Synostosis

Radioulnar Synostosis

Radioulnar synostosis literally means a bony union between the two forearm bones.  Normally, the ulna bone acts as a straight “post” to anchor the wrist to the elbow.  The radius bone rotates around the ulna to allow the forearm to turn palm up and palm down.  This rotation is helpful for daily activities and allows many actitivies such as typing on the keyboard (palm down or “pronation”) or hold change (palm up or “supination”).  Almost all rotation comes through the forearm (ie the relationship between radius and ulna) but some can come through the wrist bones also.

Some kids are born with a bony connection between the radius and ulna.  This bony “bridge” can also develop after a trauma in an adult.  When that happens, the bones are no longer separate and the ability to rotate the forearm is not present.  Because the shoulder is so mobile, we can make up for some loss of forearm rotation with shoulder movement.  It is pretty easy to pull arm away from body- abduct- and the hand assumes a palm down position.  It is less easy to move the shoulder in such a way to allow the palm up position.

The bottom line is that kids adapt amazingly well to radioulnar synostosis.  Often, families do not even realize this condition is present until after kids start school.  There is no pain and, as noted above, some rotation can be achieved through the wrist.  When both sides are affected, it may be a little more challenging to adapt.  Additionally, it matters in which position the forearm is fused.  The forearm can be “stuck” in full palm up (supination), full palm down (pronation), or anywhere in between.  The best position is half- way between (the clapping position) which allows the patient to use the shoulder to help accommodate in both directions.  Palm down is better than palm up as so many of life’s activities are palm down (keyboarding, etc).

In a small number of kids, the forearm position causes trouble with activities.  In those, a small surgery can be done to reposition the forearm in a better position for function.  The pictures below show a patient positioned with both forearm in mid rotation.  He has no issues with function despite his limited rotation.

Synostosis with full elbow extension
Synostosis with full elbow flexion
Synostosis with attempted supination- palm up

Synostosis with attempted pronation- palm down

Xray showing synostosis near elbow.  The two bones are joined together.

106 Comments

  1. I want to say thank you, I also have RUS bilateral. My left hand is worse than my right. I can rotate my left only to clapping position, my right is better and can rotate about 70 degrees, which is good since I am right handed. I agree that getting change from a drive thru is a no go for me unless I do this amazing trick where I turn my left palm up backwards. They usually look at me funny but never question. I know mine is hereditary as I have an aunt and uncle both with the same disorder not as bad as mine. I have pretty much adapted to this and for me it was normal, could never play violin or guitar but life. Has been normal. I would suggest if you are a parent with a child that has RUS, let them try and adapt, obviously depending on the degree but you would be amazed at what they can overcome. Also means we are more special! My question is do you know how many diagnosed cases there are? Seems like a bunch more than the 350 journalized cases.

    1. Deanne,
      Thank you for writing and sharing your experiences. You are correct, every child is affected differently and yours, thankfully, is better positioned and allows at least some motion compared to others. And yes, this is uncommon but not incredibly rare. It is impossible to quantify but, for perspective, I see ~8 new patients with radioulnar synostosis each year. Thanks again,
      CAG

  2. I am a 58 year old male and have this issue myself, it was / is a birth defect. Mine is slightly different in that at the elbow and wrist i have 2 bones but are then fused together about an inch or so from each joint. As the previous writer commented, i have grown up with this issue and is normal to me. I am fortunate in that my hands face down, so when they are by my side the palms face backwards.

    1. David- thank you for writing.I agree that many tolerate the position of the forearm as you note. But, a truly palm down (pronated) or palm up (supinated) position can be difficult for activities. (and especially so with bilateral issues.

  3. I am a 24 year old male and have found it extremely difficult when lifting weights and greatly hindered me when doing competitive sports like basketball and football? Are there any prognosis other than surgery. What are many results from the surgery?

    1. Rellyrell,
      Thank you for the question. As noted, the position of the forearm(s) matters to function. Sports can be a bit awkward depending on this position. A hand therapist might have some ideas about lifting weights (i.e., there can be adaptive equipment which can help). Aside from modifying your activities, there are no other nonsurgical options to my knowledge. Good luck.

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