Jeremy Field - Consultant Orthopaedic and Hand Surgeon

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This is a tightening and thickening of a fibrous tunnel that starts at the base of the thumb through which the flexor tendons pass (the flexor tendons are the tendons that bend the fingers into the palm). They are more common in females and particularly common in post-menopausal women.

There are also other associated conditions:

Gout
Diabetes
De Quervain's disease
Haemodialysis patients
Amyloidosis

However by far the most common cause of this condition is iatrogenic and this is a medical term for "we don't know".

The ring finger is the most common and the middle finger is the next most common then the little and the index is the rarest. Trigger thumb is as common as the middle finger.

There is no association with occupation.

There is no association with trauma or any form of repetitive "injury".

There is also another peak of incidence and that is in childhood with a peak age of about 3.

The analogy of the trigger thumb is a bicycle brake cable (Boden cable). The bicycle brake cable has a metal cord which is surrounded by a white plastic sheath the cord moves in and out of the sheath. If there is a lump in the cord either the cord won't go into the sheath and the brakes don't go on or the lump gets stuck inside the sheath and the brakes get stuck on. A trigger digit involves a lump in the tendon caused by a constriction of the fibrous tunnel through which it passes. That lump is similar to the lump in the bicycle brake cable.

Patients generally complain of a clicking thumb. The thumb is often painful particularly in the morning. Sometimes the thumb locks down and again can occur in the morning.

It is possible to feel a lump in the tendon just at the base of the thumb. If you place your thumb at the base of the affected thumb and press hard and then bend the thumb in and out you can feel a lump moving underneath your thumb.

In children the condition generally affects the thumb, the parents notice that the child has got a bent thumb and cannot straighten it although sometimes it does straighten and the child tends to squeal! The condition may be on both sides and there may be a familial tendency. In this type there may be spontaneous resolution in 1 out of 3 cases. This resolution drops to 10% in those identified at 3 years but the majority of the cases seen at 5 years require surgical release.

Unlike trigger fingers where the nerve that supply the finger are always on either side of the tendon the nerves to thumb commonly cross the tendon in an unpredictable way so Mr Field is disinclined to inject trigger thumbs as there is a possibility that the nerves in the thumb could be damaged by the injecting needle. A trigger thumb especially in ladies can resolve over a three month period. If it does not resolve after that time then an operation is recommended.