Patients and their surgeons will have different things to consider when discussing the possibility of a knee replacement procedure.
The patient's perspective
There are a number of things that will affect a patient's decision to have a knee replacement.
The first is their quality of life. Patients may as a leisure activity like to walk say 2-3 miles, enjoy bowling or golf and when the arthritis increases in severity so that they are unable to do these activities that keep them active and make them happy it is possibly time to think about what might be done.
The second thing is their pain-free walking distance. Of course we all walk and we all have a safe comfortable pain-free walking distance, but I would say if anybody was unable to walk less than a quarter of a mile without knee pain that would be a strong indication that they may need something doing.
There are some patients who have night pain, and disturbance of sleep is another thing that may bring a patient to the decision for a knee replacement. The problem is that they go to bed and are woken up at night due to pain - the painkiller takes half an hour to kick in and by then their routine is disturbed and they can't get back to sleep.
If all three of these are present, that is a very strong indication that something needs to be done. That intervention could be anything from activity modification, to injections to arthroscopy, but usually when the symptoms are as severe as this it suggests that the arthritis is quite advanced and a joint replacement is likely to be indicated.
If the symptoms are still early conservative management is very important. I would start off with anti-inflammatories, pain management and medications like glucosamine sulphate. I would also suggest slight reduction in activities and see if this does reduce symptoms, as it may help to avoid operation. I would also consider injections - that could be a steroid injection which is a temporising measure, or hyaluronic acid (viscosupplemtation), but in my experience if the arthritis is 'bone-on'bone' the viscosupplementation does not work that well because there is so much of a mechanical problem going on in the knee. But I would religiously try most of these conservative interventions before attempting any kind of surgery. Most patients would are experiencing all three of the symptoms I mentioned earlier - disturbed night sleep, reduced pain-free walking distance and knee pain affecting their quality of life - would have had such conservative management which has failed.
The surgeon's perspective
First and foremost before discussing surgery with a patient, I need to feel sure that the patient has had a good trial of conservative management - anti-inflammatories/pain management, activity modification, balancing their alignment (for example with insoles) physiotherapy to tone up the quadriceps muscle and see if that helps, injections- and if all has failed then I would tell patients that they are moving towards surgical intervention.
I feel it is important to focus on the patient's symptoms rather than on the x-rays. It does happen from time to time that the x-rays look really bad but the patient's symptoms are not that bad. Conversely there are patients whose x-rays do not look all that bad, but they have severe symptoms. So I like to think of x-rays as supportive evidence rather than the main evidence.
I would, when first seeing a patient, jot down their activities of daily living, including leisure activities and work, and then I would have a fair idea of the patient's activity level. Then without really challenging their desire to stay active, I might suggest to them dropping the activity level to assess the potential improvement in pain relief. If for example they walked four miles a day, I might suggest dropping it down a mile a couple of days a week - that may allow a patient to stay fit but reduce the pain to a level where surgery may be avoided for some time. Secondly if they were very involved in leisure activites in my experience patients do not want to give this up but I may suggest changing the activity - say to swinning where the knees are not challenged quite so much.
Another issue is weight. This is quite topical and I think patients do better if they reduce down to their optimal weight based on the body index where one considers height and weight. Overweight patients tend to have a higher incidence of complications following a knee replacement. I would suggest to patients that they may find that after losing one or two stones they may even find that their pain is a lot better. However in my experience few patients manage to lose the right amount but there are some well-motivated patients who do.
If I find someone with a diet problem I work with the dietician to try and get the patient eating a balanced diet.
In assessing pain I usually use a visual analogue score which I record in the notes ("what is your pain like on a scale of 1-10"), and 40-50% of patients who reduce weight get a huge boost by finding their score has reduced since they lost weight.
Range of motion is extremely important because the outcome of a knee replacement is very much dependent upon what the patient starts off with. In other words, if the patient's knee is stiff before surgery then there is a high chance of the knee being stiff after the knee replacement surgery. I would definitely talk to a patient about poor range of motion and discuss them doing exercises by themself or with the help of a physiotherapist.
The other thing that is important is flexion deformity, which is when the leg doesn't come out fully straight, usually because the patient has been using a pillow under their painful knee for comfort. What happens over a period of time is that the knee no longer goes fully straight. If I was to do a knee replacement in this case there is quite a chance of the knee not coming out fully straight after the knee replacement. So in addition to improving the range of movement, I would also advise patients to work on getting their knee to be able to straighten more fully, which is harder said than done, but with the help of specialist physiotherapists this can be achieved.
Also I would look at the patient as a whole person and assess the other knee, the hips and the ankles- such things as walking aids and arch supports can be optimised - and I really want to stress that pre-operative physiotherapy is very important.