4Notes Humerus

Overview of the Humerus

  • The humerus is the principal bone of the arm, deriving its name from the Latin word for shoulder.

  • It articulates proximally with the scapula at the glenohumeral joint (shoulder joint) and distally with the radius and ulna at the elbow joint.

Primary Bony Landmarks of the Humerus

Proximal Landmarks

  • Head of the Humerus

    • Rounded, dome-shaped structure that articulates with the glenoid cavity of the scapula.

    • Provides significant mobility at the shoulder joint but less stability.

    • Only about a third of the humeral head articulates with the glenoid cavity.

  • Anatomical Neck

    • Located just below the head of the humerus.

  • Surgical Neck

    • Circumferential area below the anatomical neck.

    • Clinically significant due to proximity to the axillary nerve and posterior humeral circumflex artery, which can be injured in a surgical neck fracture.

  • Greater Tubercle

    • Larger tuberosity on the lateral side of the proximal humerus.

    • Serves as the attachment site for three rotator cuff muscles: supraspinatus, infraspinatus, teres minor.

  • Lesser Tubercle

    • Smaller tuberosity located anteriorly, serves as the attachment site for the subscapularis muscle (fourth rotator cuff muscle).

  • Intertubercular Groove (Bicipital Groove)

    • Groove located between the greater and lesser tubercles, housing the long head of the biceps brachii.

  • Radial Groove (Spiral Groove)

    • Groove located on the posterior mid-shaft, where the radial nerve and deep brachial artery pass.

    • Mid-humeral fractures can damage the radial nerve.

  • Deltoid Tuberosity

    • A tuberosity on the lateral side of the mid-shaft for the attachment of the deltoid muscle.

Distal Landmarks

  • Trochlea

    • Structure that forms part of the elbow joint and works like a pulley, contributing to hinge motions.

  • Capitulum

    • Round, smooth structure articulating with the radial head; facilitates pronation and supination of the forearm.

    • Both trochlea and capitulum serve as condyles at the distal end of the humerus.

Epicondyles

  • Medial Epicondyle

    • Larger epickyondyle on the medial side, serves as an origin for forearm flexor muscles and landmark for the ulnar nerve (funny bone).

    • Injury may disrupt the ulnar nerve, causing numbness in the pinky and part of the ring finger.

  • Lateral Epicondyle

    • Smaller epicondyle on the lateral side, serves as an origin for forearm extensor muscles.

Fossa

  • Coronoid Fossa

    • Shallow concave surface on the front of the distal humerus where the coronoid process of the ulna fits during flexion.

  • Olecranon Fossa

    • Deeper concave surface on the back of the distal humerus where the olecranon process of the ulna fits during extension.

Importance of Learning About the Humerus

  • Understanding the anatomy and landmarks of the humerus is crucial for diagnosing and treating injuries, particularly those involving fractures and surgical procedures.

  • Knowledge of the humerus assists medical professionals in understanding arm mechanics, muscle attachments, and potential nerve injuries.