In my job, at least ... my manager got Covid right after New Years, and clocked in for half a day on our first day back after the holiday to make sure we all knew, and everything was running smoothly. Then she was available through Teams chat with a ping, but was not actively working.
So, I'd say it depends on your ability to carry out the job you're expected to do.
In the case you presented, if the employee is on pain medication, they won't be very capable minded to be doing their work, most likely, and need to relax.
If they are out of that neck of the woods, they should pro'ly judge for themselves if they'd be going into work w broken legs to do the job in general, or if the only thing putting them off doing so would be transport and stuff. If that's the case, they're probably just fine to work.
If an employer is not respectful of the fact we cannot always work from home just because our computers and phones are available, then they were probably the type to expect you to come in with the flu, anyway.