SUGGESTED CHAPTER OUTLINE

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1 CHAPTER 9: Skeletal System: Articulations CHAPTER OVERVIEW This chapter is designed to introduce students to the skeletal system joints, termed articulations. Joint motions will also be presented. The changes that occur in joints as a result of aging are discussed. Different joints have differing ranges of motions; factors that determine the range of motion at a joint are presented in this chapter. Some types of joint motions involve lever actions; different types of levers give differing mechanical advantages and differing ranges of motions. In this chapter students will obtain knowledge of the different classes of levers along with their differing mechanical advantages and differing ranges of motions. Orthopedic surgeons and sports medicine physicians constantly must evaluate and treat bone and joint problems. These physicians, along with others, must be aware of the normal range of movement at each joint, the muscular and ligamentous structures that support the joint, and how injury may impact mobility and ultimate healing of the joint. This chapter presents anatomical and physiological concepts relevant to most of the necessary areas of knowledge that a clinician treating bone and joint problems should know. Certain pathological conditions of joints are also presented in this chapter. SUGGESTED CHAPTER OUTLINE 9.1 Classification of Joints: Joints are classified by both their structural characteristics and the movements they allow. (pp ) 1. A joint, or articulation, is the place of contact between bones, between bone and cartilage, or between bones and teeth. 2. Bones are said to articulate with each other at a joint. 3. The scientific study of joints is called arthrology. 4. Joints are classified by both their structural characteristics and the movements they allow. 5. A fibrous joint has no joint cavity and occurs where bones are held together by dense regular (fibrous) connective tissue. 6. A cartilaginous joint has no joint cavity and occurs where bones are joined by cartilage. 7. A synovial joint has a fluid-filled joint cavity that separates the articulating surfaces of the bones. 8. A synarthrosis is an immobile joint. 9. An amphiarthrosis is a slightly mobile joint. 10. A diarthrosis is a freely mobile joint; all synovial joints are diarthroses. 11. There is an inverse relationship between mobility and stability in articulations. 9.2 Fibrous Joints: Articulating bones in fibrous joints are connected by dense regular connective tissue, and most fibrous joints are immobile. (pp ) A. Gomphoses (p. 300) 1. A gomphosis resembles a peg in a socket. 2. The only gomphoses in the human body are the articulations of the roots of teeth with the sockets of the mandible and the maxillae. 3. A tooth is held firmly in place by fibrous periodontal membranes. 4. The gomphosis between tooth and jaw is a synarthrosis. B. Sutures (pp ) 1. Sutures are immobile fibrous joints (synarthroses) that are found only between certain bones of the skull. 2. Sutures have distinct, interlocking, usually irregular edges. 3. Sutures permit the skull to grow as the brain increases in size during childhood. 4. In an older adult, the dense regular connective tissue in the suture becomes ossified, fusing the skull bones together and transforming the sutures into synostoses. C. Syndesmoses (p. 301) 1. Syndesmoses are fibrous joints in which articulating bones are joined by long strands of dense regular connective tissue only. 2. Syndesmoses are classified as amphiarthroses. 3. Syndesmoses are found between the radius and ulna and between the tibia and fibula. 4. The shafts of the two articulating bones are bound by a broad ligamentous sheet called an interosseous membrane, which provides a pivot where the articulating bones can move against one another. 132

