Abstract
Using the method of sheet plastination, the vascularity of the lunate bone can be investigated and analyzed. By intraosseous injection, the deep and superficial venous systems are visualized. Transparent sheets with slices of embedded specimens show a three-dimensional presentation of the vascularity of the human campus different in functional aspects. Comparing hands with a normal and ex- tended wrist position, three mechanisms of impairment of the venous drainage are observed. The anatomical results of this investigation support the hypothesis that venous congestion, resulting from intraosseous hypertension, plays a role in the development of the necrosis of the lunate bone.
Introduction
In the literature, various theories on the etiology of the necrosis of the lunate bone (Kienbock's disease) are presented: biomechanical reasons, trauma and lack of arterial blood supply have been reported. The anatomical position of the lunate bone characterizes it in a central position within the carpus [Koob, 1973; Sennwald, 1987; Schmidt, 1993]. As with the scaphoid bone, the lunate bone is under a lot of strain due to its anatomical position in the carpus [Rossak, 1966; Palmer and Wemer, 1981 ]. Variations in the normal anatomy, such as ulnar minus variance, are found in many patients with lunate bone necrosis [Hulten, 1928; Stahl, 1947; Cohen, 1956; Decoulx et al., 1957; Rossak, 1966; Beekenbaugh et al., 1980; Alexander and Lichtrnan, 1986; Kerschbaumer and Bauer, 1986]. Hyperextension injuries, fractures [Cordes, 1930; Stahl, 19471, and lunate dislocation [Kienb6ck, 19101 are assumed to cause Kienbock's disease. A further suggestion is the lack of arterial blood supply as a consequence of hyperextension injury by rupturing the palmar ligaments and vascularity [Decoulx et al., 1957; Beckenbaugh et al., 1980; Gelberman et al., 1980; Almquist, 1984; Getberman and Szabo, 1984; Williams and Gelbenan, 1993]. No evidence for either traumatic or vascular causes has been provided.
The venous problem can be considered a new hypothesis in addition to the etiologic theories in the previous literature. Comparison with published results concerning necrosis of the hip [Amoldi et al., 1972a; Amoldi and Reimann, 1979], pressure measurements [Pedersen et al., 19891 and other characteristics like the prolonging process, the gradual progress of all bone necrosis, and histological results show that the lunate bone necrosis could be seen as a problem of venous congestion [Remagen, 19901. Pressure measurements showed an increased intraosseous pressure during dorsal extension in the lunate bone [Jensen, 1993; Schiltenwolf et al., 1996], but no increase was registered in the normal wrist position or in the surrounding car- pal bones, especially the capitate bone [Marfini, 1990; Schiltenwolf and Martini, 19941. An increased intraosseous pressure could also be caused by impairment of the venous drainage of the lunate bone. This hypothesis of an impairment of the venous drainage of the lunate bone in the working position of the hand (dorsal extension) is explained by the anatomical and morphological considerations in this investigation. Material and Methods
For these investigations, twelve fresh cadaver forearms were used, amputated proximal to the elbow joint. All specimens were injected on both arterial and venous sides. The radial artery was punctured in the midportion of the forearm. After injection into the radial artery the venous system was filled by injection into either the deep venae comitantes of the radial artery or into a superficial larger vein proximal of the wrist. At last the deep venous system was filled by intraosscous injection into the distal part of the radius by a steel cannula with 1.8 mm in diameter. The cannula was positioned 2-3 cm proximal of the processus styloideus from the dorsolateral direction. As injection material, epoxy resin E 12 was used with the corresponding hardener E 1. Arteries were filled with red colored E 12, veins with brown or blue colored epoxy resin [von Hagens, 1979). The injection into the vessels was done with normal manual pressure with a 10- to 20-mi syringe. For injection into the bone a high manual pressure was needed using 1-2 ml syringes. After positioning 6 specimens in normal, 6 in extended wrist position, freezing and cutting 3-mm- thick slices using a band saw, the specimens underwent sheet plastination [von Hagens, 1979; von Hagens et al., 1987). This procedure achieved transparent, 5-mm-thick sheets representing colored intra- and extraosseous vascularity of the whole forearm and hand in the longitudinal sagittal section.
Results
On the palmar surface, one to three main arteries and two to six smaller ones enter the lunate bone. Multiple minute vessels accompany the main vessels or enter through their own smaller foramina. On the dorsal side, up to three main arteries, one to six smaller ones, and many minute vessels reach the dorsal pole. In all of the specimens examined, the main vessels enter the bone in a similar pattern. Palmarly, the main arteries enter-the radial pole and the central section of the lunate, dorsally the proximal or distal part of the dorsal pole. Small and minute vessels enter into all regions of the periosteal-covered bone areas.
