Module 24: Joints

Lesson 4: Synovial Joints

Khớp Hoạt Dịch

Nội dung bài học:
Mỗi bài học (lesson) bao gồm 4 phần chính: Thuật ngữ, Luyện Đọc, Luyện Nghe, và Bàn Luận.
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Dưới đây là danh sách những thuật ngữ Y khoa của module Joints.
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Medical Terminology: Joints

abduction
movement in the coronal plane that moves a limb laterally away from the body; spreading of the fingers
acetabular labrum
lip of fibrocartilage that surrounds outer margin of the acetabulum on the hip bone
adduction
movement in the coronal plane that moves a limb medially toward or across the midline of the body; bringing fingers together
amphiarthrosis
slightly mobile joint
annular ligament
intrinsic ligament of the elbow articular capsule that surrounds and supports the head of the radius at the proximal radioulnar joint
anterior cruciate ligament
intracapsular ligament of the knee; extends from anterior, superior surface of the tibia to the inner aspect of the lateral condyle of the femur; resists hyperextension of knee
anterior talofibular ligament
intrinsic ligament located on the lateral side of the ankle joint, between talus bone and lateral malleolus of fibula; supports talus at the talocrural joint and resists excess inversion of the foot
articular capsule
connective tissue structure that encloses the joint cavity of a synovial joint
articular cartilage
thin layer of hyaline cartilage that covers the articulating surfaces of bones at a synovial joint
articular disc
meniscus; a fibrocartilage structure found between the bones of some synovial joints; provides padding or smooths movements between the bones; strongly unites the bones together
articulation
joint of the body
atlanto-occipital joint
articulation between the occipital condyles of the skull and the superior articular processes of the atlas (C1 vertebra)
atlantoaxial joint
series of three articulations between the atlas (C1) vertebra and the axis (C2) vertebra, consisting of the joints between the inferior articular processes of C1 and the superior articular processes of C2, and the articulation between the dens of C2 and the anterior arch of C1
ball-and-socket joint
synovial joint formed between the spherical end of one bone (the ball) that fits into the depression of a second bone (the socket); found at the hip and shoulder joints; functionally classified as a multiaxial joint
biaxial joint
type of diarthrosis; a joint that allows for movements within two planes (two axes)
bursa
connective tissue sac containing lubricating fluid that prevents friction between adjacent structures, such as skin and bone, tendons and bone, or between muscles
calcaneofibular ligament
intrinsic ligament located on the lateral side of the ankle joint, between the calcaneus bone and lateral malleolus of the fibula; supports the talus bone at the ankle joint and resists excess inversion of the foot
cartilaginous joint
joint at which the bones are united by hyaline cartilage (synchondrosis) or fibrocartilage (symphysis)
circumduction
circular motion of the arm, thigh, hand, thumb, or finger that is produced by the sequential combination of flexion, abduction, extension, and adduction
condyloid joint
synovial joint in which the shallow depression at the end of one bone receives a rounded end from a second bone or a rounded structure formed by two bones; found at the metacarpophalangeal joints of the fingers or the radiocarpal joint of the wrist; functionally classified as a biaxial joint
coracohumeral ligament
intrinsic ligament of the shoulder joint; runs from the coracoid process of the scapula to the anterior humerus
deltoid ligament
broad intrinsic ligament located on the medial side of the ankle joint; supports the talus at the talocrural joint and resists excess eversion of the foot
depression
downward (inferior) motion of the scapula or mandible
diarthrosis
freely mobile joint
dorsiflexion
movement at the ankle that brings the top of the foot toward the anterior leg
elbow joint
humeroulnar joint
elevation
upward (superior) motion of the scapula or mandible
eversion
foot movement involving the intertarsal joints of the foot in which the bottom of the foot is turned laterally, away from the midline
extension
movement in the sagittal plane that increases the angle of a joint (straightens the joint); motion involving posterior bending of the vertebral column or returning to the upright position from a flexed position
extrinsic ligament
ligament located outside of the articular capsule of a synovial joint
femoropatellar joint
portion of the knee joint consisting of the articulation between the distal femur and the patella
fibrous joint
joint where the articulating areas of the adjacent bones are connected by fibrous connective tissue
fibular collateral ligament
extrinsic ligament of the knee joint that spans from the lateral epicondyle of the femur to the head of the fibula; resists hyperextension and rotation of the extended knee
flexion
movement in the sagittal plane that decreases the angle of a joint (bends the joint); motion involving anterior bending of the vertebral column
fontanelles
expanded areas of fibrous connective tissue that separate the braincase bones of the skull prior to birth and during the first year after birth
glenohumeral joint
shoulder joint; articulation between the glenoid cavity of the scapula and head of the humerus; multiaxial ball-and-socket joint that allows for flexion/extension, abduction/adduction, circumduction, and medial/lateral rotation of the humerus
glenohumeral ligament
