Introduction

The hand has a unique arterial blood supply. The primary source of all the blood in the hand originates from two arteries. These two arteries are the ulnar artery and the radial artery. The ulnar artery descends toward the hand to form the superficial palmar arch. The radial artery descends toward the hand and forms the deep palmar arch. The superficial palmar arch perfuses the ulnar side of the hand mainly. While the deep palmar arch will predominately perfuse the radial side of the hand, these two arches will provide collateral blood supply to each other.

These palmar arches will branch even further into digital arteries that will perfuse the digits. But the thumb does not receive blood from the digital arteries. The thumb gets a separate artery called the princeps pollicis artery. This artery is a direct branch from the deep palmar arch.

Structure and Function

The major artery that is the source of blood for the princeps pollicis artery is the radial artery. Since the radial artery descends toward the hand to form the deep palmar arch. The princeps pollicis artery is a small muscular artery that branches from the deep palmar arch. This artery then ascends the thumb passing between two muscles. The princeps pollicis artery splits the oblique head of the adductor pollicis muscle and the first interosseous muscle. The princeps pollicis muscle ascends and terminates at the base of the proximal phalanx. At the proximal phalanx, the princeps pollicis artery terminates beneath the flexor pollicis longus muscle's tendon. Then the princeps pollicis artery will split into two smaller arteries that will further perfuse the thumb.[1]

The function of the princeps pollicis artery is to perfuse the bones, muscles, nerves, and skin in the thumb. 

Embryology

During embryology, the blood vessels predominately develop from the mesodermal germ layer. The mesodermal germ layer contains mesenchymal tissue. The princeps pollicis artery develops from mesenchymal tissue. As the limbs grow during embryology, fibroblast growth factor induces the lengthening of bones, muscles, and blood vessels. Fibroblast growth factor and vascular endothelial growth factor (VEGF) have angiogenesis characteristics on blood vessels; this will induce the formation and growth of the princeps pollicis artery.

Blood Supply and Lymphatics

The blood supply that is provided by the princeps pollicis artery is directed towards the distal fibers of the median, radial, and ulnar nerve. The muscles that receive blood from the princeps pollicis artery are abductor pollicis brevis muscle, abductor pollicis longus muscle, extensor pollicis brevis muscle, extensor pollicis longus muscle, flexor pollicis longus muscle, flexor pollicis brevis muscle, adductor pollicis muscle,  opponens pollicis muscle, and first dorsal interosseus muscle. The skin that overlies the thumb also receives perfusion from the princeps pollicis artery.[2]

The lymphatic drainage of the thumb and the hand will drain towards the cubital fossa. At the cubital fossa, the lymph fluid will drain into the cubital lymph nodes. The lymph fluid will drain towards the axilla. Once at the axilla, the lymph fluid will enter the axillary lymph nodes. The lymph fluid eventually returns into the central circulation via the right lymphatic duct and the thoracic duct. The left thumb will drain towards the thoracic duct. While the right thumb will drain towards the right lymphatic duct.

Nerves

The princeps pollicis artery provides minor blood supply to the distal nerve fibers of three nerves in the hand:

• Ulnar nerve 
• Median nerve
• radial nerve

The princeps pollicis artery's primary function is to perfuse the muscles, bone, and skin of the thumb. The blood supply sometimes overlaps with the distal nerve fibers' territory. But the princeps pollicis artery is not the dominant blood supply to the nerves in the hand. 

Muscles

There are nine muscles and muscle tendons that will receive blood supply from the princeps pollicis artery:

• Abductor pollicis brevis muscle
• Abductor pollicis longus muscle
• Extensor pollicis brevis muscle
• Extensor pollicis longus muscle
• Flexor pollicis longus muscle
• Flexor pollicis brevis muscle
• Adductor pollicis muscle
• Opponens pollicis muscle
• First dorsal interosseous muscle

These nine muscles also receive blood from arteries that are more proximal in the hand and forearm. 

Physiologic Variants

The princeps pollicis artery usually branches from the deep palmar arch. The location where the princeps pollicis artery will branch from may vary. The length and site of termination of the princeps pollicis artery also vary. In some rare instances, the princeps pollicis artery is a branch of the superficial palmar arch instead of the deep palmar arch. This anomaly makes the ulnar artery the main blood supply to the princeps pollicis artery.[3] The variations in the princeps pollicis artery exist, but the perfusion of the thumb and the thumb's structures are consistent.[4][5][6]

Surgical Considerations

In hand surgery, the knowledge of the blood supply to the fingers and thumb is essential. The dominant blood supply to the thumb comes from the princeps pollicis artery. If the princeps pollicis artery is compromised, there could be irreversible damage to the thumb. With the proper knowledge of the vascular network within the thumb, this can lead to successful surgical reconstruction or repair of the thumb.

The reason that the princeps pollicis artery is so important in surgery is the fact that it does not receive much collateral blood flow. The princeps pollicis artery is considered a distal terminal artery.

Clinical Significance

The princeps pollicis artery is the predominant blood supply to the thumb. If the thumb appears cyanotic, this could mean the blood supply to the princeps pollicis artery is compromised, which will only happen if it is an isolated insult on the princeps pollicis artery. In some instances, if there is enough traumatic force to the Princeps pollicis artery, an aneurysm will form. While in some cases, a pseudoaneurysm may form in the princeps pollicis artery.[7]

The artery can be affected by vasculitis. Medium-size arteries or small-size arteries can be affected by a condition called "thromboangiitis obliterans or Buerger disease." This condition typically affects smokers. The pathogenesis of this disease is that it creates an inflammatory thrombosis in blood vessels. The thrombosis will lead to autoamputation of the fingers and toes.[8][9]

Other Issues

The blood supply to the forearm is from the brachial artery. The brachial artery then branches into the radial and ulnar arteries. These arteries will descend into the hand and perfuse the hand. The occlusion or compromise of any of these arteries will result in ischemia and cyanotic appearing hands. The cyanosis will lead to necrosis of the hands if the blood supply does not get restored promptly.[10]