Joints
description
Transcript of Joints
Joints
Dr. Anderson GCIT
Joints
• Where two or more bones meet
• Function– Connection (ligaments)– Movement (muscles)– Protection (joint
capsule)
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
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)
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
Gomphoses
• Peg-in-socket, fibrous joint
• Only example is the teeth in their alveolar cavities connected by the periodontal ligament
Cartilaginous Joints
• Articulating bones are united by cartilage– Synchondroses and symphyses
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
Symphyses
• Where articulating bones are lined with cartilage, which is fused to a pad or plate of fibrocartilage
– E.g. – intervertebral discs, pubic symphysis
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 -
Joint Structure
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
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
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
Synovial Joint Structure
Joint Movements• Originates from muscle contraction (of course)
• Degree of joint movement is called “range of motion”
• Three main types– Gliding– Angular– Rotation
Gliding joints
• Simplest movement– One or more flat
(usually) bone surfaces glide over another• Wrist bones• Ankle bones• Between vertebrae
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
Rotation• Turning of a bone
around its long axis– Medial rotation –
turning toward the midline
– Lateral rotation – turning away from the midline
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’)
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
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)
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
Knee Joint
• Very Complex– 4 bones• Femur, tibia, fibula,
patella
– Ligaments often injured in sports or accidents
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)
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
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)