22 Interosseous Vascularity of the Carpus

Mohamed Morsy, Nick A. van Alphen, and Steven L. Moran

22 Interosseous Vascularity of the Carpus

22.1 Introduction

The blood supply to the carpal bones plays an important role in bone development, remodeling, and healing. The interosseous arterial network to each carpal bone is capable of transporting important hormones and growth factors, allowing for ossification during development, and it also stimulates bone healing in times of trauma. ¹ Evidence of a vascular ingrowth into the lunate bone is seen as early as 14 weeks of fetal gestation. This early vascular ingrowth leads to the process of endochondral ossification. ² Subsequently, each of the developing carpal bone anlages is penetrated by isolated arterial buds which terminate in sinusoidal formations. Ossification begins near the center of each carpal bone, with the exception of the distal eccentric ossification center of the scaphoid. The vascular buds progressively retreat and are replaced with a series of nutrient trunks, which, in most cases, enter through opposing surfaces and anastomose within the bone. ³

The extrinsic blood supply to the carpal bones is provided through anastomosis between a dorsal transverse and palmar transverse carpal arterial arcade; this extraosseous system originates from the radial, ulnar, and anterior interosseous arteries. The anatomic details of this extraosseous vascular system are discussed elsewhere within the text. The extraosseous arteries penetrate the carpal bones through nutrient foramina, where they go on to form the intraosseous arterial system within each carpal bone (▶Fig. 22.1). In long bones, the blood supply to the bone comprises a combination of periosteal, nutrient, epiphyseal, and metaphyseal vessels. Vessels usually enter through noncartilaginous areas of ligamentous attachment. ⁴ ^, ⁵ In the carpus, many of the bones have a large surface area covered with articular cartilage (such as the scaphoid and lunate), thus limiting the area for blood vessel in growth.

**Fig. 22.1** Image of a latex-injected wrist showing extraosseous arterial system penetrating volar wrist capsule to contribute to the interosseous vascular blood supply. Note vessel entering volar surface of lunate (*arrow*). RA, radial artery, AIA, anterior interosseous artery, UA, ulnar artery, LRL, long radiolunate ligament, L, lunate bone, RSC, radioscaphocapitate ligament. (Copyright Mayo Clinic.)

The study of the interosseous blood supply of the carpus has been limited by technology. Early studies with long bones used India ink injections to evaluate the interosseous system. ⁶ This was followed by the use of the Spalteholz technique, in which barium sulfate is injected into the vasculature of the bone. The bone is then sequentially decalcified, dehydrated, and sectioned. Specimens are then made transparent by placing them in Spalteholz fluid. ³ ^, ⁷

In the late 1970s and early 1980s, building on the work of Crock and others, Gelberman and colleagues produced several landmark papers which sought to evaluate the complexities and intricacies of the interosseous blood supply by performing a series of experiments utilizing a modification of the Spalteholz technique. ³ ^, ⁸ ^, ⁹ From this work it was shown that carpal bones can be categorized into three groups based on the location and number of intraosseous vessels (▶Table 22.1). ⁵ Abnormalities or damage to the intraosseous blood supply can lead to bone dysmorphology and osteonecrosis. ¹⁰ ^, ¹¹ Carpal bones found in group I, the scaphoid, capitate, and a percentage of lunates, are more prone to avascular necrosis due to the dependence of a major portion of the bone on a single vessel lacking intraosseous anastomosis with other nutrient arteries. ⁵ ^, ⁹ ^, ¹²

**Table 22.1** Classification of carpal bones by intraosseous vascular anatomy ⁵
Group 1; perforators or nutrient branches penetrating on one bony surface, or a large portion of the bone is supplied by a single perforator	Scaphoid, capitate, and minority of lunate bones
Group 2; at least two perforators, but lacks intraosseous anastomosis	Trapezoid, hamate
Group 3; at least two perforators with intraosseous anastomosis	Trapezium, triquetrum, pisiform, and majority of lunate bones

Since the time of these publications, there has been substantial advancement in imaging technology with both magnetic resonance imaging (MRI) and micro-computed tomography (micro-CT). Although studies utilizing the Spalteholz technique have stood the test of time, they provide primarily two-dimensional imaging. To overcome these shortcomings, more recent studies have used micro-CT techniques to visualize the intraosseous vascular network. ¹³ ^, ¹⁴ This technology can provide accurate three-dimensional information that was not possible with more classic techniques. The image resolution of micro-CT can allow for imaging of structures of 1 to 2 µm. In addition, newer low-viscosity radiopaque substances can fill the interosseous microvasculature. Using this technology, measurements can also be made that were not previously possible, such as of vessel diameter, length, and volume. All this can be obtained without alteration of the internal bony architecture that can occur with the previous decalcification techniques. ¹⁵ ^, ¹⁶ This new information can be utilized to update our understanding of avascular necrosis and its etiology, as well as to describe safe zones for surgical intervention and instrumentation of these bones. A more thorough understanding of the intricacies of the carpal bone vascular system may have widespread ramifications on bone pathology, fracture fixation, and surgical intervention. This chapter briefly reviews the latest advances and discoveries related to intraosseous vascular anatomy of the lunate, capitate, and scaphoid, as well as the impact they may have on clinical practice.

