Joints

Joints Rigid elements of the skeleton meet at joints or articulations Greek root “arthro” means joint Structure of joints Enables resistance to crushing, tearing, and other forces

Classifications of Joints Joints can be classified by function or structure Functional classification—based on amount of movement Synarthroses—immovable; common in axial skeleton Amphiarthroses—slightly movable; common in axial skeleton Diarthroses—freely movable; common in appendicular skeleton (all synovial joints)

Classifications of Joints Structural classification based on Material that binds bones together Presence or absence of a joint cavity Structural classifications include Fibrous Cartilaginous Synovial

Classifications of Joints

Fibrous Joints Bones are connected by fibrous connective tissue Do not have a joint cavity Most are immovable or slightly movable Types Sutures Syndesmoses Gomphoses

Sutures Bones are tightly bound by a minimal amount of fibrous tissue Only occur between the bones of the skull Allow bone growth so the skull can expand with brain during childhood Fibrous tissue ossifies in middle age Synostoses—closed sutures

Syndesmoses Bones are connected exclusively by ligaments Amount of movement depends on length of fibers Tibiofibular joint—immovable synarthrosis Interosseous membrane between radius and ulna Freely movable diarthrosis

Gomphoses Tooth in a socket Connecting ligament—the periodontal ligament

Fibrous Joints (a) Suture (b) Syndesmosis (c) Gomphosis Joint held together with very short, interconnecting fibers, and bone edges interlock. Found only in the skull. Joint held together by a ligament. Fibrous tissue can vary in length but is longer than in sutures. Peg-in-socket fibrous joint. Periodontal ligament holds tooth in socket. Socket of alveolar process Suture line Fibula Tibia Root of tooth Dense fibrous connective tissue Ligament Periodontal ligament

Cartilaginous Joints Bones are united by cartilage Lack a joint cavity Two types Synchondroses Symphyses

Synchondroses Hyaline cartilage unites bones Epiphyseal plates Joint between first rib and manubrium (a) Synchondroses Bones united by hyaline cartilage Sternum (manubrium) Epiphyseal plate (temporary hyaline cartilage joint) Joint between first rib and sternum (immovable) Figure 9.2a

Symphyses Fibrocartilage unites bones; resists tension and compression Slightly movable joints that provide strength with flexibility Intervertebral discs Pubic symphysis Hyaline cartilage—present as articular cartilage

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

Synovial Joints Most movable type of joint All are diarthroses Each contains a fluid-filled joint cavity

General Structure of Synovial Joints Articular cartilage Ends of opposing bones are covered with hyaline cartilage Absorbs compression Joint cavity (synovial cavity) Unique to synovial joints Cavity is a potential space that holds a small amount of synovial fluid

General Structure of Synovial Joints Articular capsule—joint cavity is enclosed in a two-layered capsule Fibrous capsule— which strengthens joint Synovial membrane— Lines joint capsule and covers internal joint surfaces Functions to make synovial fluid

General Structure of Synovial Joints Synovial fluid A viscous fluid similar to raw egg white A filtrate of blood Arises from capillaries in synovial membrane

General Structure of Synovial Joints Reinforcing ligaments Often are thickened parts of the fibrous capsule Sometimes are extracapsular ligaments— located outside the capsule Sometimes are intracapsular ligaments— located internal to the capsule

General Structure of Synovial Joints Ligament Joint cavity (contains synovial fluid) Articular (hyaline) cartilage Fibrous capsule Articular capsule Synovial membrane Periosteum (a) A typical synovial joint

General Structure of Synovial Joints Richly supplied with sensory nerves Detect pain Most monitor how much the capsule is being stretched

General Structure of Synovial Joints Have a rich blood supply Most supply the synovial membrane Extensive capillary beds produce basis of synovial fluid Branches of several major nerves and blood vessels

Synovial Joints with Articular Discs Some synovial joints contain an articular disc Occur in the temporomandibular joint and at the knee joint Occur in joints whose articulating bones have somewhat different shapes

How Synovial Joints Function Synovial joints—lubricating devices Friction could overheat and destroy joint tissue Are subjected to compressive forces Fluid is squeezed out as opposing cartilages touch Cartilages ride on the slippery film

Bursae and Tendon Sheaths Bursae and tendon sheaths are not synovial joints Closed bags of lubricant Reduce friction between body elements Bursa—a flattened fibrous sac lined by a synovial membrane Tendon sheath—an elongated bursa that wraps around a tendon

