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Thumb Base Arthritis

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Fig 1. Steroid injection of the 1st CMC Jt (between the 1st metacarpal and trapezium)

Fig 2. Steroid injection of the 1st CMC Jt (between the 1st metacarpal and trapezium)

History
The 1st Carpometacarpal joint (1st CMC Jt) is one of the most common areas of symptomatic arthritis especially in post-menopausal women. Present at @50-70 yrs. Often a positive family history of mum/sister/grandmother having had a similar problem.
Complain of pain @ base of thumb, but also in the thenar eminence and up the thumb. Poor grip causes difficulty in opening jars etc.

Examination
The thumb base can be swollen and prominent. The thumb often becomes adducted into the palm secondary to the subluxation at the 1st CMC Jt. With the thumb stuck down in the palm, over time, the metacarpo-phalangeal joint (MCP) becomes hyper-extended due to compensation. This is the classic “Z” deformity that can occur in chronic conditions.
Palpation is painful at the 1st CMC jt and circumduction and compression (the “Grind” test) is painful.

Differential Diagnosis

Other causes of radial sided wrist/thumb pain include

  • De-Quervains tenosynovitis
  • STT Jt arthritis. This is the joint below the 1st CMC Jt and should always be checked for arthritis
  • Sequaele of scaphoid fracture, including non-unions and arthritis
  • Ganglions

Investigations
Plain Radiographs will confirm the diagnosis. The views which are needed are a Roberts view (true AP – forearm in maximal pronation & dorsum of thumb resting on the x-ray cassette) and a lateral.

Treatment
The therapeutic ladder is the best way to treat this condition, as in any arthritic joint condition:-

  • Activity modification
  • NSAID
  • Splints- the therapists at Poole and Bournemouth Hospitals will be happy to make a thermoplastic custom splint for your patient
  • Steroid injection, see below
  • Surgery:-

1.    Extension metacarpal osteotomy – only rarely used
2.    Arthroscopic 1st CMC Jt debridement – very rarely used
3.    Trapeziectomy – the main stay treatment for most surgical patients
4.    1st CMC Jt fusion – best in manual working men
5.    1st CMC Jt replacement – only in relatively young patients with a well preserved STT Jt. Long term results are not known

When to Refer
A large number of patients can be successfully treated in primary care with the non-surgical techniques above.
If symptoms continue after a period of months of conservative measures then referral is suitable.
Patients need to know that surgical techniques are successful in the majority of patients, but post operative rehabilitation is lengthy and can take up to 4-6 months to reach full benefit.

Injections 
Please refer to section on steroid injections.

What’s the Evidence ?

  • Day et al JHS 2004 29A
  • Randomized control trial. Comparing placebo to steroid.
  • Good results with steroid injection if early OA.
  • Poor results with more severe OA. i.e early recurrence

It’s my opinion that a maximum of 2 injections in a treatment cycle (i.e 1 year) is allowed. Too many lead to skin and fat atrophy which makes surgery more risky.

How to Inject

  • Blue Needle
  • 1-2 mls lignocaine, 10-20 mgs Kenalog
  • Apex of snuff box, Pull thumb
  • Don’t worry about not getting needle into centre of joint, if it’s within the capsule of the joint then the steroid will hit the spot