The superficial ulnar artery : development and clinical significance

The principal arteries of the upper limb show a wide range of variation that is of considerable interest to orthopedic surgeons, plastic surgeons, radiologists and anatomists. We present here a case of superficial ulnar artery found during the routine dissection of right upper limb of a 50-year-old male cadaver. The superficial ulnar artery originated from the brachial artery, crossed the median nerve anteriorly and ran lateral to this nerve and the brachial artery. The superficial ulnar artery in the arm gave rise to a narrow muscular branch to the biceps brachii. At the elbow level the artery ran superficial to the bicipital aponeurosis where it was crossed by the median cubital vein. It then ran downward and medially superficial to the forearm flexor muscles, and then downward to enter the hand. At the palm, it formed the superficial and deep palmar arches together with the branches of the radial artery. The presence of a superficial ulnar artery is clinically important when raising forearm flaps in reconstructive surgery. The embryology and clinical significance of the variation are discussed.


Introduction
Normally, the ulnar artery begins distal to the bend of the elbow as the larger of the two terminal divisions of the brachial artery.It runs deep to the antebrachial flexor muscles and then superficial to the flexor retinaculum.The artery ends by forming the superficial palmar arch with a contribution from the superficial branch of the radial artery.The arch gives palmar digital branches to the medial three fingers and also to the medial half of the index finger.The lateral aspect of the index finger and the thumb normally receive their arterial supply from the radial artery through the radialis indicis and the princeps pollicis arteries, respectively. 13][4] Its incidence ranges from 0.7 5 to 3.3%. 6The superficial ulnar artery has been reported with different terminologies; arteria antebrachialis superficialis ulnaris, [5][6][7] high origin of the ulnar artery 8,9 and superficial ulnar artery with a high origin. 10

Case report
The superficial ulnar artery (Figures 1 and 2) was found in the right upper limb of a 50-year-old male cadaver during routine dissections in the Melaka Manipal Medical College, Manipal, India.However, the left upper limb showed no abnormalities.The dissections of both upper extremities (right and left) of the body were carried out according to the instructions by Cunningham's manual of practical anatomy.The dissections took place during 2005-2006.The bodies were preserved by the injection of a formalin-based preservative (10% formalin) and stored at -4 ºC. 1 2

Discussion
The superficial ulnar artery is a well-known but very rarely encountered abnormality.In the present case the artery arose from the brachial artery in the proximal part of the arm.It then descended along the arm superficial and lateral to the median nerve (Figure 1).At the elbow level the artery ran superficial to the bicipital aponeurosis where it was crossed by the median cubital vein (Figure 1).After that, the artery coursed obliquely downwards and medially, superficial to the forearm flexor muscles over the antebrachial fascia and under the superficial venous system to reach the distal third of the forearm, where it was seen on the lateral side of flexor carpi ulnaris close to the ulnar nerve (Figure 2).The artery then passed anterior to the flexor retinaculum where it divided into two terminal branches.The superficial one anastomosed with the palmar branch of the radial artery to form the superficial palmar arch and the deep branch anastomosed with the radial artery to form the deep palmar arch.
The brachial artery had a normal course in the arm but at elbow level it divided into the radial and common interosseous arteries (Figure 2).The superficial ulnar artery was of a smaller caliber than both the radial and common interosseous arteries.
The superficial course of the ulnar artery over the forearm flexors has been described in two ways: under the antebrachial fascia 8,[11][12][13] or, more infrequently, as in our case, over the antebrachial fascia in a subcutaneous position, 11,14 crossed by the median cubital vein. 15The artery has been described as gaining the lateral border of flexor carpi ulnaris at midforearm level 12 or after passing deep to the palmaris longus. 11,12,16,17However, in our case this relationship was gained at the distal third of the forearm, close to the wrist joint.Our case was not associated with other arterial anomalies, although other authors have reported superficial ulnar artery associated with the presence of a median artery. 8,16,18velopmentally, the upper limb bud is initially supplied by a vascular plexus derived from four or five consecutive intersegmental branches of the dorsal aorta.Very early in development, the seventh cervical intersegmental branch enlarges and becomes consolidated as the main artery (axis artery) to the developing upper limb bud.This axis artery gives rise to the subclavian, axillary, brachial, and interosseous arteries and to the deep palmar arch.0][21][22] The developmental reason for the superficial ulnar artery in the present case may be due to the ulnar artery establishing a connection with the axis artery in the arm and the bifurcation of brachial artery into radial artery and common interosseous artery may be due to the posterior interosseous artery arising from the axis artery just distal to the connection of radial artery with the axis artery in the cubital fossa region and the continuation of the main trunk (axis artery) between radial and posterior interosseous arteries being the common interosseous artery.
Vascular anomalies occurring in common surgical sites tend to increase the likelihood of damage during surgery.Owing to its unusual origin in the arm and its subcutaneous course, the superficial ulnar artery would be particularly vulnerable in surgical procedures within the arm and forearm.In the present subject the ulnar artery was immediately subjacent to the median cubital vein.This would predispose the vessel to inadvertent penetration during attempts at venipuncture of the median cubital vein.
Although accidental intra-arterial injection of drugs is rare, if it occurs, amputation of the forearm or fingers is unfortunately sometimes necessary.Since the free forearm flap on the radial artery is often used in reconstructive surgery, if a superficial ulnar artery is present there is a risk that it may be ligated or cut instead of the superficial vein, causing disorder of circulation in the hand. 11,23On the other hand, the presence of a superficial ulnar artery can be advantageous, since it can be used to supply blood to the forearm flap. 24Radiographically, the superficial ulnar artery can lead to misinterpretation of incomplete angiographic pictures. 23herefore, it is important to know whether a patient has a superficial ulnar artery in the forearm.

Conclusion
Since a superficial ulnar artery is actually not very rare, there is a fair chance that clinicians may encounter

BFigure 2 -
Figure 2 -Superficial course of the artery along the forearm