PHT5117 - Wrist Hand Biomechanics Transcript

Unit 07: Wrist and Hand Biomechanics

Introduction

  • Overview of wrist and hand biomechanics.

  • Key focus areas include:

    • Radiocarpal joint

    • First carpometacarpal joint

    • Carpometacarpal joints

    • Metacarpal joints for digits 2-5

    • Interphalangeal joints

Radiocarpal Joint

  • Degrees of Freedom:

    • 2 degrees of freedom:

      • Sagittal Plane: Flexion and Extension.

      • Frontal Plane: Ulnar deviation and Radial deviation.

    • Circumduction: Combination of flexion, extension, ulnar and radial deviation.

  • Axis of Rotation:

    • Approximate line through the base of the capitate bone.

  • Range of Motion (ROM):

    • Flexion has slightly greater ROM than extension.

    • Ulnar deviation yields greater ROM than radial deviation due to:

      • Shape of distal radius extending further than distal ulna.

Wrist Flexion and Extension

  • Illustration of Movement:

    • Proximal row of carpals slides in the opposite direction of the motion:

      • Palpation of lunate bone shows dorsal slide during flexion and palmar slide during extension.

  • Arthrokinematics:

    • Follows convex on concave rule.

    • Ulnar Deviation: Proximal carpals glide to radial side.

    • Radial Deviation: Proximal carpals glide to ulnar side.

    • Confirmable through palpation during movements.

First Carpometacarpal Joint

  • Movement Definitions:

    • Abduction: Thumb moves away from second metacarpal (perpendicular to palm).

    • Adduction: Thumb returns to anatomical position (perpendicular to palm).

    • Extension: First metacarpal moves away from second metacarpal (parallel to palm).

    • Flexion: First metacarpal moves toward second metacarpal (parallel to palm).

  • Additional Movement:

    • Shallow saddle joint allows rotation of the first metacarpal along its axis, leading to:

      • Opposition: Thumb touches the pad of the little finger.

Saddle Joint Mechanics

  • Articulating Surfaces:

    • Convex in one plane and concave in another.

  • Movement Analysis:

    • Abduction/Adduction: Proximal first metacarpal slides in the opposite direction of osteokinematic movement.

    • Carpometacarpal Flexion/Extension: Arthrokinematic movement aligns with osteokinematic movement (concave on convex rule).

Metacarpophalangeal (MCP) Joints

  • Fingers 2-5:

    • Follow concave on convex rule.

    • Observed in abduction/adduction and flexion/extension.

    • Sliding direction matches rolling direction during movements.

Interphalangeal Joints

  • Characteristics:

    • Similar in shape and function, differing only in size.

    • Classified as hinge joints, allowing for:

      • Volitional flexion and extension only.

    • Reinforced by collateral ligaments on both sides.

    • Follow concave on convex rule with rolling and sliding in the same direction.