Modified steering may be necessary so that you can operate it with one hand whilst you are accelerating and braking with the other, it may also be necessary if you only have the use of one hand. If you have a condition that results in a weakness in the upper limbs this may cause difficulty turning the steering.
If you need to steer one handed then a steering ball would normally be recommended, there are different designs of steering ball which may be chosen for comfort or may be chosen out of necessity possibly because of a difficulty gripping an ordinary steering ball. The steering ball is clamped to the rim of the steering wheel and can be moved to the most comfortable position for you; if the car is to be used by another driver who will steer conventionally the fitting of a quick release ball would be recommended so that it can be quickly and easily removed when not required.
If you have a weakness in your upper limbs then turning the steering may be more difficult for you, this may be more of an issue if you are steering one handed. Modification to the power steering can reduce the effort required to turn the wheel – this is referred to as “lightened power steering”.