Muscles of the hand

The hands are the most distal part of our upper limbs, and they’re quite marvelous!

They’re strong enough to lift heavy boxes, and at the same time delicate and precise enough to thread a needle, or type on a keyboard.

The diverse range of movements our hands are capable of is made possible by a variety of muscles and their arrangement within the hand.

The hand is composed of intrinsic muscles, which are entirely located within the hand; and extrinsic muscles, which are forearm muscles, but act on the hand and fingers through their long tendons.

The intrinsic muscles of the hand are covered by the fibrous palmar fascia, which divides them into 4 main compartments: the thenar compartment located below the first digit, known as the thumb, the hypothenar compartment located below the fifth digit also known as the little finger, the adductor compartment located in the lateral part of the hand, and finally, the central compartment that’s found in the center of the palm.

There are also several interosseous compartments between the metacarpals.

The palmar fascia , which is the continuation of the antebrachial fascia in the forearm, forms the palmar aponeurosis centrally.

The palmar aponeurosis is a strong, thickened portion of the palmar fascia covering the central compartment and overlies the flexor tendons.

Proximally, the palmar aponeurosis blends with the tendon of palmaris longus and the flexor retinaculum, which if you remember is a transverse ligament spanning over the carpal bones creating the carpal tunnel.

Distally, the palmar aponeurosis divides into four longitudinal bands that radiate distally to attach to the bases of the proximal phalanges, where they become continuous with the fibrous digital sheaths which enclose flexor tendons going to the digits.

Within the hand, the medial border of the palmar aponeurosis becomes continuous with the thin hypothenar fascia, which covers the muscles of the hypothenar compartment.