The knee (from Latin geniculum) is the joint that connects the thigh to the leg. It allows the lengthening and flexing movements of the lower limbs.

The knee is a joint that connects the femur (which supports the thigh) to the tibia (which supports the leg). On its lower end, the femur has two protuberances, the condyles. These condyles are articulated opposite two plates on the upper end of the tibia. When the knee is bent, the condyles of the femur roll and slide at the same time on the plates of the tibia. In this joint, a third bone plays an essential role: the kneecap (or patella) which is located at the front of the knee. It is held by two tendons, the quadriceps tendon and the patellar tendon. They attach it above to the thigh muscle (the quadriceps) and below to the shin bone. The patella slides forward level with the femur, in a span called the trochlea. The patella-tendon assembly allows force to be transmitted to the muscles.

The movements of flexion and extension of the knee are provided by two ligaments which are located inside the knee, the cruciate ligaments. They make it possible to adjust and adjust the sliding and rolling of the condyles on the plates.

The ends of the femur, tibia and kneecap are covered with cartilage that allows natural and easy sliding between the surfaces of the joint.

On each side of the knee between the femur and the tibia, slide two menisci in the shape of crescent moons: the internal meniscus on the inner part of the knee and the outer meniscus on the outer part. Compared to joints, they carry the weight of the body and act as shock absorbers and stabilizers for the joint.

The knee joint is surrounded by a special tissue, the synovium. It is a kind of pocket that makes joint fluid. It decreases the friction between the surfaces of the articulation by promoting the sliding of the cartilages and avoiding the heating produced. It ensures the nutrition of the cartilage cells as well as a permanent cleaning of the wear particles of the cartilage.

The knee carries the weight of the body which, normally, is distributed in a balanced way on the two plates of the tibia.

The knees ensure the stability and mobility of the body by allowing movements of flexion (flexion of the knee) and extension (straightening of the knee).

Genu valgum : deviation in morphology outside the axis of the lower limb; the weight of the body is mainly carried by the outer plateau of the tibia of the knee joint. It results in a foot turned outwards.

Nice knee : deviation in morphology inside the axis of the lower limb; the weight of the body is mainly carried by the internal plateau of the tibia of the knee joint.

This results in arched knees.

Knee recurvatum : knee hyperlaxis or relaxation of certain ligaments. It is then possible to make hyperextension movements with the knee.

Flessum du genou : lack of knee extension, inability to fully extend the knee when standing.

Synovial effusion (or hydarthrosis): in case of knee irritation, the synovia can produce excess synovial fluid which will result in swelling of the knee. The tension caused by the fluid inside the knee can become painful. A joint puncture can be done to temporarily drain fluid.

Knee hemarthrosis: an effusion of blood inside the knee joint as a result of trauma.

Maladie d’Osgood-Schlatter : bone growth disease, it mainly affects pubescent boys. It is manifested by pain felt on the front of the knee, at the level of the attachment of the tendon of the patella to the bone. Knee function, however, is normal. Sports involving the knees with, in particular, impulse movements and running (tennis, football or basketball for example) are very restrictive.

Popliteal cyst : pocket of joint fluid (synovial fluid) that appears behind the knee crease and causes a kind of hernia to form. It pushes back the muscles and the vessels which surround it, which causes the appearance of a feeling of discomfort, even of pain.

Sprain : elongation or tearing of one or more knee ligaments following a trauma (excessive tension, flexion or extension beyond the normal amplitude, etc.). The degree of ligament damage varies, ranging from mild sprain (strained ligaments) to severe (complete tear of the ligament (s)).

Cruciate ligament rupture : serious sprain following a relatively important trauma which results in a rupture of the cruciate ligament (s). Difficult to determine a precise point of rupture: the fibers of the ligaments all give way at a different level. This deformation degrades the mechanical properties of the ligament for the proper functioning of the knee. Surgery is needed for the repair.

Aknee osteoarthritis (or gonarthrosis) : corresponds to the wear and tear of the cartilage at the ends of the femur, the tibia and the patella which are involved in the knee joint. This progressive destruction of the cartilage is manifested by pain in the joint. There are no treatments that would allow cartilage regrowth. Analgesic or anti-inflammatory drugs may be prescribed to improve pain and stiffness.

tendonitis : inflammation of the tendon which results mainly in pain, sometimes accompanied by swelling in the affected tendon. It occurs following trauma to the tendon (shock, repeated forced or poorly coordinated movements during a sporting activity).

