Showing posts with label joint. Show all posts
Showing posts with label joint. Show all posts

Tuesday, May 1, 2018

Types of Joints

Basic Anatomy , joint
Types of Joints

Types of Joints



Joints of human beings can be classified on different bases. Each base divides joints into different categories. There are three types of classifications of joints; Structural classification, Functional classification, and Regional classification. Lets have a look at all of these.

Structural Classification


Fibrous joints:
In this type of joints the bones are joined together by means of fibrous tissue. Due to the presence of fibrous tissue these joints are either immovable or permit movement to a very little extent. Fibrous joints are further divided into the following subtypes;

1. Sutures: These are peculiar to skull and are immovable. According to the shape of the bony margin the sutures may be;

    • Plane sutures
    • Serrate sutures
    • Denticulate sutures
    • Squamous sutures
    • Limbous sutures
    • Schindylesis


Types of Sutures

2 . Syndesmosis: In this type of fibrous joints the bones are connected with interosseus ligament for example the inferior tibiofibular joint.



Inferior tibiofibular joint

3 . Gomphosis: These are also known as peg and socket joints. Examples are tooth in the socket.



Gomphosis (Teeth in their Sockets)

Cartilaginous Joints


In this type of joints there is a piece of cartilage between the bones which hold the bones together and makes a joint. Cartilaginous joints are further divided into the following subtypes;

  1. Primary cartilaginous joints: (synchondrosis): In this subtype the bones are united by a plate of hyaline cartilage so that the joint is immovable and strong. These joints are temporary in nature because after a certain age the cartilaginous plate is replaced by the bone. Examples of this type of joints are joint between the epiphyses and diaphysis of a growing long bone, the costochondral joint and the first chondrosternal joint.


Joint between epiphysis 
and diaphysis with intervening 
epiphyseal plate of cartilage

2 . Secondary cartilaginous joints: (symphysis): These are also known as fibro-cartilaginous joints. There articular surface is covered by a thin layer of hyaline cartilage and the bones are united by fibro-cartilage. These joints are permanent and persist throughout the life of an individual. Typically the secondary cartilaginous joints occur in the median plane of the body and permit limited movements because of compressible pad of cartilage in them. The thickness of the fibro-cartilage in these joints is directly related to the range of movement the joint offers. Examples of this type of joints are; symphysis pubis, manubrio-sternal joint and intervertebral joints between the vertebral bodies.


Symphysis Pubis

Synovial Joints


Synovial joints are most evolved and therefore most mobile type of joints. Visit the page: Synovial Joints for more detail.

Functional Classification


Immovable joints: (Synarthroses)They are fixed joints at which there is no movement. The articular surfaces are joined by tough fibrous tissue. Often the edges of the bones are dovetailed into one another as in the sutures of the skull.

Partially moveable joints: (Amphiarthroses)
They are joints in which slight movement is possible. A pad of cartilage lies between the bone surface and there is a fibrous capsule to hold the bone and cartilage in place. The cartilages of such joints also act as shock absorbers for example the intervertebral discs between the bodies of vertebrae where the cartilage is strengthened by extra collagen fibers.

Freely moveable joints: (Diarthroses)
They are the synovial joints of structural classification. They are freely moveable though at some of them the movement is restricted by the shape of the articulating surfaces and by the ligaments which hold them together. These ligaments are of elastic connective tissue.

Regional Classification


Skull type: They are the joints of the skull and are immovable
Vertebral type: They are the joints of vertebral column and are slightly moveable
Limb type: They are the joints of upper and lower limbs and are freely moveable.






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Synovial Joints

Basic Anatomy , joint
Synovial Joints

Synovial Joints




A typical Synovial Joint 
(Image source: Madhero88/Wikipedia)

Synovial joints are most evolved and therefore most mobile type of joints. They possess the following characteristic features;


  • There articular surfaces are covered with hyaline cartilage. This articular cartilage is avascular, non nervous and elastic. Lubricated with synovial fluid, the cartilage forms slippery surfaces for free movements.

  • Between the articular surfaces there is a joint cavity filled with synovial fluid. The cavity may be partially or completely subdivided by an articular disc known as meniscus.
  • The joint is surrounded by an articular capsule which is fibrous in nature and is lined by synovial membrane. Because of its rich nerve supply the fibrous capsule is sensitive to stretches imposed by movements.
  • The synovial membrane lines the entire joint except the articular surfaces covered by hyaline cartilage. It is this membrane that secretes the slimy fluid called synovial fluid which lubricates the joint and nourishes the articular cartilage.
  • Varying degrees of movements are always permitted by the synovial joints.

