Chapter8 The Appendicular Skeleton
Your skeleton provides the internal supporting structure of the body. The adult axial skeleton consists of 80 bones that form the head and trunk. Attached to this are the limbs, whose 126 bones constitute the appendicular skeleton. These bones are divided into two groups: the bones that are located within the limbs themselves and the girdle bones that attach the limbs to the axial skeleton. The bones of the shoulder region form the pectoral girdle, which anchors the upper limbs to the thoracic cage of the axial skeleton. The lower limbs are attached to the vertebral column by the pelvic girdle.
8.1 The Pectoral Girdles
The appendicular skeleton includes all the limb bones, plus the bones that unite each limb with the axial skeleton (Figure 8.1). The bones that attach each upper limb to the axial skeleton form the pectoral girdle (shoulder girdle). This consists of two bones, the scapula and clavicle (Figure 8.2). The clavicle (collarbone) is an S-shaped bone located on the anterior side of the shoulder. It is attached on its medial end to the sternum of the thoracic cage, which is part of the axial skeleton. The lateral end of the clavicle articulates (joins) with the scapula just above the shoulder joint. You can easily palpate, or feel with your fingers, the entire length of your clavicle.
The scapula (shoulder blade) lies on the posterior aspect of the shoulder. It is supported by the clavicle and articulates with the humerus (arm bone) to form the shoulder joint. The scapula is a flat, triangular bone with a prominent ridge running across its posterior surface. This ridge extends out laterally, where it forms the bony tip of the shoulder and joins with the lateral end of the clavicle. By following along the clavicle, you can palpate out to the bony tip of the shoulder, and from there, you can move back across your posterior shoulder to follow the ridge of the scapula. Move your shoulder around and feel how the clavicle and scapula move together as a unit. Both of these bones serve as important attachment sites for muscles that aid movements of the shoulder and arm.
The right and left pectoral girdles are not joined to each other, allowing each to operate independently. In addition, the clavicle of each pectoral girdle is anchored to the axial skeleton by a single, highly mobile joint. This allows for the extensive mobility of the entire pectoral girdle, which in turn enhances movements of the shoulder and upper limb.
Clavicle
The clavicle is the only long bone that lies in a horizontal position in the body (see Figure 8.2). The clavicle has several important functions. First, anchored by muscles from above, it serves as a strut that extends laterally to support the scapula. This in turn holds the shoulder joint superiorly and laterally from the trunk, allowing for maximal freedom of motion for the upper limb. The clavicle also transmits forces acting on the upper limb to the sternum and axial skeleton. Finally, it serves to protect the underlying nerves and blood vessels as they pass between the trunk of the body and the upper limb.
Figure 8.1 Axial and Appendicular Skeletons. The axial skeleton forms the central axis of the body and consists of the skull, vertebral column, and thoracic cage. The appendicular skeleton consists of the pectoral and pelvic girdles, the limb bones, and the bones of the hands and feet.
The clavicle has three regions: the medial end, the lateral end, and the shaft. The sternal (medial) end of the clavicle has a triangular shape and articulates with the manubrium portion of the sternum. This forms the sternoclavicular joint, which is the only bony articulation between the pectoral girdle of the upper limb and the axial skeleton. This joint allows considerable mobility, enabling the clavicle and scapula to move in upward/downward and anterior/posterior directions during shoulder movements. The acromial (lateral) endof the clavicle articulates with the acromion of the scapula, the portion of the scapula that forms the bony tip of the shoulder. For the shaft of the clavicle, there are some sex differences in its morphology: in females, the clavicle tends to be shorter, thinner, and less curved; in males, the clavicle is heavier and longer, and it has a greater curvature and rougher surfaces where muscles attach, features that are more pronounced in manual workers.
Figure 8.2 Pectoral Girdle. The pectoral girdle consists of the clavicle and the scapula, which serve to attach the upper limb to the sternum of the axial skeleton.
Scapula
The scapula is also part of the pectoral girdle and thus plays an important role in anchoring the upper limb to the body. The scapula is located on the posterior side of the shoulder. It is surrounded by muscles on both its anterior (deep) and posterior (superficial) sides and thus does not articulate with the ribs of the thoracic cage.
The scapula has several important landmarks (Figure 8.3). The three margins or borders (superior, medial, and inferior) of the scapula are named for their positions within the body. The suprascapular notch is located lateral to the midpoint of the superior border. There are two corners of the triangular scapula at either end of the medial border—superior and inferior angles. The inferior angle is the most inferior portion of the scapula and is particularly important because it serves as the attachment point for several powerful muscles involved in shoulder and upper limb movements. The remaining corner of the scapula, between the superior and lateral borders, is the location of the glenoid cavity (glenoid fossa).
The scapula also has two prominent projections. Toward the lateral end of the superior border, between the suprascapular notch and glenoid cavity, is the hooklike coracoid process. This process projects anteriorly and curves laterally. At the shoulder, the coracoid process is located inferior to the lateral end of the clavicle. It is anchored to the clavicle by a strong ligament and serves as the attachment site for muscles of the anterior chest and arm. On the posterior aspect, the spine of the scapula is a long and prominent ridge that runs across its upper portion. Extending laterally from the spine is a flattened and expanded region called the acromion or acromial process.
The scapula has three depressions, each of which is called a fossa (plural = fossae). Two of these are found on the posterior scapula, above and below the scapular spine. Superior to the spine is the narrow supraspinous fossa, and inferior to the spine is the broad infraspinous fossa. The anterior (deep) surface of the scapula forms the broad subscapular fossa. All these fossae provide large surface areas for the attachment of muscles that cross the shoulder joint to act on the humerus.
Figure 8.3 Scapula. The isolated scapula is shown here from its anterior (deep) side and its posterior (superficial) side.
8.2 Bones of the Upper Limb
The upper limb is divided into three regions. These consist of the arm, located between the shoulder and elbow joints; the forearm, which is between the elbow and wrist joints; and the hand, which is located distal to the wrist. There are 30 bones in each upper limb (see Figure 8.1). The humerus is the single bone of the upper arm, and the ulna (medially) and the radius (laterally) are the paired bones of the forearm. The base of the hand contains eight bones, each called a carpal bone, and the palm of the hand is formed by five bones, each called a metacarpal bone. The fingers and thumb contain a total of 14 bones, each of which is a phalanx bone of the hand.
Humerus
The humerus is the single bone of the upper arm region (Figure 8.4). At its proximal end is the head of the humerus. This is the large, round, smooth region that faces medially. The head articulates with the glenoid cavity of the scapula to form the glenohumeral (shoulder) joint. The margin of the smooth area of the head is the anatomical neck of the humerus. Located on the lateral side of the proximal humerus is an expanded bony area called the greater tubercle. The smaller lesser tubercle of the humerus is found on the anterior aspect of the humerus. Both the greater and lesser tubercles serve as attachment sites for muscles that act across the shoulder joint. The surgical neck is located at the base of the expanded, proximal end of the humerus, where it joins the narrow shaft of the humerus. The surgical neck is a common site of arm fractures. The deltoid tuberosity is a roughened, V-shaped region located on the lateral side in the middle of the humerus shaft. As its name indicates, it is the site of attachment for the deltoid muscle.
