Chapter 9 Outline - anatomy PDF

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CHAPTER NINE Articulations 1. Classification of Joints A. Joint Design and Movement 1. Because the bones of the skeleton are relatively inflexible, movement can occur only at articulations, or joints, where two bones interconnect. 2. Each joint reflects a compromise between the need for strength and the need for mobility. As a result, articulations differ in the amount of movement permitted, and this property is known as range of motion (ROM). 3. The anatomical structure of a joint determines the type and amount of movement that may occur. B. Articulations are often categorized by range of motion and anatomical structure. 1. Structural classifications are based on the anatomical components that make up the joint. a. Fibrous joints = held together by fibrous connective tissues but lack cartilage and possess no cavity between the bones. Fibrous joints are either synarthrotic or amphiarthrotic. b. Cartilaginous joints = held together by fibrous connective tissues such as ligaments but they also possess either hyaline cartilage or fibrocartilage. Cartilaginous joints lack a joint cavity and are either synarthrotic or amphiarthrotic. c. Synovial joints = held together by fibrous connective tissues, hyaline cartilage and/or fibrocartilage, and possess a joint cavity. All synovial joints are diarthrotic. Synovial joints are quite complex in structure, are the most numerous type of joint in the body, and permit the greatest range of motion. Because of this, we will discuss synovial joints in detail. 2. Functional classifications are based on the range of motion allowed. a. Synarthrosis = no movement is permitted. At synarthrotic joints, the bony edges are quite close together and may even interlock. These extremely strong joints are located where movement between bones must be prevented. b. Amphiarthrosis = only slight movement is permitted. An amphiarthrotic joint permits more movement than a synarthrotic joint, but is much stronger than freely moveable joints. c. Diarthrosis = freely moveable joints. Diarthrotic joints provide a wide range of motion as typical in the joints of our appendages. d. Synarthrotic and amphiarthrotic joints are relatively simple in structure, with direct connections between the articulating bones. Diarthrotic joints are quite complex in structure, and they permit the greatest range of motion. e. Axis of motion i. Non-axial motion=linear movements where bones slide (vertebrocostal joints, sacroiliac joint, and intercarpal joints) ii. Uniaxial motion=movement in one planes (finger joints, elbow, knee) iii. Biaxial motion=movement in two planes (metacarpophalangeal joint, occipital condyles to atlas) iv. Multi-axial motion= movement in three planes (shoulder joint and hip joint) 9.2 Fibrous joints i. Sutures = a synarthrotic joint located only between the bones of the skull. The edges of the bones are interlocked and bound together at the suture by dense fibrous connective tissue. ii. Synostosis = a synarthrotic joint created when two bones fuse and the boundary between them disappears. In adulthood, the sutures of the skull normally transform to synostoses creating a secure cranial cavity around the brain. The epiphyseal plate of the long bones also ossifies to form a synostosis, called the epiphyseal line, in adulthood. Abnormal fusion of bones may also occur resulting synostoses where

they should not exist. One example is the premature ossification of the cranial sutures (which limits the normal growth of the brain). Another example is radio-ulnar synostosis. iii. Syndesmosis = bones are connected by an interosseous ligament and are amphiarthrotic. The most common example is the distal articulation between the tibia and fibula called the tibiofibular joint. Another example is the middle radio-ulnar joint but should not to be confused with the joints formed at the proximal and distal ends of the radius and ulna which are both synovial joints that are diarthrotic. iv. Gomphosis = a synarthrotic joint sometimes called a “peg-in-socket” joint. A gomphosis joint is found on the maxillae and mandible where the teeth are fixed securely in the sockets of the alveolar margins. The fibrous connective tissue between a tooth and its socket is a periodontal ligament. 1. Cartilaginous joints A. Synchondrosis = a rigid, hyaline cartilage bridge unites the bones of a synchondrosis joint. One example is the cartilaginous joint found between the ends of the first pair of ribs and the manubrium of the sternum (all other ribs form synovial joints). A second example is the epiphyseal plate found holding the epiphysis of a long bone to the diaphysis (remember this becomes a synostosis in adulthood when the cartilage is replaced with bone). Both of these examples are synarthrotic joints. B. Symphysis = articulating bones are separated by a wedge or pad of fibrocartilage. The articulation between the vertebrae where a thick pad of fibrocartilage forms the intervertebral disc is a common example of a symphysis. The articulation between the two pubic bones (called the pubic symphysis) is another joint typical of this category. A symphysis is considered an amphiarthrotic joint. Each vertebral joint, for example, only provides slight movement but because the vertebral column is formed by so many vertebral joints, collectively the vertebral column demonstrates a high degree of mobility. 1. Synovial joints A. Structural features of a Synovial Joint 1. Joint cavity = not only are synovial joints composed of fibrous connective tissues (as are fibrous and cartilaginous joints) and possess cartilage (as do cartilaginous joints) but they also possess a space between the articulating bones, called the synovial cavity. 2. Articular cartilages = line the surfaces of the articulating bones; composed of hyaline cartilage however these cartilages lack a perichondrium and the matrix contains more water than that of hyaline cartilage located elsewhere in the body. The articular cartilages provide a slick, smooth surface to the bones which reduces friction during movement. 3. Synovial fluid = this fluid is largely derived from blood and has a clear, viscous, egg-white consistency. Even in large joints, such as the knee, the total quantity of synovial fluid is normally less than 3 ml. There are three primary functions of synovial fluid: a. Lubrication: When part of an articular cartilage is compressed during movement, some of the synovial fluid is squeezed out of the cartilage and into the space between the opposing surfaces. In turn, this thin layer of fluid markedly reduces friction between moving surfaces. This is called weeping lubrication. b. Nutrient distribution: The synovial fluid in a joint must circulate continuously to provide nutrients and waste disposal for the chondrocytes of the articular cartilages. It circulates whenever the joint moves, and the repeated compression and expansion of the articular cartilages pump synovial fluid into and out of the cartilage matrix. c. Shock absorption: When a joint is subjected to compression, the synovial fluid provides a cushion against the shock. For example, when you jog your knees are severely compressed and the synovial fluid distributes that force evenly across the articular surfaces and outward to the joint capsule. 4. Joint capsule = layers of dense fibrous connective tissues that enclose the synovial cavity to house the synovial fluid.

