8 Joints: Part A

Joints (Articulations) Articulation—site where two or more bones meet Functions of joints: Give skeleton mobility Hold skeleton together

Functional Classification of Joints Based on amount of movement allowed by the joint Three functional classifications: Synarthroses—immovable Amphiarthroses—slightly movable Diarthroses—freely movable

Structural Classification of Joints Based on material binding bones together and whether or not a joint cavity is present Three structural classifications: Fibrous Cartilaginous Synovial

Bones joined by dense fibrous connective tissue No joint cavity Fibrous Joints Bones joined by dense fibrous connective tissue No joint cavity Most are synarthrotic (immovable) Three types: Sutures Syndesmoses Gomphoses

Fibrous Joints: Sutures Rigid, interlocking joints containing short connective tissue fibers occur between bones of the skull to hold the bones together Allow for growth during youth In middle age, sutures ossify and are called synostoses

Joint held together with very short, (a) Suture Joint held together with very short, interconnecting fibers, and bone edges interlock. Found only in the skull. Suture line Dense fibrous connective tissue Figure 8.1a

Fibrous Joints: Syndesmoses Bones connected by ligaments (cords or bands of fibrous tissue) Movement varies from immovable to slightly movable Examples: Synarthrotic distal tibiofibular joint Diarthrotic interosseous connection between radius and ulna

(b) Syndesmosis Joint held together by a ligament. Fibrous tissue can vary in length, but is longer than in sutures. Fibula Tibia Ligament Figure 8.1b

Fibrous Joints: Gomphoses Peg-in-socket joints of teeth in alveolar sockets Fibrous connection is the periodontal ligament

(c) Gomphosis “Peg in socket” fibrous joint. Periodontal ligament holds tooth in socket. Socket of alveolar process Root of tooth Periodontal ligament Figure 8.1c

Bones united by cartilage No joint cavity Two types: Cartilaginous Joints Bones united by cartilage No joint cavity Two types: Synchondroses Symphyses

Cartilaginous Joints: Synchondroses A bar or plate of hyaline cartilage unites the bones All are synarthrotic Example: epiphyseal plate

Bones united by hyaline cartilage (a) Synchondroses Bones united by hyaline cartilage Sternum (manubrium) Epiphyseal plate (temporary hyaline cartilage joint) Joint between first rib and sternum (immovable) Figure 8.2a

Cartilaginous Joints: Symphyses Hyaline cartilage covers the articulating surfaces and is fused to an intervening pad of fibrocartilage Strong, flexible amphiarthroses Example: pubic symphysis

Bones united by fibrocartilage (b) Symphyses Bones united by fibrocartilage Body of vertebra Fibrocartilaginous intervertebral disc Hyaline cartilage Pubic symphysis Figure 8.2b

Synovial Joints All are diarthrotic Include all limb joints; most joints of the body

Synovial Joints Distinguishing features: Articular cartilage covers ends of articulating bones (hyaline cartilage) Joint (synovial) cavity: small potential space filled with synovial fluid

Distinguishing features: 3. Articular (joint) capsule: Synovial Joints Distinguishing features: 3. Articular (joint) capsule: Encloses joint cavity Outer fibrous capsule of dense irregular connective tissue Inner synovial membrane of loose connective tissue

Distinguishing features: 4. Synovial fluid: Synovial Joints Distinguishing features: 4. Synovial fluid: Viscous slippery filtrate of plasma + hyaluronic acid Lubricates and nourishes articular cartilage Fills all free space within the joint cavity

Ligament Joint cavity (contains synovial fluid) Articular (hyaline) cartilage Fibrous capsule Articular capsule Synovial membrane Periosteum Figure 8.3

Distinguishing features: Synovial Joints Distinguishing features: 5. Three possible types of reinforcing ligaments to strengthen the joint: Capsular (intrinsic)—part of the fibrous capsule Extracapsular—outside the capsule Intracapsular—deep to capsule; covered by synovial membrane

