Triphalangeal Thumb

The normal thumb has two bones- 2 "phalanges"- which makes it different from the three bones of the fingers.  Occasionally, we see a thumb with 3 bones- 3 "phalanges"- and we call it a triphalangeal thumb.  I have previously blogged about different aspects of the triphalangeal thumb- 5- finger hand and another on the Five finger hand.  Also, sometimes, the triphalangeal thumb is part of radial polydactyly when there is one triphalangeal thumb and one more typical thumb with two phalanges.

I wanted to share a case in which there was a single triphalangeal thumb.  This case is somewhat typical in that the extra bone is a really small, triangular shaped bone.  This bone causes a deviation of the thumb and that is usually the reason that the family seeks help. Surgery, as shown below, is reliable in straightening the thumb but does not always restore full motion.

Triphalangeal thumb, crooked due to the extra triangular shaped bone.

Another view of the Triphalangeal thumb, crooked due to the extra triangular shaped bone.

X-ray of the triphalangeal thumb.  There is a really small triangular bone between the main 2 thumb bones.

Another view of the 

X-ray of the triphalangeal thumb.  There is a really small triangular bone between the main 2 thumb bones.

This extra bone causes the thumb to be crooked and can also limit motion.  For both reasons, the patient may be taken to the operating room to remove the extra bone and tighten the joint.  A pin is placed to allow the soft tissues to heal.

This is the extra bone after removal.

Triphalangeal thumb after removal of the extra bone.  The thumb is straight once again.

Charles A. Goldfarb, MD
My Bio at Washington University
congenitalhand@wudosis.wustl.edu

Underdeveloped Thumbs

Underdeveloped Thumbs 

It is always interesting to me when I see an older child with underdeveloped thumbs, aka hypoplastic thumbs.   Most of the time, children with small thumbs are identified early in life as small thumbs are typically part of a larger issue, radial longitudinal deficiency (RLD).  However, when isolated, underdeveloped thumbs can be easy to “miss” early in life and may only be noticed when children face increased demands on their thumbs in school or sports.

There are 3 parts to the underdeveloped thumb.
1) The thumb looks different due to a lack of the muscles at the base of the thumb, the thenar muscles.  While this may be clear to someone with training, this deficiency in muscles may not always be easy to appreciate.
2) The thumb MCP joint (connecting the thumb to the hand) is unstable.  This may be the most important part of the underdeveloped thumb from a functional standpoint.  The reason this is important is the lack of joint stability affects pinch strength and, eventually, this can cause functional limitations.    Basically, a weak pinch is not ideal and can absolutely limit what a child or adult can accomplish.
3) The web between the thumb and index finger may be shallow in the underdeveloped thumb.  While not always a problem, when this web is really shallow, it can limit the size of the object that the child can grab (such as a ball or soda can).

As mentioned above, the three signs are usually identified early as part of the bigger problem of RLD.  But sometimes, the thumb is an “isolated” problem.  We see that when one arm has severe RLD and the other seems normal.  But with close examination, the thumb on this "normal" side is really underdeveloped.  Or, as noted above, the child comes to clinic at age 10 or so complaining of different appearing thumbs that lack strength.  That is the case for this child.

Underdeveloped or hypoplastic thumbs.  Not the lack of muscle at the base of the thumb.

The underdeveloped thumb looks slightly different here but no obvious findings.

The underdeveloped thumb does not have good stability as shown in this stress picture.

X-rays of an underdeveloped thumb.  While not obvious, there is a clear difference in the thumb development compared to normal.

And why do we like to make this diagnosis?  Well, the underdeveloped thumb is a part of the spectrum of RLD.  So, even if the underdeveloped thumb is isolated, the patient still has RLD.  And, as I have blogged about Here, this carries risks for other abnormalities such as VACTRL, TAR syndrome, Holt- Oram Syndrome, and others.  If the child is properly identified, these other issues can be properly assessed.

In addition, if we identify the underdeveloped thumb, we can treat it to maximize function.  I have previously written about this Here, although that post discusses pollicization (not appropriate here) and reconstruction of the joint and the muscles (what we would consider for this patient).

Charles A. Goldfarb, MD
My Bio at Washington University
congenitalhand@wudosis.wustl.edu

Unusual Clinodactyly

I have written previously on clinodactyly with several posts.  Clinodactyly, the curved finger, is typically not a functional problem.  But, a more severe deformity is more likely to be a problem with activities and patients often complain of trouble with things like keyboarding and musical instruments.  Clinodactyly of the small finger is most common location and it almost always causes a deviation of the pinky towards the ring finger.  It is rare to see any other deformity.

This 17 year old patient has clinodactyly but with the very uncommon deviation away from the ring finger.  It does not cause pain but it does cause trouble with activities.

Notice the curved small fingers- clinodactyly- but with deviation away from the hand.

Close up view of small finger clinodactyly.

Finger flexion is good (almost always the case) in this patient with clinodactyly.

Clinodactyly.  Not the abnormal shape of the middle bone causing deviation.

Clinodactyly.  Not the abnormal shape of the middle bone causing deviation.

Thanks for reading.

Charles A. Goldfarb, MD
My Bio at Washington University
congenitalhand@wudosis.wustl.edu

The Short 4th Metacarpal

We will, from time to time, evaluate a patient presenting with a painless shortening of the 4th (and sometimes 5th) metacarpal.  Often, the complaint is of an absent knuckle or a different- appearing hand.  Here is one such 14 year old patient.  The primary issue is the shortening of the ring finger metacarpal bone although the pinky does look somewhat short also.

Patient presenting with a short 4th metacarpal.

Patient with a short 4th metacarpal- notice that she lacks a knuckle on the ring finger.

Side to side comparison of short 4th metacarpal patient affected on one side only.

Side to side comparison of short 4th metacarpal patient affected on one side only.

X-rays tell the whole story.  Notice how short the 4th metacarpal is compared to the other metacarpals.  There is no growth plate in the 4th metacarpal.

x-ray showing short 4th metacarpal.

Thankfully, in this patient and others like her, this is a painless problem and one that rarely causes a functional problem.  So, we recommended careful observation and if problems ever do occur, there are options for treatment.  The most reasonable option is to lengthen the 4th metacarpal bone- here is a previous blog post on the topic.  However, the challenge with this procedure is the balance of the tendons.  The patients muscles and tendons have grown accustomed to their current length and if we make the bone longer, the tendons do not always adjust well.  Yet another reason to not intervene unless pain or functional problems are noted.

Finally, we all wonder why this happens.  There are many possible causes.  This site summarizes the possible causes.  

- Trauma.  If the growth plate to the 4th metacarpal was injured when the patient was much younger, it might have shut down and simply not grown any further.  This patient, and most, do not recall such a trauma.

- pseudohypoparathyroidism or pseudopseudohypoparathyroidism.  OMIM describes the second issue very well here.

Finally, here is an article on the topic.

Thanks for reading.

Charles A. Goldfarb, MD
My Bio at Washington University
congenitalhand@wudosis.wustl.edu