Ulnar Impaction

Background

Ulnar impaction syndrome is a common cause of ulnar-sided wrist pain which can be overlooked if xrays are not taken correctly or if the physical examination is incomplete. In a wrist with an equally long radius and ulna, which is called an ulnar neutral wrist, the 20% of the total load across the wrist is absorbed at the level of the ulno-carpal joint which is the joint between the ulna and the wrist. If the ulna is long, then this load can triple, causing damage to various anatomical structures, and leading to pain.

Causes

This condition is caused by an ulna which is longer than the neighboring radius bone. The ulna then impinges on the wrist/carpal bones and leads to pain, swelling and discomfort, especially then the wrist is in pronation (palm down) and extension. The cause of the relatively long ulnar can be a prior wrist fracture, or congenital.

Symptoms

Pain in the ulnar side of the wrist (pinky side), possible swelling. Most often, the pain happens with activity, especially if the wrist is pronated (palm down) and extended, e.g. during push-ups.

Diagnosis

The diagnosis is often made clinically, together with xrays of the wrist. An MRI is particularly helpful in confirming the diagnosis since changes along the small wrist bones can be visible. Also, the long ulna impacting against the wrist bones often leads to a tear in the TFCC which is a ligament / disc in the wrist joint, similar to the meniscus of the knee.

Treatment

Initial treatment usually entails occupational therapy and activity modification. Occasionally, in low-demand patients a steroid injection can provide lasting relief. The more definitive solution is shortening of the ulna bone as shown in the following example.

If a TFCC tear is present at the same time, Dr. Dowlatshahi usually cleans this out using a keyhole surgery called wrist arthroscopy. In certain cases, if the issue is considered to be instability and the TFCC is fixable, a repair will be completed (peripheral tear).

The following images demonstrate the operative management. On the left side, the plate that secures the shortening of the ulna is shown. On the right, the segment of ulnar that was removed during the shortening. The bottom right hand side images show the arthroscopy portion of the case where the centrally torn and frayed TFCC was debrided/cleaned up.