Distinguishing features: 6. Rich nerve and blood vessel supply: Synovial Joints Distinguishing features: 6. Rich nerve and blood vessel supply: Nerve fibers detect pain, monitor joint position and stretch Capillary beds produce filtrate for synovial fluid

Synovial Joints: Friction-Reducing Structures Bursae: Flattened, fibrous sacs lined with synovial membranes Contain synovial fluid Commonly act as “ball bearings” where ligaments, muscles, skin, tendons, or bones rub together Reduce friction at synovial joints

Coracoacromial ligament Subacromial bursa Humerus resting Cavity in bursa containing synovial fluid Bursa rolls and lessens friction. Humerus head rolls medially as arm abducts. Humerus moving (b) Enlargement of (a), showing how a bursa eliminates friction where a ligament (or other structure) would rub against a bone Figure 8.4b

Synovial Joints: Friction-Reducing Structures Tendon sheath: Elongated bursa that wraps completely around a tendon Reduces friction at synovial joints

(a) Frontal section through the right shoulder joint Acromion of scapula Coracoacromial ligament Joint cavity containing synovial fluid Subacromial bursa Fibrous articular capsule Hyaline cartilage Tendon sheath Synovial membrane Tendon of long head of biceps brachii muscle Fibrous capsule Humerus (a) Frontal section through the right shoulder joint Figure 8.4a

Stabilizing Factors at Synovial Joints Shapes of articular surfaces (minor role) Ligament number and location (limited role) prevent excessive or unwanted movements and help to stabilize the joint the greater the number of ligaments at the joint, the greater the stability Muscle tone, which keeps tendons that cross the joint taut Extremely important in reinforcing shoulder and knee joints and arches of the foot

Synovial Joints: Movement Muscle attachments across a joint: Origin—attachment to the immovable bone Insertion—attachment to the movable bone Muscle contraction causes the insertion to move toward the origin Movements occur along transverse, frontal, or sagittal planes

Synovial Joints: Range of Motion Nonaxial—slipping movements only Uniaxial—movement in one plane Biaxial—movement in two planes Multiaxial—movement in or around all three planes

Summary of Characteristics of Body Joints Consult Table 8.2 for: Joint names Articulating bones Structural classification Functional classification Movements allowed

Table 8.2 (1 of 4)

Table 8.2 (2 of 4)

Table 8.2 (3 of 4)

Table 8.2 (4 of 4)

Movements at Synovial Joints Gliding Angular movements: Flexion, extension, hyperextension Abduction, adduction Circumduction Rotation Medial and lateral rotation

Movements at Synovial Joints 4. Special movements Supination, pronation Dorsiflexion, plantar flexion of the foot Inversion, eversion Protraction, retraction Elevation, depression Opposition

One flat bone surface glides or slips over another similar surface Gliding Movements One flat bone surface glides or slips over another similar surface Examples: Intercarpal joints Intertarsal joints Between articular processes of vertebrae

(a) Gliding movements at the wrist Figure 8.5a

Increase or decrease the angle between two bones. Angular Movements Increase or decrease the angle between two bones. Movements that occur along the sagittal plane: Flexion—decreases the angle of the joint; brings the articulating bones closer together Extension— increases the angle of the joint Hyperextension—excessive extension beyond normal range of motion

(b) Angular movements: flexion, extension, and Hyperextension Extension Flexion (b) Angular movements: flexion, extension, and hyperextension of the neck Figure 8.5b

Extension Hyperextension Flexion (c) Angular movements: flexion, extension, and hyperextension of the vertebral column Figure 8.5c

(d) Angular movements: flexion and extension at the shoulder and knee Figure 8.5d

Angular Movements Movements that occur along the frontal plane: Abduction—movement (limb or fingers) away from the midline (of body or hand) Adduction—movement (limb or fingers) toward the midline (body or hand) ADD TO BODY Circumduction—flexion + abduction + extension + adduction of a limb so as to describe a cone in space or air

Abduction Circumduction Adduction (e) Angular movements: abduction, adduction, and circumduction of the upper limb at the shoulder Figure 8.5e

