The
Palm of the Hand
Skin
The skin of the palm of the hand is thick and hairless. It
is bound down to the underlying deep fascia by numerous fibrous bands. The skin
shows many flexure creases at the sites of skin movement, which are not
necessarily placed at the site of joints. Sweat glands are present in large
numbers.
The palmaris brevis is a small muscle that arises from the
flexor retinaculum and palmar aponeurosis and is inserted into the skin of the
palm. It is supplied by the superficial branch of the ulnar nerve. Its function
is to corrugate the skin at the base of the hypothenar eminence and so improve
the grip of the palm in holding a rounded object.
The sensory nerve supply to the skin of the palm is derived
from the palmar cutaneous branch of the median nerve, which crosses in front of
the flexor retinaculum and supplies the lateral part of the palm, and the
palmar cutaneous branch of the ulnar nerve; the latter nerve also crosses in
front of the flexor retinaculum and supplies the medial part of the palm.
The skin over the base of the thenar eminence is supplied by
the lateral cutaneous nerve of the forearm or the superficial branch of the
radial nerve.
The Palmar Aponeurosis
The palmar aponeurosis is triangular and occupies the
central area of the palm. The apex of the palmar aponeurosis is attached to the
distal border of the flexor retinaculum and receives the insertion of the
palmaris longus tendon. The base of the aponeurosis divides at the bases of the
fingers into four slips. Each slip divides into two bands, one passing
superficially to the skin and the other passing deeply to the root of the
finger; here each deep band divides into two, which diverge around the flexor tendons
and finally fuse with the fibrous flexor sheath and the deep transverse
ligaments.
The medial and lateral borders of the palmar aponeurosis are
continuous with the thinner deep fascia covering the hypothenar and thenar
muscles. From each of these borders, fibrous septa pass posteriorly into the
palm and take part in the formation of the palmar fascial spaces . The function of the palmar aponeurosis is to give firm attachment to the
overlying skin and so improve the grip and to protect the underlying tendons.
Dupuytren’s
Contracture
Dupuytren’s contracture is a localized thickening and
contracture of the palmar aponeurosis, which limits hand function and may
eventually disable the hand. It commonly starts near the root of the ring
finger and draws that finger into the palm, flexing it at the metacarpophalangeal
joint. Later, the condition involves the little finger in the same manner. In long-standing
cases, the pull on the fibrous sheaths of these fingers results in flexion of
the proximal interphalangeal joints. The distal interphalangeal joints are not
involved and are actually extended by the pressure of the fingers against the
palm.
Surgical division of the fibrous bands followed by
physiotherapy to the hand is the usual form of treatment. The alternative treatment
of injection of the enzyme collagenase into the contracted bands of fibrous
tissue has been shown to significantly reduce the contractures and improve
mobility.
Carpal
Tunnel Syndrome
The carpal tunnel, formed by the concave anterior surface of
the carpal bones and closed by the flexor retinaculum, is tightly packed with
the long flexor tendons of the fingers, with their surrounding synovial
sheaths, and the median nerve. Clinically, the syndrome consists of a burning
pain or “pins and needles” along the distribution of the median nerve to the
lateral three and a half fingers and weakness of the thenar muscles. It is
produced by compression of the median nerve within the tunnel. The exact cause
of the compression is difficult to determine, but thickening of the synovial sheaths
of the flexor tendons or arthritic changes in the carpal bones are thought to
be responsible in many cases. As you would expect, no paresthesia occurs over
the thenar eminence because this area of skin is supplied by the palmar cutaneous
branch of the median nerve, which passes superficially to the flexor
retinaculum. The condition is dramatically relieved by decompressing the tunnel
by making a longitudinal incision through the flexor retinaculum.
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