23.34 The position of the upper limb

• Force vector direction varies during abduction or elevation

• In neutral rotation

  • the vector is downward when the arm is alongside the body

• From 0-60\(^{\circ}\)

  • The vector is directed upwards and medially because the shear forces are predominant

    • The vector remains inside the area of contact between the two articular sufaces

• at 90\(^{\circ}\)

  • Compression dominates

  • The vector approaches perpendicular to the glenoid which is in a mechanically favorable postion

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