In the typical patellar dislocation, the patella jumps out of the intended slideway to the outside. This leads too often to injuries of ligaments, cartilage, and bones. The first luxation event usually occurs before the age of 20.
Causes of a patellar dislocation
In most cases, this is an unfavorable combination of components that promote luxation.
From an anatomical point of view, a knock-knees, an incorrectly positioned patella (patellar dysplasia, so-called hunter’s hat patella), and a too far outwardly positioned attachment of the patellar tendon (patellar tendon) are risk factors.
From a strong point of view, an imbalance of the outer and inner front thigh muscles promotes luxation.
The more risk fractures come together -- the higher is the probability of a patella dislocation.
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Classification of patellar dislocation
Patellar stability is divided into three degrees of patellar instability:
- patellar lateralization (where the patella slides too far out) in the patellar sliding bearing
- subluxation of the patella (the patella is almost dislocated)
- dislocation of the patella (complete dislocation of the kneecap)
The first patellar luxation with an accident event is medically called traumatic patellar luxation. Renewed dislocation events are referred to as chronic recurrent (post-traumatic) patella dislocation.
A patellar dislocation that occurs without a real accident event is called a habitual patella luxation. In this case, the patella jumps out and back in without significant complaints. This instability is particularly evident in the first 45° of flexion.
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Symptoms of the patellar dislocation
Patella luxation can be diagnosed by observation alone. In almost all cases, the patella jumps outwards beyond the intended glide path. There it is visible, and the patella slide bearing is empty.
In most cases, a so-called self-reposition occurs. This means that the patella jumps back into its slideway with slight movements.
In these cases, a detailed medical history is necessary.
If the patella luxates, the inner ligamentous and retaining apparatus of the patella (medial retinaculum) ruptures. As the patella moves out of the glide path, further damage to the patella and the femur often occurs.
The consequence of the traumatic dislocation of the patella is an effusion of the knee joint (articular effusion) and sharp pressure pain under the central patella facet (tearing (rupture) of the medial retinaculum). A traumatic dislocation of the patella is indicated by the sudden collapse of the knee joint during the dislocation process (Giving way).b The symptoms of a patella dislocation (dislocation of the patella) are usually so typical that they allow the trained doctor to make a gaze diagnosis.
However, it must be remembered that very often, especially when the patella has slipped out of its position for the first time in an accident, it spontaneously slides back into its slide bearing (self-reposition).
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It is, therefore, important that a thorough anamnesis (systematic medical examination) is taken if a patella dislocation is suspected of having occurred, even if similar symptoms no longer exist at present.
In the case of patellar dislocation, the patella jumps out of the intended slideway. In most cases, a patellar dislocation ruptures the inner ligamentous and retaining apparatus, which is why it usually slips outwards beyond its intended sliding path.
Typically, the knee looks strongly deformed, the patella is no longer in its original slide bearing but further outwards.
Consequently, there is severe pain in the knee joint. Particularly when pressure is applied, the parts of the inner edge of the patella hurt most of all because the ligaments have torn off here.
Bleeding may also occur due to the torn ligaments. These bleedings into the knee joint become visible by a knee joint effusion with an accompanying swelling of the joint, which develops relatively quickly after the traumatic event.
Due to the pain and joint effusion, mobility in the knee joint is severely restricted or even impossible.
Often not only the kneecap itself but also other structures are damaged in the course of an injury, which can lead to bone fractures or chipping of cartilage or bone fragments, for example. If a patellar dislocation remains undetected or untreated, it often leads to further damage to the patella and the thigh over time, which can lead to the development of arthrosis in the long term.
Besides, such an initial event can cause the patella to become unstable in the long term and, therefore, to jump out of its position again and again, even without a direct trigger.
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Diagnosis of the patellar dislocation
If the kneecap is still luxated, the diagnosis can be made by a single observation.
Also, the knee joint effusion and the Giving way are groundbreaking for the diagnosis.
The clinical examination is the so-called Apprehension Test. In this test, an attempt is made to slide the kneecap over the outer slide bearing in a relaxed state. The test is considered positive if an involuntary defensive movement is performed or the patella can be luxated.
An x-ray of the knee joint is carried out on apparatus-based diagnostics.
In addition, an image of the kneecap is taken in three positions (patelladéfilé at 30°,60° and 90° flexion of the knee joint). This image can be used to assess patellar dysplasia (misalignment of the patella), arthrosis behind the kneecap (retropatellar arthrosis), and bony excrescences (boiling cartilage flake).
