Week 6

skeletal remains

"JOHN/JANE DOE, SKELETAL REMAINS, AGE UNKNOWN" is the initial identification given by law enforcement officials to the bones of an unidentified human being. The bones may have been found in the woods by a hiker or a hunter, or in a field after a farmer harvests his crops. Bones may be uncovered when a building is demolished, or if natural events such as floods or earthquakes disrupt the soil. Regardless of how human bones are found, questions must be answered. Who was this person? Was this a male or a female, and how old? What was the person's ethnicity? How did the person die, and how long ago? Was this person murdered, or did death come from natural causes? It's the job of a forensic anthropologist to collect, analyze, and ultimately identify the remains. Forensic anthropologists typically have extensive training in the structure of the human skeleton and are able to examine the features of the recovered bones. These scientists rely on a national forensic analysis data bank that contains measurements and observations from thousands of skeletons. In addition, forensic anthropologists are routinely called upon to testify in criminal cases as to a victim's time and cause of death. Clues about the identity and history of a deceased person can be found throughout the skeleton. Age is approximated by dentition—the structure of the teeth in the upper jaw (maxilla) and lower jaw (mandible). For example, infants aged 0-4 months have no teeth present; children aged approximately 6 through 10 have missing deciduous, or "baby" teeth; young adults acquire their last molars, or "wisdom teeth," around age 20. The age of older adults can be approximated by the number and location of missing or broken teeth. In addition, ossification of bones—that is, replacement of a baby/child's incomplete cartilage skeleton with bone—continues in an orderly fashion until about the age of 20. Studying areas of bone ossification also gives clues to the age of the deceased at the time of death. In older adults, signs of joint breakdown provide additional information about age. Hyaline cartilage becomes worn, yellowed, and brittle with age, and the hyaline cartilages covering bone ends wear down over time. The amount of yellowed, brittle, or missing cartilage helps scientists to estimate the person's age. If skeletal remains include the individual's pelvic bones, these provide the best method for determining an adult's gender (see pages 120-121). The long bones, particularly the humerus and femur, give information about gender as well. Long bones are thicker and denser in males, and points of muscle attachment are bigger and more prominent. The skull of a male has a square chin and more prominent ridges above the eye sockets or orbits (Figure 6B). Figure 6B Gender differences of the skull. (a) Note that the female skull is smaller, more delicate, and has a pointed chin. (b) The male skull is large, bulky, and has a squared-off chin. © Robert Marien/Spirit/Corbis Determining the ethnic origin of skeletal remains can be difficult because so many people have a mixed racial heritage. Forensic anthropologists rely on observed racial characteristics of the skull. In general, individuals of African or African American descent have a greater distance between the eyes, eye sockets that are roughly rectangular, and a jaw that is large and prominent. Skulls of Native Americans typically have round eye sockets, prominent cheek (zygomatic) bones, and a rounded palate. Caucasian skulls usually have a U-shaped palate and a visible suture line between the frontal bones. Additionally, the external ear canals in Caucasians are long and straight, so that the auditory ossicles (tiny bones built inside the temporal bone and used for hearing) are visible. Once the identity of the individual has been determined, the skeletal remains can be returned to the victim's family for proper burial. Although this can be a sorrowful event, the return of physical remains provides closure and solace to many families. For this reason, special teams of forensic anthropologists employed by the U.S. military are currently researching the identities of bones from soldiers who fought in World War II, as well as the Korean, Vietnam, Gulf, and Iraq/Afghanistan wars. Ancestral remains from Native Americans are protected by the Native American Grave Protection and Repatriation Act, and must be returned to the leadership of the tribe.

Osteoporosis

Imagine how your world would change if you lived with severe back pain. Not the kind that can be fixed with an Icy Hot® patch; rather, this variety only responds to drugs whose side effects might include dizziness and falling. And you're terrified of falling, because you've seen your friends and loved ones break bones after what should have been a trivial misstep. For those with osteoporosis, this pain and fear could be a daily reality. Osteoporosis is a condition caused by a reduction in density of individual bones that make up the skeleton. These weakened bones are particularly susceptible to painful and debilitating fractures, especially at the hip, vertebrae, long bones, and pelvis. Complications of these fractures can be very dangerous and potentially fatal to an older person. Simply managing pain often requires medication with serious side effects; some drugs can be addicting as well. Further, as you learned in Chapter 5, an older person immobilized by a fracture is prone to decubitus ulcers and may contract pneumonia while hospitalized. Moreover, any bedridden person is at increased risk for forming a thromboembolism, an abnormal blood clot inside blood vessels. These clots can block arteries to the heart or brain, resulting in heart attack or stroke. Although osteoporosis can result from various disease processes, it's essentially a disease of aging. Bones are continuously remodeled—built up, broken down, built up again—throughout life. In childhood, bone formation is greater than bone breakdown, and skeletal density increases until approximately age 25. Afterward, rates of bone formation and breakdown are roughly equal for the next two decades, until age 45 to 50. Then, reabsorption begins to exceed formation, and bone density slowly decreases. Over time, men are apt to lose 25%, and women 35%, of bone mass. Male bones are generally denser than female bones because testosterone (the male sex hormone) promotes bone formation and doesn't significantly decline until after about age 65. In contrast, estrogen (female sex hormone), which promotes women's bone formation, begins to decline at about age 45 with the onset of menopause. These differences in hormone levels mean that women are more likely than men to suffer osteoporosis. Women with a slight build are at greatest risk, especially those of Caucasian and Asian descent. If osteoporosis is detected early enough, treatment can slow or stop bone density decrease. Older at-risk individuals, especially postmenopausal women, should be tested using dual-energy X-ray absorptiometry (DEXA), a specialized exam used to measure bone density. DEXA can be followed by blood and urine tests to detect high levels of calcium and biochemicals that are associated with bone loss. Early bone thinning, called osteopenia, should be aggressively treated to restore bone density and reduce fracture risk. The most commonly used drugs, called bisphosphonates (Fosamax" Actonel") inhibit bone-resorbing osteoclast cells. Hormone therapy is another option, but it is used less often simply because bisphosphonates are so effective. Calcitonin and parathyroid hormone are the body's two naturally occurring hormones for calcium homeostasis. Calcitonin can be administered as a nasal spray or an injection to inhibit osteoclasts and to slow bone thinning. Parathyroid hormone is given by injection to high-risk patients to stimulate osteoblast cells to build new bone. To slow bone loss, estrogen is used for postmenopausal women and testosterone can be given to men. However, sex hormone therapy must be carefully monitored because these hormones may trigger the growth of certain reproductive tissue cancers. The breast cancer drugs tamoxifen and raloxifene are also used occasionally to stimulate the growth of new bone tissue. Whatever your age, race, or gender, there are steps you can take to avoid having osteoporosis when you get older. The most important thing you can do to protect your skeleton is to make sure your diet contains enough calcium. The U.S. National Institutes of Health advises that adults take in 1,000 mg of dietary calcium daily, accompanied by 600 IU (international units) of vitamin D to promote calcium absorption. After age 65, your calcium intake should increase to 1,200 mg. In addition, because older people have fewer vitamin D receptors in the intestinal tract, you'll need additional vitamin D as well: 800 IU are recommended. Get outside if you can, because the ultraviolet energy from mild sunlight exposure allows your skin to synthesize vitamin D. If you live on or north of an imaginary line drawn from Boston to Milwaukee, to Minneapolis, and then to Boise, chances are you're not getting enough vitamin D during the winter months. If this is the case, look for vitamin D found in fortified foods such as low-fat milk and cereal. Combine regular moderate exercise such as walking, cycling or jogging with weight training to restore and maintain bone strength. And if you're a smoker, quit! Cigarette toxins damage blood vessels, thus decreasing the blood supplied to bone. In addition, the nicotine and other chemicals from cigarette smoke destroy osteoblasts. You can find tips to help you quit smoking in Chapter 14.