Types of Synovial Joints





Scheme of Types of Synovial Joints 
(Image Source: Produnis/Wikipedia)

Synovial joints are of the following types

Plane synovial joints:
The articular surfaces of plane synovial joints are more or less plane. These joints permit gliding movements in various directions. Examples are intercarpal joints, intertarsal joints, and joints between the articular processes of vertebrae.



Plane Synovial Joints of Carpus

Hinge joints:
In these joints the articular surfaces are pulley shaped. There are strong collateral ligaments to provide stability to the joint. Movements are permitted in one plane around a transverse axis. Examples are elbow joint, ankle joint, interphaleangeal joint.



Hinge Joint (Elbow Joint)

Pivot joints:
Pivot joints are formed by a central bony pivot surrounded by an osteo-ligamentous ring. Movements are permitted in one plane around a vertical axis. Examples of this type are superior and inferior radioulnar joints and the median atlantoaxial joint.



Proximal Radioulnar Joint

Condylar joints:
These are also known as bicondylar joints. There articular surfaces consist of two distinct condyles in which one is convex surface (called the male surface) fitting into a concave surface (called the female surface) of the other bone. These joints mainly permit the movement in plane around a transverse axis. Example of this type of joints is knee joint.



Knee Joint (Posterior View)

Ellipsoid joints:
In this case the articular surfaces include an oval convex male surface fitting into an ellipsoid female surface. The movements are permitted around two axis; flexion and extension around the transverse axis and adduction and abduction round antero-posterior axis. Combination of these movements produces Circumduction. Typical rotation around a third vertical axis does not occur. Examples of this type of joints are wrist joint, metacarpophalangeal joint and atlanto-occipital joint.



Wrist Joint (ellipsoid Joint)

Saddle joints:
Articular surfaces are reciprocally concavo-convex. Movements are similar to those permitted by ellipsoid joint with addition of some rotation (conjunct rotation (rotation which accompany other movements)) around a third axis which occurs independently. Examples of this type of joints are first carpometacarpal joint, sternoclavicular joint, calcaneocuboid joint.



Saddle Joint

Ball and socket joints:
These are also called spheroidal joints. There articular surfaces include a globular head fitting into a cup shaped socket. Movement occurs around an indefinite number of axes which have common center. Flexion, extension, abduction, adduction, rotation, Circumduction all occur quite freely. Examples of this type of joints are shoulder joint, hip joint and talo-calcaneonavicular joint.



Ball and Socket Joint (Hip Joint)

Blood supply of Synovial Joints


The articular and epiphyseal branches given off by the neighboring arteries form a peri-articular arterial plexus. Numerous vessels from this plexus pierce the fibrous capsule and form a rich vascular plexus in the deeper part of the synovial membrane. The blood vessels of the synovial membrane terminate around the articular margins in a fringe of looped anastomoses termed the circulus vasculosus (circulus articularis vasculosus). It supplies the capsule, synovial membrane and the epiphyses. The articular cartilage is avascular.
After epiphyseal fusion in growing long bones the communications between the circulosus vasculosus and the end arteries of the metaphysis are established thus minimizing the chances of osteomyelitis in the metaphysis.

Lymphatic drainage of synovial joints


Lymphatics form a plexus and the subintima of the synovial membrane and drain along the blood vessels to the regional deep nodes.

Stability of synovial joints


The various factors maintaining the stability at a joint are described below in order of their importance;
  1. Muscles: The tone of different groups of muscles acting on the joint is the most important and indispensable factor in maintaining the stability. Without muscles, the knee and shoulder would have been unstable and the arches of foot would have collapsed.
  2. Ligaments: These are important in preventing any over movement and in guarding against sudden accidental stresses. However they do not help against a continuous strain because once stretched, they tend to remain elongated. In this respect the elastic ligaments (ligament flava and the ligaments of the joints of auditory ossicles) are superior to the common type of white fibrous ligaments.
  3. Bones: They help in maintaining the stability only in firm type of joints like the hip and ankle joints. Otherwise in most of the joints there role is negligible.