The turning of a bone around its own long axis Examples: Rotation The turning of a bone around its own long axis Examples: Between C1 and C2 vertebrae Rotation of humerus and femur

(f) Rotation of the head, neck, and lower limb Lateral rotation Medial rotation (f) Rotation of the head, neck, and lower limb Figure 8.5f

Movements of radius around ulna: Special Movements Movements of radius around ulna: Supination (turning hand backward)- rotating the forearm laterally so that the palm faces anteriorly or superiorly Pronation (turning hand forward)- rotating the arm medially so that the palm faces posteriorly or inferiorly

(a) Pronation (P) and supination (S) (radius rotates over ulna) Supination (radius and ulna are parallel) (a) Pronation (P) and supination (S) Figure 8.6a

Special Movements Movements of the foot: Dorsiflexion (upward movement)- decreases the angle between the top of the foot (dorsal surface) and the anterior surface of the tibia Plantar flexion (downward movement) -decreases the angle between the sole of the foot (plantar surface) and the posterior side of the tibia

(b) Dorsiflexion and plantar flexion Figure 8.6b

Special Movements Movements of the foot: Inversion (turn sole medially) Eversion (turn sole laterally)

(c) Inversion and eversion Figure 8.6c

Movements in a transverse plane: Special Movements Movements in a transverse plane: Protraction (anterior movement)- moves the mandible anteriorly, juts the jaw forward Retraction (posterior movement)- returns the mandible to its original position

(d) Protraction and retraction of mandible Retraction of mandible (d) Protraction and retraction Figure 8.6d

Special Movements Elevation (lifting a body part superiorly) Depression (moving a body part inferiorly)

(e) Elevation and depression of mandible Depression of mandible (e) Elevation and depression Figure 8.6e

Opposition of the thumb Special Movements Opposition of the thumb Movement in the saddle joint so that the thumb touches the tips of the other fingers on the same hand

Classification of Synovial Joints Six types, based on shape of articular surfaces: Plane Hinge Pivot Condyloid Saddle Ball and socket

Plane Joints Nonaxial joints Flat articular surfaces Short gliding & transitional movements

Plane joint (intercarpal joint) f Nonaxial Uniaxial Biaxial Multiaxial c b a Plane joint (intercarpal joint) a e d Figure 8.7a

Hinge Joints Uniaxial joints Motion along a single plane Flexion and extension only consist of a cylindrical projection that nests in a trough-shaped structure

Hinge joint (elbow joint) f Nonaxial Uniaxial Biaxial Multiaxial c b b Hinge joint (elbow joint) a e d Figure 8.7b

Pivot Joints Rounded end of one bone conforms to a “sleeve,” or ring of another bone Uniaxial movement (around the long axis) only

Pivot joint (proximal radioulnar joint) f Nonaxial Uniaxial Biaxial Multiaxial c b c Pivot joint (proximal radioulnar joint) a e d Figure 8.7c

Condyloid (Ellipsoidal) Joints Biaxial joints Both articular surfaces are oval Permit all angular movements consist of an oval articular surface that nests in a complementary depression

(metacarpophalangeal joint) f Nonaxial Uniaxial Biaxial Multiaxial c b d Condyloid joint (metacarpophalangeal joint) a e d Figure 8.7d

Saddle Joints Biaxial Allow greater freedom of movement than condyloid joints Each articular surface has both concave and convex areas

Saddle joint (carpometacarpal joint of thumb) Nonaxial Uniaxial Biaxial Multiaxial c b e Saddle joint (carpometacarpal joint of thumb) a e d Figure 8.7e

Ball-and-Socket Joints Multiaxial joints The most freely moving synovial joints consist of a spherical or hemispherical structure that articulates with a cuplike structure

Ball-and-socket joint (shoulder joint) f Nonaxial Uniaxial Biaxial Multiaxial c b f Ball-and-socket joint (shoulder joint) a e d Figure 8.7f

