The human skeleton has about 200 bones which are connected by joints. Bones are varies in size from the pea sized distal phalanx (bone of Hand) of the little toe to the long femur of the thigh. The human joint system vary from simple to complex. The simple joints usually have stability as a primary function. The complex joints usually have mobility as a primary function but can’t completely sacrifice stability.
Classification of human joints are named based on the structure of joints or amount of movement. Structural, joint can be classified as Fibrous, Cartilaginous and Synovial with each referring to the connective tissue that binds the bony elements together and in the present or absence of a synovial joint cavity. Synarthrosis, amphiarthrosis and diarthrosis refers to the degree of movement a joint affords.
Synarthrosis joints are those that have little or no movement and they are united by fibrous tissue.
Amphiarthrosis joints allow minimal to moderate movement and united with hyaline cartilage or fibrocartilage.
Diarthrosis joints are freely moveable joints and they are united with synovial joint structure.
Joint classification:-
Joints are classified into Fibrous, Cartilaginous and Synovial joints.
1). Fibrous joint:-
The bony components of fibrous joints are joined together by fibrous interosseous connective tissue that directly united one bone to another that allows little movement or no movement. It is functional classified as Synarthrosis.
Types of fibrous joint:-
(A) Suture – Only in the skull in early life.
(B) Gomphosis – Between a tooth and either the Mandible or Maxilla.
(C) Syndesmosis – The shaft of the radius and ulna or the shaft of tibia and fibula.
2). Cartilaginous joint:-
The material connecting the bony components in cartilaginous joints are fibrocartilage or hyaline cartilage.
Types of cartilaginous joints:-
(A) Symphysis – Intervertebral joints between bodies of vertebrae, the joint between manubrium and the body of the sternum and the Symphysis pubis in the pelvis.
(B) Synchondrosis – Articulation of the first seven ribs with sternum.
3). Synovial joint:-
In synovial joint, the ends of the bony components are free to move in relation to one another because no connective tissue is directly unites the adjacent body surface. The bony compartments are in directly connected to one another by means of a fibrous synovium lined joint capsule that enclose the joint. Examples of synovial joints are Knee and Elbow joints.
Synovial joint have the following common features:-
(1) A joint cavity that is enclosed by (2) A fibrous joint capsule that surrounds the joint (3) A synovial membrane that lines the inner surface of the fibrous capsule (4) Hyaline cartilage that covers the articular surface of the contiguous bones and (5) Synovial fluid that forms a film over the joint surface within the capsule.
Classification of Synovial joint:-
These classification describe simple geometric surfaces and include Plane, Ball and Socket, Condyloid, Saddle, Hinge and Pivot joints.
On the basis of member of axis:- Uniaxial, Biaxial and Triaxial.
Uniaxial Joint:-
These joints are those with visible rotation of the bony components in one plane around a single axis. Hinge and Pivot joints are uniaxial. (Elbow joint and Radioculnar joint)
Biaxial joint:-
These joints are those with visible rotation of the bony components in two planes around two axis. Condyloid and Saddle joints are biaxial. The term Ellipsoid is often used interchangeably with Condyloid. (Radiocarpal joint and Carpometacarpal joint of thumb)
Triaxial joint:-
These joints are those in which the bony components are free to rotation in three planes around their axis. Plane and Ball and Socket joints are triaxial. (Intercarpal or tarsal joint and Hip or Shoulder joint)