Surgical Approaches from an Angiosomal Perspective

INTRODUCTION

∗ This adapted chapter has been previously published in Fractures and Injuries of the Distal Radius and Carpus by David J. Slutsky & A. Lee Osterman.

Adequate vascularity is an acknowledged prerequisite for successful bone and soft tissue healing. Improved understanding of the cutaneous blood supply has informed and improved incision and flap design enabling surgeons to not only exceed the traditionally presumed limitations in a random-pattern flap, but also permitting the successful elevation and transmission of island pedicle flaps with wide arcs of rotation. Understanding the angiosome concept and the cutaneous microcirculation can aid in the incision planning in severely traumatized limbs to minimize wound complications.

The concept of the angiosome was initially described in the cutaneous blood supply but has subsequently been shown to pertain to the underlying viscera and skeleton. Devascularization of these deeper structures is less obvious than skin necrosis but is known to occur, resulting in problems such as nonunion of fractures and avascular necrosis of bones. The incidence of such vascular insults is unknown, but more aggressive surgical approaches and soft tissue stripping, such as that associated with open reduction and internal fixation, may exacerbate this problem. An understanding of the angiosome anatomy and concept in a volumetric, three-dimensional sense may be important to prevent such complications, particularly in vulnerable areas such as the elbow, hip, and wrist.

Numerous injection studies and Spalteholtz preparations have been used to map the vascular anatomy of the distal radius, carpal bones, and overlying skin. This information has served as the cornerstone for a multitude of composite flaps useful for reconstructing bone, nerve, and tendon and for providing soft tissue coverage. The applied anatomy has also helped to explain the differential rates of avascular necrosis of the carpal bones following trauma and provides a rational for the preferred surgical exposures to fractures. With the continued advancement of microsurgery and perforator flap surgery, the concept of the angiosome has become increasingly relevant. We seek to organize such information using the angiosome concept, to present a cogent, comprehensible surgical approach to the three-dimensional vascular anatomy of the forearm and wrist.

FUNCTIONAL MICROVASCULAR ANATOMY

The distal forearm, including the radius, ulna, carpal bones, and overlying soft tissue, is supplied by a network of longitudinal vessels: the radial artery (RA), ulnar artery (UA), anterior interosseous artery (AIA), and posterior interosseous artery (PIA). They are interconnected by dorsal and volar transverse arches ( Figs. 7-1 and 7-2 ). The overlying skin is supplied by direct or septocutaneous perforators arising from these longitudinal vessels ( Fig. 7-3 ), which are small arteries and veins that course along the fibrous septa that separate the muscles in the forearm. These perforator vessels are predictable and remarkably constant.

Most of the distal radius and proximal carpal row is supplied via the radial and anterior interosseous arteries, which have a rich collateral circulation. The single exception is the pisiform, which is supplied by the ulnar artery. In contrast, the ulna is primarily supplied by the posterior interosseous and ulnar arteries. The distal carpal row is supplied from the dorsal intercarpal arch and deep palmar arch and thus has contributions from the radial, ulnar, and anterior interosseous arteries. The skin of the distal forearm is supplied on the radial/palmar side by the radial artery, the ulnar/palmar side by the ulnar artery, and dorsally by the AIA, the PIA, and the dorsal ulnar artery. These skin territories overlap significantly as a result of the connection afforded by the subdermal and subfascial plexus.

An angiosome is a section of tissue that can remain viable based on a single feeding vessel. Of course, these angiosomes do not have absolute boundaries; otherwise, necrosis from skin incisions would be very common. There is some “built in” redundancy from the fact that each angiosome connects with the adjacent one via small arteriole branches termed choke vessels. These vessels respond to ischemic insults within an adjacent angiosome by increasing their diameter and thereby their blood flow, providing adequate collateral circulation to the adjacent compromised angiosome. This phenomenon explains the physiology behind the delay procedure commonly used to extend the margins of a flap to be transposed. This also explains the observed phenomenon that delaying surgery may prevent wound complications by allowing choke vessels to open and establish collateral circulation. In most human clinical applications, the flaps are delayed 1 to 2 weeks before flap transposition. It is interesting that adjacent angiosomes tend to interconnect within tissue rather than between intercompartmental fascial planes, which seems counterintuitive.

Another general rule is that although one angiosome may be expanded to include an adjacent angiosome, it will not reliably cover the skin territory of a more distant angiosome. Consequently, if a specific angiosome is rendered ischemic along with its neighboring angiosomes after a traumatic incident or surgical dissection, that angiosome becomes devitalized, predisposing to nonunion or infection.

