By Stephen Bunting, Specialist MSK Physiotherapist (UK)
This article is about the Z-Shaped of the Thumb. It includes the causes, diagnosis and treatment.
The information can also be seen in part of the following video.
The Z-Shaped deformity is caused by Arthritis of the Thumb CMC Joint. So it’s usually something that has slowly progressed over the years.
The deformity develops as a result of the arthritic CMC joint becoming unstable. As the joint surfaces erode and the ligaments become lax, the base of the metacarpal starts to migrate out to the side causing the classical ‘squaring’ of the thumb base. As the base of the metacarpal moves further outwards, the other end of the metacarpal moves inwards to compensate, like a sea saw.
This then causes a further compensation reaction at the MCP joint which has to hyperextend in order to keep the thumb in a functional position so you can still use it. So a Z-shaped deformity is basically a series of joint compensation reactions driven by thumb base arthritis.
Treatment
If any of the joints are painful, then they can be treated with topical gels, joint supports and injections. A thumb base splint can also be helpful but it will need be like the one pictured below which doesn’t cause pressure against the squared thumb base.
Sometimes though, a custom made heat mouldable splint is the best option as it is shaped to your individual thumb position. This can be provided by a hand therapist.
But while these treatments can sometimes help with pain, unfortunately there is nothing you can do to change the z-shaped position of the thumb other than surgery.
This article is for general information only and does not replace individual assessment. Start any exercise gently and stop if your symptoms worsen significantly. If you have severe or rapidly worsening symptoms, or you’re concerned about your health, please seek urgent advice from a qualified healthcare professional. See our full disclaimer for more information.