Mystified By the Concept of Narrative Prosthesis?

Mystified by the concept of narrative prosthesis?  Michael Davidson, in his book Concerto for the Left Hand: Disability and the Defamiliar Body, provides the following explanation:

In the humanities this social model has been accompanied by
significant readings of disabled characters in literature whose nontraditional
bodies are sites of moral failing, pity, or sexual panic. David
Mitchell and Sharon Snyder have described this analogical treatment of
disability in cultural texts as a "narrative prosthesis" in which a disabled
character serves as a crutch to shore up normalcy somewhere else. The
disabled character is prosthetic in the sense that he or she provides an illusion
of bodily wholeness upon which the novel erects its formal claims
to totality, in which ethical or moral failings in one sphere are signified
through physical limitations in another. In Richard Wright's Native Son,
for example, Mrs. Dalton's blindness could be read as a sign of the moral
limits of white liberal attitudes that mask racism. Wright is less interested
in blindness itself than the way that it enables a story about racial violence
and liberal guilt. In A Christmas Carol Charles Dickens does not use Tiny
Tim to condemn the treatment of crippled children in Victorian society
but to finesse Scrooge's awakening to charity and human kindness toward
others. By regarding disability as a "narrative prosthesis;' Mitchell and
Snyder underscore the ways that the material bodies of blind or crippled
persons are deflected onto an able-bodied normalcy that the story must
reinforce. Indeed, narrative's claim to formal coherence is underwritten
by that which it cannot contain, as evidenced by the carnival grotesques,
madwomen in attics, blind prophets, and mute soothsayers that populate
narrative theory. (Page 176)