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One of the most basic principles and rules of nature, function, movement, and motion analysis, is that structure determines function. In other words, anatomy determines movement. I hope this joint effort will result in your empowerment, as you gain knowledge (KIIP).
The articular system creates the joints of the human body (skeleton), where a "joint" is defined as the meeting area or close proximity of at least two bones. Joint articulation includes the connection of all of the joint's components and tissues. Joint partake in the creation of movement segments (the area between two adherent joints).
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There is more than one way to classify joints. They can be classified according to their content, shape and appearance, or their function. In each case, a different aspect of the joint is being emphasized. Joints are multi-factorial structure of the body, with great influence on motion, stability, balance, energetic costs, and more.
A possible distinction between different joints, is the distinction between fibrous, cartilaginous, and synovial joints. This is based upon the content of the joint.
Fibrous joints - connect bones without allowing any movement. Examples: skull, pelvis and union of the spinous processes and vertebrae.
Cartilaginous joints - include cartilage as part of the structure of the joint. cartilage is used as both a type of "glue" and shock absorber. Examples include the spine and/or ribs.
Synovial joints - allow much more movement. Cavities between bones in synovial joints are filled with synovial fluid. Bursa sacks contain the synovial fluid, and secret the synovial fluid into the joint as lubrication regularly.
Fibrous joints
Cartilaginous Joints
Synovial Joints
The articular cartilage: is a thin superficial layer and smooth surface for two bones to slide over each other, while reducing friction and thus reducing heat production within the joint during movement. cartilage furthermore spreads loads over a wide area, thereby reducing contact stress, and provides a protective lubrication that minimizes friction and mechanical wear and tear of the joint.
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A unique form that combines fibrotic tissue with cartilaginous tissues is the fibrocartilage. Fibrocartilage is soft-tissue discs or menisci that intervene between articulating bones.
Anterior view of the knee. No patella shown.
The menisci of the knee, absorb vertical mechanical force, allow relative movements of the bones, curve slightly upward on the edges to help prevent dislocation of the bones sideways, decrease friction and heat creation within the joint, and decrease wear and tear of the joint's cartilage and bones' heads.
Normal vs abnormal menisci and cartilage of the knee
Prime locations of cartilage and fibrocartilage in the human body
Another possible distinction between joints is according to how they look. Thus, we distinct between hinge, saddle, pivot, ball & socket, gliding, and condyloid joints. Of course, the joint's appearance is a result of its structure, that in turn influences the function and movements possible within that joint.
Hinge joints - commonly allow movements in the sagittal plane of motion, with little to no movement in any other plane of motion at the same time. Classic movements of a hinge joint include flexion and extension. Well known examples of hinge joints include the elbow (one of the joints within the elbow complex), the knee, and the talocrural joints.
Saddle joints - also known as sellar joints; They are very flexible joints, that allow movement back and forth and up and down; do not allow for rotation as do ball and socket joints. Saddle joints tend to include multiple little bones that "fit" each other as does a saddle to a horse. Examples of saddle joints include the wrists (carpometacarpal joint), the sternoclavicular joint of the thorax, the incudomalleolar joint of the middle ear, and the calcaneocuboid joint of the heel.
Pivot joints - also called rotary joint, or trochoid joint; structured to allow rotational movement around a rotation enabling axis. There are only three pivot joints overall in the human body. These include the atlantoaxial joint, the proximal radioulnar joint (elbow), and the distal radioulnar joint (wrist).
Ball & Socket joints - also called spheroidal joint; The joint is made of one bone with a rounded (bowl like shaped) end, that allows another bone to move within its depression. The bones the moves has a spherical shaped head (ball), the moves with the cavity of the fixated bone (socket). These joints allow the greatest range of movement, and the most directions of movement. Examples in the human body include the hip and shoulder.
Gliding joints - also known as plane joints. These joints include two extremely smooth surfaces that glide one compared to the other. If placed parallel to the ground, these joints allow forward, backward, and sideway movement. If the joint is placed vertically to the ground, the allow upward, downward, and sideway movement. These joints often move in order to allow greater movement in other joints or other bones of the same joint. In some cases gliding joints will allow flexion and extension between small bones. Examples include the wrist, ankle, spinal column, between the ribs and the sternum.
Condyloid joints - also known as ellipsoid joints; While can look somewhat similar to a ball and socket, the head of the bone moving is more egg-shaped than round, and does not allow rotation. These joints allow flexion, extension, adduction, abduction, and circumducution. Examples include the wrist, toes, and fingers.
Examples of joints by type according to location
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