Chapter 8: Joints

Joints (articulations)

The site where two bones meet, may or may not allow for movement

Mobility

• Allow movement of various body parts

• Different types of joints allow for different amount of type of moevement

Stability

• Hold skeleton together

• Prevents damage to internal structures (soft tissues)

Structural Joints (general)

Type of tissue that connects bones at articulating surface

• Fibrous, cartilaginous, synovial

Functional Joints (general)

Amount of movement allowed by joint

Synarthroses (no movement)

• Most stable joint type

Amphiarthroses (limited movement)

• Most stable joint type

Diarthroses (free movement)

Fibrous Joints (general)

Joints composed of collagen fibers of connective tissue

• No joint cavity present

• Mostly synthroses, few amphiarthroses allowed

Fibrous Joints: Syndesmoses

Bones are connected to one another only by ligaments:

• Bands of fibrous tissue that join bone to bone

• Movement allowed by joint depends on length of ligament bands

Fibrous Joints: Gomphoses

ONLY joint type that does not join bone to another bone

Joins tooth to alveolar socket in jaw bone

• Periodontal Ligament

  • Joins the bone of the mandible/maxilla to the tooth

• Fibers of joint are very short, providing very limited movement

Cartilaginous Joints (general)

Bones joined by cartilage

• Synarthroses and Amphiarthroses allowed

No joint cavity

Cartilaginous Joints: Synchondrses

Bones united with a plate of hyaline cartilage

Mostly synarthroses

• Ex: Epiphyseal plate in long bones and costal cartilage

Cartilaginous Joints: Symphyses

Fibrocartilage joins bone

• Some movement allowed but limited

Ex: Intervertebral joints

Cartilaginous Joints: Synovial

Possess a joint cavity

• Diarthroses allowed

Most joints in the body are this

Synovial Joints: Articular Cartilage

Hyaline cartilage covering bone ends

Synovial Joints: Joint Cavity

Small space between articulating bones

Synovial Joints: Articular Capsule

Two layered capsule that encloses the joint cavity

Fibrous Layer

• Outer layer that is continuous with periosteum of bones

Synovial Joints: Synovial Membrane

Inner layer that lines joint cavity

Synovial Joints: Synovial Fluid

Slippery fluid occupying space in joint capsule and articular cartilages

When Joint is not active

• Fluid is viscous

When joint is active

• Fluid becomes thin and watery

Synovial Joints: Reinforcing Ligaments

Bandlike ligaments that join articulating bones

• Dont heal quickly due to decreased blood flow

• Double jointed means reinforcing ligaments are longer than normal so they have more mobility

Synovial Joints: Innervation and Vascularization

Innervation

• Joints supplied with sensory nerve fibers

  • Allows joint to know if it is being pushed/pulled on or if the joint is moving in the right way

Vascularization

• Rich blood supply to joints

  • Keeps tissue healthy

  • You have to have blood supply to produce synovial fluid and to keep the rest of the joint structure healthy

Associated (Maybe) with Synovial Joints: Bursae

Flattened sacs that contain a small amount of synovial fluid

• Found in frequently used joints such as hips/elbows, etc

Reduces friction between adjacent structures by rolling with movement

Associated (Maybe) with Synovial Joints: Tendon Sheath

Elongated bursa that wraps completely around a tendon subjected to frequent friction

• Tendons that sit very close to each other need protection from friction

Joint Stability: Muscle Tone

Tendons attach muscle to bone and often wrap around over joints

• This braces the joint and holds it in place

Muscle tissue is always in a slightly contracted state even at rest so it constantly pulls on a tendon

