The common problems we see are osteoarthritis (wear/tear) of the knee, sprained ligaments and torn menisci (cartlage).
If you have had any trauma the knee tends to swell and may give way. Apply an ice pack in wet tea towel for 10 minutes, apply compression bandage and seek medical advice if concerned. Treatments often include exercises, medication and semi rest.
Osteoarthritis is treated with heat, acupuncture, good shock absorbing shoes and weight loss. Again exercises are advised to keep strong muscles/bones and maintain joint movement.
You may need further investigation such as X-rays or MRI scans depending on our opinion. A useful website is: www.kneeguru.co.uk