Pelvic Limb of the Dog; Structure and Function.
Sacroiliac joint. The joint between the sacrum and the ilium of the hip bone (os coxae;
L., bone of the hip). This is the joint that joins the skeleton of the pelvic limb to the
axial skeleton. It is a synovial joint but virtually no movement occurs owing to strong
dorsal, ventral, and interosseous sacroiliac ligaments. The articular surfaces of
sacrum and ilium bear a thin layer of cartilage whose planar surfaces are
complementary. With such limited movement, the joint capsule is tight.
Right and left hip bones join the wings of the sacrum dorsally at sacroiliac joints and
are united by a median symphysis pelvis ventrally. The symphysis is fibrocartilage at
birth but at five years it is completely replaced by bone. At birth we have a firm,
fibrocartilaginous, joint and at 5 years, we are dealing with two large bones joined on
the midline by an immovable, fused, symphysis pelvis and on either side by the right
and left synovial sacroiliac joints. In examining radiographs of the pelvis, we want to
remember that a fracture or subluxation (partial dislocation) in one place necessarily
indicates a fracture or subluxation in another. When examining radiographs, if you
find one hipbone fracture, be sure to find the other(s). Fracture or subluxation of the
sacroiliac joint is a common result of this animal’s being struck by a car.
Fig. 1. Dorsal view of
sacroiliac, sacrotuberal, and
hip joints. Modified from
Zietzschmann, Ackerknecht,
and Grau, Ellenberger-Baum
Handbuch der
Vergleichenden Anatomie
der Haustiere, 1943;
Springer Verlag.
dorsal sacroiliac
ligament of
sacroiliac joint
fibrous
capsule,
coxofemoral
(hip) joint
sacrotuberal
ligament,
sacrotuberal joint
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The sacroiliac joints and symphysis pelvis are essentially immoveable and the
muscles that pass from the axial skeleton to the pelvic limb have no action on these
joints.
Hip joint. The hip joint is the coxofemoral joint, formed by the head of the femur and
the socket, the acetabulum, of the hip bone. The head of the femur is spherical; this
shape tells us that all movements are possible: extension, flexion, abduction,
adduction, and circumduction. Each of these movements is limited by the ligament of
the head of the femur, which extends from the acetabular fossa to the fovea capitis of
the femoral head, and by more slight bands of fibers in the fibrous joint capsule.
Extension of the hip joint is chiefly by the middle gluteal muscle and the
hamstrings: biceps femoris, semitendinosus and semimembranosus. Flexion is
chiefly by the iliopsoas. Abduction is mainly by the superficial gluteal, the biceps
femoris, and the caudal crural abductor; adduction, mainly by the adductor muscles,
the pectineus, and the gracilis. The gluteus profundus turns the cranial face of the
thigh medially; the muscles inserting in (obturator internus, obturator externus,
gemelli) or by (quadratus femoris) the trochanteric fossa, often designated as the
“small pelvic association”, turn the cranial face of the thigh laterally. In designating
main action of muscles, we understand 1) that other muscles also participate in the
particular action but are not major players and 2) that the muscle which has the
particular action as a main action also has other actions.
Middle gluteal m.
Origin: Lateral surface of the wing of the ilium and iliac crest,
Insertion: Greater trochanter.
Biceps femoris m.
Origin: Sacrotuberous ligament and tuber ischiadicum,
Insertion: Patella, patellar ligament, tibial tuberosity, tibia (by
its insertion on the crural fascia), and, by its tarsal tendon, the
tuber calcanei.
Semitendinosus m.
Origin: Lateral part of tuber ischiadicum, medial to biceps fem.,
Insertion: Proximal medial tibia caudal to its cranial margin,
distal half of the medial tibia, (tarsal tendon) tuber calcanei.
Semimembranosus m. Origin: Medial part of the tuber ischiadicum,
Insertion: Medial epicondyle of the femur; medial margin of
the medial condyle of the tibia.
Iliopsoas m.
Origin: Transverse processes of L2 – L3, bodies of L3 – L7
(Psoas major m.), medial surface of wing and body of the ilium
(Iliacus m.),
Insertion: Lesser trochanter.
Fig. 2. Superficial rump
and thigh muscles.
2
dp glut fasc
cocc
supf glut
glut
sart
tens fasc lat
semimemb
semitend
bicps fem
fascia lata
caud crur abd
Drawn by David
S. Geary
Superficial gluteal m.
below
Origin: Lateral part of sacrum and iliac crest and sacral spines
by means of the deep gluteal fascia, Ca1,
Insertion: Roughness on greater trochanter laterally, just
the middle gluteal’s attachment.