a. Fibrous capsule = thick outer layer continuous with the periosteum around the articulating bones. As a result, this adds strength and helps to stabilize the joint. b. Synovial membrane = inner soft tissue whose network of capillaries leak plasma from the bloodstream to produce the synovial fluid. 5. Accessory structures of a typical synovial joint = in complex synovial joints, such as the knee, a variety of accessory structures provide support and additional stability. a. Ligaments = support, strengthen, and reinforce synovial joints v. Intrinsic ligament = (also called capsular ligaments) are parallel bundles of fibers creating thickenings within the joint capsule. vi. Extrinsic ligament = separate from the joint capsule and may pass outside (extracapsular) or inside (intracapsular) the joint capsule. b. Bursa = a small, fluid-filled pocket that forms in a connective tissue. It contains synovial fluid and is lined by a synovial membrane. Bursae often form where a tendon or ligament rubs against other tissues. Located around most synovial joints, bursae reduce friction and act as shock absorbers. b. Fat pads = localized masses of adipose tissue covered by a layer of synovial membrane. They are commonly superficial to the joint capsule. Fat pads protect the articular cartilages and act as packing material for the joint. When the bones move, the pat pads fill in the spaces created as the joint cavity changes shape. c. Meniscus = a pad of fibrous cartilage situated between opposing bones within a synovial joint. Menisci may subdivide a synovial cavity, channel the flow of synovial fluid, or allow for variations in the shapes of the articular surfaces. 1. Types of Body Movements A. A joint cannot be both highly mobile and very strong. The greater the range of motion at a joint, the weaker it becomes. B. A synarthrotic joint, the strongest type of joint, permits no movement. Whereas a diarthrosis, such as the shoulder, is far weaker but permits a broad range of motion. C. Types of motion 1. Gliding=bones slide across the surface of one another 2. Angular=changing the angle between two bones 3. Circumduction=draw around; conical shape or circular motion 4. Rotation=turning movement of a bone around its own axis D. Movements relative to anatomical position 1. Flexion = angular movement within the anterior-posterior plane that reduces the angle between the articulating elements (lifting dumbbell as in a biceps curl). 2. Extension = opposite of flexion; an angular movement within the anterior-posterior plane that increases the angle between the articulating elements. When in anatomical position, all of the major joints of the axial and appendicular skeleton (except the ankle) are at full extension (lowering the dumbbell back to a starting position). 3. Hyperextension = angular movement where the body part is extended past the anatomical position (looking up at the stars). 4. Dorsiflexion = flexion at the ankle joint and elevation of the sole (as when you dig in your heel). 5. Plantar flexion = opposite to dorsiflexion, extend the ankle and elevates the heel (as when you point your toes). 6. Abduction = angular movement within the lateral-medial plane that moves the body part away from the longitudinal axis (first part of a jumping jack, spreading the fingers, cocking the wrist). 7. Adduction = opposite to abduction; an angular movement within the lateral-medial plane that moves the body part toward the longitudinal axis (second part of a jumping jack, bringing fingers together, snapping the wrist).

