative changes and a failed rotator cuff? These patients have a condition called cuff tear arthropathy. In the normal shoulder, the rotator cuff keeps the head centred on the glenoid fossa. In a failed cuff the deltoid muscle on its own pulls the humeral head upward until it starts to make contact with the under surface of the acromion and obliterates the subacromial space. Damage to the humeral head can then proceed dramatically producing very severe pain and pseudoparalysis of the shoulder. This condition is most common in ladies over 75 and their lives can become extremely miserable due to pain and sleep deprivation. (Fig 4)
Figure 5
Replacement of these shoulders with a conventional shoulder replacement is likely to fail as the replacement will continue to rub on the acromion producing pain. Function remains poor as the deltoid has no fulcrum to work against. The operative solution is reverse total shoulder replacement. This has been developed to answer the problem of the degenerate shoulder with no cuff. This involves fixing a metal half sphere to the glenoid fossa and converting the humeral head into a matching cup. The deltoid muscle then has a pivot to work against increasing its power and allowing the arm to rise.(Fig 5) Results of reverse total shoulder replacement have been so good that many centres are now also using them for the treatment of the most severe proximal humeral fractures as they give reliable results.
All these examples are from my own patients and I hope they help clarify some of the recent developments that are making shoulder replacement more successful and reliable.
