V. INNERVATION OF THE HAND

A. MEDIAN NERVE - enters the palm behind the flexor retinaculum and through the carpal tunnel. Divides into lateral and medial branches. Supplies all of the thenar muscles (except the adductor pollicis) and the first two lumbricales. Provides sensory branches to the lateral 3 ½ digits. Supplies the whole palmar aspects of these digits and the distal half of the dorsal aspect of each one.

B. ULNAR NERVE - enters the palm anterior to the flexor retinaculum alongside the pisiform. Divides into a superficial and a deep branch. Provides innervation to the hypothenar muscles, palmaris brevis, third and fourth lumbricales, all of the interossei muscles and the adductor pollicis. Provides sensory branches to the palmar aspect of the medial one and one half fingers along with the distal half of the dorsal aspect of these digits.

VI. VASCULAR SYSTEM OF THE HAND

The main arterial supply to the hand is from the radial and ulnar arteries, both terminal branches of the brachial artery. The form a complex arterial arch system consisting primarily of the superficial and deep palmar arches.

The venous system in the hand consists of superficial and deep veins which form a system of arches. The superficial veins are located under the skin in the superficial fascia. The deep veins accompany the arteries.

VII. TENDONS OF THE HAND

A. FLEXOR TENDON SHEATHS - originate at the distal palmar flexion crease and extend to the distal phalanx. Bursas also present within the palm. These provide nutrition to the tendons, protection and a smooth lining for tendon gliding.

B. TENDON NUTRITION - provided via vincula which are present in the tendon sheath.

C. FLEXOR PULLEY SYSTEM - annular and cruciate pulleys are present to maintain the tendons in close proximity to the phalanges. Essential pulleys are A2 & A4.

D. EXTENSOR HOOD APPARATUS - also referred to as the extensor expansion. Complex structure which includes intrinsic and extrinsic muscles.

1. Extensor Digitorum - the central slip inserts into the middle phalanx.
2. Sagittal Bands - keep the ED in midline. Insert into the volar plate. Assists with PIP extension.
3. Lateral Bands - extend laterally on both sides where they attach to the interossei muscles and lumbricales. Assist with PIP extension. At the DIP level, they joined together to form the terminal tendon which inserts in the distal phalanx. Assists with DIP extension.
4. Triangular Ligament - dorsal structure which provides support to the lateral bands and prevents shifting.
5. Oblique Retinaculum Ligament - originate off the flexor tendon sheath and inserts on the lateral bands. It is taut when the PIP is extended and is on stack when the PIP flexes. Allows the DIP to flex.
6. Transverse Retinaculum Ligament - originates on volar plate and flexor tendon sheath at the PIP. Inserts on lateral bands. Holds the central slip and lateral banks in place.