PT Question of the week – Thumb biomechanics

You are discussing thumb biomechanics with your student, who is confused about the difference between thumb flexion, extension, abduction, and adduction. Which of the following statements is correct?

1. Extension is performed in a plane parallel to the palm of the hand, and abduction is performed in a plane perpendicular to the palm of the hand
2. Flexion is performed in a plane perpendicular to the palm of the hand, and adduction is performed in a plane parallel to the palm of the hand
3. Extension is performed in a plane perpendicular to the palm of the hand, and adduction is performed in a plane parallel to the palm of the hand
4. When referring to positions of the thumb, flexion and adduction are used synonymously and extension and abduction are used synonymously

 The solution will be posted in a few days.