Anatomy & Physiology Essentials 2e, Textbook Page 157 (173 of 624)

Copyright Goodheart-Willcox Co., Inc. Chapter 5 The Skeletal System 157 Avulsions are fractures caused when a tendon or ligament pulls away from its attachment to a bone, taking a small chip of bone with it. Explosive throwing and jumping movements may cause avulsion fractures of the medial epicondyle of the humerus and the calcaneus. Forceful bending and twisting movements can produce spiral fractures of the long bones. A common example occurs during downhill skiing. When a ski is planted in one direction, and the skier rotates while falling in a different direction, a spiral fracture of the tibia can result. The bones of children contain relatively larger amounts of collagen than the bones of adults. For this reason, children’s bones are more flexible and are generally less likely to fracture than adult bones. Compression fractures result when bone fails under a compressive force. There are several variations of compression fractures, based on the direction of the compressive force and the resulting injury to the bone. An impacted fracture is one in which the compressive force is directed along the longitudinal axis of a long bone, causing the broken ends of the bone to be forced together. Crush fractures occur most often in the weakened osteoporotic spine when the internal trabecular bone fails under a compressive load directed down the length of the spinal column, resulting in a loss of vertebral height. Vertebral crush fractures caused by postural loading are known as wedge fractures. These result from compression directed down the anterior side of the spine, often result in a wedge-shaped vertebral body with the narrow portion to the front. A greenstick fracture is incomplete. The break occurs on the convex surface of the bend in the bone. Wedge fractures A comminuted fracture is complete and splinters the bone. A spiral fracture is caused by twisting a bone excessively. An impacted fracture involves compression of a long bone along the longitudinal axis, forcing the broken ends together. A wedge fracture occurs vertically in the spinal column, resulting in a wedge-shaped vertebra. A crush fracture is one in which a bone fails under a compressive load. A stress fracture involves an incomplete break. © Body Scientific International Figure 5.36 Types of fractures.

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Copyright Goodheart-Willcox Co., Inc. Chapter 5 The Skeletal System 157 Avulsions are fractures caused when a tendon or ligament pulls away from its attachment to a bone, taking a small chip of bone with it. Explosive throwing and jumping movements may cause avulsion fractures of the medial epicondyle of the humerus and the calcaneus. Forceful bending and twisting movements can produce spiral fractures of the long bones. A common example occurs during downhill skiing. When a ski is planted in one direction, and the skier rotates while falling in a different direction, a spiral fracture of the tibia can result. The bones of children contain relatively larger amounts of collagen than the bones of adults. For this reason, children’s bones are more flexible and are generally less likely to fracture than adult bones. Compression fractures result when bone fails under a compressive force. There are several variations of compression fractures, based on the direction of the compressive force and the resulting injury to the bone. An impacted fracture is one in which the compressive force is directed along the longitudinal axis of a long bone, causing the broken ends of the bone to be forced together. Crush fractures occur most often in the weakened osteoporotic spine when the internal trabecular bone fails under a compressive load directed down the length of the spinal column, resulting in a loss of vertebral height. Vertebral crush fractures caused by postural loading are known as wedge fractures. These result from compression directed down the anterior side of the spine, often result in a wedge-shaped vertebral body with the narrow portion to the front. A greenstick fracture is incomplete. The break occurs on the convex surface of the bend in the bone. Wedge fractures A comminuted fracture is complete and splinters the bone. A spiral fracture is caused by twisting a bone excessively. An impacted fracture involves compression of a long bone along the longitudinal axis, forcing the broken ends together. A wedge fracture occurs vertically in the spinal column, resulting in a wedge-shaped vertebra. A crush fracture is one in which a bone fails under a compressive load. A stress fracture involves an incomplete break. © Body Scientific International Figure 5.36 Types of fractures.

