Articular Systems & Joints

What is the articular system made of?

Joints, associated ligaments, & accessory structures

What is a joint/articulation?

A point of contact between two bones, bones & cartilage, or bone & teeth

How are articular systems classified structurally?

• The presence or absence of space b/w the articulating bones (i.e. synovial cavity)

• Type of connective tissue that binds bone together (i.e. cartilage)

What is the articular system?

The system by which bones are jointed to one another by flexible connective tissue, permitting a degree of movement

What is cartilage?

A dense network of resilient, semi-rigid connective tissue of collagen & elastin fibres located in parts of the skeleton where more flexibility is required

• e.g. costal cartilage of ribs

How is cartilage nourished, & what is the implication of this in relation to injury?

Via diffusion; they are avascular & aneural

• Difficult to heal after injury b/c there is no blood flow & ready supply of nutrients

State the three types of cartilage

• Hyaline

• Elastic

• Fibrocartilage

What is hyaline cartilage? Provide some examples

The most common type of cartilage, covering bony articular (epiphyseal) surfaces

• Model for early foetal skeleton

• Moderate amounts of collagen

• Examples:

  • anterior ends of ribs

  • nose

  • parts of larynx

  • trachea

  • windpipe

  • branchial tubes

What is elastic cartilage? Provide some examples

Flexible cartilage which forms discrete structures in the external ear, auditory tube, & parts of larynx

• Contains bundles of elastic fibres → permits strength & elasticity while maintaining shape

• Examples:

  • Ear

  • Epiglottis (separates the windpipe & oesophagus)

What is fibrocartilage? Provide some examples

Cartilage which forms specialised joints, contributing to articular surfaces

• Mix of fibrous tissue + hyaline cartilage

• Can withstand prolonged pressure

• Substantial amounts of collagen

• Supportive structure

• Greatest strength & rigidity

• Examples:

  • intervertebral disc

  • pubic symphysis

State the 3 types of joints/articulations & they key properties

1. Synovial: moveable

2. Fibrous: solid, minimal movement

3. Cartilaginous: solid, minimal movement

What is a synovial joint?

Bones united by a joint/articular cavity, involving many associated structures

• articulating bones are joined by an articular capsule, which spans & encloses an articular cavity)

What is a fibrous joint?

Bones united by fibrous tissue, with the degree of movement dependent on the length of the fibres

What is a cartilaginous joint?

Bones united by hyaline or fibrocartilage, which provides strength & shock absorption

What are the 2 broad categories of solid joints?

• Fibrous joints

• Cartilaginous joints

What are the 3 types of fibrous joints?

• Sutures

• Syndesmosis

• Gomphosis

What is a suture joint?

A thin layer of dense, irregular connective tissue called a structural ligament, only present in the skull

What is a syndesmosis joint?

Where two adjacent bones are linked by a ligament, with the length of the ligament determining the degree of movement

What is a ligament?

A sheet of fibrous tissue

What is a gomphosis joint?

Short collagen fibres which run between the root of a tooth & its bony socket

• Joined by a periodontal ligament

• Specialised type of syndesmosis joint (b/c they are united by a ligament)

Which joints do and don’t have a joint cavity?

• Synovial joint: do have a joint cavity

• Fibrous & cartilaginous joints: do not have a joint cavity

What are the 2 main types of cartilaginous joint?

• Synchondroses (primary)

• Symphyses (secondary)

What is a synchondroses (primary) joint? Provie an example

A bar or plate of hyaline cartilage between two ossification centres of a developing bone

• Example: epiphyseal plate

What is a symphysis (secondary) joint? Provide an example

Fibrocartilage connecting two separate bones, permitting limited movement

• Example: pubic symphysis

Describe the 3 major features of synovial joints

• Articular cartilage: hyaline cartilage covers the articulating surfaces of bones

• Joint capsule:

  • Inner synovial membrane: highly vascular, → synovial fluid

  • Outer fibrous membrane: dense connective tissue which may thicken to form ligaments

    • Collagen fibres

    • Extension of periosteum of articulating bones

• Accessory structures

How are synovial joints different to synchondroses joints?

In synchondroses joints, the articulating surfaces are joined together by cartilage. In synovial joints, the articulating surfaces are just covered by cartilage, but are not joined by it

What is the synovial cavity lined with?

The synovial membrane which does NOT extend over the articular cartilage

• Secretes viscous synovial fluid from the synovial cells which fills the cavity & from interstitial fluid filtered from blood plasma

• Rich blood supply

What is the purpose of synovial fluid?

• Reduces friction at the joint --> provides lubrication against cartilage-covered surfaces

• Absorbs shock

• Produces O2 & removes CO2 from the cells in the articular cartilage (b/c cartilage is avascular)

What is the fibrous capsule of a synovial joint?

Dense irregular tissue made up of collagen fibres which encloses the synovial joint

• May be reinforced by ligaments or receive muscle attachments

What are intracapsular structures?

Structures located inside the fibrous capsule of a synovial joint

What does the fibrous capsule of a synovial joint attach to?

