A patellar fracture is a break in the patella, or kneecap, the small bone that sits at the front of your knee. This can result in longitudinal, transverse, or mixed fractures. The therapy of the patella fracture depends crucially on the type of fracture.
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Causes of the patella fracture
In most cases, it is a fall on the bent knee joint. The force of the direct impact breaks the kneecap into two or more fragments.
In traffic accidents, a patella fracture can also occur when the bent knee joint is struck. These injuries are also referred to as “dashboard injuries.”
In exceptional cases, sudden flexion of the knee joint, which is maximally stretched muscularly, can lead to a patella fracture.
Another rare cause is the dislocation of the kneecap (patella luxation), which can lead to lateral shearing off of the kneecap.
One differentiates between transverse fractures, so-called transverse fractures, and longitudinal fractures (longitudinal fractures), which break along the leg axis.
Furthermore, the number of fracture fragments is included in the classification. The position of the fragments to each other is also examined so that one speaks of non-displaced (non-dislocated) and displaced (dislocated) fractures.
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Symptoms of the kneecap fracture
A patella fracture causes pain above the patella. Typically, the lower leg cannot be actively stretched, or the knee joint cannot be kept stretched because the anterior thigh muscles (Musculus quadriceps femoris) can transmit the force via the patella to the lower leg.
The fracture of the kneecap results in a bruise/hematoma. The bruise appears under the skin as a “bruise.” The bleeding into the knee joint shows up as a knee joint effusion (intra-articular effusion, bloody effusion = haemarthrosis).
Since it is often caused by falls on the kneecap, abrasions are often found in this area.
The kneecap is embedded in the tendon of the thigh muscles, which is responsible for stretching the leg in the knee joint. The function of this muscle group (Musculus quadriceps femoris) is now no longer fully functional. As a result, the patient can no longer actively stretch the leg or keep it stretched without outside help.
Some patients also suffer from so-called “crepitations,” i.e., crackling noises when the joint is moved. This is because small pieces of bone often come off the bone during a kneecap fracture. These pieces then move freely in the joint and rub against other structures within the joint during specific movements, which causes this noise.
Depending on the cause of the kneecap fracture, other symptoms such as abrasions on the knee or legs or even fractures of the bone may also occur.
Depending on the severity of the injury, the intensity of the discomfort caused by a broken kneecap can also vary.
A thorough diagnosis should also be made in any case, as the extent of the symptoms does not always necessarily coincide with the objectifiable findings. Just because pain may not be severe, severe damage and accompanying complications can still occur, which should not be overlooked due to a high pain threshold of an affected person.
Further symptoms of a patella fracture
Classically, there is massive pain directly after the triggering violent impact.
These are felt most clearly at the front of the knee joint and above the patella. Under the effect of pressure and strain, they intensify.
The fracture of the kneecap and sometimes surrounding structures leads to bleeding into the joint. This can be felt in two ways:
- If they are relatively superficial, a bruise (hematoma) visible.
- If it bleeds into the joint, it will be more or less pronounced swelling of the knee joint as a result of the Joint effusion (haemarthrosis)
Diagnosis of a patella fracture
The diagnosis of a knee-slide fracture is usually made using an X-ray. In this case, the knee joint is x-rayed in two or, if necessary, three planes. Often, the extent of the injury cannot be adequately depicted, and a computer tomography (CT) is performed. Computed tomography can also be used to display microfractures that are not visible in the X-ray image.
Another useful measure available to the doctor is magnetic resonance imaging (MRI) of the knee. In the MRI image of the knee, the cartilage damage behind the kneecap can be better assessed. As the bone breaks, the cartilage behind the patella also breaks at the same time. Since neither X-rays nor CT images can show the cartilage, the knee MRI is a valuable source of information.
A tear of the patellar tendon (patella tendon rupture) with subsequent patella elevation or a tear of the quadriceps tendon with patella depression may be the cause of comparable damage.