Knee Joint Largest, most complex joint of body Three joints surrounded by a single joint cavity: Femoropatellar joint: Plane joint Allows gliding motion during knee flexion Lateral and medial tibiofemoral joints between the femoral condyles and the C-shaped lateral and medial menisci (semilunar cartilages) of the tibia Allow flexion, extension, and some rotation when knee is partly flexed PLAY A&P Flix™: Movement at the knee joint

(a) Sagittal section through the right knee joint Tendon of quadriceps femoris Femur Suprapatellar bursa Articular capsule Patella Posterior cruciate ligament Subcutaneous prepatellar bursa Synovial cavity Lateral meniscus Lateral meniscus Infrapatellar fat pad Anterior cruciate ligament Deep infrapatellar bursa Tibia Patellar ligament (a) Sagittal section through the right knee joint Figure 8.8a

(b) Superior view of the right tibia in the knee joint, showing Anterior Anterior cruciate ligament Articular cartilage on lateral tibial condyle Articular cartilage on medial tibial condyle Lateral meniscus Medial meniscus Posterior cruciate ligament (b) Superior view of the right tibia in the knee joint, showing the menisci and cruciate ligaments Figure 8.8b

Knee Joint At least 12 associated bursae Capsule is reinforced by muscle tendons: E.g., quadriceps and semimembranosus tendons Joint capsule is thin and absent anteriorly Anteriorly, the quadriceps tendon gives rise to: Lateral and medial patellar retinacula Patellar ligament

(c) Anterior view of right knee Quadriceps femoris muscle Tendon of quadriceps femoris muscle Patella Medial patellar retinaculum Lateral patellar retinaculum Tibial collateral ligament Fibular collateral ligament Patellar ligament Fibula Tibia (c) Anterior view of right knee Figure 8.8c

Capsular and extracapsular ligaments Knee Joint Many different types of ligaments stabilize and strengthen the capsule of the knee joint Capsular and extracapsular ligaments Help prevent hyperextension Intracapsular ligaments: Anterior and posterior cruciate ligaments Prevent anterior-posterior displacement Reside outside the synovial cavity

(d) Posterior view of the joint capsule, including ligaments Femur Tendon of adductor magnus Articular capsule Oblique popliteal ligament Medial head of gastrocnemius muscle Lateral head of gastrocnemius muscle Popliteus muscle (cut) Bursa Fibular collateral ligament Tibial collateral ligament Arcuate popliteal ligament Tendon of semimembranosus muscle Tibia (d) Posterior view of the joint capsule, including ligaments Figure 8.8d

Posterior cruciate ligament Fibular collateral ligament Medial condyle Tibial collateral ligament Lateral condyle of femur Anterior cruciate ligament Lateral meniscus Medial meniscus Tibia Patellar ligament Fibula Patella Quadriceps tendon (e) Anterior view of flexed knee, showing the cruciate ligaments (articular capsule removed, and quadriceps tendon cut and reflected distally) PLAY Animation: Rotatable knee Figure 8.8e

Lateral Medial Patella (outline) Hockey puck Tibial collateral ligament (torn) Medial meniscus (torn) Anterior cruciate ligament (torn) Figure 8.9

Shoulder (Glenohumeral) Joint Ball-and-socket joint: head of humerus and glenoid fossa of the scapula Stability is sacrificed for greater freedom of movement

Animation: Rotatable shoulder Acromion of scapula Coracoacromial ligament Synovial cavity of the glenoid cavity containing synovial fluid Subacromial bursa Fibrous articular capsule Hyaline cartilage Tendon sheath Synovial membrane Fibrous capsule Tendon of long head of biceps brachii muscle Humerus (a) Frontal section through right shoulder joint PLAY Animation: Rotatable shoulder Figure 8.10a

Reinforcing ligaments: Shoulder Joint Reinforcing ligaments: Coracohumeral ligament—helps support the weight of the upper limb Three glenohumeral ligaments—somewhat weak anterior reinforcements

