Hand Anatomy Flashcards
- What is the thickest skin in the hand?
The palmar skin has the thickest epidermis due to the stratum corneum, but the dermis is just as thick on the dorsum as
the palm.
Why are most significant hand burns on the dorsum?
The thick stratum corneum protects the palmar dermis. In addition, the dorsal skin tends to be directed toward the
flames in a burn situation. If the fist is closed, the palmar skin is further protected.
Why can we get away with single layer closure in the palm?
The thick stratum corneum hides the ingrowth of epithelium down the suture into the dermis, so sutures can be left in
place for over a week without leaving stitch marks.
Does the thick stratum corneum affect the technique of skin closure in
any other way?
The thick stratum corneum exaggerates the problems caused by skin edge overlap; thus mattress stitches often are
preferred to ensure skin edge eversion
How is the palmar skin so firmly fixed in place?
The palmar fascia is a unique structure, fixed proximally and distally, from side to side, and to the underlying
metacarpals by its vertical fibers. The palmar skin is closely attached to the palmar fascia by a tight network of its own
vertical fibers. Hence, edema cannot collect as easily on the palmar side of the hand.
Name the three planes of the palmar fascia.
The palmar fascia is aligned in longitudinal, vertical, and transverse components.
Which of the three palmar fascia planes is never involved in
Dupuytren’s disease?
The transverse fibers, located over the metacarpophalangeal joints, are never involved in Dupuytren’s disease.
Does the palmar fascia extend into the fingers?
Yes. The longitudinal fibers of the palmar fascia extend into the fingers and in the web spaces; the natatory ligaments
are part of the palmar fascia. In the proximal and middle phalanges, however, Cleland’s (dorsal) and Grayson’s (volar)
ligaments are the stabilizing structures. On the sides of the fingers, dorsal and palmar to the neurovascular bundles,
they are attached to the phalanges along the ridge giving rise to the fibroosseous tunnel. In the distal phalanx, vertical
fibers are attached directly to the underlying distal phalanx and form a honeycomb series of compartments, similar to
that in the palm between the skin and palmar fascia (Fig. 114-1).
What is the “assembly line”?
The volar lateral ridges of the proximal phalanx, in which nestle the flexor tendons and which give attachment to
the fibroosseous tunnel, the oblique retinacular ligament, and Grayson’s and Cleland’s ligaments, are the so-called
“assembly lines.”
What are the “checkrein ligaments”?
In flexion contracture of the proximal interphalangeal (PIP) joint, the proximal sliding volar plate becomes attached to the
firm assembly line structures by fibrous adhesions called the “checkrein ligaments,” which prevent the volar plate from
sliding back distally.
Name two unique types of infection on the palmar side of the hand that are due to
the firm fixation of the skin to underlying structures
A collar-button abscess in the palm starts as a tiny infection between the palmar skin and the palmar fascia. It then
erodes through the palmar fascia into the underlying loose space, forming a dumbbell- or collar button-shaped abscess,
which may be inadequately drained if the anatomy is not appreciated.
Name another closed compartment in the hand in which bacterial infections can
develop.
The synovial sheaths within the fibroosseous tunnels of each finger are relatively closed systems that can contain closed
space infections that can expand and spread quickly (“purulent tenosynovitis”).
What are the other closed spaces associated with infections?
The thenar and midpalmar bursae and the radial and ulnar bursae all are potential spaces in which infection can develop
How can these compartments communicate with each other with the spread of an
infection?
The synovial sheaths of the ulnar fingers communicate with the ulnar bursa, and the sheaths of the index finger
and thumb communicate with the radial bursa and can communicate in the midpalmar and thenar spaces (bursae),
respectively
Can the ulnar- and radial-sided synovial systems communicate?
Each is capable of draining into the space over the pronator quadratus (Parona’s space), producing a pan-palmar
infection called a “horseshoe abscess.”
How does the unique anatomy of the fingertip shape the development of a paronychia?
A paronychia is an infection of the nail fold. It seldom exists without the presence of a nail, which is first a foreign-body
irritant and then the roof of the abscess.
Can a felon spread around the distal phalanx and become a paronychia? Can a
paronychia spread around the nail plate into the palmar pulp and become a felon?
Both events are highly unlikely because of the anatomy of the fingertip. The paronychia spreads around the nail plate
and may lift the entire nail plate off the bed but ultimately drains dorsally. The felon spreads on the palmar side,
ultimately breaking through the skin. It may spread proximally into the soft tissue of the middle phalanx—or even into
the bone and distal interphalangeal (DIP) joint—but not dorsally to the nail fold.
