LEARNING OUTCOMES: 8.1 Introduction 1. List the functions of joints. 2. Explain how joints can be classified according to the type of tissue that binds the bones together and the degree of movement possible at the joint 8.2 Fibrous Joints 3. Describe how bones of fibrous joints are held together, and name an example of each type of fibrous joint. 8.3 Cartilaginous Joints 4. Describe how bones of cartilaginous joints are held together, and name an example of each type of cartilaginous joint. 8.4 Synovial Joints 5. Describe the general structure of a synovial joint. 6. Distinguish among the six types of synovial joints, and name an example of each type. 8.5 Types of Joint Movements 7. Explain how skeletal muscles produce movements at joints, and identify several types of joint movements. 8.6 Examples of Synovial Joints 8. Describe the shoulder joint, and explain how its articulating parts are held together. 9. Describe the elbow, hip, and knee joints, and explain how their articulating parts are held together. 8.7 Life-Span Changes 10. Describe life-span changes in joints. 8-1
8.1 INTRODUCTION A. Joints, or articulations, are functional junctions between bones. 1. They bind parts of the skeletal system together. 2. They make bone growth possible. 3. They permit parts of the skeleton to change shape during childbirth. 4. The enable the body to move in response to skeletal muscle contractions. B. Classification of Joints 1. Classification of joints can be based on the type of tissue that binds the bones at each junction (i.e. structural classification). Structural classification is used most commonly. The three types are: a. fibrous b. cartilaginous and c. synovial. 2. Classification can be based according to the degree of movement possible at the bony junctions (i.e. functional classification). The three types are: a. synarthroses, immovable joints b. amphiarthroses, slightly movable joints and c. diarthroses, freely movable joints. 8.2 FIBROUS JOINTS are joints composed of fibrous tissue; no joint cavity is present. 3 types: A. Syndesmosis = cord of fibrous tissue called a ligament 1. See Fig 8.1, page 270. a. amphiarthroses with "give" but no true movement b. Example = distal tibiofibular joint. B. Sutures = short fibrous CT fibers 1. See Fig 8.2 and Fig 8.3, page 271. a. synarthroses b. only found in skull C Gomphosis = tooth within its bony socket (alveolar fossa) 1. See Fig 8.4, page 272. a. synarthroses b. short periodontal ligaments 8-2
8.3 CARTILAGINOUS JOINTS = joints composed of cartilage no joint cavity. 2 types: A. Synchondrosis = a plate of hyaline cartilage 1. sites of bone growth during youth 2. eventually ossify = synarthrotic a. once ossified called a synostosis 3. Examples: a. joint between the first rib and manubrium. See Fig 8.5, page 272. b. the epiphyseal plate B. Symphysis = pad or plate of fibrocartilage 1. compressible "shock absorber" 2. limited movement = amphiarthroses 3. Examples: a. intervertebral discs b. pubic symphysis 4. See Fig 8.6, page 272. 8.4 SYNOVIAL JOINTS = fluid-filled joint cavity free movement = diartharthroses A. General Structure of a Synovial Joint = See Fig 8.7, page 273. 1. Articular cartilage = hyaline cartilage covers the surface of each bone See page 270 re: Do Glucosamine and Chondroitin Help Arthritis Pain? 2. Joint capsule = double layered capsule surrounding cavity: a. External, tough flexible fibrous capsule (continuous with periosteum of the bones) b. Synovial membrane = loose CT lining of fibrous capsule, that also covers all internal joint surfaces excluding hyaline cartilage 3. Synovial cavity = potential space between the two bones a. filled with synovial fluid 4. Synovial fluid = viscous lubricating fluid within cavity a. reduces friction between cartilages of 2 bones b. provides lubrication c. nourishes cartilage d. contains phagocytes 5. Reinforcing ligaments = ligaments that strengthen joint. a. A ligament joins a bone to another bone across a synovial joint. b. usually thickened portions of fibrous capsule (intrinsic or capsular) B. Other joint features: See Fig 8.8, page 274. 1. fatty pads (hip & knee) 2. menisci or articular discs that separate cavity into 2 compartments (knee, jaw, sternoclavicular). 3. bursa = flattened fibrous sacs with a synovial membrane and fluid that act as "ball bearings" to prevent friction on adjacent structures during joint activity a. cushion the movement of one body part over another b. located between skin and bone (where skin rubs over bone), and between muscle, tendons, ligaments and bone 8-3
