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 looks a little like a saddle – scooped up at the front and back, and draped downwards at the edges. If you can imagine a cowboy (or girl!) sitting on top of a deep horse’s saddle, the rider can rock backwards and forwards, as well as from side to side. Likewise, 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). There is no uneven pressure or unbalanced riding to unsettle the joint surfaces.
For a number of reasons, this joint configuration in the thumb 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, persistent muscle action in one direction pulls the joint repetitively across one part of the joint’s interfaces and this can cause arthritic changes.
So, what to do? Splinting and exercises can provide effective relief for CMC joint osteoarthritis. The splint (or joint support) provides temporary ‘scaffolding’ to allow the joint to settle down and prevent excessive movement, while the exercises strengthen the surrounding muscles. Eventually the muscles become strong enough to replace the supportive action of the splint.
If you are experiencing pain in this joint, team up with a hand therapist sometime soon!
Note: In New Zealand a Registered Hand Therapist is either a Registered Physiotherapist or an Occupational Therapist who has completed additional postgraduate training and has experience in upper limb and hand injuries and conditions. For more information and location of providers see www.nzaht.org.nz
Handhub aka Alison is an experienced musculoskeletal physiotherapist and hand therapist based in Christchurch. You can find her at In Touch Hand Therapy.