Two different operations
People are often told they need a shoulder replacement without it being clear that there is more than one kind. The two main types are the anatomic total shoulder replacement (ATSR) and the reverse total shoulder replacement (RTSR). They use different implants, work in different ways, and are chosen for different shoulders. The video below explains the difference.
The anatomic total shoulder replacement
An anatomic replacement keeps the natural layout of the joint. The worn ball at the top of the humerus is replaced with a metal ball, and the worn socket is resurfaced, usually with a plastic component. The ball stays on the arm side and the socket stays on the shoulder blade side, as in a normal shoulder.
Because it reproduces normal anatomy, an anatomic replacement depends on the rotator cuff to move and stabilise the joint. It is therefore suited to shoulders where the arthritis is the problem and the rotator cuff tendons are intact and working.
The reverse total shoulder replacement
A reverse replacement does what its name suggests: it swaps the configuration over. A ball, called a glenosphere, is fixed to the shoulder blade where the socket used to be, and a socket is fitted to the top of the humerus.
This arrangement changes the mechanics of the joint so that the deltoid, the large muscle over the outside of the shoulder, can raise the arm without relying on the rotator cuff. That is the key point: a reverse replacement can work in a shoulder where the rotator cuff is torn beyond repair or no longer functioning.
How the choice is made
The single biggest factor is the state of the rotator cuff. Broadly:
- Arthritis with an intact, functioning rotator cuff generally suits an anatomic replacement.
- Arthritis combined with an irreparable rotator cuff tear, sometimes called cuff tear arthropathy, generally suits a reverse replacement.
Other things that feed into the decision include how much bone remains in the socket and its shape, whether the shoulder has been operated on before, certain complex fractures of the upper humerus, age, and what the shoulder is needed for. The two types also differ in the range of movement that can be expected afterwards, particularly rotation, and in their patterns of long-term wear. These trade-offs are the substance of the pre-operative discussion.
Related information
Our anatomic total shoulder replacement and reverse total shoulder replacement pages describe each operation in detail. See also shoulder arthritis, rotator cuff tear, and our post on understanding the risks of total shoulder replacement. To arrange an assessment, see the consultation page.