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156 Anatomy & Physiology Essentials Copyright Goodheart-Willcox Co., Inc. Fractures A fracture is a break or crack in a bone. The nature of a fracture depends on the size, direction, and duration of the injurious force, as well as the health and maturity of the bone. Fractures are classified as simple when the bone ends remain within the surrounding soft tissues, and compound when one or both bone ends protrude from the skin. When the bone is splintered, the fracture is said to be comminuted. See Figure 5.36. C onsidering all of the important functions performed by bone, bone health is a vital part of general health. Bone health can be diminished by injuries and pathologies. Common Bone Injuries Perhaps the most common, and often the most visible, types of bone injuries are fractures of various types. However, other types of injuries, such as epiphyseal injuries, are also possible. hinge joint a type of diarthrosis that allows only hinge-like movements in forward and backward directions ligament a band of collagen and elastic fibers that connects bones to other bones pivot joint a type of diarthrosis that permits rotation around only one axis saddle joint a type of diarthrosis in which the articulating bone surfaces are both shaped like the seat of a riding saddle symphysis a type of amphiarthrosis in which a thin plate of hyaline cartilage separates a disc of fibrocartilage from the bones synarthrosis a fibrous joint that can absorb shock, but which permits little or no movement of the articulating bones synchondrosis a type of amphiarthrosis joint in which the articulating bones are held together by a thin layer of hyaline cartilage syndesmosis a type of synarthrosis joint at which dense, fibrous tissue binds the bones together, permitting extremely limited movement synovial joint a diarthrodial joint tendon a band of collagen and elastic fibers that connects a muscle to a bone tendon sheaths double-layered synovial structures surrounding tendons that are subject to friction because they are located so close to bones secrete synovial fluid to promote free motion of the tendons during joint movement Review Questions 1. What does it mean to say that bones articulate with each other? 2. Give two examples of immovable joints and state where they are found in the body. 3. Give two examples of slightly movable joints and state where they are found in the body. 4. Give six examples of freely movable joints and state where they are found in the body. 5. Why is it important to have a layer of cartilage between bones that articulate with each other? 6. Why does the human body need joints that permit little to no movement in the skeleton? 7. What happens when articular cartilage begins to erode from excessive wear and stress on a joint? SECTION 5.6 Injuries and Disorders of the Skeletal System Objectives • Identify the different types of bone and epiphyseal injuries, and explain the forces that can cause each of these injuries. • Discuss osteoporosis, including contributing factors, groups at risk, consequences, and prevention strategies. • Describe the common types of joint injuries, including the structures affected, symptoms, and common treatments. • Explain what is involved with arthritis and describe specific types of arthritis. Key Terms amenorrhea anorexia nervosa apophysis arthritis bulimia nervosa bursitis dislocation female athlete triad fracture osteoarthritis osteopenia osteoporosis rheumatoid arthritis sprain

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158 Anatomy & Physiology Essentials Copyright Goodheart-Willcox Co., Inc. osteoblasts deposit new bone at the site, resulting in repair of the injury. However, when overuse is repeated or continuous, the remodeling process cannot keep up with the damage being done. When this happens, the condition progresses to a stress fracture. Runners are prone to stress fractures, particularly in the tibia and the metatarsals. Consequently, greenstick fractures, or incomplete fractures, are more common in children than in adults. A greenstick fracture is caused when a bone bends or twists but does not break all the way through. Stress fractures are tiny, painful cracks in bone that result from overuse. Under normal circumstances, bone responds to stress-related injury by remodeling. Osteoclasts resorb the damaged tissue, and then Bone Tissue Engineering Fractures and malformations of the skull and face can result from birth defects, infections, cancers, or traumatic injury. These can be dangerous for patients and often require costly healthcare procedures. Current approaches to repair and reconstruction include rigid fixation of an artificial plate, bone grafting, and transfer of new bone tissue to the region. However, these techniques often involve complications, such as poor fitting of the plate or graft failure. Bone tissue engineering, one of the most challenging and exciting new fields for scientists and clinicians, offers some creative new approaches. Engineered therapies for enhanced healing and regeneration of craniofacial bone typically involve a combination of live stem cells and growth factors applied over artificial, biodegradable scaffolds. The success of bone tissue engineering relies on understanding the complex interactions among live stem cells, the regulatory signals, and the platforms used to deliver them. All of these components are collectively known as the tissue engineering triad. The live cells employed are typically mesenchymal stem cells combined with bone marrow. A surgeon harvests a small amount of mesenchymal stem cells from the patient’s iliac crest. These cells are then carefully cultured in a growth medium until they become larger cell colonies that can differentiate into cells that form bone. More recently, scientists have discovered that stem cells can also be extracted from fat. These adipose stem cells can be collected in large quantities with little patient discomfort, in contrast to the invasive and painful extraction techniques used to obtain bone marrow mesenchymal cells. Although promising, more studies are needed to standardize and refine the techniques for harvesting and culturing adipose stem cells. Whatever the source, the live bone cells are cultured and then implanted on a biomaterial scaffold. Many different growth factor delivery techniques and scaffold compositions have been explored, although none has yet emerged as universally recommended. Scientists have discovered that the size of the pores in the scaffolding material can greatly influence the ability of the cells to attach and colonize. Different scaffold materials also exert different biomechanical forces, which can profoundly affect bone cell development. Identifying biomaterials that are optimally capable of responding to physiological and mechanical changes inside the human body remains an important challenge in bone tissue engineering. Once the cells have been implanted on the scaffold, a surgeon inserts the bone cell colony and scaffold material into the site of bone damage. At this point, new challenges arise, including promoting the development of a blood supply to the implant and ensuring the survival of the live cells. Achieving long-term repair requires infusion of antibiotics and growth factors in appropriate amounts and with optimal timing during the healing and repair processes. Utilization of nanoparticles for delivery of drugs and growth factors to the region is one promising approach. Another new approach begins with a CT scan of the bone defect and extraction of a small sample of fat from the patient. The CT scan is used to create a precise, three-dimensional model of the site that requires repair. The model is then placed in a growth chamber along with stem cells from the patient’s fat sample. Ideally, in a few weeks, a perfectly fitting bony replacement part will grow from the patient’s own cells. This promising approach is currently being developed in animals. Clinical Application Jose Luis Calvo/Shutterstock.com Growing new bone tissue is quite a complicated process, as evidenced by this microscopic view of bone structure showing osteons and Haversian canals.

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