Anatomy/Skeletal System

The skeletal system is a topic of the event Anatomy for the 2020 competition, along with the integumentary system and the muscular system.

For the skeletal system you will need to know:

• The names of the bones and their surface anatomy as shown on a diagram, X-ray, CT scan, and MRI
• The name, structure, and function of joint types and the ranges allowed by each joint
• The structure of bones in cross-sectional diagrams
• The structures and function of bones, bone marrow, and cartilage
• The development aspects of bones
• How to distinguish between types of vertebrae
• Homeostatic imbalances of the skeletal system
• The effects of exercise and aging on the skeletal system and their effects on the homeostatic imbalances of the skeletal system.

Competition Level	Health Concepts
Regional/State	Bones of the axial and appendicular skeleton, including the ability to label bones on a diagram and/or X-ray Name, structure, and function of types of joints (ball and socket joints, fibrous joints, cartilagenous joints, synovial joints, etc.), including the range of motion allowed by each type Name, structure, and function of the muscles and ligament attachments that surround joints Structure, cellular composition, and function of bones, bone marrow, and cartilage, including the ability to identify components in cross-section Distinguish types of spinal vertebrae (e.g., cervical, thoracic, and lumbar) Understanding of the following diseases at the levels from the cell to the whole body, including the radiological features of each disease: osteoarthritis, osteoporosis, fractures, disc herniation, scoliosis, anterior cruciate ligament tears, medial collateral ligament damage The effect of exercise on the skeletal system and the aforementioned diseases
National	Understanding of the following additional diseases: spinal stenosis, achondroplasia, juvenile rheumatoid arthritis, spinal fractures, ankylosing spondylitis, and osteosarcoma Treatment and/or prevention of all the aforementioned diseases and disorders, including drugs, surgery, and other alternative treatments Bones of the skull, including the ability to label them on a diagram Salter-Harris fracture identification system

Bones and Skeletal Tissues

Skeletal Cartilage

Cartilage is mainly composed of water. It is not vascularized (having veins) or innervated (having nerves). Cartilage is strong, resilient, and heals poorly. Cartilage is found in the epiphyseal plate, as well as in joints to provide shock absorption. It is also found in a newborn’s body. Cartilage is replaced later on by bones that form at the site and fuse together.

• Chondroblasts are mesenchymal progenitor cells that develop into chondrocytes through endochondral ossification.
• Chondrocytes secrete extracellular matrix to maintain the cartilage.

Cartilage is surrounded by the perichondrium, a layer of dense irregular connective tissue. When the cartilage is compressed, the perichondrium prevents it from expanding outward. The extracellular matrix is a network of macromolecules that provides structural support to the cells surrounding it. Within the extracellular matrix are small cavities called lacunae, with each one housing a chondrocyte. Lacunae are connected to each other by canaliculi, which are essentially canals. Cartilage grows through appositional and interstitial growth. Appositional growth is a process that occurs when new bone matrix is secreted at the bone surface, causing its diameter to increase. Interstitial growth occurs when chondrocytes within the extracellular matrix divide and secrete new matrix. This causes the cartilage to expand from within itself.

• Hyaline cartilage is the most abundant type of cartilage. It has a glass-like appearance and has a pearl-gray color. Hyaline cartilage is flexible and resilient. It can be divided into several subtypes—articular, costal, respiratory, and nasal cartilage—depending on its location.
• Elastic cartilage is similar to hyaline cartilage, the main exception being that it has more elastic fibers. This allows it to stand up better to repeated bending. Elastic cartilage can be found in the external ear and epiglottis.
• Fibrocartilage resembles fibrous tissue, with the exception that it has chondrocytes. It is very strong and highly compressible. Fibrocartilage can be found in the menisci of the knee, the intervertebral disks, and the pubic symphysis.

Bone Classification

• Long bones are the most familiar type of bones, being longer than they are wide. They are composed of a shaft, or diaphysis, and two ends, or epiphyses. All limb bones—except for the patella, wrist, and ankle bones—are long bones. The outer layer of long bones is composed of compact bone, while the inner layer is composed of spongy bone. The surfaces that articulate with other bones contain hyaline cartilage.
• Short bones are roughly cube shaped. Examples include the carpals of your wrist and the tarsals of your ankle. Sesamoid bones are a special type of short bones that are located inside of tendons. Examples include the patella and pisiform, though numbers vary between individuals.
• Flat bones are thin, flat, and slightly curved. Examples include the ribs and cranial bones. Their function is to protect internal organs.

