you require a check up, if

• you had any injury to the knee
• you twisted your knee while walking or running
• your knee hurts on particular movements or on weight bearing
• knee hurts constantly even during sleep
• any swelling or redness around the knee
• recurrent knee swelling
• cracking sound or grating sensation on moving the knee
• any obvious knee deformity, like bow legs or knock knees
• loss of movements, either unable to bend or straighten fully
• your knee feels unstable or gives way