Chapter 8- Joints
Chapter 8 - Joints
8.1 Types of Joints
Joints (Articulations):
Functional connections between bones.
Bind parts of the skeletal system together.
Make bone growth possible.
Permit parts of the skeleton to change shape during childbirth.
Enable the body to move in response to skeletal muscle contractions.
Structural Classification of Joints
Fibrous Joints:
Held together by dense connective tissue.
Cartilaginous Joints:
Held together by cartilage.
Synovial Joints:
Have a complex structure.
Functional Classification of Joints
Synarthrotic:
Immovable joints.
Amphiarthrotic:
Slightly movable joints.
Diarthrotic:
Freely movable joints.
Fibrous Joints
Fibrous Joints:
Held together with dense connective tissue containing many collagen fibers.
Found in bones in close contact.
Types of Fibrous Joints:
Syndesmosis:
Bones bound by a sheet of dense connective tissue (interosseous membrane) or a bundle of dense connective tissue (interosseous ligament).
Amphiarthrotic (flexible, may twist).
Example: Between tibia and fibula.
Suture:
Thin layer of connective tissue (sutural ligament) connects bones.
Synarthrotic (immovable) between flat bones of skull.
Gomphosis:
Cone-shaped bony process in a socket.
Synarthrotic (immovable).
Example: Root of a tooth in maxilla or mandible held in place by periodontal ligament.
Cartilaginous Joints
Cartilaginous Joints:
Connected by hyaline cartilage or fibrocartilage.
Types of Cartilaginous Joints:
Synchondrosis:
Bands of hyaline cartilage unite bones.
Synarthrotic.
Some are temporary (e.g., epiphyseal plate converted to synostosis).
Some are permanent (e.g., between manubrium and first rib).
Symphysis:
Pad of fibrocartilage between bones.
Articular surfaces covered by hyaline cartilage.
Amphiarthrotic (limited movement).
Example: Pubic symphysis and intervertebral discs.
Clinical Application 8.1 Costochondritis
Costochondritis:
Inflammation of the costal cartilages connecting the ribs to the sternum.
Involves synchondrosis between the manubrium and first rib (costosternal joint), and synovial joints between the costal cartilages of ribs 2-7 and the sternal body (costochondral joints).
Causes chest pain during deep breaths or certain actions, along with tenderness in the area where the ribs meet the sternum.
Can be caused by overexertion during exercise like weightlifting or forceful coughing.
Synovial Joints
Synovial Joints:
Most joints are synovial.
All are diarthrotic joints.
Structure is more complex than fibrous or cartilaginous joints.
Structure of a Synovial Joint:
Articular cartilage covers articular ends of bones.
Joint capsule consists of two layers:
Outer fibrous layer composed of ligaments.
Inner layer, synovial membrane, which secretes synovial fluid.
General Structure of Synovial Joints
Synovial joints consist of:
Articular cartilage.
Joint capsule.
Ligaments.
Synovial membrane.
Synovial cavity.
Synovial fluid.
Meniscus (-i) in some joints.
Bursa (-ae) in some joints.
Types of Synovial Joints
There are 6 types of synovial joints classified by shape and movements allowed:
Ball-and-Socket Joint:
Also called spheroidal joint.
Round head in cup-shaped cavity.
Widest range of motion, multiaxial and includes rotation.
Examples: Hip, shoulder.
Condylar Joint:
Also called ellipsoidal joint.
Oval condyle fits into elliptical cavity.
Back-and-forth, side-to-side movement, biaxial with no rotation.
Example: Joints between metacarpals and phalanges.
Plane Joint:
Also called gliding joint.
Almost flat or slightly curved surfaces.
Back-and-forth and twisting, nonaxial movement.
Example: Wrist and ankle joints.
Hinge Joint:
Convex surface fits into concave surface of another bone.
Uniaxial movement (in one plane).
Example: Elbow, joints between phalanges.
Pivot Joint:
Also called trochoid joint.
Cylindrical surface rotates within a ring of another bone.
Uniaxial movement, rotation only.
Example: Atlas (C1) and dens of axis (C2).
Saddle Joint:
Also called sellar joint.
Both bones have concave and convex surfaces.
Biaxial movement (in two planes).
Example: Carpal and metacarpal of thumb.
8.2 Types of Joint Movements
Action of Skeletal Muscle:
Produces movement at synovial joints.
Key Terms:
Origin: Relatively fixed end of a skeletal muscle.
Insertion: More movable end of a skeletal muscle.
Movement at a joint occurs when a muscle contracts, pulling the insertion towards the origin.
Terms Describing Joint Movements
Flexion: Bending of parts at a joint.
Extension: Straightening of parts at a joint.
Hyperextension: Extension beyond normal anatomical position.
