Biomedical Engineering Reference
In-Depth Information
forces as generated in quadrupedal locomotion (
Rose,
1993
). The combined movement of the three areas results in
pronation and supination of the forearm. The actual range
of pronation and supination varies widely among species
but can be correlated with locomotor patterns and habitat
use.
The wrist joints include the articulation between the
distal forearm and the proximal carpal row as well as the
intercarpal articulations and articulations between the distal
carpal row and the metacarpals. In Hominoidea the head of
the ulna does not directly participate in the wrist joint
articulation since it lies proximal to an articular disc, but
the styloid process of the ulna may articulate with the
pisiform (
Lewis, 1972, 1974
). The capsule surrounding this
entire region may be subdivided into discrete parts, but
communications between them are common. The major
ligaments for the joints are on the palmar side. The liga-
ments on the dorsum are relatively thin to allow for more
mobility in the palmar direction. All of the joints in the
region combine together to produce routine movements of
the hand. The appearance of rotation of the hand is
primarily supination and pronation of the forearm which
may be supplemented by rotation in the midcarpal region in
some species (
Jenkins, 1981; Sarmiento, 1988
). Adduction
(ulnar flexion or deviation) and abduction (radial flexion or
deviation) occur primarily in the radiocarpal joint but in
some species there may be sliding between the carpal rows.
Flexion (palmar or volar movement) and extension (dorsal
movement) occur in both the radiocarpal and midcarpal
joints. The two degrees of freedom and relative movement
of bones of the wrist region of nonhuman primates are
nearly identical to that of humans.
The carpometacarpal joints of nonhuman primates
closely resemble those of humans. The joint capsules
usually communicate with the capsules surrounding the
carpus. The range of motion in the carpometacarpal joints
of the four medial (ulnar) digits is similar to humans.
Metacarpals II and III have very limited mobility whereas
metacarpal IVand particularly metacarpal Vare capable of
flexion and limited extension. This morphology allows
flexion of the ulnar side of the metacarpus and is consistent
with the ability of primates to firmly grasp relatively small
objects in their closed prehensile hands.
The carpometacarpal joint of digit I (thumb) in Old
World monkeys and great apes is very similar to that of
humans. It is a saddle joint which allows movement in three
planes and thus permits opposability of the thumb. Lesser
apes also have an opposable thumb but the carpometacarpal
joint more closely resembles a ball and socket joint. The
Cebidae New World monkeys lack the ability to longitu-
dinally rotate the thumb at the carpometacarpal joint and
thus lack true opposability of the thumb. The palmar
concavity of the hand and the separation of digit I from the
other digits, however, permit pseudo-opposability of the
thumb in these species. (See also the description of hands in
the section “Overview of limbs” (above), “Skeleton of
forelimb” (above), and “Musculature of forelimb”
(below).) Only the Callitrichidae of the higher primates
lacks any ability to functionally oppose the thumb.
The metacarpophalangeal joints of the digits allow
movement in two planes. These joints are all very similar to
each other and are almost identical to those in humans. The
characteristic prehensile hand of primates includes the
ability to adduct (converge) the digits in flexion and abduct
(diverge) the digits in extension. This ability is reflected in
the configuration of the collateral ligaments of the meta-
carpophalangeal joints. The proximal extreme of the liga-
ment is positioned more dorsally than that of the distal
extreme. Thus the ligaments become taut in flexion,
thereby limiting lateral movement, and lax in extension,
thereby facilitating lateral movement.
The interphalangeal joints of the digits of the hand
resemble pulleys which restrict motion to only one
plane and are nearly identical
to each other and to
humans.
Joints of Hindlimb
The sacroiliac joints are synovial joints between the ala of
the sacrum and the ilium on either side (
Figure 4.12D
). The
joint normally has very little movement and is supported
strongly by numerous ligaments.
Ventrally (anteriorly), the two sides of the pelvis artic-
ulate at the pubic symphysis (
Figure 4.12E,F
). As in other
quadrupeds, this symphysis is long and includes a consid-
erable part of the ischium as well as the inferior ramus of
the pubis. In nonhuman primates, the articulations of the
pelvic girdle closely resemble those in other quadrupeds
and are dissimilar to those in humans, particularly in their
shape. Degenerative changes in the pubic symphysis of
nonhuman primates are similar to humans and have been
correlated with age, sex, and parity (
Rawlins, 1975; Tague,
1990
).
The hip joint of nonhuman primates is similar to that of
other quadrupeds in its orientation to the pelvis. The soft
tissue and range of motion in three planes, however, are not
markedly different from those in humans with the excep-
tion of the increased extension necessary to maintain the
bipedal striding gait of humans. As in humans, the spiral
arrangement of the ligaments in the capsule permits the
range of abduction
adduction and mediolateral rotation of
the hip to be greater during flexion than during extension.
The actual amount of movement in any plane varies among
species and can be correlated to behavior. No nonhuman
primate has the degree of hip extension and the ability to
sustain upright posture seen in humans, but many
nonhuman primates do occasionally use bipedal gaits and/
or postures.
e
