2. Basic concepts in MSK - Joints

Question 1

What is a joint?

Answer 1

A joint is an articulation between two or more bones.

Question 2

What is the relationship between the range of movement and stability in joints?

Answer 2

Higher the range of movement, the less stable and more likely to be dislocated

Question 3

What are the three types of joints?

Answer 3

fibrous, cartilaginous, synovial

Question 4

What are fibrous joints? How stable/mobile are they?

Answer 4

Fibrous joints are united by collagen fibres. They have very limited mobility (i.e. poor range of movement) and high stability.

Question 5

Gives some examples of fibrous joints

Answer 5

• Sutures of the skull
• Inferior tibiofibular joint (at the ankle)
• Radioulnar interosseous membrane (in the forearm)
• Posterior sacroiliac joint (in the pelvis)
• Joint between roots of a tooth and the bone of the mandible or maxilla.

Question 6

What are cartilaginous joints? Where are they found? How are they categorised?

Answer 6

Joints that use cartilage to unite bones are called cartilaginous joints. They are typically found in the midline of the body and also in the epiphyseal plates of long bones.

Primary and secondary

Question 7

Describe primary cartilaginous joints. Give examples

Answer 7

• united by hyaline cartilage
• completely immobile

E.g. first sternocostal joint, xiphisternal joint, epiphyseal growth plates

Question 8

Describe secondary cartilaginous joints. Give examples

Answer 8

• aka symphyses
• articulating bones are covered with hyaline cartilage with a pad of fibrocartilage between them
• usually found in midline of the body

E.g. symphysis pubis in pelvis, intervertebral discs, manubriosternal joint

Question 9

Which joints are most mobile?

Answer 9

Synovial joints - less stable

Question 10

What is a synovial joint? Mobility?

Answer 10

Synovial joints have a Joint cavity containing synovial fluid (egg white). Lubricates articular surfaces therefore joints have high degree of mobility and widespread throughout skeleton.

Question 11

What covers the articulating surfaces of synovial joints? What are the exceptions?

Answer 11

Covered by hyaline cartilage except :
acromioclavicular joint
sternoclavicular joint
temporomandibular joint

covered with fibrocartilage

Question 12

What is the advantage of covering joints with hyaline cartilage?

Answer 12

Hyaline cartilage usually permits smooth, low-friction movement and resists
compressive forces within the joint by acting as a shock absorber.

Question 13

Describe the structure of the FIBROUS CAPSULE of synovial joints

Answer 13

• Composed of collagen in longitudinal and interlacing bundles.
• Encloses joint except where it is interrupted by synovial protrusions which form bursae.
• continuous with the periosteum covering the surface of the adjacent bones.

Question 14

Function of fibrous capsule?

Answer 14

The capsule stabilises the joint; it permits movement but resists dislocation

Question 15

Describe the structure of SYNOVIAL MEMBRANE

Answer 15

• Thin highly-vascularised membrane
• Produces synovial fluid
• Lines the joint capsule and covers any exposed osseous surfaces. It also lines tendon sheaths and bursae.
• Does not cover articular cartilage or intra-articular discs / menisci.

Question 16

What does the shape of synovial joint dictate?

Answer 16

The shape of a synovial joint dictates the type of movement that the joint can perform

Question 17

What are the types of synovial joints?

Answer 17

There are plane joints, hinge joints, saddle joints, condyloid (or
ellipsoid) joints, pivot joints and ball and socket joints

Question 18

What are plane joints?

Answer 18

• where two flat surfaces slide against each other
• allow for smooth movement in several directions along a single plane

E.g. carpal bones of wrist, tarsal bones of foot, facet joints between vertebral articular processes of the spine

Question 19

What are condyloid joints?

Answer 19

• two elliptical bowls nested
• One of the key features that differentiates condyloid joints from ball-andsocket joints is that their elliptical shape prevents rotation from occurring

E.g. Atlanto-occiptal joint at the base of the skull and the radiocaral joint of the wrist

Question 20

What are saddle joints?

Answer 20

• two bones that fit together
• allows motion in two different planes at the same time with a degree of sliding

E.g. the first carpometacarpal joint at the base of the thumb

Question 21

What are hinge joints?

Answer 21

• allow for stable flexion and extension without sliding or deviation
• Movement only takes place in a single anatomical plane

E.g. elbow joint

Question 22

What are pivot joints?

Answer 22

• comprise a peg within a ring-shaped hole
• allow rotational motion without gliding/ bending/ sideways displacement

E.g. Atlanto-axial joint between the first and second cervical vertebrae allows the head to rotate whilst maintaining the stability of the head on the neck

Question 23

What are ball and socket joints?

Answer 23

• allow movement in several directions without slippage
• most mobile synovial joint
• permit flexion-extension, abduction-adduction, lateral rotation-medial rotation, circumduction

E.g. hips and shoulders

Question 24

What are synovial joints surrounded by that maintains the blood supply regardless of the position of the joint?

Answer 24

Synovial joints are surrounded by a plexus of arteries

Question 25

Which articular surfaces are not lined by synovial membrane?

Answer 25

The knee joint contains intra-articular fibrocartilaginous menisci and thejoints between the vertebrae contain intervertebral discs. These intraarticular structures do not have a synovial covering.

Question 26

what factors will influence the range of motion of individual joints? Think about both health and disease.

Answer 26

* Structure or shape of the articulating bones * Strength and tension of the joint ligaments * Arrangement and tone of muscles around the joint * Apposition of neighbouring soft tissues (i.e. are they restrictingmovement?) * Effect of hormones (e.g. relaxin relaxes pelvic joints toward the end of pregnancy) * Disuse of a joint

Question 27

Articular cartilage is avascular, and the fibrous capsule and ligaments have a poor blood supply so how do the articulating cartilaginous surfaces received blood?

Answer 27

Synovial membrane has rich blood supply so maintains nutrient flow via synovial fluid to articulating cartilaginous surfaces.

Question 28

How do synovial joints develop?

Answer 28

• The synovial joints will form between the adjacent cartilage models, in an area called the joint interzone. • Cells at the centre of this interzone region undergo apoptosis (programmed cell death) to form the joint cavity, • while surrounding mesenchyme cells from the perichondrium will form the periosteum where they lie in contact with bone, and the joint capsule • supporting ligament lie in contact with the developing joint

Question 29

What happens when there is incomplete apoptosis of cartilage in synovial joint development?

Answer 29

What happens when there is incomplete apoptosis of cartilage in synovial joint development?

Question 30

example of first class levers?

Answer 30

Neck joint

Question 31

Example of second class levers?

Answer 31

Ankle joint

Question 32

example of third class lever

Answer 32

elbow joint

Question 33

What are first class levers?

Answer 33

Fulcrum is in the centre Load is at one end Effort is applied on the opposite side of the fulcrum to the load e.g scissors

Question 34

What are second class levers?

Answer 34

When the load is located between the fulcrum and the effort that is applied to lift the load e.g wheelbarrow

Question 35

What are third class levers?

Answer 35

The effort is applied between the fulcrum and the load | e.g forceps

Question 36

Define olecranon

Answer 36

Pointy bit of elbow