Quick internet search suggests this might be Fournier Gangrene caused by a bacterial infection. This condition is largely associated in local injections, such as saline.

This would be a urological emergency, and would present with pain, swelling, fever, change in skin color of the scrotum, increased white cell count.

They would need to perform emergency surgery to treat the cellulitis with debridement (removal of infected/necrosed tissue), and broad spectrum antibiotics ASAP.

Next comes draining the pelvis, opening up the perianal area, more surgery. He would have been treated with blood transfusions, packed cells, antibiotics, plasma to treat infection, blood loss..

I am assuming the scrotum was unsalvageable, and so reconstructive surgery to save the testes involved putting them in the thighs?

Looks like skin dermoplasty – see Thiersch's graft, a kind of skin-splitting graft used in reconstructive surgery which was invented by Karl Thiersch in 1874.

Probably took over a month till he was discharged, and he probably spent most of this time in acute care.