The Biomechanics of Human Skeletal Articulations Chapter #5

JOINT ARCHITECTURE

How can we categorize joints ?

1.Based on complexity 2.Number of axis 3.Joint geometry 4.Movement capabilities

IMMOVABLE SLIGHTLY MOVABLE FREELY MOVABLE

SYNARTHROSES/IMMOVABLE (Syn = together ; arthron = joint) Fibrous joints Dense fibrous tissue Shock absorb Allow little or no movement Sutures Syndesmoses

a. Sutures Irregularly grooved articulations of bone are held together by FIBERS These fibers are cont with PERIOSTEUM They begin to ossify in early adulthood – replaced by bone

b. Syndesmoses Held by bands/ligaments Dense fibrous tissue binds bones Permitting very limited movement

AMPHIARTHROSES Cartilaginous joints Shock absorb Permit more mobility than fibrous joints SynchondrosesSymphysis

Held by Cartilage Articular surfaces – thin hyaline cartilage

Thin plate of hyaline cartilage separate a disc of fibro-cartilage from the bone.

JOINT ARCHITECTURE IMMOVABLESUTURESSYNDESMOSES SLIGHTLY MOVABLE SYNCHONDROSESSYMPHYSISFREELY MOVABLE---

Diarthroses or synovial joints Freely movable joints allow movement in one or more directions. Majority of joints in adult human body are freely movable joints.

Typical synovial joints have following characteristics 1.Cartilage – A material which covers the end of each bone, and which helps prevent friction between the joint. 2.Joint Capsule –The outer covering of the joint that holds the bones together and protects the joint. 3.Synovial Membrane – The inner lining of the joint capsule which also produces synovial fluid. 4.Synovial Fluid – The fluid which surrounds the joint and acts like an ‘oil’, lubricating it to allow easy movement. 5.Ligaments – These are elastic straps which join bone to bone, holding the joint together. 6.Tendons – These are non-elastic straps which join muscle to bone.

CARTILAGEJOINT CAPSULE SYNOVIAL MEMBRANE SYNIVIAL FLUIDLIGAMENTSTENDONS

Types of freely movable joints 1.Gliding joints 2.Hinge joints 3.Pivot joints 4.Condyloid joints 5.Saddle joints 6.Ball and Socket joints

Synovial joints They vary widely in structure, movement capabilities and axis of rotation. Normally categorized acc to no. of axis of rotation. Uni-axial ; Bi-axial ; Multi-axial ; Non-axial ; where limited motion is present in any direction

GLIDING : Surfaces are nearly flat Non axial

HINGE (ginglymus): One art surface is convex other is concave Strong collateral ligaments limits the motion to planar, hinge like motion.

PIVOT: Rotation is permitted around single axis.

CONDYLOID/OVOID/ELLIPSOIDAL : One art surface is an OVULAR CONVEX SHAPE, and other is reciprocally concave shaped.

SADDLE/SELLAR: Resembles seat of a riding saddle. Movement capability is same as that of condyloid joint, but greater ROM is allowed.

BALL & SOCKET / SPHEROIDAL JOINT : Surfaces are reciprocally convex and concave. Rotation in all three planes of movement is permitted.