Structural classification of joints - based on the material binding the bones together

     1)fibrous: the articulating bones are held together by fibrous connective tissue. There is no joint cavity

     2)cartilaginous: the articulating bones are held together by cartilage. There is no joint cavity

     3)synovial: ligaments aid in supporting the articulating bones. There is a joint cavity

Functional classification of joints - based on the amount of movement allowed at the joint

     1)synarthroses: immovable joints

     2)amphiarthroses: slightly movable joints

     3)diarthroses: freely movable joints

     synovial fluid is produced by a highly vascular synovial membrane found on the inside of the joint capsule.

Discussion based on the structural classification of joints

Fibrous Joints

     Sutures - only found in the skull. A thin layer of dense fibrous connective tissue binds the articulating bones

     types of sutures:

          1) serrate - most common

          - interlocking articulations

          - example: sagittal suture

      2) Lap - bone overlaps bone

          - example: squamous suture between temporal and parietal bones

      3) plane - edges of articulating bones are fairly smooth.

          - example: maxillary suture between the two halves of the hard palate

      4) synostosis - only found during skull growth

          - between halves of the frontal bone

          - if fusion does not occur it is called a mytopic suture

     Syndesmoses - bones held together by collagenous fibers or interosseous ligaments

      - example: distal ends of tibia/fibula and radius/ulna

     Gomphoses - a “peg in a socket” fibrous joint

      - the only example of this type of joint in the human is a tooth in a bony alveolar socket

Cartilagenous joints

     Synchondroses - have a temporary plate of hyaline cartilage

         - example: epiphyseal plate. Once ossified it is called a synostosis.

     Symphyses - a pad of fibrocartilage separates bones.

          - example: symphyses pubis and intervertebral disc

Synovial Joints - in this type of joint the articulating bones are separated by a fluid containing joint cavity. These joints are freely movable and are functionally diarthroses. They have five distinguishing characteristics.

     1. articular cartilage - hyaline cartilage covers the ends of the opposing bones
     2. joint cavity - a potential space that is filled with lubricating synovial fluid
     3. articular capsule - a double membrane capsule surrounding the joint cavity. The inner layer is the synovial  embrane which is responsible for the production of synovial fluid. The out layer is a fibrous connective  issue that is continuous with the periosteum of the bone
     4. synovial fluid - the lubricating fluid of the joint. It is essentially a filtrate of blood plasma with hyaluronic  cid.
     5. reinforcing ligaments - surround the joint to give it extra strength. There are three types of reinforcing  ligaments
          a. intrinsic - are thicked parts of the joint capsule
          b. extrinsic - extracapsular ligaments
          c. intracapsular ligaments - deep to the joint capsule

     There are many factors that influence the stability of a synovial joint.
          1. the shapes of the articular surfaces
          2. the size and number of ligaments surrounding the joint
          3. the tone of the muscle acting across the joint

     There are generally 6 types of synovial joints:

         1) gliding - side to side, back and forth, some rotation
         2) hinge - bending in one plane
         3) pivot - rotation about an axis
             - example: proximal radius and ulna, atlas and axis
         4) condyloid - up and down, side to side
             - example: metacarpal/phalanges, radio-carpal joint
         5) saddle - base of thumb
             - example: trapezium with 1st metacarpal
         6) ball and socket - greatest range of movement of all joints
             -example: hip and shoulder
 

Discussion based on the functional classification of joints

Synarthroses immovable joints (sutures and synchondroses)

     Sutures - only found in the skull. A thin layer of dense fibrous connective tissue binds the articulating bones

         types of sutures:

          1) serrate - most common

              - interlocking articulations

              - example: sagittal suture

          2) Lap - bone overlaps bone

              - example: squamous suture between temporal and parietal bones

          3) plane - edges of articulating bones are fairly smooth.

              - example: maxillary suture between the two halves of the hard palate

          4) synostosis - only found during skull growth

              - between halves of the frontal bone

              - if fusion does not occur it is called a mytopic suture

    Synchondroses - have a temporary plate of hyaline cartilage

         - example: epiphyseal plate. Once ossified it is called a synostosis.

Amphiarthroses - limited movement

     2 types

          1) symphyses

          2) syndesmoses

     Symphyses - a pad of fibrocartilage separates bones.

          - example: symphyses pubis and intervertebral disc

     Syndesmoses - bones held together by collagenous fibers or interosseous ligaments

          - example: distal ends of tibia/fibula and radius/ulna
 

Diarthroses - freely movable joints with a joint capsule containing synovial fluid

 generally there are 6 types

     1) gliding - side to side, back and forth, some rotation
     2) hinge - bending in one plane
     3) pivot - rotation about an axis
         - example: proximal radius and ulna, atlas and axis
     4) condyloid - up and down, side to side
         - example: metacarpal/phalanges, radio-carpal joint
     5) saddle - base of thumb
         - example: trapezium with 1st metacarpal
     6) ball and socket - greatest range of movement of all joints
         -example: hip and shoulder

    In diarthroses the amount of movement at the joint is limited by 3 major factors

     1) the structure of the bones in the joint

     2) the strength and tautness of the associated ligaments, tendons, and joint capsule

     3) size, arrangement, and action of the muscles that span the joint

Do the bones of a diarthroses come in contact with each other? NO only the articular cartilages contact each other. Also see menisci in the knee

Bursa - pouchlike sacs filled with synovial fluid, usually found between muscles or where a tendon passes over a bone. Functions as a cushion.

Tendon sheath - modified bursa - surrounds and lubricates tendons of certain muscles

Movements

Movements can be angular or circular

     1) angular - increase or decrease the joint angle.

     the four types of angular movement are flexion, extension, abduction, and adduction.

     2) circular - movement covering an arc

      2 types

          1) rotation - movement of a bone around its axis, no lateral displacement, i.e. turning head side to side, pronation/supination

          2) circumduction - produces a circular or cone like pattern
 

Body movements as mechanics

Levers - magnify the force applied to a system to produce a greater force for movement

     there are 4 components of a lever
     1) a rigid bar
     2) a fulcrum (pivot)
     3) a resistance (object that is moved)
     4) force (effort)

     there are three types of levers

     1) 1st class lever - the fulcrum is positioned between the effort and the resistance

         i.e. skull at atlantooccipital joint.
         Weight of face and skull = resistance
         Neck muscles = effort

     2) 2nd class lever - resistance positioned between the fulcrum and the effort, i.e. wheelbarrow
     Calf muscles to raise up on toes

     3) 3rd class lever - effort lies between the fulcrum and the resistance
     This is the most common lever type in the body i.e. flexion at the elbow
        effort = biceps brachii
         fulcrum = elbow
         resistance = weight of forearm

Clinical

    Strain - stretching of the tendons surrounding a joint

    Sprain - tearing of the ligaments or tendons surrounding a joint. May see synovitis = inflammation of the joint capsule.

    Luxation - (dislocation) - derangement of the articulating bones that compose the joint

    Subluxation - partial dislocation

    Read about bursitis and tendonitis, and diseases of joints and treatments.

    One of the most common sports related joint injuries is found at the knee. Here we see the Terrible triad

     medial collateral ligament
     medial meniscus
     anterior cruciate ligament