Joints

1. JOINTS

2. Introduction
 A joint is defined as a connection between two bones in the skeletal system.
 Joints can be classified by the type of the tissue present
• Fibrous- bones are bound by tough, fibrous tissue.
• Cartilaginous- bones are united by fibrocartilage or hyaline cartilage.
• Synovial- presence of a fluid-filled joint cavity contained within a fibrous
capsule.
 Or by the degree of movement permitted
• Synarthrosis- immovable.
• Amphiarthrosis- slightly moveable.
• Diarthrosis- freely moveable.

3. Fibrous Joints
 A fibrous joint is where the bones are bound by a tough, fibrous tissue.
 These are typically joints that require strength and stability over range of movement.
 Fibrous joints can be further sub-classified into
• Sutures
• Gomphoses
• Syndesmoses
 Sutures
 Sutures are immovable joints (synarthrosis) and are only found between the flat, plate-
like bones of the skull.
 There is limited movement until about 20 years, after which they become fixed and
immobile.
 They are most important in birth, as at that stage, the joints are not fused, allowing
deformation of the skull as it passes through the birth canal.

4. Contd…..
 Four major sutures connect the bones of the cranium together are:
• Frontal or coronal- Connects the frontal bone to the two parietal bones
• Sagittal- Connects the two parietal bones.
• Lambdoid- Connects the two parietal bones to the occipital bone.
• Squamous- Connects the parietal bones to the temporal bones.

5. Contd….
 Gomphoses
 Gomphoses are also immovable joints.
 They are found where the teeth articulate with their sockets in the maxilla (upper teeth) or
the mandible (lower teeth).
 The tooth is bound into its socket by the strong periodontal ligament.

6. Contd….
 Syndesmoses
 Syndesmoses are slightly movable joints (amphiarthroses).
 They are comprised of bones held together by an interosseous membrane.
 The middle radioulnar joint and middle tibiofibular joint are examples of a
syndesmosis joint.

7. Cartilaginous Joint
 In a cartilaginous joint, the bones are united by fibrocartilage or hyaline cartilage.
 There are two main types:
• Synchondroses (primary cartilaginous)
• Symphyses (secondary cartilaginous)
 Synchondroses
 In a synchondrosis, the bones are connected by
hyaline cartilage.
 These joints are immovable (synarthrosis).
 An example of a synchondrosis is the
joint between the diaphysis and epiphysis
of a growing long bone.

8. Contd….
 Symphyses
 Symphysial joints are where the bones are united by a layer of fibrocartilage.
They are slightly movable (amphiarthrosis).
 Examples include the pubic symphysis and the joints between vertebral
bodies.

9. Synovial Joint
 A synovial joint is defined by the presence of a fluid-filled joint
cavity contained within a fibrous capsule.
 Characterized by the presence of an articular cavity filled with
synovial fluid surrounded by a joint capsule.
 They are freely movable (diarthrosis) and are the most common
type of joint found in the body.
 Synovial joints can be sub-classified into several different types,
depending on the shape of their articular surfaces (surface of a joint
at which the ends of the bones meet) and the movements
permitted:
1. Hinge – Permits movement in one plane – usually flexion and
extension.
• E.g. elbow joint, ankle joint, knee joint.

10. Contd….
2. Saddle – Named due to its resemblance to a saddle on a horse’s back. It is characterised by
opposing articular surfaces with a reciprocal concave-convex shape.
• E.g. carpometacarpal joints.
 If the moving joint surface is CONVEX, sliding is in the OPPOSITE direction of the angular movement of the bone.
 If the moving joint surface is CONCAVE, sliding is in the SAME direction as the angular movement of the bone.
Saddle joints allow movement with two degrees of freedom. They allow flexion / extension, abduction
/ adduction.

11. Contd….
3. Plane – The articular surfaces are relatively flat, allowing the bones to glide over one
another.
• E.g. acromioclavicular joint (formed by the cap of the shoulder, acromion and the
collar bone, clavicle), subtalar joint (articulation between two of the tarsal bones in
the foot).
• Also found in the carpal bones in the hand.

12. Contd….
4. Pivot – Allows for rotation only. It is formed by a central bony pivot, which is
surrounded by a bony-ligamentous ring.
• It consists of the rounded end of one bone fitting into a ring formed by the other bone.
This structure allows rotational movement as the rounded bone moves around its own
axis.
• An example of a pivot joint is the atlantoaxial joint- Joint of the first and second
vertebrae of the neck that allows the head to move back and forth.
• The joint of the wrist that allows the palm to be turned up and down is also a pivot
joint.
• Proximal and distal radioulnar joints.

13. Contd….
5. Condyloid – Contains a convex surface which articulates with a
concave elliptical cavity. They are also known as ellipsoid joints.
• E.g. wrist joint, metacarpophalangeal joint, metatarsophalangeal
joint.
 It consists of an oval-shaped end of one bone fitting into a similarly
oval-shaped hollow of another bone.
 This type of joint allows angular movement along two axes, as seen in
the joints of the wrist and fingers, which can move both side to side and
up and down.

14. Contd….
6. Ball and Socket – where the ball-shaped surface of one rounded bone fits into
the cup-like depression of another bone. It permits free movement in numerous
axes.
• E.g. hip joint, shoulder joint.