Similar happenstance would be getting caught in a motor-vehicle accident. Add him being trapped under said vehicle for hours before he could get help and you emulate similar conditions.

The sheer debris in his leg and the amount of 'broken muscle juices' would essentially slowly poison him as he waits for help.

Accounts of similar incidents where the leg was kept describe a permanent limp and excruciating pain.

But I think ego death that comes with have a missing body part is better for whump purposes. It's a visual reminder of what was missing staring back at him and he wasn't even concious enough to make the choice due to how dire the state of his body was when they dug him out.

Jayce having episodes of being trapped, in the dark, with his legs crushed under unrelenting, twisted metal when he gets phantom pain.

Viktor doesn't just have a bad leg. He has a specific disability, one where his femur is turned inward. It could be developmental or it could be during birth. Either way, his leg turns inward and collapses on itself. As a kid, we can see he also shows a bit of foot drop too.

He needs more than just a compressive sock on his knee to walk.

He still uses his cane with it since hes so used to it but on bad days, he will use his wheelchair.

It was a hard shift when he got fitted with his new orthotics. His leg atrophied a lot, making it hard to propel himself with just the KAFO. So the doctors recommended seated exercises and starting out slow with using it.

Jayce was there the whole time. Keeping on top of the specific movements Viktor should hit for his routines to helping Viktor take his first steps without the need of a cane or crutch by holding his hands.