High-Resolution Images are Critical When Small Joints are Involved
Kienböck's disease is a fairly rare condition affecting one of eight small carpal bones in the wrist, the lunate bone. Blood stops flowing to the tissue and, without oxygen and nutrients, the bone dies. This condition can cause the patient chronic pain and diminished function in the wrist.
The high-resolution images provided by MRIs are the best way to diagnose the disease and evaluate what stage it has reached. This is important because, when diagnosed at an early stage, patients can undergo surgery to restore blood flow to the lunate.
Case Study: A 56-year-old male with a history of injury to the right hand was referred to Main Street Radiology for a high-resolution wrist MRI.
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 to 40 years of age, with about two-thirds of those diagnosed being males.
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 solely 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. It 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.