Medical Imaging

Week 6: Describe the main imaging modalities used in MSK imaging and be able to interpret normal and abnormal standard diagnostic images (e.g. X-ray) of the upper and lower limbs

radiographic appearance description

1. attenuation

   • radiographs: radiolucent, semi-radiopaque, radiopaque

   • MRI: void, intermediate signal intensity, high signal intensitiy

   • ultrasound: anechoic (black), hypoechoic, hyperechoic (bright)

2. radiological characteristics (fracture classification)

   • comminuted

   • spiral

   • rotation

   • linear

   • transverse

   • oblique

   • compression

   • displaced (and how)

   • greenstick

   • stress

   • pathological

   • open

3. location

describe the scan + indication

loss of alignment of the 3rd metatarsophalangeal joint

describe the scan + indication

Loss of joint space (fusion of bones) indicating cartilage loss at the 1st metatarsophalangeal joint with osteophytes (sign of OA)

Loss of joint space (fusion of bones) indicating cartilage loss at the lip of the femur with osteophytes

(indicating OA, sometimes also formation of cysts - erosions are not a feature)

normal shenton’s line

• lined formed by anatomical landmarks in a normal AP scan of a hip

intra-capsular vs extra-capsular classification

• intracapsular: involving the head or neck of femur

  • fracture through neck of femur (most common in younger patients)

    • mechanism of trauma: axial loading during high force trauma (feet on dashboard)

    • if hip is abducted position

• extracapsular: involving the femur excluding head or neck of femur

  • fracture through the trochanters

comminuted fracture (radiolucent) of the left proximal femur

intertrochanteric fracture (between the two trochanters)

extra-capsular classification

intracapsular fracture

approach to lumbar xrays

ABCCP

1. Alignment

   • follow corners of vertebrae from one level to the next

2. Bones

   • Cortical outline, VB height, integrity of pedicles & transverse pro.

3. Cartilage

   • IVD grad

     Increase in height from sup-inf. L5/S1 narrower

4. Coverage

   • ensure entire lumbar spine is visible in each scan

5. Posterior Elements

   • check elements (Pedicles, lamina and Pars inter

     Articularis)

Lumbar three column model

• Divides the spine into three columns: anterior, middle, and posterior 

• Used to determine the stability of thoraco-lumbar spine fractures 

• severity depends on how many columns are implicated

• If spinal instability is suspected further imaging with CT or MRI should be considered

2. ANTERIOR (Stable):

   • Anterior compression injury

     e.g. compression fractures (most common)

   • between the anterior longitudinal ligament to the middle of the vertebral body

3. MIDDLE (unstable):

   • 'Burst' fracture (vertebral body crushed in all directions) due to axial loading

   • between middle of vertebral body to posterior longitudinal ligament

4. POSTERIOR (unstable):

   • Flexion-distraction fracture (caused by severe compression or rotation)

   • between posterior longitudinal ligament to spinous process

   • spinal cord implicated

Anterior compression injury

e.g. compression fractures (most common)

displacement

• broken bone ends are no longer aligned

• with reference to the distal/lower segment of the bone:

• medial vs lateral, posterior vs anterior

  • e.g. medial displacement of femur

25 y/o male, punched a wall, description?

Radiolucent oblique fracture of the neck of the 5th metacarpal (“boxer fracture”)

Greenstick Fracture

comprises a bend in the bone on one side and a visible break in the bone cortex on the other side, which is incomplete

due to the pliable nature of bones in children, complete fractures are less common

TORUS/BUCKLE FRACTURE

referred to as a circumferential buckle fracture, commonly of the distal radial metaphysis. No distinct fracture line, but subtle deformity of buckle of the cortex may be evident. torus = protuberance in latin

Pathological midshaft medial displaced fracture of the right femur

black spot (lower cortical density): lytic bone region

(therefore important to look at before and after fractures)

Joint effusion

• abnormal fluid acculuation within the synovial compartment due to infection, inflammation or trauma

• ‘fat pad’ sign due to a joint effusion - observed on many abnormal elbow radiographs

  • extra fat deposited to help protect the bone

• relevant in adults: head of radius fracture

• relevant in children: supracondylar fracture

• → fat pads get pushed out, become visible on an X-ray due to swelling and displacement of fat pads → obscure the fracture visibility

63 year old female:

acute pain and swelling in her distal forearm after falling on her outstretched hand.