8. Circumduction = moving a limb in a circle creating a cone in space (performing windmill exercises). 9. Medial rotation = the anterior surface of a limb turns towards midline of the body (pigeon toe in the leg). 10. Lateral rotation = opposite to medial rotation; the anterior surface of a limb turns away from the midline of the body (first position in a ballerina stance) 11. Supination = in anatomical position, the forearm is supinated with the radius and ulna lying parallel to each other and the palm facing anteriorly (as when holding a bowl of soup). 12. Pronation = the shaft of the radius rotates, the distal epiphysis of the radius rolls across the anterior surface of the ulna so that the bones are crossing. The palm faces posteriorly (pro basketball players pronate to dribble the ball). 13. Inversion = a twist motion of the foot that turns the sole inward, elevating the medial edge of the sole (seen in club foot). 14. Eversion = opposite to inversion; a twist motion of the foot that turns the sole outward, elevating the lateral edge of the sole. 15. Protraction = moving a body part anteriorly in the horizontal plane (an under-bite with the lower jaw). 16. Retraction = opposite to protraction; moving the body part posteriorly in the horizontal plane (an overbite with the lower jaw). 17. Depression = structure moves inferiorly (opening the mouth). 18. Elevation = structure moves superiorly (closing the mouth). 19. Opposition = the movement of the thumb toward the surface of the palm or the pads of the other fingers (as in snapping to music). 1. Anatomy of Selected Synovial Joints A. Anatomical classes of synovial joints are based on the shape of the articulating surfaces of the bones. B. Plane joints = also known as gliding joints; articular surfaces are flat and only allow for short gliding movements; non-axial (intercarpal and intertarsal joints, sacro-iliac joint, vertebrocostal joint, acromioclavicular and sternoclavicular joints, and between the superior and inferior articulating processes of the vertebrae). C. Hinge joints = cylindrical projection of one bone fits into a trough-shaped surface on another bone; uniaxial (elbow joint, knee joint, ankle joint, and interphalangeal joints). D. Pivot joints = rounded end of one bone protrudes into a sleeve or ring composed of bone or ligament; uniaxial (proximal radio-ulnar joint, the dens of the axis to atlas). E. Condyloid joints = also known as ellipsoid joint, oval articular surface of one bone fits into a complementary depression in another; biaxial (metacarpophalanges 2-5 or knuckles, radiocarpal joints, and metatarsophalangeal joints). F. Saddle joints = articular surfaces have a concave area on one that fits with the convex area of the other; biaxial (first carpometacarpal joint in the thumb). G. Ball and socket = the spherical end of one bone articulates with a cuplike socket of another bone; multiaxial (shoulder joint and hip joints). 7.

Development of Joints A. Joints form during embryonic development in conjunction with the formation and growth of the associated bones. B. The embryonic tissue that gives rise to all bones, cartilages, and connective tissues of the body is called mesenchyme.

8. Common Joint Injuries A. Sprain = stretching or tearing of a ligament across the joint capsule. B. Dislocation = also known as a luxation; when reinforcing structures cannot protect a joint from extreme stresses, the articulating surfaces may be forced out of position. The displacement may damage the articular cartilages, tear ligaments, or distort the joint capsule. Although the inside of a joint has no pain receptors, nerves that monitor the capsule, ligaments, and tendons are quite sensitive, so dislocations are very painful. A partial dislocation is called a subluxation. C. Bursitis = inflammation of the bursa D. Tendonitis = inflammation of the tendon E. Synovitis =inflammation of the synovial membrane A. Osteopenia and osteoporosis=inadequate ossification of bone is called osteopenia and begins between the ages of 30 and 40 years of age when osteoblast activity declines while osteoclast activity continues at previous levels. Thereafter, women begin to lose roughly 8% of their bone mass every decade (men lose 3% per decade). When the reduction in bone mass is sufficient to compromise normal function, the condition is known as osteoporosis. B. Arthritis = inflammatory or degenerative disease of the joint where synovial membranes thicken (called pannus) and fluid production decreases resulting in friction and pain. Arthroscopic surgery may be necessary to treat joint injuries or artificial joints may need to be installed when a joint is damaged beyond repair. 1. Osteoarthritis = also known as degenerative arthritis or degenerative joint disease, generally affects individuals age 60 or older. It can result from the cumulative effects of wear and tear on the joint surfaces or from genetic factors affecting collagen formation. In the U.S. population, 25% of women and 15% of men over age 60 show signs of this condition. 2. Rheumatoid arthritis = an autoimmune disease. RA can occur at any age but is more common in middle age and women get RA more often than men. Infection, genes, and hormone changes may be linked to the disease. RA usually affects joints on both sides of the body equally. Wrists, fingers, knees, feet, and ankles are the most common affected body parts. The disease often begins slowly with only minor pain but progressively becomes debilitating. 3. Gouty arthritis = Gout is caused by too much uric acid in the blood. Most of the time, having too much uric acid is not harmful. Many people with high levels in their blood never get gout. But when uric acid levels in the blood are too high, the uric acid may form hard crystals in your joints. It can cause an attack of sudden burning pain, stiffness, and swelling in a joint, usually a big toe. These attacks can happen over and over unless gout is treated. More common in men. H. Bulging and herniated discs = compression of the nucleus pulposus which may distort the anulus fibrosus (bulging disc) or protrude through the anulus fibrosus into the vertebral canal (herniated disc)....