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MSK I Elbow and Forearm - Vocabulary Flashcards

Elbow and Forearm Motions

  • Movements: Elbow flexion, elbow extension; forearm supination/pronation; alternating supination and pronation
  • Views: Posterior view (elbow); Anterior view (forearm)

Joints and Biomechanics Overview

  • Elbow complex includes 2 primary joints at the elbow plus the proximal radioulnar joint (PRUJ) acting on the forearm
  • Functions: Central hinge between shoulder and wrist/hand; distributes forces proximally and distally

Joints and Key Structures

  • Humeroulnar joint (Trochlear joint)
    • True hinge joint
    • Trochlea and trochlear notch fit tightly
    • Medial trochlea extends further distally than lateral end, contributing to carrying angle
    • Carrying angle: 10^\circ-15^\circ valgus
    • Force distribution: 43\% through the humeroulnar side
    • Normal ROM: 140^\circ
  • Humeroradial joint (Radiocapitellar joint)
    • Radial head articulates on capitellum
    • Stabilizer to valgus forces
    • Extension: minimal contact between radial fovea and capitellum
    • Flexion: increased contact (anterior capitellum)
    • Relative joint load: less when elbow is flexed vs extended (stress = force/area)
    • Force distribution: 57\% through the humeroradial side
  • Proximal Radioulnar joint (PRUJ)
    • Site of forearm rotation; head rotates ~240^\circ for pronation/supination
    • Works with DRUJ; interosseous membrane provides additional stability (mid RUJ)
    • Normal ROM: 150^\circ-180^\circ
    • Open packed position: 35^\circ of supination with elbow flexed ~50^\circ

Capsule and Ligamentous Support

  • Joint capsule: one capsule for all elbow joints
    • Open packed position: 80^\circ elbow flexion (ligaments most lax)
    • Closed packed positions: Trochlear joint = 0^\circ extension; Radiocapitellar joint = 90^\circ flexion
  • Collateral ligaments
    • Radial (Lateral) collateral ligament (RCL) and Ulnar (Medial) collateral ligament (MCL)
    • Each has anterior, posterior, and transverse parts; support medial elbow through motion
    • MCL is larger; forms floor of cubital tunnel
  • Annular ligament of the elbow
    • Primary attachment on ulna; acts as a sling to keep the radius from slipping/dislocating
    • Surrounds about 80\% of the radial head; radial head rotates within its ulna facet
    • Secondary stabilizers: UCL, interosseous membrane, oblique cord

Load Distribution and Stability

  • Ulna is wide proximally and narrow distally; radius is narrow proximally and wider distally
  • Interosseous membrane distributes/transfers weight between forearm bones

Stiffness and Adaptive Shortening

  • Elbow is prone to stiffness when conditions favor bicipital shortening, capsular tightness/restrictions, and adhesions
  • Adaptive shortening can lead to contracture with prolonged shortening

Practical Points and Implications

  • The elbow complex comprises 3 joints (2 at the elbow + PRUJ for the forearm)
  • It must balance high mobility with stability; injuries are common in athletes
  • Understanding anatomy helps prevent elbow stiffness in trauma and supports occupational performance requiring elbow flexion

Summary and Key Takeaways

  • The elbow acts as a central hinge linking shoulder and wrist/hand, distributing forces proximally and distally
  • Stability is provided by a network of capsules and ligaments (MCL, RCL, annular ligament) with specific open/closed packed positions
  • Proper management of stiffness and valgus stress is critical for protection of the elbow, especially in trauma and athletic populations