Joint Structure

Classification of JointsClassification of Joints

Fibrous (synarthroses): lacks a joint cavity and the articulating bones are held very closely together by fibrous connective tissue; they permit little or no movement– sutures– syndesmoses– gomphoses

SuturesSutures

found between the bones of the skull and are united by a thin layer of dense fibrous connective tissue

SyndesmosesSyndesmoses

fibrous connective tissue forms an interosseous membrane or ligament (distal articulation of the tibia and fibula, shafts of radius and ulna)

GomphosesGomphoses

cone-shaped peg fits into a socket (teeth)

Classification of JointsClassification of Joints

Cartilaginous (amphiarthroses): lacks a joint cavity and the articulating bones are tightly connected by cartilage – synchrondrosis– symphyses

SynchrondrosisSynchrondrosis

connecting material is hyaline cartilage (epiphyseal plate)

SymphysesSymphyses

connecting material is a broad, flat disc of fibrocartilage (pubic symphysis; bodies of vertebrae)

Classification of Joints

• Synovial (diarthroses): joint cavity (space between the articulating bones) is present; freely movable. – Gliding– Hinge– Pivot– Ellipsoidal– Saddle– Ball and socket

Synovial Joints are

freely movable

Gliding• side-to-side and back-and-forth

movements (biaxial); articulating surfaces are usually flat (intercarpal, intertarsal, sternum and clavicle)

Synovial Joints

Hinge• motions are flexion/extension

(monoaxial); convex surface of one bone fits into the concave surface of another (elbow, knee)

Synovial Joints

Pivot• rotational movement (monoaxial);

rounded, pointed, or concave surface fits into a ring formed partly by bone and partly by a ligament (atlas and axis)

Synovial Joints

Ellipsoidal• side-to-side and back-and-forth

movements (biaxial); oval shaped condyle fits into an elliptical cavity (wrist)

Synovial Joints

Saddle• side-to-side and back-and-forth

movements (biaxial); articular surfaces concave in one direction and convex in opposite direction (CMC of thumb)

Synovial Joints

Ball and socket• movement in 3 planes (triaxial); ball

like surface fits into a cuplike depression (shoulder and hip)

Synovial Joints

Components of Synovial Joints

• articular cartilage: covers surfaces of articulating bones but does not bind them together

• articular capsule: surrounds the articular surfaces and encloses the joint cavity– outer layer (fibrous capsule): attached to the

periosteum of articulating bones at a variable distance from the edge of the articulating cartilage

– inner layer (synovial membrane): secretes synovial fluid which lubricates the joint and provides nourishment for the articular cartilage

Components of Synovial Joints

• joint (synovial) cavity: enclosed space that surrounds the 2 articulating surfaces; contains the slippery lubricating fluid called synovial fluid

• ligaments: thickened collagenous bands connecting bone to bone– extracapsular ligaments are outside of the articular

capsule (MCL, LCL)– intracapsular ligaments directly attach the 2

articulating surfaces (ACL, PCL)

Components of Synovial Joints

• articular discs (menisci): pads of fibrocartilage that lie between the articular surfaces of the bones; help maintain the stability of a joint and direct the flow of synovial fluid to areas of greatest friction; not all synovial joints have them

Components of Synovial Joints

• bursae: saclike structures that contain synovial fluid to help reduce friction between:– skin and bone– tendons and bones– muscles and bones– ligaments and bones