one of the three intrinsic ligaments of the shoulder joint that strengthen the anterior articular capsule
glenoid labrum
lip of fibrocartilage located around the outside margin of the glenoid cavity of the scapula
gomphosis
type of fibrous joint in which the root of a tooth is anchored into its bony jaw socket by strong periodontal ligaments
hinge joint
synovial joint at which the convex surface of one bone articulates with the concave surface of a second bone; includes the elbow, knee, ankle, and interphalangeal joints; functionally classified as a uniaxial joint
humeroradial joint
articulation between the capitulum of the humerus and head of the radius
humeroulnar joint
articulation between the trochlea of humerus and the trochlear notch of the ulna; uniaxial hinge joint that allows for flexion/extension of the forearm
hyperextension
excessive extension of joint, beyond the normal range of movement
hyperflexion
excessive flexion of joint, beyond the normal range of movement
iliofemoral ligament
intrinsic ligament spanning from the ilium of the hip bone to the femur, on the superior-anterior aspect of the hip joint
inferior rotation
movement of the scapula during upper limb adduction in which the glenoid cavity of the scapula moves in a downward direction as the medial end of the scapular spine moves in an upward direction
interosseous membrane
wide sheet of fibrous connective tissue that fills the gap between two parallel bones, forming a syndesmosis; found between the radius and ulna of the forearm and between the tibia and fibula of the leg
intracapsular ligament
ligament that is located within the articular capsule of a synovial joint
intrinsic ligament
ligament that is fused to or incorporated into the wall of the articular capsule of a synovial joint
inversion
foot movement involving the intertarsal joints of the foot in which the bottom of the foot is turned toward the midline
ischiofemoral ligament
intrinsic ligament spanning from the ischium of the hip bone to the femur, on the posterior aspect of the hip joint
joint
site at which two or more bones or bone and cartilage come together (articulate)
joint cavity
space enclosed by the articular capsule of a synovial joint that is filled with synovial fluid and contains the articulating surfaces of the adjacent bones
joint interzone
site within a growing embryonic limb bud that will become a synovial joint
lateral (external) rotation
movement of the arm at the shoulder joint or the thigh at the hip joint that moves the anterior surface of the limb away from the midline of the body
lateral excursion
side-to-side movement of the mandible away from the midline, toward either the right or left side
lateral flexion
bending of the neck or body toward the right or left side
lateral meniscus
C-shaped fibrocartilage articular disc located at the knee, between the lateral condyle of the femur and the lateral condyle of the tibia
lateral tibiofemoral joint
portion of the knee consisting of the articulation between the lateral condyle of the tibia and the lateral condyle of the femur; allows for flexion/extension at the knee
ligament
strong band of dense connective tissue spanning between bones
ligament of the head of the femur
intracapsular ligament that runs from the acetabulum of the hip bone to the head of the femur
medial (internal) rotation
movement of the arm at the shoulder joint or the thigh at the hip joint that brings the anterior surface of the limb toward the midline of the body
medial excursion
side-to-side movement that returns the mandible to the midline
medial meniscus
C-shaped fibrocartilage articular disc located at the knee, between the medial condyle of the femur and medial condyle of the tibia
medial tibiofemoral joint
portion of the knee consisting of the articulation between the medial condyle of the tibia and the medial condyle of the femur; allows for flexion/extension at the knee
meniscus
articular disc
multiaxial joint
type of diarthrosis; a joint that allows for movements within three planes (three axes)
opposition
thumb movement that brings the tip of the thumb in contact with the tip of a finger
patellar ligament
ligament spanning from the patella to the anterior tibia; serves as the final attachment for the quadriceps femoris muscle
periodontal ligament
band of dense connective tissue that anchors the root of a tooth into the bony jaw socket
pivot joint
synovial joint at which the rounded portion of a bone rotates within a ring formed by a ligament and an articulating bone; functionally classified as uniaxial joint
plane joint
synovial joint formed between the flattened articulating surfaces of adjacent bones; functionally classified as a multiaxial joint
plantar flexion
foot movement at the ankle in which the heel is lifted off of the ground
posterior cruciate ligament
intracapsular ligament of the knee; extends from the posterior, superior surface of the tibia to the inner aspect of the medial condyle of the femur; prevents anterior displacement of the femur when the knee is flexed and weight bearing
posterior talofibular ligament
intrinsic ligament located on the lateral side of the ankle joint, between the talus bone and lateral malleolus of the fibula; supports the talus at the talocrural joint and resists excess inversion of the foot
pronated position
forearm position in which the palm faces backward
pronation
forearm motion that moves the palm of the hand from the palm forward to the palm backward position
protraction
anterior motion of the scapula or mandible
proximal radioulnar joint
articulation between head of radius and radial notch of ulna; uniaxial pivot joint that allows for rotation of radius during pronation/supination of forearm
