The three broad classes of joints include: Immovable — the two or more bones are in close contact, but no movement can occur — for example, the bones of the skull. The joints of the skull are called sutures. Slightly movable — two or more bones are held together so tightly that only limited movement is permitted — for example, the vertebrae of the spine. Freely movable — most joints within the human body are this type. Motion is the purpose of the joint. Freely moving joints The six types of freely movable joint include: Ball and socket joint — the rounded head of one bone sits within the cup of another, such as the hip joint or shoulder joint.
Movement in all directions is allowed. Saddle joint — this permits movement back and forth and from side to side, but does not allow rotation, such as the joint at the base of the thumb. Hinge joint — the two bones open and close in one direction only along one plane like a door, such as the knee and elbow joints. Condyloid joint — this permits movement without rotation, such as in the jaw or finger joints. Pivot joint — one bone swivels around the ring formed by another bone, such as the joint between the first and second vertebrae in the neck.
Gliding joint — or plane joint. Smooth surfaces slip over one another, allowing limited movement, such as the wrist joints. Types of movement To achieve movement, the joint may: Slide one broad and flat surface across another — examples include the bones in the wrist or ankle.
Increase or decrease the angle between the two bones — this only occurs in the long bones of the body arms and legs : for example, when the arm is bent or extended. Allow a circular movement — this is how ball and socket joints work: for example, the shoulder.
These prevent rubbing of the muscle during movements. A large submuscular bursa, the trochanteric bursa, is found at the lateral hip, between the greater trochanter of the femur and the overlying gluteus maximus muscle. A subtendinous bursa is found between a tendon and a bone. Examples include the subacromial bursa that protects the tendon of shoulder muscle as it passes under the acromion of the scapula, and the suprapatellar bursa that separates the tendon of the large anterior thigh muscle from the distal femur just above the knee.
A tendon sheath is similar in structure to a bursa, but smaller. It is a connective tissue sac that surrounds a muscle tendon at places where the tendon crosses a joint. It contains a lubricating fluid that allows for smooth motions of the tendon during muscle contraction and joint movements. Bursitis can be either acute lasting only a few days or chronic. It can arise from muscle overuse, trauma, excessive or prolonged pressure on the skin, rheumatoid arthritis, gout, or infection of the joint.
Repeated acute episodes of bursitis can result in a chronic condition. Treatments for the disorder include antibiotics if the bursitis is caused by an infection, or anti-inflammatory agents, such as nonsteroidal anti-inflammatory drugs NSAIDs or corticosteroids if the bursitis is due to trauma or overuse.
Chronic bursitis may require that fluid be drained, but additional surgery is usually not required. Synovial joints are subdivided based on the shapes of the articulating surfaces of the bones that form each joint. The six types of synovial joints are pivot, hinge, condyloid, saddle, plane, and ball-and socket-joints Figure 9.
At a pivot joint , a rounded portion of a bone is enclosed within a ring formed partially by the articulation with another bone and partially by a ligament see Figure 9. The bone rotates within this ring. Since the rotation is around a single axis, pivot joints are functionally classified as a uniaxial diarthrosis type of joint. An example of a pivot joint is the atlantoaxial joint, found between the C1 atlas and C2 axis vertebrae.
Here, the upward projecting dens of the axis articulates with the inner aspect of the atlas, where it is held in place by a ligament. Rotation at this joint allows you to turn your head from side to side. A second pivot joint is found at the proximal radioulnar joint. Here, the head of the radius is largely encircled by a ligament that holds it in place as it articulates with the radial notch of the ulna. Rotation of the radius allows for forearm movements.
In a hinge joint , the convex end of one bone articulates with the concave end of the adjoining bone see Figure 9. This type of joint allows only for bending and straightening motions along a single axis, and thus hinge joints are functionally classified as uniaxial joints. A good example is the elbow joint, with the articulation between the trochlea of the humerus and the trochlear notch of the ulna.
Other hinge joints of the body include the knee, ankle, and interphalangeal joints between the phalanx bones of the fingers and toes. At a condyloid joint ellipsoid joint , the shallow depression at the end of one bone articulates with a rounded structure from an adjacent bone or bones see Figure 9.
The knuckle metacarpophalangeal joints of the hand between the distal end of a metacarpal bone and the proximal phalanx bone are condyloid joints. Another example is the radiocarpal joint of the wrist, between the shallow depression at the distal end of the radius bone and the rounded scaphoid, lunate, and triquetrum carpal bones.
In this case, the articulation area has a more oval elliptical shape. Functionally, condyloid joints are biaxial joints that allow for two planes of movement. One movement involves the bending and straightening of the fingers or the anterior-posterior movements of the hand.
The second movement is a side-to-side movement, which allows you to spread your fingers apart and bring them together, or to move your hand in a medial-going or lateral-going direction. At a saddle joint , both of the articulating surfaces for the bones have a saddle shape, which is concave in one direction and convex in the other see Figure 9. This allows the two bones to fit together like a rider sitting on a saddle. Saddle joints are functionally classified as biaxial joints. The primary example is the first carpometacarpal joint, between the trapezium a carpal bone and the first metacarpal bone at the base of the thumb.
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