Topic 3.2: Musculoskeletal - Articular system and joints

articular system - summary

composed of joints, associated ligaments and accessory structures

joint/ articulation - def

point of contact between two bones, bones and cartilage, or between bone and teeth

structural classification of joints (2)

1. Presence or absence of space between articulating bones -> synovial cavity

2. Type of connective tissue that binds bones together

cartilage - summary (5)

resilient, semi-rigid connective tissue composed of collagen and elastin fibres

Located in parts of skeleton where more flexibility is required → eg. costal cartilage of ribs

Nourished via diffusion -> no blood vessels, lymph or nerves

Younger people have more cartilage -> eg. endochondral ossification

Articular cartilage produces smooth surfaces for joints

types of cartilage - list (3)

hyaline → covers body articular surfaces

elastic → flexible

fibrocartilage → forms specialised in joints and contributes to articular surfaces

types of cartilage - hyaline (3)

most common type -> covers body articular surfaces

Model for early foetal skeleton

Moderate amounts of collagen

types of cartilage - elastic (2)

Forms discrete structures in external ear, auditory tube and parts of larynx

Contains bundles of elastic fibres

types of cartilage - fibrocartilage (3 + examples)

Mix of fibrous tissue and hyaline cartilage

Can withstand prolonged pressure

Substantial amounts of collagen

Eg. intervertebral disc, meniscus, labarum

types of joints - list (3)

1. synovial → moveable

2. fibrous → solid, minimal movement

3. cartilaginous → solid, minimal movement

types of joints - fibrous summary (3)

Bones united by fibrous tissue → no joint cavity

held together by dense irregular connective tissue

Degree of movement depends on length of fibres

types of joints - cartilaginous summary (2)

Bones united by hyaline or fibrocartilage -> lack a joint cavity

Provide strength and shock absorption

types of joints - synovial summary (3)

two bones united -> articulating surfaces of these bones are covered by hyaline cartilage and separated by a small space called the synovial cavity

The synovial cavity is surrounded by a two-layered structure -> inner surface = synovial membrane and outer = fibrous joint capsule

The joint is further supported by fibrous ligaments and various accessory structures

synovial joints - major features (3)

1. Articular cartilage

2. Joint capsule

3. Accessory structures

synovial joints - articular cartilage summary

Hyaline cartilage covers articulating surface of bones

synovial joints - joint capsule components (2)

Inner synovial membrane = highly vascular and produces synovial fluid

Outer fibrous membrane = dense connective tissue -> may thicken to form ligaments

synovial joints - accessory structure categories (2)

1. intra-articular

2. intra-capsular

both help to stabilise joint or provide other mecahnsims of support

synovial joints - intra-articular accessory structures summary (5)

Within the articular cavity and typically float within synovial fluid

Made of fibrocartilage

Extend inward from articular capsule and partially or completely divide it

Allow separate movements to occur simultaneously on each side of partition

Help absorb compression forces

synovial joints - intra-articular accessory structures examples (3)

menisci in knee

articular disc in skull

labrum → fibrocartialge lip that extends from edge of joint socket to deepend joint socket and increase area of contact between bones (ball and socket)

synovial joints - intra-capsular accessory structures examples list (2)

fat pad

bursae and tendon sheaths

synovial joints - intra-capsular accessory structures (fat pad summary)

Fat pad = outside of synovial joint cavity act as space fillers -> intracapsular but extra synovial

Helps spread synovial fluid

synovial joints - intra-capsular accessory structures (bursae and tendon sheath summary) (4 + examples)

Bursae and tendon sheaths = flattened fibrous sacs lined with synovial fluid -> lubricant to reduce friction

Tendon sheaths wrap around certain tendons as they pass through bony tunnels or near joints

Bursae not strictly part of synovial joint but resemble joint capsule

More numerous in joints with greater mobility

Eg . Shoulder and knee

synovial cavity - summary (3)

space within a joint

synovial membrane lines internal surface and does not extend over articular cartilage

synovial membrane secretes synovial fluid which fills cavity

purpose of synovial fluid (2)

Reduces friction by providing lubrication against cartilage-covered surfaces

Absorbs shock

composition of fibrous capsule that encloses synovial joint (3)