Fig. 3. Lateral view of
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rump and thigh. Sartorius,
tensor fasciae latae, supf.
coccygeus
levator ani
piriformis
obt int gemelli
ischiourethralis
glut prof
quadratus femoris
glut med
rectus femoris
adductor
Lat. view. Sartorius,
tensor fasciae latae,
superficial gluteal,
biceps femoris and
caudal crural
abductor removed.
semitendinosus
vastus lat
semimembranosus
gastrocnemius, lat hd
Drawn by David S.
Geary
patellar ligament
Adductor m.
Pectineus m.
Origin: Symphysial tendon, neighboring ventral surface of the
ischium and pubis,
Insertion: Proximal caudal surface of the femur (facies
aspera).
Origin: Iliopubic eminence, prepubic tendon.
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Insertion: Medial lip of the facies aspera and medial border of
the femoral shaft to the distal epiphysis.
Fig. 4. Superficial
muscles of medial
thigh.
obturator int
coccygeus
lev ani
psoas minor
psoas maj
iliacus
symphysial tendon
and severed
adductor fibers
rectus femoris
gracilis
vastus medialis
pectineus
adductor
semitendinosus
sartorius
semimembranosus
gastrocnemius,
medial head
patella
Drawn by David
S. Geary
patellar ligament
tibial tuberosity
Gracilis m.
Origin: Symphysial tendon (with its fellow),
Insertion: Distal half of the medial tibia by a common tendon
with the semitendinosus and sartorius and, by its tarsal
tendon, which joins that of the semitendinosus, the tuber
calcanei.
Fig. 5. Medial thigh
muscles; sartorius,
tensor fasciae latae, and
gracilis removed.
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coccygeus
obturator int.
lev ani
symphysial tendon
with adductor fibers
attaching
gracilis tendon of origin
psoas minor
iliacus
rectus femoris
adductor
pectineus
vastus
medialis
semitendinosus
semimemb.
Drawn by David S.
Geary
gastrocnemius,
medial head
popliteus
Fig. 6. Deep dissection,
caudomedial view.
coccygeus
levator ani
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obturator int.
psoas minor
quadratus femoris
semitendinosus
adductor
quadriceps
gastrocnemius,
medial head
Drawn by David
S. Geary
The piriformis (Fig. 3) arises from the ventral surface of the sacrum and inserts on the
greater trochanter deep to the tendon of the gluteus medius. Both muscles extend the
hip joint and both, inserting lateral to the hip joint, have some action in abduction. The
cranial part of the tensor fasciae latae, the cranial belly of the sartorius, and the rectus
femoris of the quadriceps act to extend the knee (stifle) joint and to flex the hip joint.
Owing to the difference in the mass to be moved, the action of these muscles is
chiefly to extend the more distal knee joint, which has the lesser mass. The caudal
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belly of the sartorius acts to flex the hip and the knee joints. The caudal part of the
tensor fasciae latae also acts to flex the hip joint; it has no action on the knee joint.
Knee joint. The knee or stifle joint is composed of femoropatellar and femorotibial
joints. The articular surfaces of the femoropatellar joint are the articular surface of the
patella and the trochlea of the femur. The patella is a large sesamoid bone
intercalated in the tendon of the quadriceps femoris, which inserts, as the patellar
ligament, on the tibial tuberosity. The femorotibial joint is formed by the articular
surfaces of the medial and lateral condyles of the femur and the corresponding
condyles of the tibia. The condyles of the bones are not congruent but adapted to one
another by C-shaped meniscal cartilages. The convexity of each meniscal cartilage
matches the condyles at their perimeter; its concavity permits direct contact of the
articular surfaces centrally. There are three joint capsules: femoropatellar joint, the
medial femorotibial joint, and the lateral femorotibial joint. The three joint capsules
meet centrally at the junction of the trochlea with the femoral condyles. The joint
capsules are large, permitting the large excursion of femur and tibia in extension and
flexion of the knee joint. With moderate flexion of the joint, limited rotation of the tibia
(with the attached fibula) on its long axis can be carried out.
