Lecture 9 Articular System (Joints) PDF

Introduction To Human Anatomy 7101101 Lecture 8 (2hrs): Articular system (Joints) Bones of neonatal skull Classification of joints Joints (articulations) are unions or junctions between two or more bones or rigid parts of the skeleton. Joints exhibit a variety of forms an...

Introduction To Human Anatomy 7101101 Lecture 8 (2hrs): Articular system (Joints) Bones of neonatal skull Classification of joints Joints (articulations) are unions or junctions between two or more bones or rigid parts of the skeleton. Joints exhibit a variety of forms and functions, three classes of joints are described based on the manner or type of material by which the articulating bones are united. 1. Synovial joints 2. Fibrous joints 3. Cartilaginous joints Synovial joints The articulating bones are united by a joint capsule (articular capsule) composed of an outer fibrous layer lined by a serous synovial membrane) spanning and enclosing an articular cavity. The joint cavity of a synovial joint, like the knee, is a potential space that contains a small amount of lubricating synovial fluid, secreted by the synovial membrane. Synovial joints Inside the capsule, articular cartilage covers the articulating surfaces of the bones; all other internal surfaces are covered by synovial membrane. The periosteum investing the participating bones external to the joint blends with the fibrous layer of the joint capsule. Note: Images of such joints usually exaggerate the joint cavity dimensions Synovial joints The most common type of joints Provide free movement between the bones they join; they are joints of locomotion, typical of nearly all limb joints Usually reinforced by accessory ligaments Some synovial joints have other distinguishing features, such as a fibrocartilaginous articular disc or meniscus There are six major types of synovial joints classified according to the shape of the articulating surfaces and/or the type of movement they permit Synovial joints: 1. Plane joints Permit gliding or sliding movements (and slight rotation to some extent) in the plane of the articular surfaces. The opposed surfaces of the bones are flat or almost flat, with movement limited by their tight joint capsules. numerous and are nearly always small Example the acromioclavicular joint between the acromion of the scapula and the clavicle. intercarpal joints between individual carpal bones Synovial joints: 1. Plane joints Synovial joints: 2. Hinge joints Permit flexion and extension only, movements occur in one plane (usually sagittal) around a single axis that runs transversely; thus hinge joints are uniaxial joints. The elbow joint and the Interphalangeal joints are synovial hinge joints  Synovial joints: 2. Hinge joints The joint capsule of these joints is thin and lax anteriorly and posteriorly where movement occurs The bones are joined by strong, laterally placed collateral ligaments. Synovial joints: 3. Saddle joints The opposing articular surfaces are shaped like a saddle (i.e., they are reciprocally concave and convex). Permit abduction and adduction as well as flexion and extension, and the circular sequence (circumduction) is also possible. Movements occurring around two axes at right angles to each other; thus saddle joints are biaxial joints that allow movement in two planes, sagittal and frontal. Synovial joints: 3. Saddle joints The carpometacarpal joint at the base of the 1st digit (thumb) is a saddle joint. Synovial joints: 4. Ball and socket joints Highly mobile joints in which a spheroidal surface of one bone moves within the socket of another. Allow movement in multiple axes and planes: Flexion and extension, abduction and adduction, medial and lateral rotation, and circumduction; thus ball and socket joints are multi-axial joints. Synovial joints: 4. Ball and socket joints The hip joint is a ball and socket joint in which the spherical head of the femur rotates within the socket formed by the acetabulum of the hip bone (the red part of the following animation). Synovial joints: 5. Condyloid joints Similar to ball and socket joints but the bone head has an oval shape while the socket is elliptical Permit flexion and extension as well as abduction and adduction; thus condyloid joints are also biaxial Movement in one plane (sagittal) is usually greater (freer) than in the other. Circumduction, more restricted than that of saddle joints, is also possible. Rotation is very limited Synovial joints: 5. Condyloid joints A great example of a condyloid joint is the wrist (radiocarpal) joint. The metacarpophalangeal joints (knuckle joints) are condyloid joints Synovial joints: 6. Pivot joints In these joints, a rounded process of bone rotates within a sleeve or ring. ( A cylindrical bone fits into a ring of bone and ligament) Permit rotation around a central axis; thus they are uniaxial. Example: the proximal radio-ulnar joint which allows pronation and supination  The median atlantoaxial joint is a pivot joint in which the atlas (C1 vertebra) rotates around a finger-like process, the dens of the axis (C2 vertebra), during rotation of the head.  