Final answer:
Opposition and reposition are movements occurring at the first carpometacarpal joint of the thumb. These actions allow the thumb to touch the fingertips (opposition) and then return to its position alongside the index finger (reposition), essential for hand functionality and grip strength.
Step-by-step explanation:
Opposition and reposition are specific movements that refer to the actions of the thumb and they occur exclusively at the first carpometacarpal joint of the thumb. The first carpometacarpal joint is classified as a saddle joint and it is formed by the articulation between the trapezium carpal bone and the first metacarpal bone.
Opposition is the unique movement of the thumb that allows the tip to touch the tips of the other fingers, which is essential for the ability to grasp and manipulate objects. This movement consists of a combination of flexion and abduction. On the other hand, reposition is the motion that brings the thumb back alongside the index finger, returning it to its initial anatomical position.
These movements are crucial for hand functionality and give the thumb its wide range of motion, which is separated from the other metacarpal bones. While the second and third metacarpal bones are immobile, the fourth and fifth metacarpal bones allow limited anterior-posterior mobility, enhancing the strength of grip. However, only the first carpometacarpal joint at the base of the thumb allows the distinctive movements of opposition and reposition.