When I saw the hand therapist for my wrist pain, she did some interesting tests on me. She would put my wrist and hand in one position and tell me to remember how that felt. I wasn't allowed to look during the test. Then she shook my wrist and hand out and asked me to go back to the position I was in before she shook me out. I was surprised how accurate I was. What's the mechanism behind this?
When you move your wrist up and down and back and forth, you are able to sense just how much movement is occurring. The sense of joint position and movement makes up what we call proprioception and kinesthesia.
For a long time, we thought the information about proprioception and kinesthesia that was sent to the brain via the sensory nerves all came from the joint itself. But over the years with scientific investigation, researchers have been able to show that there are kinesthetic and proprioceptive sensory receptors located in many places in the joint and soft tissues.
Knowing that transmission of information about joint proprioception can come from the ligaments, tendons, muscles, joint surface, and skin is important. Surgery cutting into any of these structures can destroy them. Then the joint's ability to detect motion and position could potentially be altered.
There is evidence that joints aren't the only ones involved in producing proprioceptive messages. In fact, if anything, sensory receptors in the articular surface of joints don't send messages until the joint is at its extreme ends of motion (full flexion or full extension).
The sensory receptors in the joint surfaces appear to have more of a protective role. There may be reflexes at the ligament-muscle interface that help regulate muscle contraction and regulate load on the joints. Evidence to support this idea point to the role of ligaments in joint stability AND motion.
The complete package of joint proprioception and kinesthesia is quite complex. Besides recognizing sense of joint position and movement through space, each joint also transmits to the brain any sensation of force and heaviness during muscle contraction, timing of motor control, and sensation of body orientation. All of these mechanisms are behind your skill as demonstrated during the test you were given by the hand therapist.