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Osseous Anatomy and Microanatomy of the Lunate
Abstract
The lunate is the keystone of the wrist, and the primary pathological structure of Kienböck’s avascular necrosis. The normal lunate has a thin single layer of proximal subchondral bone plate, which is at risk of fracture, which does occur in Kienböck’s disease. There are spanning trabeculae between the proximal and thick distal subchondral bone plate. The Kienböck’s avascular necrosis “at-risk” wrist includes a radius with negative ulnar variance and flatter radial inclination. The lunate is small with a thin proximal cortex and is a Viegas type 1 and Zapico type 1 lunate.
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Kienböck's disease is idiopathic osteonecrosis of the lunate, leading to its fracture and collapse. This study compares internal and external bone micro‐architecture of normal and fractured lunates (Kienböck's), by using high‐resolution three‐dimensional (3D) micro‐computed tomography (micro‐CT) on the whole bone of the two lunate types, and histology.
Fractured Kienböck‐diseased lunates were obtained from patients undergoing proximal‐row‐carpectomy, while normal cadaveric lunates served as controls. 3D‐micro‐CT‐imaging of control lunates revealed an encircling cortex surrounding trabecular bone. Trabeculae were arranged in a radial pattern, spanning from the distal to the proximal subchondral plate. Kienböck's lunates exhibited clear fracture lines, with fragmented bone, both proximally and distally, in areas the radially‐patterned trabeculae and enveloping cortex were absent, producing height loss. In trabecular bone, Kienböck's lunates revealed increased bone volume fraction, trabecular thickness and number, and decreased trabecular separation and structure model index. Histologically, Kienböck's lunates revealed osteonecrosis, as well as remodeling fronts with osteoblasts and osteoid surrounding bone marrow. Whole‐bone high‐resolution 3D examination of normal and Kienböck's diseased lunates contributes to a better understanding of micro‐architectural changes occurring in the pathology. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:826–833, 2014.
Kienböck disease is a disorder of impaired lunate vascularity which ultimately has the potential to lead to marked degeneration of the wrist and impaired wrist function. The aetiology of the avascular necrosis is uncertain, but theories relate to ulnar variance, variability in lunate vascularity and intraosseous pressures. Clinical symptoms can be subtle and variable, requiring a high index of suspicion for the diagnosis. The Lichtmann classification has historically been used to guide management. We present a review of Kienböck disease, with a focus on the recent advances in assessment and treatment. Based on our understanding thus far of the pathoanatomy of Kienböck’s disease, we are proposing a pathological staging system founded on the vascularity, osseous and chondral health of the lunate. We also propose an articular-based approach to treatment, with an arthroscopic grading system to guide management.
To determine if the absence (type I lunate) or presence (type II lunate) of a medial hamate facet on the lunate affects the radiographic characteristics of patients presenting with Kienböck disease.
A retrospective review was performed on all patients evaluated at our institution from 2002 to 2010 with a diagnosis of Kienböck disease confirmed on plain radiographs in concert with magnetic resonance imaging (MRI) and/or bone scan. Study groups consisted of patients with type I versus type II lunates, as determined by radiographs, MRI, and/or computed tomography. Measured variables included the modified Lichtman stage on presentation, radioscaphoid angle, presence or absence of a coronal plane fracture of the lunate, modified carpal height, ulnar variance, and ulnar translocation of the carpus at the time of presentation.
A total of 106 wrists were examined, of which 75 were type I (71%) and 31 were type II (29%) lunates. At the time of presentation, there was significantly more advanced disease (stage IIIA or greater) in patients with type I (N = 64, 86%) compared with those with type II lunates (N = 19, 61%). Coronal fractures of the lunate were more prevalent in patients with type I (N = 58, 75%) compared with type II lunates (N = 18, 58%). In the absence of a coronal fracture, radioscaphoid angles were greater in patients with a type I (53°) versus a type II lunate (45°).
Lunate morphology may affect the severity of Kienböck disease at the time of initial presentation. Type II lunates appear to be protective against coronal fractures and scaphoid flexion deformities. This study provides further evidence that lunate morphology affects carpal pathology and may have implications for treatment options in Kienböck disease.
Prognostic III.
Copyright © 2015 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.
Purpose:
The lunate is classified into two types, one with a single distal facet and the other with two distal facets. The effect of lunate type on the incidence of wrist disease and trauma remains unclear. The purpose of this study is to evaluate a potential association between lunate morphology and wrist disorders.
Methods:
We retrospectively reviewed the cases of 637 patients who had undergone wrist arthroscopy for wrist disorders. Patient charts and arthroscopic video images were reviewed retrospectively. We defined lunate type based on the Viegas classifications, according to its distal facet from a midcarpal arthroscopic image. Patient wrist disorders were divided into four groups: fractures and dislocations, Kienböck's disease, ulnar wrist pain, and degenerative disease.