Composed of dense connective tissue made of collagen fibres

May be reinforced by ligaments or receive muscle attachments

Continuation of periosteum between bones

purpose of fibrous capsule of synovial joints

helps prevent joint from dislocating whilst also permitting movement

categorisation of synovial joints - summary

based on shape of their articular surfaces

categorisation of synovial joints - nonaxial movement (1)

plane joint

categorisation of synovial joints - uniaxial movement (2)

pivot joint

hinge joint

categorisation of synovial joints - biaxial movement (2)

condylar joint

saddle joint

categorisation of synovial joints - multiaxial movement (1)

ball and socket joint

types of synovial joints - plane joint

allow sliding or gliding movements when one bone moves across the surface of another

intercarpal joints

types of synovial joints - hinge joint

allow movement at right angles to the joint -> produces flexion/ extension

elbow joints, interphalangeal joint

types of synovial joints - pivot joint

allow movement in line with longitudinal axis od the bones -> produces rotation

proximal radioulnar joints (rotate hand)

types of synovial joints - condylar joint

allow movement around two access at right angles -> produces flexion, extension, adduction and abduction

metacarpophalangeal joints, wrist joints

types of synovial joints - saddle joint

allow movement around two aces at right angle (bones are saddle shaped) -> produces flexion, extension, adduction, abduction

carpometacarpal joints of thumb

types of synovial joints - ball and socket joint

allow movement around 3 axes (bones shaped like a ball-and-socket joint) -> produces flexion, extension, adduction, abduction, circumduction and rotation

shoulder joints, hip joints

stabilisation of synovial joints - structures and features (4)

Fit of bones together → Eg. elbow vs knee

Strength and tightness of joint capsule → Eg. shoulder vs hip

Additional ligaments → Eg. cruciate in knee

Muscles that wrap around or over joint → Eg. rotator cuff muscle in shoulder

types of fibrous joints - summary list (3)

1. sutures

2. syndesmosis

3. gomphosis

types of fibrous joints - sutures

thin layers of connective tissue called sutural ligament

only present in skull

types of fibrous joints - syndesmosis

occurs when two adjacent bones are linked by a ligament

length of ligament determines degree of movement

eg. syndesmosis between tibia and fibula

types of fibrous joints - gomphosis

short collect fibres running between the root of a tooth and its bony socket

only occur around teeth

types of cartilaginous joints - summary list (2)

1. synchondroses (primary)

2. symphyes

types of cartilaginous joints - synchondroses

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

Usually temporary structures

Eg. epiphyseal plates and hyaline cartilage

types of cartilaginous joints - symphyses

fibrocartilage connects two separate bones

Eg. intervertebral discs, pubic symphysis

factors affecting joint mobility - synovial joint ROM

determined by how articular surfaces contact one another

factors affecting joint mobility - general list (6)

1. Structure/shape of articulating bones

2. Strength and tension of joint ligaments

3. Arrangement and tension of muscles

4. Contact of soft parts

5. Hormones

6. Disuse

factors affecting joint mobility - structure/shape of articulating bones

determines how closely they fit together

Eg. ball and socket joints have greatest ROM because of how they fit together

factors affecting joint mobility - strength and tension of joint ligaments

different components of fibrous capsule are tense only when joint is in certain positions

Tense ligaments restrict ROM

Eg. ACL is taught and PCL is loos when knee is straight -> reverse when knee is bent

factors affecting joint mobility - arrangement and tension of muscles

muscle tension reinforces tension provided by ligaments

Eg. flexed thigh and extended knee restricts flexion of hip because of hamstring tension -> hamstring limits max flexion of hip joint

factors affecting joint mobility - contact of soft parts

movement limited by point at which one body surface contacts another

Eg. soft-tissue envelope of thigh limits max flexion of knee joint

factors affecting joint mobility - hormones

joint flexibility can be affected by hormones

Eg. relaxin production near end of pregnancy increases flexibility of fibrocartilage of pubic symphysis -> loosens ligaments between sacrum, hip bones and coccyxx to permit expansion of pelvis to assist in child brith

factors affecting joint mobility - disuse

ROM restricted if joint not used for an extended period

Reduced synovial fluid and flexibility of ligaments and tendons -> leads to muscle atrophy