Figure 8.4 Humerus and Elbow Joint. The humerus is the single bone of the upper arm region. It articulates with the radius and ulna bones of the forearm to form the elbow joint.
The distal end of the humerus has two articulation areas, which join the ulna and radius bones of the forearm to form the elbow joint. The more medial of these areas is the trochlea, a spindle- or pulley-shaped region that articulates with the ulna bone. Immediately lateral to the trochlea is the capitulum, a knoblike structure located on the anterior surface of the distal humerus. The capitulum articulates with the radius bone of the forearm. Just above these bony areas are two small depressions. These spaces accommodate the forearm bones when the elbow is fully bent (flexed).
Ulna
The ulna is the medial bone of the forearm. It runs parallel to the radius, which is the lateral bone of the forearm (Figure 8.5). The proximal end of the ulna resembles a crescent wrench with its large, C-shaped trochlear notch. This region articulates with the trochlea of the humerus as part of the elbow joint. The inferior margin of the trochlear notch is formed by a prominent lip of bone called the coronoid process of the ulna. Just below this on the anterior ulna is a roughened area called the ulnar tuberosity. The posterior and superior portions of the proximal ulna make up the olecranon process, which forms the bony tip of the elbow.
More distal is the shaft of the ulna. The small, rounded area that forms the distal end is the head of the ulna. Projecting from the posterior side of the ulnar head is the styloid process of the ulna, a short bony projection. This serves as an attachment point for a connective tissue structure that unites the distal ends of the ulna and radius.
Radius
The radius runs parallel to the ulna, on the lateral (thumb) side of the forearm (see Figure 8.5). The head of the radius is a disc-shaped structure that forms the proximal end. The small depression on the surface of the head articulates with the capitulum of the humerus as part of the elbow joint, whereas the smooth, outer margin of the head articulates with the radial notch of the ulna at the proximal radioulnar joint. The neck of the radius is the narrowed region immediately below the expanded head. Inferior to this point on the medial side is the radial tuberosity, an oval-shaped, bony protuberance that serves as a muscle attachment point. The shaft of the radius is slightly curved and has a small ridge along its medial side. The lateral end of the radius has a pointed projection called the styloid process of the radius. This provides attachment for ligaments that support the lateral side of the wrist joint. Compared to the styloid process of the ulna, the styloid process of the radius projects more distally, thereby limiting the range of movement for lateral deviations of the hand at the wrist joint.
Figure 8.5 Ulna and Radius. The ulna is located on the medial side of the forearm, and the radius is on the lateral side. These bones are attached to each other by an interosseous membrane.
Carpal Bones
The wrist and base of the hand are formed by a series of eight small carpal bones (see Figure 8.6). The carpal bones are arranged in two rows, forming a proximal row of four carpal bones and a distal row of four carpal bones.
The carpal bones form the base of the hand. Within the carpal bones, the four proximal bones are united to each other by ligaments to form a unit. Only three of these bones (the scaphoid, lunate, and triquetrum) contribute to the radiocarpal joint. The scaphoid and lunate bones articulate directly with the distal end of the radius, whereas the triquetrum bone articulates with a fibrocartilaginous pad that spans the radius and styloid process of the ulna. The distal end of the ulna thus does not directly articulate with any of the carpal bones.
The four distal carpal bones are also held together as a group by ligaments. The proximal and distal rows of carpal bones articulate with each other. Together, the radiocarpal and midcarpal joints are responsible for all movements of the hand at the wrist. The distal carpal bones also articulate with the metacarpal bones of the hand.
Figure 8.6 Bones of the Wrist and Hand. The eight carpal bones form the base of the hand. These are arranged into proximal and distal rows of four bones each. The metacarpal bones form the palm of the hand. The thumb and fingers consist of the phalanx bones.
In the articulated hand, the carpal bones form a U-shaped grouping. A strong ligament called the flexor retinaculum spans the top of this U-shaped area to maintain this grouping of the carpal bones. Together, the carpal bones and the flexor retinaculum form a passageway called the carpal tunnel, with the carpal bones forming the walls and floor and the flexor retinaculum forming the roof of this space.
Metacarpal Bones
The palm of the hand contains five elongated metacarpal bones. These bones lie between the carpal bones of the wrist and the bones of the fingers and thumb (see Figure 8.6). The proximal end of each metacarpal bone articulates with one of the distal carpal bones. The metacarpal bones are numbered 1–5, beginning at the thumb.
The first metacarpal bone, at the base of the thumb, is separated from the other metacarpal bones. This allows it a freedom of motion that is independent of the other metacarpal bones, which is very important for thumb mobility. The remaining metacarpal bones are united to form the palm of the hand. The second and third metacarpal bones are firmly anchored in place and are immobile. However, the fourth and fifth metacarpal bones have limited anterior-posterior mobility, a motion that is greater for the fifth bone. This mobility is important during power gripping with the hand (Figure 8.7). The anterior movement of these bones, particularly the fifth metacarpal bone, increases the strength of contact for the medial hand during gripping actions.
Figure 8.7 Hand During Gripping. During tight gripping—compare (b) to (a)—the fourth and, particularly, the fifth metatarsal bones are pulled anteriorly. This increases the contact between the object and the medial side of the hand, thus improving the firmness of the grip.
Phalanx Bones
The fingers and thumb contain 14 bones, each of which is called a phalanx bone (plural = phalanges), named after the ancient Greek phalanx (a rectangular block of soldiers). The pollex (thumb) is digit number 1 and has two phalanges, a proximal phalanx, and a distal phalanx bone (see Figure 8.6). Digits 2 (index finger) through 5 (little finger) have three phalanges each, called the proximal, middle, and distal phalanx bones.
8.3 The Pelvic Girdle and Pelvis
The pelvic girdle (hip girdle) is formed by two bones: the right and left hip bones or coxal bones (coxal = “hip”), which serve as the attachment points for each lower limb. Each hip bone, in turn, is firmly joined to the axial skeleton via its attachment to the sacrum of the vertebral column. The right and left hip bones also converge anteriorly to attach to each other. The bony pelvis is the entire structure formed by the two hip bones, the sacrum, and, attached inferiorly to the sacrum, the coccyx (Figure 8.8).
Unlike the bones of the pectoral girdle, which are highly mobile to enhance the range of upper limb movements, the bones of the pelvis are strongly united to one another to form a largely immobile, weight-bearing structure. This is important for stability because it enables the weight of the body to be easily transferred laterally from the vertebral column, through the pelvic girdle and hip joints, and into either lower limb whenever the other limb is not bearing weight. Thus, the immobility of the pelvis provides a strong foundation for the upper body as it rests on top of the mobile lower limbs.
Figure 8.8 Pelvis. The pelvic girdle is formed by two hip bones. The hip bones attach the lower limb to the axial skeleton through their articulation with the sacrum. The right and left hip bones, plus the sacrum and the coccyx, together form the pelvis.
