Joints PDF

# Joints The joint is the articulation between two or more bones together. ## Classification of Joints There are 3 types of joints: 1. Fibrous Joints: * Fixed joints in which the surface of articulating bones are connected together by fibrous tissue. * There are 3 types: * **Sy...

# Joints The joint is the articulation between two or more bones together. ## Classification of Joints There are 3 types of joints: 1. Fibrous Joints: * Fixed joints in which the surface of articulating bones are connected together by fibrous tissue. * There are 3 types: * **Syndesmosis:** Present inferior tibiofibular joint. The lower end of tibia and fibula are connected together by Fibrous tissue called interosseous ligament. * **Gomphosis:** Present in teeth. The roots of teeth are connected to their sockets in the bones by fibrous tissue called periodontal ligament. * **Sutures:** Present in skull. The bones of skull are connected together by a thin layer of fibrous tissue called sutural ligament. They obliterate in old age. 2. The Cartilaginous Joints: (False joint) * In these joints the surfaces of the articulating bones are connected together by a disc of cartilage. * There are 2 types: * **Primary Cartilaginous Joint:** * Site: at the ends of long bone. * Fixed Joint. * Structure: Epiphyseal plate of hyaline cartilage between the epiphysis and metaphysis in the developing long bones in children. * **Secondary Cartilaginous Joint:** * Permanent joint. * Present in themid Line e.g. intervertebral discs & symphysis Pubis. * No or limited movement which is allowed by the elasticity of the fibro-cartilaginous disc. 3. Synovial Joints: * They are mobile joints present mostly in the limbs. * Structure of synovial joints: * **Fibrous Capsule:** The synovial joint is surrounded completely by a fibrous capsule which is lined by synovial membrane. This capsule is supported and strengthened by ligament. It's pierced by blood vessels and nerves which supply the joint. * **Articular Cartilage:** Hyaline cartilage covers the articular surfaces of bones. It has very smooth and is lubricated by the synovial fluid. Nutrition: from synovial supply. * **Joint Cavity:** It's a potential cavity which appears if fluid, blood or pus collects into it. Normally it contains a very thin film of synovial fluid. * **Synovial Membrane:** Thin, moist, smooth and glistening membrane that covers all structures inside the joint except the articular surfaces. It also lines the fibrous capsule. It secretes and absorbs the synovial fluid. * **Synovial Fluid:** Pale yellow viscid fluid similar to egg-albumin. It contains free cells (synovial cells, macrophages and lymphocytes). * **Function:** Lubrication & nutrition of the articular cartilage. Prevents erosion of articular cartilage. * **Ligaments:** Extracapsular and intracapsular ligaments which support and strengthen the joint. * **Structures which may be present inside the cavity of synovial joints:** * **Articular Disc:** Disc of fibrocartilage which divides the joint cavity into two compartments (upper and lower) e.g Temporo - Mandibular joint * **Menisci (semilunar cartilages):** e.g The two semilunar plates of fibrocartilage present inside the knee joint. * **Ligament:** e.g. Cruciate ligament inside the knee joint. * **Tendon:** e.g. The tendon of longhead of biceps muscle inside the shoulder joint. ## Factors Affecting the Stability of the Joint 1. Shape and fitting of articulating surfaces 2. Thickness and strength of the capsule 3. Position and strength of ligaments. 4. Strength of muscles surrounding the joint ## Factors Affecting the Range of Movement 1. Tension of capsule, ligaments & structures surrounding the joint. 2. Contraction of the antagonistic muscles. 3. Approximation and contact of the articulating bones and soft tissue around the joint ## Movements of the Joints 1. **Flexion:** Approximation of two ventral surfaces to each others (bending). 2. **Extension:** The two ventral surfaces move away from each other (straightening). 3. **Abduction:** Movement of the limbs laterally away from the middle line. In the fingers moving away from the center of middle finger while in the toes moving away from the center of second toe. 4. **Adduction:** Movement of the limb medially towards the middle line. In the fingers moving towards the center of middle finger, while in the toes moving towards the center of second toe. 5. **Rotation:** Medial or lateral of the limb around a vertical axis. 6. **Circumduction:** Combination of all above movements. 7. **Supination:** The lateral rotation of the forearm. 8. **Pronation:** The medial rotation of the forearm. 9. **Inversion:** The sole of the foot is directed inwards. 10. **Eversion:** The sole of foot is directed outwards. 11. **Opposition:** The thumb comes in contact with the other 4 fingers.