Cartilaginous Joints

Where bones are joined by hyaline cartilage or fibrocartilage, the joint that forms is usually slightly movable. The ribs are joined to the sternum by costal cartilages, which are hyaline cartilage (see Fig. 6.11). The epiphyseal plate that separates the diaphysis and epiphyses of growing bones is also a hyaline cartilage joint. The bodies of adjacent vertebrae are separated by fibrocartilage intervertebral disks, which increase vertebral flexibility. The pubic symphysis, the joint between the two pubic bones (see Fig. 6.16), consists largely of fibrocartilage. Due to hormonal changes, this joint becomes more flexible during late pregnancy, allowing the pelvis to expand during childbirth.

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After birth, the epiphyses of a long bone continue to grow, but soon secondary ossification centers appear in these regions. Here spongy bone forms and doesn't break down. A band of cartilage called an epiphyseal plate remains between the primary ossification center and each secondary center. The limbs keep increasing in length and width as long as epiphyseal plates are still present. The rate of growth is controlled by hormones, such as growth hormones and the sex hormones. Eventually, the epiphyseal plates become ossified, and the bone stops growing in length. Long bone growth ends when the epiphyseal plates are ossified, but it is possible for bones to increase their diameter by Page 107appositional growth. In this process, osteoprogenitor cells in the inner periosteum convert to osteoblast cells, which in turn add more matrix to the outer surface of the bone. Osteoblasts in the matrix are then converted to osteocytes. Appositional growth causes the bone to become thicker and stronger.

back pain example

Back pain is going to be an inevitable part of almost everyone's life at some point. It might begin when you bend over to pick up a heavy load and stand up suddenly. Perhaps it comes on gradually with those extra 30 pounds you've put on over the last 10 years. Maybe it was caused by the fall when you were ice skating and landed abruptly on your posterior. Regardless of its cause, in 90% of cases, back pain will slowly improve over time with minimal treatment. Pain management, weight control, gentle massage, physical therapy, and exercise all help to make the patient comfortable and restore mobility. In all but about 5% of back pain cases, the pain is resolved within three months or less. Many back pain sufferers lack the patience and persistence to allow the back to heal itself normally. These folks often inquire about surgical options to alleviate their back pain. However, back and neck surgery is recommended only in the most extreme cases. For example, excessive movement of the vertebrae or compression of the spinal cord (as in a herniated disk, for example) are reasons to attempt back surgery. Surgery may also be required for those with nerve damage caused by kyphosis, scoliosis, or fractured vertebrae. Loss of bowel and/or bladder control, tingling in the arms or legs, or pain that spreads down arms or legs are all signs of nerve damage. Traditional surgeries include laminectomy, where the bony lamina is cut from the vertebra and surgically removed (the lamina is shown in Fig. 6.10b). This procedure can relieve pressure on a pinched spinal cord or spinal nerve. Removal of a herniated disk, called a diskectomy, is usually followed by fusion of vertebrae. However, once vertebrae are fused together, motion and flexibility between vertebrae are limited. Other available options seek to avoid removing the intervertebral disk, and thus avoid having to fuse vertebrae. Intradiscal electrothermal therapy (IDET) involves inserting a needle into a ruptured disk. The needle is heated to high temperatures for approximately 20 minutes. The tissues of the disk wall become thickened in response to the heat, and the ruptured area is sealed. A diskectomy and vertebral fusion won't be necessary because the disk will be able to heal. Vertebroplasty and kyphoplasty are techniques that allow compressed vertebrae to be lifted and separated from one another. In vertebroplasty, bone cement is directly injected into the space between two compressed vertebrae, while in kyphoplasty, a small balloon is inserted between the vertebrae and then inflated. Bone cement is injected into the space created by the balloon, expanding the existing vertebrae. Both of these techniques relieve pressure on the trapped spinal nerve. If vertebrae are fractured (in a car accident, for example), the same technique can be used. Artificial vertebral disks can completely replace an intervertebral disk for some patients. The artificial disk is similar to implants used for hip and knee implants. To install the artificial disk, the patient's own intervertebral disk is first removed, then two metal plates are surgically inserted onto the bodies of the superior and inferior vertebrae. In between, a polyethylene-covered titanium disk re-creates the space originally occupied by the intervertebral disk and allows normal motion of the spinal column.

