Pre-EMT Course: Skeletal System PDF

Pre-EMT Course: Skeletal System Douglas Wilkin, Ph.D. Niamh Gray-Wilson To access the online version of this FlexBook click the link below: https://flexbooks.ck12.org/user:5b16472013b2/cbook/pre-emt- course:-sk...

Pre-EMT Course: Skeletal System Douglas Wilkin, Ph.D. Niamh Gray-Wilson To access the online version of this FlexBook click the link below: https://flexbooks.ck12.org/user:5b16472013b2/cbook/pre-emt- course:-skeletal-system/r6/ 2 To access a customizable version of this book, as well as AU T HO R S other interactive content, visit www.ck12.org Douglas Wilkin, Ph.D. Niamh Gray-Wilson CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-source, collaborative, and web-based compilation model, CK-12 pioneers and promotes the creation and distribution of high- quality, adaptive online textbooks that can be mixed, modified and printed (i.e., the FlexBook® textbooks). Copyright © 2024 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections, must be attributed according to our attribution guidelines. https://www.ck12info.org/about/attribution-guidelines Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the CK-12 Curriculum Materials License https://www.ck12info.org/curriculum-materials-license Complete terms for use for the CK-12 website can be found at: http://www.ck12info.org/terms-of-use/ Printed: October 9, 2024 (PST) 3 MAIN CONTENT 1 The Skeleton - Advanced 1.1 The Skeleton - Advanced 6 1.2 References 11 2 Bone Formation - Advanced 2.1 Bone Formation - Advanced 13 2.2 References 18 3 Joints - Advanced 3.1 Joints - Advanced 20 3.2 References 29 4 Skeletal System Diseases and Disorders - Advanced 4.1 Skeletal System Diseases and 31 Disorders - Advanced 4.2 References 36 4 CHAPTER 1 The Skeleton - Advanced Chapter Outline 1.1 The Skeleton - Advanced 1.2 References 5 1.1. The Skeleton - Advanced www. 12.org 1.0 The Skeleton - Advanced FlexBooks 2.0 > Pre-EMT Course: Skeletal System > The Skeleton - Advanced [Figure 1] The skeletal system consists of all the bones of the body. How important are your bones? Try to imagine what you would look like without them. You would be a soft, wobbly pile of skin, muscles, and internal organs, so you might look something like a very large slug. Not that you would be able to see yourself—folds of skin would droop down over your eyes and block your vision because of your lack of skull bones. You could push the skin out of the way, if you could only move your arms, but you need bones for that as well! The Skeleton How important is your skeleton? Can you imagine what you would look like without it? You would be a wobbly pile of muscle and internal organs, maybe a little similar to the slug in Figure below. Not that you would be able to see yourself anyway, due to the folds of skin that would droop over your eyes because of your lack of skull bones. You could push the skin out of the way, if you could only move your arms! 6 https://ck12.org/flx/b/28109455/69579694 1.1. The Skeleton - Advanced www. 12.org [Figure 2] Banana slugs (Ariolimax spp.), unlike you, can live just fine without a bony skeleton. They can do so because they are relatively small, and their food source (vegetation) is plentiful and tends not to run away from them. Slugs move by causing a wave-like motion in their foot (the ventral (bottom) area of the slug that is in contact with the ground). Slugs and other gastropods also live in environments very different to human environments. Just think of how a bony skeleton would be of limited use to a slug whose lifetime is spent under a log munching on rotting leaf litter. Humans are vertebrates, which are animals that have a vertebral column, or backbone. Invertebrates, like the banana slug in Figure above, do not have a vertebral column, and they use a different mechanism than vertebrates to move about. The sturdy internal framework of bones and cartilage that is found inside vertebrates, including humans, is called an endoskeleton. The adult human skeleton consists of approximately 206 bones, some of which are named in Figure below. Cartilage, another component of the skeleton, can also be seen in Figure below. Cartilage is a type of dense connective tissue that is made of tough protein fibers. The function of cartilage in the adult skeleton is to provide smooth surfaces for the movement of bones at a joint. A ligament is a band of tough fibrous tissue that connects bones together. Ligaments are not very elastic, and some even prevent the movement of certain bones. The skeletons of babies and children have many more bones and more cartilage than adults have. As a child grows, these “extra” bones, such as the bones of the skull (cranium) and the sacrum (tailbone), fuse together, and cartilage gradually hardens to become bone tissue. 