History:

• postmenopausal

• bone mineral density from forearm indicated osteoporosis

Physical Examination:

• deformity of distal forearm

• posterior displacement of distal radius 

• Acute tenderness and swelling of distal forearm/wrist 

• Paraesthesia over lateral palm /digits & weakness in thumb opposition

Radiolucent distal radius fracture with posterior and medial displacement

Paediatric patient

• fall from the monkey bars, landing on extended hand

• very painful elbow

• Swelling and bruising is evident in the area

• Unable to make an ‘OK’ sign (flexion of thumb IPJ and index finger DIPJ)

• Weak radial pulse

radiolucent supracondylar fracture of the medial epicondyle (damage to the median nerve)

65 year old male:

• fall onto left side while getting out of bed

• AP radiograph of the hip

• Prior DXR (bone density) scan showed marked osteoporosis

(extracapsular classification)

radiolucent intertrochanteric fracture of the left proximal femur

or

radiolucent oblique fracture through the greater trochanter and neck of the femur on the left side

57-year-old man:

• found face-down outside a bar

• poorly responsive and unable to provide a history

• scattered abrasions over the arms and legs

• swelling of the right hand

radiolucent ‘boxer’s fracture’/fracture + lateral displacement of the head of the fifth metacarpal

ultrasound: skeletal muscle

Hypoechoic fiber bundles interspersed with hyperechoic stromal connective tissue

ultrasound: fascia

Thin, hyperechoic (bright) structure

ultrasound: cortical bone

Hyperechoic (bright) linear line with posterior acoustic shadowing due to complete reflect

(high density of molecules, with hard material properties)

ultrasound: cyst

anechoic

ultrasound: nerve

'Honey-comb' appearance in transverse view; 'train track' in longitudinal view

ultrasound: articular cartilage

Anechoic (black) layer overlying the periosteum

ultrasound: tendon

• comprise multiple individual, longitudinally oriented, parallel collagen fibers that are tightly bundled, resulting in a fibrillary pattern on ultrasound

• This results in the characteristic hyperechoic appearance of tendons when the US beam is oriented 90 degrees to the tendon

rotation

• bone breaks due to a twisting or rotational force

• evident by superimposition (overlap) of structures

colles fracture

• common extra-articular fracture

  • bone break that does not involve the articular surface (the surface of the bone that forms part of a joint)

• occurs as a result of a fall on an outstretched hand

• posterior displacement

• medial angulation of the distal radius (tilting of the distal fragment of the radius bone toward the ulna)

left scaphoid fracture

• pain in the anatomical snuffbox → median nerve damage

• numbness in the radial three digits of the hand

attenuation of any fracture

radiolucent

occult fracture

not readily visible on standard X-rays, often requiring further imaging like MRI for diagnosis

might see joint effusion

AP image

anteroposterior

xray machine in front of patient, film receptor behind patient’s back

(often used when patient is supine)

e.g. kidney scan

PA scan

posteroanterior

xray machine behind patient’s back, film receptor in front of patient

e.g. heart scan, hand scans

A 22 year old woman presents to her local hospital following an electric scooter accident. She presents with significant pain and weakness, limiting movement at the shoulder and elbow.

radiolucent, oblique fracture of the shaft of the left humerus, with medial displacement

A 17 year old elite gymnast presents to her GP with a 5-month history of lower back pain, which increases in intensity upon hyperextension.

Lateral lumbar-spine x-ray reveals translation of a vertebral body due to a bilateral pars interarticularis fracture.

Which vertebral body and which columns are abnormal?

radiolucent fracture is seen at the pars interarticularis (facet joint) of L4 and L5, causing anterior dislocation (spondylolisthesis) of the vertebral body (L5 in this case)

Middle column: posterior shift at the L5 vertebral level

This would also stretch/displace the anterior longitudinal ligament due to posterior translation in the anterior column

pars interarticularis fracture

• pars interarticularis (pars) lies between the superior and inferior articular process at each zygapophyseal/facet joint

• usually L5 level

• bilateral: spondylolisthesis

• unilateral: spondylolysis

spondylolisthesis

bilateral pars interarticularis fracture at the L4/L5 level

disc has slipped posteriorly

stretches/displaces the anterior longitudinal ligament due to posterior translation in the anterior column

spondylolysis

unilateral pars interarticularis fracture

disc has not moved

A 30 year old woman fell off a push-bike onto the left arm. A lateral radiograph shows elbow joint effusion, indicated by the 'sail sign' (yellow dot) of the anterior fatpad.

• anterior fat pad is visible and raised

• posterior fat pad visible

• Their visibility is a result of an elbow joint effusion

• adult → occult fracture of the radial head

posteroanterior hand radiograph of a 63-year-old female who fell

• colles fracture

• Radiolucent, linear (?? i think this is meant to be transverse) fracture of the distal radius, with rotation

  • rotation evident by superimposition (overlap) of structures

• Angulation and displacement cannot be commented on without a lateral view

sail sign

• anterior fat pad, usually concealed within the coronoid fossa, becomes elevated and takes on a triangular shape

• indicates joint effusion

• In adults: sign of an occult fracture of the radial head

• in children: supracondylar (distal humerus) fracture

A six year old boy presents to the emergency department following a fall from the monkey bars.

Clinical examination demonstrates tenderness, significant swelling and deformity of the left elbow.

distal humerus fracture (comminuted)

damage to median nerve

suprapatellar bursitis (likely not examined)

(T2 MRI)

prepatellar bursitis

A round high signal intensity structure, consistent with a fluid given the T2 weighted MRI, is located superficial to the patella ligament

(inflammation within the prepatellar bursa)

(prepattar = most common)