Ligaments of the femoropatellar and femorotibial joints. There are medial and lateral
collateral ligaments of the femoropatellar and femorotibial joints. Those of the
femoropatellar joint arise from the corresponding sesamoid bone of the
gastrocnemius and insert on the patella at the margin of the articular surface; they are
not very distinct and are much weaker than the collateral femorotibial ligaments. Of
the collateral femorotibial ligaments, each arises from the corresponding epicondyle
of the femur. The medial has its distal attachment on the medial margin of the medial
condyle of the tibia. The lateral collateral ligament has its distal attachment on the
head of the fibula. There are cranial and caudal cruciate ligaments, which are named
according to their attachment on the tibia. They have their proximal attachment in the
intercondylar fossa of the femur, the cranial ligament arising from the medial side of
the lateral condyle and the caudal more centrally. The distal attachment of the cranial
ligament is the intercondylar eminence of the tibia. The distal attachment of the
caudal cruciate ligament is a little below the medial side of the popliteal notch of the
tibia.
The menisci are held in place by (unnamed) cranial and caudal meniscal ligaments
that attach to the tibia only, and by a transverse genual ligament that extends
between their cranial ends. A meniscofemoral ligament extends from the caudal end
of the lateral meniscus to the intercondylar surface of the lateral condyle. Ligaments
of the knee joint are shown in the following photographs.
Fig. 7. Knee joint,
cranial view.
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lateral collateral
ligament
Fig. 8. Knee joint,
caudal view.
9
10
Fig. 9. Knee joint,
lateral view.
Ligament function. Ligaments discussed here are designated capsular ligaments
because they are closely associated with the fibrous joint capsule. This distinguishes
them from extracapsular ligaments like, for example, the ligamentum nuchae, which is
far from any joint capsule. The capsular ligaments are composed chiefly of
collagenous fibers and do not stretch or have only a very limited stretch. All function
to limit the range of joint movement. Injury to ligaments is diagnosed in a number of
ways but the ultimate loss in function is a change in the range of joint movment. Joints
have a good sensory supply and, owing to the pain involved, examination of joint
injury may require the patient’s sedation or anesthesia.
Collateral ligaments limit medial and lateral flexion of the knee joint. The medial
ligament limits lateral flexion; the lateral ligament limits medial flexion. (Note: The
medial ligament is attached to the medial, convex, surface of the medial meniscus;
whereas, the lateral ligament is separated from the lateral, convex, surface of the
lateral meniscus by the popliteus tendon. This is discussed in a later presentation.)
Cruciate ligaments limit the sliding of the tibia forward and backward in relation
to the femur. Rupture of the cranial cruciate allows the tibia to be drawn forward on
the femoral condyles, the cranial “drawer” sign; rupture of the caudal allows the tibia
to be drawn caudally, the caudal “drawer” sign). Both the collateral and cruciate
ligaments limit rotation of the tibia on its long axis. The meniscofemoral ligament
maintains a constant relation of the lateral meniscus to the femur. Its more precise
function is unclear.
Vara and valga. These terms are used in describing the angle at which the femoral
shaft meets the neck of the femur (coxa vara, coxa valga). Coxa vara is a condition in
which the angle formed by the axis of the head and neck of the femur with the axis of
the shaft is substantially more acute than normal. Coxa valga is the condition in which
that angle is materially more obtuse than normal. These terms generally arise in the
context of orthopedics.
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Muscles acting on the knee joint (Figs. 2 – 6). The joint allows only extension and
flexion and, when flexed, limited rotation of the tibia on its long axis.
Main extensors are the quadriceps femoris and, with the limb weight-bearing,
the hamstrings. The patellar attachment of the biceps femoris acts to extend the joint
whether the limb is weight-bearing or not. Other muscles which extend the knee joint
are: cranial belly of the sartorius, tensor fasiae latae, and the popliteus (Fig. 8; also,
see Fuss, Anat.Rec. 225:251-256 (1989) regarding the function of this muscle).
Owing to its origin at the extensor fossa, the long digital extensor muscle (Fig. 7; seen
but unmarked in Fig. 9) also tends to extend this joint. Main flexors, when the limb is
not weight-bearing, are the semitendinosus, the tibial attachment of the biceps
femoris and semimembranosus, and the caudal belly of the sartorius. Other muscles
which also tend to flex the joint are the gastrocnemius and superficial digital flexor.
.
Quadriceps femoris m. Origin: medial and lateral roughnesses cranial to the
acetabulum (rectus femoris); medial, cranial, and lateral
surfaces of the femur (vastus medialis, vastus intermedius,
and vastus lateralis),
Insertion: Patella and, by its tendon (the patellar ligament), the
tibial tuberosity.
