Knee complaints - Pain - Sagging - Blockage - Instability

Knee pain

In order to arrive at a correct diagnosis it is extremely important to know where exactly the pain is experienced, and when the pain is felt or how it started. It is also important, but rather more difficult to identify the type of pain: sharp pain, nagging pain, radiating pain, etc. Osteoarthritis (or wear and tear) of the knee joint typically results in activity-related, mechanical pain that often limits the function (walking, running, climbing stairs). A strain injury manifests more as a focal, nagging pain felt during or after a period of increased activity. Acute injuries (cruciate ligament rupture, torn meniscus, fracture, etc.) are often accompanied by a lot of pain, which may be localised or affect the whole knee. Pain at night usually indicates inflammation as the cause.

Location of the pain

The whole knee is often painful but there is usually a trend. Pain at the front of the knee may be caused by osteoarthritis of the kneecap, tendon inflammation or bursa inflammation. Pain on the inside may indicate a torn meniscus, torn collateral ligament or osteoarthritis. Pain on the outside of the knee may indicate: a torn meniscus, tendon inflammation or osteoarthritis. Pain in the back of the knee: a torn meniscus or a Baker’s cyst, both possibly the result of osteoarthritis.


A lump or swelling (fluid in the knee) is common, and could have several causes. If the swelling appeared very suddenly after a trauma this is usually the result of bleeding in the joint caused by a fracture, cruciate ligament tear, meniscus tear or kneecap dislocation. If the swelling appears slowly it is often caused by reactive fluid related to some kind of mechanical irritation. The cause may be osteoarthritis, a cartilage injury or a torn meniscus. If the swelling appeared slowly and is accompanied by obvious heat, this points more to inflammation as the cause. In this case it is sometimes necessary to prick the joint and examine the fluid to arrive at the correct diagnosis. If, in addition to the swelling there is pain at night and stiffness in the morning, the cause may be a rheumatological condition, such as rheumatoid arthritis, gout, ankylosing spondylitis and so on. If this is the case, you will first be referred to a rheumatologist. If the knee is swollen, feels hot and the patient has a fever, septic arthritis (infection of the knee) must first be ruled out. This is a medical emergency.


A blockage means that the knee is blocked and can only move with difficulty, or not at all. We distinguish between two scenarios here. A genuine mechanical blockage. There is something in the knee joint blocking the knee. This is usually a fragment of torn meniscus or loose cartilage injury. A pseudo-blockage: there is no mechanical blockage but the body prevents the knee from moving to protect it from pain. Causes may be anatomical (muscle/tendon injuries, collateral ligament injuries, knee dislocation etc.) or non-anatomical (inflammation). In the case of osteoarthritis or severe swelling of the knee we see a reduction in the mobility/movement amplitude of the knee, but not usually a genuine blockage.

Buckling knee

The knee buckles, you feel unstable, the knee ‘gives way’, you no longer trust the knee, etc. This is a common complaint. There are a number of causes of these complaints. If the knee always feels unstable it is usually the result of a condition of the structures that should stabilise the knee: the collateral ligaments, cruciate ligaments and the tendons and muscles. If the knee feels stable but it still gives way sometimes this indicates a meniscus or cartilage injury. It is usually accompanied by a click or sharp pain in the knee. The feeling of the knee buckling also occurs in many other conditions. This is the result of reflective muscle relaxation of the quadriceps in response to a pain stimulus that the body experiences in or around the knee.

This content was written by : Dr. Paul Gunst, Dr. Thomas LuyckxDr. Lieven Missinne, Dr. Jan Noyez, Dr. Peter StuerDr. Alexander Ryckaert, Dr. Luc Van den Daelen, Dr. Philip Winnock de Grave

More info about disorders of the Knee - Knee replacement - Meniscus - Ligament