anatomy of bones

Bones are classified according to their shape. As the name implies, long bones are longer than they are wide. Short bones are cube shaped—that is, their lengths and widths are about equal. Flat bones, such as those of the skull, are platelike with broad surfaces. Irregular bones have varied shapes that permit connections with other bones. Round bones are circular in shape (Fig. 6.1). A long bone, such as the one in Figure 6.2a, can be used to illustrate certain principles of bone anatomy. The bone is enclosed in a tough, fibrous, connective tissue covering called the periosteum, which is continuous with the ligaments that join bones and the tendons that anchor muscles to bones. The periosteum contains blood vessels that enter the bone and supply its cells. At both ends of a long bone is an expanded portion called an epiphysis ( pl., epiphyses); the portion between the epiphyses is called the diaphysis. As shown in the section of an adult bone in Figure 6.2, the diaphysis, or shaft, of a long bone, is not solid but has a medullary cavity containing yellow marrow. Yellow marrow contains large amounts of fat. The medullary cavity is bounded at the sides by compact bone. The epiphyses contain spongy bone. Beyond the spongy bone is a thin shell of compact bone and, finally, a layer of hyaline cartilage called the articular cartilage. Articular cartilage is so named because it occurs where bones articulate (come together to form a joint). Articulation is the joining together of bones at a joint. The medullary cavity and the spaces of spongy bone are lined with endosteum, a thin, fibrous membrane. In infants, red bone marrow, a specialized tissue that produces blood cells, is found in the medullary cavities of most bones. In adults, red blood cell formation, called hematopoiesis, occurs in the spongy bone of the skull, ribs, sternum (breastbone), and vertebrae, and in the ends of the long bones.

cells for bone growth/repair

Bones are composed of living tissues, as exemplified by their ability to grow and undergo repair. Several different types of cells are involved in bone growth and repair: Osteoprogenitor cells are unspecialized cells present in the inner portion of the periosteum, in the endosteum, and in the central canal of compact bone. Osteoblasts are bone-forming cells formed from osteoprogenitor cells. They are responsible for secreting the matrix characteristic of bone. Osteocytes are mature bone cells derived from osteoblasts. Once the osteoblasts are surrounded by matrix, they become the osteocytes in bone. Osteoclasts are thought to be derived from monocytes, a type of white blood cell present in red bone marrow. Osteoclasts perform bone resorption; that is, they break down bone and assist in depositing calcium and phosphate in the blood. The work of osteoclasts is important to the growth and repair of bon

joints

Bones articulate at the joints. There are two systems for classifying joints. First, joints can be classified according to the amount of movement they allow. A joint called a synarthrosis is immovable, while an amphiarthrosis allows slight movement. A diarthrosis joint is freely movable. The second classification system (and the convention followed here) is to categorize joints according to their structure: Fibrous joints occur where fibrous connective tissue joins bone to bone. These joints are typically immovable (thus, synarthrosis joints), although exceptions exist. Cartilaginous joints occur where fibrocartilage or hyaline cartilage joins bones. These are generally slightly movable (amphiarthrosis joints), with a few exceptions. Synovial joints are formed when bone ends do not contact each other, but are enclosed in a capsule. These are usually freely movable (diarthrosis joints). Again, there are a few exceptions.

effects of aging

Both cartilage and bone tend to gradually deteriorate as a person ages. The chemical nature of cartilage changes, and the bluish color typical of young cartilage changes to an opaque, yellowish color. The chondrocytes die, and reabsorption occurs as the cartilage undergoes calcification, becoming hard and brittle. Calcification interferes with the ready diffusion of nutrients and waste products through the matrix. The articular cartilage may no longer function properly, and symptoms of osteoarthritis can appear. As you know, decades of constant heavy use of a joint can speed the development of arthritis. Osteoporosis, discussed in the Medical Focus on page 106, is present when weak and thin bones lead to fractures. However, it's important to remember that many of the degenerative changes seen in cartilage and bone can be slowed or stopped by regular weight-bearing exercise.

compact bone

Compact bone, or dense bone, contains many cylinder-shaped units called osteons. Osteons are formed by concentric layers of matrix called lamellae. Between lamellae are lacunae, tiny chambers where osteocytes (bone cells) can be found. Canaliculi are small canals that connect lacunae. Oxygen and nutrients can pass through canaliculi to supply the osteocytes in each lacuna. The matrix contains collagenous protein fibers and mineral deposits, primarily of calcium and phosphorus salts. In each osteon, the lamellae and lacunae surround a single central canal. Canaliculi from adjacent lacunae open into the central canal, and blood vessels and nerves from the periosteum travel within it. These same blood vessels and nerves can travel from one central canal to another by way of perforating canals (Fig. 6.2). Because osteocytes send cell extensions into the canaliculi, the osteocytes are connected to each other and also to the central canal.