Irregular bones are any bones that do not fit under the preceding categories. Examples include hip bones, vertebrae, and more.

Bone Functions

• You may recognize that the skeleton is essentially just a framework of bones. This framework serves to support the body.
• This framework also serves to protect vital structures including the brain, spinal cord, and thoracic organs.
• Bones, muscles, cartilage, tendons, ligaments, joints, and other connective tissue compose the skeletomuscular system. They work together to make movement possible.
• Bones are also responsible for the storage of triglycerides inside of yellow bone marrow. They also serve as a reservoir for minerals.
• Bones produce hormones such as osteocalcin and some growth factors.

Bone Structure

All bones are made up of an outer layer of compact bone, which looks smooth and solid. The inside is composed of spongy bone (referred to as diploë in flat bones). Spongy bone contains many bands or columns of connective tissue called trabeculae, which help the bone resist stress. Spongy bone contains many pores, which are filled with bone marrow. The long axis of the bone is the diaphysis, or the shaft. It is constructed of compact bone that surrounds the medullary cavity, which contains bone marrow. This bone marrow can be in the form of red bone marrow, which produces blood cells, or yellow bone marrow, which stores fat. Red bone marrow is replaced by yellow bone marrow as you age. In cases of extreme blood loss, the body may willingly revert yellow bone marrow back to red bone marrow, increasing the production of blood cells. The ends of the bone are called the epiphyses. The exterior is composed of compact bone, while the interior is composed of spongy bone. The joint surface of each epiphysis is covered by a thin layer of articular cartilage. The metaphysis is located where the diaphysis and the epiphysis meet. The epiphyseal line is a disc of hyaline cartilage that is located in the metaphysis of adult long bones. The periosteum is a white membrane that covers the external surface of bones. The outer layer of the periosteum is the fibrous layer, made up of dense irregular connective tissue. The inner layer is known as the osteogenic layer, made up of osteogenic cells. The periosteum is secured to the bone by collagen fibers known as Sharpey’s fibers. The endosteum is a membrane made up of delicate connective tissue that covers the internal surface of bones, along the medullary cavity. This membrane is made up of osteogenic cells. Osteons, the structural units of long bones, are long cylinders parallel to the long axis of bones. They function as small, weight-bearing pillars. A Haversian canal runs through the center of each osteon, while perforating canals, also called Volkmann's canals, run perpendicular to these. These enable vessels and nerves to enter the bone to supply nutrients.

Bone Markings

Bone markings are surface features on bones that serve various functions. These include enabling joint motion, locking bones in place, providing structural support, providing stabilization, and providing protection.

• Several bone markings serve as sites of muscle and ligament attachment.
  • A tuberosity is a lange, rounded projection that is often roughened. A good example is the ischial tuberosity.
  • A crest is a narrow, prominent ridge of bone. A good example is the iliac crest.
  • A trochanter is a very large, blunt, irregularly shaped process. The only trochanters are the greater and lesser trochanters of the femur.
  • A line is a narrow ridge of bone that is less prominent than a crest. A good example of a line is the intertrochanteric line of the femur.
  • A tubercle is a small, rounded projection or process. A good example is the adductor tubercle of the femur.
  • An epicondyle is a raised area located on or above a condyle. A good example is the medial epicondyle of the femur, which is located above the medial condyle of the femur.
  • A spine is a sharp, slender, pointed projection. A great example of a spine is the ischial spine.
  • A process is a bony prominence. These are abundant markings and an example is the spinous processes of the vertebrae.
• Other bone markings serve to help form joints.
  • A head is the expanded articular end of an epiphysis, separated from the diaphysis or shaft by a neck. A good example is the head of the humerus.
  • A neck is a narrow connection between the epiphysis and diaphysis. A good example is the neck of the humerus.
  • A facet is a smooth, nearly flat articular surface. A good example is the costal facet located on each rib.
  • A condyle is a smooth, rounded articular process. A good example is the medial condyle of the femur.
  • A ramus is an armlike or branchlike bar of bone. An example of a ramus is the ramus of the mandible.
  • A trochlea is a smooth, grooved articular process shaped like a pulley. An example is the trochlea of the femur.
• Some bone markings are depressions and openings.
  • A groove, or sulcus, is a furrow in a bone. An example is the mylohyoid groove, or sulcus of the mandible.
  • A fissure is a narrow, slitlike opening. A great example is the inferior orbital fissure.
  • A foramen is a round opening through a bone that serves as a passageway for structures to pass through. Most foramina are found in the skull, an example being the foramen magnum.
  • A meatus is a canal-like passageway through a bone. An example is the internal acoustic meatus.
  • A sinus is a cavity within a bone, filled with air and lined with mucous membrane. An example is the paranasal sinus.
  • A fossa is a shallow, basinlike depression in a bone. Good examples include the posterior, middle, and anterior cranial fossa.