Shoulder joint Reinforcing muscle tendons: Tendon of the long head of biceps: Travels through the intertubercular groove Secures the humerus to the glenoid cavity Four rotator cuff tendons encircle the shoulder joint: Subscapularis Supraspinatus Infraspinatus Teres minor PLAY A&P Flix™: Rotator cuff muscles: An overview (a) PLAY A&P Flix™: Rotator cuff muscles: An overview (b)

(c) Anterior view of right shoulder joint capsule Acromion Coracoid process Coracoacromial ligament Articular capsule reinforced by glenohumeral ligaments Subacromial bursa Coracohumeral ligament Subscapular bursa Greater tubercle of humerus Tendon of the subscapularis muscle Transverse humeral ligament Scapula Tendon sheath Tendon of long head of biceps brachii muscle (c) Anterior view of right shoulder joint capsule Figure 8.10c

of biceps brachii muscle Acromion Coracoid process Articular capsule Glenoid cavity Glenoid labrum Tendon of long head of biceps brachii muscle Glenohumeral ligaments Tendon of the subscapularis muscle Scapula Posterior Anterior (d) Lateral view of socket of right shoulder joint, humerus removed Figure 8.10d

Radius and ulna articulate with the humerus Elbow Joint Radius and ulna articulate with the humerus Hinge joint formed mainly by trochlear notch of ulna and trochlea of humerus Flexion and extension only PLAY A&P Flix™: Movement at the elbow joint

(a) Median sagittal section through right elbow (lateral view) Articular capsule Synovial membrane Humerus Synovial cavity Articular cartilage Fat pad Coronoid process Tendon of triceps muscle Tendon of brachialis muscle Ulna Bursa Trochlea Articular cartilage of the trochlear notch (a) Median sagittal section through right elbow (lateral view) Figure 8.11a

Anular ligament—surrounds head of radius Elbow Joint Tendons of several arm muscles, the biceps and the triceps, also provide additional stability by crossing the elbow joint. Anular ligament—surrounds head of radius Two capsular ligaments restrict side-to-side movement: Ulnar collateral ligament Radial collateral ligament

(b) Lateral view of right elbow joint Humerus Anular ligament Radius Lateral epicondyle Articular capsule Radial collateral ligament Olecranon process Ulna (b) Lateral view of right elbow joint Figure 8.11b

Animation: Rotatable elbow Articular capsule Anular ligament Humerus Coronoid process Medial epicondyle Ulnar collateral ligament Radius Ulna (d) Medial view of right elbow PLAY Animation: Rotatable elbow Figure 8.11d

Ball-and-socket joint Hip (Coxal) Joint Ball-and-socket joint Head of the femur articulates with the acetabulum Good range of motion, but limited by the deep socket Acetabular labrum—enhances depth of socket PLAY A&P Flix™: Movement at the hip joint: An overview

(a) Frontal section through the right hip joint Coxal (hip) bone Articular cartilage Ligament of the head of the femur (ligamentum teres) Acetabular labrum Femur Synovial cavity Articular capsule (a) Frontal section through the right hip joint Figure 8.12a

Reinforcing ligaments: Hip Joint Reinforcing ligaments: Iliofemoral ligament Pubofemoral ligament Ischiofemoral ligament Ligamentum teres

Iliofemoral ligament Ischium Ischiofemoral ligament Greater trochanter of femur (c) Posterior view of right hip joint, capsule in place PLAY Animation: Rotatable hip Figure 8.12c

Iliofemoral Anterior inferior ligament iliac spine Pubofemoral Greater trochanter (d) Anterior view of right hip joint, capsule in place Figure 8.12d

Temporomandibular Joint (TMJ) Mandibular condyle articulates with the temporal bone Two types of movement Hinge—depression and elevation of mandible Gliding—e.g. side-to-side (lateral excursion) grinding of teeth Most easily dislocated joint in the body contains an articular disc that divides the synovial cavity into compartments that support each type of movement lateral aspect of the fibrous capsule contains a lateral ligament that reinforces the joint