vertebrae

Figure 6.10a shows that a typical vertebra has an anteriorly placed body and a posteriorly placed vertebral arch. The vertebral arch forms the wall of a vertebral foramen (pl., foramina). When stacked on top of one another, the foramina become a canal through which the spinal cord passes. The structure of a single vertebra can be likened to a house (the vertebral arch) sitting on a hill (the body of the vertebra). Pedicles are the upright walls of the house and the laminae form a slanting roof. The single spinous process, or spine, is like a flagpole, and the transverse processes are gutters projecting sideways at the corners where pedicles join laminae. Each of these bony projections on an actual vertebra serves as a site for muscle attachment. In addition, superior and inferior articular processes form joints between an upper and a lower vertebra. When stacked this way, the articular processes create paired openings called intervertebral foramina on both sides of the vertebral column (see Fig. 6.8). Spinal nerves exit from the spinal cord through these openings and travel to both sides of the body. The vertebrae have regional differences. For example, as the vertebral column descends, the bodies get bigger and are better able to carry more weight. In the cervical region, the spines are short and tend to have a split, or bifurcation. The exception is the C7 vertebra, whose long spinous process is clearly seen posteriorly when a person touches his or her chin to the chest (try it!). Thus, C7 is the prominent vertebra, or in Latin, vertebra prominens. It's an important feature that allows health-care providers to determine the transition between cervical and thoracic vertebrae. In addition, cervical vertebrae all have an opening in the transverse process, called a transverse foramen. The vertebral arteries and veins pass through the first six transverse foramina (C1 to C6). The vertebral arteries help to supply blood to the brain, and the veins return blood to the heart. The thoracic and lumbar vertebrae also have their own unique structural features. The thoracic spines are long and slender and project downward. Further, the bodies and transverse processes of thoracic vertebrae have articular facets, called costal facets, for connecting to ribs. The lumbar spines are massive and square and project posteriorly. Atlas and Axis The first two cervical vertebrae are not typical (Fig. 6.10c). The atlas supports and balances the head. It has two depressions that articulate with the occipital condyles, allowing movement of the head up and down (as though nodding "yes"). The axis has an odontoid process (also called the dens) that projects Page 116into the ring of the atlas. When the head moves from side to side, the atlas pivots around the odontoid process (as though shaking the head "no"). Sacrum and Coccyx The five sacral vertebrae are fused to form the sacrum. The sacrum articulates with the pelvic girdle and forms the posterior wall of the pelvic cavity (see Fig. 6.16). The coccyx, or tailbone, is the last part of the vertebral column. It is formed from a fusion of three to five vertebrae.

remodeling of bones

In the adult, bone is continually being broken down and built up again. Osteoclasts derived from monocytes in red bone marrow break down bone, remove worn cells, and assist in depositing calcium in the blood. After a period of about three weeks, the osteoclasts disappear, and the bone is repaired by the work of osteoblasts. As they form new bone, osteoblasts take calcium from the blood. Eventually some of these cells get caught in the matrix they secrete and are converted to osteocytes, the cells found within the lacunae of osteons. Though it might seem strange, adults apparently require at least as much calcium in the diet (about 1,000 to 1,200 mg daily) as do actively growing children. Calcium promotes the work of osteoblasts in adults and children. Although adults no longer experience growth in the long bones, high levels of calcium are necessary to prevent osteoporosis. In osteoporosis, bones are thin, weak, and fracture easily (see the Medical Focus on osteoporosis, previous page). Growth of bone is a complex process involving over 20 different known hormones and other messenger chemicals. Three of the most important hormones that regulate bone growth are parathyroid hormone, calcitonin, and growth hormone. Their effects on bone are discussed in Chapter 10.

joint damage/repair

Joints can be damaged, and even destroyed, by overuse or chronic inflammation. Joint inflammation and destruction is termed arthritis. The most common form, osteoarthritis, is caused by deterioration of the articular cartilage of a joint. The damage might be caused by chronic overuse. Typical cases of osteoarthritis are seen in joints of older persons after decades of heavy use, or in knee joints of football players after constant misuse and/or abuse. Rheumatoid arthritis (RA) occurs when the synovial membrane becomes inflamed and grows thicker cartilage. RA is caused by an autoimmune reaction in which the body's immune system mistakenly attacks the synovial membrane. RA is more common with age, but it can occur in children and younger adults. Gout, or gouty arthritis, results from excessive buildup of uric acid (a metabolic waste) in the blood. Crystals of uric acid are deposited in the joints, causing inflammation. Arthritis causes joint pain and stiffness. The afflicted joint is often swollen and may feel warm to the touch. Without the protective hyaline cartilage, exposed bone ends can grate against each other and cause bone destruction. On an X ray, the joint space is thinner and narrower than normal. Treatment of arthritis should begin immediately to preserve function. Pain management is an important first step, followed by physical therapy and exercise. It's important that arthritis sufferers keep moving. Without regular exercise, the muscles around the joint will atrophy (shrink in size). Tendons and ligaments around a joint weaken, and the bones at a joint can be dislocated more easily. Tissue culture (growing cells outside of the patient's body in a special medium) can help younger people and athletes with knee or ankle injuries to regenerate their own hyaline cartilage. In autologous chondrocyte implantation (ACI) surgery, a piece of healthy hyaline cartilage from the patient's joint is first removed surgically. The chondrocyte cells are grown outside the body in tissue culture medium, and then injected into the joint and left to grow. However, ACI isn't always successful, and it can't be used for elderly or overweight patients. When other treatments for arthritis fail, surgical replacement of a joint can restore movement and relieve pain (Fig. 6.24). Knees and hips are the most common joints to be replaced, but shoulders, elbows, ankles, and even finger joints can be replaced with surgical implants. After ACI or joint replacement, the patient faces a lengthy rehabilitation. Physical therapy after ACI will stimulate cartilage growth without overstressing the area being repaired. In joint replacement patients, physical therapy will prevent muscle degeneration and promote bone growth around the new implant.