Hip Bone
The hip bone, or coxal bone, forms the pelvic girdle portion of the pelvis. The paired hip bones are the large, curved bones that form the lateral and anterior aspects of the pelvis. Each adult hip bone is formed by three separate bones that fuse together during the late teenage years. These bony components are the ilium, ischium, and pubis (Figure 8.9). These names are retained and used to define the three regions of the adult hip bone.
The ilium is the fanlike, superior region that forms the largest part of the hip bone. It is firmly united to the sacrum at the largely immobile sacroiliac joint (see Figure 8.8). The ischium forms the posteroinferior region of each hip bone. It supports the body when sitting. The pubis forms the anterior portion of the hip bone. The pubis curves medially, where it joins to the pubis of the opposite hip bone at a specialized joint called the pubic symphysis.
Figure 8.9 The Hip Bone. The adult hip bone consists of three regions. The ilium forms the large, fan-shaped superior portion, the ischium forms the posteroinferior portion, and the pubis forms the anteromedial portion.
Ilium
When you place your hands on your waist, you can feel the arching, superior margin of the ilium along your waistline (see Figure 8.9). This curved, superior margin of the ilium is the iliac crest. The shallow depression located on the anteromedial (internal) surface of the upper ilium is called the iliac fossa. The large, inverted U-shaped indentation located on the posterior margin of the lower ilium is called the greater sciatic notch.
Ischium
The ischium forms the posterolateral portion of the hip bone (see Figure 8.9). The large, roughened area of the inferior ischium is the ischial tuberosity. This serves as the attachment for the posterior thigh muscles and also carries the weight of the body when sitting. You can feel the ischial tuberosity if you wiggle your pelvis against the seat of a chair. Projecting superiorly and anteriorly from the ischial tuberosity is a narrow segment of bone called the ischial ramus. The slightly curved posterior margin of the ischium above the ischial tuberosity is the lesser sciatic notch. The bony projection separating the lesser sciatic notch and greater sciatic notch is the ischial spine.
Pubis
The pubis forms the anterior portion of the hip bone (see Figure 8.9). The enlarged medial portion of the pubis is the pubic body. The superior pubic ramus is the segment of bone that passes laterally from the pubic body to join the ilium.
The pubic body is joined to the pubic body of the opposite hip bone by the pubic symphysis. Extending downward and laterally from the body is the inferior pubic ramus. The pubic arch is the bony structure formed by the pubic symphysis and the bodies and inferior pubic rami of the adjacent pubic bones. The inferior pubic ramus extends downward to join the ischial ramus.
Pelvis
The pelvis consists of four bones: the right and left hip bones, the sacrum, and the coccyx (see Figure 8.8). The pelvis has several important functions. Its primary role is to support the weight of the upper body when sitting and to transfer this weight to the lower limbs when standing. It serves as an attachment point for trunk and lower limb muscles and also protects the internal pelvic organs. When standing in the anatomical position, the pelvis is tilted anteriorly. In this position, the anterior superior iliac spines and the pubic tubercles lie in the same vertical plane, and the anterior (internal) surface of the sacrum faces forward and downward.
The three areas of each hip bone (the ilium, pubis, and ischium) converge centrally to form a deep, cup-shaped cavity called the acetabulum. This is located on the lateral side of the hip bone and is part of the hip joint. The large opening in the anteroinferior hip bone between the ischium and pubis is the obturator foramen. This space is largely filled in by a layer of connective tissue and serves for the attachment of muscles on both its internal and external surfaces.
Several ligaments unite the bones of the pelvis (Figure 8.10). The largely immobile sacroiliac joint is supported by a pair of strong ligaments that are attached between the sacrum and ilium portions of the hip bone. These ligaments help support and immobilize the sacrum as it carries the weight of the body (only a few will be listed here).
Figure 8.10 Ligaments of the Pelvis. The posterior sacroiliac ligament supports the sacroiliac joint. The sacrospinous ligament spans the sacrum to the ischial spine, and the sacrotuberous ligament spans the sacrum to the ischial tuberosity. The sacrospinous and sacrotuberous ligaments contribute to the formation of the greater and lesser sciatic foramina.
The space enclosed by the bony pelvis is divided into two regions (Figure 8.11). The broad superior region, defined laterally by the large, fanlike portion of the upper hip bone, is called the greater pelvis (greater pelvic cavity). This broad area is occupied by portions of the small and large intestines, and because it is more closely associated with the abdominal cavity, it is sometimes referred to as the false pelvis. More inferiorly, the narrow, rounded space of the lesser pelvis (lesser pelvic cavity) contains the bladder and other pelvic organs and thus is also known as the true pelvis. The pelvic brim (also known as the pelvic inlet) forms the superior margin of the lesser pelvis, separating it from the greater pelvis. The pelvic brim is defined by a line formed by the upper margin of the pubic symphysis anteriorly and the pectineal line of the pubis, the arcuate line of the ilium, and the sacral promontory (the anterior margin of the superior sacrum) posteriorly. The inferior limit of the lesser pelvic cavity is called the pelvic outlet. This large opening is defined by the inferior margin of the pubic symphysis anteriorly and the ischiopubic ramus, the ischial tuberosity, the ligament, and the inferior tip of the coccyx posteriorly. Because of the anterior tilt of the pelvis, the lesser pelvis is also angled, giving it an anterosuperior (pelvic inlet) to posteroinferior (pelvic outlet) orientation.
Figure 8.11 Male and Female Pelvis. The female pelvis is adapted for childbirth and is broader, with a larger subpubic angle, a rounder pelvic brim, and a wider and shallower lesser pelvic cavity than the male pelvis.
Comparison of the Female and Male Pelvis
The differences between the adult female and male pelvis relate to function and body size. In general, the bones of the male pelvis are thicker and heavier, adapted for support of the male’s heavier physical build and stronger muscles. The greater sciatic notch of the male hip bone is narrower and deeper than the broader notch of females. Because the female pelvis is adapted for childbirth, it is wider than the male pelvis, as evidenced by the distance between the anterior superior iliac spines (see Figure 8.11). The ischial tuberosities of females are also farther apart, which increases the size of the pelvic outlet. Because of this increased pelvic width, the subpubic angle is larger in females (greater than 80 degrees) than it is in males (less than 70 degrees). The female sacrum is wider, shorter, and less curved, and the sacral promontory projects less into the pelvic cavity, thus giving the female pelvic inlet (pelvic brim) a more rounded or oval shape compared to males. The lesser pelvic cavity of females is also wider and shallower than the narrower, deeper, and tapering lesser pelvis of males. Because of the obvious differences between female and male hip bones, this is the one bone of the body that allows for the most accurate sex determination. Table 8.1 provides an overview of the general differences between the female and male pelvis.