RADIAL ARTERY ANGIOSOME

The radial artery ( Fig. 7-4 ) directly supplies the bone (radius, scaphoid, trapezium), muscle (pronator teres), extensor carpi radialis longus (ECRL) and brevis (ECRB), brachioradialis, flexor carpi radialis (FCR), flexor digitorum sublimis (FDS), flexor pollicis longus (FPL), and overlying volar radial skin of the forearm to include the mobile extensor wad ( Fig. 7-5 ). The radial forearm flap based on this angiosome has been used as a pedicled septocutaneous flap for coverage of the antecubital fossa, as a pedicled reverse flow septocutaneous flap for hand coverage, and as a free flap to provide skin, muscle, and bone to distant sites. The radial artery travels between the brachioradialis and the FCR, and gives off numerous perforators along the lateral intermuscular septum that either ascend to the overlying skin or dive down to supply the underlying radius and FPL. The versatility of this pedicle and its associated composite flaps is well documented. Note that the radial artery not only supplies the voloradial aspect of the distal radius but also the dorsal aspect of the bone via the 1,2 intercompartmental supraretinacular artery (1,2 ICSRA) and the dorsal radiocarpal arch (DRCA). The 1,2 ICSRA originates from the radial artery approximately 5 cm proximal to the radiocarpal joint. It traverses superficial to the extensor retinaculum over the 1,2 intercompartmental septum sending branches down to the cortical and rarely cancellous bone. Sheetz and colleagues, however, described a branch from the 1,2 ICSRA to the second compartment floor that does penetrate into cancellous bone. This artery then connects variably to the radial artery, DRCA, or dorsal intercarpal artery (DICA). The 1,2 ICSRA also gives off the dorsal supraretinacular arch (DSRA), which connects variably to the 2,3 intercompartmental supraretinacular artery (2,3 ICSRA), fourth intercompartmental artery (ICA), fifth ICA, or ulnar artery. The DRCA arises from a direct branch off the radial artery and gives several small feeding vessels to the ridge of the radius at the radiocarpal joint; these vessels descend to the cancellous bone of the metaphysis.

The radial artery supplies the volar distal radius in a retrograde fashion via the palmar metaphyseal arch (PMA) and palmar radiocarpal arch (PRCA). The PMA originates from the palmar AIA within the pronator quadratus and courses through the muscle to connect with the radial artery, giving off scattered perforating branches to the underlying largely cortical bone. Sheetz and colleagues point out that the more proximal perforating branches are more likely to penetrate into cancellous bone. This observation was consistent for all of the penetrating vessels of the distal radius. The PMA pedicle has been used for vascularized bone grafts to the scaphoid. Some consider the results of this vascularized bone graft to be inconsistent; this is likely due to the variable penetrating vessels. A larger bone graft rather than a smaller one based on this pedicle is therefore advisable to capture as many perforators as possible. Also, the more proximally the bone graft is harvested to obtain a larger arc of rotation, the more likely it is to have a perforator that penetrates into cancellous bone.

The PRCA is located just proximal to the radiocarpal joint, travels within the palmar wrist capsule, and connects with the palmar AIA and ulnar artery. The PRCA is subdivided into a radial and ulnar component by the palmar AIA, which forms a T anastomosis, as described by Haerle and colleagues (see Fig. 7-1 ). The radial PRCA gives off multiple branches to the distal radius periosteum supplying cortical and cancellous bone. This pedicle has also been used as a source of vascularized bone. Mathoulin and Haerle published a report of 17 patients successfully treated for scaphoid nonunion with this vascularized bone graft.

The radial artery supplies the carpus from proximal to distal through branches of the (1) DRCA, (2) branches to the scaphoid tubercle and dorsal ridge, (3) branch to the dorsal intercarpal arch, (4) branch to the trapezium, and (5) branches off the deep palmar arch ( Fig. 7-6 ). The DRCA arises at the level of the radiocarpal joint and supplies the distal radius, lunate, and triquetrum. It continues to connect to the ulnar artery and possibly the AIA. The branches to the scaphoid arise at the level of the scaphotrapezial joint to enter the distal scaphoid. The volar scaphoid branch frequently connects with the superficial palmar arch and the dorsal branch connects with the dorsal intercarpal arch ( Fig. 7-7 ). These arches serve as collateral circulation if the radial artery becomes occluded proximally. The DICA originates just distal to the dorsal scaphoid branch and supplies the distal carpal row. Like the DRCA, the DICA traverses the wrist to connect with the AIA and ulnar arteries. The branch to the trapezium is the last branch to the carpus before continuing as the dominant vessel to the deep palmar arch. Further details of the vascular anatomy of the arches are discussed later in this chapter.

ANTERIOR INTEROSSEOUS ARTERY ANGIOSOME

The AIA ( Fig. 7-8 ) supplies bone (central distal radius, portions of the proximal carpal row); muscles, that is, the abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), pronator quadratus, and part of the FPL; and the skin and soft tissues of the deep volar and distal dorsal forearm and hand ( Fig. 7-5 ). The AIA travels along the anterior surface of the interosseous membrane, then divides into a palmar and dorsal branch just before the pronator quadratus muscle. The palmar AIA gives rise to the PMA and then forms the radial and ulnar palmar radial carpal arches. As previously discussed, the PRCA is subdivided into a radial and ulnar component by the palmar AIA. The radial PRCA gives off multiple branches to the distal radius, and the ulnar PRCA originating just proximal to the radial PRCA supplies the distal palmar ulnar head. The ulnar PRCA frequently connects to the ulnar artery or the PIA via the oblique dorsal artery to the distal ulna.