7 https://ck12.org/flx/b/28109455/69579694 1.1. The Skeleton - Advanced www. 12.org [Figure 3] The skeleton is the bone and cartilage scaffolding that supports the body and allows it to move. Bones act as attachment points for the muscles and tendons that move the body. Bones are also important for protection. For example, your skull bones (cranium) protect your brain, and your ribcage protects your heart and lungs. Cartilage is the light-gray material that is found between some of the bones and also between the ribcage and sternum. The bones of the skeleton can be grouped into two divisions: the axial skeleton and appendicular skeleton. The axial skeleton includes the bones of the head, vertebral column, ribs, and sternum and is shown in the right portion of Figure below. There are 80 bones in the axial skeleton. The appendicular skeleton includes the bones of the limbs (arms and legs) along with the scapula and the pelvis. It is shown on the left in Figure below. There are approximately 126 bones in the appendicular skeleton. Limbs are connected to the rest of the skeleton by collections of bones called girdles. The pectoral girdle consists of the clavicle (collar bone) and the scapula (shoulder blade). The pelvic girdle consists of two pelvic bones (hipbones). The vertebral column attaches to the top of the pelvis; the femur of each leg attaches to the bottom. The humerus is joined to the pectoral girdle at a joint and is held in place by muscles and ligaments. 8 https://ck12.org/flx/b/28109455/69579694 1.1. The Skeleton - Advanced www. 12.org [Figure 4] The two divisions of the human skeleton. The bones of the axial skeleton are blue, and the bones of the appendicular skeleton are pink. 9 https://ck12.org/flx/b/28109455/69579694 1.1. The Skeleton - Advanced www. 12.org https://braingenie.ck12.org/skills/embed/107606 Summary Children are born with significantly more bones and cartilage than adults; the cartilage hardens to become bone, and smaller bones fuse together to become the 206 adult bones. There are two parts of the human skeleton - the axial and appendicular skeletons. Review 1. What is the axial skeleton? 2. What is the appendicular skeleton? 3. What purpose does cartilage serve? Ligaments? 10 https://ck12.org/flx/b/28109455/69579694  REFERENCES 1.2 Image Attributions Credit: CK-12 Foundation Source: CK-12 Foundation License: CK-12 Curriculum Materials License Source: http://www.flickr.com/photos/acaben/516493964/ License: CC BY-SA Credit: Mariana Ruiz Villarreal Source: http://commons.wikimedia.org/wiki/File:Human_skeleton_front_en.svg License: Public Domain Credit: Mariana Ruiz Villarreal Source: http://commons.wikimedia.org/wiki/Image:Axial_skeleton_diagram.svg, http://commons.wikimedia.org/wiki/Image:Appendicular_skeleton_diagram.svg License: Public Domain (both) 11 CHAPTER 2 Bone Formation - Advanced Chapter Outline 2.1 Bone Formation - Advanced 2.2 References 12 2.1. Bone Formation - Advanced www. 12.org 2.0 Bone Formation - Advanced FlexBooks 2.0 > Pre-EMT Course: Skeletal System > Bone Formation - Advanced [Figure 1] How do bones grow? Bones are hard structures. So how do they grow? Well, bones are living tissue. They have a blood supply and grow from the cartilage at their ends. You are consistently making new bone. In fact, the human skeleton is replaced every 7-10 years. Development of Bones Ossification, or osteogenesis, is the process of bone formation. This process begins early in fetal development, usually by the end of the eighth week after conception. By this point, the skeletal pattern is formed by cartilage and connective tissue membranes, and ossification begins. Early in fetal development, the skeleton is made of cartilage. Cartilage is a type of dense connective tissue that is composed of collagen and/or elastin fibers and cells called chondrocytes, which are all set in a gel-like substance called the extracellular matrix. Cartilage does not contain any blood vessels, so nutrients diffuse through the matrix to the chondrocytes. Cartilage serves several functions such as providing a framework upon which bone deposition can begin and supplying smooth surfaces for the movement of bones at a joint. Cartilage is shown in Figure below. 