The periosteum of the articulating bones

State the 6 types of synovial joints

1. Plane

2. Hinge

3. Pivot

4. Condyloid

5. Saddle

6. Ball & socket

What is a plane joint? Provide an example

Articulating surfaces are flat/slightly curved, allowing for sliding or gliding movements when one bone moves across the surface of another

• Example:

  • Intercarpal joints b/w bones of the wrist

  • Sternoclavicular joint b/w the sternum & clavicle

  • Vertebrocostal joints b/w the ribs & the vertebrae

What is a hinge joint? Provide an example

Surfaces of the articulating bones are rounded, allowing movement at right angles to the joint (producing flexion/extension)

• Examples:

  • Ankle joints

  • Elbow joints

What is a pivot joint? Provide an example

Articulating surfaces are usually a rounded/pointed surface articulating with a ring (formed partly by another bone & partly by a ligament), allowing for movement in line with the longitudinal axis of the bones (rotation)

• Examples:

  • Atlantoaxial joint (neck) b/w first 2 vertebra → head rotation

  • Radioulnar joint - rotates palm of hand from facing upwards → downwards

What is a saddle joint? Provide an example

One bone is saddle shaped & the other bone fits into that saddle, allowing for movement around two axes at right angles (flexion/extension & adduction/abduction)

• Examples:

  • Carpometacarpal joint

What is a condyloid/ellipsoid joint? Provide an example

Convex oval projection of one bone fits into an oval shaped depression of another bone, allowing for movement around two axes at right angles (flexion/extension & abduction/adduction)

• Examples:

  • Metacarpophalangeal

What is a ball-and-socket joint? Provide an example

Ball-like surface of one bone fits into the cap-like depression of another bone, allowing for movement around multiple axes

• Flexion/extension, adduction/abduction, circumdation & rotation

• Examples:

  • Glenohumeral joint

  • Shoulder

  • Hip

What determines the stability of a synovial joint?

• How well the bones fit together

  • E.g. elbow vs knee

• How strong & tight the joint capsule is

  • E.g. shoulder vs hip

• Presence or absence of additional ligaments

  • E.g. cruciates in knee

• The presence or absence of muscles that wrap around/over the joint

  • E.g. rotator cuff muscles in the shoulder

What are accessory structures?

Structures that help stabilise the joint or provide other mechanisms of support

What are intra-articular structures?

Accessory structures which are located within the articular cavity & float within the synovial fluid

What are the 3 main types of intra-articular structures?

• Menisci

• Articular discs

• Labra

What are menisci?

• Cresent-shaped pads of fibrocartilage which are found inside some synovial joints, extend inward from the articular capsule & partially or completely divide it

• Allow separate movements to occur simultaneously on each side of partition

• Help absorb compression force

• Help the fit between the articulating bones

What are articular discs?

• Disc-like structures which are made of connective tissue & fibrocartilage

• Divide the synovial cavity into 2 separate chambers → allow for 2 separate movements in the same joint space

  • Binds strongly to the inside of the fibrous membrane (outside of the synovial membrane) of the joint capsule

• Separation of discs → different movements occur in each of the spaces

• Found in the jaw (temporomandibular joint)

What are labra?

• Wedge-shaped structures typically located at the outer margins of ball-&-socket joints (hip & shoulder joints)

• Made of fibrocartilage

• Enlarges the articulating surfaces of the joints → deepens the joint socket & ^ the contact SA b/w the articulating bones

What are extracapsular structures?

Located outside the fibrous capsule of a synovial joint

What are the 2 main types of extracapsular structures?

• Fat pads

• Bursae & tendon sheaths

What are fat pads?

• Sit b/w the synovial & fibrous joint capsules

• Provide cushioning for moving joints

• Accumulation of adipose tissue

• Act as space fillers

• Actually intracapsular, but are extrasynovial

• Help spread synovial fluid

What are bursae & tendon sheaths?

• Flattened sac-like structures/bags of lubricant → situated to alleviate friction in the joints

  • Tendon sheaths wrap around certain tendons as they pass through bony tunnels or near joints → ensures they are protected when rubbing against the rough exterior

• Typically located in greater numbers in joints with greater mobility

What is bursitis?

Acute or chronic inflammation of a bursa, caused by repeated exertion at a joint

Are bursae strictly part of the synovial joint?

No, but they are quite similar in structure to joint capsules

• Walls = outer fibrous membrane filled w/ synovial fluid

• Outer membrane produces the synovial fluid

What is the range of motion (ROM) of a joint?

The range, measured in degrees of a circle (360 degrees) through which the bones of a joint can be moved

What are the 6 factors affecting the ROM of a joint?

• Structure/shape of the articulating bones

  • Complementary → interlocking → rotation

• Strength & tension of joint ligaments

  • Tension restricts ROM & direct movement

• Arrangement & tension of muscles

  • Muscle tension reinforces the restraint places on a joint by its ligament

• Contact of soft spots

• Hormones

  • E.g. relaxin produced by placenta & ovaries during pregnancy → loosens & ^ flexibility of fibrocartilage of pubic symphis

• Disuse

  • decreases the amount of synovial fluid & flexibility of ligaments & tendons around the joint

What are the 2 key properties of cartilage that particularly suit it to various skeletal roles?

• Semi-rigidity; somewhat flexible → allows for movement

• Different components for different joints (i.e. different proportions of collagen, elastine & fibrous tissue)

What is the key benefit of hyaline cartilage being avascular & aneural?

• Avascular:

  • Low friction surface

  • ^ compression resistance

  • Optimal nutrition through diffusion

  • Support of high-water content

• Aneural:

  • No pain during motion

  • Protective against damage from internal structures

  • Control of posture & movement

What is synovitis?

Thickening of the synovium → excess synovial fluid → stifness, warmth & swelling

What is the position called in which a joint has maixmum stability?

Close-packed position

What is the function of collateral ligaments at hinge joints?

Thickenings of capsule @ either side of hinge joint → prevent excessive side-to-side motion

What type of ligament configuration allows the greatest range of movement whilst also being more likely to get sprained?

A ligament that is arranged in discrete parts