Female pelvis | Male pelvis | |
|---|---|---|
Pelvic weight | Bones of the pelvis are lighter and thinner | Bones of the pelvis are thicker and heavier |
Pelvic inlet shape | Pelvic inlet has a round or oval shape | Pelvic inlet is heart-shaped |
Lesser pelvic cavity shape | Lesser pelvic cavity is shorter and wider | Lesser pelvic cavity is longer and narrower |
Subpubic angle | Subpubic angle is greater than 80 degrees | Subpubic angle is less than 70 degrees |
Pelvic outlet shape | Pelvic outlet is rounded and larger | Pelvic outlet is smaller |
8.4 Bones of the Lower Limb
Like the upper limb, the lower limb is divided into three regions. The thigh is that portion of the lower limb located between the hip joint and knee joint. The leg is specifically the region between the knee joint and the ankle joint. Distal to the ankle is the foot. The lower limb contains 30 bones. These are the femur, patella, tibia, fibula, tarsal bones, metatarsal bones, and phalanges (see Figure 8.1). The femur is the single bone of the thigh. The patella is the kneecap and articulates with the distal femur. The tibia is the larger, weight-bearing bone located on the medial side of the leg, and the fibula is the thin bone of the lateral leg. The bones of the foot are divided into three groups. The posterior portion of the foot is formed by a group of seven bones, each of which is known as a tarsal bone, whereas the midfoot contains five elongated bones, each of which is a metatarsal bone. The toes contain 14 small bones, each of which is a phalanx bone of the foot.
Femur
The femur, or thigh bone, is the single bone of the thigh region (Figure 8.12). It is the longest and strongest bone of the body and accounts for approximately one-quarter of a person’s total height. The rounded, proximal end is the head of the femur, which articulates with the acetabulum of the hip bone to form the hip joint. The fovea capitis is a minor indentation on the medial side of the femoral head that serves as the site of attachment for the ligament of the head of the femur. This ligament spans the femur and acetabulum but is weak and provides little support for the hip joint. It does, however, carry an important artery that supplies the head of the femur.
Figure 8.12 Femur and Patella. The femur is the single bone of the thigh region. It articulates superiorly with the hip bone at the hip joint and inferiorly with the tibia at the knee joint. The patella only articulates with the distal end of the femur.
The narrowed region below the head is the neck of the femur. This is a common area for fractures of the femur. The greater trochanter is the large, upward bony projection located above the base of the neck. Multiple muscles that act across the hip joint attach to the greater trochanter, which, because of its projection from the femur, gives additional leverage to these muscles. The greater trochanter can be felt just under the skin on the lateral side of your upper thigh. The lesser trochanter is a small, bony prominence that lies on the medial aspect of the femur, just below the neck. A single, powerful muscle attaches to the lesser trochanter. Running between the greater and lesser trochanters on the anterior side of the femur is the roughened intertrochanteric line. The trochanters are also connected on the posterior side of the femur by the larger intertrochanteric crest.
The elongated shaft of the femur has a slight anterior bowing or curvature. At its proximal end, the posterior shaft has the gluteal tuberosity, a roughened area extending inferiorly from the greater trochanter. More inferiorly, the gluteal tuberosity becomes continuous with the linea aspera. This is the roughened ridge that passes distally along the posterior side of the mid-femur. Multiple muscles of the hip and thigh regions make long, thin attachments to the femur along the linea aspera.
The distal end of the femur has medial and lateral bony expansions. On the lateral side, the smooth portion that covers the distal and posterior aspects of the lateral expansion is the lateral condyle of the femur. The roughened area on the outer, lateral side of the condyle is the lateral epicondyle of the femur. Similarly, the smooth region of the distal and posterior medial femur is the medial condyle of the femur, and the irregular outer, medial side of this is the medial epicondyle of the femur. The lateral and medial condyles articulate with the tibia to form the knee joint. The epicondyles provide attachment for muscles and supporting ligaments of the knee. Posteriorly, the medial and lateral condyles are separated by a deep depression called the intercondylar fossa. Anteriorly, the smooth surfaces of the condyles join together to form a wide groove called the patellar surface, which provides for articulation with the patella bone. The combination of the medial and lateral condyles with the patellar surface gives the distal end of the femur a horseshoe (U) shape.
Patella
The patella (kneecap) is the largest sesamoid bone of the body (see Figure 8.12). A sesamoid bone is a bone that is incorporated into the tendon of a muscle where that tendon crosses a joint. The sesamoid bone articulates with the underlying bones to prevent damage to the muscle tendon due to rubbing against the bones during movements of the joint. The patella is found in the tendon of the quadriceps femoris muscle, the large muscle of the anterior thigh that passes across the anterior knee to attach to the tibia. The patella articulates with the patellar surface of the femur and thus prevents rubbing of the muscle tendon against the distal femur. The patella also lifts the tendon away from the knee joint, which increases the leverage power of the quadriceps femoris muscle as it acts across the knee. The patella does not articulate with the tibia.
Tibia
The tibia (shin bone) is the medial bone of the leg and is larger than the fibula, with which it is paired (Figure 8.13). The tibia is the main weight-bearing bone of the lower leg and the second-longest bone of the body, after the femur. The medial side of the tibia is located immediately under the skin, allowing it to be easily palpated down the entire length of the medial leg.
The proximal end of the tibia is greatly expanded. The two sides of this expansion form the medial condyle of the tibia and the lateral condyle of the tibia. The tibia does not have epicondyles. The top surface of each condyle is smooth and flattened. These areas articulate with the medial and lateral condyles of the femur to form the knee joint. Between the articulating surfaces of the tibial condyles is the intercondylar eminence, an irregular, elevated area that serves as the inferior attachment point for two supporting ligaments of the knee.
Figure 8.13 Tibia and Fibula. The tibia is the larger, weight-bearing bone located on the medial side of the leg. The fibula is the slender bone of the lateral side of the leg and does not bear weight.
The tibial tuberosity is an elevated area on the anterior side of the tibia, near its proximal end. It is the final site of attachment for the muscle tendon associated with the patella. More inferiorly, the shaft of the tibia becomes triangular in shape.
The anterior apex of this triangle forms the anterior border of the tibia, which begins at the tibial tuberosity and runs inferiorly along the length of the tibia. Both the anterior border and the medial side of the triangular shaft are located immediately under the skin and can be easily palpated along the entire length of the tibia.
The large expansion found on the medial side of the distal tibia is the medial malleolus. This forms the large bony bump found on the medial side of the ankle region. Both the smooth surface on the inside of the medial malleolus and the smooth area at the distal end of the tibia articulate with the talus bone of the foot as part of the ankle joint. On the lateral side of the distal tibia is a wide groove called the fibular notch.
Fibula
The fibula is the slender bone located on the lateral side of the leg (see Figure 8.13). The fibula does not bear weight. It serves primarily for muscle attachments and thus is largely surrounded by muscles. Only the proximal and distal ends of the fibula can be palpated.
The head of the fibula is the small, knoblike, proximal end of the fibula. The thin shaft of the fibula has the interosseous border of the fibula, a narrow ridge running down its medial side for the attachment of the interosseous membrane that spans the fibula and tibia. The distal end of the fibula forms the lateral malleolus, which forms the easily palpated bony bump on the lateral side of the ankle. The deep (medial) side of the lateral malleolus articulates with the talus bone of the foot as part of the ankle joint. The distal fibula also articulates with the fibular notch of the tibia.
