Clinical History: 32 year-old construction worker with persistent wrist pain. A gradient-echo coronal MR image of the wrist is provided below. What are the findings? What is your diagnosis?
Diffusely decreased signal intensity is present within the lunate (arrow). Negative ulnar variance with compensatory thickening of the triangular fibrocartilage (arrowhead) is also present.
Kienbock’s Disease (avascular necrosis of the lunate).
In 1910, Dr. Robert Kienbock, an Austrian Professor of Radiology, described the clinical and radiographic features of Kienbock’s disease, which he termed “traumatic malacia of the lunate”. Dr. Kienbock felt that the process was due to a “disturbance of nutrition” at the lunate. To this day, the exact etiology of Kienbock’s disease, or avascular necrosis of the lunate, remains somewhat controversial, though most agree that the process is related to prior trauma. This belief is supported by the fact that Kienbock’s disease is more common in patients with negative ulnar variance, a condition known to place increased load upon the lunate, and by the finding that Kienbock’s disease is more prevalent within the dominant hand of male laborers.
To understand the etiology of Kienbock’s disease, it is helpful to review the vascular anatomy of the lunate. The large majority of the lunate is covered with articular cartilage, leaving only small areas accessible to nutrient vessels along the dorsal and volar poles. These “bare areas” correspond to ligamentous insertion sites, and thus trauma may result in avulsion injuries to the entering arteries. Internally, the lunate blood supply forms patterns resembling a Y (59%), an I (31%), or an X (10%).
These patterns share a preponderance of vasculature within the mid lunate and a relative paucity of vessels extending to the proximal lunate. In addition, the vessels that supply the proximal lunate are terminal branches without significant anastamoses. Horizontal fractures within the mid lunate thus have a high likelihood of disrupting the vascular supply, particularly to the proximal lunate. Indeed, the earliest MR manifestation of Kienbock’s disease is a linear intramedullary fracture traversing the mid lunate.
MR is a highly effective means for evaluating the wrist in patients with Kienbock’s disease. MR is much more sensitive than plain films and is more specific than bone scintigraphy. Kienbock’s disease may be staged based upon its MR appearance:
- Stage 0 -MR reveals a linear fracture line within the mid lunate on T1-weighted images without a diffuse marrow signal abnormality. Plain films are normal.
- Stage I -MR demonstrates focal or diffusely decreased signal intensity on T1-weighted images. T2*-weighted images reveal low signal intensity, perhaps due to hemorrhage, though hyperintensity may be present on STIR or fat-suppressed T2-weighted exams. Plain films remain normal.
- Stage II -Progressively decreased signal intensity on T1-weighted images and heterogeneously increased signal on T2-weighted images is present. Sclerosis is evident on plain films.
- Stage III – The lunate undergoes progressive collapse in the coronal plane and elongation in the sagittal plane. Associated scapholunate ligamentous tearing with rotary subluxation of the scaphoid takes one from IIIA to IIIB.
- Stage IV – All of the stage III features are present in addition to generalized arthritic changes at the carpus.
The ability of MR to accurately detect and stage Kienbock’s disease has significant clinical implications. In Stage 0 or Stage I cases, the abnormality is treated conservatively, in hopes that the underlying fracture that causes Kienbock’s disease will heal. Conservative therapy is generally ineffective by Stage II. The operative choice in patients with Stage II disease, however, is controversial. Some surgeons feel that this is the time for surgical revascularization, necessary to correct the underlying ischemic process. Others feel that the increased load-bearing stress upon the lunate is the most important pathological factor, and advocate correction of the length discrepancy between the radius and ulna to heal or at least arrest the disease. In evaluating Stage II patients, the degree of hyperintensity on T2-weighted images may have diagnostic importance, as areas of high signal intensity are thought to indicate regions of retained vascularity. Similarly, fat-suppressed T1-weighted images following contrast administration may be utilized to assess the amount of residual vascularized tissue. By Stage III or IV, most believe that Kienbock’s disease is irreversible, and treatment with palliative fusion procedures predominates.
Kienbock’s disease is a frequently encountered clinical entity, and MR is the modality of choice for its detection and evaluation. The ability of MR to accurately detect and stage the process is important in the management of Kienbock’s disease.
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