bones of face

Maxillae The two maxillae form the upper jaw. Aside from contributing to the floors of the orbits and to the sides of the floor of the nasal cavity, each maxilla has the following processes: alveolar process (Fig. 6.6a). The alveolar processes contain the tooth sockets for teeth: incisors, canines, premolars, and molars. palatine process (Fig. 6.7a). The left and right palatine processes form the anterior portion of the hard palate (roof of the mouth). Palatine Bones The two palatine bones contribute to the floor and lateral wall of the nasal cavity (Fig. 6.5). The horizontal plates of the palatine bones form the posterior portion of the hard palate (Fig. 6.7a). Notice that the hard palate consists of (1) portions of the maxillae (i.e., the palatine processes) and (2) horizontal plates of the palatine bones. A cleft palate results when either (1) or (2) have failed to fuse. Zygomatic Bones The two zygomatic bones form the sides of the orbits (Fig. 6.7a). They also contribute to the "cheekbones." Each zygomatic bone has a temporal process. A zygomatic arch, the most prominent feature of a cheekbone, consists of a temporal process connected to a zygomatic process (a portion of the temporal bone). Lacrimal Bones The two small, thin lacrimal bones are located on the medial walls of the orbits (Fig. 6.6). A small opening between the orbit and the nasal cavity serves as a pathway for a duct that carries tears from the eyes to the nose. Nasal Bones The two nasal bones are small, rectangular bones that form the bridge of the nose (see Fig. 6.5). The anterior distal portion of the nose is cartilage, which explains why the nose is not seen on a skull. Vomer Bone The vomer bone joins with the perpendicular plate of the ethmoid bone to form the nasal septum (see Figs. 6.5 and 6.6a). Inferior Nasal Conchae The two inferior nasal conchae are thin, curved bones that form a part of the inferior lateral wall of the nasal cavity (see Fig. 6.6a). Like the superior and middle nasal conchae, they project into the nasal cavity and support the mucous membranes that line the nasal cavity. Mandible The mandible, or lower jaw, is the only movable portion of the skull. The horseshoe-shaped front and horizontal sides of the mandible, referred to as the body, form the chin. The body has an alveolar process (see Fig. 6.6a), which contains tooth sockets. Superior to the left and right angle of the mandible are upright projections called rami. Each ramus has detailed features: mandibular condyle (see Fig. 6.6b), which articulates with a temporal bone; coronoid process (see Fig. 6.6b), which serves as a place of attachment for the muscles used for chewing.

broken bones

Raising a child is always an adventure, but having an active, busy child can bring its share of traumas. Wise parents don't want to limit their children's activities unless it's necessary for safety. Lively children often require emergency care for bone fractures. When energetic children grow into adolescence, they often suffer sports-related fractures as well. A fracture is complete if the bone is broken through and incomplete if the bone isn't separated into two parts. A fracture is simple if bone ends don't pierce the skin and compound if skin is torn open by bone. When the broken ends are wedged into each other, the fracture is impacted. A spiral fracture occurs when the break is ragged due to bone twisting. Repair of a fracture is called reduction. Closed reduction involves realigning the bone fragments into their normal position without surgery. Open reduction requires surgical repair of the bone using plates, screws, or pins. Parents or caregivers should always suspect a fracture if a child feels pain in a limb, or if the limb is swollen or bruised. If the child can't move the limb normally, or the limb appears deformed, a fracture is also likely. Emergency care of a fracture involves immobilization of the limb. A temporary splint can be created using rolled-up newspapers or magazines. Caregivers should constantly monitor the affected limb because nerves and blood vessels may be damaged by the injury. If tissues begin turning blue and/or a pulse can't be felt, blood vessel damage might be occurring. Tingling or numbness indicate possible nerve damage. Treatment must begin immediately in these situations. Pain management should begin as soon as possible—fractures are very painful! Fractures are typically diagnosed with X rays, but a CT scan or MRI is sometimes necessary. The fracture is permanently immobilized using a cast or splint. Bone repair occurs in a series of four steps (Fig. 6A): Hematoma—Within six to eight hours after a fracture, blood escapes from ruptured blood vessels and forms a hematoma (mass of clotted blood) in the space between the broken bones. Fibrocartilaginous callus—Tissue repair begins, and fibrocartilage fills the space between the ends of the broken bone. Bony callus—Osteoblasts produce trabeculae of spongy bone and convert the fibrocartilaginous callus to a bony callus that joins the broken bones together and lasts about three to four months. Remodeling—Osteoblasts build new compact bone at the periphery, and osteoclasts reabsorb the spongy bone, creating a new medullary cavity. In some ways, bone repair parallels the development of a bone. However, a hematoma indicates that injury has occurred. Fibrocartilage precedes the production of compact bone (instead of hyaline cartilage, as in growing bone). Parents and caregivers should also be aware that bone fractures may sometimes indicate child/elder abuse. In cases where abuse is suspected, health-care professionals are required by law to investigate the circumstances of the injury.

types of synovial joints

Saddle joint. Each bone is saddle-shaped and fits into the complementary regions of the other. A variety of movements are possible. Example: the joint between the carpal and metacarpal bones of the thumb. Ball-and-socket joint. The ball-shaped head of one bone fits into the cup-shaped socket of another. Movement in all planes, as well as rotation, are possible. Examples: the shoulder and hip joints. Pivot joint. A small, cylindrical projection of one bone pivots within the ring formed of bone and ligament of another bone. Only rotation is possible. Examples: the joint between the proximal ends of the radius and ulna, and the joint between the atlas and axis (see Fig. 6.10). Hinge joint. The convex surface of one bone articulates with the concave surface of another. Up-and-down motion in one plane is possible. Examples: the elbow and knee joints. Gliding joint. Flat or slightly curved surfaces of bones articulate. Sliding or twisting in various planes is possible. Examples: the joints between the bones of the wrist and between the bones of the ankle. Condyloid joint. The oval-shaped condyle of one bone fits into the elliptical cavity of another. Movement in different planes is possible, but rotation is not. Examples: the joints between the metacarpals and phalanges.