13 https://ck12.org/flx/b/28109455/69579695 2.1. Bone Formation - Advanced www. 12.org [Figure 2] A micrograph of the structure of hyaline cartilage, the type of cartilage that is found in the fetal skeleton and at the ends of mature bones. The bones of the body gradually form and harden throughout the remaining gestation period and for years after birth in a process called endochondrial ossification. However, not all parts of the fetal cartilage are replaced by bone; cartilage remains in many places of the body including the joints, the rib cage, the ears, the tip of the nose, the bronchial tubes, and the discs between vertebrae. Endochondral Ossification Endochondral ossification is the process of replacing cartilage with bony tissue, as shown in Figure below. Most of the bones of the skeleton are formed in this way. During the third month after conception, blood vessels form and grow into the cartilage, transporting osteoblasts, osteoclasts, and stem cells into the interior. These begin to change the cartilage into bone tissue. The osteoblasts form a bone collar of compact bone around the diaphysis, or central shaft, of the bone. Osteoclasts remove material from the center of the bone and form the central cavity of long bones. Ossification continues from the center of the bone toward the ends of the bones. The cartilage at the ends of long bones are called the epiphyses. These continue to grow, so the developing bone increases in length. Later, usually after birth, secondary ossification centers form in the epiphyses, as shown in Figure below. Ossification in the epiphyses is similar to that in the center of the bone except that the spongy bone is kept instead of being broken down to form a cavity. When secondary ossification is complete, the cartilage is 14 https://ck12.org/flx/b/28109455/69579695 2.1. Bone Formation - Advanced www. 12.org totally replaced by bone except in two areas. A region of cartilage remains over the surface of the epiphysis as articular cartilage, and another area of cartilage remains inside the bone at either end. This area is called the epiphyseal plate or growth region. [Figure 3] Long bones ossify and get longer as they grow and develop. The process of endochondrial ossification happens when the skeleton is developing during fetal development and in childhood. When a bone develops from a fibrous membrane, the process is called intramembranous ossification. Intramembranous ossification usually happens in flat bones such as the cranial bones and the clavicles. During intramembranous ossification in the developing fetus, the future bones are first formed as connective tissue membranes. Osteoblasts migrate to the membranes and secrete osteoid, which becomes mineralized and forms bone matrix. When the osteoblasts are surrounded by matrix, they are called osteocytes. Eventually, a bone collar of compact bone develops, and marrow develops inside the bone. Bone Elongation An infant is born with zones of cartilage called epiphyseal plates, as shown in Figurebelow, between segments of bone to allow further growth of the bone. When the child reaches skeletal maturity (between the ages of 18 and 25 years), all of the cartilage in the plate is replaced by bone, which stops further growth. 