Lateral flexion: Bending to the side.
Abduction: Moving a part of the body away from the midline.
Adduction: Moving a part of the body toward the midline.
Additional Joint Movements
Dorsiflexion: Ankle movement that points toes upward.
Plantar flexion: Ankle movement that points toes downward.
Circumduction: Movement of a part of the body in a circular path.
Rotation: Moving a part of the body around an axis.
Medial rotation: Movement of limb so anterior surface moves towards midline.
Lateral rotation: Movement of limb so anterior surface moves away from midline.
Supination: Forearm rotation so palm faces upward or forward, or lying down face up (supine).
Pronation: Forearm rotation so palm faces downward or backward, or lying down face down (prone).
More Terms Describing Joint Movements
Inversion: Turning of foot so plantar surface faces midline.
Eversion: Turning of foot so plantar surface faces away from midline.
Protraction: Movement of a body part forward.
Retraction: Movement of a body part backward.
Elevation: Raising a body part.
Depression: Lowering a body part.
8.3 Examples of Synovial Joints
Examples of large, complex synovial joints include:
Jaw (Temporomandibular Joint, TMJ):
Modified hinge joint between mandibular condyle and mandibular fossa of temporal bone.
Surrounding structures include joint capsule, articular disc (fibrocartilage), and main ligaments (sphenomandibular ligament, lateral (temporomandibular) ligament).
Movements include elevation and depression for chewing, slight gliding movements for biting.
Shoulder Joint:
Ball-and-socket joint between head of humerus and glenoid cavity of scapula.
Loose joint capsule, with several ligaments to prevent displacement, including coracohumeral ligament and glenohumeral ligaments.
Elbow Joint:
Contains two articulations: hinge joint (between trochlea of humerus and trochlear notch of ulna) allowing flexion/extension, and a plane joint (between capitulum of humerus and fovea on head of radius) allowing pronation/supination.
Major ligaments include radial collateral ligament, ulnar collateral ligament, anular ligament.
Hip Joint:
Ball-and-socket joint consisting of head of femur and acetabulum of hip bone, with an acetabular labrum and heavy joint capsule.
Movements allowed include a variety of movements, though less than the shoulder joint.
Major ligaments include iliofemoral ligament, pubofemoral ligament, ischiofemoral ligament.
Knee Joint:
Largest and most complex synovial joint consisting of femur, tibia, and patella.
Modified hinge joint allowing flexion/extension, with some rotation when flexed.
Strengthened by many ligaments and tendons and cushioned by bursae, with menisci separating femur and tibia.
Major ligaments include patellar ligament, oblique popliteal ligament, arcuate popliteal ligament, tibial (medial) collateral ligament, fibular (lateral) collateral ligament, anterior cruciate ligament, posterior cruciate ligament.
Clinical Application 8.3: Joint Disorders
Joint Injuries:
Result from trauma, overuse, infection, inappropriate immune attack, degeneration.
Arthroscopy: Used to treat shoulder, elbow, knee injuries and to diagnose certain conditions.
Dislocations: Displacement of articulating surfaces; common in shoulder, knee, fingers, jaw.
Sprain: Tearing of connective tissue in joint without bone dislocation.
Torn Ligament: Result from twisting, overextension, lifting heavy objects, or falls.
Bursitis: Inflammation of a bursa due to overuse or stress.
Arthritis: Inflammation, swelling, and pain in a joint.
Rheumatoid arthritis: Autoimmune disease.
Osteoarthritis: Degenerative, the most common type, occurs with aging.
Lyme arthritis: Caused by Lyme disease passed through tick bite.
Gout: A type of inflammatory arthritis caused by uric acid crystallizing in joints, typically the big toe; normally uric acid is excreted in the urine.
Clinical Application 8.4: Replacing Joints
Joint Replacement:
Synthetic materials are used to replace joints damaged by arthritis or injury.
Materials include steel and titanium for larger joints, silicone for smaller joints, and ceramic options.
Hip replacements are the most common type of joint replacement surgery.
New Technology in Joint Replacement:
Use of materials resembling natural body chemicals (e.g., hydroxyapatite coatings).
Use of 3D printing technology for custom replacement joints.
8.4 Lifespan Changes
Joint Stiffness:
An early sign of aging.
Many people develop arthritis as they age.
Changes in Joints:
Fibrous joints are the first to change; can strengthen over a lifetime.
Cartilage in synchondroses may stiffen.
Ligaments lose elasticity.
Changes in symphysis joints of the vertebral column diminish flexibility and decrease height (due to water loss from intervertebral discs).
Synovial joints lose function as capillary supply diminishes.
Disuse hampers nutrient supply to joints, speeding up stiffness.
Activity and exercise can help maintain joint function for a longer duration.