Elements of Arthrology Arthrology-study of joints Arthritis- inflammation of the joint Classification of joints Degree of movement Joining material

Degree of movement i. Synarthrotic joint- no movements e.g ii.Amphyarthrotic joints-limited movements iii. Diarthrotic joints- free movements Joining material i. Fibrous joints ii. Cartilaginous joints iii. Synovial joints

Fibrous joints Articulating bones are held by fibrous tissue. Most joints are immovable. A few allow a small degree of mobility. Degree of mobility depends on the length of fibers (collagen) uniting the articulating bones. a)Sutures: Joints of skull bones. Edges of articulating bone interlock and tightly held by a thin layer of fibrous tissue. b)Syndesmosis: Bones are held by a sheet of fibrous tissue (ligament or interosseous membrane) Unlike in sutures here there is some degree of mobility. Examples: radioulnar, tibiofibullar joints c)Gomphosis: Peg-end-socket between the tooth and mandible/maxilla

Suture joints

Fig. Synovial joint

Cartilaginous joints Also called synchondrosis. Bones are united by hyaline or a fibrocartilage. a)Primary cartilaginous joint: Are united by hyaline cartilage and permit no movement. Examples: epiphyseal cartilage between the epiphysis and diaphysis. Allows bone growth in young subject and in the adult it’s replaced by bone; so a synchondrosis is converted into synostosis. Another example is the costochondral articulation of the sternum b) Secondary cartilaginous joint: Also called symphysis and situated in the axial skeleton. Articulating material is a fibrocartilage. The bones are covered by a thin hyaline cartilage. The joints are strong and slightly movable. Examples are pubic symphysis, intervetebral discs and the manubrium sterni.

Synovial joints Common types of joints responsible for the various movements we perform. The bones are held by a fibrous capsule which encloses a joint cavity. Ligaments/tendons inside or outside the capsule strengthen the joint. A synovial membrane lines the joint cavity. The membrane has cells that secrete synovial fluid (synovia) into the joint cavity for lubrication. Articulating surfaces are lined by a thin hyaline cartilage. Some joints may be traversed an articular disc temporomandibular, sternoclavicular, acromioclavicular, radioulnar and knee joints. The disc attached to the joint capsule.

Types of synovial joints i) Plane joints: Flat articular surfaces which permit gliding/slipping or twisting of one bone on the other. E.g. intercarpal, intertarsals, acromioclavicular, sternoclavicular joints. ii) Hinge (ginglymus) joints: Uniaxial joints permitting flexion and extension) The articulating surface of bones is concave and that of the other bone is convex. E.g elbow, ankle, knee and interphalangeal joints iii) Pivot joints: Also uniaxial permitting rotational movement. A rounded piece of bone rotates within a ring made up of bone and strong ligaments. E.g proximal radioulnar and atlanto-axial joints.

Types of synovial joints iv) Condyloid joints: Biaxial joints permitting extension, flexion and abduction, adduction movements. Have two convex articular surfaces that articulate with two concave surfaces. E.g metacapophalangeal, metatarsaophalangeal, atlanto-occipital joints. v) Ellipsoid joints: Also biaxial; allow flexion, extension, abduction and adduction movements. One surface of articulating bone is oval and another is a socket. E.g (radiocarpal) joint. vi) Saddle joints: Articulating bones are concave and convex opposite to one another. Multiaxial joints which allow movements back and forth and up and down but does not allow rotation movement. E.g. carpo-metacarpal joint of the thumb. vii) Ball and socket joints: Multiaxia joint that allow flexion, extension, abduction, adduction, rotation and circumduction. E.g. shoulder and hip joints.

Joints Saddle Pivot

Joints Ellipsoid Condyloid

Joint stability i) Articulating surfaces: Bone shape plays an important role in joint stability; e.g a concave socket and a convex head form a stable joint such as the hip joint. ii) Ligaments: Fibrous or elastic ligaments stabilize joints. iii) Muscle tone: Muscle tone around a joint control stability E.g rotator cuff muscles and qadriceps femoris stabilize elibow and knee joints

Related structures Bursa: Small fluid-filled sac located at the point where a muscle or tendon slides across bone. Bursae serve to reduce friction between the two moving surfaces. The synovial fluid in the bursa moistens the interior of the bursa. Synovial Sheath: A synovial sheath is a flat bursa that surrounds certain tendons particularly in the hands and feet

Hilton’s law A Nerve that innervates a joint also innervates the muscles that move the joint and the skin that covers the distal attachments of the muscles