Arthritis at the base of the thumb, technically affects the carpo-metacarpal (CMC) joint, i.e. the joint between the bones of the wrist and the first bone of the thumb. This is quite a remarkable joint as it allows the thumb to move in virtually all directions.
The thumb is absolutely critical to our ability to do many activities, so when it becomes painful it can be incredibly frustrating. Unfortunately for women CMC joint arthritis is far more common than in men. There are a number of different theories which include increased laxity in the joint in women, with tighter contact pressures but there is probably a genetic component as well.
Options for treatment to control the pain include, using a protective support or brace for work and household tasks, physiotherapy and a cortisone injection into the joint. Functional bracing, i.e. using a brace for a specific activity can be very helpful. These braces can be commercial or made to measure. Cortisone injections placed into the arthritic joint can help to reduce the inflammation and therefore, the pain. The period of relief is very variable from a few weeks to months or occasionlly into years. It may buy time before surgery may be required. The surgical options include, trapeziumectomy, fusion and a joint replacement.
The aim of surgery for osteoarthritis of the base of the thumb is to relieve pain and to produce a stable, reasonably mobile thumb. One of the traditional surgical methods of dealing with osteoarthritis of the CMC joint has been to remove the little bone at the base of the thumb. This bone is called the trapezium and after its removal ((1) a false joint is created using soft tissue.
In effect this forms a fibrous joint. There have been a number of variations of the surgical method but the simplest is often the best; forming the 'fibrous' joint by simply folding in adjacent soft tissue, primarily the thickened capsule of the arthritic joint (2) and securing the new construct with dissolvable sutures (3). However, to develop the stability the thumb requires, it is necessary for the hand to be immobilised in a cast for about 6 weeks.
In some parts of the world fusion of the trapezium to the metacarpal is a favoured operation. We do not like the concept of relying on the joint below (trapezium to scaphoid) for mobility as it is quite common for this joint to have some degeneration as well.
As technology has developed so has the ability to design smaller and smaller joint replacements. There have been a number available in the last few years and I have trialled the use of a surface replacement (made by Avanta). There are some potential advantages and disadvantages with this technique. The main disadvantage is that eventually all joint replacements will fail so we do not know how long these 'new' joints will last. The main reason for failure is loosening. Thus if one chooses this option it has to be appreciated that another operation will be required at some stage in that person's lifetime. Another major disadvantage is the slightly higher risk of infection as in effect foreign material (the implants) are being inserted in the body. The risk is of the order of 1% whereas the risk of infection following trapeziumectomy is of the order of 0.1%. The theoretical advantage of the replacement is that it preserves the length of the thumb and therefore ought to give better function. Certainly experience suggests that the range of movement and dexterity is very good but the results after trapeziumectomy are also very good so the 'jury is still out'. More recent longer term experience is suggesting that these newer joint replacements are likely to fail whereas trapeziumectomy rarely if ever fails.
It is critical that there is no evidence of arthritis in the joint below the trapezium, the scapho-trapezial-trapezoid joint as treatment of this condition could affect the biomechanics of the joint replacement and lead to failure. It is also critical that the next joint along the thumb, the metacarpo-phalangeal (MCP) joint is normal.
1 week after surgery
6 weeks onwards