July 2012 - Donna Magid, M.D., M.Ed.
Shoulder for Pragmatists
“Shoulder’ is actually several joints including glenohumeral (GH), acromioclavicular (AC), sternoclavicular (SC), and scapulothoracic articulations. Specify to which you are referring! Clinicians usually mean ‘GH’ when they say ‘Shoulder’—but not always.
GH Joint: shallow ball-and-socket, head larger than glenoid. Allows enormous range of motion at cost of stability.
- Fibrocartilaginous labrum deepens the glenoid ‘socket’, incrase contact area ~50%.
- Rotator cuff (RC), capsule, cohesive/adhesive forces, help hold head against glenoid.
- Coracoclavicular arch heavy ligament, overhangs GH, with RC prevents cephalad migration.
Rotator cuff: supra and infraspinatous, subscapularis, teres minor
AC Joint: minimally mobile articulation transmitting forces upper extremity UE ←→axial skeleton.
SC Joint: often not included on ‘shoulder’ radiographs. Only TRUE link of UE to axial skeleton; stabilizer for throwing/pushing motions.
Scapulothoracic Articulation is actually muscle of chest wall, stabilizing and modifying scapula during complex range of motion (ROM). Rarely the focus of radiography.
Positioning texts show more views for the shoulder (primarily GH) than any other joint, reflecting its extreme mobility. In reality, traumatized patients hypersensitive to motion and pressure. Most common standard views in Emergency Dept ( vs. outpt. Sports Medicine Clinic):
- AP: scapula parallel to image plane, beam perpendicular to coracoid. Usually 2 APs:
- EXT. Rotation: true anatomic AP prox. Humerous, shows tuberosity
- INT. Rotation: lateral of humerus (‘light bulb’, not tuberosity seen).
There is no such thing as a ‘lateral shoulder’ (massive superimposition) therefore alternatives:
- AXILLARY ‘worm’s eye’ or ‘bird’s eye’ abduction view, for GH margins. “Coracoid points anteriorly” to get oriented.
- Y view lateral scapula, oblique pt., arms at side: humeral head centered in “Y’ (Reverse Grashy similar, arm flexed over chest or back).
- Transthoracic lateral if cannot abduct for axillary (usually limited use; superimposition, obesity limit quality). (Many others: Grashey, coracoids, scapular, rolled film, West Point, etc—not common in EMed)
Figure 1. Shoulder Views and Dislocation
GH DISLOCATION (do NOT use ‘shoulder dislocation”; layperson’s term) = most common injury; described and illustrated (Fig. 2 Kochner technique) in the Eber medical papyrus 3000 BCE, and by Hippocrates.
- 90% of patients who were < 20 y.o. at first dislocation will recur
- Only 14% of GH disloc. Are > 40; ie, fracture instead of disloc. Increases with age
Figure 2. Kochner Technique
ANTERIOR DISLOCATION: 95% (subcoracoid, subglenoid variants)
- Head may impact under inferior glenoid → palpable in most patients impaction creates
- HILL SACHS sign posterior-lateral head and corresponding BANKHART impaction lesion inferior glenoid
- Inferior component augments radiographic visibility
- Older pts: more likely to have associated fxs, check post-reduction
- All pts - clinicians must document neurovascular status pre/post reduction
POSTERIOR DISLOCATION: rare, 2-4% of GH dislocations
- 50% missed at initial exam (“flat’ shoulder—check for symmetry, but posterior disloc. can be bilateral)
- Takes far more force: seizure, electrical shock, ECT w/o relaxants. Axial load to adducted internally rotated shoulder; sudden contraction internal rotators which are 2x as powerful as external rotators.
- Reverse Hill-Sachs = impaction of anterior humeral head against posterior glenoid.
- Trough sign: subchondral head line paralleling articular surface
- Head may overlap glenoid fossa, normal ‘C’ of articular surfaces (the rim) gone; far less likely to displace inferiorly and far MORE likely to be missed clinically/radiographically.
- Fixed internal rotation.
INFERIOR (LUXATIO ERECTA): very rare, axial force to overhead arm or forced hyperabduction (motorcycle with high handlebars, construction worker). Inferior capsule tears, humeral head goes inferiorly, arm locks overhead—pt. arrives abducted with arm flexed over head. HIGH INCIDENCE of brachial plexus, other nerve injury.
PSEUDOSUBLUXATION: widening of the GH joint (widened ‘C’ formed by parallel margins)
- Head drifts out of glenoid secondary to capsule distention with fluid, hemarthrosis (most common), chronically stretched capsule or muscle, hemiplegia (stroke) and marked muscle/tissue laxity, nv/brachial plexus injury.
- Axial view will show GH is NOT subluxed. Important to think of pseudosubluxation or hemarthrosis to prevent (futile, painful, harmful) attempts to ‘relocate’ a widened pseudosubluxed GH joint.
July 2012 - Donna Magid, M.D., M.Ed.