LOWER LIMB

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LOWER LIMB




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Foot


The foot consists of 26 bones (Figs. 6-1 and 6-2):





The bones of the foot are similar to the bones of the hand. Structural differences permit walking and support of the body’s weight. For descriptive purposes, the foot is sometimes divided into the forefoot, midfoot, and hindfoot. The forefoot includes the metatarsals and toes. The midfoot includes five tarsals—the cuneiforms, navicular, and cuboid bones. The hindfoot includes the talus and calcaneus. The bones of the foot are shaped and joined together to form a series of longitudinal and transverse arches. The longitudinal arch functions as a shock absorber to distribute the weight of the body in all directions, which permits smooth walking (see Fig. 6-2). The transverse arch runs from side to side and assists in supporting the longitudinal arch. The superior surface of the foot is termed the dorsum or dorsal surface, and the inferior, or posterior, aspect of the foot is termed the plantar surface.





TARSALS


The proximal foot contains seven tarsals (see Fig. 6-1):



Beginning at the medial side of the foot, the cuneiforms are described as medial, intermediate, and lateral.


The calcaneus is the largest and strongest tarsal bone (Fig. 6-3). Some texts refer to it as the os calcis. It projects posteriorly and medially at the distal part of the foot. The long axis of the calcaneus is directed inferiorly and forms an angle of approximately 30 degrees. The posterior and inferior portions of the calcaneus contain the posterior tuberosity for attachment of the Achilles tendon. Superiorly, three articular facets join with the talus. They are called the anterior, middle, and posterior facets. Between the middle and posterior talar articular facets is a groove, the calcaneal sulcus, which corresponds to a similar groove on the inferior surface of the talus. Collectively, these sulci constitute the sinus tarsi. The interosseous ligament passes through this sulcus. The medial aspect of the calcaneus extends outward as a shelflike overhang and is termed the sustentaculum tali. The lateral surface of the calcaneus contains the trochlea.



The talus, irregular in form and occupying the superiormost position of the foot, is the second largest tarsal bone (see Figs. 6-1 to 6-3). The talus articulates with four bones—tibia, fibula, calcaneus, and navicular bone. The superior surface, the trochlear surface, articulates with the tibia and connects the foot to the leg. The head of the talus is directed anteriorly and has articular surfaces that join the navicular bone and calcaneus. On the inferior surface is a groove, the sulcus tali, that forms the roof of the sinus tarsi. The inferior surface also contains three facets that align with the facets on the superior surface of the calcaneus.


The cuboid bone lies on the lateral side of the foot between the calcaneus and the fourth and fifth metatarsals (see Fig. 6-1). The navicular bone lies on the medial side of the foot between the talus and the three cuneiforms. The cuneiforms lie at the central and medial aspect of the foot between the navicular bone and the first, second, and third metatarsals. The medial cuneiform is the largest of the three cuneiform bones, and the intermediate cuneiform is the smallest.


The seven tarsals can be remembered using the following mnemonic:

























Chubby Calcaneus
Twisted, Talus
Never Navicular
Could Cuboid
Cha Cuneiform—medial
Cha Cuneiform—intermediate
Cha Cuneiform—lateral



Leg


The leg has two bones: the tibia and fibula. The tibia, the second largest bone in the body, is situated on the medial side of the leg and is a weight-bearing bone. Slightly posterior to the tibia on the lateral side of the leg is the fibula. The fibula does not bear any body weight.



TIBIA


The tibia (Fig. 6-4) is the larger of the two bones of the leg and consists of one body and two expanded extremities. The proximal end of the tibia has two prominent processes—the medial and lateral condyles. The superior surfaces of the condyles form smooth facets for articulation with the condyles of the femur. These two flatlike superior surfaces are called the tibial plateaus, and they slope posteriorly about 10 to 20 degrees. Between the two articular surfaces is a sharp projection, the intercondylar eminence, which terminates in two peaklike processes called the medial and lateral intercondylar tubercles. The lateral condyle has a facet at its distal posterior surface for articulation with the head of the fibula. On the anterior surface of the tibia, just below the condyles, is a prominent process called the tibial tuberosity, to which the ligamentum patellae attach. Extending along the anterior surface of the tibial body, beginning at the tuberosity, is a sharp ridge called the anterior crest.



The distal end of the tibia (Fig. 6-5) is broad, and its medial surface is prolonged into a large process called the medial malleolus. Its anterolateral surface contains the anterior tubercle, which overlays the fibula. The lateral surface is flattened and contains the triangular fibular notch for articulation with the fibula. The surface under the distal tibia is smooth and shaped for articulation with the talus.





