Biomedical Engineering Reference
In-Depth Information
The knee (stifle) joint in nonhuman primates is nearly
identical to that of humans in both structure and motion.
The patella, two meniscii, and the band-like collateral and
anterior and posterior cruciate ligaments lie in the same
positions. Although the knee joint is primarily a hinge joint,
as in humans, some rotation is permitted when the joint is
flexed but not when the joint is extended. The knee joint of
nonhuman primates usually does not fully extend to 180
as
in humans, but the range of motion in flexion and extension
is always considerable.
The proximal and distal tibiofibular joints are articula-
tions between two distinct, well-developed bones. As in
humans, neither of the two joints permit much movement,
particularly the distal tibiofibular joint which is a syndes-
mosis. The predominant fiber direction of the interosseous
membrane which connects the shafts of the two bones
reflects the direction of transmission of the predominant
forces during locomotion.
The ankle (talocrural) joint is primarily the articulation
between the tibia and the talus but the distal fibula
contributes stability to the lateral aspect of the articulation
(the lateral malleolus). The morphology of this joint in
nonhuman primates is similar to that of humans except that
limited rotation is possible in most species. The joint
capsule of the ankle joint has strong fan-shaped collateral
ligaments and is usually separate from the joint capsules of
the rest of the tarsal region.
The tarsal joints can be subdivided into two basic
groups according to their positions. The first group is
composed of the talocalcaneal joints, which lie between
these two bones. The second group is collectively called
the transverse tarsal joint. This is the general name used
for the joints between the talus and calcaneus and the
more distal tarsals. The configuration of all of these
joints, the continuity of the joint capsules, and the
arrangement of the ligaments are very similar to those in
humans. The major difference between the joints of the
tarsal regions of humans and nonhuman primates is the
presence of permanent longitudinal and transverse arches
in the human foot. These arches are integral parts of the
adaptation to the striding gait which characterizes human
bipedalism. The foot of nonhuman primates lacks these
semirigid arches, and its plantar concavity is similar to
that seen in the palm of the hand. As in the hand, foot
movements involve a variety of joints. Plantarflexion and
dorsiflexion occur primarily at the talocrural joint,
abduction and adduction occur in both the talocalcaneal
and talocrural joints, rotation occurs in the talocalcaneal
and transverse tarsal joints, and inversion and eversion
occur in all of the joints.
The tarsometatarsal joints are very similar to the car-
pometacarpal joints for the lateral four digits (digits II, III,
IV, and V). The big toe (hallux) of nonhuman primates is
divergent and the degree of divergence varies between
species. Although the tarsometatarsal joint of the big toe
(digit I) permits considerable mobility in two planes, it does
not freely permit longitudinal rotation of the metatarsal,
and thus the big toe is only pseudo-opposable.
The metatarsophalangeal joints are similar to the met-
acarpophalangeal joints and show a similar pattern for digit
divergence and convergence. The motions permitted are
plantarflexion, dorsiflexion, abduction (divergence), and
adduction (convergence). Depending on the species, some
nonhuman primates have considerable dexterity in their
feet and use them much like hands. This region of the
nonhuman primate foot more closely resembles the
equivalent area in the hand rather than the bipedally
adapted foot of humans.
The interphalangeal joints of the toes are very similar to
those of the hand and have very similar planes of motion.
The grasping ability of the toes is particularly well devel-
oped in more arboreal species.
Musculature of Forelimb
The muscles of the forelimb of higher nonhuman primates
are very similar to those of other mammals in general and
humans in particular. (See
Howell and Straus (1933a)
for
detailed descriptions of the muscles in rhesus macaques
and
Gregory (1950)
for Raven's anatomy of the gorilla.)
The orientation of muscles in the shoulder region differs
slightly between quadrupedal primates and humans
primarily due to the greater flattening of the thorax and
more dorsal positioning of the scapulae in humans
(
Figure 4.8C
). The overall similarities, however, are much
greater than the differences. Like humans, nonhuman
primates utilize their forelimbs for a wide variety of both
locomotor and nonlocomotor activities.
The distal segments of all primate forelimbs reflect
a single pattern for the muscles of the hand. The degree of
isolation of fibers and nerves reflects the dexterity and
manipulative abilities of the hand as well as the fine motor
control of the digits. The extrinsic muscles of the hand are
well developed and the fibers for each individual digit are
usually clearly defined. The intrinsic muscles of the hand
are also well developed with a typical digit receiving
one muscle from each of the four intrinsic groups
(e.g. lumbricals, contrahentes, palmar interossei, and dorsal
interossei). The side and position of each insertion are
related to the function performed by that particular muscle
grouping. The third ray is the midline axis for abduction
and adduction of the manual digits. The development of the
thenar and hypothenar eminences are closely correlated
with the degree and strength of individual movements
routinely performed by the thumb (pollex) and little finger
(digit V) respectively. The functional division of the hand is
generally between the thumb (digit I) and index finger
(digit
II), but some higher primates routinely, or
in
