Joints
description
Transcript of Joints
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Joints
Dr. Anderson GCIT
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Joints
• Where two or more bones meet
• Function– Connection (ligaments)– Movement (muscles)– Protection (joint
capsule)
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Joint ClassificationStructural FunctionalFibrous – synostoses (immovable), syndesmoses (variable movement), gomphoses (peg-in-socket)
Synarthroses – bones don’t move relative to each other
Cartilaginous – synchondroses, symphyses
Amphiarthroses – “slightly” moveable
Synovial – articulating bones are separated by a fluid-filled cavity (most joints)
Diarthroses – freely moveable
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Sutures
• Fibrous joints, slightly mobile in youth, immobile as adult (e.g. cranial sutures)– Limited mobility allows
brain to grow during development
– Immovability as adult serves as a protective function
Top of Skull (newborn baby)
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Syndesmoses
• Bones connected exclusively by ligaments
• Movement varies according to length of the ligaments forming the joint, e.g.:– Very limited movement
between tibia and fibula– Very pronounced
movement of ulna around radius
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Gomphoses
• Peg-in-socket, fibrous joint
• Only example is the teeth in their alveolar cavities connected by the periodontal ligament
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Cartilaginous Joints
• Articulating bones are united by cartilage– Synchondroses and symphyses
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Synchondroses
• Cartilage that unites two bones (such as the epiphyses to the diaphyses in the long bones of children and young adults)
• E.g. Epiphyseal plates
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Symphyses
• Where articulating bones are lined with cartilage, which is fused to a pad or plate of fibrocartilage
– E.g. – intervertebral discs, pubic symphysis
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Synovial Joints• Features
1. Articular cartilage – covers opposing bone surface2. Synovial cavity – space that contains synovial fluid3. Articular Capsule – provides tensile strength and covers all surfaces not lines with cartilage4. Synovial fluid – provides joint lubrication, released from the cartilage itself during activity (weeping lubrication)5. Reinforcing ligaments6. Nerves and blood vessels -
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Joint Structure
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Articular Discs (Menisci)
• Fibrocartilage pads that partially or completely divide the synovial cavity – (Knee, jaw meniscus)
• Improve the fit of some articular surfaces in the joint
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Bursae and Tendon Sheaths
• Fibrous connective tissue that serves as a pliable “ball bearing” for some joints (e.g. shoulder) and closely packed tendons (e.g. wrist)
• Bursa rolls in opposing direction of movement
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What holds joints together?
• Articular Surfaces -Deeply fitting articulations more stable than shallow ones
• Ligaments – “cables” of dense regular connective tissue that hold the joint together– Relatively little stretch (can snap)
• Muscle Tone – low levels of contractile activity – more tone = more stable joints
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Synovial Joint Structure
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Joint Movements• Originates from muscle contraction (of course)
• Degree of joint movement is called “range of motion”
• Three main types– Gliding– Angular– Rotation
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Gliding joints
• Simplest movement– One or more flat
(usually) bone surfaces glide over another• Wrist bones• Ankle bones• Between vertebrae
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Angular Movement• Flexion – pulling the joint angle closed
• Extension – opening the joint angle– Hyperextension – greater than normal extension
• Abduction – moving a limb away from the median line of the body
• Adduction – moving a limb toward the median line of the body
• Circumduction – moving a limb in a cone-shaped path in space
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Rotation• Turning of a bone
around its long axis– Medial rotation –
turning toward the midline
– Lateral rotation – turning away from the midline
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Supination and Pronation
• Refer to movement of radius around the ulna
• With arms down at sides:– Supination is a lateral rotation of the palms (palms
anterior or up)– Pronation is a medial rotation of the palms (palms
face posteriorly, radius and ulna cross each other, forming an ‘X’)
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Ankle and Foot Movement
• Dorsi flexion – moves foot up (superiorly)
• Plantar flexion – moves foot down (inferiorly)
• Inversion – sole of foot turns medially
• Eversion – sole turns laterally
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Jaw movements
• Protraction and retraction – jutting jaw out and bringing it back, respectively
• Elevation and Depression – Moving a body part superiorly or inferiorly (e.g. jaw)
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Synovial Joint Types• Plane (Gliding) – allow only short, gliding movements
(wrist and ankle)• Hinge (One angular direction) - allows motion only along a
single plane (flexion and extension only)• Pivot (Rotation) – allows the bone to rotate around its axis• Condyloid (All angular directions)– Oval articulating
surfaces that permit movement in all directions• Saddle (All angular directions)– both articular surfaces
have a convex AND a concave side that articulate together• Ball-and-Socket - (Universal movement) allows movement
in all directions, including limited rotation
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Knee Joint
• Very Complex– 4 bones• Femur, tibia, fibula,
patella
– Ligaments often injured in sports or accidents
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Knee Injuries• Cruciate Ligaments– ACL (anterior)– PCL (posterior)
• Deep in joint cavity of knee (intracapsular)– Can tear and separate
femur from the tibia– Most often happens
when the knee is rotated during full extension
Torn ACL (Arthroscopic view)
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Knee Injuries• Most dangerous
injuries are lateral blows to the fully extended knee– Torn menicsi– Torn collateral
ligaments• Tibial (Medial or
MCL)– outside hit• Fibular (Lateral or
LCL)– inside hit
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Jaw Joint Problems• Jaw Joint (mandible and
mandibular fossa) is called the tempero-mandibular joint (TMJ)
• Loosely connected – has a greater range of motion than other hinge joints– Condyle of mandible can
move out of the fossa, (anterior disarticulation)