• MOST important stabilizing feature

Nonaxial Movement

No axis around which movement takes place

• Bones that articulate have flat surfaces

Movement Allowed

• Grinding

Joint Shape

• Plane (flat surface) joint

• Ex: intercarpal, ankles, wrists

Uniaxial Movement

Allows for movement of joint around a single axis

Movement allowed

• Flexion OR extension OR rotation

Joint Shapes

• Hinge Joint

  • Ex: between humerus and ulna

  • Looks and operates similar to a door hinge

• Pivot Joint

  • Ex: Radius and ulna

Biaxial Movement

Allows for movement of a joint around two axes

Movement Allowed

• Flexion/extension AND adduction/abduction

Joint Shapes

• Condylar Joint

  • Ex: Knuckle

• Saddle Joint

  • Ex: Base of thumb

Multiaxial Movement

Allows for movement of a joint around multiple axes

Movement Allowed

• Flexion/extension, abduction/adduction, AND rotation

Joint Shape

• Ball and socket

  • Shoulder and hip joints

Examples of Synovial Joints: TMJ

Where the mandible articulates to the temporal bone

Joint Shape

• Modified hinge joint

Articular disc divides synovial cavity into superior and inferior portions

• Superior allows for lateral excursion (side to side)

• Inferior allows for elevation/depression

Examples of Synovial Joints: Glenohumeral (shoulder) joint

Where the humerus articulates with the scapula

Most freely moving joint in the body, but needs some stability

• Coracohumeral ligament (posterior of joint)

• Glenohumeral ligament (anterior of joint)

  • Less of these ligaments = more likely to dislocate due to less stability

Glenohumeral (shoulder) joint: Rotator Cuff

4 Muscles (and their tendons) encircle the joint

• Most important

Can be damaged fairly easily (overstretched)

Glenohumeral (shoulder) joint: Glenoid Labrum

Rim of fibrocartilage around glenoid fossa

Provides some stability

• Provides depth to glenoid fossa so it allows the bone to sit in more deep

Examples of Synovial Joints: Elbow Joint

Where the humerus articulates with the ulna

Stability provided by

• Close fit of trochlea (on humerus) and trochlear notch (on ulna)

• Muscle and tendon of arm muscles wrap around elbow to provide further flexibility

Ulnar collateral ligament (medial side) and radial collateral ligament (lateral side) prevent lateral movement

Examples of Synovial Joints: Coxal Joint

Where the head of the femur articulates with the os coxa

Stability provided by articular surfaces and strong ligaments

• Acetabulum of os coxa has acetabular labrum to future deepen socket

Ligaments of Articular Capsule

• Iliofemoral Ligament

• Pubofemoral Ligament

• Ichnogenera Ligament

Ligamentum Teres

• Ligament of the head of the femur

  • Uses fibrous tissue to anchor the tissue in place

  • There is nervous system supply

Examples of Synovial Joints: Knee Joint

Single cavity shared by 3 separate joints

• Femoropatellar Joint (1)

  • Between patella and femur

• Tibiofemoral Joint (2)

  • Between femur and tibia

  • 1 medial, 1 lateral

Muscle and tendon reinforces joint with several ligaments

Important Stabilizing Structures of Knee Joint: Menisci

Thin layer of fibrous cartilage at outer margins of tibiofemoral joints that forms ridges along outer margins of joint

• Functionally similar to the labrum (slightly depending the tibiofemoral joint to prevent it from coming apart)

Problem with this is that it only attaches to the tibia at one part and the rest are loose cartilage tissue

• Very fast lateral movements, bones bend oddly, flaps will flip outside and will tear since it is loosely hanging

Important Stabilizing Structures of Knee Joint: Extras-capsular and Capsular Ligaments

Prevent hyperextension of knee

• In between tibiafemoral joints (inside the knee)

Important Stabilizing Structures of Knee Joint: Intracapsular Ligaments (cruciate ligaments)

Secure articulating bones, prevent displacement and hyperextension of knee

ACL

• Prevents forward sliding of tibia

• Attaches to anterior portion of tibia

• Smaller, more easily damages

PCL

• Prevents backwards sliding of tibia and forward sliding of femur

• Attaches to posterior portion of tibia