movements permitted

Skeletal muscles are attached to bones by tendons that cross joints. When a muscle contracts, one bone moves in relation to another bone. The more common types of movements are described here. Angular Movements (Fig. 6.23a): Flexion decreases the joint angle. Flexion of the elbow moves the forearm toward the arm; flexion of the knee moves the leg toward the thigh. Dorsiflexion is flexion of the foot upward, as when you stand on your heels; plantar flexion is flexion of the foot downward, as when you stand on your toes. Extension increases the joint angle. Extension of the flexed elbow straightens the upper limb. Hyperextension occurs when a portion of the body part is extended beyond 180°. It is possible to hyperextend the head and the trunk of the body, and also the shoulder and wrist (arm and hand). Adduction is the movement of a body part toward the midline. For example, adduction of the arms or legs moves them back to the sides, toward the body. Abduction is the movement of a body part laterally, away from the midline. Abduction of the arms or legs moves them laterally, away from the body. Circular Movements (Fig. 6.23b): Circumduction is the movement of a body part in a wide circle, as when a person makes arm circles. Careful observation of the motion reveals that, because the proximal end of the arm is stationary, the shape outlined by the arm is actually a cone. Page 125Rotation is the movement of a body part around its own axis, as when the head is turned to answer "no" or when the arm is twisted toward the trunk (medial rotation) and away from the trunk (lateral rotation). Supination is the rotation of the forearm so that the palm is upward; pronation is the opposite—the movement of the forearm so that the palm is downward. Special Movements (Fig. 6.23c): Inversion and eversion apply only to the feet. Inversion is turning the foot so that the sole faces inward, and eversion is turning the foot so that the sole faces outward. Elevation and depression refer to the lifting up and down, respectively, of a body part, as when you shrug your shoulders or move your jaw up and down.

fibrous joints

Some bones, such as those that make up the adult cranium, are sutured together by a thin layer of fibrous connective tissue and are immovable. Review Figures 6.5, 6.6, and 6.7, and note the following immovable sutures: coronal suture, between the parietal bones and the frontal bone; lambdoidal suture, between the parietal bones and the occipital bone; squamosal suture, between each parietal bone and each temporal bone; sagittal suture, between the parietal bones (not shown). The joints formed by each tooth in its tooth socket are also fibrous joints.

spongy bone

Spongy bone, or cancellous bone, contains numerous bony bars and plates, called trabeculae. Although lighter than compact bone, Page 105spongy bone is still designed for strength. Like braces used for support in buildings, the trabeculae of spongy bone follow lines of stress.

synovial joints

Synovial joints are generally freely movable because, unlike the joints discussed so far, the two bones are separated by a joint cavity (Figs. 6.20 and 6.21). The joint cavity is lined by a synovial membrane, which produces synovial fluid, a lubricant for the joint. The absence of tissue between the articulating bones allows them to be freely movable but means that the joint has to be stabilized in some way. The joint is stabilized by the joint capsule, a sleevelike extension of the periosteum of each articulating bone. Ligaments, which are composed of dense regular connective tissue, bind the two bones to one another and add even more stability. Tendons, which are cords of dense regular connective tissue that connect muscle to bone, also help stabilize a synovial joint. The articulating surfaces of the bones are protected in several ways. The bones are covered by a layer of articular (hyaline) cartilage. In addition, the joint, such as the knee, contains menisci (sing., meniscus), crescent-shaped pieces of cartilage, and fluid-filled sacs called bursae, which ease friction between all parts of the joint. Inflammation of the bursae is called bursitis. Tennis elbow is a form of bursitis. Articular cartilage can be worn away by years of constant use, such as when performing a sport.

hypoid bone

The U-shaped hyoid bone (see Fig. 6.4) is located superior to the larynx (voice box) in the neck. It Is the only bone in the body that does not articulate (form a joint) with another bone. Instead, it is suspended from the styloid processes of the temporal bones by the stylohyoid muscles and ligaments. It anchors the tongue and serves as the site for the attachment of several muscles associated with swallowing.

skeletal system interacts..

The bones protect the internal organs. The rib cage protects the heart, lungs, and kidneys; the skull protects the brain; and the vertebrae protect the spinal cord. Certain endocrine organs such as the pituitary gland, pineal gland, and thymus, are also protected by bone. The pelvic bones safeguard the pelvic reproductive structures, thus helping to make reproduction possible. The bones assist all phases of respiration. The rib cage assists the breathing process, enabling oxygen to enter the blood. Red bone marrow produces the blood cells, including the red blood cells that transport oxygen to the tissues. Without a supply of oxygen, the cells of the body could not efficiently produce ATP, the primary cellular energy source. The bones store and release calcium needed by the muscular and nervous systems. Hormones control the balance between the concentrations of calcium in the bones and in the blood. Calcium ions play a major role in muscle contraction and nerve conduction. Calcium ions also help regulate cellular metabolism. Protein hormones, which cannot enter cells, are called the first messenger, and a second messenger such as calcium ions jump-starts cellular metabolism, directing it to proceed in a particular way. The bones assist the lymphatic system and immunity. Red bone marrow produces the white cells, which congregate in the lymphatic organs. White blood cells defend the body against pathogens and cancerous cells. Without the ability to withstand foreign invasion, the body may quickly succumb to disease and die. The bones assist digestion. The bones used for chewing break food into pieces small enough to be swallowed and chemically digested. Without digestion, needed nutrients would not enter the body. The skeleton is necessary to locomotion. Our jointed skeleton forms a framework for muscle attachment, and muscle contraction causes joint movement. Thus, we can seek out and move to a more suitable external environment in order to maintain homeostasis. Other Body Systems Interact with the Skeletal System How do the other systems of the body help the skeletal system function? The integumentary system and the muscles help the skeletal system protect internal organs. The digestive system absorbs the calcium from food, and the plasma portion of blood transports calcium from the digestive system to the bones. The endocrine system regulates the storage of calcium in the bones, as well as Page 128the growth of bone and other tissues. The cardiovascular system transports oxygen and nutrients to bone, and wastes from bone. The urinary and digestive systems excrete bone wastes. Movement of the bones would be impossible without contraction of the muscles. In these and other ways, the systems of the body help the skeletal system carry out its functions.

