What Does Ulnar Negative Variance Mean on a Kienbock MRI?

Seeing the term “ulnar negative variance” on an MRI report can sound alarming, but it is simply a way to describe the natural shape and length of the bones in your forearm. In plain terms, ulnar negative variance means that your ulna (the bone on the pinky side of your forearm) is slightly shorter than your radius (the bone on the thumb side) where they meet at your wrist.

This unevenness is a common anatomical variation that many people have without ever experiencing wrist problems. However, in the context of Kienbock disease, it is considered a relevant anatomical risk factor because of how it alters the way pressure is distributed across your wrist joints ^[1].

Note: While your MRI report might mention ulnar negative variance, hand surgeons typically confirm the exact measurement using standardized wrist X-rays, as the apparent length of the bones can change depending on how your arm is positioned during the scan.

How Ulnar Negative Variance Affects the Lunate Bone

In a healthy wrist, the radius bone naturally carries the majority of the load when you use your hand. When you have ulnar negative variance, this load distribution is altered, which can increase the specific mechanical stress placed on the radiolunate joint—the area where the radius meets the lunate (the small wrist bone affected by Kienbock disease) ^[2].

Because Kienbock disease involves osteonecrosis (bone tissue that has lost its blood supply), the lunate becomes vulnerable to damage. The altered mechanical pressure caused by a shorter ulna does not necessarily cause Kienbock disease on its own, but it is recognized as a factor that may worsen the mechanical environment and is associated with greater lunate collapse over time ^[1][3][4].

Relieving the Pressure: Joint-Leveling Surgery

If your wrist has uneven pressure contributing to lunate damage, your care team may suggest a procedure designed to balance the load. This approach is often called joint-leveling surgery or an unloading procedure, and the most common type is a radial shortening osteotomy.

During a radial shortening osteotomy, a surgeon carefully removes a small sliver of bone from the longer radius. The goal is not necessarily to make the bones perfectly equal, but to reduce the excessive load transmitted across the affected lunate bone ^[5][2].

Unloading this pressure does not directly restore blood supply to the bone, but it aims to protect the lunate from further mechanical stress ^[6]. In many patients, leveling the wrist can improve pain and help preserve the shape of the lunate ^[2]. However, symptom relief is not guaranteed, and the procedure involves standard surgical risks, including a period of immobilization, stiffness, delayed bone healing (nonunion), or irritation from the surgical hardware (plates and screws) that might require a second surgery to remove.

The Importance of Your Disease Stage

Ulnar negative variance alone does not mean you need surgery. Your treatment options depend heavily on your symptoms, the health of your wrist cartilage, and your exact Lichtman stage ^[7]:

• Stages II and IIIA: The lunate may be showing signs of damage or beginning to collapse, but the overall alignment of the other wrist bones remains normal. Unloading surgeries like radial shortening osteotomy are most commonly considered in these stages ^[2].
• Stage IIIB: The lunate has collapsed significantly, causing the surrounding wrist bones to shift out of alignment.
• Stage IV: Severe collapse has led to arthritis in the wrist joints.

For advanced stages (IIIB and IV), joint-leveling is often less effective, and surgeons may recommend salvage procedures (like partial wrist fusion or removing certain carpal bones) to address the broader joint damage ^[7][8].

Other Unloading Options

Depending on your specific anatomy, a surgeon might recommend capitate shortening, which shortens a different wrist bone (the capitate) to relieve pressure on the lunate ^[9]. Other options, such as vascularized bone grafts (which bring a new blood supply to the bone) or arthroscopic procedures, may also be considered based on the viability of the lunate and the condition of the surrounding cartilage ^[7][10][11].