Displaced fractures of the distal radius are frequently associated with tearing and damage to the pronator quadratus. This likely damages the AIA contributions to the distal radial metaphysis and epiphysis via the PMA and PRCA. Thus, the PRCA contributions to the distal radius via flow from the adjacent radial artery angiosome become important to retain vascularity. Since care is taken to avoid damage to the volar radiocarpal ligaments in the volar approach, avoiding injury to the PRCA and its connection to the radial artery is also prudent.

The dorsal branch of the AIA travels through the interosseous membrane into the posterior compartment to supply the dorsal distal radius and contributes to the dorsal arterial arches. Either the common AIA or the proximal dorsal AIA gives off a second dorsal perforating branch, which travels through the interosseous membrane and travels within a septum between the EPB and EPL that segmentally supplies the overlying skin of the distal dorsal radius. These septocutaneous branches have been used as the vascular basis of reversed flaps that are able to incorporate skin, dorsal distal radius, and distal posterior interosseous nerve as a composite flap.

The 2,3 ICSRA arises variably from the common AIA, or dorsal branches of the AIA. It then courses over the extensor retinaculum and Lister’s tubercle, sending deep perforating branches that usually penetrate into cancellous bone. The 2,3 ICSRA then connects to the DICA. Other anastomoses between the 1,2 ICSRA, DRCA, and the fourth ICA have been described. As with the 1,2 ICSRA, Sheetz and colleagues describe a branch from the 2,3 ICSRA to the second compartment floor.

The fourth ICA is a branch off the dorsal AIA or the fifth ICA and runs in the fourth compartment just lateral to the posterior interosseous nerve connecting with the DICA and variably the DRCA, 2,3 ICSRA, or fifth ICA. Along the floor of the fourth compartment, the fourth ICA gives off branches to the underlying bone, which frequently enter cancellous bone.

The fifth ICA arises from the dorsal AIA and also connects distally with the DICA. Sheetz and colleagues found contributions to the distal radius from the fifth ICA dorsal compartment in only 39% of their specimens. Thus, in the majority of cases the fifth ICA does not directly supply the distal radius or carpus, but serves as a conduit between the radial artery, AIA, and ulnar artery via the DICA.

POSTERIOR INTEROSSEOUS ARTERY ANGIOSOME

The PIA supplies bone (ulnar head and neck); muscles (APL, extensor digitorum communis [EDC], extensor digiti quinti [EDQ], extensor carpi ulnaris [ECU], EPB, extensor indicis proprius; and skin of the proximal dorsal forearm (see Fig. 7-5 ). Proximally in the forearm after entering the posterior compartment at the level of the distal edge of the supinator, the PIA continues on top of the APL and beneath the EDM and ECU. It then becomes more superficial in the mid-forearm traveling between the ECU and EDM. Between the ECU and EDM lies a septum from which multiple cutaneous perforators arise, supplying the overlying skin of the proximal and mid-dorsal forearm. Pedicled flaps for elbow coverage, reverse flow pedicled flaps for distal dorsal hand coverage, and free flaps using this pedicle have been described.

The PIA supplies the distal ulna via the oblique dorsal arteries, which arise from an arch formed by the PIA and the dorsal AIA. The oblique dorsal artery gives off branches that supply the ulnar neck and head, and frequently connects to the ulnar artery. The PIA does not have a significant contribution to the radius or carpus (see Fig. 7-2 ).

ULNAR ARTERY ANGIOSOME

The ulnar artery supplies bone (ulna, pisiform, distal carpal row); muscle (flexor carpi ulnaris [FCU], palmaris longus, FCR, FDS, and flexor digitorum profundus; and skin of the ulnar forearm (see Fig. 7-7 ). The ulnar artery travels on the radial side of the flexor carpi ulnaris with the ulnar nerve in the distal two thirds of the forearm. The ulnar artery gives off multiple septocutaneous branches within the medial intermuscular septum to supply the volar/ulnar skin of the entire forearm and wrist. Branches from the ulnar artery to the FDS of the ring and small finger allow for vascularized tendon transfers along with overlying fascia and skin. The ascending branch of the dorsal ulnar artery, a branch from the ulnar artery arising 2 to 5 cm proximal to the pisiform, travels superficially and proximally to supply a large area of skin (up to 20 cm long), which may be transferred as a pedicled flap for hand soft tissue coverage.

The ulnar artery gives off multiple branches to the distal ulna and carpus largely through the volar and dorsal arches. From proximal to distal the branches are to the (1) dorsal radiocarpal arch (RCA); (2) palmar RCA; (3) proximal pisiform and triquetrum; (4) palmar ICA; (5) distal pisiform and medial hamate, which continues to the dorsal ICA; (6) basal metacarpal arch; and finally the (7) superficial and (8) deep palmar arches ( Figs. 7-9 and 7-10 ). Therefore, the ulnar artery directly supplies only the ulnar head, pisiform, and medial hamate.