Vascular Anatomy of the Palmar Surfaces of the Distal Radius And Ulna: Its Relevance to Pedicled Bone Grafts at the Distal Palmar Forearm

INTRODUCTION

Decreased vascularity occurs in the proximal pole of the scaphoid after fracture and with avascular necrosis of the lunate (Kienböck’s disease). Surgeons have tried to address this problem by attempting to restore or improve vascular perfusion and osteoneogenesis of these bones. Hori et al. (1979) showed angio- and osteoneogenesis after simple implantation of blood vessels into the bone. Experimental studies in animals have shown that vascularized bone grafts promote new bone formation with normal morphology (Busa et al., 1999), maintain enhanced bone circulation in the long term (Tu et al., 2000) and accelerate bone healing (Brunelli et al., 1987). Pedicled vascularized bone grafts have been harvested on branches of the radial (Zaidemberg et al., 1991), ulnar (Guimberteau and Panconi, 1990), and metacarpal (Brunelli et al., 1992) arteries. Kawai and Yamamoto (1988) have described a graft pedicled on the pronator quadratus muscle. Martini (1987) used the pisiform bone as a pedicled graft while others prefer to use free vascularized bone grafts (Doi et al., 2000; Gabl et al., 1999). There are now several indications for retrograde pedicled bone grafts which are harvested from the dorsal aspect of the radius (Sheetz et al., 1995; Shin and Bishop, 2001).

The creation of a pedicled bone graft from the palmar aspect of the distal radius would be valuable as the palmar approach to the scaphoid allows better reconstruction of its normal shape if there is nonunion through the waist of the bone with a humpback deformity. Even if the choice between a palmar or dorsal approach is dictated by the location of the pseudarthrosis, Gelberman and Menon (1980) think that a palmar approach carries less risk of disruption of the proximal pole’s blood supply. This is as the major blood supply to the scaphoid enters through branches along its dorsal ridge.

The anatomical basis of a bone graft pedicled on the palmar carpal arch was first described by Kuhlmann and Guerin-Surville (1980). In this study, we investigate the properties of such grafts in order to confirm the presence of a reliable pedicle and assess its anatomical variability before using it in surgery (Mathoulin and Haerle, 1998).

MATERIAL AND METHODS

Forty arms of fresh cadavers were injected with coloured latex solution. This (100 ml Neoprene Latex/10 ml green colour pigment) was injected into the brachial artery in the axillary region and the dissections were performed 24–48 h later using magnifying loupes and a dissecting microscope. The dermoepidermis layer of the distal palmar forearm was resected down to the superficial arches of the hand. The ulnar and radial arteries were dissected and their branches were identified in the distal third of the forearm. All the flexor tendons were then removed carefully from the wrist, and the palmar carpal arch was dissected. The pronator quadratus muscle was excised and the anterior interosseous artery and its palmar branches were dissected. After measuring all the relationships of these arteries with the forearm bones, their potential lengths as vascular pedicles were assessed. Due to the arterial injection and dissection technique, the small venae commitantes could not be studied.

Median values and their ranges were calculated for all the measurements.

RESULTS

The palmar carpal arch arises in the distal forearm at a median of 1.2 (range 1–2.5) cm proximal to the tip of the radial styloid. This artery, together with its venae commitantes, crosses the palmar aspect of the distal forearm, close to the radiocarpal joint and just distal to pronator quadratus muscle (Fig 1). It runs inside a periosteal-capsular membrane of the radioulnar joint. At this level a ‘‘T-shaped’’ anastomosis with the anterior branch of the anterior interosseous artery is always found. The palmar carpal arch then runs ulnarly to reach the ulnar artery. For didactic reason, we have divided the palmar carpal arch into two parts which are divided by its anastomosis with the anterior interosseous artery. We call the radial part the radial carpal artery and the ulnar part the ulnar carpal artery (Fig 2).

The radial carpal artery and the anterior branch of the anterior interosseous artery were constant in all our dissections. The radial carpal artery gives origin, especially in its ulnar part, to numerous periosteal and cortical perforating branches (Kuhlmann and Guerin-Surville, 1980). The radial carpal artery diameter was large (1 mm or more) in 26, medium sized (0.8 mm) in eight and small (0.5 mm) in five of our dissections. In one case the artery was smaller than 0.5 mm. The radial carpal artery was dominant in all but three cases in which the ulnar carpal artery had an equal diameter.

The ulnar carpal artery was not always present (absent in 13 arms) and was often very slim. Its diameter was medium (0.8 mm) in seven, small (0.5 mm) in 11 and very small (less than 0.5 mm) in nine of our dissections. The anastomosis between the palmar carpal arch and the anterior branch of the anterior interosseous artery occurred in all our dissections.

