Hand

The hand refers to the part of upper limb distal to the wrist joint. It consists of three sub-parts: the carpus (wrist), metacarpus (palm or dorsum of the hand), and digits or fingers.

Bony framework:

A.      The carpus (wrist) contains eight carpal bones arranged in two rows:

• Proximal row (medial to lateral): scaphoid, lunate, triquetrum, and pisiform.

• Distal row (medial to lateral): trapezium, trapezoid, capitate, and hamate.

• Intercarpal synovial joints exist between the carpal bones.

B.      The proximal row of carpal bones articulates with the distal end of the radius, forming the wrist joint (radiocarpal joint).

C.      The carpal bones in the distal row articulate with the metacarpals, forming carpometacarpal synovial joints.

D.      Additional joints in the digits include the metacarpophalangeal, proximal, and distal interphalangeal joints.

Long tendons of extrinsic hand muscles:

• Long tendons from the extrinsic forearm muscles cross over the wrist to enter the hand, on the palmar and dorsal sides. These tendons assist in forceful gripping and are held in place by the retinacular thickenings of the deep fascia: the flexor retinaculum on the palmar side and the extensor retinaculum on the extensor side of the wrist.

• On the palmar (flexor) side of the wrist, the flexor retinaculum forms the roof of the carpal tunnel. Multiple long tendons pass through this tunnel, including four tendons each of the flexor digitorum superficialis and flexor digitorum profundus, as well as one tendon of the flexor digitorum profundus. The median nerve also passes through this tunnel and can become compressed, causing carpal tunnel syndrome, which is commonly seen in individuals with repetitive hand movements involving flexion and extension.

• The anatomical snuff box is an important region on the dorsum of the wrist and hand. It is bounded laterally by the long tendons of the abductor pollicis longus and extensor pollicis brevis muscles, and medially by the extensor pollicis longus tendon. The floor of the snuff box is formed by the scaphoid bone, which is frequently fractured in falls onto outstretched hands and results in severe wrist pain.

Intrinsic hand muscles:

• Unlike the extrinsic muscles, the intrinsic muscles of the hand are confined to the hand region and enable precise movements of the fingers and thumb.

• These muscles include:

1. Thenar group of muscles: facilitate medial rotation (opposition), abduction, and flexion of the thumb at the metacarpophalangeal joint

2. Hypothenar group of muscles: assist in lateral rotation (opposition), abduction, and flexion of the little finger at the metacarpophalangeal joint

3. Four worm-like lumbricals: arise from the tendons of the flexor digitorum profundus and insert into the extensor hood as they pass dorsally from the lateral side of each finger. They cause flexion at the metacarpophalangeal joints and extension at the interphalangeal joints.

4. Interossei (palmar and dorsal): insert into the proximal phalanges and extensor hoods, causing abduction on the dorsal side and adduction on the palmar side of the fingers. They also produce flexion at the metacarpophalangeal joints and extension at the interphalangeal joints

5. Adductor pollicis muscle: responsible for thumb adduction.

6. Palmaris brevis: enhances the grip.

Innervation:

• All intrinsic hand muscles are innervated by the ulnar nerve, except for the thenar muscles and the lateral two lumbricals (3rd and 4th), which are innervated by the median nerve.

• The sensory innervation of the hand’s skin is provided by cutaneous branches of the median nerve (lateral three and half fingers and adjoining palmar region), ulnar nerve (medial one and a half fingers and adjacent palmar area), and radial nerve (dorsum of the hand).

Vasculature:

• Arterial blood supply to the hand comes from radial and ulnar arteries, interconnected through superficial and deep palmar arches. These branches give rise to palmar common digital arteries and palmar proper digital arteries for the fingers. Additionally, the radial artery forms a dorsal carpal arch on the back of the hand.

• Deep veins run alongside the arteries

• On the back of the hand, a superficial venous arch is present, which branches into a basilic vein on the outer side and a cephalic vein on the inner side of the hand.