Chapter 9 - Joints

Joints

• Rigid elements of the skeleton meet at joints or “articulations”

• Structures enable resistance to crushing, tearing, & other forces

• Hold bones together

• Allow rigid skeleton some flexibility

Classifications of Joints

• Can be classified by function or structure

  • Functional classification - based on amount of movement allowed

    • Synarthroses - immovable; common in axial skeleton

      • ex) sutures are synarthrotic joints

    • Ampiarthroses - slightly movable; common in axial skeleton

    • Diarthroses - freely movable; common in appendicular skeleton/limbs (includes all synovial joints)

  • Structural classification - dependant on the material used to bind the articulating bones  together

    • Fibrous (adjoined by collagen fibers)

    • Cartilaginous (adjoined by cartilage)

    • Synovial (adjoined by a joint capsule lined w/ synovial fluid)

Fibrous Joints

• Bones are connected by fibrous connective tissue

• Most are immovable or slightly movable

• 3 different types

1. Suture - held together w/ very short, interconnecting fibers; found only in the skull

2. Syndesmosis - held together by a ligament  (fibrous tissue can vary in length but longer than sutures) 

3. Gomphosis - held together by periodontal ligament; connects the tooth to its corresponding alveolus

Cartilaginous Joints

• Bones are united by cartilage

• 2 different types

  • Synchondroses - united by hyaline cartilage

    • ex) epiphyseal plate

    • ex) joint between first rib and manubrium

  • Symphyses - united by fibrocartilage

    • ex) intervertebral discs 

    • ex) pubic symphysis

Synovial Joints

• Most movable type of joint

• All are diarthroses

• Joint cavity (unique to synovial joints)

• Synovial fluid

  • Occupies the joint cavity

  • A viscous fluid similar to raw egg white

  • A filtrate of blood

  • Made from fibroblasts that also secrete glycoprotein molecules

• General structure

  • Articular (hyaline) cartilage - line the articulating bones

    • Absorbs compression

  • Articular capsule - encloses the joint cavity

    • 2 layers 

      • synovial membrane (deep) - loose CT 

        • lines joint capsule & covers internal joint surfaces

        • where the filtered synovial fluid is made

      • fibrous capsule (superficial) - dense irregular CT

  • Reinforcing ligament - dense regular CT

    • Usually found at the thickened portion of the fibrous capsule

  • Highly vascularized and innervated

Aberrations/Diseases Occuring In Synovial Joints

• Arthritis  - general term referring to chronic inflammation or abnormality in the normal structure of the joint 

  • Osteoarthritis - “wear and tear”

    • Cartilage degradation, causing pain due to bones to rubbing against one another 

    • More local

  • Rheumatoid arthritis

    • More systemic

    • Cartilage degradation occurs all over the body

Movements Allowed by Synovial Joints

• 3 basic types of movement caused by skeletal muscles contracting

  • Gliding 

  • Angular movement

  • Rotation 

Gliding Joints

• Flat surfaces of 2 bones slip across each other

• Gliding occurs between

  • Carpals (proximal & distal row)

  • Articular processes of vertebrae

  • Tarsals

Angular Movements

• Movements change the angle between bones & apply to the limbs

Rotation

• Turning movement around a bone’s long axis

• Only movement allowed between atlas and axis vertebrae

• Occurs at the hip and shoulder joints

  • Lateral rotation - turns the limb away from the midline

  • Medial rotation - turns the limb toward the midline

Special Movements

• Elevation - lifting a body part superiorly

  • Ex) Lifting the mandible to close the mouth

• Depression - moving the elevated part inferiorly

  • Ex) Opening the mouth

• Protraction - non angular movement anteriorly

• Retraction - non angular movement posteriorly

• Supination -  rotating laterally FROM anatomical position TO posterior position

  • Radius & ulna will end up parallel

• Pronation - rotating medially FROM posterior position TO anatomical position

  • Radius will crossover ulna to form the letter x

• Opposition - thumb moves across the palm to touch the tips of other fingers

  • Due to saddle joint between metacarpal 1 and trapezius

• Inversion - sole of the foot turns medially

• Eversion - sole of the foot turns laterally

• Dorsiflexion - lifting superior surface of the foot towards the shin

• Plantar flexion - depressing the foot away from the shin

Synovial Joints Classified by Shape of Articulating Surfaces

• Plane joints

  • Articular surfaces are flat planes

    • Ex) Intertarsal and intercarpal joints

  • Only short gliding movements are allowed

    • Movements are nonaxial

    • Gliding does not involve rotation around any axis

• Hinge Joint

  • Cylindrical end of one bone fits into a trough on another bone

  • Angular movement is allowed in one plane

  • Elbow, ankle, and joints between phalanges

    • Ex) trochlea fits into the trough shaped trochlear notch of the ulna

  • Movement is uniaxial - allows movement around one axis only (only flexion and extension, no others)

