Is riding a stationary bike with knee tendonitis in both knees good for rehab?

Ok. It should be fine as long as you start with low or even no resistance on the bike and exercise with comfort. If your knees are screaming at you during the exercise or if you have prolonged (greater than an hour) soreness after exercise, you are doing too much. Do not increase the resistance or the duration by more than 10% every couple of weeks and you should be fine. If not talk with pt or doc.
Generally yes. For most "soft tissue" injuries (muscle, tendon, or ligament), non-impact activities can be very beneficial for rehabilitation and healing. However, accurate identification of the injury is important to develop the proper therapy plan. This is particularly important for more serious injuries. See you family doctor, orthopedist, or physiatrist for a referral to a physical therapist if necessary.

Related Questions

Can you have jumpers knee (patellar tendonitis) in both knees if you only engage in a moderate amount of exercise per week?

Yes. If at some point you aggravated your knees doing a workout, you can start the inflammatory process and if you don't properly manage the tendonitis it can chronically ache and not recover properly. A good stretching and proper strengthening program monitored by a physical therapist under your doctors supervision is appropriate. Read more...

I have tendonitis in both knees (persists in off-season of sports; I'm in high school) & am planning to hike a small mountain in 2 days. Ok idea?

Probably not. Tendonitis can be worsened by increased stress on the joint affected which is what will happen when you climb. that is not to say you will not be able to ever go hiking but allow a period of healing prior to undertaking this activity. Read more...

Overworked aching 10 months both knees been diagnosed with osgood schlatters, patellar tendonitis, patellofemoral syndrome. Icing, pt, Advil (ibuprofen) don't work?

Go to next level. You what the problem you have doctor give more stronger anti-inflammatory medication and may be MRI to see how your knee from inside. Read more...
Clarify diagnosis. You need re-evalaution, muscle strengthening with the pt but also on your own many times a day. Will need x-rays and maybe ultrasound/mri in addiiton to clarify the diagnosis. Need to clarify what you meen and don't work. Read more...