(a) Location of the joint in the skull Mandibular fossa Articular tubercle Zygomatic process Infratemporal fossa External acoustic meatus Lateral ligament Articular capsule Ramus of mandible (a) Location of the joint in the skull Figure 8.13a

(b) Enlargement of a sagittal section through the joint Articular disc Articular tubercle Mandibular fossa Superior joint cavity Articular capsule Synovial membranes Mandibular condyle Ramus of mandible Inferior joint cavity (b) Enlargement of a sagittal section through the joint Figure 8.13b

Lateral excursion: lateral (side-to-side) movements of the mandible Superior view Outline of the mandibular fossa Lateral excursion: lateral (side-to-side) movements of the mandible Figure 8.13c

Common Joint Injuries Sprains Cartilage tears The ligaments are stretched or torn Partial tears slowly repair themselves Complete ruptures require prompt surgical repair Cartilage tears Due to compression and shear stress (meniscus) Fragments may cause joint to lock or bind Cartilage rarely repairs itself Repaired with arthroscopic surgery Often at the knee

Torn meniscus Figure 8.14

Dislocations (luxations) Common Joint Injuries Dislocations (luxations) Occur when bones are forced out of alignment Accompanied by sprains, inflammation, and joint immobilization Caused by serious falls or playing sports Subluxation—partial dislocation of a joint

Inflammatory and Degenerative Conditions Bursitis An inflammation of a bursa, usually caused by a blow or friction Treated with rest and ice and, if severe, anti-inflammatory drugs Tendonitis Inflammation of tendon sheaths typically caused by overuse Symptoms and treatment similar to bursitis

Arthritis >100 different types of inflammatory or degenerative diseases that damage joints Most widespread crippling disease in the U.S. Symptoms; pain, stiffness, and swelling of a joint Acute forms: caused by bacteria, treated with antibiotics Chronic forms: osteoarthritis, rheumatoid arthritis, and gouty arthritis

Osteoarthritis (OA) Common, irreversible, degenerative (“wear-and-tear”) arthritis 85% of all Americans develop OA, more women than men Probably related to the normal aging process

Osteoarthritis (OA) More cartilage is destroyed than replaced in badly aligned or overworked joints Exposed bone ends thicken, enlarge, form bone spurs, and restrict movement Treatment: moderate activity, mild pain relievers, capsaicin creams, glucosamine and chondroitin sulfate

Rheumatoid Arthritis (RA) Chronic, inflammatory, autoimmune disease of unknown cause Usually arises between age 40 and 50, but may occur at any age; affects 3 times as many women as men Signs and symptoms include joint pain and swelling (usually bilateral), anemia, osteoporosis, muscle weakness, and cardiovascular problems

Rheumatoid Arthritis RA begins with synovitis of the affected joint Inflammatory blood cells migrate to the joint, release inflammatory chemicals Inflamed synovial membrane thickens into a pannus Pannus erodes cartilage, scar tissue forms, articulating bone ends connect (ankylosis)

Figure 8.15

Rheumatoid Arthritis: Treatment Conservative therapy: aspirin, long-term use of antibiotics, and physical therapy Progressive treatment: anti-inflammatory drugs or immunosuppressants New biological response modifier drugs neutralize inflammatory chemicals

Gouty Arthritis Deposition of uric acid crystals in joints and soft tissues, followed by inflammation More common in men Typically affects the joint at the base of the great toe In untreated gouty arthritis, the bone ends fuse and immobilize the joint Treatment: drugs, plenty of water, avoidance of alcohol

Lyme Disease Caused by spirochete bacteria transmitted by the bites of ticks (usually living on deer or mice) Symptoms: skin rash, flu-like symptoms, and foggy thinking May lead to joint pain and arthritis Treatment: antibiotics

Developmental Aspects of Joints By embryonic week 8, synovial joints resemble adult joints A joint’s size, shape, and flexibility are modified by use Advancing years take their toll on joints: Ligaments and tendons shorten and weaken Intervertebral discs become more likely to herniate Most people in their 70s have some degree of OA Exercise that coaxes joints through their full range of motion is key to postponing joint problems