bones of cranium

The cranium protects the brain and is composed of eight bones. These bones are separated from each other by immovable joints called sutures. Newborns have membranous regions called fontanels, where the bones of the cranial vault have not yet fused together. The fontanels permit the bones of the skull to shift during birth as the head passes through the birth canal. The largest fontanel is the anterior fontanel (often called the "soft spot"), which is located where the two parietal bones meet the two unfused parts of the frontal bone. The anterior fontanel usually closes by the age of two years. Besides the frontal bone, the cranium is composed of two parietal bones, one occipital bone, two temporal bones, one sphenoid bone, and one ethmoid bone (Figs. 6.6 and 6.7). Frontal Bone One frontal bone forms the forehead, a portion of the nose, and the superior portions of the orbits (bony sockets of the eyes). Parietal Bones Two parietal bones are just posterior to the frontal bone. They form the roof of the cranium and also help form its sides. Occipital Bone One occipital bone forms the most posterior part of the skull and the base of the cranium. The spinal cord joins the brain by passing through a large opening in the occipital bone called the foramen magnum. The occipital condyles are rounded processes on either side of the foramen magnum that articulate with the first vertebra of the spinal column. Temporal Bones Two temporal bones are just inferior to the parietal bones on the sides of the cranium. They also help form the base of the cranium (Figs. 6.5 and 6.6a). Each temporal bone has the following special features: external acoustic meatus, a canal that leads to the middle ear; mandibular fossa, which articulates with the mandible; Page 113 mastoid process, which provides a place of attachment for certain neck muscles; styloid process, which provides a place of attachment for muscles associated with the tongue and larynx; zygomatic process, which projects anteriorly and helps form the cheekbone. Sphenoid Bone The sphenoid bone helps form the sides and floor of the cranium and the rear wall of the orbits. The sphenoid bone is shaped like a butterfly. Its complex shape allows it to articulate with and hold together the other cranial bones (Fig. 6.7). Within the cranial cavity, the sphenoid bone has a saddle-shaped midportion called the sella turcica (Fig. 6.7b), which houses the pituitary gland in a depression. Ethmoid Bone The ethmoid bone is anterior to the sphenoid bone and helps form the floor of the cranium. It contributes to the medial sides of the orbits and forms the roof and sides of the nasal cavity (Figs. 6.5, 6.6, and 6.7). Important components of the ethmoid bone include: crista galli (cock's comb, Fig. 6.7), a triangular process that serves as an attachment for membranes that enclose the brain; cribriform plate (Fig. 6.7), with tiny holes that serve as passageways for nerve fibers from the olfactory receptors (nerve endings that give us our sense of smell); perpendicular plate (Fig. 6.5), which projects downward to form the superior part of the nasal septum; superior and middle nasal conchae, which project toward the perpendicular plate. These increase the surface area of the nasal cavity. Projections support mucous membranes that line the nasal cavity.

Intervertebral Disks

The fibrocartilaginous intervertebral disks located between the vertebrae act as cushions. The disks are filled with gelatinous material, which prevents the vertebrae from grinding against one another and absorbs shock caused by such movements as running, jumping, and even walking. The disks also allow motion between the vertebrae so that a person can bend forward, backward, and from side to side. Unfortunately, these disks become weakened with age, and they can slip or even rupture (called a herniated disk). A damaged disk pressing against the spinal cord or the spinal nerves causes pain. Such a disk may need to be removed surgically. If a disk is removed, the vertebrae are fused together, limiting the body's flexibility.

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The manubrium articulates with the costal cartilages of the first and second ribs; the body articulates with costal cartilages of the second through seventh ribs; and the xiphoid process doesn't articulate with any ribs. The xiphoid process is the third part of the sternum. Composed of hyaline cartilage in the child, it becomes ossified (converted into bone) in the adult. The variably shaped xiphoid process serves as an attachment site for the diaphragm, which separates the thoracic cavity from the abdominal cavity.

rib cage

The rib cage (Fig. 6.11), sometimes called the thoracic cage, is composed of the thoracic vertebrae, the ribs and their costal cartilages, and the sternum. The rib cage demonstrates how the skeleton is protective but also flexible. The rib cage protects the heart and lungs; yet it swings outward and upward upon inspiration and then downward and inward upon expiration. The rib cage also provides support for the bones of the pectoral girdle (see page 118).

skeleton functions

The skeleton supports the body. The bones of the lower limbs support the entire body when we're standing, and the pelvic girdle supports the abdominal cavity. The skeleton protects soft body parts. The bones of the skull protect the brain; the rib cage protects the heart and lungs. The skeleton produces blood cells. All bones in the fetus have red bone marrow that produces blood cells. In the adult, only certain bones produce blood cells. The skeleton stores minerals and fat. All bones have a matrix that contains calcium phosphate, a source of calcium ions and phosphate ions in the blood. Blood calcium is essential for nerves and muscles to function properly. Fat is stored in yellow bone marrow. The skeleton, along with the muscles, permits flexible body movement. While articulations (joints) occur between all the bones, we associate body movement in particular with the bones of the limbs.

skull

The skull is formed by the cranium and the facial bones. These bones contain sinuses, air spaces lined by mucous membranes that reduce the weight of the skull and give the voice a resonant sound. The paranasal sinuses empty into the nose and are named for their locations. They include the maxillary, frontal, sphenoidal, and ethmoidal sinuses (the frontal and sphenoid sinuses are shown in Fig. 6.5). Sinusitis is infection or inflammation of the paranasal sinuses. The two mastoid sinuses drain into the middle ear. Mastoiditis, a condition that can lead to deafness, is an inflammation of these sinuses.

sternum

The sternum, or breastbone, is a flat bone that has the shape of a blade. The sternum, along with the ribs, helps protect the heart and lungs. During surgery the sternum may be split to allow access to the organs of the thoracic cavity. The sternum is also where a first responder will place his or her hands when performing CPR (see Chapter 14). The sternum is composed of three bones that fuse during fetal development (Fig. 6.11). These bones are the manubrium, Page 117the body, and the xiphoid process. The manubrium is the superior portion of the sternum. The body is the middle and largest part of the sternum, and the xiphoid process is the inferior and smallest portion of the sternum. The manubrium joins with the body of the sternum at an angle. This joint is an important anatomical landmark because it occurs at the level of the second rib, and therefore allows the ribs to be counted. Counting the ribs is sometimes done to determine where the apex (most inferior portion) of the heart is located—usually between the fifth and sixth ribs. Medical Focus