15 https://ck12.org/flx/b/28109455/69579695 2.1. Bone Formation - Advanced www. 12.org [Figure 4] The location of the epiphyseal plate in an immature long bone. The chondrocytes in the epiphyseal plate are very metabolically active, as they constantly reproduce by mitosis. As the older chondrocytes move away from the plate, they are replaced by osteoblasts that mineralize this new area, and the bone lengthens. Bones grow in length at the epiphyseal plate by a process that is similar to endochondral ossification. The chondrocytes in the region of the epiphyseal plate grow by mitosis and push older chondrocytes down toward the diaphysis. Eventually, these chondrocytes age and die. Osteoblasts move into this region and replace the chondrocytes with bone matrix. This process lengthens the bone and continues throughout childhood and the adolescent years until the cartilage growth slows down and finally stops. When cartilage growth stops (usually in the early twenties), the epiphyseal plate completely ossifies so that only a thin epiphyseal line remains, and the bones can no longer grow in length. Bone growth is under the influence of growth hormone from the anterior pituitary gland and sex hormones from the ovaries and testes. Even though bones stop growing in length in early adulthood, they can continue to increase in thickness or diameter throughout life in response to stress from increased muscle activity or weight-bearing exercise. 16 https://ck12.org/flx/b/28109455/69579695 2.1. Bone Formation - Advanced www. 12.org https://flexbooks.ck12.org/flx/render/embeddedobject/186995 Summary Bones grow through a process called ossification. Long bones consist of a central shaft (the diaphysis) and cartilaginous ends called epiphyses. It is at the epiphyses and the epiphyseal plates that chondrocytes undergo mitosis to lengthen the bones. Review 1. What is ossification? 2. What purpose does matrix serve? 3. How do bones grow in length? Report Content Errors 17 https://ck12.org/flx/b/28109455/69579695  REFERENCES 2.2 Image Attributions Credit: Laura Guerin Source: CK-12 Foundation License: CK-12 Curriculum Materials License Credit: Emmanuelm Source: http://commons.wikimedia.org/wiki/File:Cartilage_polarised.jpg License: CC BY 3.0 Credit: LadyofHats License: CC BY-NC-SA 3.0 Credit: USFG Source: Adapted from http://training.seer.cancer.gov/anatomy/skeletal/growth.html License: Public Domain 18 CHAPTER 3 Joints - Advanced Chapter Outline 3.1 Joints - Advanced 3.2 References 19 3.1. Joints - Advanced www. 12.org 3.0 Joints - Advanced FlexBooks 2.0 > Pre-EMT Course: Skeletal System > Joints - Advanced [Figure 1] What allows running? Running. A means of terrestrial locomotion that allows humans and other animals to move rapidly on foot. The knees, which connect one part of the leg to the other, have to allow the legs to move. The knee is a joint, the part of the skeletal system that connects bones. Joints A joint (also called an articulation) is a point at which two or more bones make contact. They are constructed to allow movement and provide mechanical support for the body. Joints are a type of lever, which is a rigid object that is used to increase the mechanical force that can be applied to another object. This reduces the amount of energy that needs to be spent 20 https://ck12.org/flx/b/28109455/69579696 3.1. Joints - Advanced www. 12.org when moving the body around. The articular surfaces of bones, which are the surfaces that meet at joints, are covered with a smooth layer of articular cartilage. There are three types of joints: immovable, partly movable, and synovial. https://flexbooks.ck12.org/flx/render/embeddedobject/215 Immovable Joint At an immovable joint (or a fixed joint), bones are connected by dense connective tissue, which is usually collagen. Immovable joints, like those connecting the cranial bones, have edges that tightly interlock and do not allow movement. The connective tissue at immovable joints serves to absorb shocks that might otherwise break the bone. Partly Movable Joints At partly movable joints (or cartilaginous joints), bones are connected entirely by cartilage. Cartilaginous joints allow more movement between bones than a fibrous (fixed) joint does, but much less than the highly mobile synovial joint. Examples of partly-movable joints include the ribs, the sternum, and the vertebrae, which are shown in Figure below. Partly- movable joints also form the growth regions of immature long bones. 