Bursae and Tendon Sheaths Coracoacromial ligament Acromion of scapula Subacromial bursa Coracoacromial ligament Subacromial bursa Joint cavity containing synovial fluid Fibrous articular capsule Cavity in bursa containing synovial fluid Humerus resting Hyaline cartilage Bursa rolls and lessens friction. Tendon sheath Synovial membrane Tendon of long head of biceps brachii muscle Fibrous capsule Humerus Humerus head rolls medially as arm abducts. Humerus moving (a) Frontal section through the right shoulder joint (b) Enlargement of (a), showing how a bursa eliminates friction where a ligament (or other structure) would rub against a bone

Movements Allowed by Synovial Joints Three basic types of movement Gliding—one bone across the surface of another Angular movement—movements change the angle between bones Rotation—movement around a bone's long axis

Gliding Joints Flat surfaces of two bones slip across each other Gliding occurs between Carpals Articular processes of vertebrae Tarsals Gliding (a) Gliding movements at the wrist

Angular Movements Increase or decrease angle between bones Movements involve Flexion and extension Abduction and adduction Circumduction

Angular Movements Extension Flexion (b) Angular movements: flexion and extension of the neck

Angular Movements Extension Flexion (c) Angular movements: flexion and extension of the trunk

Angular Movements Flexion Extension Flexion Extension (d) Angular movements: flexion and extension at the shoulder and knee

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

Rotation Involves turning movement of a bone around its long axis The only movement allowed between atlas and axis vertebrae Occurs at the hip and shoulder joints

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

Special Movements Elevation—lifting a body part superiorly Depression—moving the elevated part inferiorly Elevation of mandible Depression of mandible Elevation Lifting a body part superiorly Depression Moving a body part inferiorly

Special Movements Protraction—nonangular movement anteriorly Retraction—nonangular movement posteriorly Protraction of mandible Retraction of mandible (b) Protraction Moving a body part in the anterior direction Retraction Moving a body part in the posterior direction

Special Movements Supination—forearm rotates laterally, palm faces anteriorly Pronation—forearm rotates medially, palm faces posteriorly Brings radius across the ulna

Special Movements Pronation (radius rotates over ulna) Supination (radius and ulna are parallel) (c) Pronation (P) Rotating the forearm so the palm faces posteriorly Supination (S) Rotating the forearm so the palm faces anteriorly

Special Movements Opposition—thumb moves across the palm to touch the tips of other fingers Opposition (d) Opposition Moving the thumb to touch the tips of the other fingers

Special Movements Inversion and eversion Special movements at the foot Inversion—turns sole medially Eversion—turns sole laterally

Special Movements Inversion Eversion (e) Inversion Turning the sole of the foot medially Eversion Turning the sole of the foot laterally

Special Movements Dorsiflexion and plantar flexion Up-and-down movements of the foot Dorsiflexion—lifting the foot so its superior surface approaches the shin Plantar flexion—depressing the foot, elevating the heel

Special Movements Dorsiflexion Plantar flexion (f) Dorsiflexion Lifting the foot so its superior surface approaches the shin Plantar flexion Depressing the foot elevating the heel

Synovial Joints Classified by Shape Plane joint Articular surfaces are flat planes Short gliding movements are allowed Intertarsal and intercarpal joints Movements are nonaxial Gliding does not involve rotation around any axis

Plane Joint Nonaxial movement Metacarpals Carpals Gliding (a) Plane joint

Synovial Joints Classified by Shape Hinge joints Cylindrical end of one bone fits into a trough on another bone Angular movement is allowed in one plane Elbow, ankle, and joints between phalanges Movement is uniaxial—allows movement around one axis only

Hinge Joint Uniaxial movement Humerus Medial/ Lateral axis Ulna Flexion and extension (b) Hinge joint

Synovial Joints Classified by Shape Pivot joints Classified as uniaxial – rotating bone only turns around its long axis Examples Proximal radioulnar joint Joint between atlas and axis

Pivot Joint Vertical axis Ulna Radius Rotation Pivot joint

Synovial Joints Classified by Shape Condyloid joints Allow moving bone to travel Side to side—abduction-adduction Back and forth—flexion-extension Classified as biaxial—movement occurs around two axes

