1.1 - Radiology in MSK Flashcards
What is an X-ray
- Aka plain radiograph
- Generated by passage of X-rays through an object
- Detector plate turns dark when X-rays hit the plate
- The more X-rays detected, the darker the image appears
- Therefore the image depends on the number of X-rays penetrating the object and hitting the plate
- X rays are also absorbed by dense materials (those containing a lot of electrons) eg bone and metal. These X-rays do not hit the detector plate → appear white
What are the 4 main densities in x-rays
- Bone is most dense
- Soft tissue
- Fat
- Air is least dense
Advantages + disadvantages of x-rays
advantages
- Quick
- Readily available
- Inexpensive
- Good resolution of objects, allowing pathology to be seen
disadvantages
- Involves radiation → slight increased risk to cancer etc
- Poor soft tissue contrast resolution
What are the different types of fractures
- transverse where there is a break across the bone
- linear where there is a break down the bone
- oblique non displaced when there is a break across the bone at an angle
- oblique displaced break across bone at angle, and two fragments have shifted out of alignment
- spiral is like oblique but the fracture spirals round the perimeter of the bone
- greenstick are more common in kids. Crack on one side – not fully broken (more detail on separate card)
- comminuted where there are several breaks in the bone
What is the definition of a fracture
Complete or incomplete break in the continuity of the bone
What are greenstick fractures + why do they occur
- Most common in kid’s long bones
- One side of the cortex has broken but the other side hasn’t
- Therefore one side of cortex remains intact
- Results as a ‘bendy’ looking bone that has a crack/break on one side
- This is because the bones in kids are softer and more bendy
- Kids = ossification is not yet complete
Radiographic changes on kid’s x-rays seen during childhood development
- Bone starts of as cartilage, which gradually becomes calcified throughout development
- Cartilage is less dense than bone and cannot be easily seen on x-ray
- Therefore the epiphyseal plate will not show
- These will eventually fuse, so bone will be complete in adults
What are the two layers of the periosteum
- Periosteum forms around bones
- Inner layer secretes osteoprogenitor cells (ie osteoblasts)
- Outer layer allows for attachment of tendons, ligaments and muscles
What are the phases of fracture healing
inflammatory
- Haematoma formation
- Tissue death
- Inflammation + cellular proliferation
- Duration of hours – days
- No radiographic callus
reparative
- Callus formation
- First soft (fibrocartilaginous) callous formation ☞ scaffolding bone that is not as dense as normal, but forms in the interim
- Then consolidation ☞ hard callus formation
- Duration of days – weeks
- Callus formation is seen on x-rays
remodelling
- Eventually fracture line will become completely absorbed
- Remodelling of the callus
- Duration of months – years
What is CT
- Aka computed tomography or CAT scanning
- Uses radiation to build cross-sectional scans (slices) of the body
- Soft tissue detail is seen better than that on x-rays
- Can be performed very quickly on whole body to look for bone or soft tissue injury
- Subtle undisplaced fractures are best visualised on CT
- Slices can be reformatted to create multiplanar and 3D images
Pros + cons of CT
pros
- Very quick
- Can see huge amounts of detail
cons
- Radiation dose is relatively high
- Motion artefact if the patient moves
- Poor soft tissue detail compared with MRI (but better than x-rays)
Interpreting CT scans (colours)
- Density of body tissues is measured in Hounsfield units (HU)
- Air + fat appear black
- Water appears very dark grey, almost black
- Soft tissue appears as shade of grey
- Trabecular + cortical bone appear as white
What is CT windowing
Need to apply different ‘windows’ to assess different parts of anatomy for CT scanning. Allows us to see different elements in varying amount of detail
What is MRI
- Magnetic resonance imaging
- Utilises magnetic resonance of hydrogen nuclei in the body to produce high quality cross-sectional images of the body in any plane
- No use of ionising radiation
- Utilises radiofrequency pulses in presence of carefully controlled magnetic field
- Used for assessment of bones, joints and associated soft tissues
- Better than CT and x-ray for assessment of soft tissues
- Poor at showing the micro-architecture of the bone
- Two types of sequences: T1 and T2 (more detail on next card)
What is T1 and T2 sequencing on MRIs
These are for depicting anatomy differently
T1 is where fat appears white
T2 is where fat and fluid appears white. Aka a ‘fluid sensitive sequence’ so can see CSF fluid etc