• Pivot Joints

  • Rounded end of a bone fits into the ring of another bone & encircled by a ligament

  • Movement as uniaxial - rotating bone only turns around its long axis

    • Ex) Proximal radioulnar joint

    • Ex) Joint between atlas and axis

• Condyloid Joints

  • One egg shape end fits into oval concavity of another bone

    • Ex) metacarpophalangeal joints (the knuckles)

  • Allows moving bone to travel

    • Back & forth - flexion/extension

    • Side to side - abduction/adduction

  • Classified as biaxial - movement occurs around 2 axes

• Saddle joints

  • Each articular surface has concave & convex surfaces

  • Shaped like a saddle

  • Classified as biaxial

    • Back & forth - flexion/extension

    • Side to side - abduction/adduction

    • Ex) first carpometacarpal joint

      • allows opposition of the thumb

• Ball-and-socket joints

  • Spherical head of one bone fits into round socket of another

  • Classified as multiaxial - allow movement in all axes

    • Ex) Shoulder and hip joints 

Glenohumeral Joint - Ball & Socket

• Diarthrotic joint

• Glenoid labrum - rim of fibrocartilage at the glenoid cavity

  • Deepens the glenoid cavity

• Fibrous articular capsule

• Ligament joining the bone to bone

  • There to help stabilize the joint

• The rotator cuff is made up of 4 muscles and their associated tendons

1. Subscapularis - attached to subscapular fossa

2. Supraspinatus - attached to supraspinous fossa

3. Infraspinatus - attached to infraspinous fossa

4. Teres minor - runs along the lateral border

• Rotator cuff injuries are common shoulder injuries

• 2 main ligaments for stabilizing the joint

  • Coracohumeral ligament - between coracoid process of scapula and humerus

    • Strengthens the articular capsule

    • Supports the weight of the upper limb

  • Glenohumeral ligament - between glenoid cavity and humerus

Elbow Joint - Hinge

• Diarthrotic joint

• Trochlea of humerus fits into trochlear notch of ulna (humeroulnar joint)

• Only movement allowed is flexion and extension

• Ligaments

  • Annular ligament - loops around the head of the radius

  • Radial collateral ligament - a.k.a. lateral collateral ligament

  • Ulnar collateral ligament - a.k.a. can be called medial collateral ligament)

Hip Joint - Ball & Socket

• Ligaments

  • Iliofemoral ligament - upside down V shape

    • Mostly visible anteriorly

  • Ishiofemoral ligament - spiraling structure

    • Found posteriorly

  • Pubofemoral ligament - triangle shape

    • Found inferiorly, anteriorly

  • Ligament of the femoral head (ligamentum teres) - runs from fovea capitis to the acetabulum

• Acetabular labrum - rim of fibrocartilage on the acetabulum

  • Serves to deepen acetabulum and stabilize the hip joint

Knee Joint - Modified Hinge Joint

• “Modified” because they dont quite fulfill the requirements of a regular hinge joint

  • Cylindical part of femur doesnt have a trough to fit into

  • Posterior bending (flexion) and anterior straightening (extension) movement

• Ligaments

  • Fibular collateral ligament (a.k.a. lateral collateral ligament)

  • Tibial collateral ligament (a.k.a. Medial collateral ligament)

  • Anterior cruciate ligament (ACL) - runs FROM back of femur TO front of tibia

    • Prevents tibia from sliding forward and femur from slipping backward

    • When ruptured, the knee joint becomes highly unstable and the articular cartilage starts to degrade (osteoarthritis)

  • Posterior cruciate ligament (PCL) - runs FROM femur TO the back of tibia

    • Prevents tibia from sliding posteriorly and femur from forward displacement

  • Patellar ligament - Joins patellar to the tibial tuberosity

    • May appear longer on model, but that’s because it’s showing the quadriceps tendon attached to it as well

• Menisci - C shaped discs that help w/ stabilization

  • Lateral meniscus

  • Medial meniscus

  • Depressed on the inside to accommodate the femoral condyles

  • Prevent side to side slipping of the bones

  • Even out the distribution of compressive load