Biomechanical Analysis of the Stress Force on Midcarpal Joint in Kienböck's Disease

Abstract

Two types of lunate were recognized in the midcarpal joint. Type I lunate has no facet articulation with the hamate, and Type II lunate has a facet articulation with the hamate. The purposes of this study are to estimate the biomechanical contribution of Type II lunate for Kienböck's disease, and to elucidate the change of the contact surface between the lunate and hamate during radial and ulnar deviation for both Type I and Type II. Twenty-four contralateral unaffected wrists with Kienböck's disease were used for the first purpose. The radiographic force analysis was performed with a modified two-dimensional rigid-body spring model computer-simulation technique. Six wrists of volunteers (3 of Type I and 3 of Type II lunates) were used for the second purpose. Dynamic examination on lunohamate joint was carried out using magnetic resonance imaging. The force distribution between the radius and Type II lunate was greater than that between the radius and Type I lunate statistically. Furthermore, the impingement of articular cartilages between Type II lunate and hamate was observed in ulnar deviation on dynamic study. These results suggest that Type II lunate was one of the anatomical risk factors for Kienböck's disease.

Imaging Recognition of Morphological Variants at the Midcarpal Joint

“…Nakamura et al reported that the shortest distance between the capitate and triquetrum (C-T distance) was the best determinant of lunate type, and that the C-T distance increased as the actual width of the lunate ulnar facet increased. 33 Nakamura et al defined type I lunates as those having a C-T distance of Ͻ2 mm and type II lunates as those having a C-T distance of Ͼ4 mm. 20 Hamate type: The hamate was analyzed for the presence or absence of the hamate groove and distal hamate ridge on its midcarpal surface.…”

“…23 Nakamura et al reported that the shortest distance between the capitate and triquetrum (the C-T distance), measured on plain AP radiographs or coronal CT, was the best determinant of lunate type, and that the C-T distance increased as the actual width of the ulnar facet increased. 33 Nakamura et al defined type I lunates as having a C-T distance of Ͻ2 mm and type II lunates as having a C-T distance of Ͼ4 mm. 20 In this study, the average C-T distance of type I lunates was 2.50 mm (R, 0.70 -3.65; SD, 1.05), which was higher than that reported by Nakamura et al 33 Lunates with small, cartilaginous ulnar facets had an average C-T distance of 2.68 mm (R, 2.20 -3.18; SD, 0.49).…”

“…33 Nakamura et al defined type I lunates as having a C-T distance of Ͻ2 mm and type II lunates as having a C-T distance of Ͼ4 mm. 20 In this study, the average C-T distance of type I lunates was 2.50 mm (R, 0.70 -3.65; SD, 1.05), which was higher than that reported by Nakamura et al 33 Lunates with small, cartilaginous ulnar facets had an average C-T distance of 2.68 mm (R, 2.20 -3.18; SD, 0.49). This suggests that C-T distance measured on plain AP radiographs cannot discriminate between type I lunates and type II lunates with small cartilaginous facets, and radiographs could therefore not be used routinely to differentiate lunate types.…”

“…37 The authors found no clear definition of a type II lunate in the literature. The absence of a clear definition of a type II lunate has led to inconsistencies in the reporting of lunate type, with some studies including lunates with a small ulnar cartilaginous facet in a type I group, 33,37,40 and others including them in a type II group. 3,12,13,17,23,24,30,36 The authors believe that lunate type is better described as a spectrum, with type I lunate at 1 end and type II at the other.…”

“…Accuracy of the Imaging Techniques for Identification of Morphological Variants Where Some Observer Agreement Was Demonstrated33 …”