pubofemoral ligament
intrinsic ligament spanning from the pubis of the hip bone to the femur, on the anterior-inferior aspect of the hip joint
radial collateral ligament
intrinsic ligament on the lateral side of the elbow joint; runs from the lateral epicondyle of humerus to merge with the annular ligament
reposition
movement of the thumb from opposition back to the anatomical position (next to index finger)
retraction
posterior motion of the scapula or mandible
rotation
movement of a bone around a central axis (atlantoaxial joint) or around its long axis (proximal radioulnar joint; shoulder or hip joint); twisting of the vertebral column resulting from the summation of small motions between adjacent vertebrae
rotator cuff
strong connective tissue structure formed by the fusion of four rotator cuff muscle tendons to the articular capsule of the shoulder joint; surrounds and supports superior, anterior, lateral, and posterior sides of the humeral head
saddle joint
synovial joint in which the articulating ends of both bones are convex and concave in shape, such as at the first carpometacarpal joint at the base of the thumb; functionally classified as a biaxial joint
subacromial bursa
bursa that protects the supraspinatus muscle tendon and superior end of the humerus from rubbing against the acromion of the scapula
subcutaneous bursa
bursa that prevents friction between skin and an underlying bone
submuscular bursa
bursa that prevents friction between bone and a muscle or between adjacent muscles
subscapular bursa
bursa that prevents rubbing of the subscapularis muscle tendon against the scapula
subtalar joint
articulation between the talus and calcaneus bones of the foot; allows motions that contribute to inversion/eversion of the foot
subtendinous bursa
bursa that prevents friction between bone and a muscle tendon
superior rotation
movement of the scapula during upper limb abduction in which the glenoid cavity of the scapula moves in an upward direction as the medial end of the scapular spine moves in a downward direction
supinated position
forearm position in which the palm faces anteriorly (anatomical position)
supination
forearm motion that moves the palm of the hand from the palm backward to the palm forward position
suture
fibrous joint that connects the bones of the skull (except the mandible); an immobile joint (synarthrosis)
symphysis
type of cartilaginous joint where the bones are joined by fibrocartilage
synarthrosis
immobile or nearly immobile joint
synchondrosis
type of cartilaginous joint where the bones are joined by hyaline cartilage
syndesmosis
type of fibrous joint in which two separated, parallel bones are connected by an interosseous membrane
synostosis
site at which adjacent bones or bony components have fused together
synovial fluid
thick, lubricating fluid that fills the interior of a synovial joint
synovial joint
joint at which the articulating surfaces of the bones are located within a joint cavity formed by an articular capsule
synovial membrane
thin layer that lines the inner surface of the joint cavity at a synovial joint; produces the synovial fluid
talocrural joint
ankle joint; articulation between the talus bone of the foot and medial malleolus of the tibia, distal tibia, and lateral malleolus of the fibula; a uniaxial hinge joint that allows only for dorsiflexion and plantar flexion of the foot
temporomandibular joint (TMJ)
articulation between the condyle of the mandible and the mandibular fossa and articular tubercle of the temporal bone of the skull; allows for depression/elevation (opening/closing of mouth), protraction/retraction, and side-to-side motions of the mandible
tendon
dense connective tissue structure that anchors a muscle to bone
tendon sheath
connective tissue that surrounds a tendon at places where the tendon crosses a joint; contains a lubricating fluid to prevent friction and allow smooth movements of the tendon
tibial collateral ligament
extrinsic ligament of knee joint that spans from the medial epicondyle of the femur to the medial tibia; resists hyperextension and rotation of extended knee
ulnar collateral ligament
intrinsic ligament on the medial side of the elbow joint; spans from the medial epicondyle of the humerus to the medial ulna
uniaxial joint
type of diarthrosis; joint that allows for motion within only one plane (one axis)
zygapophysial joints
facet joints; plane joints between the superior and inferior articular processes of adjacent vertebrae that provide for only limited motions between the vertebrae
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Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
Synovial joints are the most common type of joint in the body (Figure 1). A key structural characteristic for a synovial joint that is not seen at fibrous or cartilaginous joints is the presence of a joint cavity. This fluid-filled space is the site at which the articulating surfaces of the bones contact each other. Also unlike fibrous or cartilaginous joints, the articulating bone surfaces at a synovial joint are not directly connected to each other with fibrous connective tissue or cartilage. This gives the bones of a synovial joint the ability to move smoothly against each other, allowing for increased joint mobility.
Synovial joints are characterized by the presence of a joint cavity. The walls of this space are formed by the articular capsule, a fibrous connective tissue structure that is attached to each bone just outside the area of the bone’s articulating surface. The bones of the joint articulate with each other within the joint cavity.

