sandyRoe - the walls and ceiling of the grotto at Lourdes is indeed festoooned with crutches, i have seen it.
But there is a proven medical condition - the psychosomatic paralysis, where the patient believes that they cannot walk, and so their limbs fail to function - and will pass any medical test.
The cliche 'mind over matter' is a cliche becuase, like all cliches, it is true. So if the person has a strong faith, and believes they have been 'cured' then the mental supression of the use of their limb(s) is lifted, and an apparent mircale has occured.
This is no more valid than believing that a sacrifice to the sun will give good crops next year - it is simply a belief system that sustains some people - and, as in my case, not others.