OUTLINE

SUMMARY OF PROJECTIONS

ANATOMY

The lower limb, or extremity, and its girdle (considered in Chapter 7) are studied in four parts: (1) foot, (2) leg, (3) thigh, and (4) hip. The bones are composed, shaped, and placed so that they can carry the body in the upright position and transmit its weight to the ground with a minimal amount of stress to the individual parts.

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.

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.

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 PATHOLOGY

EXPOSURE TECHNIQUE CHART ESSENTIAL PROJECTIONS

RADIOGRAPHY

Toes

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