A support assembly includes a fixable portion and a rotatable portion. The fixable portion is adapted to be fixedly mounted to a wheelchair and includes a shaft having a keyway formed therein that is supported by one or more mounts. The rotatable portion is received on the shaft and is in selective locked engagement therewith. The rotatable portion includes a bracket body with an opening into which the shaft of the fixable portion is received and a key member providing a key. The key member is supported by the bracket body and is movable in linear translation between an engaged position in which the key is engaged with the keyway to lock a rotational orientation of the bracket body relative to the shaft and a disengaged position in which the key is disengaged from the keyway permitting the rotatable portion to rotate relative to the fixable portion.