CMC-1 osteoarthritis - N. Koekebakker, certified Hand Therapist

CMC-1 osteoarthritis is a common disorder of the carpometacarpal joint of the thumb, also referred to as degenerative joint disease.

The carpometacarpal joint of the thumb consists of the first metacarpal (os metacarpale) and the trapezium bone (os trapezium). Together, they constitute the saddle joint, the two planes which do not fit together exactly. It is in fact an incongruent joint. If the ligament of this joint slackens, the joint may become unstable.
Incongruence and instability cause increasing stress on the joint. Such chronic stress on the joint may adversely affect the degenerative process.
There is wear of the surface of the cartilage that covers both ends of the bones that constitute the joint. The quality of the cartilage decreases and it may even disappear completely. Movements of the joint cause pain as the ends of the bones touch. The joint may also thicken and joint distortions may occur in the form of bone spurs, the so-called “osteophytes”. This wear is an irreversible process.
This type of wear often causes misalignment of the thumb. The carpometacarpal joint of the thumb slides and forms a distinct lump; the thumb aligns with the index finger and overstretches. This is called a zigzag deformity.

> Complaints

The primary complaints consist of pain in the ball of the thumb. Pain complaints initially occur in stressing thumb movements, such as daily pinching and twisting movements. These may include wringing out a tea cloth, opening jar or bottle caps, opening vacuum packaging, turning a key, using zippers or buttons, holding a book, writing, etc.
In a later stage, this pain may be more continuous and often occurs at night. The base of the thumb may be swollen and the joint may produce a crackling feeling/noise during movement. Stiffness of the joint and loss of strength in the joint may also occur in this stage.

> Causes of osteoarthritis

Osteoarthritis has various causes.
It is usually caused by normal wear, a natural process during ageing. It is more common in women than in men, and manifests itself in particular after the age of forty. 16-25% of postmenopausal women are affected by osteoarthritis of this joint. As age increases, it is found that 1 in every 4 women and 1 in every 12 men of 70 years and older is affected by osteoarthritis of the CMC-1 joint. Overstressing caused by specific stressing activities or instability of the joint may play a role in the development of osteoarthritis. If the complaint is caused by previous injury of the joint, for example by a bone fracture extending through the joint, this is called posttraumatic osteoarthritis.

> Treatment

At the early stages of osteoarthritis, non-steroidal anti-inflammatory drugs (NSAIDs), a specific brace, and exercises prescribed by a hand therapist, may be used to control the complaints.
The essence of a brace is that it stabilises the carpometacarpal joint and places the metacarpal in a functional position. This creates the so-called “thumb arch”, which decreases the stress on the carpometacarpal joint. If the other joints of the thumb and the fingers remain free, this guarantees optimal hand functioning.
The hand therapist will focus on optimising thumb stability and strength, training a "functional thumb arch", and giving recommendations for daily use of the hand.

N. Koekebakker, active member of the Dutch Association of Hand Therapists, working at 4hands, a private hand therapy clinic in Amsterdam