Condyloid Joint Biaxial movement Phalanges Anterior/ posterior axis Medial/ lateral axis Metacarpals Flexion and extension Adduction and abduction (d) Condyloid joint

Synovial Joints Classified by Shape Saddle joints Each articular surface has concave and convex surfaces Classified as biaxial joints 1st carpometacarpal joint is a good example Allows opposition of the thumb

Synovial Joints Classified by Shape Metacarpal 1 Medial/ lateral axis Anterior/ posterior axis Adduction and abduction Flexion and extension Trapezium (e) Saddle joint

Synovial Joints Classified by Shape Ball-and-socket joints Spherical head of one bone fits into round socket of another Classified as multiaxial—allow movement in all axes Shoulder and hip joints are examples

Ball-and-Socket Joint Multiaxial movement Scapula Medial/lateral axis Anterior/posterior axis Vertical axis Humerus Flexion and extension Adduction and abduction Rotation (f) Ball-and-socket joint

Factors Influencing Stability of Synovial Joints Articular surfaces Shapes of articulating surfaces determine movements possible Seldom play a major role in joint stability Exceptions that do provide stability Hip joint, elbow joint, and ankle

Factors Influencing Stability of Synovial Joints Ligaments Capsules and ligaments prevent excessive motions On the medial or inferior side of a joint – prevent excessive abduction Lateral or superiorly located—resist adduction

Factors Influencing Stability of Synovial Joints Ligaments (continued) Anterior ligaments—resist extension and lateral rotation Posterior ligaments—resist flexion and medial rotation The more ligaments, usually stronger and more stable

Factors Influencing Stability of Synovial Joints Muscle tone Helps stabilize joints by keeping tension on tendons Is important in reinforcing: Shoulder and knee joints Supporting joints in arches of the foot

Selected Synovial Joints Sternoclavicular joint Is a saddle joint Four ligaments surround the joint Anterior and posterior sternoclavicular ligaments Interclavicular ligament Costoclavicular ligament Performs multiple complex movements

Selected Synovial Joints Anterior sternoclavicular ligament and joint capsule Articular disc Interclavicular ligament Elevation Retraction Posterior rotation Clavicle Protraction Depression Manubrium of sternum Costoclavicular ligament Costal cartilage of 1st rib (a) Sternoclavicular joint, anterior view (b) Sternoclavicular movements

Selected Synovial Joints Temporomandibular Joint Is a modified hinge joint The head of the mandible articulates with the temporal bone Lateral excursion is a side-to-side movement Two surfaces of the articular disc allow Hinge-like movement Gliding of superior surface anteriorly

The Temporomandibular Joint Figure 9.10c

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

Selected Synovial Joints Elbow joint Allows flexion and extension The humerus’ articulation with the trochlear notch of the ulna forms the hinge Tendons of biceps and triceps brachii provide stability

Elbow Joint Allows flexion and extension The humerus’ articulation with the trochlear notch of the ulna forms the hinge Tendons of biceps and triceps brachii provide stability Articular capsule Synovial membrane Humerus Synovial cavity Articular cartilage Fat pad Coronoid process Tendon of triceps muscle Tendon of brachialis muscle Ulna Bursa Trochlea Humerus Articular cartilage of the trochlear notch Anular ligament (a) Mid-sagittal section through right elbow (lateral view) Radius Lateral epicondyle Articular capsule Radial collateral ligament Olecranon process Ulna (b) Lateral view of right elbow joint

Wrist Joint Stabilized by numerous ligaments Composed of radiocarpal and intercarpal joint Radiocarpal joint—joint between the radius and proximal carpals (the scaphoid and lunate) Allows for flexion, extension, adduction, abduction, and circumduction Intercarpal joint—joint between the proximal and distal rows or carpals Allows for gliding movement

Wrist Joint Palmar radiocarpal ligament Radius Ulna Lunate Radial collateral ligament Ulnar collateral ligament Scaphoid Intercarpal ligaments Pisiform Hamate Trapezium Carpo- metacarpal ligaments Capitate (c) Ligaments of the wrist, anterior (palmar) view

Selected Synovial Joints Hip joint A ball-and-socket structure Movements occur in all axes Limited by ligaments and acetabulum Head of femur articulates with acetabulum Stability comes chiefly from acetabulum and capsular ligaments Muscle tendons contribute somewhat to stability

