Wrist Motion and Related Musculature

Jul 22, 2024

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Wrist Motion and Related Musculature

Planes of Wrist Motion

  • Flexion/Extension
    • Occurs in the sagittal plane with a frontal axis.
  • Radial/Ulnar Deviation
    • Occurs in the frontal plane with a sagittal axis.
    • Also referred to as abduction (radial deviation) and adduction (ulnar deviation) in some textbooks.

Common Misunderstandings

  • Circumduction vs. Rotation
    • Circumduction: A combination of all wrist movements (
      • Extension → Radial deviation → Flexion → Ulnar deviation → Neutral.
    • Rotation: Often confused with circumduction but involves rolling and gliding, not spinning.

Midcarpal Joints

  • Arthrokinematics
    • Using the capitate as a reference:
      • Ulnar deviation: Carpal bones roll to the ulnar side and glide to the radial side.
      • Radial deviation: Carpal bones roll to the radial side and glide to the ulnar side.
    • Confirmed through X-ray imaging.
  • Ligament Role
    • Ligaments ensure the stability of carpal bones.
    • Ligament injury leads to instability and problems in hand function.
    • Ligaments are made of type I collagen, slow to heal leading to prolonged inconvenience.

Muscles Contributing to Wrist Motion

Wrist Flexors

  • Flexor Carpi Ulnaris (FCU)
  • Flexor Carpi Radialis (FCR)
  • Palmaris Longus (PL)
    • Not present in all individuals.
    • Plays a minimal role in wrist flexion and deviation.

Wrist Extensors

  • Superficial layer muscles
    • Extensor Carpi Radialis Longus (ECRL)
      • Originates from the humerus.
      • Inserts at the base of the 2nd metacarpal.
    • Extensor Carpi Radialis Brevis (ECRB)
      • Originates from the humerus.
      • Inserts at the base of the 3rd metacarpal.
    • Extensor Carpi Ulnaris (ECU)
      • Originates from the humerus.
      • Inserts at the base of the 5th metacarpal.

Deviation Movements

  • Ulnar Deviation
    • Involves contraction of ECU and FCU.
  • Radial Deviation
    • Involves contraction of ECRL, ECRB, and FCR.

Clinical Implications

Muscle Testing and Repair

  • ECU
    • Strong in ulnar deviation and assists in extension.
  • ECRL and ECRB
    • Strong extenders, but not as strong in radial deviation.
  • FCR and FCU
    • FCR: Strong in flexion but weaker in radial deviation.
    • FCU: Strong in flexion and ulnar deviation.
  • Palmaris Longus (PL)
    • Often used for tendon transfer surgeries.
  • ECRB
    • Loss leads to significantly weaker wrist extension; requires rehabilitation and compensatory training.