CHAPTER 9
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CHAPTER 9 Joints
Joints can be classified by function or structure
Functional classification focuses on the amount of movement allowed
Synarthroses: immovable joints
Amphiarthroses: slightly movable joints
Diarthroses: freely movable joints
Structural classification is based on the material that binds the bones together and the presence or absence of a joint cavity
Fibrous joints: bones connected by fibrous tissue, no joint cavity
Sutures: bones tightly bound by minimal fibrous tissue, found only in the skull
Syndesmoses: bones connected by ligaments, amount of movement depends on length of connecting fibers
Gomphoses: peg-in-socket joint, example is the articulation of a tooth with its socket
9.2 FIBROUS JOINTS
Fibrous joints are classified as immobile (synarthrosis) or slightly mobile (amphiarthrosis)
Examples of fibrous joints:
Sutures: bones held together with short, interconnecting fibers, found only in the skull
Syndesmoses: bones held together by ligaments, fibrous tissue can vary in length
Gomphoses: peg-in-socket fibrous joint, held together by a short periodontal ligament
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9.3 CARTILAGINOUS JOINTS
Cartilaginous joints are united by cartilage and lack a joint cavity
Two types of cartilaginous joints:
Synchondroses: bones united by hyaline cartilage, examples include epiphyseal plates and joint between first rib's costal cartilage and sternum
Symphyses: bones united by fibrocartilage, examples include intervertebral discs and pubic symphysis of the pelvis
9.4 SYNOVIAL JOINTS
Synovial joints are the most movable joints and contain a fluid-filled joint cavity
All synovial joints are diarthroses (freely movable)
Synovial joints have structural characteristics shared by all
Weeping lubrication plays a role in the function of synovial joints
Articular discs, bursae, and tendon sheaths are structures found in synovial joints
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Chapter 9 Joints
Synovial fluid
Resembles raw egg white
Filtrate of blood from capillaries in synovial membrane
Contains glycoprotein molecules secreted by fibroblasts in synovial membrane
Acts as a slippery lubricant for joint movement
Occurs within articular cartilages
Mechanism called weeping lubrication nourishes cells in articular cartilages and lubricates free surfaces of cartilages
Reinforcing ligaments
Some synovial joints are reinforced and strengthened by bandlike ligaments
Ligaments can be capsular, extracapsular, or intracapsular
9.4a General Structure of Synovial Joints
Articular cartilage
Ends of opposing bones are covered by articular cartilages composed of hyaline cartilage
Absorb compressive forces and prevent bone ends from being crushed
Joint (articular) cavity
Potential space that holds a small amount of synovial fluid
Articular capsule
Two-layered structure enclosing the joint cavity
Outer fibrous layer of dense irregular connective tissue continuous with periosteum layer of joining bones
Inner layer is synovial membrane composed of loose connective tissue
Synovial membrane lines joint capsule and covers internal joint surfaces not covered by cartilage
Nerves and vessels
Synovial joints are richly supplied with sensory nerve fibers that innervate the articular capsule
Fibers detect pain and monitor joint stretching
Synovial joints have a rich blood supply, with most blood vessels supplying the synovial membrane
Each synovial joint is served by branches from several major nerves and blood vessels
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Extracapsular ligaments
Located outside the capsule
Examples include fibular and tibial collateral ligaments of the knee
Intracapsular ligaments
Located inside the capsule
Examples include anterior and posterior cruciate ligaments in the knee
Nerves and vessels (continued)
Branches from major nerves and blood vessels supply overlapping areas of the joint capsule
Functional redundancy ensures joint nourishment even if a blood vessel is compressed or injured
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Joints and their components
Synovial membrane and synovial fluid
Articular cartilage
Bursae and tendon sheaths
Articular discs and their function
Bursae and tendon sheaths and their function
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Types of body movements at synovial joints
Gliding
Angular movements (flexion, extension, abduction, adduction, circumduction)
Flexion and extension
Hyperextension
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Angular movements (continued)
Rotation
Special body movements
Pronation and supination
Dorsiflexion and plantar flexion
Inversion and eversion
Protraction and retraction
Elevation and depression
Opposition
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Special body movements (continued)
Elevation and depression of the mandible
Protraction and retraction of the mandible
Supination and pronation of the forearm
Inversion and eversion of the foot
Dorsiflexion and plantar flexion of the foot
Opposition of the thumb
Note: This note provides an overview of the main ideas and supporting details from the transcript. It covers the components of joints, the function of articular discs, the role of bursae and tendon sheaths, and the different types of body movements at synovial joints. It also includes specific examples of special body movements.
