Synonyms
Patella fracture, patella fracture, patella tendon, patella tendon, patellar tendon, chondropathia patellae, retropatellar arthrosis, patella luxation, patella luxation Medical: Patella
- Normal patella
- Dysplastic patella
- Dysplastic patella with lateralization
- Retropatellar cartilage damage
Function
The kneecap transfers the force of the front thigh muscles to the shin via the knee joint. The patella of the kneecap acts as a physical force diverter (hypomochlion). During maximum flexion and extension, the kneecap can slide approx. 10 cm in the gliding groove of the femur.
Patellar dislocation
In patellar dislocation (patella luxation), the patella has jumped out of its predetermined path of the thigh. If the patella has jumped out, the capsular ligaments are always torn. Risk factors for patellar dislocation are knock-knees, a loose ligament apparatus (hyperlax) and a raised patella. The patella is practically always outwardly out of its glide path. A kneecap that has jumped out once again bears the risk of jumping out again.
Diseases of the kneecap
The most common disease of the kneecap (patella) is arthrosis of the patella (retropatellar arthrosis). There are many causes for patellar arthrosis. Possible causes can be poor cartilage quality due to the anal position, malposition of the patella (facet hypoplasia, incorrect ridge angle), knock-knees, bow legs, patella lateralisation (the patella slides too far out in the gliding groove, etc.
), or the patella is not properly aligned. (chondromalacia according to Outerbridge) from top to bottom:
- Chondromalacia grade 1
- Chondromalacia grade 2
- Chondromalacia grade 3
- Chondromalacia grade 4
Chondropathia patellae is a mostly harmless but often very painful overload of the kneecap in children and adolescents. These manifest themselves as pain behind the kneecap when climbing stairs and taking deep squats.
In most cases this pain subsides until the age of 25 – 30 years. It must be ensured, however, that there is no cause of illness behind the complaints. Osgood-Schlatter’s disease is defined as a painful irritation of the insertion point of the patellar tendon (= patellar tendon).
The point of attachment is located at the front of the tibia. In juvenile osteochondrosis, there is an additional risk that bone fragments may detach from the tibia and die off, becoming necrotic. The dead bone part is also known as aseptic osteonecrosis.
Aseptic in this context means that it is not caused by an infection. Osgood-Schlatter disease primarily affects younger people, often between the ages of 10 and 14. It has also been observed that boys are four times more likely to suffer from Osgood-Schlatter’s disease than girls.
The disease can affect only one knee or both. It is assumed that excessive sport (especially jogging or jumping) causes very small injuries, which are the cause of the disease. During patellal lateralization, the kneecap runs too far out in the gliding groove of the thigh.
This results in an asymmetrical load on the patella (the outside is subjected to increased stress). This is usually caused by misalignment of the patella and/or the sliding bearing in combination with a weakness of the inner front thigh muscles (Musculus vastus medialis). Large sliding surfaces are required to allow the patella to slide.
There are two bursa sacs on the knee joint that enable this sliding. Directly in front of the kneecap is the so-called bursa praepatellaris, which can become inflamed in the event of minor skin injuries, sometimes without any apparent cause. An inflammation of this bursa (bursitis praepatellaris) can have far-reaching consequences.
Pronounced inflammation can lead to knee infection (knee joint empyema) or blood poisoning. For this reason, the bursa must be removed if the infection is severe. Sindling-Larsen’s disease is a rare disease of the growth age (usually 10 – 14 years of age).
It is a circulatory disorder of the lower patella pole. In most cases this disease heals without consequences even without therapy with sports leave. In some cases, the patella is doubled or there is no fusion of different bone nuclei.In most cases there is an additional bone (patella bipartita) in the upper outer quadrant of the patella, which in itself has no disease value.
A total of up to six bones can be found. However, as the number of fragments increases, the risk of premature cartilage abrasion behind the patella increases. Athletes often suffer from patellar tip syndrome.
It is a chronic, painful, degenerative overload disease of the patellar extensor apparatus at the bone-tendon junction of the patellar tip. When the patella springs out of its normal position, this is also called patella dislocation. Some risk factors can promote patella dislocation.