bone development/growth

The term ossification refers to the formation of bone. The bones of the skeleton form during embryonic development in two distinctive ways—intramembranous ossification and endochondral ossification. In intramembranous ossification, bone develops between sheets of fibrous connective tissue. Cells derived from connective tissue become osteoblasts that form a matrix resembling the trabeculae of spongy bone. Other osteoblasts associated with a periosteum lay down compact bone over the surface of the spongy bone. The osteoblasts become osteocytes when they are surrounded by a mineralized matrix. The bones of the skull develop in this manner. Most of the bones of the human skeleton form by endochondral ossification. Hyaline cartilage models, which appear during fetal development, are replaced by bone as development continues. During endochondral ossification of a long bone, the cartilage begins to break down in the center of the diaphysis, which is now covered by a periosteum (Fig. 6.3). Osteoblasts and blood vessels enter the central region. There, these osteoblasts begin to lay down spongy bone in what is called a primary ossification center. Other osteoblasts lay down compact bone beneath the periosteum. As the compact bone thickens, the spongy bone of the diaphysis is broken down by osteoclasts, and the cavity created becomes the medullary cavity.

spine

The vertebral column extends from the skull to the pelvis. It consists of a series of separate bones, the vertebrae, separated by pads of fibrocartilage called the intervertebral disks (Fig. 6.8). The vertebral column is located in the posterior region of the body at Page 114the midline, where it forms the body's vertical axis. The skull rests on the superior end of the vertebral column, which also supports the rib cage and serves as a point of attachment for the pelvic girdle. The vertebral column also protects the spinal cord, which passes through a vertebral canal formed by the vertebrae. The vertebrae are named according to their location: seven cervical (neck) vertebrae, twelve thoracic (chest) vertebrae, five lumbar (lower back) vertebrae, five sacral vertebrae fused to form the sacrum, and three to five coccygeal vertebrae fused into one coccyx (tailbone). When viewed from the side, the vertebral column has four normal curvatures, named for their location (Fig. 6.8). The cervical and lumbar curvatures are concave posteriorly, and the thoracic and sacral curvatures are convex posteriorly. In the fetus, the vertebral column has only one curve, and it is convex posteriorly (the curved "fetal position"). The cervical curve develops three to four months after birth, when the child begins to hold his or her head up. The lumbar curvature develops when a child begins to stand and walk, around one year of age. The curvatures of the vertebral column provide more support than a straight column would, and they also provide the balance needed to walk upright. The curvatures of the vertebral column are subject to abnormalities (Fig. 6.9). An abnormally exaggerated lumbar curvature is called lordosis, or "swayback." People who are balancing a heavy midsection, such as pregnant women or men with "potbellies," may have swayback. An increased roundness of the thoracic curvature is kyphosis, or "hunchback." This abnormality sometimes develops in older people as the center sections of thoracic vertebrae become compressed. An abnormal lateral (side-to-side) curvature is called scoliosis. Occurring most often in the thoracic region, scoliosis is usually first seen during late childhood.

the ribs

There are 12 pairs of ribs. All 12 pairs connect directly to the thoracic vertebrae in the back, by attaching to costal facets built into the thoracic vertebrae. After connecting with thoracic vertebrae, each rib first curves outward and then forward and downward. The first pair of ribs attaches to the body of the first thoracic vertebra, or T1. It also attaches to the transverse process of T1, at the facet for the joint with the rib. The next eight pairs of ribs (ribs 2-9) attach to the vertebrae at three places (see Fig. 6.10a). First, each attaches to the body of the same numbered vertebra (rib 4, for example, is attached to the body of the 4th thoracic vertebra). Next, each attaches to the body of the vertebra immediately superior (so, rib 4 also attaches to the body of the 3rd thoracic vertebra). Finally, each rib attaches to the transverse process of the same numbered vertebra (rib 4 attaches to the transverse process of the 4th thoracic vertebra). Rib pairs 10 through 12 attach only to their respective vertebrae. The upper seven pairs of ribs connect directly to the sternum by means of costal cartilages. These are called the "true ribs," or the vertebrosternal ribs. The next five pairs of ribs are called the "false ribs" because they attach indirectly to the sternum or are not attached at all. Ribs 8, 9, and 10 are called vertebrochondral ribs; each attaches its costal cartilage to the cartilage of the rib superior to it. All three ribs attach indirectly to the sternum using the costal cartilage of rib 7. Ribs 11 and 12 are vertebral, or "floating," ribs. These are short ribs with no attachment to the sternum (Fig. 6.11).

Intro

Will you please quit doing that?! Keep it up and you'll get arthritis!" Habitual knuckle-crackers might stop their annoying habit when confronted with this threat, but is there any truth to it? Knuckles are freely moving synovial joints (see page 123). In a synovial joint, ligaments join bones and create a fluid-filled capsule. Stretching the ligaments suddenly creates an air bubble in the fluid. Popping the bubble causes the "crack" noise. Any synovial joint—toes, ankles, fingers—can crack, but numerous studies have shown that arthritis doesn't result from it. However, ligaments will weaken with habitual cracking, and the bones at a joint can then be dislocated more easily. If you're tempted to crack those stiff joints, massage and gently stretch them instead.

skeleton anatomy

he skeleton is divided into the axial skeleton and the appendicular skeleton. The tissues of the axial and appendicular skeletons are bone (both compact and spongy), cartilage (hyaline, fibrocartilage, and elastic cartilage), and dense connective tissue, a type of fibrous connective tissue. (The various types of connective tissues were extensively discussed in Chapter 4.) In Figure 6.4, the bones of the axial skeleton are colored gray, and the bones of the appendicular skeleton are colored tan for easy distinction. Notice that the axial skeleton lies in the midline of the body and contains the bones of the skull, the hyoid bone, the Page 110vertebral column, and the thoracic cage (composed of the ribs and the sternum, or breastbone). Six tiny middle ear bones (three in each ear) are also in the axial skeleton; we will study them in Chapter 9 in connection with the ear. The appendicular skeleton includes the pectoral girdle, upper limbs, pelvic girdle, and lower limbs.