Joints

JOINTS

Definition of Joint

Q. Define joint.
A. Joint (articulation ) is a junction between two or more bones.

Functions of Joints

Q. What are the functions of joints?
A. Functions of joints are:

•  They allow movement
• They allow growth
•  They allow moulding of head during childbirth.
• They allow transmission of forces.

Classification of Joints

Q. Classify joints on the basis of structure and function.
A. Joints can be classified on the basis of function or structure.

Structural classification is based on:

o Material that binds bones together.
o Presence or absence of a joint cavity.

Structural classifications include:
Fibrous joints

o Bones are connected by fibrous connective tissue
o Do not have a joint cavity
o Most are immovable or only slightly movable

Cartilaginous joints

o Bones are united by cartilage
o Most are slightly movable.
o Lack a joint cavity.

Synovial joint

o Joint cavity is present between the bones, and the joint is surrounded by articular capsule.
o Most movable type of joint.
o Most are “simple” and have just two articulating surfaces.
o Some are “compound” with more than two articulating surfaces (e.g. elbow (humerus, radius and ulna) and knee (femur, tibia, fibula, patella) joints).

Functional classification – based on  degree of mobility. 

o Synarthroses (immovable): common in axial skeleton (Fibrous joints – sutures).
o Amphiarthroses(slightly movable):common in axial skeleton ( secondary cartilaginous joints) .
o Diarthroses(freely movable): common in appendicular skeleton (synovial joints).

Q. Name the different types of fibrous joints and give example of each.
A. Following are the three types of fibrous joints:

1. Sutures

• Bones are bound together by sutural ligaments.
• In adults, sutures allow almost no movement between the bones.
• Sutural joints are present between the bones which ossify in membrane.
• They are present between the bones of skull ( e.g. coronal suture between frontal and parietal bones
 and sagittal suture between the two parietal bones).

2. Syndesmosis

• Bones are held together by the interosseous membrane or ligament.
• Slight movement is possible.
•e. g. intermediate radioulnar and inferior tibiofibular joints.

3. Gomphosis
• Cone shaped root of tooth fits into the socket of the jaw.(like a peg in the socket).
• The tooth is attached to the alveolar socket by periodontal ligament.
• The joint is immovable.

fibrous joints

Q. What are the different types of cartilaginous joints? Give example of each.
A. There are two types of cartilaginous joints:
Primary cartilaginous joint (synchondrosis)

o The articulating bones are connected via hyaline cartilage.
o The joints are immovable and temporary in nature i.e. after certain age the cartilaginous plate is replaced by bone (synostosis).
o e.g. between epiphysis and diaphysis (epiphyseal plate).

Secondary cartilaginous joint (symphysis)

o The articulating bones are connected via fibrocartilage.
o They are slightly movable joints.
o These are permanent joints and persist throughout life.
o They are present in the median plane.
o e.g. between two vertebral bodies (intervertebral disc), pubic symphysis and manubriosternal joint.

cartilagenous joints

Q. What are the characteristic features of a typical synovial joint? Draw a labelled diagram of a typical synovial joint.
A. Following are the characteristic features of a typical synovial joint:

• Presence of synovial cavity.
• Joint is surrounded by fibrous articular capsule.
• The fibrous capsule is lined by synovial membrane(it produces synovial fluid which percolates into the joint cavity and lubricates the articular surfaces..
• Ends of the articulating bones are covered by articular cartilage (mostly hyaline cartilage)
     (The articular surfaces of bones which are formed by membranous ossification are covered by fibrocartilage. e.g. temporomandibular and sternoclavicular joint).

typical synovial joint

Q. Classify synovial joints and give example of each.
A. Following are the different types of synovial joints according to the axis of movement and shape of articular surfaces.

1. Plane joints: Articular surfaces are flat(plane) . They allow only gliding/sliding movement.  e.g. Intercarpal joints, intertarsal joints, acromioclavicular joint.

plane synovial joint

 

2. Uniaxial joints: Allow movement around one axis.
o Pivot joint:  One of the articular surfaces is like a central pivot(peg) and the other is an osseocartilagenous ring. Allow rotational movements. e.g. atlanto-axial and superior radioulnar joints.

Pivot joint
o Hinge joint :  The articular surfaces are pully shaped. Allow movement across transverse axis (flexion and extension). e.g.elbow, ankle and interphalangeal joints.

hinge joint

3. Biaxial joints: Allow movements  around two axes.
o Ellipsoid joint:  One of the articular surface is oval shaped and convex and the other is  reciprocally elliptical and concave. They allow movement around transverse axis (flexion and extension) and adduction and abduction around another axis. e.g. – wrist and metacarpophalangeal joints.

ellipsoid joint
o Condylar joint: one of the articular surface is a condyle ( convex) and the other is reciprocally concave. They allow movement mainly around transverse axis ( flexion and extension) and slight rotation around  vertical axis. e.g.knee joint, atlanto-occipital joint, temporomandibular joint (bicondylar).

condylar joint

4. Multiaxial joints: Allow movement across multiple axes.
o Ball & socket joint: One of the articular surface is a globular head and the other is like a socket. Movements occur across multiple axes ( flexion, extension, adduction, abduction, medial and lateral rptation and  circumduction.- shoulder and hip joint.

ball and socket joint
o Saddle joint:   both the articular surfaces are reciprocally concavoconvex. Movements occur across multiple axes.  e.g– 1st carpometacarpal and sternoclavicular joints.
saddle joint

Q.  Describe briefly the following types of joints.

  • Simple joint
  • Compound joint
  • Complex joint

A. Simple Joint: Only two bones articulate. e.g. shoulder joint, hip joint.

Compound joint:  more than two bones articulate. e.g. Elbow joint (humerus, radius and ulna) and knee joint ( femur, tibia and patella).

    Complex joint: Joint cavity is divided into two parts by an intra-articular disc. e.g. temporomandibular joint, sternoclavicular joint.

simple, compound and complex joints

Q. What is  Hilton’s law?

A. Hilton’s law states that the  the nerve that supplies a muscles which acts on the joint also supplies the joint and the skin covering the joint.

 

Q. What is the difference between dislocation and sublaxation of a joint?

A. A dislocation is complete separation of articular surface bones forming a joint.  A sublaxation is an incomplete or partial dislocation.

Q. What is the anatomical basis for stiffness of joint in winter and especially in the mornings?

A.  The viscosity of synovial fluid increase with decrease in temperature. This is the reason for stiffness of joints in the winter.  Mobility of joints enhances lubrication of joints, therefore the stiffness  

 

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