8.4 SYNOVIAL JOINTS C. Types of Synovial Joints: See Figure 8.9, page 275 and Table 8.1 page 276. 1. Ball-and-socket joints = most freely movable joints all angular movement a. The head of one bone fits into the socket of another b. Examples = hip and shoulder 2. Condyloid joints (ellipsoidal) = permit all angular motions, except rotation. a. Examples = wrists and knuckles 3. Gliding joints = cartilaginous joints a. Example = intervertebral discs 4. Hinge joints = permit flexion & extension only a. Examples = elbow and knee 5. Pivot joints = permit rotation a. Example = first intervertebral joint (atlantoaxial joint) 6. Saddle joints = allows opposition Example = thumb 8.5 TYPES OF JOINT MOVEMENTS A. Definitions: 1. Origin = part of muscle attached to the immovable bone 2. Insertion = part of a muscle attached to the movable bone * When a muscle contracts across a joint, its insertion is pulled toward its origin. B. Terms used to describe movements at joints that occur in different directions and in different planes: See Figures 8.10-8.12, pages 277-278. 1. Flexion = decreasing the angle between 2 bones (i.e. head toward chest). 2. Extension = increasing the angle between 2 bones (i.e. straightening the knee). 3. Hyperextension = increasing the angle greater than at anatomical position (i.e. bending the head back). 4. Dorsiflexion = bringing toes toward shin. 5. Plantar flexion = pointing one's toe (flexion toward the sole). 6. Abduction = moving a limb away from the midline (i.e. raising arm or thigh laterally). 7. Adduction = moving a limb toward the midline. 8. Rotation = turning movement of a bone along its long axis. 9. Circumduction = moving a limb in a circular (cone-shaped) manner. 10. Supination = thumbs up. 11. Pronation = thumb down. 12. Eversion = sole outward. 13. Inversion = sole inward. 14. Protraction = moving a part forward (i.e. chin thrust forward). 15. Retraction = moving a part backward (i.e. pulling the head back). 16. Elevation = raising a part (i.e. shoulder shrug). 17. Depression = lowering a part (i.e. depressing the mandible). 8-4
8.6 EXAMPLES OF SYNOVIAL JOINTS A. Shoulder joint (2 joints) See Fig 8.13, page 280 and Fig 8.14, page 281. 1. Ball and socket is the glenohumeral joint. o joins glenoid cavity and head of humerus 2. Syndesmosis is called the acromioclavicular joint. o acromial end of clavicle and the acromion process of the scapula 3. Ball and socket is surrounded by many reinforcing ligaments and tendons collectively called the rotator cuff. * See box on page 280 re: rotator cuff injury. 4. Many bursae also lubricate the shoulder. 5. Movement can occur in any angular plane * See box on page 281 re: shoulder dislocation. B. Elbow joint (2 joints) See Fig 8.15 and 8.16, page 282. 1. Hinge is between trochlea of humerus and trochlear notch of ulna. 2. Gliding joint is between capitulum of humerus and head of radius. 3. very stable joint with many reinforcing ligaments 4. only allows flexion and extension C. Hip joint (coxal joint) See Fig 8.17-8.19, pages 283-284. 1. Ball and socket between head of femur and acetabulum of coxal bone a. Recall fovea capitis on femur head See Fig 8.17a, page 283. 2. contains many large reinforcing ligaments 3. allows same movements as shoulder, but with less range due to bony limitations D. Knee (3 joints) See Fig 8.20, page 285 and Fig 8.21, page 286. 1. largest, most complex joint 2. Functions as a hinge even though 3 joints work together. 3. Medial condyles of femur and tibia make one condyloid joint. 4. Lateral condyles of femur and tibia make another condyloid joint. 5. Patellar surface of femur and patella make a gliding joint. 6. flexion and extension with some slight rotation 7. contains many reinforcing structures a. Extracapsular ligaments found outside joint capsule patellar ligament, tibial (medial) collateral ligament MCL, fibular (lateral) collateral ligament LCL b. Intracapsular ligaments found inside joint capsule anterior cruciate ligament ACL c. Menisci - medial meniscus, lateral meniscus o C-shaped fibrocartilage pads o Reshape the tibial condyles for a better fit and absorb shock o See box on page 286 re: torn or displaced meniscus. d. many bursae 8-5
8.7 LIFE-SPAN CHANGES A. Fontanels of skull harden in first 2 years B. Epiphyseal plates harden from ages 14-20 years. C. Fibrocartilage loses water, decreasing flexibility of intervertebral joints and knees D. Collagen changes causing stiffening beginning at age 30. E. Exercise decreases onset of joint stiffening. OTHER INTERESTING TOPICS: A. Arthrocentesis. See box on page 273. B. Arthroscopy. See box on page 282. C. Clinical Application 8.1: Replacing Joints. See page 285. D. Clinical Application 8.2: Joint Disorders. See pages 288-289. CHAPTER SUMMARY see pages 288-290. CHAPTER ASSESSMENTS see page 291. INTEGRATIVE ASSESSMENTS/CRITICAL THINKING see page 291. 8-6
JOINT SUMMARY TABLE: (Examples keyed at the end of this outline) NAME OF JOINT STRUCTURAL OF JOINT FUNCTIONAL OF JOINT BONES INVOLVED IN ARTICULATION SPECIFIC MOVEMENTS ALLOWED BY JOINT OF JOINT BASED ON MOVEMENTS ALLOWED 8-7
JOINT SUMMARY TABLE: (Examples keyed at the end of this outline) NAME OF JOINT HIP SUTURE PUBIC SYMPHYSIS STRUCTURAL OF JOINT SYNOVIAL FIBROUS CARTILAGINOUS (SYMPYSIS OF FIBROCARTILAGE) FUNCTIONAL OF JOINT DIARTHROTIC SYNARTHROTIC AMPHIARTHROTIC BONES INVOLVED IN ARTICULATION HEAD OF FEMUR WITH ACETABULUM OF COXAL SKULL BONES PUBIS PORTIONS OF COXAL BONES SPECIFIC MOVEMENTS ALLOWED BY JOINT FLEXION, EXTENSION, ABDUCTION, ADDUCTION, CIRCUMDUCTION, ROTATION NONE GLIDING OF JOINT BASED ON MOVEMENTS ALLOWED BALL N- SOCKET N/A PLANE 8-8