Femur


The femur is the longest, strongest, and heaviest bone in the body (Figs. 6-6 and 6-7). This bone consists of one body and two articular extremities. The body is cylindric, slightly convex anteriorly, and slants medially 5 to 15 degrees (see Fig. 6-6, A). The extent of medial inclination depends on the breadth of the pelvic girdle. When the femur is vertical, the medial condyle is lower than the lateral condyle (see Fig. 6-6, C). About a 5- to 7-degree difference exists between the two condyles. Because of this difference, on lateral radiographs of the knee the central ray is angled 5 to 7 degrees cephalad to “open” the joint space of the knee. The superior portion of the femur articulates with the acetabulum of the hip joint (considered with the pelvic girdle in Chapter 7).




The distal end of the femur is broadened and has two large eminences: the larger medial condyle and the smaller lateral condyle. Anteriorly, the condyles are separated by the patellar surface, a shallow, triangular depression. Posteriorly, the condyles are separated by a deep depression called the intercondylar fossa. A slight prominence above and within the curve of each condyle forms the medial and lateral epicondyles. The medial condyle contains the adductor tubercle, which is located on the posterolateral aspect. The tubercle is a raised bony area that receives the tendon of the adductor muscle. This tubercle is important to identify on lateral knee radiographs because it assists in identifying overrotation or underrotation. The triangular area superior to the intercondylar fossa on the posterior femur is the trochlear groove, over which the popliteal blood vessels and nerves pass.


The posterior area of the knee, between the condyles, contains a sesamoid bone in 3% to 5% of people. This sesamoid is called the fabella and is seen only on the lateral projection of the knee.



Patella


The patella, or knee cap (Fig. 6-8), is the largest and most constant sesamoid bone in the body (see Chapter 3). The patella is a flat, triangular bone situated at the distal anterior surface of the femur. The patella develops in the tendon of the quadriceps femoris muscle between 3 and 5 years of age. The apex, or tip, is directed inferiorly, lies ½ inch (1.3 cm) above the joint space of the knee, and is attached to the tuberosity of the tibia by the patellar ligament. The superior border of the patella is called the base.




Knee Joint


The knee joint is one of the most complex joints in the human body. The femur, tibia, fibula, and patella are held together by a complex group of ligaments. These ligaments work together to provide stability for the knee joint. Although radiographers do not produce images of these ligaments, they need to have a basic understanding of their positions and interrelationship. Many patients with knee injuries do not have fractures, but they may have torn one or more of these ligaments, which can cause great pain and may alter the position of the bones. Fig. 6-9 shows the following important ligaments of the knee:




The knee joint contains two fibrocartilage disks called the lateral meniscus and medial meniscus (Fig. 6-10; see Fig. 6-9). The circular menisci lie on the tibial plateaus. They are thick at the outer margin of the joint and taper off toward the center of the tibial plateau. The center of the tibial plateau contains cartilage that articulates directly with the condyles of the knee. The menisci provide stability for the knee and act as a shock absorber. The menisci are commonly torn during injury. Either a knee arthrogram or a magnetic resonance imaging (MRI) scan must be performed to visualize a meniscus tear.




Lower Limb Articulations


The joints of the lower limb are summarized in Table 6-1 and shown in Figs. 6-11 and 6-12. Beginning with the distalmost portion of the lower limb, the articulations are as follows.





The interphalangeal (IP) articulations, between the phalanges, are synovial hinges that allow only flexion and extension. The joints between the distal and middle phalanges are the distal interphalangeal (DIP) joints. Articulations between the middle and proximal phalanges are the proximal interphalangeal (PIP) joints. With only two phalanges in the great toe, the joint is known simply as the IP joint.


The distal heads of the metatarsals articulate with the proximal ends of the phalanges at the metatarsophalangeal (MTP) articulations to form synovial ellipsoidal joints, which have movements of flexion, extension, and slight adduction and abduction. The proximal bases of the metatarsals articulate with one another (intermetatarsal articulations) and with the tarsals (tarsometatarsal [TMT] articulations) to form synovial gliding joints, which permit flexion, extension, adduction, and abduction movements.


The intertarsal articulations allow only slight gliding movements between the bones and are classified as synovial gliding or synovial ball-and-socket joints (see Table 6-1). The joint spaces are narrow and obliquely situated. When the joint surfaces of these bones are in question, it is necessary to angle the x-ray tube or adjust the foot to place the joint spaces parallel with the central ray.


The calcaneus supports the talus and articulates with it by an irregularly shaped, three-faceted joint surface, forming the subtalar joint. This joint is classified as a synovial gliding joint. Anteriorly, the calcaneus articulates with the cuboid at the calcaneocuboid joint. This joint is a synovial gliding joint. The talus rests on top of the calcaneus (see Fig. 6-12). It articulates with the navicular bone anteriorly, supports the tibia above, and articulates with the malleoli of the tibia and fibula at its sides.