22.2 The Lunate

The lunate lies at the center of the proximal row and plays an important biomechanical and clinical role in carpal kinematics. ¹⁷ It acts as a pillar for the lunate–capitate column and as a major stabilizer of the proximal row. The arterial blood supply to the lunate is derived from either volar or dorsal nutrient vessels with intraosseous anastomoses. ⁵ ^, ⁸ ^, ¹⁸ ^– ²¹ These vessels enter near the short radiolunate ligament palmarly and dorsally through the attachments of the radiocarpal ligament. Although traumatic fracture of the lunate is uncommon, the lunate is the second most common carpal bone to undergo avascular necrosis, a process referred to as Kienbock’s disease. ²² ^, ²³

Gelberman and colleagues identified three patterns for the interosseous anastomosis of the nutrient vessels within the lunate. These are described according the their shape as they pass through the bone as the letters Y (occurring in 59% of specimens), X (occurring in 10% of specimens), and I (occurring in 31% of specimens; ▶Fig. 22.2). ⁸ It has been shown that up to 20% of the lunates are dependent solely on either a volar or a dorsal nutrient system, potentially making them more prone to avascular necrosis if this single nutrient system were to be damaged. ⁵ ^, ⁸ ^, ²² ^, ²⁴ ^, ²⁵

**Fig. 22.2** (**a–c**) An illustration of the different patterns of intraosseous vascularity of the lunate. (Reproduced with permission from Gelberman RH, Bauman TD, Menon J, Akeson, WA. The vascularity of the lunate bone and Kienbock’s disease. *J Hand Surg* 1980;5:276.)

In a recently published study using micro-CT imaging, Van Alphen and colleagues further examined the intraosseous vascular patterns of the lunate bone. They noted that all specimens could be classified according to the previously described Y, X, and I classification scheme. In addition, these patterns were found to occur in similar distributions as those reported by Gelberman and colleagues ⁸ ^, ¹⁴ (▶Fig. 22.3). The vascular pattern seen within each specimen was not found to be associated with the presence or absence of a hamate facet on the lunate. ¹⁴ The presence or absence of a hamate facet has been postulated as a factor contributing to the development of Kienbock’s disease ²⁶ ^, ²⁷

**Fig. 22.3** Multiple images of a lunate cadaveric specimen imaged with micro-CT and rendered in three dimensions following vascular injection. The red structure correlates with the path of the nutrient artery. This lunate fits within the general “I”-type intraosseous vascular pattern. The various views seen include distal (a), volar (b), radial (c), dorsal (d), and ulnar (e). Note the dorsal and volar locations of main nutrient foramina. *White arrow* points to accessory nutrient vessel which has no perceivable anastomosis to main central arterial system. (Copyright Mayo Clinic.)

With more accurate measurement of the number, diameter, and total cross-sectional area of the interosseous vessels, Van Alphen also found that the nutrient vessels from the volar and dorsal sides were comparable in diameter and cross-sectional area; however, some specimens had only a volar vessel (no dorsal nutrient vessel) as the lunates’ sole source of interosseous blood supply. There were no specimens identified where there was a sole dorsal blood supply. ¹⁴ Lunates with an isolated single volar vessel may be at risk for traumatic or iatrogenic injury, which could have an impact on the development of localized bone ischemia and future ability to respond to trauma.

Iatrogenic avascular necrosis of the lunate and scaphoid has been described in the literature. ²⁸ ^– ³¹ Based on the previous findings, a dorsal approach would have the lowest chance of irreversible injury to the lunates blood supply, as no specimen was noted to have an isolated dorsal blood supply to the lunate. ¹⁴ Van Alpehen goes on to describe safe zones for surgical fixation and intervention on the lunate. These sites may favor hardware placement, as they are areas with a lower likelihood of injuring a dominant nutrient vessel (▶Fig. 22.4). ¹⁴ Volar approaches to the lunate, for ligament reconstruction or perilunate injury, may result in localized ischemia in a subset of patients with an absent dorsal nutrient vessel.