Joints
Joints
Definition
Joint (Articulation): An articulation where two or more bones meet.
Condyle: A round protuberance at the end of some bones, forming an articulation with another bone.
Discs: Cushion-like structures that act as shock absorbers, allowing movement (bending, twisting) and providing space for nerves.
Functional Classifications of Joints
Synarthroses: Immovable joints.
Amphiarthroses: Slightly movable joints.
Diarthroses: Freely movable joints.
Structural Classifications of Joints
Fibrous Joints: Generally immovable, bones united by fibrous tissue.
Sutures: Immobile fibrous joints found in skull bones.
Syndesmoses: Fibrous joints allowing more movement than sutures but still immobile.
Gomphoses: Immobile fibrous joints found where teeth meet facial bones.
Cartilaginous Joints: Immovable or slightly movable, bones connected by cartilage.
Synchondrosis: Immobile cartilaginous joints found in epiphyseal plates.
Symphysis: Slightly movable joints, found in the pubic symphysis and intervertebral joints.
Synovial Joints: Freely movable, articulating bones separated by a joint cavity containing synovial fluid.
Articular cartilage: Cartilage covering the ends of bones in synovial joints.
Articular capsule: A capsule enclosing synovial joints.
Reinforcing ligaments: Ligaments supporting the joint structure.
Joint cavity: The fluid-filled space between bones in freely movable joints.
Bursae: Flattened fibrous sacs lined with synovial membranes and filled with synovial fluid.
Tendon sheath: An elongated bursa that surrounds a tendon.
Types of Synovial Joints
Plane Joint: Flat articular surfaces allowing short gliding movements (e.g., intertarsals).
Hinge Joint: Cylindrical end of one bone fits into a trough on another, allowing movement around one axis (e.g., elbow).
Pivot Joint: A uniaxial joint where one bone rotates around its long axis (e.g., neck).
Condylar Joint: A biaxial joint allowing side-to-side and back-and-forth movement (e.g., metacarpophalangeal joint).
Saddle Joint: Biaxial joints allowing opposition of the thumb (e.g., opposition of thumb).
Ball-and-socket Joint: Multiaxial joints allowing movement in all axes (e.g., shoulder or hip).
Specific Joint Classifications and Functions
Skull bones: Sutures - no function.
Temporomandibular Joint (TMJ): Synovial - modified hinge biaxial.
C0 - C1 (Atlanto-occipital): Synovial - condylar joint biaxial.
C1-C2 (Atlanto-axial): Synovial - pivot uniaxial.
Facet Joints: Synovial - gliding.
Intervertebral Joints: Cartilaginous - no function.
Costovertebral Joints: Synovial - gliding non-axial.
Sternoclavicular: Synovial - modified saddle multiaxial.
Sternocostal Joints (2-7): Synovial - gliding non-axial.
Acromioclavicular Joint: Synovial - plane gliding non-axial.
Glenohumeral Joint: Synovial - ball & socket multiaxial arm.
Elbow: Synovial - hinge uniaxial.
Proximal Radioulnar: Synovial - pivot uniaxial.
Distal Radioulnar: Synovial - pivot.
Additional Synovial Joints
Wrist (Radiocarpal): Synovial - condylar.
Intercarpal: Synovial - hinge.
Thumb (Trapezium-Metatarsal 1): Synovial - saddle.
Carpometacarpal of 2-5: Synovial - gliding.
Metacarpal-phalangeal: Synovial - condylar biaxial.
Interphalangeal Joints: Synovial - hinge.
Sacroiliac: Synovial - plane gliding.
Hip Joint: Synovial - ball & socket multiaxial leg.
Pubic Symphysis: Cartilaginous - no function.
Tibiofemoral Joint (knee): Synovial - modified hinge biaxial.
Femoropatellar Joint (knee): Synovial - plane.
Superior Tibiofibular: Synovial - plane.
Inferior Tibiofibular: Fibrous - no function.
Ankle: Synovial - hinge.
Intertarsal: Synovial - plane.
Tarsometatarsal: Synovial - plane.
Metatarsophalangeal: Synovial - condylar biaxial.
Interphalangeal: Synovial - hinge.
Major Ligaments
Coracohumeral Ligament: Superior to the glenohumeral joint; helps support the weight of the upper limb.
Glenohumeral Ligaments: Three weak ligaments supporting the glenohumeral joint.
Anular Ligament of Radius: A ring around the head of the radius.
Radial & Ulnar Collateral Ligaments: Prevent lateral and medial movement at the elbow.
Iliofemoral Ligament: Strong, V-shaped, anteriorly located; runs from the ilium to the greater trochanter of the femur.
Pubofemoral Ligament: Triangular thickening of the capsule's inferior region; runs from the pubic bone to the femur.
Ischiofemoral Ligament: Spiraling, posteriorly located; runs from the ischium to the greater trochanter of the femur.
Ligament of Head of Femur: Flat, intracapsular band running from the head of the femur to the inferior acetabulum; contains an artery that supplies the head of the femur.
Vascular Necrosis: Lack of blood to an area, potentially causing tissue death.
The Knee Joint
The knee joint is the largest and most complex joint.
It is a compound bicondylar joint.
Anterior Cruciate Ligament (ACL): A crucial, strong tissue band connecting the femur to the tibia; prevents anterior sliding of the tibia.
Posterior Cruciate Ligament: Runs from the posterior tibia to the medial condyle; locks the knees while standing and prevents the femur from sliding forward.
Medial Collateral Ligament (MCL): A strong band of tissue on the inner knee, connecting the femur to the tibia; provides stability against excessive medial rotation.
Lateral Collateral Ligament (LCL): A strong band of tissue on the outside of the knee, connecting the femur to the tibia; also stops the knee from hyperextension.
Standing Position: When standing, femoral condyles roll onto the tibia.
Welcome to today's episode where we explore the structural framework of the human body: Joints. In this session, we'll break down the types of articulations and how they keep us moving.
Introduction to Joints
To start, a joint, or articulation, is simply where two or more bones meet. But it’s not just bone-on-bone contact. We have condyles—those rounded protuberances—and discs that act as shock absorbers, ensuring our nerves have space and our movements stay smooth.
How We Classify Them
We look at joints through two lenses: functional and structural.
Functional classification tells us how much they move. We have Synarthroses (immovable), Amphiarthroses (slightly movable), and Diarthroses (the freely movable ones).
Structural classification focuses on what holds them together.
Fibrous joints (like the sutures in your skull) are held by fibrous tissue.
Cartilaginous joints (like your pubic symphysis) use cartilage.
Synovial joints are the ones you usually think of—they have a fluid-filled cavity and allow for a wide range of motion.
The Superstars: Synovial Joints
Synovial joints come in many flavors. You have hinge joints like your elbow, pivot joints in your neck, and the highly mobile ball-and-socket joints in your shoulder and hip. Each is reinforced by ligaments and often cushioned by bursae—fluid sacs that reduce friction.
A Closer Look: The Knee
We can't talk about joints without mentioning the knee. It's a compound bicondylar joint and the largest one we have. It’s held together by a 'cross' of ligaments: the Anterior Cruciate Ligament (ACL) and the Posterior Cruciate Ligament (PCL), which prevent the bones from sliding out of place.
Stability and Strength
From the Iliofemoral ligament in the hip (the strongest V-shaped support) to the Radial and Ulnar Collateral ligaments in the elbow, our body uses these bands of tissue to ensure that while we are mobile, we are also stable.
That wraps up our quick tour of joints! Next time, we'll dive into muscle mechanics.