21 https://ck12.org/flx/b/28109455/69579696 3.1. Joints - Advanced www. 12.org [Figure 2] An illustration of a synovial disk, which is a cartilaginous joint. These partly-movable joints are found between the vertebrae. An X-ray of the cervical (neck) vertebrae is on the right. Synovial joints Synovial joints, also known as movable joints, are the most mobile joints of all. They are also the most common type of joint in the body. Synovial joints contain a space between the bones of the joint (the articulating bones), which is filled with synovial fluid. Synovial fluid is a thick, stringy fluid that has the consistency of egg albumin. The word "synovial" comes from the Latin word for "egg." The fluid reduces friction between the articular cartilage and other tissues in joints and lubricates and cushions them during movement. There are many different types of synovial joints and many different examples. A synovial joint is shown in Figure below. 22 https://ck12.org/flx/b/28109455/69579696 3.1. Joints - Advanced www. 12.org [Figure 3] A diagram of a synovial joint. Sinovial joints are the most common type of joint in the body, and they allow a wide range of motions. Think of how difficult walking would be if your knees and hips were only partly movable like your spine. The outer surface of the synovial joint contains ligaments that strengthen joints and hold bones in position. The inner surface (the synovial membrane) has cells that produce synovial fluid to lubricate the joint and prevent the two cartilage caps on the bones from rubbing together. Some joints also have tendons, which are bands of connective tissue that link muscles to bones. Bursae are small sacs filled with synovial fluid that reduce friction in the joint. The knee joint contains 13 bursae. Synovial joints can be classified by the degree of mobility that they allow, as shown in Figure below. 23 https://ck12.org/flx/b/28109455/69579696 3.1. Joints - Advanced www. 12.org [Figure 4] Types of synovial joints. These fully-movable joints between bones allow for a wide range of bodily motions. They also help reduce the amount of energy needed to move the body. In a ball and socket joint, the ball-shaped surface of one bone fits into the cup-like depression of another. Examples of ball and socket joints include the hip (Figure below) and shoulder. In an ellipsoidal joint, an ovoid articular surface fits into an elliptical cavity in such a way as to permit some back and forth movement, but not side-to-side motion. The wrist joint and knee (Figure below) are examples of this type of joint. 24 https://ck12.org/flx/b/28109455/69579696 3.1. Joints - Advanced www. 12.org [Figure 5] The knee joint is an ellipsoidal joint. 25 https://ck12.org/flx/b/28109455/69579696 3.1. Joints - Advanced www. 12.org [Figure 6] The hip joint is a ball and socket joint. In a saddle joint, the opposing bone surfaces are fit together like a person sitting in a saddle. The movements at a saddle joint are the same as in an ellipsoidal joint. The best example of this is the joint between the carpals and metacarpals of the thumb. In the hinge joint, the articular surfaces fit together in such a way as to permit motion only in one plane: forward and backward. The extent of motion, however, is considerable. An example of a hinge joint is the elbow. The pivot joint is formed by a process that rotates within a ring; the ring is formed partly of bone and partly of ligament. An example of a pivot joint is the joint between the radius and ulna that allows you to turn the palm of your hand up and down. A gliding joint, also known as a plane joint, is a joint that allows one bone to slide over another, such as between the carpels of the fingers. Gliding joints are also found in your wrists and ankles. Not all bones are directly interconnected; there are 6 bones in the middle ears called the ossicles (three on each side) that articulate only with each other. The hyoid bone, which is 26 https://ck12.org/flx/b/28109455/69579696 3.1. Joints - Advanced www. 12.org located in the neck and serves as the point of attachment for the tongue, does not articulate with any other bones in the body, but is supported by muscles and ligaments. The longest and heaviest bone in the body is the femur, and the smallest is the stapes in the middle ear. In an adult, the skeleton makes up around 20% of the total body weight. https://flexbooks.ck12.org/flx/render/embeddedobject/186996 Summary Joints are the points at which two or more bones make contact. There are 3 types of joints: immovable, partly movable, and synovial joints, which are movable. There are 6 types of synovial joints: ball and socket, ellipsoidal, saddle, hinge, pivot, and gliding. Review 1. What differentiates a synovial joint from other types of joints? 