Each of the three parts of the subtalar joint is formed by reciprocally shaped facets on the inferior surface of the talus and the superior surface of the calcaneus. Study of the superior and medial aspects of the calcaneus (see Fig. 6-3) helps the radiographer to understand better the problems involved in radiography of this joint.


The intertarsal articulations are as follows:



The ankle joint is commonly called the ankle mortise, or mortise joint. It is formed by the articulations between the lateral malleolus of the fibula and the inferior surface and medial malleolus of the tibia (Fig. 6-13, A). The mortise joint is often divided specifically into the talofibular and tibiofibular joints. These form a socket type of structure that articulates with the superior portion of the talus. The talus fits inside the mortise. The articulation is a synovial hinge type of joint. The primary action of the ankle joint is dorsiflexion (flexion) and plantar flexion (extension); however, in full plantar flexion, a small amount of rotation and abduction-adduction is permitted. The mortise joint also allows inversion and eversion of the foot. Other movements at the ankle largely depend on the gliding movements of the intertarsal joints, particularly the one between the talus and calcaneus.



The fibula articulates with the tibia at its distal and proximal ends. The distal tibiofibular joint is a fibrous syndesmosis joint allowing slight movement. The head of the fibula articulates with the posteroinferior surface of the lateral condyle of the tibia, which forms the proximal tibiofibular joint, which is a synovial gliding joint (see Fig. 6-13, A).


The patella articulates with the patellar surface of the femur and protects the front of the knee joint. This articulation is called the patellofemoral joint; when the knee is extended and relaxed, the patella is freely movable over the patellar surface of the femur. When the knee is flexed, which is also a synovial gliding joint, the patella is locked in position in front of the patellar surface. The knee joint, or femorotibial joint, is the largest joint in the body. It is called a synovial modified-hinge joint. In addition to flexion and extension, the knee joint allows slight medial and lateral rotation in the flexed position. The joint is enclosed in an articular capsule and held together by numerous ligaments (see Figs. 6-9 and 6-13, B).




SUMMARY OF ANATOMY
















SUMMARY OF PATHOLOGY












































































Condition Definition
Bone cyst Fluid-filled cyst with a wall of fibrous tissue
Congenital clubfoot Abnormal twisting of the foot, usually inward and downward
Dislocation Displacement of a bone from the joint space
Fracture Disruption in the continuity of bone
 Pott Avulsion fracture of the medial malleolus with loss of the ankle mortise
 Jones Avulsion fracture of the base of the fifth metatarsal
Gout Hereditary form of arthritis in which uric acid is deposited in joints
Metastases Transfer of a cancerous lesion from one area to another
Osgood-Schlatter disease Incomplete separation or avulsion of the tibial tuberosity
Osteoarthritis or degenerative joint disease Form of arthritis marked by progressive cartilage deterioration in synovial joints and vertebrae
Osteomalacia or rickets Softening of the bones owing to vitamin D deficiency
Osteomyelitis Inflammation of bone owing to a pyogenic infection
Osteopetrosis Increased density of atypically soft bone
Osteoporosis Loss of bone density
Paget disease Chronic metabolic disease of bone marked by weakened, deformed, and thickened bone that fractures easily
Tumor New tissue growth where cell proliferation is uncontrolled
 Chondrosarcoma Malignant tumor arising from cartilage cells
 Enchondroma Benign tumor consisting of cartilage
 Ewing sarcoma Malignant tumor of bone arising in medullary tissue
 Osteochondroma or exostosis Benign bone tumor projection with a cartilaginous cap
 Osteoclastoma or giant cell tumor Lucent lesion in the metaphysis, usually at the distal femur
 Osteoid osteoma Benign lesion of cortical bone
 Osteosarcoma Malignant, primary tumor of bone with bone or cartilage formation






Radiation Protection


Protecting the patient from unnecessary radiation is a professional responsibility of the radiographer (see Chapter 1 for specific guidelines). In this chapter, the Shield gonads statement at the end of the Position of part sections indicates that the patient is to be protected from unnecessary radiation by restricting the radiation beam, using proper collimation, and placing lead shielding between the gonads and the radiation source.





Toes



image AP OR AP AXIAL PROJECTIONS


Because of the natural curve of the toes, the IP joint spaces are not best shown on the AP projection. When demonstration of these joint spaces is not critical, an AP projection may be performed (Figs. 6-14 and 6-15). An AP axial projection is recommended to open the joint spaces and reduce foreshortening (Figs. 6-16 and 6-17).















PA PROJECTION








Mar 4, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on LOWER LIMB
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