At many synovial joints, additional support is provided by the muscles and their tendons that act across the joint. A tendon is the dense connective tissue structure that attaches a muscle to bone. This type of indirect support by muscles is very important at the shoulder joint, for example, where the ligaments are relatively weak.
A few synovial joints of the body have a fibrocartilage structure located between the articulating bones. This is called an articular disc , which is generally small and oval-shaped, or a meniscus , which is larger and C-shaped. These structures can serve several functions, depending on the specific joint. In some places, an articular disc may act to strongly unite the bones of the joint to each other.
Examples of this include the articular discs found at the sternoclavicular joint or between the distal ends of the radius and ulna bones.
At other synovial joints, the disc can provide shock absorption and cushioning between the bones, which is the function of each meniscus within the knee joint. Finally, an articular disc can serve to smooth the movements between the articulating bones, as seen at the temporomandibular joint.
Some synovial joints also have a fat pad, which can serve as a cushion between the bones. Additional structures located outside of a synovial joint serve to prevent friction between the bones of the joint and the overlying muscle tendons or skin.
They are located in regions where skin, ligaments, muscles, or muscle tendons can rub against each other, usually near a body joint Figure 9. Bursae reduce friction by separating the adjacent structures, preventing them from rubbing directly against each other.
Bursae are classified by their location. A subcutaneous bursa is located between the skin and an underlying bone. It allows skin to move smoothly over the bone.
Examples include the prepatellar bursa located over the kneecap and the olecranon bursa at the tip of the elbow. A submuscular bursa is found between a muscle and an underlying bone, or between adjacent muscles. 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 phalanges 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 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. Synovial joints achieve movement at the point of contact of the articulating bones.
Structural and functional differences distinguish synovial joints from cartilaginous joints synchondroses and symphyses and fibrous joints sutures, gomphoses, and syndesmoses. Several movements may be performed by synovial joints. Abduction is the movement away from the midline of the body. Adduction is the movement toward the middle line of the body. Extension is the straightening of limbs increase in angle at a joint.
Flexion is bending the limbs reduction of angle at a joint. Rotation is a circular movement around a fixed point. Body Movements I : Image demonstrating the various joint movements. There are six types of synovial joints. Some are relatively immobile but more stable than mobile joints. Others have multiple degrees of freedom, but at the expense of greater risk of injury.
The six types of joints include:. Six Types of Synovial Joints : Image demonstrating the six different types of synovial joints. There are six different types of synovial joint based on their shapes, each allowing a different kind of movement. There are six basic types of synovial joints.
Anatomical joints may consist of a combination of two or more joint types. Some synovial joints are relatively immobile but stable. The types of the synovial joints are based on their shapes and can be classified as plane, hinge, pivot, condyloid, saddle, and ball-and-socket. The following descriptions are in ascending order of mobility:. In this example, the condyles of the femur join with condyles of tibia and the saddle joint, where the lower end of the femur joins with the patella.
Plane Joint : The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula. Ball and Socket Joint : Hip joint: the ball of the femur head fits in the socket of the acetabulum of the pelvis.
Saddle Joint : Sternoclavicular articulation. Anterior view. Privacy Policy. Skip to main content. Search for:. Synovial Joints. Structure of Synovial Joints A synovial joint or diarthrosis occurs at articulating bones to allow movement. Learning Objectives Identify the structures of the synovial joint that allow it to move freely. Key Takeaways Key Points The bones of a synovial joint are surrounded by a synovial capsule, which secretes synovial fluid to lubricate and nourish the joint while acting as a shock absorber.
The ends of the joint bones are covered with smooth, glass-like hyaline cartilage which reduces friction during movement. A synovial joint contains a synovial cavity and dense, irregular connective tissue that forms the articular capsule normally associated with accessory ligaments. Key Terms articulation : A joint or the collection of joints at which something is articulated, or hinged, for bending.
With its yolk-like consistency, its principal role is to reduce friction between the articular cartilage of synovial joints during movement. A major constituent of the embryonic and young vertebrate skeleton, converted largely to bone with maturation.
The adult human body contains bones and approximately joints, or points where two bones meet. Most joints are synovial joints, such as knees and knuckles. All synovial joints allow for movement and are susceptible to arthritis. Synovial joints allow for movement, but are also susceptible to arthritis. Synovial joints vary in structure—for example, the shoulder is a ball-and-socket joint and the knee is a hinge joint—but they all have the following in common:.
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