Types of Joints in Human Anatomy

Types of joints

• Joints are formed when two or more bones come together, allowing for movement or preventing it.
• Classification based on the tissue between the bones:
  • Fibrous joints: Connected via fibrous tissue, allowing very limited movement. Examples: Sutures in the skull, inferior tibiofibular joint.
  • Cartilaginous joints: Two types:
    • Primary cartilaginous: Bones connected by hyaline cartilage, no movement. Examples: Epiphysis-diaphysis junction, 1st rib-manubrium joint.
    • Secondary cartilaginous: Bones connected by fibrocartilage, slight movement. Examples: Joints between vertebral bodies, symphysis pubis.
  • Synovial joints: Articulating surfaces covered by hyaline cartilage, separated by a joint cavity. Allows for a high degree of movement.

Features of Synovial joints

• Synovial membrane: Lines the joint cavity, extending from one articular surface to the other. Protected by the joint capsule.
• Synovial fluid: Lubricates the articular surfaces, produced by the synovial membrane.
• Articular discs: Fibrocartilage wedges found in some joints like the knee, providing cushioning and shock absorption.
• Fatty pads: Found in certain joints like the hip and knee, located between the synovial membrane and the fibrous capsule or bone.

Factors limiting movement in Synovial joints

• Shape of bones: The shape of the bones involved in the joint restricts movement.
• Adjacent anatomical structures: Surrounding structures like muscles, tendons, and ligaments limit movement.
• Ligaments: Fibrous ligaments hold bones together, preventing excessive movement.

Synovial joint classifications

• Plane joints: Flat articular surfaces allow for sliding movement. Examples: Sternoclavicular and acromioclavicular joints.
• Hinge joints: One bone moves on another like a hinge on a door, allowing flexion and extension. Examples: Elbow, knee, and ankle joints.
• Pivot joints: A central bony pivot rotates within a bony-ligamentous ring, allowing only rotation. Examples: Atlantoaxial and superior radioulnar joints.
• Condyloid joints: Convex surface articulates with two concave surfaces, allowing flexion, extension, abduction, adduction, and limited rotation. Examples: Metacarpophalangeal joints (knuckle joints).
• Ellipsoid joints: Elliptical convex surface fits into an elliptical concave surface, permitting flexion, extension, abduction, and adduction, but not rotation. Example: Wrist joint.
• Saddle joints: Reciprocally concavoconvex surfaces resembling a saddle, allowing flexion, extension, abduction, adduction, and rotation. Example: Carpometacarpal joint of the thumb.
• Ball-and-socket joints: Ball-shaped head fits into a socket-like concavity, allowing extensive movement in all planes. Examples: Shoulder and hip joints.

Joint stability

• Primarily depends on:
  • Shape, size, and arrangement of the articular surfaces: Well-fitting surfaces provide inherent stability.
  • Ligaments: Fibrous ligaments prevent excessive movement, but can stretch under prolonged stress.
  • Muscle tone: Muscle activity provides the main source of stability.

Ligaments and stability

• Fibrous ligaments: Prevent excessive movement. Can stretch with prolonged stress.
• Elastic ligaments: Return to their original length after stretching. Important in the auditory ossicles.

Muscle tone and stability

• Muscle tone: Essential for maintaining stability. Muscle weakness can lead to joint instability.

Nerve Supply of Joints

• Joints receive extensive sensory nerve supply to the capsule and ligaments.
• A nerve supplying a joint also supplies the muscles that move it and the overlying skin. This principle is known as Hilton's law.
• A single nerve can supply multiple joints.

Case Study discussion

• The student suffered damage to the outer surface of his left knee, resulting in paralysis of muscles in the anterior and lateral compartments of the leg.
• This caused:
  • Footdrop: Inability to dorsiflex the ankle.
  • Eversion: Inability to evert the foot.
• He also experienced diminished sensation in the leg and foot, suggesting nerve damage.