This article is about the common finger and thumb deformities that we see in clinical practice, namely Mallet Finger, Swan Neck Deformity, Boutonniere, the Z-Shaped Thumb Deformity and Dupuytren’s Contracture. The information can also be seen in video format below.
For Each of the 5 finger / thumb deformities, you will find a picture of the deformity and a simple description of the injury. For more information, please click the title or the picture for the full article about the condition.
Mallet Finger
In a mallet finger injury the very end joint of a finger (the DIP joint) or thumb (IP joint) droops down in a bent position, giving it the appearance of a mallet or hammer.
The injury is causes when the finger tip suddenly catches against something or gets stubbed against an object, or is hit by an object. So it can occur when catching a ball awkwardly where the finger tip is suddenly forced into a bent position. It’s therefore a common injury in baseball where it has the alternate name of ‘baseball finger’ and also in cricket. It also happens frequently when changing bed sheets, as the finger tip catches on the mattress, so it’s also a common injury with hotel housekeepers.
Swan Neck Deformity
A swan neck deformity is where the PIP joint of the finger bends backwards the wrong way, a position called hyperextension. And then the DIP joints adopts a flexed position. So the overall finger position resembles the position of a swans neck. And if you have a swan neck deformity you might struggle with gripping, making a fist and with fine dexterity activities. The PIP joint might also snap or flick suddenly from the hyperextend position to the flexed position when you try and make a fist.
Swan necks can be painful but not usually. It’s more of a finger movement problem than a painful problem in most cases. There can be many causes of a swan neck deformity but the most common ones are as result of Rheumatoid arthritis, due to an injury or as a result of having hypermobile joints such in hypermobility syndrome or Ehlers-Danlos Syndrome. And with all these causes, the result is the same. An imbalance in the way the extensor tendon works.
Boutonnière Deformity
A boutonnière deformity is the opposite of a swan neck. So instead of hyperextension of the PIP joint, we now have a bent position of the PIP. And instead of the DIP joint being flexed as in a swan neck, it’s now hyperextended.
A boutonniere deformity is caused by an injury to part of the extensor tendon called the central slip. This part of the tendon is responsible for straightening the PIP joint and without it, the PIP joint falls into a bent position and you won’t be able to straighten the finger. The injury creates a hole in the central slip which the head of the proximal phalanx bone can push through, like a button pushing through a button hole, which is where it gets its name from – boutonnière means ‘button hole’ in French.
Z-Shaped Deformity of the Thumb
This deformity is caused by arthritis of the thumb CMC joint. So it’s usually something that has slowly progressed over the years. What happens is that the arthritic CMC joint becomes 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. And 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.
Dupuytren’s Contracture
Dupuytren’s contracture is a genetic disorder which causes firm lumps and sometimes bands of tight tissue to develop in the palm and sometimes the fingers of the hand. It’s completely harmless and its only symptom is the thickened tissue but sometimes that tissue can tighten and cause the adjacent finger(s) to bend. It usually affects the little and ring fingers but it can affect any finger. So if you have a hand with some thickened lumps or bands in the palm and fingers that looks like the picture below, that you can’t straighten, although you can bend them OK, then it’s likely that you have a Dupuytren’s contracture.
Summary
If you think you might have one of these finger deformities, then click on the title of the deformity or the picture, to take you to the full article which discusses each condition in detail including how they are treated.
This content is provided for general information only and does not replace professional medical advice. Some articles may contain affiliate links. Full medical disclaimers and affiliate disclosure details are available on the relevant pages of this website.