In the old days we would do something similar with a black velvet drape, make a negative of the draped image, using a sharp needle engrave the "cracks" into the emulsion side of the neg then print. The print emulsion is then is scraped away or etched from the paper base to create the look of the broken torso of figure or arms or legs. The missing knee would be done again with the black velvet which has virtually no reflectance of light draped over the bent knee. The art work again on the print rather than the neg. Last, Re photograph to get a master negative.
This may not be how Allen did this, but I know what I have described will work and has been done on other subject matter.
Regardless of "how was done" it is very well done and shows great imagination and thought. Good job Allen!!!!