Bone Cells

• Osteoblasts are bone forming cells. They can be found in areas of high metabolism within the bone.
• Osteocytes are mature bone cells; they develop from osteoblasts. Osteocytes help maintain healthy bone tissue by secreting enzymes and controlling calcium released from bone tissue into the bloodstream.
• Osteogenic cells respond to trauma by giving rise to bone forming cells, or osteoblasts, and bone destroying cells, or osteoclasts.
• Bone-lining cells develop from osteoblasts. They are located along the surface of most adult bones. Bone-lining cells regulate the movement of calcium and phosphate into and out of the bones.
• Osteoclasts develop from hematopoietic stem cells. They are large, multinucleate cells that are located at sites of bone resorption. Osteoclasts break down bone tissue and are important to bone growth, healing, and remodeling.

Bone Development

Ossification is the process by which bones form in embryos. In adults, however, ossification is the process of bone remodeling and repair.

• Endochondral ossification is the replacement of hyaline cartilage with endochondral bone.
• Intramembranous ossification is the development of fibrous membranes into membrane bones.

Bone Homeostasis

• Every day, up to half a gram of calcium leaves the adult skeleton.
• Every week, we recycle five to seven percent of our bone mass.
• Every three to four years, all of our spongy bone is replaced.
• Every ten years, all of our compact bone is replaced.

The aforementioned things occur due to bone remodeling, which is made up of two processes: bone deposit and bone resorption.

• Bone deposit is the process by which osteoblasts deposit hydroxyapatite crystals into the bone matrix.
• Bone resorption is the process by which osteoclasts secrete lysosomal enzymes that break down bone tissue, transferring calcium into the blood.

Calcitriol, the active form of vitamin D, inhibits the release of calcitonin. Calcitonin inhibits the release of calcium from bone, reducing blood levels of calcium ions. When blood levels of calcium ions decline, parathyroid hormone is released. This stimulates bone resorption, which once again increases blood levels of calcium ions. Leptin is a hormone released by adipose tissue to regulate bone density. Serotonin, when produced outside of the brain, inhibits bone formation.

Joints

Joint Classification

Joints can be classified functionally based on the amount of movement allowed at the joint. Synarthroses are immovable joints, amphiarthroses are slightly movable joints, and diarthroses are freely movable joints.

• Fibrous joints are joined together by dense fibrous connective tissue; they have no joint cavities.
  • Sutures are synarthroses; they are nearly rigid splices that knit the skull together. During middle age, sutures ossify and the skull bones fuse together to form synostoses.
  • Syndesmoses are amphiarthroses; they are connected exclusively by ligaments. If the joint possesses short connecting fibers, movement is very limited. If the joint possesses long connecting fibers, movement is ample.
  • Gomphoses are peg-in-socket joints. The only occurrences of these joints in humans are the articulations of teeth with their alveolar sockets. Gomphoses are classified functionally as synarthroses.
• Cartilaginous joints are joined together by cartilage; they have no joint cavities.
  • Synchondroses are amphiarthroses; they are connected by articular cartilage.
  • Symphyses are amphiarthroses; they are connected by fibrocartilage.
• Synovial joints are diarthroses; they possess a fluid-filled joint cavity, the synovial cavity. The fluid, synovial fluid, reduces friction at the joint to keep the joint surfaces from rubbing away.
  • Ball and socket joints are joints in which a rounded bone fits into a cup-like socket of another bone. This allows for a huge range of movements. These joints can be found in the hip and shoulder.
  • Condyloid joints are joints in which an ovoid bone fits into an elliptical cavity of another bone. This allows for all movements except axial rotation. These joints can be found in the wrist and at the base of the index finger.
  • Saddle joints are joints in which a saddle-shaped bone fits beneath a bone shaped like someone riding on a horse. This allows similar movements to condyloid joints. These joints can be found in the thumbs.
  • Hinge joints are joints that only allow flexion and extension, similar to a door hinge. They can be found in the elbow, knee, and in the phalanges.
  • Pivot joints are joints in which one bone rotates around another. This allows rotation similar to that of a lid on a jar.
  • Plane joints are joints that only allow side to side movement.