2 9.3 Cartilaginous Joints: Cartilaginous joints have cartilage between the articulating bones and are either immobile or slightly mobile. (pp ) A. Synchondroses (pp ) 1. An articulation in which bones are joined by hyaline cartilage is called a synchondrosis. 2. All synchondroses are synarthroses. 3. Examples of synchondroses are the epiphyseal plate in children, the spheno-occipital synchondrosis, the costochondral joints of the ribs, and the first sternocostal joint. 4. Clinical View: Costochondritis (p. 301) a. Costochondritis - inflammation and irritation of the costochondral joints, resulting in localized chest pain. b. The cause of costochondritis is usually unknown c. Costochondritis may be mistaken for pain from a myocardial infarction. d. Costochondritis may be treated with NSAIDs, and symptoms typically disappear after several weeks. B. Symphyses (p. 302) 1. A symphysis has a pad of fibrocartilage between the articulating bones, which resists compression and tension stresses. 2. All symphyses are amphiarthroses. 3. Examples of a symphysis include the pubic symphysis and the intervertebral discs. 9.4 Synovial Joints: Synovial joints have a fluid-filled joint cavity and are freely mobile articulations. (pp ) A. Distinguishing Features and Anatomy of Synovial Joints (pp ) 1. All synovial joints are classified as diarthroses. 2. Each synovial joint is composed of a double-layered capsule called the articular capsule. 3. The outer layer of the articular capsule is the fibrous layer, which is formed from dense connective tissue and strengthens the joint. 4. The inner layer of the articular capsule is the synovial membrane, which is composed primarily of areolar connective tissue and helps produce synovial fluid. 5. All articulating bone surfaces in a synovial joint are covered by a thin layer of hyaline cartilage called articular cartilage, which lacks a perichondrium. 6. Only synovial joints house a joint cavity, a space that permits separation of the articulating bones. 7. Synovial fluid is a viscous, oily substance located within a synovial joint and is produced from the synovial membrane and filtrate from blood plasma. 8. Synovial fluid has three functions: It lubricates the articular cartilage, nourishes the chondrocytes of the articular cartilage, and acts as a shock absorber. 9. Ligaments are composed of dense regular connective tissue; they connect one bone to another bone and stabilize, strengthen, and reinforce most synovial joints. 10. Extrinsic ligaments are outside of the joint capsule; intrinsic ligaments represent thickenings of the articular capsule itself. 11. All synovial joints have numerous sensory nerves and blood vessels that innervate and supply the articular capsule and associated ligaments. 12. Tendons are like ligaments and are composed of dense regular connective tissue, but they are not part of the synovial joint itself. 13. Tendons attach muscle to bone; they stabilize joints, provide mechanical support, and limit the range of movement of joints. 14. A bursa is a fibrous, saclike structure that contains synovial fluid and is lined internally by a synovial membrane. 15. Bursae may be either connected to the joint cavity or completely separate from it. 16. An elongated bursa called a tendon sheath wraps around tendons where there may be excessive friction, particularly in the wrist and ankle. 17. Fat pads are often distributed along the periphery of a synovial joint. 18. Fat pads act as packing material and provide protection for the joint. 19. Clinical View: Cracking Knuckles (p. 303) a. Cavitation occurs when gases dissolved in joint fluid form bubbles, due to the stretching or pulling of a synovial joint and the resultant decrease in pressure. 133

3 b. When the joint is stretched to a certain point, the pressure in the joint drops further, so the bubbles burst, resulting in a popping or cracking sound. c. Contrary to popular belief, cracking your knuckles does not cause arthritis. B. Classification of Synovial Joints (p. 304) 1. Synovial joints are classified by the shapes of their articulating surfaces and the types of movement they allow. 2. A joint is said to be uniaxial if the bone moves in just one plane or axis. 3. A joint is biaxial if the bone moves in two planes or axes. 4. A joint is multiaxial (or triaxial) if the bone moves in multiple planes or axes. 5. A plane joint is the simplest synovial articulation and the least mobile type of diarthrosis. 6. Plane joints are described as uniaxial because they mostly provide movement in one direction, with limited sideto-side movements. 7. The articular surfaces of the bones of plane joints are flat. 8. Examples of plane joints include the intercarpal and intertarsal joints. 9. A hinge joint is a uniaxial joint formed by the convex surface of one articulating bone fitting into a concave depression on the other bone in the joint. 10. An example of a hinge joint is the elbow joint. 