Discuss the posterior compartment of the arm. Include contents, compartments, relationships, boundaries, fascial specializations, vascularization, innervation, lymphatics, muscles and movements, and compensation in the case of nerve injury.

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Hey all, I thought I'd contribute a little, since Dr. Evey said to "study the heck" out of the compartments. Please correct where necessary. I'm sure this isn't quite as thorough as Dr. Evey would have it...And please bear with my lack of computer-saaviness...

General

  • Extends forearm & arm
  • Muscles served by radial nerve; cutaneous innervation from lower lateral cutaneous nerve of arm, posterior cutaneous nerve of arm and posterior cutaneous nerve of forearm
  • blood supply from profunda brachii and branches
  • Boundaries (these may need some help)
    • Superior-glenohumeral joint; deltoid (posterior portion)
    • Inferior-elbow joint
    • Anterior-humerus; medial and lateral intermuscular septa
    • Posterior-brachial fascia; tela subcutanea; skin (dermis, epidermis) *Medial and lateral-would skin/fascia be acceptable here as well? of course the medial aspect of the posterior arm is related medially to the lateral thoracic wall, but it's not really a border
  • Fascia-contents surrounded by brachial fascia-continuation of axiallary fascia *lateral & medial intermuscular septa-divide anterior/posterior compartments

Contents

Muscles

  • Triceps brachii--three heads: long, lateral & medial
    • Long head: O: infraglenoid tubercle
    • Lateral head: O: humerus, superior to radial groove
    • Medial head (better thought of as the deep head: O: humerus, inferior to radial groove; I-M septa
    • All three insert on upper surface of olecranon of ulna
    • Innervation: radial nerve
    • Vascularization: profunda brachii & collaterals (radial, superior ulnar, middle)
    • Action of muscles:
      • 3 heads contribute unequally in elbow extension: Medial head is ALWAYS active; lateral and long heads are recruited when there is resistance to overcome
      • Long head also assists slightly in adduction and extension of arm
  • Anconeus-small, flat, triangular muscle O: lateral epicondyle of humerus
    • Ins: lateral side of olecranon & adjacent body of ulna
    • Upper border blends with medial head of triceps
    • Innervation: radial nerve!
    • Vascular suppy: superior ulnar collateral ulnar; posterior ulnar recurrent (from the elbow anastomosis)
    • Action: assists triceps in extending forearm
  • Articularis cubiti-"made up of some deep fibers of the medial head of the triceps. It inserts into the capsule of the elbow joint, prevents it from being caught by the olecranon." (Hollinshead, p 257. I didn't know how important this was...)

Nerves

  • Radial nerve-from posterior cord of brachial plexus (C5-T1)
    • enters behind brachial artery (Hollinshead said behind...), inferior to teres major
    • turns posteriorly and enters compartment with the profunda brachii artery-between long head of triceps and humerus
    • courses between deep and superfcial heads of triceps--it's path is close to the radial groove (closer to bone than other nerves; therefore it is more vulnerable to injury in humeral fractures)
    • exits posterior compartment at lateral edge of humerus by piercing the lateral I-M septum and passes anteriorly over elbow/cubital fossa
  • Ulnar nerve- enters posterior compartment distally as it pierces the medial intermuscular septum
    • passes inferiorly, posterior to elbow

Vascularization

  • profunda brachii-accompanies radial nerve on its course
  • branches:
    • Ascending branch (aka deltoid branch)-contributes to the shoulder anastomosis with the posterior circumflex humeral
    • Middle collateral branch-posterior and in the middle of humerus-anastomoses with interosseus recurrent artery to supply elbow posteriorly--terminal branch
    • Radial collateral branch- parallels the radial nerve; pierces the lateral I-M septum and anastomoses with the radial recurrent artery --terminal branch
  • superior ulnar collateral artery--enters the posterior compartment via the medial I-M septum along with the ulnar nerve; anastomoses with posterior ulnar recurrent artery
  • as usual, veins parallel arteries (venae comitantes around profunda brachii)

Injuries to nerve

  • Characteristic wrist drop
  • depending on location of the injury, the posterior compartment may not be affected-if it is affect the patient may compensate by using gravity to extend the arm (therefore these muscles are tested when the arm is abducted to 90 degrees)

Lymphatics (help here!)

I couldn't really find much on specific lymphatic drainage of the posterior compartment of the arm. The most I can figure is that they end up in the axillary nodes to the apical nodes then to the subclavian trunks. From here, it depends on the side of the body (right/left). The right subclavian trunk drains to the right lymphatic trunk and to the jugular/subclavian angle; the left drains to the thoracic trunk to the left jug/subcl. angle.

Comments and Suggestions

Add to and edit as necessary! I hope this is helpful and not completely off-base.
 

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Topic revision: r1 - 04 Oct 2006, UnknownUser
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