The Axial Skeleton

The Skull

The skull is composed of twenty-two bones, eight cranial bones and fourteen facial bones, all connected by sutures. The cranium protects the fragile brain and furnishes attachment sites for head and neck muscles. The cranial vault forms the superior, lateral, and posterior aspects of the skull, as well as the forehead. The cranial base forms the inferior aspect of the skull.

• The frontal bone forms the forehead, superior part of the orbits, and superior part of the nose.
• The paired parietal bones form the superior and lateral aspects of the cranium.
• The occipital bone forms the posterior and inferior aspects of the cranium.
• The paired temporal bone form the inferolateral aspect of the cranium.
• The sphenoid bone forms the anteromedial aspect of the cranium; it is the keystone of the cranium, meaning it is in contact with all other cranial bones.
• The ethmoid bone forms part of the nasal septum and the lateral walls and roof of the nasal cavity.

The facial skeleton forms the framework of the face, contains cavities for sensory organs, provides openings for air and food, secures the teeth, and anchors the facial muscles.

• The mandible forms the lower jaw.
• The paired maxillae form the upper jaw; they are the keystones of the facial skeleton, meaning they are in contact with all other facial bones.
• The paired zygomatic bones form the cheeks and lateral parts of the orbits.
• The paired nasal bones form the bridge of the nose.
• The paired lacrimal bones form the front part of the medial orbit walls.
• The paired palatine bones form the posterior part of the hard palate.
• The vomer forms the inferior part of the nasal septum.
• The paired inferior nasal conchae form part of the lateral nasal cavity.

The Vertebral Column

The vertebral column consists of twenty-six irregular bones that form a flexible, curved structure. In the fetus and infant, it consists of thirty-three vertebrae, nine of which fuse to form the sacrum and coccyx. It serves as the axial support of the trunk and transmits the weight of the trunk to the lower limbs. It surrounds and protects the spinal cord and provides attachment points for the ribs and muscles of the back and neck.

• The seven cervical vertebrae of the neck are numbered C1 through C7. The topmost cervical vertebra, C1, is called the atlas; it functions to support to head. Inferior to this is C2, the axis; it functions to pivot the neck. The bottommost cervical vertebra, C7, is called the vertebra prominens because it sticks out near the top of the shoulder blades.
• The twelve thoracic vertebrae of the thorax are numbered T1 through T12; they are attached to the ribs.
• The five lumbar vertebrae of the lower back are numbered L1 through L5. They provide flexibility and stability to the trunk.
• The triangular sacrum is formed by five vertebrae, numbered S1 through S5, that fuse together during adulthood.
• The tiny, triangular coccyx is formed by four vertebrae that fuse together during adulthood; it is a vestigial structure.

The Thoracic Cage

The thoracic cage is the bony framework of the thorax, or chest. It forms a protective cage around the thoracic organs, supports the shoulder girdles and upper limbs, and provides attachment points for many muscles.

• The sternum forms the central part of the thorax; it is a flat bone. The sternum consists of three bones—the manubrium superiorly, the body medially, and the xiphoid process inferiorly—that fuse during adulthood.
• The twelve pairs of ribs form the sides of the thoracic cage, attaching to the thoracic vertebrae. The seven superior rib pairs attach directly to the sternum. These are called true ribs or vertebrosternal ribs. The five inferior rib pairs attach indirectly to the sternum or entirely lack a sternal attachment. These are called false ribs. Rib pairs eight through ten attach indirectly to the sternum. These are also called vertebrochondral ribs. Rib pairs eleven through twelve entirely lack a sternal attachment. These are also called floating ribs or vertebral ribs.

The Appendicular Skeleton

The Pectoral Girdle

The pectoral girdle attaches the upper limbs to the axial skeleton.

• The clavicles are slender, S-shaped bones that lie horizontally between the scapulae and sternum.
• The scapulae are thin, triangular flat bones that form the shoulder blades.

The Upper Limb

Each upper limb is formed by thirty separate bones.

