| Ulna Variance as it Relates to Kienbock's Disease |
Origin and OpinionsWhile not thought to be causal, it appears evident that there is a statistical relationship between negative ulnar variance and Kienböck disease. This relationship was established in 1928 when Hulten made the association between uInar variance and lunatomalacia. After radiographically evaluating 400 normal wrists he found that 61% were uInar neutral, 23% of ulnas were shorter than the radius (uInar negative), and 16% of the ulnas were longer than the radius (uInar positive). He then examined 23 cases of Kienbock's disease and found that in 74% of those diagnosed with Kienbock's disease, the ulna was shorter than the radius (uInar negative), and in the remaining 26%, the ulna was equal in length to the radius. He also noted that none of the wrists in which the ulna was longer than the radius developed Kienbock's disease, but rather developed a cyst-like formation in the uInar aspect of the lunate, similar to what we now call uInar impaction syndrome. The ulnar-minus variant has been shown experimentally to cause an abnormal increase in the force transmitted across the lunate. Additionally, the triangular fibrocartilage complex (TFCC) is thicker in people with the unla-minus variant, which increases the loading between it and the ulnar edge of the radius. De Smet, however, counters that true correlation between the ulnar-minus variant and Kienböck disease has not been proven when appropriate sex and age matched controls and radiographs have been used. A Japanese survey suggested that ulnar variance is highly unlikely to be an important predisposing factor in Kienbock's disease when the effects of age and sex on ulnar variance are taken into account. Another Japanese report states that negative ulnar variance was not important in the aetiology of Kienbock's disease in a Japanese population. This has been replicated by other studies from other countries. While several investigators have confirmed Hulten's observation, doubt has been cast on the significance of the "ulnar-minus variant," and so the importance of standardized radiological views when measuring ulnar variance must be emphasized. Theoretically the "ulna-minus variant" could increase the shear stress on the lunate, although the striking step between the radius and ulna seen on radiographs is of course occupied by the radiolucent triangular fibrocartilage. Kienbock's disease does not inevitably occur when there is a gross discrepancy in length between radius and ulna, so other factors must be involved.
Ulnar Lengthening and Radial ShorteningRadial shortening has become preferable to most because it does not require a second surgical incision to harvest the bone graft, and like ulnar lengthening, it burns no bridges. The literature suggests good results in 87% treated with radial shortening. Radial shortening and ulnar lengthening are relatively simple procedures to perform and have yielded consistently good, predictable, and reproducible results in stage 2 and early stage 3 however, it seems unlikely that joint-leveling can restore an already collapsed lunate, therefore, these procedures remain questionable in advanced stage 3 or beyond. While the results of these procedures have been consistently good, there are also drawbacks of which one should be aware. A non-union of the bone is a distinct possibility with either procedure, and would require prolonged immobilization and restrictions. A non-union occurs when the bone does not knit back together. This may occur for one or more of several reasons, including thermal damage from the saw while performing the procedure. Smoking may increase the chances of non-union. Generally, non-unions can be treated successfully with a bone growth stimulator. The stimulator produces electromagnetic pulses around the area of the wound, which increases blood flow, promoting bone growth. During either procedure, an orthopedic plate is secured with screws to the bone to align it and compress the ends at the site of the osteotomy or graft. The plate and screws are made of either stainless steel or titanium. In some cases, this hardware can present problems in some patients. People with small bone structure are more likely to have problems as are people with metal allergies. People with known metal allergies should always use titanium implants as they are non-toxic and not likely to be rejected. With both the radial shortening and ulna lengthening, there always exists the possibility of a second operation to remove the orthopedic plate. In the ulna lengthening, because the ulna is lengthened, the anatomy of the distal radioulnar joint (DRUJ) is affected and may be a source of postoperative discomfort. Care must be taken not to overlengthen the ulna. For the same reason, ulnar deviation may also be restricted by this procedure. If too much bone is removed while performing the radial shortening, it can often result in chronic, nagging ulnar-sided wrist pain. Neither the radial shortening or ulnar lengthening should be done in the presence of significant collapse of the lunate, as they are unlikely to restore height and normal carpal kinematics. Their application is contraindicated in patients with neutral and positive ulnar variance.
Zero Rotation Views: Measuring Ulnar Variance On X-raysThe technique used to take neutral position, zero-rotation views is to have the shoulder abducted 90 degrees, the elbow flexed 90 degrees, and forearm is held in neutral rotation. To take the AP View, the patient places the forearm flat on the cassette with the central beam directed at the center of the carpus. For the Lateral View, the patient is standing with ulnar border of forearm flat on the cassette and the central beam is directed at the center of the carpus.
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