This is an awesome sketch. I think you should define the lines and do some smudge or charcoal shading to bring out the definition. Heck color it in after you outline it and damn it would make an amazing piece of art.
Looking upon this piece purely objectively I see what I said in the first comment...
But true art is in the process by which you achieve your image, and what you say with the piece, and how you chose to say it. After feeling like a heel for several minutes I began to imagine your process. I began to imagine every part of the process and in many different ways it could be done... ways it may have to be done. I imagined also the feelings that come with limited mobility (not that I could fully understand without being quadriplegic myself)
The story and imagery behind this drawing makes it beautiful to me. This is a triumph to be celebrated.
Your drive to do what you love is something you should never let anyone disway you from.