Deep Palmar Arch

Introduction

Introduction to the Deep Palmar Arch

The deep palmar arch is the deeper of the two arterial arcades in the palm. It lies on the palmar aspect of the bases of the metacarpal bones and the interosseous muscles, deep to the long flexor tendons. Formed mainly by the terminal part of the radial artery, with a variable contribution from the deep palmar branch of the ulnar artery, the deep arch provides the primary blood supply to the thumb and radial side of the index finger, and gives off palmar metacarpal arteries that connect with the superficial palmar arch. Its deep location protects it from most penetrating injuries, but its anatomical variations are critical in reconstructive hand surgery and in understanding collateral hand perfusion.

This module details the origin, course, relations, branches, variations, and clinical significance of the deep palmar arch.

Study

1. Formation and Course

The deep palmar arch is formed primarily by the radial artery. After crossing the floor of the anatomical snuffbox, the radial artery pierces the two heads of the first dorsal interosseous muscle and enters the deep palm. It then passes medially across the palmar surfaces of the bases of the second to fifth metacarpals and the interosseous muscles. Near the proximal end of the fifth metacarpal space, it anastomoses with the deep palmar branch of the ulnar artery, completing the arch.

The arch lies approximately one finger‑breadth proximal to the superficial palmar arch and deep to the flexor digitorum profundus tendons and lumbricals. The deep branch of the ulnar nerve lies within the concavity of the arch.

2. Branches

The deep palmar arch gives off several named branches:

Princeps pollicis artery: Usually the first branch, arising as the radial artery enters the palm. It descends on the palmar aspect of the first metacarpal and divides into two proper palmar digital arteries for the thumb.

Radialis indicis artery: A branch that runs along the radial side of the index finger to the distal phalanx. It may arise with the princeps pollicis from a common trunk, or directly from the deep arch.

Palmar metacarpal arteries (three or four): These run distally in the second, third, and fourth intermetacarpal spaces, on the palmar interossei. At the web spaces, they anastomose with the common palmar digital arteries from the superficial arch via perforating branches.

Perforating branches: Pass dorsally between the metacarpal heads to join the dorsal metacarpal arteries.

Recurrent branches: Small vessels that ascend proximally to supply the carpal bones and joints.

3. Relations

Superficial to the deep palmar arch lie the flexor digitorum profundus tendons, the lumbrical muscles, the superficial palmar arch, and the terminal branches of the median nerve. Deep to the arch are the palmar interosseous muscles and the bases of the metacarpals. The deep branch of the ulnar nerve (motor) runs in the concavity of the arch, medial to the artery.

4. Anatomical Variations

The deep palmar arch is complete in about 95% of individuals. Its primary source is the radial artery, but the contribution from the deep palmar branch of the ulnar artery can vary from minor to dominant. In a 'median‑dominant' circulation, a persistent median artery may replace or augment the deep arch. The princeps pollicis and radialis indicis arteries may arise from a common trunk, or the superficial arch may supply the thumb and index finger instead of the deep arch. These variations influence the choice of flaps and the safety of radial artery harvesting.

5. Clinical Significance

The deep arch is the main blood supply to the thumb and radial index finger; its patency is vital for pinch and precision grip. In radial artery harvest for coronary bypass or forearm flaps, collateral flow to the thumb via the deep arch from the ulnar artery must be confirmed (modified Allen's test). Penetrating injuries to the deep palm may disrupt the arch, causing severe bleeding and potential thumb ischemia. The close relationship of the deep branch of the ulnar nerve to the deep arch places the nerve at risk during ligation or repair of the vessel.

Summary

Summary of the Deep Palmar Arch

The deep palmar arch is formed mainly by the radial artery and completed by the deep branch of the ulnar artery. It lies on the metacarpal bases and interossei, deep to the flexor tendons. Its principal branches are the princeps pollicis artery, the radialis indicis artery, and the palmar metacarpal arteries. The deep arch supplies the thumb and radial index finger and connects with the superficial arch via perforating branches. Understanding its anatomy is essential for hand revascularisation, radial artery procedures, and assessing collateral hand perfusion.