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DrX Whiz Niraj
Joints: Classification & Movements
Master the structural and functional classification of joints, types of synovial joints, and articulation movements for B.Pharm exams.
A Joint (Articulation) is a point of contact between two bones, between bone and cartilage, or between bone and teeth. It binds the skeleton together and allows for body movement.
- Arthrology: The scientific study of joints.
- Kinesiology: The study of motion of the human body.
Joints are classified in two ways: Structurally (based on anatomical characteristics) and Functionally (based on the type of movement they permit).
| Structural Classification (What connects them?) |
Functional Classification (How much do they move?) |
Examples |
|---|---|---|
| 1. Fibrous Joints Held together by dense connective tissue. No synovial cavity. |
Synarthrosis (Immovable) |
Sutures of the skull, Gomphoses (teeth sockets). |
| 2. Cartilaginous Joints Bones held together by cartilage. No synovial cavity. |
Amphiarthrosis (Slightly Movable) |
Pubic symphysis, Intervertebral discs (spine). |
| 3. Synovial Joints Have a synovial cavity. Articular capsule connects bones. |
Diarthrosis (Freely Movable) |
Shoulder, Knee, Hip, Elbow joints. |
Synovial joints are freely movable (Diarthroses) and are categorized into 6 subtypes based on the shapes of the articulating bone surfaces.
1. Ball-and-Socket
Ball-like surface of one bone fits into a cup-like depression of another. Triaxial (freely movable in all directions).
Examples: Shoulder and Hip joints.
2. Hinge Joint
Convex surface of one bone fits into the concave surface of another. Uniaxial (opening and closing motion like a door).
Examples: Knee, Elbow, and Ankle joints.
3. Pivot Joint
A rounded/pointed surface fits into a ring formed by bone and a ligament. Uniaxial (allows rotation).
Examples: Atlanto-axial joint (turning head side-to-side to say "no").
4. Planar (Gliding)
Flat or slightly curved surfaces sliding over each other. Biaxial.
Examples: Intercarpal joints (in the wrist), Intertarsal joints.
5. Condyloid Joint
An oval-shaped projection fits into an oval-shaped depression. Biaxial.
Examples: Radiocarpal (wrist) joint, Metacarpophalangeal joints.
6. Saddle Joint
Articular surface of one bone is saddle-shaped, and the other bone sits in it like a rider. Biaxial.
Example: Carpometacarpal joint of the thumb.
Movements at synovial joints are grouped into 4 main categories: Gliding, Angular, Rotation, and Special Movements.
Key Movements:
- Flexion: Decrease in the angle between articulating bones (e.g., Bending the elbow).
- Extension: Increase in the angle between articulating bones (e.g., Straightening the arm).
- Abduction: Movement of a bone away from the midline (e.g., Raising arms sideways).
- Adduction: Movement of a bone toward the midline (e.g., Bringing arms back to the body).
- Rotation: A bone revolves around its own longitudinal axis (e.g., Turning head side-to-side).
Special Movements:
- Supination / Pronation: Turning the palm upward / downward.
- Dorsiflexion / Plantar flexion: Bending foot upward / Pointing toes downward.
Clinical Correlation (Joint Disorders)
Arthritis refers to inflammation of one or more joints. Main types include:
- Osteoarthritis (OA): "Wear-and-tear" arthritis. The articular cartilage deteriorates due to aging or obesity, causing bone to rub against bone.
- Rheumatoid Arthritis (RA): An autoimmune disease where the body's immune system attacks its own cartilage and joint linings, causing severe inflammation, swelling, and pain.
- Gouty Arthritis (Gout): Caused by the deposition of Uric acid crystals in the joints (often starting in the big toe).