Antique Cabinet Card of Crippled Boy

IMAGE NOT TO BE REPRODUCED FOR ANY REASON.
A sister and a brother in this cabinet card, judging by the close resemblance. The younger brother is seated and there is a crutch with him. Polio perhaps? The interesting thing that I found about this photo was that the boy did not have to have the crutch in the picture, and without it there would be no indication of his infirmity. He would be simply seated for the photo, while the older sister is standing. So why the crutch? Did he defiantly want it to be there because it was part of his life, and was going to continue to be part of his life for the foreseeable future? Or did the parents want to include it? Or was it just an oversight? I found it to be a strange choice to use the crutch in the photo. The card has a very plain backstamp from Mereness of Oneonta, NY, but there is no ID info on the sister and brother.