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Joints and their movements
Thumb opposition allows the thumb to touch the tips of other fingers on the same hand.
Inversion and eversion are special movements of the foot at the intertarsal joints.
Dorsiflexion and plantar flexion are up-and-down movements of the foot at the ankle.
Synovial joints are classified based on their shape and function.
Nonaxial, uniaxial, biaxial, and multiaxial are the functional classifications of synovial joints.
Synovial joints can be structurally classified as plane, hinge, pivot, condylar, saddle, and ball-and-socket joints.
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Factors influencing the stability of synovial joints
The stability of a synovial joint depends on the shapes of the articular surfaces, the number and position of stabilizing ligaments, and muscle tone.
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Special movements of joints
Abduction and adduction move a body part along the frontal plane.
Circumduction is moving a limb or finger in a circular motion.
Rotation is the turning movement of a bone around the longitudinal axis.
Elevation and depression refer to lifting and lowering a body part.
Protraction and retraction are nonangular movements in the anterior and posterior directions.
Supination and pronation refer to movements of the radius around the ulna.
Opposition is a movement allowed by the saddle joint between metacarpal I and the trapezium.
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Ligaments and joint capsules of "double-jointed" individuals are looser and more stretchable than those of most people
Joint ligaments and capsules are important for joint stabilization
Muscle tone helps stabilize joints by keeping tension on muscle tendons that cross over joints
Muscle tone functions like a ligament in holding bone surfaces together
Joint sockets with deep sockets or grooves provide stability
Examples include the hip joint, elbow joint, and ankle joint
Ligaments help hold bones together and prevent excessive or undesirable motions
Ligaments resist abduction, adduction, extension, flexion, and rotation
The more ligaments a joint has, the stronger it is
Ligaments can stretch beyond their normal length before snapping apart
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Important synovial joints include the acromioclavicular joint, shoulder joint, elbow joint, wrist joint, and various joints in the hand
Each joint has a specific structural type and functional type
Movements allowed at these joints include gliding, rotation, flexion, extension, abduction, adduction, circumduction, and opposition
Joints can be classified as uniaxial, biaxial, or multiaxial based on their shape and range of movement
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Temporomandibular Joint (TMJ) is a modified hinge joint located just anterior to the ear.
TMJ allows for distinct kinds of movement:
Hinge-like movement of depressing and elevating the mandible.
Anterior gliding of the mandible when the mouth is opened wide.
Anterior movement of the mandible braces it against the dense bone of the articular tubercle to prevent it from being forced superiorly through the thin roof of the mandibular fossa when biting hard foods.
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The TMJ is susceptible to temporomandibular disorders, usually caused by painful spasms of the chewing muscles.
Temporomandibular disorders can result from stress-induced teeth grinding, TMJ injury, or poor occlusion of the teeth.
Common symptoms of temporomandibular disorders include pain in the ear and face, tenderness of the jaw muscles, popping or clicking sounds when the mouth opens, and stiffness of the TMJ.
Treatment for temporomandibular disorders focuses on relaxing the jaw muscles through massage, stretching, applying moist heat or ice, administering muscle-relaxant drugs, using bite guards for sleeping, and adopting stress-management techniques.
The TMJ is the most easily dislocated joint in the body due to its shallow socket.
Dislocation of the TMJ usually occurs anteriorly, with the condylar process of the mandible ending up in the infratemporal fossa of the skull.
To realign a dislocated TMJ, the physician places their thumbs in the patient's mouth between the lower molars and the cheeks, and then pushes the mandible inferiorly and posteriorly.
Page 16: Shoulder (Glenohumeral) Joint
The shoulder joint is a ball-and-socket joint formed by the head of the humerus and the shallow glenoid cavity of the scapula.
The glenoid cavity is slightly deepened by the glenoid labrum, but it contributes little to joint stability.