The 6 specimens in the normal position show an abundant arterial blood supply of the lunate bone accentuated on the palmar side due to the more extended periosteal surface. The veins mostly accompany the arteries, exiting the lunate parallel to the arteries or through their own foramina. The venous drainage occurs mainly in the direction of the proximal plexus around the radiocarpal arches. In a few cases, veins run to the distal plexus around the intercarpal arches. From collecting veins around the palmar and dorsal radio- and intercarpal arches, perforating veins drain to the large superficial venous system. The palmar and dorsal radiocarpal plexuses also drain into the deep venous system, i.e. the venae comitantes of the radial artery. The 6 specimens in the extended wrist position show another pattern of vascularity. The difference is not registered in the quantity of the entering vessels but in the course of the extraosseous vessels . In all specimens, palmar vessels are registered to be thinner than the dorsal ones and in comparison with nor- mal-positioned specimens. A reorientation to the dorsal supply is noted. The veins leaving the dorsal surface appear to be larger than the arteries and veins in normal-positioned specimens and so appear to be congested, whereas on the palmar surface the course of the veins cannot be registered. The extraosseous vascularity of the other surrounding carpal bones is not impaired. The intraosseous arterial pattern shows that there is no significant impairment of arterial blood supply to the lunate bone because there is no difference in the intraosseous arterial pattern in both groups, the normal and the extended specimen group.
Discussion
The representation of the veins is not as extended as that of the arteries. The difficulty in differentiating between red colored arteries and brown colored veins could be solved using either special light or blue colored E 12. Extravasal leakage, seen only in the preparation and drilling sites, does not disturb the examined region.
While arterial injection into the radial artery was easily performed, filling the venous side still remains a problem. In the literature, there is no report dealing with the representation of the venous anatomy of small bones, such as the carpal bones and especially the lunate. Handley and Pooley [1991] tried to inject directly into the bone, being examined, the scaphoid, by dorsal puncture representing the palmar venous drainage of the scaphoid bone. The advantage of our method, the injection into the distal radius thus visualizing the whole deep venous system in the carpus, is that there was almost no extravasal leakage, and both the pal- mar and dorsal draining veins could be shown; no structures around the lunate are damaged by preparation or drilling. The location for intraosseous injection must be outside the wrist capsule, as leakage would otherwise fill the whole joint. The plastination method makes it possible to study the original anatomy of the forearm and hand in 5-mm-thick sheets of longitudinally embedded slices. A three-dimensional documentation of the vascularity in different functional aspects, i.e. comparison between normal and extended hands, is achieved and the specimens are pre- served forever. No extensive preparations and digestion of tissue are needed, as is necessary using the Spalteholz method [Spalteholz, 1911; Panagis et al., 1983; Gelberrnan and Szabo, 1984; Eitel et al., 1986]. Photographs taken for documentation could not really represent the three-dimensional effect of the sheets. The 1-mm cut damage was corrected by alternate cutting of the other specimens. There are three mechanisms impairing the extraosseous vascularity, especially concerning the venous drainage of the lunate bone, in the extended wrist position. (1) The main vessels on the palmar surface are compressed by the flexor tendons and the tension of the palmar wrist capsule during extension in the wrist. (2) The dorsal vessels are kinked and wedged between the dorsal surface of the capitate bone and the dorsal rim of the radius. (3) In the extended wrist position, the dorsal vessels are stretched, due to the rotation of the lunate around its horizontal axis, lengthening the distance between the radio- carpal arch and entrance or exit of the vessels on the bone's dorsal surface (fig. 3). All mechanisms impair the venous vessels to a greater extent due to the anatomy of the vessel wall. Although these anatomical examinations cannot be translated into physiological conditions with normal blood circulation, they confirm the results about pressure measurements in the lunate bone in patients [Martini, 1990; Jensen, 1993; Schiltenwolf et al., 1996] and could explain the hypothesis of venous congestion with the consequence of intraosseous venous pooling and high intraosseous pressure. At first venous congestion can be assumed, secondarily the arterial blood supply could be impaired by high intraosseous pressure in the lunate. The comparison between the normal and extended wrist position demonstrates a significant impairment of the venous outflow directly at the lunate bone, while there is no congestion in the other carpal bones, especially the capitate bone. The three mechanisms of impairment are recorded under static conditions of anatomical specimens. Muscle actions and other physiological functions are not respected. The results of this anatomical study and of earlier investigations, i.e. rinse examination of cadaver limbs [Laarmann, 1944; Koken, 1975; SteinhAuser et al., 19751, confirming the results about high intraosseous pressure in the lunate bone in vivo [Martini, 1990; Jensen, 1993; Schiltenwolf et al., 19961, establish a new aspect in the etiopathology of Kienbock's disease. Venous congestion could play a significant role in the development of necrosis of the lunate bone.
Conclusions
This study characterizes the lunate bone as a bone at venous risk. Venous congestion could be a further etiologic factor in the pathogenesis of lunate bone necrosis. Together with other important etiologic factors, such as Hulten's ulnar minus variance [Hulten, 1928; Stahl, 1947; Decoulx et al., 1957; Beckenbaugh et al., 1980; Alexander and Lichtmann, 1986; Kerschbaumer and Bauer, 19861, venous congestion could be the first step in lunate bone necrosis. A primary impairment of the arterial blood supply appears to be less probable, because the intraosseous arterial filling is abundant in all cases and therefore independent of the wrist position. Plastination is a method easily representing the arterial and venous vascularity in specimens even in different joint positions. In sheet plastination, the vascularity is represented in a three-dimensional way in its original anatomical environment in several functional aspects.