A short, honest answer
Knee pain is common. Not every ache needs a scan. Persistent pain, an injury you felt, or a knee that no longer feels trustworthy does need a proper look.
What knee pain can feel like
People describe a dull ache after sitting, sharp pain on stairs, swelling by evening, or a sudden pop during sport. These are different problems. The timeline and the mechanism of injury matter more than the word you found online.
Possible causes
After sport: ligament sprain, meniscus injury or bone bruise. After years of use: early or established arthritis. After a fall: fracture or cartilage injury. None of these can be confirmed from a description alone.
When to seek medical care
Book a visit if pain lasts beyond two weeks, the knee locks or gives way, swelling appears after an injury, or you cannot bear weight. Go to emergency care for an open wound, obvious deformity, or a cold, numb foot.
Treatment overview
A first visit usually includes history and examination. X-rays or MRI are used when they will change the plan. Many people start with activity changes and physiotherapy. Surgery is discussed only when a structural injury is unlikely to recover well without it.