The articular capsule is thin and loose, allowing for freedom of movement.
The superior coracohumeral ligament supports the weight of the upper limb.
The anterior part of the capsule has three weak glenohumeral ligaments.
Muscle tendons, such as the tendon of the long head of the biceps brachii muscle and the rotator cuff muscles, contribute to the joint's stability.
The rotator cuff muscles include the subscapularis, supraspinatus, infraspinatus, and teres minor.
Vigorous arm movements can stretch or tear the rotator cuff.
Page 16: Sternoclavicular Joint
The sternoclavicular joint is a saddle joint found in two locations: the sternoclavicular joint and the joint between the trapezium and metacarpal I.
The joint is formed by the clavicular facet of the sternum, the first costal cartilage, and the clavicle.
An articular disc divides the joint cavity.
Ligaments, including the anterior and posterior sternoclavicular ligaments, the interclavicular ligament, and the costoclavicular ligament, surround the joint.
Muscles originating from the sternum also contribute to the joint's stability.
The sternoclavicular joint allows for multiple complex movements and is critical for the mobility of the upper extremity.
Forceful blows directed medially can result in clavicle fracture rather than dislocation of the sternoclavicular joint.
Page 17: Shoulder Joint Anatomy
The shoulder joint is formed by the head of the humerus and the shallow glenoid cavity of the scapula.
The joint is supported by the articular capsule, which is reinforced by glenohumeral ligaments.
The coracohumeral ligament helps support the weight of the upper limb.
The tendon of the long head of the biceps brachii muscle attaches to the superior margin of the glenoid labrum and secures the head of the humerus tightly against the glenoid cavity.
The rotator cuff muscles, including the subscapularis, supraspinatus, infraspinatus, and teres minor, encircle the shoulder joint and merge with the joint capsule.
The subscapularis muscle has a tendon that attaches to the lesser tubercle of the humerus.
The supraspinatus muscle has a tendon that passes under the acromion and attaches to the greater tubercle of the humerus.
The infraspinatus muscle has a tendon that attaches to the greater tubercle of the humerus.
The teres minor muscle has a tendon that attaches to the greater tubercle of the humerus.
An MRI of the shoulder joint can show the bony features of the scapula and humerus.
Page 18: Elbow Joint
The elbow joint is a hinge joint that allows only extension and flexion.
The ulna's trochlear notch forms the hinge and stabilizes the joint.
The articular capsule attaches to the humerus and ulna and to the anular ligament of the radius.
The capsule thickens into strong ligaments that prevent lateral and medial movements.
Tendons of arm muscles, such as the biceps brachii and triceps brachii, cross the elbow joint and provide stability.
Page 19: Wrist Joint
The wrist has two major joint surfaces: the wrist joint (radiocarpal) and the intercarpal joint.
The wrist joint is the joint between the radius and the proximal carpals, allowing movements of flexion, extension, adduction, abduction, and circumduction.
The intercarpal joint is located between the proximal and distal rows of carpals, allowing gliding movements.
The wrist is stabilized by several ligaments, including the palmar radiocarpal ligament, dorsal radiocarpal ligament, radial collateral ligament of the wrist joint, and ulnar collateral ligament of the wrist joint.
Clinical Application: Shoulder Dislocations
Shoulder dislocations are common injuries due to the weak structures reinforcing the shoulder joint anteriorly and inferiorly.
The head of the humerus easily dislocates forward and downward.
Glenoid cavity provides poor support when the humerus is rotated laterally and abducted.
Shoulder dislocations can occur from tackles in football or diving for a ball in baseball.
Clinical Application: Elbow Trauma
Elbow dislocation is usually caused by falling onto an outstretched arm and breaking the fall with the hand.
Elbow dislocation can push the ulna posteriorly and may also dislocate the radius.
Athletes who repeatedly swing a racket or throw a ball can weaken and rupture the ulnar collateral ligament.
Surgical reconstruction of the ulnar collateral ligament, known as "Tommy John surgery," involves replacing it with a tendon from the patient's own forearm, knee, or foot.
Page 20: Hip Joint
The hip joint has a ball-and-socket structure.
The joint is formed by the spherical head of the femur and the deeply cupped acetabulum of the hip bone.