The anterior interosseous artery runs down the forearm along the interosseous membrane, reaching the proximal border of the pronator quadratus muscle (Fig 1). At this point its posterior branch arises and this perforates the interosseous membrane and anastomoses with the posterior interosseous artery. The anterior branch of the anterior interosseous artery runs distally from its origin, first lying on the interosseous membrane and then on the radioulnar joint. It lies dorsal to the pronator quadratus muscle and joins the palmar carpal arch with a ‘‘T-shaped’’ anastomosis at the level of the distal radioulnar joint (Fig 2). At its origin the anterior branch of the anterior interosseous artery had a mean diameter of 1.1 mm. At the level of its anastomosis with the palmar carpal arch its diameter was large (1 mm) in four, medium (0.8 mm) in 28 and small (0.5 mm) in eight cases. The anterior interosseous artery and its anterior branch give off frequent periosteal collateral branches (one every 1–2 cm) to the anterior and posterior aspects of the forearm bones (Fig 3). Therefore, as shown in other studies (Menck et al., 1994; Pagliei et al., 1991) it contributes to both the periosteal and endosteal blood supplies of the ulna and the radius. These periosteal branches form an anastomotic network based on the horizontal branches of the anterior interosseous artery. Furthermore, in the distal forearm the artery provides many branches to the anterior forearm muscles, especially to the pronator quadratus. In four of our dissections there was a collateral branch of substantial calibre (about 1 mm) running from the anterior interosseous artery obliquely and distally to the radial artery. This ran between the muscular fibres of the pronator quadratus muscles.

The areas from which bone grafts can be harvested from the anterior surface of the radius or ulna are virtually without bounds as the periosteal network provides an extensive and diffuse vascular tree to these bones.

The first possible pedicle which we investigated was the radial carpal artery. If the origin of the radial carpal artery is, as in most cases (39 of 40 cases), just proximal to the radiocarpal joint, the bone graft can be harvested on the palmar–ulnar aspect of the radius, close to the distal radioulnar and radiocarpal joints (Fig 4). The pivot point of the pedicle is its origin from the radial artery. The median length of the pedicle, measured between its origin and the ‘‘T point’’ is 3 (range 2–3.5) cm which is sufficient to allow the placement of the bone graft within the lunate or the scaphoid bone without flexion of the wrist (Fig 5). In two of our cases, the radial carpal artery originated more proximally from the radial artery (2.5 cm from the tip of the radial styloid) and ran obliquely rather than horizontally towards the T-shaped anastomotic point. In these cases, the length of the pedicle might not be sufficient to allow the bone graft to be rotated into the proximal carpal row without flexion of the wrist.

To avoid this problem, we investigated the feasibility of harvesting a bone graft proximal to the distal radioulnar joint, pedicled on the anterior branch of the anterior interosseous artery. The pivot point of this pedicle is the T-shaped anastomotic point with the palmar carpal arch. Bone grafts can be harvested on this pedicle from the anteromedial aspect of the radius, and also from the ulna, using the horizontal collateral periosteal branches at this level (Fig 6).

Grafts can be harvested just distal to the division of the anterior and posterior branch of the anterior interosseous artery (Fig 7). This point of division was found to be a mean of 4.6 cm proximal to the radiocarpal joint and in this case defines the length of the pedicle. This is in the range of other authors findings (Hu et al., 1994; Pahl and Schmidt, 1994). The graft can now be rotated at a T-point and the length of the pedicle is sufficient to allow the bone graft to reach the wrist easily (Fig 8a and b).

The more proximal the graft is harvested, the less cancellous bone will be available. As always, longer pedicles have a higher risk of intra-arterial thrombosis and for dissection the skin incision has to be extended more proximally and the insertion of the pronator quadratus muscle has to be elevated.

If for any reason a longer pedicle is required, the rotation point of the pedicle can be moved from the ‘‘T-anastomosis’’ to the origin of the radial carpal artery (Fig 9a and b). A pedicle length of about 7 cm could easily be achieved by doing so in the cadaver extremity.

In rare cases in which a vascularized bone graft is required more distally, the same pedicle can be used and the bone graft is then harvested proximal to the division of the anterior and posterior branches of the anterior interosseous artery. Ligation of the posterior branch will then be necessary.

DISCUSSION

The presence, length and calibre of the radial carpal artery (radial poition of palmar carpal arch) are appropriate to serve as the pedicle for vascularized bone grafts for insertion into the lunate or scaphoid. One of its major advantages is that the palmar approach to the scaphoid is frequently employed for nonunion procedures.

The existence of the palmar carpal arch and its constant anastomosis with the anterior branch of the anterior interosseous artery was recognized by early anatomists (Heitzmann, 1875; Kopsch, 1909). Even though it is not mentioned in more recent anatomy text books, its presence and relevance for carpal bone vascularity and surgical usage has been recognized (Gelberman et al., 1983; Kuhlmann and Guerin-Surville, 1980).

However, surgeons studying the possibility of harvesting tissues on the interosseous arteries have not considered this vascular axis (Dellon and Mackinnon, 1984). Our findings show that bone grafts harvested from the forearm bones can be pedicled on the anterior branch of the anterior interosseous artery with retrograde flow through the palmar carpal arch. Other tissues, such as muscle flaps (pronator quadratus muscle flaps) or combinations such as osteocutaneous flaps (Chinese flap) can also be based on this pedicle which does not depend on the division of the anterior and posterior branches of the anterior interosseous artery but on the palmar carpal arch.

Having said this, little is known about viability of these vascularized grafts after insertion into the carpal bones, though the good results obtained in scaphoid nonunion surgery with vascularized bone grafts suggests that they remain viable and stimulate angio- and osteoneogenesis.