History:
56 year-old male with a history of injury to the right hand. The
patient was referred to Main Street Radiology for a high-resolution
wrist MRI.
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Figure
1 |
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Figure
2 |
Findings:
The lunate bone demonstrates decreased signal intensity on the
T1-weighted sequence (arrow on Figure 1), and variable heterogeneous
to increased signal intensity on the proton-density fat-saturated
sequence (arrow on Figure 2), compatible with osteonecrosis.
Discussion:
Kieböck’s Disease represents osteonecrosis of the lunate bone.
The most common sign/symptom is dorsal
tenderness about the lunate. Clinically the patient may present with
limited motion, diffuse swelling, and grip weakness. The disease is
most commonly seen in patients 20-40 years of age, and the male to
female ratio is 2:1.
Single or repeated trauma to the lunate
bone or dislocation of the bone may impair its blood supply and cause
it to become necrotic. However, the development of Kienböck's disease
may not be soley attributable to extrinsic trauma. An interesting but
controversial hypothesis links this condition with negative ulnar
variance in individuals whose ulna projects more proximally. They may
be predisposed to developing Kienböck's disease due to compression of
the lunate against the irregular articular surface created by the
discrepancy in radial and ulnar lengths.
Once lunate necrosis begins, an
established, progressive sequence of events is set in motion. This
progression is marked by lunate flattening and elongation, proximal
migration of the capitate, scapholunate dissociation, and finally
osteoarthritis of the radiocarpal joint. This series of changes also
forms the basis for the classification of Kienböck's disease.
Clinically, stage I is indistinguishable from a wrist sprain. Wrist
radiographs may be completely normal, and only CT may detect a subtle
linear fracture. Bone scan may show increased uptake of the
radiotracer by the lunate. MRI may demonstrate the abnormality,
displaying decreased signal intensity of the lunate on T1-weighted
images. As the condition progresses (stage II), conventional
radiographs show increased density of the lunate accompanied by some
degree of flattening on the radial side of this bone. In stage III,
the radiographs demonstrate marked decrease in height of the lunate
and proximal migration of the capitate. Necrotic and cystic
degeneration may lead to a further fragmentation and collapse.
Scapholunate dissociation is a prominent feature of this stage. Stage
IV is marked by almost complete disintegration of the lunate and
development of radiocarpal arthritis.
MR is considered the best imaging tool.
MR is superior in early detection of stage I changes including
identification of fracture and marrow edema/sclerosis. MR can also be
used to follow the outcome of radial shortening for revascularization
of the lunate.
Merely diagnosing Kienböck's disease
is not sufficient from the orthopedic point of view, rather, it is
essential for the radiologist to demonstrate the integrity of the
bone. The reason for this is that at an early stage of disease, in the
absence of fracture or fragmentation, a revascularization procedure
aimed at restoring circulation to the lunate may prevent further
progression of the necrotic process or fragmentation of the lunate.
Alternatives to revascularization, such as silastic arthtroplasy or,
in the absence of a collapse deformity, ulnar lengthening or radial
shortening, would then have to be considered.
It is crucial to obtain the highest
resolution possible when imaging small joints such as elbows, wrists,
and ankles. At MSR we utilize a high field (1.5T) magnet with
dedicated surface coils providing highest quality images.
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