The acetabular labrum, a circular rim of fibrocartilage, enhances the depth of the acetabulum.
The joint capsule runs from the rim of the acetabulum to the neck of the femur.
Three external ligamentous thickenings of the capsule reinforce the joint: iliofemoral ligament, pubofemoral ligament, and ischiofemoral ligament.
Muscle tendons and fleshy parts of hip and thigh muscles also contribute to the stability of the hip joint.
Page 21: Knee Joint
The knee joint primarily acts as a hinge but also permits some medial and lateral rotation.
It is the largest and most complex joint in the body.
The knee joint is compound and bicondyloid, with two condylar surfaces on both the femur and tibia.
The femur's condyles roll along the tibia's condyles like tires on a road.
The knee joint also includes the femoropatellar joint, a plane joint that allows the patella to glide across the distal femur.
The knee joint has a complex synovial cavity with several incomplete subdivisions and extensions.
Several bursae are associated with the knee joint, including the subcutaneous prepatellar bursa.
Note: The transcript contains more information, but due to the token limit, only the main ideas and supporting details from the specified pages are included in the note.
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The knee joint contains two fibrocartilage menisci that attach externally to the condyles of the tibia.
The menisci help distribute compressive load and synovial fluid.
They stabilize the joint by guiding the condyles during movement and preventing side-to-side rocking of the femur on the tibia.
The articular capsule of the knee joint covers most parts of the femoral and tibial condyles.
The anterior area is covered by three broad ligaments: the patellar ligament and the medial and lateral patellar retinacula.
The patellar ligament is a continuation of the tendon of the quadriceps femoris muscle.
The knee joint is reinforced by several capsular and extracapsular ligaments.
The extracapsular fibular and tibial collateral ligaments prevent lateral and medial movement of the leg at the knee.
The oblique popliteal ligament stabilizes the joint and is part of the tendon of the semimembranosus muscle.
The arcuate popliteal ligament stabilizes the joint and arcs superiorly from the head of the fibula over the popliteus muscle.
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The knee joint is stabilized by two strong intracapsular ligaments called cruciate ligaments.
The anterior cruciate ligament (ACL) attaches to the anterior part of the tibia and prevents anterior sliding of the tibia.
The posterior cruciate ligament (PCL) arises from the posterior intercondylar area of the tibia and prevents forward sliding of the tibia.
The cruciate ligaments function together to lock the knee when fully extended.
The tendons of the quadriceps femoris and semimembranosus muscles reinforce the joint capsule and stabilize the knee joint.
Clinical Application:
Knee injuries occur frequently in contact sports.
Lateral blows to the knee can tear the tibial collateral ligament, medial meniscus, and anterior cruciate ligament (ACL), known as the "unhappy triad."
ACL injuries are increasing in noncontact sports, especially in women athletes.
Factors contributing to the higher incidence of ACL injuries in women include wider pelvis, narrower intercondylar fossa, effects of female hormones on joint laxity, and slower muscle reaction times.
ACL injuries often occur when a runner stops and changes direction quickly, twisting a hyper-extended leg.
ACL injuries require surgical replacement, usually with a graft from the patellar ligament, calcaneal tendon, or semitendinosus tendon.
Training regimens are being developed to decrease the incidence of ACL injuries in women athletes.
Injuries to the posterior cruciate ligament (PCL) caused by posteriorly directed blows to the upper tibia are less common and can heal on their own.
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The knees have a built-in locking device that provides steady support for the body in the standing position.
As a person stands up, the flexed leg begins to extend at the knee.
The femoral condyles roll like ball bearings on the tibial condyles.
The lateral femoral condyle stops rolling before the medial condyle stops.
This causes the femur to rotate medially on the tibia until both cruciate and collateral ligaments stretch tight and halt all movement.
The ankle joint is a hinge joint between the united inferior ends of the tibia and fibula, and the talus of the foot.
The ankle joint allows only dorsiflexion and plantar flexion.
Inversion and eversion occur at the intertarsal joints.
The ankle joint has a capsule that is thin anteriorly and posteriorly, but thickened with ligaments medially and laterally.
