Osteoarthritis of the thumb is one of the main arthritic problems that a hand therapist* can help with. The joint in question is the one at the very base of the thumb down near the wrist joint. You may hear the term ‘CMC’ joint being referred to, or the ‘basal joint of the thumb’. CMC stands for ‘carpometacarpal’ …in other words the joint between the metacarpal and the carpus (in this instance the trapezium bone).

This beautiful joint is in the configuration of a saddle – scooped up at the front and back, and also draped downwards at the edges. If you can imagine a cowboy (or girl!) sitting on top of a deep horse’s saddle, he can rock both backwards and forwards, as well as from side to side. So, the joint needs a strong but mobile joint capsule around it to support it, as well as muscles contracting in each direction to keep it stable. These keep the cowboy (base of the metacarpal) sitting steadily in the centre of the saddle (trapezium), no uneven pressure or unbalanced riding to unsettle the joint surfaces.

In the thumb, for a number of reasons, this joint configuration can let us down by becoming arthritic. Either the joint capsule has been damaged and stretched in the past allowing too much uneven movement, or the joint may already be naturally hypermobile allowing uneven pressure over the joint surface. Often, as we age, persisting uni-directional muscle action pulls the joint repetitively across one part of the articular surface resulting in arthritic changes in the joint.

So, what to do? There is good evidence in the literature that both splinting and exercises can prove effective relief for CMC joint osteoarthritis (Aebischer, Elsig & Taeymans, 2016) and this is certainly the case in clinical practice. The splint (or joint support) provides temporary ‘scaffolding’ to allow the joint to settle down and prevent excessive movement, whilst the exercises strengthen up the surrounding muscles, eventually to replacing the supportive action of the splint.

If you are experiencing pain in this joint, team up with a hand therapist sometime soon!

Aebischer, B., Elsig, S., Taeymans J. Effectiveneness of physical and occupational therapy on pain, function and quality of life in patients with trapeziometacarpal osteoarthritis: a systematic review and metaanalysis. Hand Ther (2016) 21:5-15.

*Hand Therapist – in NZ a Registered HT is either a Registered Physiotherapist or OT who has completed additional postgraduate training and experience in upper limb and hand injuries and conditions. For more information and location of providers see http://www.nzaht.org.nz/