Tarsal Bones
The posterior half of the foot is formed by seven tarsal bones (Figure 8.14). The most superior bone is the talus. This has a relatively square-shaped upper surface that articulates with the tibia and fibula to form the ankle joint. Three areas of articulation form the ankle joint: The superomedial surface of the talus bone articulates with the medial malleolus of the tibia, the top of the talus articulates with the distal end of the tibia, and the lateral side of the talus articulates with the lateral malleolus of the fibula. Inferiorly, the talus articulates with the calcaneus (heel bone), the largest bone of the foot, which forms the heel. Body weight is transferred from the tibia to the talus to the calcaneus, which rests on the ground.
The cuboid bone articulates with the anterior end of the calcaneus bone. The cuboid has a deep groove running across its inferior surface, which provides passage for a muscle tendon. The talus bone articulates anteriorly with the navicular bone, which in turn articulates anteriorly with the three cuneiform bones. These bones are the medial cuneiform, the intermediate cuneiform, and the lateral cuneiform. Each of these bones has a broad superior surface and a narrow inferior surface, which together produce the transverse (medial-lateral) curvature of the foot. The navicular and lateral cuneiform bones also articulate with the medial side of the cuboid bone.
Figure 8.14 Bones of the Foot. The bones of the foot are divided into three groups. The posterior foot is formed by the seven tarsal bones. The midfoot has the five metatarsal bones. The toes contain the phalanges.
Metatarsal Bones
The anterior half of the foot is formed by the five metatarsal bones, which are located between the tarsal bones of the posterior foot and the phalanges of the toes (see Figure 8.14). These elongated bones are numbered 1–5, starting with the medial side of the foot. The first metatarsal bone is shorter and thicker than the others. The second metatarsal is the longest. The base of the metatarsal bone is the proximal end of each metatarsal bone. These articulate with the cuboid or cuneiform bones. The base of the fifth metatarsal has a large, lateral expansion that provides for muscle attachments. This expanded base of the fifth metatarsal can be felt as a bony bump at the midpoint along the lateral border of the foot. The expanded distal end of each metatarsal is the head of the metatarsal bone.
Phalanges
The toes contain a total of 14 phalanx bones (phalanges), arranged in a similar manner to that of the phalanges of the fingers (see Figure 8.14). The toes are numbered 1–5, starting with the big toe (hallux). The big toe has two phalanx bones, the proximal and distal phalanges. The remaining toes all have proximal, middle, and distal phalanges. A joint between adjacent phalanx bones is called an interphalangeal joint.
Arches of the Foot
When the foot comes into contact with the ground during walking, running, or jumping activities, the impact of the body weight puts a tremendous amount of pressure and force on the foot. During running, the force applied to each foot as it contacts the ground can be up to 2.5 times your body weight. The bones, joints, ligaments, and muscles of the foot absorb this force, thus greatly reducing the amount of shock that is passed superiorly into the lower limb and body. The arches of the foot play an important role in this shock-absorbing ability. When weight is applied to the foot, these arches will flatten somewhat, thus absorbing energy. When the weight is removed, the arch rebounds, giving “spring” to the step. The arches also serve to distribute body weight side to side and to either end of the foot.
The foot has a transverse arch, a medial longitudinal arch, and a lateral longitudinal arch (see Figure 8.14). The transverse arch forms the medial-lateral curvature of the midfoot. It is formed by the wedge shapes of the cuneiform bones and bases (proximal ends) of the first to fourth metatarsal bones. This arch helps distribute body weight from side to side within the foot, thus allowing the foot to accommodate uneven terrain.
The longitudinal arches run down the length of the foot. The lateral longitudinal arch is relatively flat, whereas the medial longitudinal arch is larger (taller). The longitudinal arches are formed by the tarsal bones posteriorly and the metatarsal bones anteriorly. These arches are supported at either end, where they contact the ground. This support is provided posteriorly by the calcaneus bone and anteriorly by the heads (distal ends) of the metatarsal bones.
The talus bone, which receives the weight of the body, is located at the top of the longitudinal arches. Body weight is then conveyed from the talus to the ground by the anterior and posterior ends of these arches. Strong ligaments unite the adjacent foot bones to prevent disruption of the arches during weight-bearing. On the bottom of the foot, additional ligaments tie together the anterior and posterior ends of the arches. These ligaments have elasticity, which allows them to stretch somewhat during weight-bearing, thus allowing the longitudinal arches to spread. The stretching of these ligaments stores energy within the foot rather than passing these forces on to the leg. Contraction of the foot muscles also plays an important role in this energy absorption. When the weight is removed, the elastic ligaments recoil and pull the ends of the arches closer together. This recovery of the arches releases the stored energy and improves the energy efficiency of walking.
Key Terms
- acetabulum:
- Large, cup-shaped cavity located on the lateral side of the hip bone; formed by the junction of the ilium, pubis, and ischium portions of the hip bone.
- acromial (lateral) end of the clavicle:
- Lateral end of the clavicle that articulates with the acromion of the scapula.
- acromion (acromial process):
- Flattened bony process that extends laterally from the scapular spine to form the bony tip of the shoulder.
- anatomical neck:
- Line on the humerus located around the outside margin of the humeral head.
- ankle joint:
- Joint that separates the leg and foot portions of the lower limb; formed by the articulations between the talus bone of the foot inferiorly, and the distal end of the tibia, medial malleolus of the tibia, and lateral malleolus of the fibula superiorly.
- anterior border of the tibia:
- Narrow, anterior margin of the tibia that extends inferiorly from the tibial tuberosity.
- arm:
- Region of the upper limb located between the shoulder and elbow joints; contains the humerus bone.
- base of the metatarsal bone:
- Expanded, proximal end of each metatarsal bone.
- bony pelvis:
- The entire structure formed by the two hip bones, the sacrum, and, attached inferiorly to the sacrum, the coccyx.
- calcaneus:
- Heel bone; posterior, inferior tarsal bone that forms the heel of the foot.
- capitulum:
- Knoblike bony structure located anteriorly on the lateral, distal end of the humerus.
- carpal bones:
- Eight small bones that form the wrist and base of the hand; these are grouped as a proximal row consisting of (from lateral to medial) the scaphoid, lunate, triquetrum, and pisiform bones, and a distal row containing (from lateral to medial) the trapezium, trapezoid, capitate, and hamate bones.
- carpal tunnel:
- Passageway between the anterior forearm and hand formed by the carpal bones and flexor retinaculum.
- clavicle:
- Collarbone; elongated bone that articulates with the manubrium of the sternum medially and the acromion of the scapula laterally.
- coracoid process:
- Short, hooklike process that projects anteriorly and laterally from the superior margin of the scapula.
- coronoid process of the ulna:
- Projecting bony lip located on the anterior, proximal ulna; forms the inferior margin of the trochlear notch.
- coxal bone:
- Hip bone.
- cuboid:
- Tarsal bone that articulates posteriorly with the calcaneus bone, medially with the lateral cuneiform bone, and anteriorly with the fourth and fifth metatarsal bones.
- deltoid tuberosity:
- Roughened, V-shaped region located laterally on the midshaft of the humerus.
- elbow joint:
- Joint located between the upper arm and forearm regions of the upper limb; formed by the articulations between the trochlea of the humerus and the trochlear notch of the ulna, and the capitulum of the humerus and the head of the radius.
