Causes of Knee pain
With every step you take, your knees not only bend and straighten but also bear the weight of your body. The knees usually accomplish these tasks without symptoms, but this is not always the case. Pain provoked by straightening your knee can arise from acute injuries or chronic disorders affecting numerous structures in and around the joint, including cartilage, tendons, ligaments, bursae, muscles, bones or the synovial membrane. Several different common conditions can cause knee pain when bending.
Runner’s knee is when moving the kneecap puts extra stress on the cartilage when bending. Biomechanics, muscle weakness, or muscle tightness can cause this type of problem. The pain is usually just below or to the sides of the kneecap in the front. It begins gradually and can manifest itself with a grinding or grating sound.
Bursitis is friction and inflammation of the bursa, the small sacs between the bone and soft tissue that are filled with fluid. Two of them are in the knee and pressure on them can cause the pain. Repetitive or prolonged kneeling or falling onto the knee can cause inflammation of the prepatellar bursa below the kneecap on the front of the knee. Excess fluid in the knee joint that seeps back into the bursa can cause swelling and pain on the back of the knee.
A sprain of one of the four ligaments that help stabilize the knee can also cause pain while bending. If one of the ligaments tears or stretches too much, the pain can cause minor to severe pain. The symptoms usually come on immediately or shortly after an injury
The meniscus is a thick layer of cartilage lining the knee joint to protect and cushion it. If it tears, it cannot cushion as well and can get inflamed or limit movement. If your knee pain happens mostly while squatting or going up stairs, it could be a meniscus tear.
Inflamed joints from arthritis can also cause pain while bending. If the pain comes after sitting for a long time or in the morning, this could be the cause. Gentle movement can ease some of the pain. The symptoms develop over time and are not constant.