Loved this series, but one thing bothered me

Paul Milner's character loses a leg in the Norwegian Campaign and has a prosthetic leg. In the episode Enemy Fire, Milner meets Dr Wrenn, who had amputated his leg while at the hospital. When Milner asks the doctor if he remembered him, Dr Wrenn recalls, "Left leg. An inch below the tibia. Yes, of course". This means he is amputated just below the knee. Yet, during the course of the series, he is uncannily active; he has no limp, fights the bad guys, tackles them to the ground, dodges a car just before it hits him, etc. If they were to write a character to be that active, why create a story about losing a leg and a prosthetic? In one of the early episodes (I forgot which), he does suggest he has an 'advanced prosthetic' leg, but this is the 1940s; how advanced could the prosthetic be to allow him to be that physical. This bothered me.