Frontal Section and Anterior View of the Hip Joint Acetabular labrum Synovial membrane Ligament of the head of the femur (ligamentum teres) Head offemur Articular capsule (cut) (b) Photo of the interior of the hip joint, lateral view Articular cartilage Coxal (hip) bone Ligament of the head of the femur (ligamentum teres) Synovial cavity Articular capsule Acetabular labrum Femur (a) Frontal section through the right hip joint

Selected Synovial Joints Knee joint The largest and most complex joint Primarily acts as a hinge joint Has some capacity for rotation when leg is flexed Structurally considered compound and bicondyloid Two fibrocartilage menisci occur within the joint cavity Femoropatellar joint—shares the joint cavity Allows patella to glide across the distal femur

Sagittal Section of Knee Joint Tendon of quadriceps femoris Suprapatellar bursa Femur Articular capsule Patella Posterior cruciate ligament Subcutaneous prepatellar bursa Synovial cavity Lateral meniscus Lateral meniscus Anterior cruciate ligament Infrapatellar fat pad Deep infrapatellar bursa Tibia Patellar ligament (a) Sagittal section through the right knee joint Figure 9.15a

Knee Joint Capsule of the knee joint Covers posterior and lateral aspects of the knee Covers tibial and femoral condyles Does not cover the anterior aspect of the knee Anteriorly covered by three ligaments Patellar ligament Medial and lateral patellar retinacula

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

Knee Joint Ligaments of the knee joint Become taut when knee is extended These extracapsular and capsular ligaments are Fibular and tibial collateral ligament Oblique popliteal ligament Arcuate popliteal ligament

Posterior View of Knee Joint Tendon of adductor magnus Femur Articular capsule Medial head of gastrocnemius muscle Oblique popliteal ligament 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

Knee Joint Intracapsular ligaments Cruciate ligaments Cross each other like an “X” Each cruciate ligament runs from the proximal tibia to the distal femur Anterior cruciate ligament Posterior cruciate ligament

Anterior View of Flexed Knee Posterior cruciate ligament Fibular collateral ligament Medial condyle Medial femoral condyle Anterior cruciate ligament Medial meniscus on medial tibial Patella (f) Photograph of an opened knee joint; view similar to (e) 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)

Knee Joint Intracapsular ligaments Cruciate ligaments—prevent undesirable movements at the knee Anterior cruciate ligament—prevents anterior sliding of the tibia Posterior cruciate ligament—prevents forward sliding of the femur or backward displacement of the tibia

Stabilizing function of cruciate ligaments 1 During movement of the knee the anterior cruciate prevents anterior sliding of the tibia; the posterior cruciate prevents posterior sliding of the tibia. 2 When the knee is fully extended, both cruciate ligaments are taut and the knee is locked. Quadriceps muscle Femur Anterior cruciate ligament Patella Medial condyle Anterior cruciate ligament Lateral meniscus Posterior cruciate ligament Posterior cruciate ligament Tibia (a) (b)

The “Unhappy Triad” Lateral blows to the knee can tear: Tibial collateral ligament and medial meniscus Anterior cruciate ligament

The “Unhappy Triad” Lateral Medial Patella (outline) Lateral force Tibial collateral ligament (torn) Medial meniscus (torn) Anterior cruciate ligament (torn) Anterior view

Selected Synovial Joint Ankle joint A hinge joint between United inferior ends of tibia and fibula The talus of the foot Allows the movements Dorsiflexion and plantar flexion only Medially and laterally stabilized by ligaments Medial (deltoid) ligament Lateral ligament Inferior ends of tibia and fibula are joined by ligaments Anterior and posterior tibiofibular ligaments

The Ankle Joint Tibialis posterior muscle Tibia Calcaneal tendon Ankle (talocrural) joint Talocalcaneal ligament Talus Talonavicular joint Cuneonavicular joint Tarsometatarsal joint Metatarsal bone (II) Metatarsophalangeal joint Interphalangeal joint Calcaneus Subtalar joint Navicular bone Intermediate cuneiform bone Tendon of flexor digitorum longus (a) Cadaver photo of ankle and foot, sagittal section

Ligaments of the Ankle Joint Fibula Anterior tibiofibular ligament Tibia Posterior tibiofibular ligament Lateral malleolus Anterior talofibular ligament Talus Lateral ligament Posterior talofibular ligament Metatarsals Calcaneofibular ligament Calcaneus Cuboid (c) Right ankle, lateral view