- femur:
- Thigh bone; the single bone of the thigh.
- fibula:
- Thin, non-weight-bearing bone found on the lateral side of the leg.
- fibular notch:
- Wide groove on the lateral side of the distal tibia for articulation with the fibula at the distal tibiofibular joint.
- flexor retinaculum:
- Strong band of connective tissue at the anterior wrist that spans the top of the U-shaped grouping of the carpal bones to form the roof of the carpal tunnel.
- foot:
- Portion of the lower limb located distal to the ankle joint.
- forearm:
- Region of the upper limb located between the elbow and wrist joints; contains the radius and ulna bones.
- fossa (plural = fossae):
- Shallow depression on the surface of a bone.
- fovea capitis:
- Minor indentation on the head of the femur that serves as the site of attachment for the ligament to the head of the femur.
- glenoid cavity (also glenoid fossa):
- Shallow depression located on the lateral scapula, between the superior and lateral borders.
- gluteal tuberosity:
- Roughened area on the posterior side of the proximal femur, extending inferiorly from the base of the greater trochanter.
- greater pelvis (also greater pelvic cavity or false pelvis):
- Broad space above the pelvic brim defined laterally by the fanlike portion of the upper ilium.
- greater sciatic notch:
- Large, U-shaped indentation located on the posterior margin of the ilium, superior to the ischial spine.
- greater trochanter:
- Large, bony expansion of the femur that projects superiorly from the base of the femoral neck.
- greater tubercle:
- Enlarged prominence located on the lateral side of the proximal humerus.
- hallux:
- Big toe; digit 1 of the foot.
- hand:
- Region of the upper limb distal to the wrist joint.
- head of the femur:
- Rounded, proximal end of the femur that articulates with the acetabulum of the hip bone to form the hip joint.
- head of the fibula:
- Small, knoblike, proximal end of the fibula; articulates with the inferior aspect of the lateral condyle of the tibia.
- head of the humerus:
- Smooth, rounded region on the medial side of the proximal humerus; articulates with the glenoid fossa of the scapula to form the glenohumeral (shoulder) joint.
- head of the metatarsal bone:
- Expanded, distal end of each metatarsal bone.
- head of the radius:
- Disc-shaped structure that forms the proximal end of the radius; articulates with the capitulum of the humerus as part of the elbow joint, and with the radial notch of the ulna as part of the proximal radioulnar joint.
- head of the ulna:
- Small, rounded distal end of the ulna; articulates with the ulnar notch of the distal radius, forming the distal radioulnar joint.
- hip bone:
- Coxal bone; one of two paired bones that form the pelvic girdle; each consists of three areas: the ilium, ischium, and pubis.
- hip joint:
- Joint located at the proximal end of the lower limb; formed by the articulation between the acetabulum of the hip bone and the head of the femur.
- humerus:
- Single bone of the upper arm.
- iliac crest:
- Curved, superior margin of the ilium.
- iliac fossa:
- Shallow depression found on the anterior and medial surfaces of the upper ilium.
- ilium:
- Superior portion of the hip bone.
- inferior angle of scapula:
- The most inferior portion of the scapula, particularly important because it serves as the attachment point for several powerful muscles involved in shoulder and upper limb movements.
- inferior pubic ramus:
- Narrow segment of bone that passes inferiorly and laterally from the pubic body; joins with the ischial ramus to form the ischiopubic ramus.
- infraspinous fossa:
- Broad depression located on the posterior scapula, inferior to the spine.
- intercondylar eminence:
- Irregular elevation on the superior end of the tibia, between the articulating surfaces of the medial and lateral condyles.
- intercondylar fossa:
- Deep depression on the posterior side of the distal femur that separates the medial and lateral condyles.
- intermediate cuneiform:
- Middle of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, medially with the medial cuneiform bone, laterally with the lateral cuneiform bone, and anteriorly with the second metatarsal bone.
- interosseous border of the fibula:
- Small ridge running down the medial side of the fibular shaft for attachment of the interosseous membrane between the fibula and tibia.
- intertrochanteric crest:
- Short, prominent ridge running between the greater and lesser trochanters on the posterior side of the proximal femur.
- intertrochanteric line:
- Small ridge running between the greater and lesser trochanters on the anterior side of the proximal femur.
- ischial ramus:
- Bony extension projecting anteriorly and superiorly from the ischial tuberosity; joins with the inferior pubic ramus to form the ischiopubic ramus.
- ischial spine:
- Pointed, bony projection from the posterior margin of the ischium that separates the greater sciatic notch and lesser sciatic notch.
- ischial tuberosity:
- Large, roughened protuberance that forms the posteroinferior portion of the hip bone; weight-bearing region of the pelvis when sitting.
- ischiopubic ramus:
- Narrow extension of bone that connects the ischial tuberosity to the pubic body; formed by the junction of the ischial ramus and inferior pubic ramus.
- ischium:
- Posteroinferior portion of the hip bone.
- knee joint:
- Joint that separates the thigh and leg portions of the lower limb; formed by the articulations between the medial and lateral condyles of the femur, and the medial and lateral condyles of the tibia.
- lateral condyle of the femur:
- Smooth, articulating surface that forms the distal and posterior sides of the lateral expansion of the distal femur.
- lateral condyle of the tibia:
- Lateral, expanded region of the proximal tibia that includes the smooth surface that articulates with the lateral condyle of the femur as part of the knee joint.
- lateral cuneiform:
- Most lateral of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, medially with the intermediate cuneiform bone, laterally with the cuboid bone, and anteriorly with the third metatarsal bone.
- lateral epicondyle of the femur:
- Roughened area of the femur located on the lateral side of the lateral condyle.
- lateral malleolus:
- Expanded distal end of the fibula.
- leg:
- Portion of the lower limb located between the knee and ankle joints.
- lesser pelvis (also lesser pelvic cavity or true pelvis):
- Narrow space located within the pelvis, defined superiorly by the pelvic brim (pelvic inlet) and inferiorly by the pelvic outlet.
- lesser sciatic notch:
- Shallow indentation along the posterior margin of the ischium, inferior to the ischial spine.
- lesser trochanter:
- Small, bony projection on the medial side of the proximal femur, at the base of the femoral neck.
- lesser tubercle:
- Small, bony prominence located on the anterior side of the proximal humerus.
- ligament of the head of the femur:
- Ligament that spans the acetabulum of the hip bone and the fovea capitis of the femoral head.
- linea aspera:
- Longitudinally running bony ridge located in the middle third of the posterior femur.
- medial condyle of the femur:
- Smooth, articulating surface that forms the distal and posterior sides of the medial expansion of the distal femur.
- medial condyle of the tibia:
- Medial, expanded region of the proximal tibia that includes the smooth surface that articulates with the medial condyle of the femur as part of the knee joint.
- medial cuneiform:
- Most medial of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, laterally with the intermediate cuneiform bone, and anteriorly with the first and second metatarsal bones.
- medial epicondyle of the femur:
- Roughened area of the distal femur located on the medial side of the medial condyle.
- medial malleolus:
- Bony expansion located on the medial side of the distal tibia.
