x-ray anatomy elbow

Question 1

what does the capitellum articulate with on a lateral elbow view

Answer 1

radial head

Question 2

what does the trochlea articulate with on an AP view

Answer 2

olecranon

Question 3

where are the anterior and posterior fat pads of the elbow located

Answer 3

in the coronoid (anterior) and olecranon (posterior) fossae

Question 4

an intra-articular fracture will cause leakage of blood and marrow into the joint to give a joint effusion, displacing the fat pads from the bone.

describe how you identify an abnormal fat pad / how is it different from normal

Answer 4

• normal anterior fat pad = sits closely/ Lucent line hugging anterior humeral cortex
• abnormal anterior fat pad = sail sign/ thorn sign, elevated anteriorly
• normal posterior fat pad = never seen radiographically
• abnormal posterior fat pad = visible posterior fat pad, due to large effusion

Question 5

normal fat pads dont exclude fracture

injury to elbow may rupture the joint capsule causing haemarthrosis to drain from joint, consequently raised fat pads won’t be seen

Question 6

what method can be used to identify a supracondylar fracture (fracture going above the condyles in elbow)?

Answer 6

NORMALLY, on lateral elbow, you can draw a straight line from anterior surface of humeral shaft and extend it, and it should pass through the 2nd 3rd of the capitellum (as they are articulating)

BUT

if the extended line is in the anterior/ 1/3 of the capitellum, then it shows the characteristic posterior displacement of the distal humorous due to a supracondylar fracture

Question 7

how can injury be identified using the correlation of the radial head and capitellum

Answer 7

normal = line drawn through radial head and neck extending into joint should pass through articulating capitellum

abnormal = line drawn through radial head and neck extending into joint does not pass through capitellum (can indicated dislocation of radial head)

Question 8

what are the 6 ossification centres progressively found till the ages of 12?

Answer 8

C = capitellum
R = radial head
I = internal /medial epicondyle
T = trochlea
O = olecranon
L = lateral epicondyle

Question 9

radial head/neck fractures can be very subtle, what are 3 things to look for

Answer 9

• linear lucency extending into joint
• cortical break at neck
• positive fat pad sign

Question 10

a coronoid process fracture can easily be misinterpreted as radial head fracture due to superimposition of coronoid process and radial head. (on lateral elbow projection)

Question 11

what artery and nerve can be injured if there is an anterior fracture displacement of the elbow

Answer 11

brachial artery
median nerve

Question 12

what is a monteggia fracture-dislocation of the elbow

Answer 12

fracture of proximal ulnar shaft AND dislocation of radial head

Question 13

if ossification avulsion is greatly displaced, it will lie within the joint where it may be mistaken for the trochlea ossification centre.

This is when knowledge of the correct sequence of appearance of the ossification centres is important and CRITOL can be used.

e.g if ossification centre of trochlea is seen and not medial epicondyle then avulsion of epicondyle must be suspected

(in kids)