Chapter 9

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.

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.

Functional Classification of the Joints

a. Synarthrosis b. Amphiarthrosis c. Diarthrosis Functional classifications are based on the range of motion allowed.

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).

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.

Amphiarthrosis

only slight movement is permitted. An amphiarthrotic joint permits more movement than a synarthrotic joint, but is much stronger than freely moveable joints.

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).

Strain

stretching or tearing a tendon or muscle.

Sprain

stretching or tearing of a ligament across the joint capsule.

Classes of Synovial Joints

- Anatomical classes of synovial joints are based on the shape of the articulating surfaces of the bones. - Plane joints - Hinge joints - Pivot joints - Condyloid joints - Saddle joints - Ball and Socket joints

Types of motion

- Gliding=bones slide across the surface of one another - Angular=changing the angle between two bones - Circumduction=draw around; conical shape or circular motion - Rotation=turning movement of a bone around its own axis

Common Joint Injuries

- Sprain - Strain - Dislocation - Bursitis - Tendonitis - Synovitis - Arthritis

Movements Provided by Synovial Joints

1. A joint cannot be both highly mobile and very strong. The greater the range of motion at a joint, the weaker it becomes. 2. 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. 3. Axis of motion - Non-axial - Uni-axial - Bi-axial - Multi-axial

Structural Classification of the Joints

Fibrous joints - Sutures - Synostosis - Gomphosis - Syndesmosis Cartilaginous joints - Synchondrosis - Symphysis Synovial joints

Components of a Synovial Joint

Joint cavity Articular Cartilages Synovial Fluids

Fibrous joints

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. 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. 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. 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. held together by fibrous connective tissues but lack cartilage and possess no cavity between the bones. Fibrous joints are either synarthrotic or amphiarthrotic.

Cartilaginous joints

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. 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.

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.

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).

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).

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).

Diarthrosis

freely moveable joints. Diarthrotic joints provide a wide range of motion as typical in the joints of our appendages. 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.

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.

Accessory structures of a typical synovial joints

in complex synovial joints, such as the knee, a variety of accessory structures provide support and additional stability. - Ligaments - Bursa - Fat Pads - Meniscus

Bursitis

inflammation of the bursa

Synovitis

inflammation of the synovial membrane

Tendonitis

inflammation of the tendon

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.

Non-axial

linear movements where bones slide (vertebrocostal joints, sacroiliac joint, and intercarpal joints)

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.

Uni-axial

movement in one planes (finger joints, elbow, knee)

Multi-axial

movement in three planes (shoulder joint and hip joint)

Bi-axial

movement in two planes (metacarpophalangeal joint, occipital condyles to atlas)

Ligaments

support, strengthen, and reinforce synovial joints i. Intrinsic ligament = (also called capsular ligaments) are parallel bundles of fibers creating thickenings within the joint capsule. ii. Extrinsic ligament = separate from the joint capsule and may pass outside (extracapsular) or inside (intracapsular) the joint capsule.

Ball and Socket joints

the spherical end of one bone articulates with a cuplike socket of another bone; multi-axial (shoulder joint and hip joints).