Sartorius m.
Origin: Tuber coxae,
Insertion: Patella (cranial belly), distal half of the medial tibia
by a common tendon with the semitendinosus and gracilis
muscles.
Tensor fasciae latae m.
Origin: Tuber coxae,
Insertion: Cranial part: fascia lata, and by that means, the
patella and patellar ligament; caudal part: lateral lip of the
facies aspera.
Fig. 10. Cranial view.
Sartorius, tensor
fasciae latae removed.
gluteus medius
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levator ani
obturator internus
rectus femoris
Iliopsoas
pectineus
adductor
vastus lateralis
gastrocnemius,
lateral head
gracilis
vastus medialis
stump of sartorius
patella
Fig. 11. Caudal view.
Drawn by David
S. Geary
gluteus medius
lev ani
sacrotuberal ligament
semimembranosus
obturator internus
biceps femoris
ischiourethralis
ischiocavernosus
semitendinosus
gracilis
biceps femoris
caudal crural abductor
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popliteal lymph node
gastrocnemius, medial head
Drawn by David
S. Geary.
Hamstring action on the knee joint. The hamstring muscles are the biceps femoris,
semitendinosus, and semimembranosus. All have their origin from the tuber
ischiadicum; the biceps in addition from the neighboring lower part of the sacrotuberal
ligament. All attach at the knee joint, the biceps at the patella, patellar ligament and
cranial margin of the tibia, the semitendinosus on the medial tibia, the
semimembranosus on the distal femur and medial tibial condyle. Thus they extend
from a caudodorsal position, the tuber ischiadicum, to one cranioventral, the knee
joint. It is the fact that the tuber ischiadicum is caudal to the knee that determines their
action in extending the knee joint when the limb is weight-bearing.
In the weight-bearing limb, the weight is borne almost entirely by the metacarpal and
metatarsal pads. All of the limbs are in dorsal flexion (also designated
hyperextension) at the metacarpo-(metatarso-) phalangeal joints and the digital pads
become weight-bearing only as these same joints are extended in walking, leaping,
and running. Weight-bearing fixes the distal limb; it is not moved forward or backward
while the animal is weight-bearing.
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Drawing is by Susan
Abrams, (Harare,
Zimbabwe).
Fig. 12. The pull of the hamstring muscles.
Skeletal muscle contracts to approximate its attachments. When, in weight-bearing,
the hamstrings contract, there are two components of force: vertical and horizontal.
The vertical component is confined by the hip joint and the knee does not move
toward the trunk; however, the horizontal component, unimpeded, is effective in
pulling the knee caudally, extending it. If the distal end of the limb is not fixed in
weight-bearing, owing to their tibial attachment, these same muscles act to flex the
knee joint.
Fig. 13. Components of
the force-vector of the
hamstrings.
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In walking and running, contraction of the digital flexors first extends the
metatarsophalangeal and the digital joints. The dog moves forward or, if leaping,
upward off the supporting surface. In walking and running, the weight borne by the left
limb is shifted to the opposite, right, limb. As this occurs, the paw is lifted off the
ground and the extension movement of the left limb continues as plantar flexion. The
joints of the left limb are flexed, the limb is moved forward by the hip joint flexors and
then returned to weight-bearing by the limb extensors. In leaping off the ground, the
movement of both limbs creates momentum, which lifts the entire body off the
supporting surface.
The functional significance of the large hamstrings is that they are weight-bearing
muscles. They are extensors of the knee joint. Their flexor action is not that arduous.
The limb distal to the knee joint doesn’t weigh that much. It’s their extensor weightbearing action that explains the size of these muscles. Try this: The next time that you
are climbing stairs or even just walking, feel the back your thigh. The hamstring
tendons will be firm and active with each step upward on the stair or with each step
forward in walking. The tuber ischiadicum of our own bodies is dorsocaudal to the
knee joint and what works for the dog works for us!
The quadriceps is the main extensor of the knee joint and appears to be necessary
for a coordinated, smooth, extension of the joint. The main, cranial or upper part of
the biceps femoris also inserts on the patella, the patellar ligament, and the tibial
tuberosity. In tapping the patellar tendon to elicit the patellar reflex, the neuromuscular
spindles of the biceps are also stimulated. Even with loss of innervation to the
quadriceps, the patellar reflex will be carried out by the biceps if its innervation is
intact. A positive patellar reflex without examining the muscles carrying it out is no
assurance that the quadriceps’ innervation is intact.
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