6 The foot consists of 26 bones (Figs. 6-1 and 6-2): The proximal foot contains seven tarsals (see Fig. 6-1): 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 seven tarsals can be remembered using the following mnemonic: 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. The fibula is slender compared with its length and consists of one body and two articular extremities. The proximal end of the fibula is expanded into a head, which articulates with the lateral condyle of the tibia. At the lateroposterior aspect of the head is a conic projection called the apex. The enlarged distal end of the fibula is the lateral malleolus. The lateral malleolus is pyramidal and marked by several depressions at its inferior and posterior surfaces. Viewed axially, the lateral malleolus lies approximately 15 to 20 degrees more posterior than the medial malleolus (see Fig. 6-5, C). 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 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. 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. 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 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 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). *kVp values are for a three-phase, 12-pulse generator or high frequency. †Relative doses for comparison use. All doses are skin entrance for average adult at cm indicated. ‡Tabletop, extremity IR. Screen-film speed 100. §Tabletop, standard IR. Screen-film speed 300 or equivalent CR. 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). • With the patient in the supine or seated position, flex the knees, separate the feet about 6 inches (15 cm), and touch the knees together for immobilization. • Center the toes directly over one half of the IR (see Figs. 6-14 and 6-16), or place a 15-degree foam wedge well under the foot and rest the toes near the elevated base of the wedge (Fig. 6-18). • Adjust the IR half with its midline parallel to the long axis of the foot, and center it to the third MTP joint. • Perpendicular through the third MTP joint (see Fig. 6-14) when showing the joint spaces is not critical. To open the joint spaces, either direct the central ray 15 degrees posteriorly through the third MTP joint (see Fig. 6-16), or if the 15-degree foam wedge is used, direct the central ray perpendicularly (Fig. 6-19). • Place the toes in the appropriate position by elevating them on one or two small sandbags and adjusting the support to place the toes horizontal. • Place the IR half under the toes with the midline of the side used parallel with the long axis of the foot, and center it to the third MTP joint (Fig. 6-20).
LOWER LIMB
Foot
TARSALS
Chubby
Calcaneus
Twisted,
Talus
Never
Navicular
Could
Cuboid
Cha
Cuneiform—medial
Cha
Cuneiform—intermediate
Cha
Cuneiform—lateral
Leg
TIBIA
FIBULA
Femur
Patella
Knee Joint
Lower Limb Articulations
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
EXPOSURE TECHNIQUE CHART ESSENTIAL PROJECTIONS
Toes
PA PROJECTION
LOWER LIMB
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