- metacarpal bone:
- One of the five long bones that form the palm of the hand; numbered 1–5, starting on the lateral (thumb) side of the hand.
- metatarsal bone:
- One of the five elongated bones that form the anterior half of the foot; numbered 1–5, starting on the medial side of the foot.
- navicular:
- Tarsal bone that articulates posteriorly with the talus bone, laterally with the cuboid bone, and anteriorly with the medial, intermediate, and lateral cuneiform bones.
- neck of the femur:
- Narrowed region located inferior to the head of the femur.
- neck of the radius:
- Narrowed region immediately distal to the head of the radius.
- obturator foramen:
- Large opening located in the anterior hip bone, between the pubis and ischium regions.
- olecranon process:
- Expanded posterior and superior portions of the proximal ulna; forms the bony tip of the elbow.
- patella:
- Kneecap; the largest sesamoid bone of the body; articulates with the distal femur.
- patellar surface:
- Smooth groove located on the anterior side of the distal femur, between the medial and lateral condyles; site of articulation for the patella.
- pectoral girdle:
- Shoulder girdle; the set of bones, consisting of the scapula and clavicle, which attaches each upper limb to the axial skeleton.
- pelvic brim:
- Pelvic inlet; the dividing line between the greater and lesser pelvic regions; formed by the superior margin of the pubic symphysis, the pectineal lines of each pubis, the arcuate lines of each ilium, and the sacral promontory.
- pelvic girdle:
- Hip girdle; consists of a single hip bone, which attaches a lower limb to the sacrum of the axial skeleton.
- pelvic inlet:
- Pelvic brim.
- pelvic outlet:
- Inferior opening of the lesser pelvis; formed by the inferior margin of the pubic symphysis, the right and left ischiopubic rami and sacrotuberous ligaments, and the tip of the coccyx.
- pelvis:
- Ring of bone consisting of the right and left hip bones, the sacrum, and the coccyx.
- phalanx bone (plural = phalanges):
- One of the 28 bones that form the fingers, thumbs, and toes.
- pollex:
- Thumb; digit 1 of the hand.
- pubic arch:
- Bony structure formed by the pubic symphysis and the bodies and inferior pubic rami of the adjacent pubic bones.
- pubic body:
- Enlarged, medial portion of the pubis region of the hip bone.
- pubic symphysis:
- Joint formed by the articulation between the pubic bodies of the right and left hip bones.
- pubis:
- Anterior portion of the hip bone.
- radial tuberosity:
- Oval-shaped, roughened protuberance located on the medial side of the proximal radius.
- radiocarpal joint:
- Wrist joint; located between the forearm and hand regions of the upper limb; articulation formed proximally by the distal end of the radius and the fibrocartilaginous pad that unites the distal radius and ulna bone, and distally by the scaphoid, lunate, and triquetrum carpal bones.
- radius:
- Bone located on the lateral side of the forearm.
- sacroiliac joint:
- Joint formed by the articulation between the auricular surfaces of the sacrum and ilium.
- scapula:
- Shoulder blade bone located on the posterior side of the shoulder.
- shaft of the clavicle:
- Body of the clavicle bone.
- shaft of the femur:
- Cylindrically shaped region that forms the central portion of the femur.
- shaft of the fibula:
- Elongated, slender portion located between the expanded ends of the fibula.
- shaft of the humerus:
- Narrow, elongated, central region of the humerus.
- shaft of the radius:
- Narrow, elongated, central region of the radius.
- shaft of the tibia:
- Triangular, central portion of the tibia.
- shaft of the ulna:
- Narrow, elongated, central region of the ulna.
- spine of the scapula:
- Prominent ridge passing mediolaterally across the upper portion of the posterior scapular surface.
- sternal (medial) end of the clavicle:
- Medial end of the clavicle that articulates with the manubrium of the sternum.
- sternoclavicular joint:
- Articulation between the manubrium of the sternum and the sternal end of the clavicle; forms the only bony attachment between the pectoral girdle of the upper limb and the axial skeleton.
- styloid process of the radius:
- Pointed projection located on the lateral end of the distal radius.
- styloid process of the ulna:
- Short, bony projection located on the medial end of the distal ulna.
- subpubic angle:
- Inverted V-shape formed by the convergence of the right and left ischiopubic rami; this angle is greater than 80 degrees in females and less than 70 degrees in males.
- subscapular fossa:
- Broad depression located on the anterior (deep) surface of the scapula.
- superior pubic ramus:
- Narrow segment of bone that passes laterally from the pubic body to join the ilium.
- suprascapular notch:
- Small notch located along the superior border of the scapula, medial to the coracoid process.
- supraspinous fossa:
- Narrow depression located on the posterior scapula, superior to the spine.
- surgical neck:
- Region of the humerus where the expanded, proximal end joins with the narrower shaft.
- talus:
- Tarsal bone that articulates superiorly with the tibia and fibula at the ankle joint; also articulates inferiorly with the calcaneus bone and anteriorly with the navicular bone.
- tarsal bone:
- One of the seven bones that make up the posterior foot; includes the calcaneus, talus, navicular, cuboid, medial cuneiform, intermediate cuneiform, and lateral cuneiform bones.
- thigh:
- Portion of the lower limb located between the hip and knee joints.
- tibia:
- Shin bone; the large, weight-bearing bone located on the medial side of the leg.
- tibial tuberosity:
- Elevated area on the anterior surface of the proximal tibia.
- trochlea:
- Pulley-shaped region located medially at the distal end of the humerus; articulates at the elbow with the trochlear notch of the ulna.
- trochlear notch:
- Large, C-shaped depression located on the anterior side of the proximal ulna; articulates at the elbow with the trochlea of the humerus.
- ulna:
- Bone located on the medial side of the forearm.
- ulnar tuberosity:
- Roughened area located on the anterior, proximal ulna inferior to the coronoid process.
Chapter Review
8.1 The Pectoral Girdles
The pectoral girdle, consisting of the clavicle and the scapula, attaches each upper limb to the axial skeleton. The clavicle is an anterior bone whose sternal end articulates with the manubrium of the sternum at the sternoclavicular joint. The acromial end of the clavicle articulates with the acromion of the scapula at the acromioclavicular joint. This end is also anchored to the coracoid process of the scapula by the coracoclavicular ligament, which provides indirect support for the acromioclavicular joint. The clavicle supports the scapula, transmits the weight and forces from the upper limb to the trunk of the body, and protects the underlying nerves and blood vessels.
The scapula lies on the posterior aspect of the pectoral girdle. It mediates the attachment of the upper limb to the clavicle and contributes to the formation of the glenohumeral (shoulder) joint. This triangular bone has three sides called the medial, lateral, and superior borders. The suprascapular notch is located on the superior border. The scapula also has three corners, two of which are the superior and inferior angles. The third corner is occupied by the glenoid cavity. Posteriorly, the spine separates the supraspinous and infraspinous fossae and then extends laterally as the acromion. The subscapular fossa is located on the anterior surface of the scapula. The coracoid process projects anteriorly and passes beneath the lateral end of the clavicle. The distal carpal bone articulates with the scaphoid proximally, the second metacarpal distally, the trapezium laterally, and the capitate medially.