Friction between the bones at a synovial joint is prevented by the presence of the articular cartilage, a thin layer of hyaline cartilage that covers the entire articulating surface of each bone. However, unlike at a cartilaginous joint, the articular cartilages of each bone are not continuous with each other. Instead, the articular cartilage acts like a Teflon® coating over the bone surface, allowing the articulating bones to move smoothly against each other without damaging the underlying bone tissue. Lining the inner surface of the articular capsule is a thin synovial membrane. The cells of this membrane secrete synovial fluid (synovia = “a thick fluid”), a thick, slimy fluid that provides lubrication to further reduce friction between the bones of the joint. This fluid also provides nourishment to the articular cartilage, which does not contain blood vessels. The ability of the bones to move smoothly against each other within the joint cavity, and the freedom of joint movement this provides, means that each synovial joint is functionally classified as a diarthrosis.

Outside of their articulating surfaces, the bones are connected together by ligaments, which are strong bands of fibrous connective tissue. These strengthen and support the joint by anchoring the bones together and preventing their separation. Ligaments allow for normal movements at a joint, but limit the range of these motions, thus preventing excessive or abnormal joint movements. Ligaments are classified based on their relationship to the fibrous articular capsule. An extrinsic ligament is located outside of the articular capsule, an intrinsic ligament is fused to or incorporated into the wall of the articular capsule, and an intracapsular ligament is located inside of the articular capsule.

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. As forces acting on a joint increase, the body will automatically increase the overall strength of contraction of the muscles crossing that joint, thus allowing the muscle and its tendon to serve as a “dynamic ligament” to resist forces and support the joint. 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. A bursa (plural = bursae) is a thin connective tissue sac filled with lubricating liquid. They are located in regions where skin, ligaments, muscles, or muscle tendons can rub against each other, usually near a body joint (Figure 2). 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.
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.

Pivot Joint

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 3a). 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.

Hinge Joint

In a hinge joint, the convex end of one bone articulates with the concave end of the adjoining bone (see Figure 3b). 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.

Condyloid Joint

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 3e). 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.

Saddle Joint

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 3c). 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. This joint provides the thumb the ability to move away from the palm of the hand along two planes. Thus, the thumb can move within the same plane as the palm of the hand, or it can jut out anteriorly, perpendicular to the palm. This movement of the first carpometacarpal joint is what gives humans their distinctive “opposable” thumbs. The sternoclavicular joint is also classified as a saddle joint.

Plane Joint

At a plane joint (gliding joint), the articulating surfaces of the bones are flat or slightly curved and of approximately the same size, which allows the bones to slide against each other (see Figure 3d). The motion at this type of joint is usually small and tightly constrained by surrounding ligaments. Based only on their shape, plane joints can allow multiple movements, including rotation. Thus plane joints can be functionally classified as a multiaxial joint. However, not all of these movements are available to every plane joint due to limitations placed on it by ligaments or neighboring bones. Thus, depending upon the specific joint of the body, a plane joint may exhibit only a single type of movement or several movements. Plane joints are found between the carpal bones (intercarpal joints) of the wrist or tarsal bones (intertarsal joints) of the foot, between the clavicle and acromion of the scapula (acromioclavicular joint), and between the superior and inferior articular processes of adjacent vertebrae (zygapophysial joints).

Ball-and-Socket Joint

The joint with the greatest range of motion is the ball-and-socket joint. At these joints, the rounded head of one bone (the ball) fits into the concave articulation (the socket) of the adjacent bone (see Figure 3f). The hip joint and the glenohumeral (shoulder) joint are the only ball-and-socket joints of the body. At the hip joint, the head of the femur articulates with the acetabulum of the hip bone, and at the shoulder joint, the head of the humerus articulates with the glenoid cavity of the scapula.