11. A pivot joint is a uniaxial joint in which one articulating bone with a rounded surface fits into a ring formed by a ligament and another bone. 12. Examples of a pivot joint include the proximal radioulnar joint and the atlantoaxial joint. 13. Condylar joints are biaxial joints with an oval, convex surface on one bone that articulates with a concave articular surface on the second bone of the joint. 14. Examples of condylar joints are the metacarpophalangeal joints of fingers 2 through 5, or knuckles. 15. A saddle joint is a biaxial joint that is so named because the articular surfaces of the bones have convex and concave regions that resemble the shape of a saddle. 16. An example of a saddle joint is the carpometacarpal joint of the thumb. 17. Ball-and-socket joints are multiaxial joints in which the spherical articulating head of one bone fits into the rounded, cuplike socket of a second bone. 18. Examples of ball-and-socket joints include the coxal and glenohumeral joints. 9.5 Synovial Joints and Levers: Anatomists often compare the movement of synovial joints to the mechanics of a lever, a practice called biomechanics. (pp ) A. Terminology of Levers (pp ) 1. A lever is an elongated, rigid object that rotates around a fixed point called a fulcrum. 2. Levers have the ability to alter or change the speed and distance of movement produced by a force, the direction of an applied force, and the force strength. 3. Movement occurs when an effort applied to one point on the lever exceeds a resistance located at some other point. 4. The part of a lever from the fulcrum to the point of effort is called the effort arm. 5. The lever part from the fulcrum to the point of resistance is the resistance arm. 6. In the body, a long bone acts as a lever, a joint serves as the fulcrum, and the effort is generated by a muscle attached to the bone. B. Types of Levers (pp ) 1. A first-class lever has a fulcrum in the middle, between the effort and the resistance. 2. An example of a first-class lever in the body is the atlanto-occipital joint of the neck. 3. The resistance in a second-class lever is between the fulcrum and the applied effort. 4. Second-class levers are rare in the body, but one example is the plantar flexion of the foot so that a person can stand on tiptoe. 5. A third-class lever is observed when the effort is applied between the resistance and the fulcrum. 6. Third-class levers are the most common levers in the body; examples include the elbow joint and the temporomandibular joint. 9.6 The Movements of Synovial Joints: Four types of motion occur at synovial joints: gliding, angular, rotational, and special movements. (pp ) A. Gliding Motion (p. 307) 134

4 1. Gliding is a simple movement in which two opposing surfaces slide slightly back-and-forth or side-to-side with respect to one another. 2. The angle between the bones does not change, and only limited movement is possible in any direction. 3. Gliding motion typically occurs along plane joints. B. Angular Motion (pp ) 1. Angular motion either increases or decreases the angle between two bones. 2. Angular motion occurs at many of the synovial joints. 3. Angular motion includes flexion and extension, hyperextension, lateral flexion, abduction and adduction, and circumduction. 4. Flexion is movement in the anterior-posterior plane of the body that decreases the angle between the bones; the opposite of flexion is extension. 5. When a joint is extended more than 180 degrees, the movement is called hyperextension. 6. Lateral flexion occurs when the trunk of the body moves in a coronal plane laterally away from the body. 7. Abduction is a lateral movement of a body part away from the body midline; the opposite of abduction is adduction. 8. Circumduction is a sequence of movements in which the proximal end of an appendage remains relatively stationary while the distal end makes a circular motion, making an imaginary cone shape. C. Rotational Motion (pp ) 1. Rotation is a pivoting motion in which a bone turns on its own longitudinal axis. 2. Lateral rotation turns the anterior surface of a bone laterally, while medial rotation turns the anterior surface medially. 3. Pronation is the medial rotation of the forearm so that the palm of the hand is directed posteriorly; supination occurs when the forearm rotates laterally so that the palm is in the anatomical position. D. Special Movements (pp ) 1. Some movements occur only at specific joints and do not readily fit into any of the functional categories previously discussed, including depression and elevation, dorsiflexion and plantar flexion, eversion and inversion, protraction and retraction, and opposition. 