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5 key things MRIs are good at
- high contrast resolutino
- soft tissue (tendon and ligament) detail and pathology -- better than CT
- can detect occutlt fractures not seen on radiographs or CT
- abnormal edema or fluid
- structural abnormalities (gaps, discontinuity in tendons and ligs)
main skill of CTs
- high spatial resolution (can differentiate things close together, find tiny lesions)
- better at this than both MRI and x-ray
MRI standard planes
planes for shoulder MRI
obtain 3 planes: typically axial, sagital, and coronal
- BUT for shoulder to optimize detection of rotator cuff tears get
- coronal oblique (parallel to long aspect of supraspinatus),
- sagital oblique (perpendicular to long axis of supraspinatus),
fat and fluid in T1
fat is bright, fluid is dark
fat and fluid in T2
fat is bright, fluid is bright
fat sat T2 aka STIR, how's the fat and fluid
fat is dark, fluid is bright (reverse of T1)
8 things on your mental checklist when you're reading an x-ray
- ID normal bones
- look for cortical continuity
- look at alignment
- look for extra densities or lucencies within or outside bone
- look at soft tissues (for swelling or effusions)
- look at adjacent joints
- compare with prior studies if there are any
- if there's still concern, consider ordering CT or MRI
3 arcs to look for in a hand x-ray
arc I: proximal articular surface of scaphoid, lunate, triquetrium
- scaphoid lunate triquetrium pisiform
- trapezium trapezoid capitate hamate
arc II in the hand x-ray
distal articular surface of scaphoid, lunate, triquetrium
arc III in hand x-ray
proximal articular surface of capitate & hamate
how does hook of hamate look in an x-ray?
it's a circle inf to the 4th + 5th fingers, denser around the boarder of the circle
hand x-ray lateral view, what 4 bones should line up?
radius, lunate, capitate, third metacarpal
6 signs of fractures on a radiograph (starred slide)
- cortical discontinuity or deformity
- radiolucent fracture lines
- abnormally white or dense areas representing overlapping bony fragments or impaction of bone
- extra or unexplained fragments of bone
- soft tissue swelling / joint effusions
- callus formationin healing fracture
gamekeeper's thumb aka rabbit hunter's thumb aka skier's thumb
- disruption of UCL of first MCP joint
- (the UCL holds the metacarpal to the first phalanx on the ulnar side)
displacement of UCL superficial to aponeurosis of adductor pollicis
mallet finger is due to what coming unattached?
- avulsion of the lateral slips of the extensor digitorum
- leads to extension of the DIP
There's a high rate of AVN w scaphoid fracture. Why?
blood supply to scaphoid begins distally and runs proximally, so the prox pole can get AVN
(if high clinical supsicion of fracture (trauma w pain over snuff box) wrist should be cased and MRI or repeat x-rays taken in a week)
fat pad sign in elbow
- darkness surrounding joint (radiolucency ant and/or post) on a lateral radiograph of elbow bent 90 degrees
- the ant fat paid is normally seen as a faint line that is more radiolucent than adjoacent muscle and is parallel to the anterior distal humerus. Posterior fat pad is normally pressed into the deep olecranon fossa by the triceps tendon and anconeus muscle is invisible
- suggesting an occult fx and effusion
how can you id olecranon bursitis in an x-ray?
lateral view x-ray will show massive soft tissue swelling post/inf to olecranon
essex lopresti fracture-dislocation
fracure of radial head + dislocation of radio-ulnar joint (interosseous membrane disruption)
- fracure of ulna and dilocation of prox radius (nightstick fracture)
- if dislocation is missed can lead to AVN
- Galeazi = fx of radius and dislocation of distal ulna (less common)
Y-scapula x-ray thing
- it's a side view, where the acromion is to the left, the coracoid is to the right, and the bottom of the scap contributes to make a Y
- the humeral head should sit right in the center. If it is shifted toward acromion or coracoid you know it's post or ant dislocation
axillary view of GH joint
the corocoid looks high with the acromion low, and you can tell if it's ant/post dislocation based on where the head is rel. to those two
Hill Sachs lesion
fx of sup-lat hum head from collision w glenoid rim when hum is dislocated ant
- supero-lateral aspect of humeral head
- best seen in AP internal rotation plain film
- inferior aspect of glenoid labrum is injured due to repeated ant shoulder dislocations
- may req. CT to visualize
for which bones would you typically get just 2 views of x-rays?
- long bones (arm, leg, forearm, calf)
- get 2 orthoganal views (90 degrees to each other)
- AVP + lat
x-rays, when would you typically get 3 views: AP, lat, oblique
joints - wrist, hand foot, ankle, elbow, knee
what 3 x-rays to typically get for trauma to shoulder
what 2 x-rays to typicaly get for non-traumatic shouulder
AP views in IR & ER
typical pelvis & hips 2 x-ray views?
if lunate is pushed anteriorly and angulated volarly (as in one of the slides) it can impinge on what nerve?
what's happening in a "perilunate dislocation" (one of his slides)
the lunate stays with the radius while the rest of the carpals sublux dorsally & proximally
AP view of shoulder, how to know if the hum is IR or ER
- in ER you can see the crest of the greater tub on the lateral side of the hum head
- in IR the head just looks round
in posterior dislocation of shoulder, what motion goes with the post mvmnt?
what usually causes posterior dislocation (w/IR) of shoulder?
convulsions, not trauma
what hits when in post dislocation of humeral head?
ant head -- post glenoid fossa
why is it hard to diagnose post dislocation of hum head on x-ray?
can mimic adhesive capsulitis or frozen shoulder ... need to get a CT or MRI to check
what percent of shoulder dislocations are ant? post? inf/luxatio?
- ant: 95-97%
- post: 2-4%
- luxatio/inf: 0.5%