Music is considered as a combination of sounds form instruments into a rhythmic and harmonic pattern pleasing and attractive to the ears of everyone. This implies that we have to make it accessible to any person who is handicapped in the least form. Thus in making a choice of instrument, we must address the concerns of our beloved handicapped brothers and sisters. We can either make our instruments accessible to them or provide a separate one that will match to their conditions.
Our first concern should address their physical conditions. Operating a musical instrument involves many parts on the body. These parts most of the time do coordinate to successfully function well. For example, the hand, eyes and ears are all involved in playing a piano. A player with a slight disability on the left hand will find it difficult to play this musical instrument.
Consider the size of the player. It is true that some instruments are and must be bigger than others. How big an instrument is will be a relative term. A small instrument to you may be big for me with a smaller mass. The manufacturers have provided the same instruments with various types of edition which can suit all sizes of persons. For example, the guitar has been fabricated into so many sizes.

A number of appliances call for more bodily strength than others. This can be corrected by adjusting or adapting the device or its playing position or obtaining other supports so that every person with any bodily potency can get access to that instrument. If you are considering physical support in relation to the instrument, I will advocate you visit a counselor who is well vested in the special needs of the disable. You can equally visit charitable and other trust foundations which has concerns for the handicapped.
Consider the suitability of that instrument to the player. Do you think that given his deficiency, he will be drawn to that instrument? This will determine his interest, determination and perseverance to learn or play that instrument.
Consider other sensual disabilities especially audio –visual disabilities. Some players will be short or long eye sighted. Go for a piano whose wordings are readable and visible to all. Make sure the sound system makes it possible for all to listen to what is being played. Take note that these concerns are not only for players. They are for the audience as well.
If you intend that a handicap person should become skilled at playing a particular instrument, consider the possibility of having an instructor in that field or one who will be willing and able to sacrifice his efforts to the conditions and needs of that handicap person. This might also be very costly. Are you prepared for the expenses?
In all, you should contact the manufacturer who can be of great help to you. He knows what is suitable or how an instrument can be adapted to meet the needs of the disabled.