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Monday, April 30, 2018

Joint

Basic Anatomy , joint
Joint

Joint




A typical Joint 
(Image source: Madhero88/Wikipedia)

Joint is a junction between two or more bones or cartilages. It is a device to permit movements in a hard and rigid skeleton. Joints are formed in such a way that they keep a balance between the movement, stability and strength of human skeleton. However there are some types of joints where movements are sacrificed for stability and in other cases the stability is sacrificed for movements. For example the shoulder joint and hip joint are both ball and socket joints but shoulder joint is more mobile and less stable while hip joint is more stable and less mobile. Also there are certain types of joints where motion does not occur. These joints are called immovable joints and are primarily meant for growth and they permit molding during child birth.
There are more joints in a child then in an adult because as growth proceeds some of the bones fuse together e.g. the ischium, ilium and pubis fuse together to form the pelvic bone (hip bone). Similarly the two halves of the infant frontal bone and of the infant mandible fuse together, five sacral vertebrae form one sacrum and four coccygeal vertebrae form one coccyx.

Defining some basic terms related to joints


Male surface: An articulating surface which is larger in surface area and always convex in all directions.
Female surface: An articulating surface which is smaller and concave in all directions.
Simple joints: Joints with only two articulating surfaces; male and female.
Compound joints: Joints possessing more than two articulating surfaces.
Degrees of freedom: Number of axes at which the bone in a joint can move.
Uni-axial movement: Movement of bone at a joint limited to one axis only that is with one degree of freedom
Bi-axial movement: Movement of a bone at a joint with two degrees of freedom
Multi-axial movement: Movement of a bone at a joint limited to three axes with intermediate positions as well.

Terms used for movements of joints


Angular movements: Movements in which the angle between two adjoining bones is changed. They are of two types;
  1. Flexion and extension: These are bending and straightening respectively.
  2. Adduction and abduction: Movement towards and away from the midline of the body respectively:
Circumduction: When a long bone circumscribes a conical space.
Rotation: Bone moves around a longitudinal axis.
Adjunct rotation: Independent rotation
Conjunct rotation: Rotation which accompany other movements.
Spin: Simple rotation around the bone’s stationary mechanical axis.
Swing: Any displacement of the bone and its mechanical axis other than spin. Swing may be pure or impure (swing + element of spin).
Ovoid of motion: This represents an imaginary surface which will include all possible paths of a point on the mechanical axis of the bone at some distance from its related joint.Cardinal swing: When the mechanical axis moves in the shortest pathway when bone moves
Arcuate swing: When the mechanical axis moves in the longest pathway when bone moves.
Co-spin: When the effect of adjunct rotation is additive to the normal spin
Anti-spin: When the effect of adjunct rotation is nullifying on the normal spin.

Shapes of articular surfaces


Ovoid: When the ovoid is convex it is called male ovoid and when the ovoid is concave it is called female ovoid.
Saddle shaped: These are convex in one plane and concave in the other perpendicular plane.

Applied anatomy of joints


Dislocation of joint:
This is a condition in which the articular surfaces of the joint are abnormally displaced so that one surface loses its contact completely with the other. If a partial contact is still retained, it is better called subluxation rather than dislocation. Dislocation is commonly caused by trauma and is characterized by pain, deformity and loss of function. X-ray is used for confirmation.



X-ray showing Dislocation of Joint 
(Image Source: GEMalone/Wikipedia)

Sprain:
It is the severe pain in the joint caused by ligamentous tear, but without any associated dislocation or fracture. The tear leads to effusion into the ligament and joint causing great pain.



Sprained Ankle with Bruising

Arthritis:
It is the inflammation of one or more joints. It can be caused by a variety of diseases but the common types of arthritis are rheumatic, rheumatoid, osteoarthritis and tuberculoses. The involved joint is commonly swollen and its movements are restricted and painful.



Hands Affected with Arthritis

Osteoarthritis:
It represents the ageing process. In old age the articular cartilage shows degenerative changes in the center (fibrillation of cartilage) and proliferative changes around the edges. Due to this lips are formed around the edges of joints.



Severe Osteoarthritis of Carpal Joints


Stiffness of joints related to weather


The viscosity of synovial fluid increases with fall in temperature. This accounts for stiffness of the joints in cold weather. Mobility of the joint itself is an important factor in promoting lubrication. Thus the stiffness of the joints experienced in the morning gradually passes off as the movements are resumed.
Neuropathic joint:
It is the result of complete denervation of the joint so that all reflexes are eliminated and the joint is left unprotected and liable to mechanical damage. A neuropathic joint shows painless swelling, excessive mobility and bony destruction. It is commonly caused by leprosy, tabes dorsalis and syringomyelia.




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