2. Depression is the inferior movement of a part of the body; elevation is the superior movement of a body part. 3. Dorsiflexion occurs when the talocrural (ankle) joint is bent such that the dorsum of the foot and toes moves toward the leg; plantar flexion is a movement of the foot at the talocrural joint so that the toes point inferiorly. 4. Inversion occurs when the sole of the foot turns medially; eversion occurs when the sole of the foot turns to face laterally. 5. Protraction is the anterior movement of a body part from the anatomic position; retraction is the posteriorly directed movement of a body part from the anatomic position. 6. Opposition occurs at the carpometacarpal joint, when the thumb crosses the hand to grasp objects; reposition is the opposite movement. 9.7 Features and Anatomy of Selected Joints: The structure and function of the more commonly known articulations of the axial and appendicular skeletons are examined, though many more joints exist than are discussed. (pp ) A. Temporomandibular Joint (p. 312) 1. The temporomandibular joint (TMJ) is the articulation formed at the point where the head of the mandible articulates with the temporal bone. 2. A loose articular capsule surrounds the joint and promotes an extensive range of motion. 3. Inside the articular capsule is an articular disc that is a thick pad of fibrocartilage separating the articulating bones and extending horizontally to divide the synovial cavity into two separate chambers; thus, the TMJ is really two synovial joints. 4. The sphenomandibular ligament is a thin band that extends anteriorly and inferiorly from the sphenoid to the medial surface of the mandibular ramus. 5. The temporomandibular ligament is composed of two short bands that extend inferiorly and posteriorly from the articular tubercle to the mandible. 6. The TMJ exhibits hinge, gliding, and some pivot joint movements. 7. Clinical View: TMJ Disorders (p. 312) 135

5 a. The TMJ is subject to various disorders, which are often seen in people who habitually chew gum or grind or clench their teeth. b. The most common TMJ disorder occurs as a result of alterations in the ligaments that secure the joint, causing progressive internal displacement of the articular disc, producing a clicking or popping noise. c. Pain from the TMJ disorder is widespread, rather than limited to the TMJ, because many structures, including the muscle and jaws are innervated by the trigeminal nerve. B. Shoulder Joint (pp ) 1. The sternoclavicular joint is a saddle joint formed by the articulation between the manubrium of the sternum and the sternal end of the clavicle. 2. An articular disc partitions the sternoclavicular joint into two parts and forms two separate synovial cavities, allowing a wide range of movement including elevation, depression, and circumduction. 3. The acromioclavicular joint is a plane joint between the acromion and the lateral end of the clavicle. 4. The fibrous joint capsule is strengthened superiorly by an acromioclavicular ligament, and a very strong coracoclavicular ligament binds the clavicle to the coracoid process of the scapula. 5. Clinical View: Shoulder Joint Dislocation (p. 316) a. Dislocation is a joint injury in which the articulating bones have separated. b. The term shoulder dislocation most of the time refers to a dislocation of the acromioclavicular joint or glenohumeral joint rather than the sternoclavicular joint; when the dislocation occurs at the acromioclavicular joint, it can be termed a shoulder separation. c. Shoulder dislocation often results from a hard blow to the joint. d. The symptoms of shoulder dislocation include tenderness and edema in the area of the joint, and pain when the arm is abducted more than 90 degrees; the acromion will also appear very prominent and more pointed. e. Treatment ranges from rest to surgical intervention, depending on severity. f. Since the glenohumeral joint is very mobile and relatively unstable, dislocations are common, especially when a fully abducted humerus is struck hard. g. In a glenohumeral dislocation, the head of the humerus is pushed into the inferior part of the capsule and tears it as the humerus dislocates; chest muscles then pull superiorly and medially on the humeral head, causing it to lie just inferior to the coracoid process. h. A dislocated glenohumeral joint appears flattened and squared-off. i. Some glenohumeral dislocations can be popped back into place, but more severe dislocations may need surgical repair. 