What Is Ulnar Impaction Syndrome?

Ulnar Impaction Syndrome is also referred to by a few other terms. One is Ulnar Abutment and the other term is Ulno Carpal Loading. Notice how all of them have that one word in common: ulna.

Very broadly speaking, Ulnar Impaction Syndrome (UIS) is a condition of the area where the arm meets the hand or, more specifically, the wrist area and affects the ulnar nerve. It is a degenerative syndrome, meaning that it is marked by progressive damage of something (and you’ll find out exactly what that is later) within the area that ultimately leads to a painful situation.

So, before going any further, let’s get a bit into the ulna part. What is an ulna?

Put simply, the ulna is a bone (the area that causes the impaction syndrome and wrist pain). More specifically, it is one of two bones in your forearm, the other bone being the radius. The ulna spans from the elbow down the smallest finger. In terms of function, it forms part of the wrist joint as well as the elbow joints. However, when in the anatomical position (anatomical meaning a body facing forward, arms hanging down, palms facing out), it is said to be on the medial side of the forearm, which means that it is located toward the middle or center of the body while the radius is lateral, or to the side of the body, or away from the center. In terms of width, it is wider near the elbow region, and it narrows as it gets closer to the wrist. (You can see that by looking at your elbow that is much wider than your wrist.)

Let’s get a bit more specific (sorry, but it is crucial for understanding UIS completely). The ulna joins (or articulates) with several other parts in both the elbow as well as wrist joins. Pertaining to the elbow, the ulna forms a joint (a hinge joint, meaning they are connected in such a way that movement only in one plane is possible) with the humerus, which is the bone in your upper arm that spans from the shoulder to the elbow. It joins the radius near the elbow by means of a pivot joint so that when you move your hand in and out, the radius can cross the ulna and allow you to do that as smoothly as possible. The ulna also joins the radius along its side by means of something called the interosseous membrane (a fibrous sheet that fits between the ulna and the radius) and forms a joint that is called a syndesmosis joint (or fibrous joint between the ulna and the radius). At the other end, in the wrist area, the ulna joins the distal radius (meaning the other end of the radius bone) in a location called the ulnar notch (an indentation in the radius that allows the ulna to fit in nicely and rotate as needed).

Bones of the wrist

There is another joint that the ulna forms with the bones of the wrist. There is a total of eight carpal bones that make up what is called the carpus, connecting the hand to the forearm. The term carpus is of Greek heritage (karpos) that literally means “wrist.”

Then there are the ligaments and fibrous moieties that ensure that bones remain attached to one another and that they can rub against one another as smoothly as possible so that we can remain the smooth operating movers that we are. There are definitely a lot of ligaments, but of specific relevance here is something called the triangular fibrocartilage complex (TFCC) that primarily functions to cover the ulna, to take on some of the load and to enable smooth movement of the forearm by virtue of providing a strong and flexible connection between the radius and the ulna. Lastly, the TFCC supports the area of the carpus that is close to the ulna or, simply put, the ulnar portion of the carpus. The “complex” part of the TFCC simply refers to the fact that it is an umbrella term referring to three other components that we don’t have to get into now. OK, that’s enough on anatomy for now.

But remember that we were originally talking about the UIS? The main reason behind UIS is an ulna that is too long or simply longer than the radius, and there are several reasons for this. One is prior dislocation or injury that has resulted in an improper location of the ulna and another is a genetic predisposition that results in a longer bone. Whatever the reason behind it, this resulting length discrepancy causes the TFCC to be pinched (as the ulna and the radius are no longer well aligned). Over time, this leads to progressive damage (degeneration) of the cartilage and a lot of pain. Remember how we said that the TFCC is a stabilizer of as well as a partial load bearer in the wrist? Now that it is degenerating, these bones that it held together cannot function is harmoniously as before causing wrist pain.

Ulnar impaction is mostly diagnosed in middle age; however, by virtue of the genetic aspect, it can also develop very early on in life. That being said, as with many bone conditions, it is diagnosed through one of many imaging techniques and there is surgery to correct it.

So, there you have it. We began with a term that you may not have known entirely, to you know being a semi-expert of the bones and cartilages as well as a condition of the upper, mid and lower arm.

Laura Day