These include, above all, an underdeveloped patella, the so-called patella dysplasia. In this case, the patella is often too small and is not sufficiently fixed by the ligamentous apparatus of the knee. This allows it to slip out of its support quickly.
However, such a patellar dysplasia is usually first noticed before the age of 20 due to a dislocation and the dislocations occur again and again. Other factors that favor this type of dislocation are a maldevelopment of the ligamentous apparatus of the knee, knock-knees (genu valgum), a weakness of the connective tissue, and muscular imbalances between the upper and lower leg. All these factors can cause a reduced fixation of the kneecap so that it can luxate.
Another cause of patella luxation is accidents. In most cases, it is a twisting of the knee as part of a sports injury. The patella usually slides to the outside of the knee.
Women are affected slightly more frequently than men. Overall, the slipping of the kneecap is very painful. Diagnostically, a patella luxation is usually visible at first glance from the outside.
In addition, there is often a joint effusion, which can be bloody. In most cases, the patella then returns to its original position by itself (reduction). Nevertheless, the dislocation may leave behind ligament or cartilage damage that requires medical clarification.
If the patella has not returned to its normal position by itself, it must be repositioned by a doctor. The knee is stretched slowly and the kneecap is held firmly with one hand so that it does not bounce back too abruptly. It can then be slowly returned to its normal position.
In this way, ligament and cartilage injuries are avoided. An X-ray of the knee should then be taken to check the position of the patella. In addition, any bony damage can be identified on the X-ray image.
If the patella repeatedly slips out of its position, for example due to congenital patella dysplasia, surgical therapy may be indicated to prevent recurrent dislocations in the future. If the patella is loose and frequently slips out of its position (patella dislocation), this is usually due to a weakness of the intervertebral disc, a malformation of the patella itself (patella dysplasia) or a malformation of the sliding bearing of the patella (trochleadysplasia). The patella is fixed in place by the tendon of the quadriceps muscle at the front of the thigh, which serves to stretch the lower leg.
It is also stabilized by the remaining ligament structures of the knee joint. This allows it to slide on the cartilaginous surface of the trochlea, which is formed by the ends of the thigh and lower leg bones. If the shape of the kneecap is not exactly congruent to its sliding bearing, an imbalance will occur, which will lead to a loosening of the kneecap in its support.
This makes it more flexible in its position. The same applies to an unstable ligamentous apparatus, which does not sufficiently fix the patella. This also results in a hypermobility of the patella.
In case of muscular imbalance, it is also possible that the patella is not optimally fixed in its slide bearing. A knee malposition, for example a knock-knee position, can also have a beneficial effect. Young girls are particularly affected by a loose kneecap.
A contusion of the kneecap is also called a knee contusion and is usually caused by a sports accident or a fall. This causes a strong force to be exerted on the kneecap, which is briefly compressed strongly with the surrounding tissue.There is no major injury to the skin, but blood and lymph vessels in the patella area can be damaged and the patella itself can also be damaged. As a result of the vascular injury, there is bleeding into the tissue.
From the outside, the bruise is visible as a red-blue discoloration of the skin and soft tissue swelling. In addition, the joint area is usually overheated and reddened. The effusion can cause severe pain and functional impairment of the knee joint.
Especially bending the knee (for example when climbing stairs) is perceived as painful. As an immediate measure, it is advisable to stop any stress on the affected knee immediately so as not to increase the discomfort. The leg should also be positioned as high as possible, since the swelling can be aggravated by the hydrostatic pressure when standing.
It is best to cool the knee with ice, as this constricts the blood vessels and stops bleeding more quickly. Pain can also be relieved in this way. Finally, a light pressure from the outside can reduce the swelling (for example by applying a bandage).
It is important to ensure that the bandage is not too tight so as not to cut off the blood supply. If the pain is very severe, pain-relieving ointments or medication can also be used. If the joint effusions are very severe, puncture and suction of the fluid can provide relief.
If the patella is bruised, it is always advisable to consult a doctor. By examining the knee in detail, the doctor can clarify whether important structures of the knee (ligaments) or the kneecap itself have been injured. If the kneecap slips, this is often caused by a congenital predisposition in the form of patellar dysplasia.
