How are joints classified ?he most mobile.
Joints are classified into 3 types according to the tissues that connect the bones :
- Fibrous joints
- Cartilagenous joint
- Synovial joints
What are the types of fibrous joints ?
- Sutures : They ossify with age. They allow little or no movement.
Ex : skull sutures - Syndesmosis : They don’t ossify. Bones are united together bu interosseous ligaments. They allow little or no movement.
Ex : inferior tibiofibular ligament. - Gomphosis : Normally they are immobile and any movement is considered as a pathological issue. They are found between teeth and mandible or maxilla.
What are the type of cartilagenous joints ?
The bones are united by cartilages and they are divided into two groups :
A. Primary cartilagenous joints :
1. This type is immobile.
2. The two bones are united by hyaline cartilage that finally ossifies.
Ex : 1. Epiphyseal plate between epiphysis and diaphysis of the long bones ( permits the growth in length ).
2. Between rib and its costal cartilage
3. Between the costal cartilage of the 1st rib and the manubrium of the sternum.
B. Secondary cartilagenous joints :
The bones are united together by fibrocartilage. They are slightly mobile and found in the midline.
Ex: 1. Symphysis menti.
2. Symphysis pubis.
3. Intervertebral disc
4. Joints between manubrium and body of the sternum , the stermun and the xiphoid process.
Describe the structure of the synovial joints.
They are the most common type and the most mobile.
It has characteristics :
1. Articular surfaces of bones are covered by thin layer of hyaline cartilages.
2. The joint has outer fibrous capsule connecting the articulating bone.
3. The joint has a cavity.
4. The fibrous capsule is lined by a synovial membrane that covers the non articular parts of the bone inside the joint.
5. The synovial membrane secretes synovial fluid that fills the joint cavity and lubricates the articulating surfaces to decrease wear of the articulating cartilages.
6. The joint has accessory ligaments supporting the joint capsule.
7. Additional structures may be found inside the joint cavity , discs in temporo-mandibular joint , meisci in knee joint , labrum in shoulder in shoulder and hip joints , tendons as biceps brachii in shoulder joint.
How are the synovial joints classified ?
Synovial joints are classified according to the number of axes :
- Uniaxial joints : They allow two movements along one axis. They are subdivided into :
a. Hinge joints : articular surfaces resemble hinge of the door. Movement occur along a horizontal axis. They permit flexion and extension only. Ex: elbow and knee joints.
b. Pivot joint : a bony pivot rotates inside a ring . Movement occur around a vertical axis. Ex: superior radio-ulnar joint and atlanto-axial joint. - Biaxial joint : They allow four movements along two axes
a. Ellipsoid joints : a condyle articulates with an elliptical depression. Ex: wrist joint ( flexion / extension , abduction/adduction movements )
b. Condyloid joints : have to distict convex surfaces that articulate with two concave surfaces. They allow flexion / extension , abduction/adduction. Ex: metacarpophalangeal joint or knucle joint
c. Saddle joint ( seller ) joint : concavo-covex surfaces articulate together. Ex: carpometacarpal joint of thumb. The joint permits flexion/extension , adduction/abduction and some rotation. - Polyaxial (multiaxial) joints :
a. Ball and socket ( spheroidal ) joint : They permit all types of movements. Ex: shoulder and hip joints
b. Plane joints ( gliding ) : the articular surfaces are flat. Theypermit sliding to one another. Ex: acrmio-clavicular joint.
What are the factors maintaining joint stability ?
- The shape of the articular surfaces. Ex: the ball and socket arrangement in hip joints is a good example of stability.
- Strength of the ligaments.
- Tone of the surrounding muscles.
How do nerves supply the joints ?
The capsule and the ligaments are rich in sensory nerves.
Hilton’s law , a nerve supplying a joint also supplies the muscles moving the joint and the skin over the insertion of the muscles.
