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
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.
dp glut fasc
tens fasc lat
caud crur abd
Drawn by David S. Geary
Superficial gluteal m. Origin: Lateral part of sacrum and iliac crest and sacral spines by means of the deep gluteal fascia, Ca1,
Fig. 3. Lateral view of rump and thigh. Sartorius, tensor fasciae latae, supf. gluteal and biceps femoris removed..
Insertion: Roughness on greater trochanter laterally, just below the middle gluteal’s attachment.
Lat. view. Sartorius, tensor fasciae latae, superficial gluteal, biceps femoris and caudal crural abductor removed.
obturator int. accc, and graccccilis re,oved..kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk
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 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.
lateral collateral ligament
Fig. 8. Knee joint, caudal view.
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.
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.
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.
Drawing is by Susan Abrams, (Harare, Zimbabwe).also e, Zimbabwe.n Abrams,mstring muscles.ng it out is no assurance that the quadriceps 's ihe tibialtuberosity.nsion of the jo
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.
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 weight-bearing 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.