6. The glenohumeral joint is a ball-and-socket joint formed by the articulation of the head of the humerus and the glenoid cavity. 7. The coracoacromial ligament extends across the space between the coracoid process and the acromion; the large coracohumeral ligament is a thickening of the superior part of the joint capsule, extending from the coracoid process to the humeral head. 8. The glenohumeral ligaments are three thickenings of the anterior portion of the articular capsule, and provide minimal support. 9. Most of the joint s strength is due to the rotator cuff muscles surrounding it, which work as a group to hold the head of the humerus in the glenoid cavity. 10. Bursae help decrease friction at the specific places on the shoulder where both tendons and large muscles extend across the joint capsule. C. Elbow Joint (p. 317) 1. The elbow joint is a hinge joint composed of two articulations: the humeroulnar joint and the humeroradial joint; both joints are enclosed within a single articular capsule. 2. The humeroulnar joint is where the trochlear notch of the ulna articulates with the trochlea of the humerus. 3. The humeroradial joint is where the capitulum of the humerus articulates with the head of the radius. 4. The elbow is extremely stable because of its thick articular capsule, the interlocking of the humerus and ulna, and the multiple strong ligaments that reinforce the articular capsule. 5. The radial collateral ligament is responsible for stabilizing the joint at its lateral surface; the ulnar collateral ligament stabilizes the medial side of the joint. 6. An anular ligament surrounds the neck of the radius and binds the proximal head of the radius to the ulna. 136

6 7. Clinical View: Subluxation of the Head of the Radius (p. 317) a. The term subluxation refers to an incomplete dislocation- contact between the bony joint surfaces is altered, but they are still in partial contact. b. In subluxation of the head of the radius, the head is pulled out of the anular ligament. c. This injury occurs commonly and almost exclusively in children because a child s anular ligament is thin and the head of the radius is not fully formed. d. Treatment is simple: The pediatrician applies posteriorly placed pressure to the head of the radius while slowly supinating and extending the child s forearm, screwing the radial head back into the anular ligament. D. Hip Joint (pp ) 1. The hip joint, or coxal joint, is the articulation between the head of the femur and the relatively deep, concave acetabulum of the os coxae. 2. A fibrocartilaginous acetabular labrum further deepens this socket. 3. The hip joint is much stronger and more stable than the glenohumeral joint; it is therefore also less mobile. 4. The articular capsule extends from the acetabulum to the trochanters of the femur, enclosing both the femoral head and neck. 5. The retinacular fibers reflect around the neck of the femur, providing additional stability to the capsule; retinacular arteries travel through these fibers and supply almost all of the blood to the head and neck of the femur. 6. The iliofemoral ligament is a Y-shaped ligament that provides strong reinforcement for the anterior region of the articular capsule. 7. The ischiofemoral ligament is a spiral-shaped, posteriorly located ligament. 8. The pubofemoral ligament is a triangular thickening of the capsule s inferior region. 9. The ligament of the head of the femur does not provide strength to the joint, but rather contains a small artery that supplies the head of the femur. 10. Movements possible at the hip joint include flexion, extension, abduction, adduction, rotation, and circumduction. 