Results:
A Viegas type 1 lunate was observed in 349 wrists and a type 2 lunate in 288 wrists. Incidence of the type 2 lunate was different between the groups and was significantly lower for the Kienböck's disease and ulnar wrist pain groups than for the trauma and degenerative groups.
Conclusions:
The present study revealed a variable incidence of lunate type in wrist disorders. The proportion of type 2 lunates was lower in Kienböck's disease and ulnar wrist pain.
The aetiology of Kienböck's disease is unknown. Ulnar variance and lunate shape are possible mechanical risk factors. This study assessed the trabecular structure in 29 cadaveric lunates using microCT and correlated this with ulnar variance and lunate shape on plain radiographs and with bone density assessed using conventional CT. The bony trabeculae within the lunate were shown to run almost perpendicular to the proximal and distal joint surfaces in the coronal plane; these trabeculae met the subchondral bone at an angle between 72-102 degrees. In lunates whose proximal and distal articular surfaces are not parallel, the trabecular orientation may be less able to resist compressive forces and more susceptible to fracture.
The correlation between negative ulnar variance and the occurrence of Kienbock's disease was evaluated in Taiwan. Two groups of subjects were studied. The first group consisted of 1000 normal subjects and the second of 18 patients with Kienbock's disease. Student's t-test was used to evaluate the significance of the difference between this and other published series. The mean was 0.313 mm in Group 1 and ---1.222 mm in Group 2. The percentage with significant negative ulnar variance (the distal ulnar was at least 2 mm shorter than the radius) was 6.0% in Group 1 and 55.6% in Group 2. The difference between the two groups was significant. The mean ulnar variance of normal subjects in Taiwan differed significantly from the variance in Swedes and American blacks but not American whites. En Chinese patients with Kienbock's disease, the ulnar variance was predominantly negative, and the distribution of ulnar variance was similar to that of Swedish or American white patients. This study confirmed the association between negative ulnar variance and the occurrence of Kienbock's disease. This supports Hulten's hypothesis that negative ulnar variance may predispose certain individuals to the occurrence of Kienbock's disease.
(C) Lippincott-Raven Publishers.
One hundred sixty-five cadaveric wrists were dissected to assess the incidence of a medial (hamate) facet on the lunate and any associated pathologic conditions. Forty-seven of these specimens and 137 clinical patients' radiographs were reviewed to attempt to recognize and further assess the incidence of a medial (hamate) facet on the lunate. Two types of lunate were identified. Type I, in which there was no medial facet, was evident in 34.5% of the dissected specimens and type II, in which there was a medial facet, was evident in 65.5% of the dissected specimens. The medial facets in the type II lunates ranged from a shallow 1 mm facet to a deep 6 mm facet. Significant cartilage erosion with exposed subchondral bone at the proximal pole of the hamate, which was not identifiable by radiograph, was evident at dissection in 44.4% of the type II lunates, while none (0%) of the type I lunates had such associated hamate pathologic conditions. This type II lunate, with the high incidence of associated hamate pathology, may be an unidentified cause of wrist pain on the ulnar side.
A case of unilateral ulnar minus variant, almost certainly caused by trauma to the distal ulnar growth plate, and ipsilateral Kienböck's disease is described. The contralateral wrist was normal in all respects. This constitutes additional evidence for the etiologic relationship between Kienböck's disease and the presence of the ulnar minus variant.
The extraosseous and intraosseous vascularity of the lunate was studied in 35 fresh cadaver limbs. The specimens were injected with latex, debrided by a nondissection technique, and cleared by a modified Spalteholtz method. The extraosseous vascularity was profuse through two to three dorsal and three to four volar vessels feeding dorsal and volar capsular plexuses. One ot two nutrient vessels were observed entering the dorsal and volar poles of the lunate from both plexuses. The intraosseous vascularity formed one of three consistent patterns with anastomoses of dorsal and volar vessels in each specimen. The vascular patterns support a theory of compression fracture from repeated trauma as the most likely cause of Kienböck's disease.
Contralateral unaffected wrists from 41 males with Kienböck's disease were compared with wrists from 66 normal males. From X-rays, various features of the lunate and radius were measured. In patients with Kienböck's disease, the lunate tended to be smaller and inclined more radially than in normal subjects and the radial inclination was flatter. Discriminant analysis showed that 85% of the unaffected contralateral wrists in patients with Kienböck's disease and 74% of the wrists in normal subjects were accurately discriminated to their respective groups. It may be possible to identify subjects who are at risk for Kienböck's disease prior to onset using discriminant analysis.
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