The medial (deltoid) ligament runs from the medial malleolus of the tibia down to a long line of insertion on the navicular and talus bones, and on the sustentaculum tali of the calcaneus bone.
The lateral ligament consists of three bands that run from the fibula's lateral malleolus to the foot bones: the horizontal anterior and posterior talofibular ligaments, and the calcaneofibular ligament.
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The ankle joint continued.
Posterior talofibular ligament, posterior tibiofibular ligament, interosseous membrane, calcaneofibular ligament, fibula, tibia, medial (deltoid) ligament, calcaneus, sustentaculum tali, talus, navicular, metatarsal I.
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Cartilage fragments can cause joints to lock or bind.
Surgical removal of damaged cartilage is the recommended treatment.
Arthroscopic surgery is a remarkable outpatient procedure that uses miniaturized video and surgical equipment inserted into the joint through a single small incision.
Arthroscopic surgery can be used in many joints, not just the knee.
Joints are vulnerable to a variety of disorders.
Joint injuries include torn cartilage, sprains, and dislocations.
Torn cartilage often involves tearing of the meniscus in the knee.
Sprains occur when the ligaments reinforcing a joint are stretched or torn.
Ankle sprains are the most common sports injuries and are caused by excessive inversion of the foot.
Autologous cartilage implantation is a procedure where a patient's own chondrocytes are cultured in the lab and then grafted onto joint surfaces to produce new hyaline cartilage.
Joints and Arthritis
Osteoarthritis (Degenerative Joint Disease)
Osteoarthritis is the most common type of arthritis.
It is a chronic degenerative condition often called "wear-and-tear arthritis."
It affects the articular cartilages, causing them to soften, fray, crack, and erode.
The cause of osteoarthritis is unknown, but it is believed to be related to normal use causing joints to release cartilage-destroying enzymes.
Badly aligned or overworked joints are more likely to develop osteoarthritis.
The bone directly below the articular cartilage is also affected, becoming dense and stiff.
Bone spurs may grow around the margins of the damaged cartilages, restricting joint movement.
Symptoms include pain, stiffness, swelling, and crunching noise during joint movement.
Osteoarthritis commonly affects the fingers, knuckles, hips, knees, and vertebral joints.
It is a slow and irreversible disease, but symptoms can be controlled with pain relievers and low-impact exercise.
Joint replacement is a common treatment for severely damaged joints.
Rheumatoid Arthritis
Rheumatoid arthritis is a chronic inflammatory disorder.
It usually occurs between the ages of 30 and 60.
It is characterized by inflammation of the synovial membrane, leading to joint pain, stiffness, and swelling.
Rheumatoid arthritis can affect multiple joints symmetrically.
It is an autoimmune disease, where the immune system mistakenly attacks the body's own tissues.
Treatment includes medications to reduce inflammation and slow down the progression of the disease.
Dislocations and Inflammatory Conditions
Dislocations
A dislocation occurs when the bones of a joint are forced out of alignment.
It is usually accompanied by sprains, inflammation, pain, and difficulty in moving the joint.
Dislocations can result from falls, blows, or sports injuries.
Commonly dislocated joints include the jaw, shoulder, finger, and thumb joints.
Dislocations must be reduced by a physician to return the bone ends to their proper positions.
Subluxation is a partial or incomplete dislocation of a joint.
A joint that has been dislocated once is more susceptible to repeated injury.
Inflammatory Conditions
Inflammatory conditions that affect joints include bursitis, tendonitis, and tenosynovitis.
Bursitis is inflammation of a bursa, often caused by physical blow or friction.
Tendonitis is inflammation of a tendon.
Tenosynovitis is inflammation of a tendon sheath.
Bursitis and tendonitis commonly occur together.
Treatment for severe cases may involve injecting inflammation-reducing drugs or fluid removal by needle aspiration.
Nursemaid's Elbow
Nursemaid's elbow is a common injury in young children.
It is a subluxation of the proximal radioulnar joint.
It occurs when the forearm is pulled with the arm outstretched, resulting in entrapment of the anular ligament.
Symptoms include immediate pain and reluctance to use the injured arm.
Treatment involves a simple reduction that allows immediate return to use of the arm.