11. Clinical View: Fracture of the Femoral Neck (p. 321) a. The term fractured hip is often incorrectly applied, as it refers to the breaking of the femoral neck, rather than the breaking of the os coxae. b. Fractures of the femoral neck are intertrochanteric or subcapital. c. Intertrochanteric fractures of the femoral neck occur distally to or outside the hip joint capsule; the fracture line runs between the greater and lesser trochanters. Subcapital fractures of the femoral neck occur within the hip articular capsule, very close to the head of the femur itself; this type of fracture usually occurs in elderly people. d. Subcapital fractures result in a tearing of the retinacular arteries that supply the head and neck of the femur; as a result, the head and neck of the femur lose their blood supply and may develop avascular necrosis. e. Frequently, hip replacement surgery is needed to replace the dying bone. E. Knee Joint (pp ) 1. The knee joint is the largest and most complex diarthrosis of the body. 2. The knee joint is primarily a hinge joint, but when the knee is flexed, it is also capable of slight rotation and lateral gliding. 3. The knee is composed of two separate articulations: The tibiofemoral joint is between the condyles of the femur and the condyles of the tibia, and the patellofemoral joint is between the patella and the patellar surface of the femur. 4. The articular capsule of the knee joint does not cover the anterior surface; rather, the quadriceps femoris muscle tendon passes over the anterior surface. 5. The patella is embedded within the quadriceps femoris tendon, and the patellar ligament extends beyond the patella and continues to where it attaches on the tibial tuberosity of the tibia. 6. The fibular collateral ligament reinforces the lateral surface of the joint and prevents hyperadductions of the leg; the tibial collateral ligament reinforces the medial surface of the knee joint and prevents hyperabductions of the leg. 137

7 7. Deep to the articular capsule and within the knee joint itself are a pair of C-shaped fibrocartilage pads positioned on the condyles of the tibia, called the medial meniscus and the lateral meniscus. 8. Two cruciate ligaments are deep to the articular capsule; the anterior cruciate ligament (ACL) prevents hyperextensions, and the posterior cruciate ligament (PCL) prevents hyperflexion. 9. Clinical View: Knee Ligament and Cartilage Injuries (p. 323) a. The tibial collateral ligament is frequently injured when the leg is forcibly abducted at the knee. b. Injury to the fibular collateral ligament can occur if the medial side of the knee is struck, resulting in hyperadduction of the leg at the knee. c. The anterior cruciate ligament (ACL) can be injured when the leg is hyperextended. d. To test for ACL injury, a physician gently tugs anteriorly on the tibia; in this anterior drawer test, too much forward movement indicates an ACL tear. e. Posterior cruciate ligament (PCL) injury may occur if the leg is hyperflexed or if the tibia is driven posteriorly on the femur. f. To test for PCL injury, a physician gently pushes posteriorly on the tibia; in this posterior drawer test, too much posterior movement indicates a PCL tear. g. Tears in the meniscus may occur due to blows to the knee or due to general overuse of the joint; these tears must be surgically treated. h. The unhappy triad of injuries refers to a triple injury of the tibial collateral ligament, medial meniscus, and anterior cruciate ligament; this is the most common type of football injury. i. The treatment of ligamentous knee injuries ranges from rest to surgical treatment, depending on severity. j. Arthroscopy is a type of conservative surgical treatment where a small incision is made in the knee and then an arthroscope is inserted in the knee, allowing the surgeon to clearly see the surgical area. F. Talocrural (Ankle) Joint (pp ) 1. The talocrural (ankle) joint is a highly modified hinge joint that permits both dorsiflexion and plantar flexion. 2. The ankle joint includes two articulations within one joint capsule: one between the distal end of the tibia and the talus, the other between the distal end of the fibula and the lateral aspect of the talus. 3. The medial and lateral malleoli of the tibia and fibula, respectively, prevent the talus from sliding side-to-side. 4. The articular capsule covers the distal surfaces of the tibia, the medial malleolus, the lateral malleolus, and the talus. 5. A multipart deltoid ligament binds the tibia to the foot on the medial side and prevents over-eversion of the foot; a multipart lateral ligament binds the fibula to the foot on the lateral side and prevents over-inversion of the foot. 6. Two tibiofibular ligaments (anterior and posterior) bind the tibia to the fibula. 