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The impact of lunate morphology on Kienböck’s disease

Kienböck’s disease is a progressive disorder characterized by aseptic necrosis of the lunate bone, and its etiology remains unclear. Viegas et al. (1990) described two types of lunate. Viegas’ classification is based on the distal facet of the lunate. Type 1 has a single facet and type 2 has an accessory facet for the hamate. The lunate type alters the biomechanics of the carpus. But whether lunate type affects the occurrence of Kienböck’s disease is still unclear. We hypothesized that a significant difference in the proportion of type 1 and type 2 occurs in Kienböck’s disease and that the morphology affects prognosis. All study protocols were approved by the institutional review board. We retrospectively reviewed 110 cases that had undergone arthroscopy for Kienböck’s disease from 1989 to 2010. We excluded cases in which radiographs were not available (30 cases). In this study, we included 80 patients (55 men, 25 women; mean age 34 years). Diagnosis was made by a plain radiograph and MRI. We performed arthroscopic evaluations to determine the surgical procedure. If the arthroscopy showed mild cartilage damage of the lunate, then we selected the radial closing wedge osteotomy. We performed radial closing wedge osteotomies in 67 patients and partial wrist arthrodeses in 10 cases, vascularized pisiform transfers in two cases, and a partial lunate resection in one case. We used the classifications of Viegas (Figure 1). Lunate morphology was determined by two observers at different times. We compared this to the proportion of lunate types in 51 patients with non-traumatic diseases of the wrist (e.g., ganglion or monoarthritis). The final evaluation of wrist function was performed using the Mayo wrist score and included assessments of pain, functional status, range of motion, and grip strength at final follow-up (average 39 months). Statistical analysis was conducted using chisquare tests to compare the different lunate types between Kienböck’s disease and non-traumatic disease. Ulnar variance, range of motion, and grip strength among lunate types were analyzed using the Mann–Whitney U-test. The kappa value was computed to assess interobserver reproducibility. Values of p < 0.05 were considered statistically significant. The kappa value (0.91) showed excellent interobserver reproducibility. Arthroscopic investigation showed type 1 (58.72%) and type 2 (22.28%) wrists in Kienböck’s disease and type 1 (20.39%) and type 2 (31.61%) in patients with nontraumatic wrist diseases. Three cases showed a different radiographic lunate type from the contralateral side. There were no significant differences between lunate types with regard to sex or ulnar variance. Non-traumatic wrist patients had a significantly greater proportion of type 2 lunates compared with Kienböck’s disease (p = 0.0002). Clinical results of the radial osteotomies showed no significant differences based on lunate type (Table 1). Anatomical factors such as negative ulnar variance, small and radially inclined lunate, and higher radial inclination may increase the risk of Kienböck’s disease (Tsuge et al., 1993). The present study revealed that the patient group with Kienböck’s disease had a lower proportion of type 2 lunate than the non-traumatic wrist group. Prevalence of the type 2 lunate in Kienböck’s disease in the present study (28%) was much lower than previously reported for other conditions (45% of fractures and dislocation patients; 65.5% of the dissected specimens) (Tatebe et al., 2012; Viegas et al., 1990). These data imply that the lunate type is related to Kienböck’s disease. This study has some limitations. The study was retrospective. We evaluated only the surgical cases of Kienböck’s disease and could not compare them with our normal population. In conclusion, we have observed a higher incidence of type 1 lunates in patients with Kienböck’s disease than in patients without Kienböck’s disease in our study.