KIENBÖCK DISEASE
In Kienböck disease,
also known as lunatomalacia, the collapse of the carpal lunate occurs because
of avascular necrosis. The disease occurs most often in young adults between 15
and 40 years of age and is usually unilateral. The actual cause of the vascular
impairment has not been determined, although several etiologic factors have
been proposed: (1) single or repetitive microfractures that result in vascular
embarrassment; (2) traumatic disruption of circulation or ligamentous injury with
subsequent degeneration; (3) primary circulatory disease; and (4) shortening of
the ulna relative to the radius, which decreases the support for the lunate. The
current theory is that the disease occurs in persons with a mechanical and/or
vascular predisposition, when repetitive compression of the lunate between the capitate
and distal radius disrupts the intraosseous structures. Chronic compression of
the lunate (which is unavoidable in normal wrist function), effusion, and synovitis
may interfere with healing and provide a mechanism for progressive collapse of
the bone.
CLINICAL
MANIFESTATIONS
The primary
signs and symptoms of Kienböck disease are wrist pain that radiates up the
forearm and stiffness, tenderness, and swelling over the lunate. Passive dorsiflexion
of the middle finger produces the characteristic pain. Physical examination
reveals limitation of wrist motion, usually dorsiflexion, and a striking
weakness of grip. The pain and weakness increase as the lunate collapses and
degenerative changes develop, making the disability both severe and chronic.
RADIOGRAPHIC
FINDINGS
The
avascular necrosis of the lunate may vary in degree but produces consistent and
typical radiographic changes. Initial radiographic findings may be normal
except for a short ulna, but sclerosis of the lunate the radiographic
hallmark of the disease develops
with time. The lunate progressively loses height and eventually fragments.
Further lunate collapse leads to carpal instability and resultant degenerative
joint changes, including the formation of cysts within the lunate. The
degenerative changes may ultimately involve the entire wrist. The Lichtman
classification utilizes radiographic findings to stage disease severity (see
table on Plate 3-37). This classification helps guide treatment and allows
the evaluation of disease progression with time.
TREATMENT
Because the
specific etiology of Kienböck disease is not fully understood, no reliable
treatment has been established, although many have been proposed. Prolonged
immobilization relieves symptoms, but the revascularization of the lunate does
not occur readily in adults, and a decrease in range of motion in the wrist and
grip strength gradually occurs. A simple excision of the lunate produces good
results initially, but, ultimately, the remaining carpal bones migrate, leading
to joint incongruity, limited wrist motion and grip strength, and degenerative
osteoarthritis.
Current
surgical options aim to either unload the lunate, revascularize the lunate, or
perform limited or complete
wrist fusions to halt disease progress and diminish symptoms. Joint-leveling
procedures (shortening the radius) have produced excellent long-term results,
particularly if performed early in the disease process. Wrists that have either
neutral or positive ulnar variance cannot reliably be treated with shortening
of the radius. Capitate shortening has been utilized to unload the lunate in
these situations. Vascularized bone grafting, most frequently from the dorsal
radius, is often combined with
these unloading procedures with the aim of improving the likelihood for lunate
revascularization. Recently, there have been reports of decompressing the
distal radial metaphysis via a limited radial incision; this simple procedure
has shown promise in earlier stages of Kienböck disease. With advancing stages
of collapse and/or degenerative changes, surgical options are limited to
partial versus complete wrist fusion.