7. Clinical View: Ankle Sprains and Pott Fractures (p. 324) a. A sprain is a stretching or tearing of ligaments, without fracture or dislocation of the joint. b. Ankle sprains almost always result from over-inversion. c. A mild sprain is from stretching of the ligaments; a severe sprain is from tearing of the ligaments. d. If over-eversion does occur, the injury that usually results is a Pott fracture, in which the deltoid ligament pulls off the medial malleolus of the tibia. e. Without the support of the medial malleolus, the lateral movement of the talus fractures the fibula as well. 9.8 Development and Aging of the Joints: Mesenchyme forms the three major joint types in the embryo and fetus. (pp ) 1. Joints start to form by the sixth week of development. 2. In the area of future fibrous joints, the mesenchyme differentiates into dense regular connective tissue. 3. In cartilaginous joints, the mesenchyme differentiates into fibrocartilage or hyaline cartilage. 4. In synovial joints, the most laterally placed mesenchyme forms the articular capsule and supporting ligaments of the joint; in the medial region of the joint, the mesenchyme forms the synovial membrane; and the centrally located mesenchyme can form menisci or articular discs. 5. Prior to the closure of the epiphyseal plates, some injuries to a young person may result in subluxation or fracture of an epiphysis, with potential adverse effects on development and health of the joint, including incomplete growth or arthritic-like changes. 6. The health of joints is directly related to moderate exercise. 7. Moderate exercise stimulates the flow of synovial fluid and strengthens the muscles that support and stabilize the joint. 8. Clinical View: Arthritis (p. 326) 138

8 a. Arthritis is a group of inflammatory or degenerative diseases of joints that produces symptoms of swelling of the joint, pain, and stiffness. b. Gouty arthritis occurs as a result of an increased level of uric acid in the blood, causing urate crystals to accumulate in the blood, synovial fluid, and synovial membranes. c. The body s inflammatory response to the urate crystals results in joint pain. d. Osteoarthritis is the most common type of arthritis, in which repeated use of a joint gradually wears down the articular cartilage. e. Without the protective articular cartilage, bone rubs against bone, and joints become stiff and painful. f. The most common joints affected by osteoarthritis are those of the fingers, knuckles, hips, knees, and shoulders. g. Rheumatoid arthritis is an autoimmune disorder in which the body s immune system targets its own tissues, producing pain and swelling of the joints, muscle weakness, osteoporosis, and problems with heart and blood vessels. h. Rheumatoid arthritis begins with synovial membrane inflammation, eventually producing scar tissue which ossifies and fuses the bone ends together (a process called ankylosis), immobilizing the joint. i. First-line medications to treat rheumatoid arthritis include NSAIDs and corticosteroids for pain relief; second-line medications, such as methotrexate and hydroxychloroquine, help put the disease into remission and slow down joint destruction. DISCUSSIONS, IN CLASS VISUALS, AND DEMONSTRATIONS 1. Chart the joints and their structural characteristics. 2. Discuss the viscosity of synovial fluid, explaining that mobilization of the joint decreases its viscosity; use a mechanical lubricant to demonstrate why the low viscosity of synovial fluid is so important for synovial joint movement. 3. Discuss the role of fat pads at joints. 4. Discuss how a physician would obtain a tentative diagnosis of a joint disorder by physical examination alone. 5. Discuss craniosacral therapy. 6. Demonstrate the movements at various synovial joints; demonstrate movements at two uniaxial joints, biaxial joints, and multiaxial joints. 7. Discuss the term crepitus and how it is used in the diagnosis of a joint disorder. 8. Discuss various types of joint disorders. 9. Discuss why a large majority of professional athletes that played heavy contact sports, such as football, get knee problems later in life. ADDITIONAL TOPICS FOR DISCUSSION 1. Discuss the procedure, purpose, and diagnostic usefulness of a synovial fluid tap, known as arthrocentesis. 2. Discuss the procedure and diagnostic usefulness of arthroscopy. 3. Discuss the arthroscopic surgery procedure; explain the usefulness of arthroscopic surgery. 4. Discuss tennis elbow, also known as lateral epicondylitis. 5. Discuss the ganglion cyst. 139