During your knee replacement surgery, you will be under general anaesthesia and there will be an incision made on your knee to allow surgical tools to move in and out of the knee. Once the damaged portions of the knee are removed and the artificial joints placed into the knee and attached using adhesive materials, the knee will be sutured together and you will be pushed to the recovery room.
The recovery period starts immediately after the surgery and even though you are still feeling the effects of the anaesthesia, you will be encouraged to start moving your knee. High chance are that you have not used the knee for physical activities for quite some time due to the pain which led to you undergoing the knee replacement surgery. As a result, the muscles are weak and you need to start building up and strengthen the muscles to allow better control of your new joint. A physical therapist will prescribe some physical therapy exercises for you to do yourself at home. You will be able to get discharged around 3 days after surgery and during this period, you will start to learn how to move around with the help of crutches until your knee is able to take your body weight. Once the knee is strengthened and is able to bear weight, you can slowly reduce your dependency on your crutches.
The first 3 months post surgery is a risky period as the replacement joint is still not fully attached to the surrounding muscles and tissues firmly. You knee can often give way so make sure you keep doing strengthening exercises to strengthen the region. You will also feel pain in the knees rather often during this period and this is perfectly normal. You will be prescribed painkillers but do not rely totally on the painkillers. If you notice any abnormal swelling or abnormal pain in the knee, make sure you go back to your surgeon for a check. Although the operating theatre is sterile, infection can still happen but this is rare. If you see any infection in the site of the incision, you need to go back to your surgeon as well. You should aim to regain your knee's full range of motion within this 3 months and this will help to prevent any scar tissues from building up or arthrofibrosis.
The first 3 months post surgery is totally about recovery and regaining back the functions of your knees. It is probably the toughest part of the whole surgery process and you will feel extremely useless. However it is the most important part and a bad recovery can lead to even more problems in future.