Ball-and-socket joints are classified functionally as multiaxial joints. The femur and the humerus are able to move in both anterior-posterior and medial-lateral directions and they can also rotate around their long axis. The shallow socket formed by the glenoid cavity allows the shoulder joint an extensive range of motion. In contrast, the deep socket of the acetabulum and the strong supporting ligaments of the hip joint serve to constrain movements of the femur, reflecting the need for stability and weight-bearing ability at the hip.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

Synovial joints allow for smooth movements between the adjacent bones. The joint is surrounded by an articular capsule that defines a joint cavity filled with synovial fluid. The articulating surfaces of the bones are covered by a thin layer of articular cartilage. Ligaments support the joint by holding the bones together and resisting excess or abnormal joint motions.

Bursae are fluid-filled sacs that serve to prevent friction between skin, muscle, or tendon and an underlying bone. Three major bursae and a fat pad are part of the complex joint that unites the femur and tibia of the leg.

The six types of synovial joints allow the body to move in a variety of ways. (a) Pivot joints allow for rotation around an axis, such as between the first and second cervical vertebrae, which allows for side-to-side rotation of the head. (b) The hinge joint of the elbow works like a door hinge. (c) The articulation between the trapezium carpal bone and the first metacarpal bone at the base of the thumb is a saddle joint. (d) Plane joints, such as those between the tarsal bones of the foot, allow for limited gliding movements between bones. (e) The radiocarpal joint of the wrist is a condyloid joint. (f) The hip and shoulder joints are the only ball-and-socket joints of the body.

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Script:
  1. Synovial joints are the most common type of joints in the body.
  2. They are characterized by the presence of a joint cavity, inside of which the bones of the joint articulate with each other.
  3. The articulating surfaces of the bones at a synovial joint are not directly connected to each other by connective tissue or cartilage, which allows the bones to move freely against each other.
  4. The walls of the joint cavity are formed by the articular capsule.
  5. Friction between the bones is reduced by a thin layer of articular cartilage covering the surfaces of the bones, and by a lubricating synovial fluid, which is secreted by the synovial membrane.
  6. Synovial joints are strengthened by the presence of ligaments, which hold the bones together and resist excessive or abnormal movements of the joint.
  7. Ligaments are classified as extrinsic ligaments, intrinsic ligaments, or intracapsular ligaments.
  8. Some synovial joints also have an articular disc (or meniscus), which can provide padding between the bones, smooth their movements, or strongly join the bones together to strengthen the joint.
  9. Muscles and their tendons acting across a joint can also increase their contractile strength when needed, thus providing indirect support for the joint.
  10. Bursae contain a lubricating fluid that serves to reduce friction between structures.
  11. Subcutaneous bursae prevent friction between the skin and an underlying bone, submuscular bursae protect muscles from rubbing against a bone or another muscle, and a subtendinous bursa prevents friction between bone and a muscle tendon.
  12. Tendon sheaths contain a lubricating fluid and surround tendons to allow for smooth movement of the tendon as it crosses a joint.
  13. Based on the shape of the articulating bone surfaces and the types of movement allowed, synovial joints are classified into six types.
  14. At a pivot joint, one bone is held within a ring by a ligament and its articulation with a second bone.
  15. Pivot joints only allow for rotation around a single axis.
  16. These are found at the articulation between the C1 (or atlas) and the dens of the C2 (or axis) vertebrae, which provides the side-to-side rotation of the head.
  17. Hinge joints, such as at the elbow, knee, ankle, or interphalangeal joints allow only for bending and straightening of the joint.
  18. Condyloid joints are found where the shallow depression of one bone receives a rounded bony area formed by one or two bones.
  19. Condyloid joints are found at the base of the fingers (or metacarpophalangeal joints) and at the wrist (or radiocarpal joint).
  20. At a saddle joint, the articulating bones fit together like a rider and a saddle.
  21. An example is the first carpometacarpal joint located at the base of the thumb.
  22. Both condyloid and saddle joints are functionally classified as biaxial joints.
  23. Plane joints are formed between the small, flattened surfaces of adjacent bones.
  24. These joints allow the bones to slide or rotate against each other, but the range of motion is usually slight and tightly limited by ligaments or surrounding bones.
  25. This type of joint is found between the articular processes of adjacent vertebrae, or at the intercarpal joints of the hand and intertarsal joints of the foot.
  26. Ball-and-socket joints, in which the rounded head of a bone fits into a large depression or socket, are found at the shoulder and hip joints.
  27. Both plane and ball-and-sockets joints are classified functionally as multiaxial joints.
  28. However, ball-and-socket joints allow for large movements, while the motions between bones at a plane joint are small.
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