• The humerus is a typical long bone that forms the arm, or brachium. It is the largest, longest, strongest bone of the upper limb.
• The radius and ulna form the forearm, or antebrachium. They are connected along their entire length by a flat, flexible ligament called the interosseous membrane. In supination, the radius lies laterally and the ulna lies medially; in pronation, the distal end of the radius crosses over the ulna and the bones form an “X.”
• The eight carpals are marble-sized short bones that form the wrist, or carpus. The mnemonic “Sally Left The Party To Take Cindy Home” is used to memorize the carpals—the scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, and hamate.
• The five metacarpals are small long bones that form the palm, or metacarpus; they are number metacarpals I through V from the thumb to the pinky.
• The fourteen phalanges are miniature long bones that form the fingers. Each finger has three phalanges—distal, middle, and proximal—except for the thumb, or pollex, which lacks a middle phalange.

The Pelvic Girdle

The pelvic girdle attaches the lower limbs to the axial skeleton, transmits the full weight of the upper body to the lower limbs, and supports the pelvic organs. Each hip bone consists of three large, irregular bones that fuse during adulthood.

• The ilium is a large flaring bone that forms the superior region of the hip bone.
• The ischium is an arc-shaped bone that forms the posteroinferior part of the hip bone.
• The pubis is a V-shaped bone that forms the anterior portion of the hip bone.

The hip bones, sacrum, and coccyx form a structure called the pelvis. The female pelvis is wider, shallower, lighter, and rounder; it is modified for childbearing.

The Lower Limb

Each lower limb is formed by thirty separate bones.

• The femur is a typical long bone that forms the thigh. It is the largest, longest, strongest bone in the body.
• The patella is a triangular sesamoid bone located in the quadriceps tendon. It protects the knee joint and improves the leverage of the thigh muscles.
• The tibia and fibula form the leg. They are connected along their entire length by a flat, flexible ligament called the interosseous membrane. The tibia transmits the weight of the body from the femur to the foot. The fibula is a stick-like bone that stabilizes the ankle joint.
• The seven tarsals form the posterior half of the foot, or tarsus. The body weight is primarily carried by the two largest and most posterior tarsals, the talus and calcaneus. The mnemonic “Tiger Cubs Need MILC” is used to memorize the tarsals—the talus, calcaneus, navicular, medial cuneiform, intermediate cuneiform, lateral cuneiform, and cuboid.
• The five metatarsals are small long bones that form the middle part of the foot, or metatarsus; they are numbered I through V from the great toe to the pinky toe.
• The fourteen phalanges are miniature long bones that form the toes. Each toe has three phalanges—distal, middle, and proximal—except for the great toe, or hallux, which lacks a middle phalange.

