Types of Joints Lecture

Types of Joints

• Joints connect two or more bones and are classified into two main categories: synarthrosis and diarthrosis.
• Synarthrosis: Non-synovial joints lacking a joint cavity.
• Diarthrosis: Synovial joints containing a joint cavity; examples include hip, knee, shoulder, and elbow joints.

Characteristics of Diarthrosis Joints

• Joint cavity enclosed by a fibrous elastic capsule.
• Hyaline cartilage covers the bone surfaces within the joint.
• Synovial fluid coats joint surfaces, facilitating movement.
• Synovial membrane lines the inner capsule surface.
• Joint capsule has two layers: outer fibrous membrane and inner synovial membrane.
• Synovial fluid is compositionally similar to blood plasma but has lower protein content and higher hyaluronan concentration.

Classification of Synovial Joints

• Simple/Uniaxial Joints: Single pair of articular surfaces (one convex, one concave); examples include hinge and trochoid joints.
• Compound/Biaxial Joints: Single joint capsule with multiple articulating surfaces; includes condyloid and saddle joints.
• Complex/Multiaxial Joints: Incorporate inter-articular structures like menisci or discs; includes plain and ball-and-socket joints.

Types of Synovial Joints

• Ball and Socket Joints (Spheroid): Allows motion in all three planes; examples are the femur at the hip and the humerus at the shoulder.
• Hinge Joints (Ginglymoid): Characterized by a spool-like surface fitting into a concave surface; example is the elbow joint.
• Saddle Joints (Sellar): Have both convex and concave surfaces; an example is the carpometacarpal joint of the thumb.
• Ellipsoid Joints: Similar to ball and socket joints but allow limited movement; an example is the wrist joint (radiocarpal articulation).
• Pivot Joints (Trochoid): Allow rotational movement around a ring; an example is the humeral radial joint at the elbow.
• Planar Joints (Gliding): Feature flat surfaces that slide over one another without axial motion; examples include some metatarsal and carpal joints.
• Condyloid Joints: Characterized by an oval articular surface permitting flexion, extension, adduction, and circumduction, but not axial rotation; can be bicondylar if it has two surfaces.