Which tissues contribute to growth of the nail plate?
The entire nail bed, including the overlying eponychial fold, contributes material to the developing and growing nail. The
proximal nail bed (germinal matrix) forms the early developing nail, the overlying fold contributes the smooth surface,
and the distal bed (sterile matrix) continues to add bulk so that the nail plate does not become too thin from wear.
What is the lunula?
The white arc just distal to the eponychium, called the lunula, is a result of persistence of nuclei in the cells of the
germinal matrix as they flow distally, creating the nail. As the nuclei disintegrate distal to the lunula, the nail becomes
transparent.
What is the safe position for splinting the hand?
It is useful to think of joints as having certain positions that tend to produce stiffness and other positions that can be
maintained for long periods without developing stiffness. The metacarpophalangeal (MP) and interphalangeal (IP) joints
are good examples of this concept. The MP joints recover well from flexion, and the IP joints recover well from extension.
When splinting the hand, the MP joints should be placed in flexion (70° to 90°), and the IP joints should be maintained in
extension. The thumb should be abducted and the wrist maintained in mild extension. This is the position from which it
is easiest to regain mobility of the joints after prolonged immobilization.
Why is flexion the safe position for the MP joint?
The MP joint is characterized by variable tightness of the collateral ligaments, depending on the position of the joint,
because of the unique shape of the metacarpal head and the origin of the collateral ligaments dorsal to the axis of
rotation of the joint. The head is ovoid in the sagittal plane (creating a cam effect) and possesses a palmar flare in the
transverse plane, which requires the collateral ligaments to span a greater distance in flexion than extension. Therefore
the collateral ligaments are stretched tight in flexion but are lax in extension. Because ligaments tend to shorten when
maintained in a lax position, prolonged extension leads to shortening of the collateral ligaments, rendering them unable
to accommodate the joint in flexion and thus producing an extension contracture (Fig. 114-2).
If flexion is the safe position for the MP joint, what do you do if you have to splint
the joint in extension, as for extensor tendon repairs or palmar fascia excision
for Dupuytren’s disease?
The MP joints can tolerate a few weeks of extension, especially in younger patients without widespread injury. Older
patients can tolerate up to 4 weeks of extension following isolated injuries or surgical procedures (e.g., extensor tendon
repair) but only 2 or 2.5 weeks following extensive Dupuytren’s surgery. For burn injuries with extensive edema,
MP joints should be protected and maintained in flexion from the beginning.
Why is extension the safe position for the IP joints?
The collateral ligaments of the IP joints tend to have the same tightness in flexion and extension and thus are not as
important in consideration of safe splinting. Two other points are important instead: (1) the extensor mechanism in
the region of the PIP joint and (2) the volar plates. The volar plate overlies the cartilaginous surface of the phalangeal
condyles in extension but in flexion slides proximal to the condyles, where it readily becomes adherent to the filmy
soft tissue between the tendon sheath and periosteum. Maintenance of this position produces a flexion contracture.
The other consideration is that the extensor mechanism is highly stable in extension but is under stress in flexion. This
problem is particularly significant when the PIP joint is injured, as in a burn injury. Inflammation may cause attenuation
of the delicate extensor mechanism, resulting in disruption of the transverse retinacular ligaments when the joint is
stressed in flexion. The lateral bands then slip volarly, creating a boutonnière deformity.
The IP joint can be thought of as a box, with the articular surfaces of the phalanges
forming the proximal and distal ends. What forms the other sides?
The volar plate forms the bottom and the collateral ligaments the sides. The collateral ligaments extend from their points
of origin into a broad, fan-shaped insertion into the phalanx distally and the sides of the volar plate volarly. The volar
portion of the collateral ligament is referred to as the accessory collateral ligament. The top or lid of the box is formed by
the extensor mechanism, which contributes little to the structural stability of the joint (Fig. 114-3).
Which is the most mobile carpometacarpal joint?
The carpometacarpal (CMC) joint of the thumb is a saddle joint with motion in three axes, giving the thumb unique mobility.
Which are the least mobile CMC joints?
The second and third metacarpals are bound firmly to the trapezoid and capitate, forming a stable structure known as
the “fixed unit of the hand.” Thus the second and third CMC joints are the least mobile.
What is the last muscle innervated by the ulnar nerve as it courses through the palm?
The first dorsal interosseus is the last muscle to receive motor fibers from the ulnar nerve after it passes through the
adductor of the thumb, which is next to last.
