Most classifications describe 4 types of ulnar deficiency (or ulnar longitudinal deficiency- ULD). These classifications only address the bony deficiency (and not the important other issues such as muscles, tendons, nerves, etc). While there are a number of classifications, the basic description is as follows:
Type I is a slightly short ulna
Type II is a notably short ulna
Type III is an absent ulna
Type IV is a completely absent ulna with fusion of the radius and the humerus.
We have helped to extend the classification in both directions. When the ulna is normal and there are only abnormalities of the hand (such as metacarpal synostosis, absent digits, etc) , this can be described as a Type 0 ulnar deficiency: http://www.ncbi.nlm.nih.gov/pubmed/16344190
On the other end of the spectrum, some kids have a severely shortened extremity. Traditionally, these children have been classified as having a phocomelia. Phocomelia (which will be the topic of another post) technically implies a segmental deficiency in which, for example the hand is attached to the arm (i.e., humerus) without a forearm. However, in another investigation we were able to demonstrate that most kids with a diagnosis of phocomelia actually have a diagnosis of either radial deficiency or ulnar deficiency: http://www.ncbi.nlm.nih.gov/pubmed?term=ezaki%20goldfarb%20manske
The importance of making the correct diagnosis cannot be understated, most importantly for 2 reasons: the genetics related to the diagnosis and the associated conditions. The genetics of a particular diagnosis will allow for information regarding the risks that the parents should understand for having another child with the same diagnosis and also the risk that the patient will someday have a child with the same diagnosis. The other issue is associated conditions. Some diagnoses carry a risk for associated conditions such as a heart or kidney problem whereas others do not. Therefore, making the correct diagnosis allows the ideal medical evaluation of the patient.
Here is an example of severe ulnar deficiency, or Type 5 ulnar deficiency. Note the short extremity and the three conjoined fingers.
|Ulnar deficiency on right|
|Another view of ulnar deficiency|
|Note the 3 fingers with syndactyly in ulnar deficiency|
|Radiograph of ulnar deficiency. There is one bone which has a split (kind of like a wishbone). There is no separate radius and ulna.|