8.2 Bones of the Upper Limb
Each upper limb is divided into three regions and contains a total of 30 bones. The upper arm is the region located between the shoulder and elbow joints. This area contains the humerus. The proximal humerus consists of the head, which articulates with the scapula, the greater and lesser tubercles separated by the intertubercular (bicipital) groove, and the anatomical and surgical necks. The humeral shaft has the roughened area of the deltoid tuberosity on its lateral side. The distal humerus is flattened, forming a lateral ridge that terminates at the small lateral epicondyle. The medial side of the distal humerus has the large, medial epicondyle. The articulating surfaces of the distal humerus consist of the trochlea medially and the capitulum laterally. Depressions on the humerus that accommodate the forearm bones during bending (flexing) and straightening (extending) of the elbow include the radial fossa and the olecranon fossa.
The forearm is the region of the upper limb located between the elbow and wrist joints. This region contains two bones, the ulna medially and the radius on the lateral (thumb) side. The elbow joint is formed by the articulation between the trochlea of the humerus and the trochlear notch of the ulna, plus the articulation between the capitulum of the humerus and the head of the radius. The proximal ulna also has the olecranon process, forming an expanded posterior region, and the coronoid process and ulnar tuberosity on its anterior aspect. On the proximal radius, the narrowed region below the head is the neck; distal to this is the radial tuberosity. The shaft portions of both the ulna and radius have an interosseous border, whereas the distal ends of each bone have a pointed styloid process. The distal end of the radius articulates with the proximal carpal bones, but the ulna does not.
The base of the hand is formed by eight carpal bones. The carpal bones are united into two rows of bones. The proximal and distal carpal rows articulate with each other at the midcarpal joint. The carpal bones, together with the flexor retinaculum, also form the carpal tunnel of the wrist.
The five metacarpal bones form the palm of the hand. The metacarpal bones are numbered 1–5, starting with the thumb side. The first metacarpal bone is freely mobile, but the other bones are united as a group. The digits are also numbered 1–5, with the thumb being number 1. The fingers and thumb contain a total of 14 phalanges (phalanx bones). The thumb contains a proximal and a distal phalanx, whereas the remaining digits each contain proximal, middle, and distal phalanges.
8.3 The Pelvic Girdle and Pelvis
The pelvic girdle, consisting of a hip bone, serves to attach a lower limb to the axial skeleton. The hip bone articulates posteriorly at the sacroiliac joint with the sacrum, which is part of the axial skeleton. The right and left hip bones converge anteriorly and articulate with each other at the pubic symphysis. The combination of the hip bone, the sacrum, and the coccyx forms the pelvis. The pelvis has a pronounced anterior tilt. The primary function of the pelvis is to support the upper body and transfer body weight to the lower limbs. It also serves as the site of attachment for multiple muscles.
The hip bone consists of three regions: the ilium, ischium, and pubis. The ilium forms the large, fanlike region of the hip bone. The medial surface of the upper ilium forms the iliac fossa, with the arcuate line marking the inferior limit of this area. The posterior margin of the ilium has the large greater sciatic notch.
The posterolateral portion of the hip bone is the ischium. It has the expanded ischial tuberosity, which supports body weight when sitting. The ischial ramus projects anteriorly and superiorly. The posterior margin of the ischium has the shallow lesser sciatic notch and the ischial spine, which separates the greater and lesser sciatic notches.
The pubis forms the anterior portion of the hip bone. The body of the pubis articulates with the pubis of the opposite hip bone at the pubic symphysis. The inferior pubic ramus projects inferiorly and laterally. The inferior pubic ramus joins the ischial ramus to form the ischiopubic ramus. The subpubic angle is formed by the medial convergence of the right and left ischiopubic rami.
The lateral side of the hip bone has the cuplike acetabulum, which is part of the hip joint. The large anterior opening is the obturator foramen. The sacroiliac joint is supported by the anterior and posterior sacroiliac ligaments. The sacrum is also joined to the hip bone by the sacrospinous ligament, which attaches to the ischial spine, and the sacrotuberous ligament, which attaches to the ischial tuberosity. The sacrospinous and sacrotuberous ligaments contribute to the formation of the greater and lesser sciatic foramina.
The broad space of the upper pelvis is the greater pelvis, and the narrow, inferior space is the lesser pelvis. These areas are separated by the pelvic brim (pelvic inlet). The inferior opening of the pelvis is the pelvic outlet. Compared to the male, the female pelvis is wider to accommodate childbirth, has a larger subpubic angle, and has a broader greater sciatic notch.
8.4 Bones of the Lower Limb
The lower limb is divided into three regions. These are the thigh, located between the hip and knee joints; the leg, located between the knee and ankle joints; and, distal to the ankle, the foot. There are 30 bones in each lower limb. These are the femur, patella, tibia, fibula, seven tarsal bones, five metatarsal bones, and 14 phalanges.
The femur is the single bone of the thigh. Its rounded head articulates with the acetabulum of the hip bone to form the hip joint. The head has the fovea capitis for attachment of the ligament of the head of the femur.
The narrow neck joins inferiorly with the greater and lesser trochanters. Passing between these bony expansions are the intertrochanteric line on the anterior femur and the larger intertrochanteric crest on the posterior femur. On the posterior shaft of the femur is the gluteal tuberosity proximally and the linea aspera in the midshaft region. The expanded distal end consists of three articulating surfaces: the medial and lateral condyles and the patellar surface. The outside margins of the condyles are the medial and lateral epicondyles.
The patella is a sesamoid bone located within a muscle tendon. It articulates with the patellar surface on the anterior side of the distal femur, thereby protecting the muscle tendon from rubbing against the femur.
The leg contains the large tibia on the medial side and the slender fibula on the lateral side. The tibia bears the weight of the body, whereas the fibula does not bear weight.
The proximal tibia consists of the expanded medial and lateral condyles, which articulate with the medial and lateral condyles of the femur to form the knee joint. Between the tibial condyles is the intercondylar eminence. On the anterior side of the proximal tibia is the tibial tuberosity, which is continuous inferiorly with the anterior border of the tibia. The bony expansion on the medial side of the distal tibia is the medial malleolus. The groove on the lateral side of the distal tibia is the fibular notch.
The head of the fibula forms the proximal end and articulates with the underside of the lateral condyle of the tibia. The distal fibula articulates with the fibular notch of the tibia. The expanded distal end of the fibula is the lateral malleolus.
The posterior foot is formed by the seven tarsal bones. The talus articulates superiorly with the distal tibia, the medial malleolus of the tibia, and the lateral malleolus of the fibula to form the ankle joint. The talus articulates inferiorly with the calcaneus bone. Anterior to the talus is the navicular bone, and anterior to this are the medial, intermediate, and lateral cuneiform bones. The cuboid bone is anterior to the calcaneus.
The five metatarsal bones form the anterior foot. The bases of these bones articulate with the cuboid or cuneiform bones. The metatarsal heads, at their distal ends, articulate with the proximal phalanges of the toes. The big toe (toe number 1) has proximal and distal phalanx bones. The remaining toes have proximal, middle, and distal phalanges.