Kienbock's disease (avascular necrosis of the lunate)

Overview

Kienbock’s disease is an idiopathic condition, meaning there is no known cause. Narrowing of the arteries reduces blood supply and subsequent necrosis (death of cells and tissue) in the lunate, one of the primary bones of the wrist.

As the lunate collapses from lack of nourishment, the wrist undergoes a predictable pattern of arthritic degeneration and instability. Patients will often complain of site-specific pain, weakness, and mechanical symptoms (clicking, clunking, subjective instability and stiffness). Depending on the stage at presentation, different treatments are available.

The earliest symptom is pain at the mid-dorsal (back) aspect of the wrist. It might be preceded by a history of trauma. Some physicians believe avascular necrosis results from repetitive micro-trauma; however, most cases are not precipitated by any identifiable injury.

Along with the pain, patients may report local swelling, weakness and decreased wrist extension. Pain precedes findings on X-rays. The condition might be detected earlier on magnetic resonance imaging (MRI). A diagnosis of Kienbock’s merits immediate referral to an orthopaedic surgeon.

Symptoms

The earliest symptom of avascular necrosis is central dorsal wrist pain that is aggravated by loading maneuvers, such as compression in wrist extension (for example, a push-up position). Initially patients report wrist pain that radiates up the forearm with associated stiffness, tenderness and swelling over the lunate. Passive upward flexing (toward the back of the hand) of the middle finger may produce characteristic pain.

As the condition progresses, patients will note a limitation of wrist motion (usually extension), and weakness of grip. As the lunate collapses and degenerative changes develop, the pain, weakness and stiffness will increase, causing severe and chronic disability.

Causes

Kienbock’s is idiopathic, meaning there is no known cause. However, it likely results from both being anatomically predisposed to the condition (with a triangular lunate, negative ulnar variance or “I” pattern artery) as well as being exposed to environmental influences (repetitive trauma). No single factor has been attributable to causing Kienbock’s disease.

Anatomy

Kienbock’s is avascular necrosis of the lunate, which a central bone of the wrist, or radiocarpal joint. The lunate articulates directly with the radius (one of two bones in the lower arm) and has key ligament attachments that stabilize the wrist area. When the lunate collapses, the wrist’s biomechanics are altered in such a way that causes sequential degenerative changes throughout its myriad joints.

Lifestyle risk factors

Exposure to repetitive trauma is a risk factor. Activities that involve compression loading of the wrist, particularly in extension – such using a jackhammer – could potentially cause vascular injury.

Other generic risk factors for avascular necrosis include history of steroid use, sickle cell anemia, exposure to increased barometric pressure – such as diving -- and smoking. These risk factors are not particular to Kienbock’s and have been documented more commonly in the hip, knee and shoulder.

Injury and trauma risk factors

Trauma is the most common suggested cause for Kienbock’s. This can take the form of a single traumatic episode, such as a fracture dislocation of the wrist from a car accident or it may include repetitive microtrauma, such as compression loading from using a jackhammer.

Diagnosis

To determine what's causing your pain, the doctor will ask about your medical history and your current signs and symptoms. He or she will want to know what actions increase your pain and what relieves it.  In order to diagnose avascular necrosis, your doctor might request images to get a closer look at your bones. Common tests for avascular necrosis include:
  • X-rays: X-rays usually appear normal in people who have early-stage avascular necrosis. Later stages may be more evident on an X-ray.
  • Magnetic resonance imaging (MRI): MRI scans can show early changes in the bone that can indicate avascular necrosis.

Depending on your signs and symptoms, your doctor may use other tests to diagnose avascular necrosis. In rare cases, your doctor may surgically remove a small piece of bone (biopsy) for laboratory examination.

Complications

Avascular necrosis that goes untreated will continue to deteriorate the bone. Eventually the bone may become weakened enough that it collapses, causing pain and disability. Letting your avascular necrosis go untreated could lead to severe pain and loss of movement within two to five years.

Recovery

There is no means to prevent Kienbock’s since it is impossible to identify individuals at risk.

Manual jackhammers have largely been replaced with hydraulic ones. Other than this workplace intervention, no guidelines exist to guard against Kienbock’s.

Reducing the weight and stress on your affected bone may slow the damage of avascular necrosis. You may need to restrict physical activity. Certain exercises may help maintain or improve your joint’s range of motion. A physical therapist can choose exercises specifically for your condition and teach you how to do them