Originally Posted by FBinNY

Years (decades) ago, I used to fit bicycles for recovering patients of a local knee surgeon. This was before the scope, so knee surgery involved a much longer recovery process.

The surgeon was a big believer that bicycles were a useful aid in post operative recovery, and I'd see people come in on crutches and ride away.

The basic elements for riding with knee issues.

1- saddle as high as possible, shy of where the knee would straighten completely. Usually we'd go to where the person was reaching slightly and riding with a toe down foot angle.
2- low gears. This is absolutely critical. The bikes were set up with higher gears locked out. The object is to restrict the amount of weight that could go into the knee
3- shorter cranks if possible, to reduce the total flex cycle. Not much of an issue for taller people, but for shorter ones, we fitted some modified childrens cranks.
4- limit hill climbing, and avoid steep hills entirely. This, along with gearing, is adjusted according to strength, but you want to avoid loading the knee when bent
5- changing the pedaling rhythm delaying maximum power until later in the cycle. You want to apply more power when the leg is straighter to the extent you can train yourself to do it.

Foot orientation wasn't an issue back then because it was before step in (clipless) pedals, and the foot could find it's own alignment. With clipless, cleat alignment is critical because a misaligned cleat causes twisting forces in the knee. Also you want to find an alignment that causes the knees to travel straight up and down, rather than wobbling.

So, done right, not only won't cycling hurt the knee, it can be a big part of knee therapy.

So you can keep riding, but listen to your knee, and if you have pain, or notice instability as you ride, stop and have it rechecked.