The additional bone piece is located in the upper outer quadrant of the patella. Since this anomaly often exists on both sides, an X-ray of the patella can be helpful.
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In the treatment of a patella fracture, it is prescribed by means of a knee orthosis with limited mobility. The flexion should not exceed 60° within the first three weeks and not exceed 90° until the sixth week.
The knee joint should only be loaded with 40 lb within the first three weeks and should be loaded to full load until the sixth week. Thrombosis prophylaxis, e.g., with low-molecular-weight heparin, must be carried out until the knee joint is actually fully loaded.
Deviations from this post-treatment scheme must be made in individual cases.
Patellar fractures with displaced fractures and a step formation of more than 2 mm and a divergence of the fracture fragments of more than 3 mm should be treated surgically. Especially cross fragment fractures and multi fragment fractures require surgical therapy.
The decision on the type of surgical treatment must be adapted to the individual findings.
For surgical treatment, so-called tension belt osteosyntheses, cerclages, and screw fixation of the fracture are available.
Tension belts are often used for transverse fractures with few fragments and are therefore the most common type of treatment. Two wires are inserted through both fragments in the longitudinal course of the patella. A wire loop in the form of an eight is placed around these two wires. By pulling these wire loops, the fragments are put together again and can heal.
Besides, the fracture can be secured by a so-called equatorial cerclage, especially in the case of multi-fragment fractures.
In the case of a patella fracture in the form of a transverse fracture with few fragments, a screw connection can also be used as an alternative.
In hopeless cases, in which no gradual restoration is possible, the complete removal of the patella must be considered (patellectomy), as otherwise arthrosis causing symptoms to develop in the short term.
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The knee joint should only be flexed by a maximum of 60° within the first three weeks after the kneecap fracture operation and by a maximum of 90° until the 6th week.
The load on the operated leg should not exceed 40 lb at the beginning and should be increased to full load by the end of the sixth week.
Deviations from this post-operative treatment scheme must be made in individual cases.
X-ray examinations should be carried out after 2, 4, and 6 weeks.
The smaller the damage to the patella, the better the long-term prognosis. Approximately 1/3 of all patients with a patella fracture have to expect load-dependent or permanent pain despite optimally treated patella fracture.
In particular, in the case of multi-fragment fractures, comminuted fractures, and fractures that can only be rejoined by forming steps, the risk of permanent pain is increased.n The occurrence of patellar arthrosis (retropatellar arthrosis) is significantly increased after a patella fracture. There is also the risk of joint scarring (arthrofibrosis).
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Duration of a patella fracture
If the patella fracture is treated surgically, it usually takes about six weeks until the fracture has healed enough to allow full weight-bearing.
Of course, the duration of regeneration varies from patient to patient, so that the six weeks should only be seen as a rough guide.
For example, it happens again and again that patients do not achieve freedom from symptoms beyond the six weeks. In some cases, the time until complete healing takes several years, and in exceptional cases, patients even have to struggle with patellar complaints for the rest of their lives after a patella fracture.
In order to have a positive influence on the healing period of the patella fracture, the operative treatment is followed by rehabilitation.
The rehabilitation, which is led by physiotherapists and sports therapists, includes exercises to strengthen the surrounding leg muscles and to stabilize the leg axis on the one hand and coordination exercises and the wearing of movement splints on the other hand.
Depending on requirements, the duration can extend beyond a hospital stay of several days to a week. In the form of tiny exercise units, e.g., moving the feet, rehabilitation begins on the first day after the operation.
The duration of the rehab depends on factors such as age, severity of the patella fracture, and possible previous illnesses. In general, there is no prescribed length of stay, but discharge is usually planned for the 2nd day after the operation.
If complications occurred during the operation or if wound healing is difficult, it is at the discretion of the attending physician to postpone the date of discharge for another day.
The inability to work after a patella fracture is about six weeks. Depending on the activity to be performed, the inability to work can be more prolonged, e.g., if work has to be performed in the knee or is generally extremely stressful for the knee.
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