Severe knee pain is usually caused due to wear and tear of the cartilage covering the knees. Cartilage cushions the bone ends within each joint by acting as a shock absorber. Cartilage breakdown results in painful bone-on-bone contact in the knee joint. Osteoarthritis is one of the most common causes of cartilage breakdown in the knee. Genetics, age, obesity, past joint injuries like torn ligaments or fractured patella also increase the risk of osteoarthritis.