Info

Figure

(a) Radiograph of the right knee (anterior view), showing the ends of the femur, tibia, and fibula. Thinner areas of bone, such as part of the head of the fibula and the patella, barely show in this radiograph. (b) Anterior view of the right lower limb. (c) Lateral view of the right knee. (d) Posterior view of the right knee.

Femur

The femur, or thigh bone, is the longest bone in the body and extends from the hip to the knee. A large, rounded head at its proximal end projects medially into the acetabulum of the coxal bone. On the head, a pit called the fovea capitis marks the attachment of a ligament. Just below the head are a constriction, or neck, and two large processes—a superior, lateral greater trochanter and an inferior, medial lesser trochanter. These processes provide attachments for muscles of the lower limbs and buttocks. On the posterior surface in the middle third of the shaft is a longitudinal crest called the linea aspera. This rough strip is an attachment for several muscles (fig. 7.53).

At the distal end of the femur, two rounded processes, the lateral and medial condyles, articulate with the tibia of the leg. A patella also articulates with the femur on its distal anterior surface.

On the medial surface at its distal end is a prominent medial epicondyle, and on the lateral surface is a lateral epicondyle. These projections provide attachments for muscles and ligaments.

Patella

The patella, or kneecap, is a flat sesamoid bone located in a tendon that passes anteriorly over the knee (see fig. 7.52). Because of its position, the patella controls the angle at which this tendon continues toward the tibia, so it functions in lever actions associated with lower limb movements.

Fovea capitis -?

As a result of a blow to the knee or a forceful unnatural movement of the leg, the patella sometimes slips to one side. This painful condition is called a patellar dislocation. Doing exercises that strengthen muscles associated with the knee and wearing protective padding can prevent knee displacement. Unfortunately, once the soft tissues that hold the patella in place are stretched, patellar dislocation tends to recur.

Tibia

The tibia, or shin bone, is the larger of the two leg bones and is located on the medial side. Its proximal end is expanded into medial and lateral condyles, which have concave surfaces and articulate with the condyles of the femur. Below the condyles, on the anterior surface, is a process called the tibial tuberosity, which provides an attachment for the patellar ligament (a continuation of the patella-bearing tendon). A prominent anterior crest extends downward from the tuberosity and attaches connective tissues in the leg.

Greater trochanter

Lateral epicondyle

Fovea capitis -?

Greater trochanter

Lateral epicondyle

Proximal Tiobia Blood Vessels

Gluteal tubercle

Linea aspera

Lateral condyle

Intercondylar fossa

Figure 7.53

(a) Anterior surface and (b) posterior surface of the right femur.

Gluteal tubercle

Linea aspera

Lateral condyle

Intercondylar fossa

Figure 7.53

(a) Anterior surface and (b) posterior surface of the right femur.

At its distal end, the tibia expands to form a prominence on the inner ankle called the medial malle-olus (mah-le'o-lus), which is an attachment for ligaments. On its lateral side is a depression that articulates with the fibula. The inferior surface of the tibia's distal end articulates with a large bone (the talus) in the foot (fig. 7.54).

Lateral condyle

Head of fibula

Fibula

Lateral condyle

Head of fibula

Fibula

Intercondylar eminence

Medial condyle

Tibial tuberosity

Anterior crest

Tibia

Medial malleolus

Figure 7.54

Bones of the right leg, anterior view.

Intercondylar eminence

Medial condyle

Tibial tuberosity

Anterior crest

Tibia

Medial malleolus

Lateral malleolus

Figure 7.54

Bones of the right leg, anterior view.

The skeleton is particularly vulnerable to injury during the turbulent teen years, when bones grow rapidly. Athletic teens sometimes develop Osgood-Schlatter disease, which is a painful swelling of a bony projection of the tibia below the knee. Overusing the thigh muscles to straighten the lower limb irritates the area, causing the swelling. Usually a few months of rest and no athletic activity allows the bone to heal on its own. Rarely, a cast must be used to immobilize the knee.

Fibula

The fibula is a long, slender bone located on the lateral side of the tibia. Its ends are slightly enlarged into a proximal head and a distal lateral malleolus. The head articulates with the tibia just below the lateral condyle; however, it does not enter into the knee joint and does not bear any body weight. The lateral malleolus articulates with the ankle and protrudes on the lateral side (fig. 7.54).

Ankle and Foot

The ankle and foot consists of a tarsus (tahr'sus), a metatarsus (met"ah-tar'sus), and five toes. The tarsus is composed of seven tarsal bones. These bones are arranged so that one of them, the talus (ta'lus), can move freely where it joins the tibia and fibula, thus forming the ankle. The remaining tarsal bones are bound firmly together, forming a mass supporting the talus. Figures 7.55 and 7.56 name the individual bones of the tarsus.

The largest of the tarsals, the calcaneus (kal-ka'ne-us), or heel bone, is located below the talus where it projects backward to form the base of the heel. The calcaneus helps support the weight of the body and provides an attachment for muscles that move the foot.

The metatarsus consists of five elongated metatarsal bones, which articulate with the tarsus. They are numbered 1 to 5, beginning on the medial side (fig. 7.56). The heads at the distal ends of these bones form the ball of the foot. The tarsals and metatarsals are arranged and bound by ligaments to form the arches of the foot. A longitudinal arch extends from the heel to the toe, and a transverse arch stretches across the foot. These arches provide a stable, springy base for the body. Sometimes, however, the tissues that bind the metatarsals weaken, producing fallen arches, or flat feet.

An infant with two casts on her feet is probably being treated for clubfoot, a very common birth defect in which the foot twists out of its normal position, turning in, out, up, down, or some combination of these directions. Clubfoot probably results from arrested development during fetal existence, but the precise cause is not known. Clubfoot can almost always be corrected with special shoes, or surgery, followed by several months in casts to hold the feet in the correct position.

The phalanges of the toes are shorter, but otherwise similar to those of the fingers, and align and articulate with the metatarsals. Each toe has three phalanges—a proximal, a middle, and a distal phalanx—except the great toe, which has only two because it lacks the middle phalanx (fig. 7.56). Table 7.12 summarizes the bones of the pelvic girdle and lower limbs.

99 Locate and name each of the bones of the lower limb. ^9 Explain how the bones of the lower limb articulate with one another.

^9 Describe how the foot is adapted to support the body.

Name Phalanges The Great Toe

(b) Tarsus

Figure 7.55

(a) Radiograph of the right foot viewed from the medial side. (b) The talus moves freely where it articulates with the tibia and fibula.

(b) Tarsus

Figure 7.55

(a) Radiograph of the right foot viewed from the medial side. (b) The talus moves freely where it articulates with the tibia and fibula.

Calcaneus

Proximal Tiobia Blood Vessels

Proximal phalanx

Figure 7.56

(a) The right foot viewed superiorly. (b) Radiograph of the right foot viewed superiorly.

Calcaneus

Talus

Navicular Cuboid

Lateral cuneiform Intermediate cuneiform Medial cuneiform

Tarsals

Proximal phalanx

Middle phalanx Distal phalanx

Figure 7.56

(a) The right foot viewed superiorly. (b) Radiograph of the right foot viewed superiorly.

Shier-Butler-Lewis:

II. Support and Movement 7. Skeletal System

1 © The McGraw-Hill

Human Anatomy and

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Post a comment