Introduction
- A joint is the place where two or more bones or cartilages meet. It acts as a connection between bones and helps in movement of different body parts. Some joints allow free movement, while some remain fixed and provide stability.
- In the human body, joints are very important because they make movements such as walking, running, bending, writing, chewing, and turning possible.
- In children, the number of joints is more than in adults because some bones fuse together during growth. For example, pelvic bones and sacral vertebrae fuse with age.
Classification of Joints
Joints are classified in different ways.
1. Structural Classification of Joints
According to the material joining bones, joints are divided into three main types:
- Fibrous joints
- Cartilaginous joints
- Synovial joints
Fibrous Joints
In fibrous joints, bones are connected by fibrous connective tissue. These joints are usually immovable or allow very little movement.
Types of Fibrous Joints
a) Sutures
These are found only in skull bones.
Examples:
- Coronal suture
- Sagittal suture
- Lambdoid suture
Characteristics:
- Immovable
- Strong
- Help protect brain
b) Syndesmosis
Bones are connected by ligaments.
Example:
- Inferior tibiofibular joint
c) Gomphosis
Peg and socket type joint.
Example:
- Tooth fixed in socket of jaw
Cartilaginous Joints
In these joints, bones are connected by cartilage.
They allow slight movement.
Types of Cartilaginous Joints
a) Primary Cartilaginous Joint (Synchondrosis)
Bones are united by hyaline cartilage.
Characteristics:
- Temporary joint
- Later converted into bone
Examples:
- Epiphyseal plate
- First chondrosternal joint
- Costochondral joint
b) Secondary Cartilaginous Joint (Symphysis)
Bones are connected by fibrocartilage.
Characteristics:
- Permanent
- Slight movement possible
- Shock absorber function
Examples:
- Pubic symphysis
- Intervertebral disc
- Manubriosternal joint
Synovial Joints
These are the most movable joints in the body.
They have a joint cavity filled with synovial fluid.
Main Features of Synovial Joint
- Articular cartilage covers bone ends
- Joint cavity present
- Synovial membrane present
- Fibrous capsule surrounds joint
- Synovial fluid acts as lubricant
Types of Synovial Joints
1. Plane Joint
Flat surfaces slide over each other.
Examples:
- Intercarpal joints
- Intertarsal joints
Movement:
- Gliding
2. Hinge Joint
Movement in one plane only.
Examples:
- Elbow joint
- Ankle joint
- Interphalangeal joints
Movement:
- Flexion and extension
3. Pivot Joint
One bone rotates around another.
Examples:
- Superior radioulnar joint
- Atlantoaxial joint
Movement:
- Rotation
4. Condylar Joint
Two condyles fit together.
Examples:
- Knee joint
- Temporomandibular joint
Movement:
- Flexion
- Extension
- Limited rotation
5. Ellipsoid Joint
Oval convex surface fits into oval concave surface.
Examples:
- Wrist joint
- Metacarpophalangeal joint
Movement:
- Flexion
- Extension
- Abduction
- Adduction
6. Saddle Joint
Surfaces are concavo-convex.
Examples:
- First carpometacarpal joint
- Sternoclavicular joint
Movement:
- Flexion
- Extension
- Abduction
- Adduction
- Limited rotation
7. Ball and Socket Joint
Most movable joint.
Examples:
- Shoulder joint
- Hip joint
Movement:
- Flexion
- Extension
- Abduction
- Adduction
- Rotation
- Circumduction
Movements of Joints
Angular Movements
- Flexion = decreasing angle
- Extension = increasing angle
- Abduction = away from midline
- Adduction = toward midline
Rotational Movement
- Bone turns around axis
Circumduction
- Circular movement
Gliding
- Sliding movement
Synovial Fluid Functions
Synovial fluid is very important because it:
- Lubricates joint
- Reduces friction
- Nourishes articular cartilage
- Allows smooth movement
Blood Supply of Joints
Blood supply comes from surrounding arteries forming periarticular arterial plexus.
Functions:
- Supplies capsule
- Supplies synovial membrane
- Supplies epiphysis
Articular cartilage itself has no blood supply.
Nerve Supply of Joints
Joint nerves provide:
- Pain sensation
- Position sense
- Reflex protection
Hilton’s Law
A nerve supplying muscle acting on a joint also supplies:
- Joint capsule
- Skin over joint
Factors Maintaining Joint Stability
1. Muscles
Most important factor.
2. Ligaments
Prevent excessive movement.
3. Bones
Provide stability in some joints like hip.
Clinical Importance of Joints
1. Arthritis
Inflammation of joints.
Types:
- Rheumatoid arthritis
- Osteoarthritis
Rheumatoid Arthritis
- Small joints affected
- Synovial membrane inflamed
- Finger deformity common
Osteoarthritis
- Large weight-bearing joints affected
- Cartilage degenerates
- Pain during movement
2. Dislocation
Bone leaves its normal position in joint.
3. Subluxation
Partial dislocation.
4. Disc Prolapse
Intervertebral disc protrudes and presses spinal nerve.
This may cause:
- Sciatica
- Back pain
5. Bursitis
Inflammation of bursa.
Bursa reduces friction around joints.