The Importance of Sensibility and Joint Position Sense
Our sensory system conveys the information we need to our brains so we can make the right decisions in daily life. Huge amounts of information flow in to our brain at all times and we must decide the importance or otherwise of this. Hearing, touch and sight are clearly used by use to manage our responses to the challenges of normal life but there are other sensory modalities which are just as important in our mobility. The feelings coming in from all our bodily structures such as our muscles, ligaments, discs and joints are very important for normal movement function. Joint position sense is more specifically related to our joints and is also called proprioception.
Waking up with a dead, completely numb arm is a good example of the loss of sensory input having a strong effect on what we can do. I woke up one night with an arm across my chest, making me hotter than I already was in bed. I was a bit irritable and moved the arm off my chest at least twice until I woke up a bit and began to realise what was going on. I followed the arm, which I couldn't feel at all, up to the shoulder only to find out it was mine. The profound loss of feeling in the arm meant I had no idea it was mine until I found out it was attached. I could do nothing with it independently.
In my work as a physiotherapist I have treated all kinds of conditions and some of these interactions were very instructive. A patient who had had a stroke got hold of my hand and moved it back and forth, bending and straightening the fingers and stretching the wrist. Suddenly I realised that he thought it was his arm! He could feel nothing from his own arm when he did the same movements to it, so moving my arm seemed entirely natural until he looked more closely at it and realised it wasn't his. The next time you get a dead arm in bed, try and move it. Apart from feeling unpleasant, the limb is extraordinarily difficult to move, it feels right out of control and just lies there despite you willing it to move.
Sensory input, the constant incoming signals to the brain from the various parts of the body, informs us what is going on and where we are in space. This is much more important than we realise. Losing muscle power is difficult but people adapt and manage well but losing sensory information from a body part makes it extremely difficult or impossible to use the part. Losing sensibility is more troublesome than losing muscle power, although both are important.
In stroke we see the lack of movement easily, what we don't see is the underlying sensory abnormality which may be partly or wholly responsible for the disability. Joint position sense (JPS), also called proprioception, is the body sense which indicates to our brain where our joints are at all times. The sense also tells us what state our joints are in such as what angle they are at, what muscular effort is being exerted and in which direction the effort is being expended.
Monitoring of the positions, stresses and effort being exerted through all our joints is streaming in to our brains all the time from the joint position sense and other sense organs in our muscles and tendons. We need all this incoming information to make sense of where our limbs are so that we are in a position to do the next actions we desire. Accurate JPS information is essential if we are to be able to plan our next movement.
Losing the sense of feeling our body parts accurately is fundamentally important to our ability to manage independent movement in our daily lives. Paraplegia, stroke and direct nerve trauma can cause loss of proprioception but lesser injuries can reduce this sense also. Anterior cruciate ligament rupture or even an ankle sprain can reduce the precision of the JPS and make treatment advisable. Physiotherapy rehabilitation skills are used to develop increased proprioception in many conditions and both stroke and sports therapists must be equally aware of its importance.