Oftentimes when speaking with patients, they report that their doctor states that they have a positive ulnar variance. They are discouraged as it sounds permanent and only resolved with surgery. I thought it was an important topic to discuss. Ulnar variance is a measurement that is taken from X-rays to define the length of the ulna bone relative to the radius.
This is an important measurement because the dynamics of the wrist are dependent on the ulna and radius translating force through the wrist. Normally, the translation of forces 80/20. 80% translates to the radius and 20% to the ulna. This is one of the reasons we see more radius fractures than ulna fractures.
There is only one genetic disease where one is born with an ulnar variance, Madelung's deformity. Radiopedia states,
"Madelung deformity is due to defective development of ulnar third of the epiphysis of the distal radius, which results in a radial shaft that is bowed with an increased interosseous space, and dorsal subluxation of the distal ulna.
It can be bilateral in 50-66% of patients. It often occurs as rare congenital deformity and does not usually manifest until 10-14 years. It may also be seen as an acquired consequence of trauma to the growth plate, e.g. Salter V fracture. The congenital form has an autosomal dominant inheritance with a variable penetrance."
For the rest of us, there are many reasons that one acquires an ulnar variance, but in my humble opinion, the sharp increase in diagnosis of Positive Ulnar Variance is suspicious. I have found that the interpretation of X-rays is highly variable amongst radiologists. Anyone with this diagnosis should understand some important dynamics. Firstly, the analysis of Ulnar variance is quite detailed- a mm difference is a big deal. Anytime we are dealing in mm, there is a lot of room for error.
The best discussion about Ulnar variance can be found at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3193630/
I would highly recommend that you read this article thoroughly and consider printing it for your next visit.
Although not yet done, I have often hypothesized that when the TFCC is disrupted, there is a spreading of the distal radius and ulna. This spreading lends to a view of a longer ulna. Is it the long ulna that caused the tear or the tear that caused the view of a long ulna? A simple research study would include imaging the wrist with and without the WristWidget®. If a blinded radiologist could view the ulna variance change with the WristWidget® on, it would support the theory of the TFCC causing an ulnar variance.
Also of note, the position of the elbow matters. The article above clearly shows the changes to the ulna variance when the elbow is positioned in neutral, pronation and supination with grip. Look closely at the time frame- 2009-2011. This is new knowledge and takes awhile to infiltrate into the world of medicine. The importance of the pronated grip view cannot be underestimated in the evaluation of the wrist. When I ask patients about their X-rays, few describe receiving a pronated grip view!
In every TFCC case, the elbow should not be excluded. Every patient should understand the value of knowledge in your own care. Enjoy!