A junction between 2 or more bones/cartilages is called a JOINT. Joint permits mobility and stability. A human skeletal has approximately more than 200 bones that are connected by joints. Also, joints help to form cavities like cranial, thoracic, abdominal & pelvic cavities. There are more joints in the child than in an adult because with age some bones fuse.
CLASSIFICATION OF JOINTS:
1] STRUCTURAL CLASSIFICATION
1.Fibrous Joints
-The bones are joined by fibrous tissue and these are mostly immovable or slightly movable joints.
3 Subtypes:-
a)Sutures
-They are present only in the “skull”. In this type, bones are connected by connective tissue called a sutural ligament. Fusion of bony components occurs later in life leading to the formation of bony union. In infants, there is an anatomical feature in the skull comprising soft membranous gaps called “FONTANELLE”.
Eg: Suture between frontal & parietal bone, temporoparietal suture
b)Syndesmosis
In this type, bones are connected directly by an interosseous ligament/fibrous cord/aponeurotic membrane. A slight amount of motion is seen in these joints.
Eg: distal tibiofibular joint, radioulnar joint
c)Gomphosis
-The bones are connected to each other like a peg in the hole by fibrous connective tissue.
Eg: joint between tooth and mandible/maxilla
2.Cartilaginous joints
-The bones of this joint are connected by fibrocartilage OR hyaline cartilage. They allow some movements between bones.
2 Subtypes:-
a)Primary cartilaginous joints
-They are also called ‘SYNCHONDROSIS’.The bones are united by a plate of hyaline cartilage. After some age, the cartilaginous plate is replaced by bone. these joints also permit bone growth while providing stability and very small mobility. Epiphyseal plates near the ends of long bones and pelvis are synchondrosis unions. They are temporary joints because after some age cartilaginous plate is replaced by bone.
Eg: spheno-occipital, first chondrosternal, costochondral joints, xiphisternal
b)Secondary cartilaginous joints
-They are also called ‘SYMPHYSIS’.The bones are covered by a thin layer of hyaline cartilage and united by a disc of fibrocartilage. They are permanent joints and persist throughout life.
Eg: symphysis pubis, manubriosternal, intervertebral joints
3.Synovial joint
-They are most mobile joints. The bones are free to move because no connective tissue unites them. The articular surface is covered by hyaline cartilage and in Inbetween the joint articular surface there is a joint cavity that is filled with synovial fluid. The synovial membrane lines the inner surface of the fibrous capsule. All the synovial joints are crossed by muscles or their tendons.
7 Subtypes:-
a)Plane synovial joint
-The articular surfaces are flat(plane). So movement occurs in 3 planes and axis and therefore also called as ‘Triaxial/Multiaxial’ joint. (3 degrees of freedom)
Eg: intercarpal & intertarsal joints, superior tiboifibular, interchondral , costovertebral, costotransverse, acromioclavicular, carpometacarpal, tarsometatarsal, intermetacarpal, intermetatarsal, chondrosternal and sacroiliac joints
b)Hinge joint
-The articular surfaces are pulley-shaped. The movement occurs only in 1 plane and axis and therefore also called as’Uniaxial’joint. (1degree of freedom)
Eg: elbow, ankle, interphalangeal joints
c)Pivot joint
-The articular surfaces comprise a central bony peg which is surrounded by an osteoligamentous ring. The movement occurs only in 1 plane and axis and so also called a ‘Uniaxial’ joint. (1 degree of freedom)
Eg: superior & inferior radioulnar joint, median atlantoaxial joint
d)Condylar joint
-The articular surfaces are having two different surfaces, the convex surface fits in the concave surface. The movements occur in 2 planes and axis therefore also called ‘Biaxial’ joints. (2 degrees of freedom)
Eg: knee joint, temporomandibular joint
e)Ellipsoid joint
-The articular surfaces are oval or concave and convex as the condylar joint. The movements occur in 2 planes and axis therefore also called as biaxial joints. (2 degrees of freedom)
Eg: atlantooccipital, wrist, metacarpophalangeal joints
f)Saddle/Sellar joint
-The articular surfaces are concave-convex/convexo-concave. The movements occur in 2 planes and axis therefore also called ‘Biaxial’ joints. (2 degrees of freedom)
Eg: 1st carpometacarpal, sternoclavicular, calcaneocuboid & patelofemoral joint
g)Ball and Socket joint
-The articular surfaces are globular heads fitting in a cup-shaped socket. The movements occur in all 3 planes and axis and so they are also known as ‘Triaxial/Multiaxial’ joints. (3 degrees of freedom)
Eg: shoulder, hip, talocalcaneonavicular joints
2] FUNCTIONAL CLASSIFICATION
1.Synarthroses
-These joints are fixed joints at which there are no movements. The articular surfaces are joined by fibrous tissue.
Eg: sutures
2.Amphiarthroses
-These joints are having slight movement. The articular surfaces are covered by hyaline cartilage.
Eg: symphysis pubis, manubriosternal, intervertebral joints
3.Diarthroses
-These joints are having free movement mostly but some of them have restricted motion due to the shape of articular surfaces. The bone has a connection with elastic connective tissue.
Eg: shoulder, elbow ankle joints
3.BASED ON NO. OF ARTICULATING BONES
1.Simple joint
- When only two bones articulate it forms a simple joint. The primary function is stability.
-Eg: Interphalengeal joints
2.Compound joint
-When more than 2 bones articulate within the capsule it forms a compound joint.
-Eg: elbow, wrist joint
3.Complex joint
-When a joint cavity is divided by an intra-articular disc it forms a complex joint. the primary function is mobility but cannot completely sacrifice stability.
-Eg: temperomandibular, sternoclavicular joint.