Fibrous joints The articulating bones are united by fibrous tissue No joint cavity In most cases, the joint movement depend on the length of fibers linking the bone Partially movable or not movable at all Types Sutures Syndesmosis Dentoalveolar syndesmosis (Gomphosis)  Fibrous joints: Sutures Only between bones of skull bones held close together, either interlocking along a wavy line or overlapping with short interconnecting fibers (immovable) fuse in middle age: now technically called “synostoses”= bony junctions  Fibrous joints: Syndesmosis Unites the bones with a sheet of fibrous tissue, either a ligament or a fibrous membrane. Example: the interosseous membrane in the forearm which is a sheet of fibrous tissue that joins the radius and ulna Fibers are longer than in sutures thus partially movable. Interosseous = inter “between” + osseous “Of, relating to, or made of bone; bony”, Latin -os- “bone”  Fibrous joints: Dentoalveolar syndesmosis (Gomphosis) The joint is formed from a peglike process (the root of the tooth) which fits into a socket articulation (the alveolar process of the jaw) The two structures are joined by a fibrous connective tissue structure called the periodontal ligament Fibrous joints: Dentoalveolar syndesmosis (Gomphosis) Mobility of this joint (a loose tooth) indicates a pathological state affecting the supporting tissues of the tooth. However, microscopic movements here give us information (via the sense of proprioception) about how hard we are biting or clenching our teeth and whether we have a particle stuck between our teeth. Cartilaginous joints The articulating structures are united by hyaline cartilage or fibrocartilage and lack a joint cavity Two types: 1. Primary cartilaginous joints (Synchondroses): Bones are united by hyaline cartilage, which permits slight bending during early life. Usually temporary unions, such as those present during the development of a long bone, where the bony epiphysis and the shaft are joined by an epiphysial plate. Cartilaginous joints: 1. Primary cartilaginous joints (Synchondroses) (contd.) Permit growth in the length of a bone. When full growth is achieved, the epiphysial plate converts to bone and the epiphyses fuse with the diaphysis. Examples: Epiphyseal plates Joint between first rib’s costal cartilage and manubrium of the sternum Cartilaginous joints 2. Secondary cartilaginous joints (Sympheses): strong, slightly movable joints united by fibrocartilage Provide strength and shock absorption flexibility Examples Intervertebral discs Pubic symphysis of the pelvis  Joints of the Newborn Cranium The bones of the calvaria (skullcap) of a newborn infant's cranium do not make full contact with each other At these sites, the sutures form wide areas of fibrous tissue called fontanelles. Joints of the Newborn Cranium The fontanelles in a newborn are often felt as ridges because of the overlapping of the cranial bones by molding of the calvaria as it passes through the birth canal. Molding tends to resolve without intervention over the first few days of life Joints of the Newborn Cranium The anterior fontanelle is the most prominent; “soft spot.” Normally, the anterior fontanelle is flat. A bulging fontanelle may indicate increased intracranial pressure; however, the fontanelle normally bulges during crying. A depressed fontanelle may be observed when the baby is dehydrated. Pulsations of the fontanelle reflect the pulse of cerebral arteries. Degenerative Joint Disease Synovial joints are well designed to withstand wear, but heavy use over several years can cause degenerative changes. Some destruction is inevitable during such activities as jogging, which wears away the articular cartilages and sometimes erodes the underlying articulating surfaces of the bones. The normal aging of articular cartilage begins early in adult life and progresses slowly thereafter, occurring on the ends of the articulating bones, particularly those of the hip, knee, vertebral column, and hands (Salter, 1998). Degenerative Joint Disease These irreversible degenerative changes in joints result in the articular cartilage becoming a less effective shock absorber and lubricated surface. As a result, the articulation becomes increasingly vulnerable to the repeated friction that occurs during joint movements. In some people, these changes do not produce significant symptoms; in others, they cause considerable pain. Degenerative joint disease or osteoarthritis is often accompanied by stiffness, discomfort, and pain. Degenerative Joint Disease Osteoarthritis is common in older people and usually affects joints that support the weight of their bodies (e.g., the hips and knees). Most substances in the bloodstream, normal or pathological, easily enter the joint cavity. Similarly, traumatic infection of a joint may be followed by arthritis, inflammation of a joint, and septicemia, blood poisoning. Arthroscopy The cavity of a synovial joint can be examined by inserting a cannula and an arthroscope (a small telescope) into it. This surgical procedure enables orthopedic surgeons to examine joints for abnormalities, such as torn menisci (partial articular discs of the knee joint). Some surgical procedures can also be performed during arthroscopy (e.g., by inserting instruments through small puncture incisions). Because the opening in the joint capsule for inserting the arthroscope is small, healing is more rapid after this procedure than after traditional joint surgery.