2. For each joint, give the type of joint it is and a general description of how that joint type can move. a. Ulna/Radius. b. Knee. c. Elbow. 27 https://ck12.org/flx/b/28109455/69579696 3.1. Joints - Advanced www. 12.org d. Thumb carpal/metacarpal. e. Shoulder. f. Finger carpal/metacarpal. Report Content Errors 28 https://ck12.org/flx/b/28109455/69579696  REFERENCES 3.2 Image Attributions Credit: CK-12 Foundation Source: CK-12 Foundation License: CK-12 Curriculum Materials License Source: http://en.wikipedia.org/wiki/Image:Gray298.png http://www.flickr.com/photos/ciscel/382453477/ License: Public Domain; CC BY-SA Credit: Laura Guerin Source: CK-12 Foundation License: CC BY-NC 3.0 Credit: Zachary Wilson, using skeleton by User:GregorDS/Wikimedia Commons Source: CK-12 Foundation (skeleton available at http://commons.wikimedia.org/wiki/File:Human_skeleton_diagram_trace.svg License: CC BY-NC 3.0; Skeleton: Public Domain Credit: mtkopone Source: http://www.flickr.com/photos/mtkopone/2343141506/ License: CC BY 2.0 Credit: Henry Gray Source: http://commons.wikimedia.org/wiki/File:Gray343.png License: Public Domain 29 CHAPTER 4 Skeletal System Diseases and Disorders - Advanced Chapter Outline 4.1 Skeletal System Diseases and Disorders - Advanced 4.2 References 30 4.1. Skeletal System Diseases and Disorders - Advanced www. 12.org 4.0 Skeletal System Diseases and Disorders - Advanced FlexBooks 2.0 > Pre-EMT Course: Skeletal System > Skeletal System Diseases and Disorders - Advanced [Figure 1] Do you think this would hurt? Why? That would probably hurt a lot. Broken bones, or fractures, may be one of the more common problems of the skeletal system. And this one would need surgery to fix. But, in addition to broken bones, there are other problems and diseases of the skeletal system. Homeostatic Imbalances of Bone Despite their great strength, bones can fracture, or break. Fractures can occur at different places on a bone and are usually due to excessive bending stress on the bone. Fractures can be complete, in which the bone is completely broken, or incomplete, in which the bone is cracked or chipped but not broken all the way. Immediately after a fracture, blood vessels that were torn leak blood into surrounding tissues, and a mass of clotted blood, called a hematoma, forms. The area becomes swollen and sore. Within a few days, capillaries begin 31 https://ck12.org/flx/b/28109455/69579697 4.1. Skeletal System Diseases and Disorders - Advanced www. 12.org to grow into the hematoma, and white blood cells clean up the dead and dying cells. Fibroblasts, osteoblasts, and chondroblasts arrive and begin to rebuild the bone. Fibroblasts produce collagen fibers that span the area of the break and connect the ends of the broken bone together. Osteoblasts begin to form spongy bone, and chondroblasts form cartilage matrix. The cartilage and spongy bone are replaced by a bony growth called a callus, which forms about 3 to 4 weeks after the fracture. This growth continues until the break is firmly sealed 2 to 3 months later. Eventually, the bony callus is replaced by spongy and compact bone, similar to the rest of the bone. Rickets Rickets is a softening of the bones in children, which potentially leads to fractures and deformity; bowing of the leg bones is shown in Figure below. Rickets is among the most frequent childhood diseases in many developing countries. The most common cause is a vitamin D deficiency. Vitamin D is needed by the body to absorb calcium from foods and to form bones. However, lack of calcium in one's diet may also cause rickets. Although it can occur in adults, most cases of rickets occur in children who suffer from severe malnutrition, which usually results from starvation during early childhood. Osteomalacia is the term used to describe a similar condition occurring in adults, which is also generally due to a deficiency of vitamin D. Osteomalacia can result in bone pain, difficulty in putting weight on bones, and sometimes fractures. Some studies show that most people get enough Vitamin D through their food and exposure to ultraviolet (UV) radiation in sunlight. Vitamin D is produced by certain skin cells from a compound found inside the cells. The skin cells need UV light for this reaction to happen. However, eating foods fortified with Vitamin D or taking a dietary supplement pill is usually preferred to UV exposure due to the increased risk of sun burn and skin cancer. Many countries have fortified certain foods, such as milk, bread, and breakfast cereals, with Vitamin D to help prevent deficiency. 