Understanding Wrist Motion and Musculature

Aug 11, 2024

Wrist Motion and Musculature Lecture Notes

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.
    • Radial deviation is also called abduction.
    • Ulnar deviation is also called adduction.
  • Circumduction vs. Rotation:
    • Circumduction is a combination of wrist movements (extension, radial deviation, flexion, ulnar deviation, back to neutral).
    • Often confused with rotation, but it involves rolling and gliding without spinning.

Arthrokinematics and Ligaments

  • Mid-Carpal Joints:
    • Use the capitate as a reference for radial and ulnar deviation.
    • 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.
  • Ligaments:
    • Ligaments secure the carpal bones, causing them to move together.
    • Ligament injury can lead to instability and hand function problems.
    • Ligaments are formed by type I collagen and take time to heal.

Muscles Involved in Wrist Motion

  • Wrist Flexors:
    • Flexor carpi ulnaris (FCU): Ulnar side.
    • Flexor carpi radialis (FCR): Radial side.
    • Palmaris longus: Not present in everyone.
    • Pure wrist flexion: Both FCU and FCR contract together, with extensors canceling out deviation.
  • Wrist Extensors:
    • Extensor carpi radialis longus (ECRL): Originates from the humerus to the base of the 2nd metacarpal.
    • Extensor carpi radialis brevis (ECRB): Originates lower on the humerus to the base of the 3rd metacarpal.
    • Extensor carpi ulnaris (ECU): Originates from the humerus to the base of the 5th metacarpal.
    • These three muscles work together for pure wrist extension.
  • Deviation Muscles:
    • Ulnar deviation: ECU and FCU.
    • Radial deviation: ECRL, ECRB, and FCR.

Lab Tests and Surgical Considerations

  • Muscle Testing: Helps determine the role of each muscle in wrist motion and assists surgeons in deciding on procedures.
  • Nerve Injuries: Surgeons might cut and transfer muscles for nerve repair.
  • Palmaris Longus (PL): Often used in tendon transfers due to its minimal role in deviation.
  • ECRB Injury: Leads to weakened wrist extension, requiring rehab or compensatory training.