Anterior Shoulder Dislocation

History:  Acute left shoulder pain.

So maybe there was discussion of possible dislocation in the EMR.  They just didn't think it was relevant to your radiographic search.

When evaluating an acute shoulder XR,  look for Hill Sachs and Bankart injuries compatible with recent or prior anterior glenohumeral dislocation. 
 

Hill Sachs - impaction of the posterosuperior humeral head.  Look "behind" the greater tuberosity for concave or vertical lines of sclerosis (dotted red line) with adjacent relative lucency in the posterosuperior humerus where you would expect to see the continuation of the humeral head sphere (blue line).   I have found it helpful to start at the apex of the humeral head and follow the line posteriorly. 

This is a beautiful AP examination - they have the humerus internally rotated, making it much easier to see the expected posterior silhouette of the humeral head sphericity.  You won't get many that look this good. Soak it in.

Bankart Injuries- inspect the anterior to inferior glenoid margins and the adjacent tissues for tiny fractures (red arrow).  A true osseous Bankart injury is a fracture through the anteroinferior articular surface, so it should be a bone chunk like demonstrated below.  Not uncommonly, you can see the faint ring of density associated with labrum and/or periosteum avulsion injuries which correlate with non-osseous Bankart injuries. 

Chart from Rad Assistant. Please don't memorize this chart unless you are taking a MSK board exam at some point in your future. 

Source: https://radiologyassistant.nl/musculoskeletal/shoulder/instability

Another example:  Follow up on a known anterior dislocator. 

Small but still a concave sclerosis with adjacent lucency.  Depending on the ordering crowd, a CT or MR is likely coming to prove or disprove your hypothesis, but at least throw it out there if the story fits.

See, a little magnet-based verification never hurts. 

On the same case, there is a really nice example of a subtle Bankart injury.  Appreciate the faint displaced curve of density that has the expected contour of the glenoid. 

Of course,  have all the disastergrams you can get too.  It's good to see end of spectrum disease too so you can extrapolate and also be thankful it's not your shoulder. 

A brief taste of what it looked like at the time of most recent dislocation.

For funsies, here is a nice simultaneous anterior dislocation in a seizure patient.  Of note seizure does not automatically mean posterior dislocation; posterior dislocations are just often associated with seizures. 

Post reduction below.  Another great example of a vertical or concave sclerotic line (red dashes) interrupting the normal spherical portion of the posterosuperior head with adjacent relative lucency (highlighter) where the impacted bone used to be. Can even see some faint avulsion stuff along the anteroinferior margin of the glenoid (blue arrow)

Apologies for the long and winding road.

Hill Sachs

• Start with your eyes at the humeral head apex on the best internal rotated view (usually AP) and follow that line peripherally.  Follow the sphere. Get excited if you see a sudden, angular drop in the line trajectory
   
• Look through the greater tuberosity for a vertical or concave sclerotic line with adjacent lucency.

Bankart type injuries:

• Bone chunks or semi-circular faint sclerosis just peripheral to the anterior or inferior glenoid margin. Trace that line with your eyes.

Have a great holiday weekend!

Some articles below. 

Hill Sachs: https://radiopaedia.org/articles/hill-sachs-defect?lang=us

Bankart: https://radiopaedia.org/articles/bankart-lesion?lang=us