Knee fractures : they occur following a violent trauma and concern the femur, the kneecap and the tibia. If the fracture is not displaced, the knee will be immobilized in a cast or knee brace. If the fracture is displaced, surgery is needed to reposition the bone pieces and secure them to each other with a screw, plate, or staples. And immobilization (plaster or knee brace) will also follow.

In some cases, the fracture is open, that is, it is accompanied by an opening of the skin at the level of the fracture. Surgical intervention is required.

Patella dislocation : occurs when the patella leaves the bony rail of the femur in which it normally moves. A dislocation can occur during an accident or a shock but also during a strong muscular contraction.

Hoffa’s disease : inflammation of a small fat ball, “Hoffa’s fat ball”, located on the front of the knee, below the kneecap. Rare but benign disease, it causes pain.

Plica : important fold formed by the synovial pocket. A plica can be located at different levels of the knee. Usually benign, they do not interfere with the proper mechanics of the knee.

Osteoarthritis and risk factors

Generally, osteoarthritis appears without a well-defined cause and it is rather the combination of several risk factors that causes wear of the knee: overweight, advanced age and a deviation of the knee (genu varum or genu valgum) . It can also be secondary to a former trauma of the knee (fracture, sprain, rupture of ligaments, surgical operations…).

Prevention of knee problems and sports

Some sports do not use the knee joint, such as running, cycling or swimming. On the other hand, other sports make use of pivot movements and more or less supported contacts; this is the case for tennis, skiing, football or basketball for example. It is for the latter that the constraints on the knee are the most important.

It is not impossible to avoid knee problems when you are an athlete by following a few recommendations: it is advisable to avoid suddenly increasing the intensity of the practice of a sport demanding for the knees; having a coach or trainer allows you to adopt the right postures and techniques; wearing appropriate sneakers for each sport is important and necessary. These tips are not exhaustive. Do not hesitate to contact your health professional who will be competent to guide you in this prevention.

Physical examination : carried out by the doctor, it first includes the questioning (general then focused on the symptoms – pain, instability, swelling, blockage – which led the patient to consult). It is followed by the physical examination of the knee: inspection and palpation (mobility, pain, stability of the patella and knee) 4. This examination should make it possible, if not to make the diagnosis, to orient it in order to choose the appropriate additional examinations.

Additional tests :

• Radiography: medical imaging technique that uses X-rays. This is the standard reference examination, the first step in additional examinations.
• Ultrasound: imaging technique that relies on the use of ultrasound to visualize the internal structure of an organ. In the case of the knee examination, the muscles, tendons, cysts and superficial ligaments are particularly visible.
• Scanner: imaging technique which consists of “scanning” a given region of the body in order to create cross-sectional images, thanks to the use of an X-ray beam. This examination is generally carried out before an operation to obtain data. particular: more in-depth study of the bone, better visualization of the cartilage, obtaining anatomical measurements, etc.
• Arthroscanner: CT scan of the knee associated with the injection of a contrast product into the joint which makes it possible to highlight the menisci and ligaments that are not very visible on a simple CT scan.
• Arthrography: X-ray of the knee with injection into the joint of a contrast agent. It allows the observation of soft tissues, cartilage, ligaments and their interactions with bone structures, which cannot easily be visualized with a standard x-ray.
• MRI (magnetic resonance imaging): medical examination for diagnostic purposes carried out using a large cylindrical device in which a magnetic field and radio waves are produced. It makes it possible to obtain very precise images of all the elements of the joint (bone, muscle, tendon, meniscus, ligament, cartilage and synovium).
• Bone scintigraphy: an imaging technique that involves administering a radioactive tracer to the patient, which circulates in the blood. The product is highly concentrated in the bone or joint areas which have abnormalities.

Our joints and tendons contain structures that are sensitive to variations in atmospheric pressure, the baro-receptors (pain receptors). This pressure is directly related to climatic conditions: when the humidity of the air increases, there is a decrease in atmospheric pressure which is detected by the baro-receptors which then trigger the pain mechanism. Thus, some people (especially the elderly with osteoarthritis and those who have had fractures) say they can anticipate rain or snow depending on the pain felt in the joints, particularly those of the knee (5).