Episode 1 · MSK-01 · Follow-along slides

Shoulder Anatomy, Instability, and Impingement

Audio corrections
  • In the audio: A score of four or higher in an adult, or six or higher in a child, formally defines generalized joint hypermobility.Correct: By the 2017 hypermobile Ehlers-Danlos criteria, the adult threshold is 5 or higher out of 9 (puberty to age 50), 6 or higher before puberty, 4 or higher after 50. The older Brighton criteria used 4 or higher in adults.
  • In the audio: their recurrence rate approaches an astonishing 90 to 100 percent.Correct: Recurrence after non-op care of a first dislocation is ~85-90% under 20 or in young contact/overhead athletes, ~two-thirds under 30, and below a third after 30; near 100% only with repeat dislocations.

The written chapter is correct. Trust the text over the audio here.

Slide 1 of 50
Setup1 / 8 topics
No figure

Classic mechanism: forced abduction + external rotation (arm cocked at 90° abduction) → anterior dislocation

Apprehension sign: recreation of the at-risk position (abduction + ER) reproduces fear of re-dislocation

Welcome to the Musculoskeletal Medicine Series. Picture a 19-year-old quarterback. He drops back in the pocket, winds up for a deep pass,

arm cocked back when a linebacker hits him blindly from the side.

Oh, that's a brutal mechanism.

Right. His throwing arm is pinned at exactly 90 degrees of abduction, and it's rotated as far outward as it will physically go.

He feels a sickening pop. The arm goes completely dead. He ends up in the emergency department where they sedate him and reduce the joints.

Standard protocol.

Yeah. But two weeks later, he is back in your clinic terrified. He tells you that any time he reaches behind his head to grab something,

it feels like his shoulder's about to just slide right out again.

I mean, that single case is basically a compressed masterclass.

Exactly. The position of the arm at the moment of injury, the exam maneuver that reproduces his fear, the specific x-ray views that confirm what tore,

the goal of this deep dive is to unpack the entire shoulder for the boards.

It's so high yield.

We are going to look at the normal range of motion, the intricate web of stabilizers, the acromioclavicular joint,

and then tear it all down by exploring the two major clinical syndromes that will dominate your exam and your practice, instability and impingement.

It really is the perfect clinical vignette because it forces you to stop memorizing and start visualizing the underlying mechanics.

You know, you can't just know that the shoulder dislocated.

Right. You have to know exactly why it failed.

Exactly. Why the architecture failed in that specific split second.

Next figure · in 0:41

Fig 1.1 · Glenohumeral architecture

1 / 50