Joints

Question 1

What is a joint?

Answer 1

A joint is an articulation between two or more bones

Question 2

State the trade off with joints with regards to joint range of motion?

Answer 2

There is always a trade-off between mobility and stability; the most mobile joints are the least stable

Question 3

What are fibrous joints?

Answer 3

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

Question 4

What are examples of fibrous joints?

Answer 4

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 5

What are primary cartilagionous joints?

Answer 5

Joined by hyaline cartilage and are completely immobile.

Examples - the first sternocostal joint (between the sternum and the first rib, xiphisternal joint (between the body of the sternum and the xiphoid process), and the epiphyseal growth plates of the long bones

Question 6

What are secondary cartilaginous joints?

Answer 6

Known as symphyses

Articulating bones are covered with hyaline cartilage with a pad of fibrocartilage between them

. Examples - the symphysis pubis (in the pelvis), intervertebral discs and the manubriosternal joint (between the manubrium sterni and the body of the sternum)

Question 7

Describe synovial joints?

Answer 7

Has a joint cavitiy containing synovial fluid which provides lubrication to articular surfaces - therefore they have a high degree of mobility

Question 8

What synovial joints are not covered with hyaline cartilage?

Answer 8

The acromioclavicular (between the acromion of the scapula and the clavicle), sternoclavicular (sternum and clavicle), and temporomandibular (skull and mandible [jaw bone]) joints are covered with fibrocartilage

Question 9

Describe articulating surfaces within a synovial joint?

Answer 9

Articulating surfaces within the joint are covered with hyaline cartilage which permits smooth, low friction movement and resists compressive forces because it acts as a shock absorber

Question 10

Describe the fibrous capsule of synovial joints?

Answer 10

The fibrous capsule surrounding the joint is composed of collagen in longitudinal and interlacing bundles.

Completely encloses the joint except from bursae forming synovial projections.

Stabilises the joint - permits movement but resists dislocation

Continous with the periosteum

Question 11

Describe the synovial membrane?

Answer 11

Thin highly vascularised membrane which produces synovial fluid.

Lines joint capsule and covers exposed osseus surfaces

Lines tendon sheets and bursae

Does not cover articular cartilage or intra-articular discs / menisc

Question 12

What are plane joints?

Answer 12

Occur when two flat surface slide against each other

Allow for smooth movement in several directions along a single plane

Question 13

What are condyloid joints?

Answer 13

Similar to plane joints but are like two bowls nested together.

Examples - the atlanto-occiptal joint at the base of the skull and the radiocarpal joint (between he radius and the carpal bones) of the wrist

Question 14

What are saddle joints?

Answer 14

Characterised by two bones that fit together like a rider in a saddle. This type of articulation allows motion in two different planes at the same time, together with a degree of sliding. An example is the 1st carpometacarpal joint at the base of the thumb.

Question 15

What are hinge joints?

Answer 15

Joints which allow for stable flexion and extension without sliding or deviation. Movement only takes place in a single anatomical plane. The elbow joint between humerus and ulna is a hinge synovial joint

Question 16

What are pivot joints?

Answer 16

Comprise a peg within a ring-shaped hole. They allow rotational motion without gliding. This type of joint allows for rotation without bending or sideways displacement. The atlanto-axial (joint between the first and second cervical vertebrae) is a pivot synovial joint and allows the head to rotate whilst maintaining the stability of the head on the neck

Question 17

What are ball and socket joints?

Answer 17

Allow stable movement in several directions without slippage. They are the most mobile type of synovial joint and often permit flexion-extension. abduction-adduction, lateral rotation-medial rotation and circumduction (which is a combination of the movements in the other planes). The hip and shoulder joints are examples of ball-and-socket joints

Question 18

What is a bursa?

Answer 18

A small sac of synovial fluid lined by a synovial membrane and contains a thin layer of synovial fluid

Provides a cushion between bones/tendon or muscules around a joint

Helps to reduce friction between the bones and allows free movement

Question 19

What are tendon sheaths?

Answer 19

Elongated bursae that wrap around a tendon and reduce the friction associated with movement of the tendon

Question 20

Describe synovial fluid?

Answer 20

Clear or pale yellow, viscous and slightly alkaline

Contains hyaluronic acid, lubricin, protinases and collagenases

Functions are to reduce friction, act as a shock absorber and to transport nutrients to the articular cartilage of the joint

Question 21

Describe the embrological development of synovaial joints?

Answer 21

A synovial joint is an interruption in the cartilage model of a bone.

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 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 articular capsule and supporting ligaments where they lie in contact with the developing joint