For those in their mid-80s, hip or femur injuries are extremely dangerous

‌My grandfather and my wife's grandmother passed away like this.
They were very healthy and vigorous, but because elderly people have weak bones,
a simple fall on their buttocks while trying to sit on a park bench can cause a hip fracture
or a femur fracture. Once that happens,
someone who was perfectly fine will suddenly become frail and pass away about six months later.
I don't know the exact reason, but since their immunity is much lower than that of young people,
when a major bone in the body breaks, the immune system becomes overloaded,
leading to illnesses elsewhere, such as pneumonia.
As a result, their body gradually shuts down. Even for someone who was vigorous,
where the surgery went well and the bone healed properly,
they might be unable to get up after just a few months, remaining bedridden until they pass away.
When a person stays lying down, it is equivalent to a zero-gravity state, so muscle mass is lost very quickly.
When I broke my arm in my 30s and was hospitalized for two weeks,
even just returning to daily life at work for about three weeks was a struggle.
I remember wondering why climbing just two or three flights of stairs was so difficult...
If even young people lose muscle mass from lying down,
it goes without saying for the elderly over 80.