Avascular Necrosis / Lunatomalacia / Kienböck’s Disease
Avascular necrosis is a disease that affects the lunate bone. This bone is one of the carpal bones, which along with the scaphoid bone, forms the part of the wrist closest to the radius of the forearm. Avascular necrosis often occurs in patients with ulnar-variance (the ulna is shorter in comparison to the radius).
Avascular necrosis or Lunatomalacia is also known as Kienböck’s disease or Morbus Kienböck (after the university professor from Vienna). All of these terms describe deterioration to the lunate bone (os lunatum). The term malacial is a localized softening of the bone, whereas necrosis is the dying of bone tissue due to a localized interruption in blood supply.
For unknown reasons (however, increased pressure on the lunate is suspected), there is disrupted blood supply to the lunate bone, which causes pain in the middle of the flexing side of the wrist. Sometimes Kienböck’s disease occurs after delayed repositioning of the lunate after its dislocation following a fall on the hand (“perilunate dislocation” – high-speed trauma, motorbike accident, fall from great height etc.). Further possible causes include trauma to the wrist through years of working with heavy equipment, such as a pneumatic jack-hammer, or if the ulna is shorter in comparison to the radius.
At first, pain will be caused by putting stress on or moving the wrist. Later the pain will be present when the wrist is at rest. In the advanced stages of the disease, a reduction in strength and limited flexibility in the wrist is expected.
The disease is categorized in stages according to its severity. It is diagnosed using both X-ray and MRI scans because X-ray scans determining a particular categorized stage of the disease do not always correlate to the patient’s actual pain levels.
Stages of Avascular Necrosis
Note. The stages of the disease have occasionally been categorized as 0-III, however, with regards to content, they correspond to the following:
In Stage 1 it is necessary to additionally examine using and MRI scan and contrast dye as X-rays alone are not expected to reveal any visible deterioration. In stage II an X-ray will show the lunate as hardened and MRI scans will show complete bone death (necrosis) without any reduction in bone height. Stage IIIa is as stage II, but the bone has begun to collapse and has already lost height. An X-ray will show the bone as mosaic-like, but the neighbouring bones are not out of position. In Stage IIIb the bone has degenerated to the extent that it leads to wrist dysfunction. A partial, i.e., localized arthrosis exists. The advanced Stage IV is irreversible arthritis of the wrist with completely collapsed lunate.
Treatment of Kienböck’s disease depends on the stage of the disease itself. In stage I, after the patient wears a support bandage and has regular check-ups for one to several months, it can be ascertained whether the disease will progress or not. Should the disease progress to stage II, then a reduction in pressure on the lunate is attempted. To achieve this, the radius is shortened and stabilized with a plate as long as it is not already shorter than the ulna. Otherwise, operative partial fusion of the wrist (STT-Arthrodesis and partial intercarpal arthrodesis) is considered. This procedure involves using screws or transfixing wires to fuse the lunate and scaphoid bones to two further carpal bones (trapezium and trapezoid) As a result, tilting of the scaphoid towards the radius is prevented and pressure on the lunate is reduced.
Additionally, the nerves causing pain can be cut (denervation), which can result in improved circulation and simultaneously ease pain. After the operation, the patient wears a cast around the wrist to rest it for 6-8 weeks. Screws used can remain in the bone whereas wires should be removed.
In the most advanced stage of Keinböck’s disease, the entire wrist has been so severely degenerated that usually the first row of carpal bones are removed (PRC: "Proximal row carpectomy"). If the arthrosis is so advanced, then the wrist must be totally fused in order to eliminate pain. Despite having limited use of the hand, the patient will still be able to move the fingers.