Applied Clinical Anatomy Joint Structures

Joints

an articulation, or the place of union or junction, between two or more rigid components

Components of Joints

• bone

• cartilage

• joint capsule

• ligament

• synovial fluid

Cartilage

• dense structure that resembles a firm gel made up of collagen and elastic fibers

• contains ground substance and proteins forming proteoglycans

• two layers: outer layer and inner layer

• it is avascular (no blood supply) and anerual (no nerve supply)

• there are 3 major types of cartilage

Outer layer of cartilage

provides protection and mechanical support

Inner layer of cartilage

important for growth and maintenance of cartilage

Hyaline Cartilage

• provides support and flexibility/. to different parts of your body

• found in structures like nose, ears respiratory system, epiphyseal plates, and on the ends of bones

• articular cartilage is a type of hyaline cartilage

Articular Cartilage Function

a type of hyaline cartilage that covers opposing bony surfaces in many joints

smooth out irregular bony contours resists repetitive loading and shearing forces, allows for sliding/gliding easily (low coefficient of friction)

Zones of Articular Cartilage

• superficial

• middle

• deep

• calcified

orientation: superficial = parallel for gliding joints; deep = perpendicular for joint compression

Articular Cartilage Nutritional Supply

• void of blood supply (avascular)

• nourishment comes from synovial fluid

• diffusion is how synovial fluid provides nourishment to the cartilage (like a sponge)

Diffusion

1. blood is supplied to the deep zone from the bony endplate

2. compression and distraction forces are created by movement at the joint (two bones moving)

3. this movement creates an exchange of nutrients passing from the deep zone into the articular cartilage

Note: lack of compression/distraction or prolonged compression can lead to degeneration because the cartilage does not get the nutrition. this means “motion is lotion” = movement is good = job security

Articular Cartilage Composition

1-7 mm thick covering of hyaline cartilage that covers load-bearing surfaces of a synovial joint; made up of collagen (mostly type II), proteoglycans (proteins-polysaccharides), and water (65-85% of total weight)

Fibrocartilage Function

• toughest of the 3 types of cartilage

• space fillers, increase congruency

• shock absorbers

• improve weight distribution. decreases point force

Fibrocartilage Composition

• dense bundles of collagen fibers (mostly type II)

• proteoglycans

• similar to hyaline/articular cartilage

Fibrocartilage Examples

• discs, meniscus, and labrum

• these can be found all over the body

Labrum

A fibrocartilage disk that attaches to the rim of the ball and socket joint. The inner surface of a labrum is coated with synovial, while the outer surface blends to capsule.

Labrum Function

• adds flexability to the edge of the socket = allows movement

• deepens the socket = provides stability

• serves as an attachment site for ligaments and the capsule

Elastic Cartilage Function

• flexible and resilient

• provide a matrix for definition

• resists deformation from repetitive movement

• ex: nose and ears

Elastic Cartilage composition

absence of elastic fibers

Joint Capsules

• fibrous tissue surrounds a synovila joint

• two distinct layers

Stratum Fibrosum

• outer layer of joint capsule

• tough fibrous layer that attaches to bone via Sharpey’s fibers

• highly innervated with mechanoreceptors and pain receptors

Stratum Synovial

• synovial membrane

• highly vascular

• poor innervation

• produces synovial fluid

Synovial Fluid

• made up of plasma proteins and hyaluronic acid

  • no blood in synovial fluid

• color is clear to pale yellow

• assits in joint lubrication

• provides nutrients to internal joint structures

Joint Classifications

• Fibrous Joints

• Cartilaginous Joints

• Synovial Joints

Synarthroses

• immoveable fibrous joints

• articulates bones are joined by fibrous tissue

Syndesmosis

the bones are joined by an interosseous ligament or a sheet of fibrous tissue

• example: interosseous membrane joining the forearm radius and ulna

• slightly moveable

Suture

the flat bones are very close together united by fibrous tissue interlocking across a wavy line

• example coronal suture

• essentially immoveable

Gomphosis

peg like process fits into a socket

• example: the articulation between the root of the tooth and the alveolar process

Amphiarthroses

• slightly moveable cartilaginous joints

• united by either hyaline cartilage or fibrocartilage

Synchondrosis (primary)

• the bony epiphysis and body are joined by an epiphyseal plate with hyaline cartilage

  • epiphyseal plates in developing long bones

  • between ribs and sternum (sternocostal joint)

Symphysis (secondary)

building tissue with fibrocartilage

• pubic symphysis

• disc between two spinal vertebrae

Diarthroses

• Freely movemable synovial joitns

• two bones are separated by the characteristics joint cavity but are joined by an articular capsule allowing for movement

• most common joint found in the body

Joint Capsule Components

• joint capsule

• joint cavity

• synovial membrane

• synovial fluid

• articular cartilage

Types of Synovial Joints

• plane

• pivot

• hinge/modified hinge

• saddle

• condyloid

• ball and socket

Plane Joint

• permit gliding or sliding movements between two flat surfaces

• degree of freedom: 1

• examples: zygoapophyseal joint

• acromioclavicular joint

Pivot Joint

• a rounded process of bones fits into a bony ligamentous socket permitting rotation

• uniplaner rotation

• degrees of freedom: 1

• examples: altanto-axil joint, proximal radio-ulnar joint

Hinge joint

• permit uniaxial motion (flexion and extension)

• degrees of freedom = 1

• example: humero-ulnar joint

Modified Hinge Joint

• hinge type of joint that allows for felxion/ extension but also limits the amount of rotation flexion

• permits flexion, extension, rotation

• degrees of freedom = 2

• example: tibiofemoral joint

Saddle Joint

• saddle-shaped heads permit movement in two different planes (biaxial)

• degrees of freedom = 2

• example: sternoclavicular joint, carpometacarpal joint (thumb)

condyloid joint

• allows for biaxial movement

• permits flexion/extension, abduction/adduction, and circumlocution

• degrees of freedom = 2

• example: metacarpophalangeal joint

Ball and socket

• a rounded head fits into a concavity, permitting movement in three planes (multiaxel)

• permits flexion/extension, abduction/adduction, and internal/external rotation

• degrees of freedom: 3

• examples: glenohumeral joint (shoulder), and femoroacetabular joint (hip)