TO THE EDITOR:
I read with interest the excellent article "Kienböck Disease and Negative Ulnar Variance" (80-A: 1154—1157, Aug. 1998), by Bonzar et al., in which the authors reported an association between negative ulnar variance and Kienböck disease. They also reported a negative association between age and negative ulnar variance in both the control subjects and the patients who had Kienböck disease. Bonzar et al. cited a study by Chan and Huang1, who reported a preponderance of positive ulnar variance and no instances of Kienböck disease in a Chinese population.
My colleagues and I, in a study of a Chinese population in Taiwan, observed different findings than did Chan and Huang1. From 1976 to 1997, we managed forty-five patients who had Kienböck disease. We reported the results for our early patients in 1988 and 19902,3. The mean ulnar variance was 0.313 ± 1.274 millimeter in 1000 normal subjects and -1.22 ± 1.944 millimeters in our first eighteen patients3. At a recent follow-up examination, the mean ulnar deviation for the forty-five patients was -1.24 ± 1.087 millimeters. With use of the Student t test, it was found that the difference in mean ulnar variance between the normal subjects and the patients who had Kienböck disease was significant (p < 0.0005). As many patients in Taiwan who had a problem related to the wrist were managed by bone-setters without proper physical examination and radiographic evaluation, we believe that Kienböck disease may be more frequent than previously anticipated. The Chinese are not immune to Kienböck disease.
Although the association between negative ulnar variance and Kienböck disease has been observed in all series except that by D'Hoore et al.5, most people who have negative ulnar variance do not have Kienböck disease. Thus, I believe that negative ulnar variance is a predisposing rather than a causative factor and that other anatomical, mechanical, or physiological factors are more important. The predisposition of negative ulnar variance to the development of Kienböck disease could be defined mechanically. The relative shortness of the ulna shifts compressive and shear forces to the radiolunate joint and increases the stress in the lunate. The high stress may cause minor fractures, focal avascularity, and necrosis of the lunate. It also predisposes the focally weakened necrotic bone to stress fractures in the area of revascularization, leading to fragmentation and collapse. The effectiveness of decompressive procedures such as radial shortening or ulnar lengthening in relieving pain and preventing further collapse of the lunate can be explained by the reduction of compressive and shear stresses in the lunate4.
The negative association between age and ulnar variance reported by Bonzar et al. as well as by Nakamura et al.6 is interesting. My colleagues and I did not observe such an association in our normal subjects or in our patients who had Kienböck disease2,3. However, what those authors were studying was the association between ulnar variance and age at the time that the radiographs were made in small selective groups of normal subjects and patients who had Kienböck disease. In order to confirm a negative association between age and ulnar variance, longitudinal studies following the same groups of subjects and patients through the course of aging are required.
Wun-Schen Chen, M.D.: Department of Orthopedic Surgery, Chang-Gung Memorial Hospital at Kaohsiung, Kaohsiung, Taiwan
Dr. McCabe replies:
We are very interested in the studies done by Dr. Chen and his colleagues2,3, and we thank him for bringing them to our attention. They provide additional evidence of an association between Kienböck disease and negative ulnar variance. Although the strength of the association is one factor that is important in establishing causation, the observation that Kienböck disease does not develop in all persons who have negative ulnar variance does not disprove the possibility of causation.
Dr. Chen's comments about the biological importance of negative ulnar variance seem logical. It is through the gradual accumulation of evidence that the association will be accepted as causative.
Dr. Chen's comments about the negative association between age and ulnar variance are well taken. We were very interested in the relationship of age to ulnar variance and of age to the development of Kienböck disease because this combination (age, ulnar variance, and Kienböck disease) is a classic confounder that can be seen in cohort and case-control studies. We have not proved that ulnar variance changes with age, but it seems less likely that ulnar variance is unrelated to the age of the individual and will change over time throughout the entire population. Although this is unlikely, it is not impossible; we are getting taller and larger in girth.
Steven J. McCabe, M.D., F.R.C.S.: Christine M. Kleinert Institute for Hand and Micro Surgery, 225 Abraham Flexner Way, Louisville, Kentucky 40202-3840