Homeostatic Imbalances

Diseases of the Skeletal System

Disease Name	Cause	Symptoms	Treatment	Prevention	Effect on the Body
Osteoarthritis	The protective cartilage that cushions the ends of your bones wears down over time; extra strain on joints and joint injuries contribute to this.	The main symptoms of osteoarthritis are joint pain, stiffness, limited joint movement, tenderness, and swelling.	Acetaminophen and NSAIDs (Non-Steroidal Anti-Inflammatory Drugs) may be used to treat osteoarthritis.	Exercising, maintaining a healthy weight, and avoiding joint injuries help prevent osteoarthritis.	Osteoarthritis causes arthralgia and the wearing down of joint cartilage.
Osteoporosis	The body loses too much bone or produces too little bone. Age and sex influence one's risk factor for osteoporosis.	Back pain, stooped posture, easily broken bones, and loss of height are common symptoms of osteoporosis.	Calcitonin and bisphosphonates may be used to treat osteoporosis.	Following a nutritious diet, exercising, and abstaining from smoking or drinking alcohol help prevent osteoporosis.	Osteoporosis thins the bone and makes it porous.
Fracture	Fractures may be caused by trauma, pathologies, and overuse.	Symptoms of fractures include swelling and tenderness in a localized area, bruising, and deformity.	Fractures may be treated using a cast or brace, traction, and fixation.	Fractures can be prevented by following a proper diet and exercising.	Fractures may seriously damage tissues such as the skin, nerves, blood vessels, muscles, and organs.
Disc Herniation	Herniated discs are caused by wear and tear, injuries, and excess strain on intervertebral discs. Age influences the likelihood of disc herniation.	Symptoms of disc herniation include numbness, weakness, leg pain, and muscle pain.	Treatments for disc herniation include limiting activities, applying ice or heat, aspirin, and NSAIDs (Non-Steroidal Anti-Inflammatory Drugs).	Disc herniation may be prevented by maintaining healthy body weight, exercising, abstaining from smoking, and practicing good posture.	Disc herniation may cause you to stumble or be incapable of lifting items.
Scoliosis	Scoliosis may be caused by neonatal pathologies, attained injuries, infections, and other things.	Scoliosis can be detected by a sideways curvature of the spine or one shoulder sticking out more than the other.	Treatments for scoliosis include using a back brace and taking pain-relieving medications such as aspirin and ibuprofen.	Scoliosis cannot be prevented aside from avoiding injuries and infections.	Scoliosis may deplete nutritional resources and damage major organs.
ACL Tear	An ACL tear occurs when your anterior cruciate ligament is sprained or torn. This often occurs during sports that involve sudden stops or changes in direction, jumping, and landing.	Symptoms include knee swelling, instability, and pain.	Treatments include arthroscopy, ACL reconstruction, and therapy.	Preventative measures include practicing good technique and eating a balanced diet.	An ACL tear may make it difficult to walk, leading to stumbling and falling.
MCL Damage	MCL damage occurs when the medial collateral ligament is stretched, partially torn, or completely torn.	Symptoms include knee swelling, instability, and pain.	Treatments include arthroscopy, MCL reconstruction, and therapy.	Preventative measures include practicing good technique and eating a balanced diet.	MCL damage may make it difficult to walk, leading to stumbling and falling.
Spinal Stenosis	Spinal stenosis is caused by a narrowing of the spaces within your spine that can be attributed to osteoarthritis and the formation of bone spurs in your spine.	Symptoms include pain, loss of balance, and loss of bladder control, though some cases are asymptomatic.	Treatments include physical therapy, NSAIDs (Non-Steroidal Anti-Inflammatory Drugs), resting, limiting your activity, and using a back brace.	Preventative measures include exercising, using good body mechanics, maintaining a healthy weight, and practicing good posture.	Spinal stenosis narrows the spaces within your spine, putting pressure on the nerves that travel through your spine.
Achondroplasia	Achondroplasia is a congenital disease caused by a gene alteration in the FGFR3 gene.	Achondroplasia is characterized by dwarfism, a limited range of motion at the elbows, large head size, small fingers, and normal intelligence.	Hormones may be taken to increase height. In rare cases, surgery can help correct an abnormal curvature of the spine.	There are no preventative measures for achondroplasia as it is a congenital disease.	Achondroplasia prevents cartilage in the arms and legs to change to bone.
Juvenile Rheumatoid Arthritis	Juvenile rheumatoid arthritis is an autoimmune disease, meaning your immune system mistakenly attacks your own body.	Symptoms include joint pain, swelling, and irritability.	Treatments include exercise, assistive devices, NSAIDs (Non-Steroidal Anti-Inflammatory Drugs), and DMARDs (Disease Modifying Anti-Rheumatic Drugs)	Juvenile rheumatoid arthritis cannot be prevented.	Juvenile rheumatoid arthritis causes your joints to be destroyed.
Spinal Fracture	Spinal fractures often occur from car accidents, falls, gunshots, and sports.	Symptoms may include back or neck pain, numbness, tingling, muscle spasm, weakness, bowel or bladder changes, and paralysis.	Treatments for spinal fractures include braces, orthotics, instrumentation, fusion, vertebroplasties, and kyphoplasties.	Spinal fractures may be prevented by avoiding accidents and injuries.	Spinal fractures can cause bone fragments to pinch and damage the spinal nerves or spinal cord.
Ankylosing Spondylitis	Those who have a gene called HLA-B27 have an increased risk of obtaining ankylosing spondylitis.	Symptoms typically appear in early adulthood and include reduced flexibility in the spine, which eventually results in a hunched-forward posture. Pain in the back and joints is also common.	Treatments may include physical therapy, NSAIDs (Non-Steroidal Anti-Inflammatory Drugs), immunosuppressants, steroids, and sometimes surgery.	This disease is genetic, so there is no way to prevent it.	Ankylosing spondylitis causes your spine to be less flexible and causes your posture to be hunched forward.
Osteosarcoma	Osteosarcoma is caused by acquired gene changes that result from radiation therapy and other things.	Symptoms include localized bone pain and swelling.	Treatment typically involves surgery, chemotherapy, and radiation.	Very few preventative measures exist for osteosarcoma, but maintaining a healthy weight and abstaining from smoking help.	Osteosarcoma may metastasize to other tissues in the body.