Rheumatoid Arthritis (RA)
Chronic inflammation and swelling deteriorate connective tissues surrounding the joint
Loss of integrity of joint capsules in metacarpophalangeal and interphalangeal joints leads to characteristic deformities in the hand
Inflamed synovial membrane thickens into a pannus (coat of granulation tissue) that erodes cartilage and underlying bone
Cartilage destruction leads to fibrous scar tissue formation, which eventually ossifies and fuses bone ends, causing ankylosis (immobilization of joint)
Ankylosis often produces bent, deformed fingers
Treatment options for RA include anti-inflammatory drugs, immunosuppressants, and joint prostheses
No cure for RA, long-term medication required
Gouty Arthritis (Gout)
Uric acid levels rise abnormally in the blood and body fluids due to low excretion rate
Uric acid precipitates as solid crystals of urate in synovial membranes
Inflammatory response occurs as the body tries to attack and digest the crystals, causing painful gouty arthritis
Initial attack usually involves a single joint, often at the base of the big toe
Gout is more common in men due to higher levels of uric acid in their blood
Untreated gout can cause joint immobilization through fusion of articulating bones
Effective treatment available for gout
Rheumatoid Arthritis (RA) Details
Variable course, can develop gradually or in spurts years apart
Marked by flare-ups and remissions
Affects many joints simultaneously and bilaterally, especially small joints of fingers, wrists, ankles, and feet
Manifestations of RA include pain, swelling of joints, osteoporosis, muscle weakness, and cardiovascular problems
Autoimmune disease where the body's immune system attacks its own tissues
Cause of immune system reaction unknown, but may follow infection by certain bacteria and viruses with similar surface molecules to those in joints
Inflammation of synovial membrane initiates RA, with leakage of tissue fluid and white blood cells into joint cavity
Visuals
Figure 9.19: Osteoarthritis of the knee, showing reduced joint space and bone spurs
Figure 9.20: Rheumatoid arthritis, with prominent ulnar deviation of digits and swelling in metacarpophalangeal joints
Joints and Aging
Development of Joints (Page 29)
Joints develop from mesenchyme that fills the spaces between cartilaginous "bone models" in the late embryo.
The outer region of the intervening mesenchyme condenses to become the fibrous layer of the joint capsule.
The inner region hollows to become the joint cavity.
By week 8, these joints resemble adult joints in form and arrangement.
Modification of Joints by Use (Page 29)
After birth, a joint's size, shape, and flexibility are modified by use.
Active joints grow larger and have thicker capsules, ligaments, and bony supports.
Injuries to joints during youth can tear or knock the epiphysis off the shaft.
Vulnerability to such injuries ends after the epiphyseal plates close in early adulthood.
Comparable injuries after epiphyseal plate closure result in sprains.
Osteoarthritis and Joint Health (Page 29)
Osteoarthritis is the most common joint problem associated with advancing age.
Exercise squeezes synovial fluid in and out of articular cartilages, providing nourishment to cartilage cells.
Exercise strengthens joints, slows degeneration of articular cartilages, and strengthens the muscles that stabilize the joints.
Overexercising worsens osteoarthritis.
Exercise in water relieves stress on weight-bearing joints and helps retain good joint function throughout life.
Arthritis Types (Check Your Understanding) (Page 29)
(a) Crystalization of uric acid in synovial membranes.
(b) Erosion of articular cartilage.
(c) Autoimmune response causing inflammation of the synovial membrane.
Susceptibility to Repeat Injury (Check Your Understanding) (Page 29)
An injured joint is more susceptible to repeat injury following a sprain or subluxation.
Age of Development for Synovial Joints (Check Your Understanding) (Page 29)
Synovial joints are formed by the age of development.
Related Clinical Terms (Page 29)
Ankylosing spondylitis: A distinctive kind of rheumatoid arthritis that mainly affects men.
Arthroplasty: Replacing a diseased joint with an artificial joint.
Chondromalacia patellae: Damage and softening of the articular cartilages on the patella and femur.
Lyme disease: An inflammatory disease that often results in joint pain and arthritis.
Patellofemoral pain syndrome: Persistent pain behind the patella.
Synovitis: Inflammation of the synovial membrane of a joint.
Valgus and varus injuries: Bending outward or inward, respectively, causing injury to the knee and elbow