In this case the patella is malformed. It is therefore either too small or has a shape that is not congruent with its slide bearing. As a result, its guidance at the knee joint is reduced and it can slip more quickly.
Movements that predispose to this are especially fast rotational movements in the knee. Accordingly, the kneecap most often slips in the context of a sports injury. Loose ligaments in the knee area also increase the risk of the kneecap slipping out of position.
Normally, it is sufficiently fixed by the taut ligamentous apparatus consisting of inner and outer ligaments and the tendon of the quadriceps muscle. If this is not the case, it can slip. The instability can also lead to cartilage damage in the knee joint, which usually manifests itself as pain in the anterior knee area.
Therapeutically, the instability is treated in particular by reconstructing the ligamentous apparatus so that the kneecap is better fixed. In some cases, further stabilizing measures are necessary. If patellar stability only occurs during growth, it is often possible to wait until the problem has resolved itself at the end of the growth phase.
If not, a surgical therapy can be considered here as well. If the kneecap rests resiliently on the knee joint, can be moved downwards by applying pressure and then jumps up again, the phenomenon of the “dancing patella” is present. This is considered a sure sign of a joint effusion and is tested by doctors as soon as a knee joint effusion is suspected.
For this purpose, the leg is stretched out and the recessus directly above the knee joint is stroked out downwards with one hand. Since there is a bursa there that can absorb relevant amounts of fluid, it should be expressed in this way. The fluid then collects below the kneecap.
Afterwards – while continuing to exert pressure on the recessus – pressure is applied to the patella. In the case of a joint effusion, the patella can now be pressed resiliently towards the knee joint and jumps up again when it is released, as it is buoyed by the liquid level. This jumping of the kneecap is called the “dancing patella”.
If the patella jumps out of its anatomically correct position during sports, for example, without a joint effusion being present, it is a patella dislocation, which is usually caused either by a malformation of the patella, a ligamentous apparatus that is too weak, or a muscular imbalance. If the kneecap breaks, this is medically referred to as a patella fracture.This usually happens in the context of a fall or a direct violent impact on the knee. Typical symptoms of a patella fracture are a knee that is no longer extendable and no longer able to bear weight, as well as significant swelling, overheating and bruising in the knee area.
The leg can no longer be bent because the kneecap serves as an abutment for the tendon of the quadriceps muscle and transmits the force from the upper to the lower leg. In the case of a fracture, the transmission of force is interrupted. Accordingly, there is usually severe pain and a feeling of complete instability in the knee joint.
More rarely, fractures are found in which the entire soft tissue is torn apart (open fracture). In order to confirm the diagnosis, in addition to a regular examination of the knee joint, an x-ray is taken, on which the fragments are clearly visible. In this way, the treating physician can already decide on the indicated therapy.
Because the kneecap is connected to strong muscles, the fracture pieces are usually pulled apart so that they do not lie next to each other, but rather dislocated in the knee joint area. Accordingly, a fractured kneecap cannot usually be treated conservatively, but requires a surgical procedure. Adequate therapy with correct restoration of the anatomical conditions is particularly important, since otherwise permanent functional limitations of the knee joint may occur.
The incorrect position of the patella fragments can cause further injuries to the knee joint and lead to malpositioning with secondary body malpositioning and consequential damage to the foot and hip. Conservative treatment in the form of immobilization in a plaster cast is only possible if the fracture is not displaced, i.e. the fragments remain in their correct position. The plaster is intended to prevent later displacement so that the patella can heal normally again.
If surgical therapy is necessary, the fragments are fixed together and the sometimes injured ligamentous apparatus is restored. In addition, the patella is x-rayed intraoperatively to check that it has been correctly reassembled. Even malpositions of one millimeter can later lead to relevant restrictions in the function of the knee joint.
It is particularly important that the fixation of the fragments is very stable, otherwise they can be pulled apart again by the strong pull of the thigh muscles. If the joint surface is thus not restored correctly, arthrosis can easily develop as a result, accompanied by pain and restricted mobility. In order to avoid a patella fracture from the outset, knee pads should be worn, especially for sports with increased risk (inline skating, ice skating, skateboarding, cycling).
In the event of a fall, these lead to the force not acting directly on the patella, but being absorbed and better distributed. As a result, fractures can usually be prevented.