Fracture Classification

• Depending on whether the bones do or do not pierce the skin, the fracture may be classified as open fractures (compound fractures) or closed fractures (simple fractures), respectively.
• Fractures may also be classified as nondisplaced fractures or displaced fractures, depending on whether the broken bones are or are not aligned with each other.
• Depending on whether the bones involved are or are not completely separated from each other, the fracture may be classified as a complete fracture or an incomplete fracture, respectively. Complete fractures can be classified as transverse fractures or oblique fractures, depending on whether the fracture occurs straight across the bone or at an angle, respectively. Incomplete fractures are known as greenstick fractures.
• An avulsion fracture occurs when a tendon or ligament pulls off a piece of bone.
• A fissure fracture occurs when a crack extends from the surface of the bone inside of it, but does not pass through the bone.
• An impacted fracture occurs when the bones are jammed together.
• A linear fracture occurs when the bones are broken but not moved.
• A longitudinal fracture occurs along the long axis of the bone.
• A pathological fracture occurs due to a pathological disease.
• A segmental fracture is composed of two or more fracture lines that isolate a segment of the bone.
• A spiral fracture occurs when torque is applied to a bone.
• A stress fracture is a small crack in a bone.

Salter-Harris Fracture Classification

Fractures can be classified using the Salter-Harris classification system. The mnemonic used for Salter-Harris fractures is “Straight across, Above, Lower (or beLow), Two (or Through), and ERasure of growth plate (or cRush).”

• Approximately 5% of Salter-Harris fractures are classified as Type I. These fractures are the least concerning and heal the quickest. This occurs when the fracture passes through the growth plate.
• About 75% of Salter-Harris fractures are classified as Type II. This involves fracturing of the growth plate, or physis, and the metaphysis. These fractures heal quickly and only minimally prohibit bone growth.
• About 10% of Salter-Harris fractures are classified as Type III. This involves fracturing of the growth plate, or physis, and the epiphysis. When this occurs, the joint needs to be reduced and fixated. These fractures may result in growth deformity.
• About 10% of Salter-Harris fractures are classified as Type IV. This occurs when the fracture passes through the growth plate, or physis, the metaphysis, and the epiphysis. These fractures may result in growth disturbances and angular deformities.
• Less than 5% of Salter-Harris fractures are classified as Type V. This involves compression or crushing of the growth plate, or physis. This usually results in growth deformities and disturbances.

Sample Questions

Resources

• SOInc: Anatomy and Physiology
• Anatomy Atlases - Bones of the Skull - 1
• Anatomy Atlases - Bones of the Skull - 2
• Anatomy Atlases - Bones of the Trunk - 3
• Anatomy Atlases - Bones of the Trunk - 4
• Anatomy Atlases - Bones of the Upper Limb - 5
• Anatomy Atlases - Bones of the Lower Limb - 6
• Anatomy Atlases - Ligaments of the Head, Vertebral Column, Pelvis, and Upper Limb - 7
• Anatomy Atlases - Ligaments of the Vertebral Column, Pelvis, and Lower Limb - 8
• eSkeletons - Skull
• GetBodySmart - An Online Examination of the Skeletal System
• InnerBody - Skeletal System
• Loyola University Chicago - The Bone Box
• OpenStax - Bone Tissue and the Skeletal System
• OpenStax - Axial Skeleton
• OpenStax - The Appendicular Skeleton
• OpenStax - Joints
• Penn State University - Skeletal System
• Rensselaer Polytechnic Institute - The 206 Bones of the Human Body
• University of Arkansas for Medical Sciences - Bones
• University of Arkansas for Medical Sciences - Joints
• The University of British Columbia - Skeleton: The Bones
• University of Utah School of Medicine - Osteoporosis
• University of Washington - Osteoporosis and Bone Physiology
• University of Wisconsin-La Crosse - The Axial Skeleton
• University of Wisconsin-La Crosse - The Axial Skeleton Tests
• University of Wisconsin-La Crosse - The Appendicular Skeleton
• University of Wisconsin-La Crosse - The Appendicular Skeleton Tests
• University of Wisconsin-La Crosse - Histology of Bone and Cartilage
• University of Wisconsin-La Crosse - Histology of Bone and Cartilage Tests