Musculoskeletal

Anatomy

Region: Neck to axilla, roots C5–T1.
Key Structures: Roots → trunks → divisions → cords → branches; gives the axillary, radial, median, ulnar, and musculocutaneous nerves.
Clinical Correlation: Upper trunk (C5–6) injury → Erb’s palsy (waiter’s tip); lower trunk (C8–T1) → Klumpke’s (claw hand).

High-Yield Pearl

Erb’s = upper trunk (“waiter’s tip”); Klumpke’s = lower trunk (“claw hand”).

Region: Tibiofemoral joint.
Key Structures: ACL, PCL, MCL, LCL; medial & lateral menisci.
Clinical Correlation: ACL tear: pivot injury, audible pop, positive Lachman/anterior drawer; the “unhappy triad” = ACL + MCL + medial meniscus.

High-Yield Pearl

Lachman is the most sensitive test for an ACL tear; the MCL is the most commonly injured knee ligament.

Region: Glenohumeral (shoulder) joint.
Key Structures: Supraspinatus, Infraspinatus, Teres minor, Subscapularis (SITS).
Clinical Correlation: Supraspinatus is the most commonly torn/impinged; weak abduction initiation with a positive empty-can test.

High-Yield Pearl

SITS muscles — the supraspinatus is the one most often injured (empty-can test).