32 https://ck12.org/flx/b/28109455/69579697 4.1. Skeletal System Diseases and Disorders - Advanced www. 12.org [Figure 2] An image of the typical bowing of the femurs that occurs in rickets. Rickets causes poor bone mineralization, which results in the bones bending under the weight of the body. Osteoporosis Osteoporosis is a disease in which the breakdown of bone matrix by osteoclasts is greater than the building of bone matrix by osteoblasts. This results in greatly decreased bone mass, causing bones to become lighter and more porous. Bones are then more prone to breakage, especially the vertebrae and femurs. Compression fractures of the vertebrae and hip breaks, in which the top (or head) of the femur breaks, are common and can lead to further immobility, making the disease worse. Osteoporosis mostly occurs in older women and is linked to the decrease in production of sex hormones. However, poor nutrition, especially diets that are low in calcium and vitamin D, increases the risk of osteoporosis in later life. One of the easiest ways to prevent osteoporosis is to eat a healthy diet that has adequate calcium and vitamin D. 33 https://ck12.org/flx/b/28109455/69579697 4.1. Skeletal System Diseases and Disorders - Advanced www. 12.org https://flexbooks.ck12.org/flx/render/embeddedobject/216 [Figure 3] Total replacement of the hip joint. One of the leading reasons for hip replacements is osteoarthritis of the joint. The cartilage around the top of the femur deteriorates over time and causes the bones of the joint to grind painfully against each other. This can result in a narrowing of the space in the ball and socket joint structure, causing limited movement of the hip and constant pain in the hip joint. 34 https://ck12.org/flx/b/28109455/69579697 4.1. Skeletal System Diseases and Disorders - Advanced www. 12.org Osteoarthritis Osteoarthritis is a condition in which wearing and breakdown of the cartilage that covers the ends of the bones leads to pain and stiffness in the joint. Decreased movement of the joint because of the pain may cause muscles that are attached to the joint to become weaker, and ligaments may become looser. Osteoarthritis is the most common form of arthritis. Some of the most common causes include old age, sports injuries to the joint, bone fractures, and being overweight or obese. A total hip replacement is a common treatment for osteoarthritis. An X-ray image of a replacement hip joint is shown in Figureabove. Skeletal Dysplasias The skeletal dysplasias are a group of hundreds (more than 380 conditions ) of genetic conditions that affect bone and cartilage growth. A child born with skeletal dysplasia will have abnormal differences in the size and shape of their legs, arms, trunk, or skull. He or she may be very short in stature. Additionally, he or she may have arms and legs that are not in proportion with the rest of the body. Achondroplasia, the most common form of dwarfism, is a skeletal dysplasia. Achondroplasia is discussed in the Human Genetics: Genetic Disorders (Advanced) concept. Summary Fractures are the most common form of injury to bones. Vitamin D or calcium deficiency can lead to rickets and/or osteoporosis. Osteoporosis and osteoarthritis are both more common in the elderly. Review 1. What can cause osteoarthritis other than old age? 2. Why is Vitamin D so important for healthy bones? 3. What is osteomalacia? Report Content Errors 35 https://ck12.org/flx/b/28109455/69579697  REFERENCES 4.2 Image Attributions Credit: Taokinesis Source: https://pixabay.com/photos/fracture-bone-xray-skeleton-2333164/ License: Pixabay License Credit: CK-12 Foundation Source: CK-12 Foundation License: CK-12 Curriculum Materials License Credit: X-ray Image ID: 3684. Photographer: Unknown. Source: http://commons.wikimedia.org/wiki/File:Hip_replacement_Image_3684-PH.jpg License: public domain 36