If there is a strong suspicion of cartilage shearing at the rear surface of the patella or the outer femoral condyle, a magnetic resonance tomography of the knee joint (MRI knee) should be carried out to determine the extent of the damage.
In addition to the cartilage damage, ligament injury can also be assessed in magnetic resonance imaging of the knee joint, especially of the medial retinaculum of the kneecap, which often tears entirely in the case of an outward dislocation of the patella.
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Therapy of a patellar dislocation
In most cases, a patellar dislocation does not require any treatment because it usually returns to its slide bearing by itself (self-reposition), especially when the knee joint is brought into an extended position.
However, if this does not happen, it is essential to treat a patellar dislocation quickly and adequately to avoid possible consequential damage. The aim is to bring the patella back into its slide bearing permanently since the probability of cartilage damage increases with each new dislocation.
First of all, the patella must be brought back into its correct position as quickly as possible. This repositioning can be done either by a doctor or an experienced sports trainer. Here it is essential to stretch the knee slowly while keeping the kneecap firmly in place so that no sudden unwanted movements can occur. If the reduction is successful, the patient will immediately notice an improvement in pain. If possible, an x-ray or computed tomography (CT) should then be performed to confirm the correct position of the kneecap.
Depending on the extent of the damage caused, there are various treatment options to choose from.
Magnetic resonance imaging (MRI) can be used to determine whether the ligamentous and supporting apparatus has been damaged. If this is not the case, a conservative (non-surgical) treatment is usually sufficient to repair the defect. It is often sufficient to stabilize and immobilize the knee joint for about six weeks with the help of a guide rail (orthosis), a plaster sleeve, or a bandage.
Preparations from the antirheumatic group (non-steroidal antirheumatic drugs, NSAIDs) such as diclofenac or ibuprofen are particularly helpful in this case. Cooling ointments can also help reduce swelling and relieve pain. In rare cases, it may be advisable to relieve a more massive knee joint effusion using a puncture.
Besides these acute measures, physiotherapy should be carried out over a more extended period. This means that the patient should, by no means, allow the resting phase to become too long and should be mobilized quickly afterward, preferably under medical or physiotherapeutic supervision. On the one hand, this serves to prevent a regression of the musculature and a stiffening of the knee joint. On the other hand, muscle-building training should be carried out to improve strength and coordination, thus making a renewed dislocation of the kneecap less likely.
However, if there is extensive cartilage damage or defects of the ligamentous apparatus or a shearing of a cartilage-bone fragment (flake), surgical therapy should be performed.
Even after repeated dislocations, surgery is usually resorted to at some point in time to ensure long-term healing.
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Taping the patellar luxation
The treatment of a patellar dislocation usually begins with a conservative attempt before resorting to surgical measures, although in 50% of cases, this can already lead to permanent success.
Only if the therapy is unsuccessful or a new dislocation occurs will surgical therapy be used. The conservative therapy approach here consists of physiotherapy and the application of bandages, orthoses, plaster sleeves, or tapes.
With the help of these measures, an attempt is first made to immobilize and strengthen the patellar muscles (especially the quadriceps muscle). The application of tapes – preferably Kinesio-tapes – is aimed at bringing the patella into the correct position or into its guide rail in order to allow smooth movement in the knee joint and prevent (re)slipping. It, therefore, serves to fix the patella in its correct position quickly.
In addition, the application of a Kinesio tape can also reduce pain and inflammation, provided that one of the two has previously existed in the context of the patella dislocation or the existing patella malposition.
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Patellar luxation surgery
The correct treatment following a patellar dislocation is of great importance, as otherwise, consequential damage such as arthrosis can develop very frequently. In addition, there is an increased risk of suffering a new patella dislocation, and thus the probability of complications increases.
Initially, one usually tries to perform the treatment conservatively, i.e., without an operation.
Under certain circumstances, however, it may be necessary to have a surgical intervention.
Factors that speak in favor of an operation:
- The non-response to conservative therapy
- Multiple luxations
- Pervasive cartilage damage
- Shearing of cartilage-bone fragments (flakes)
- Damage to the holding and band apparatus
Of course, the patient’s wishes are always decisive in determining whether or not the operation is ultimately performed.
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Which of the available operations is preferred in an individual case depends on:
- patient’s age..,
- the extent of the injury (instabilities, frequency of dislocations)
- primary anatomical conditions (malpositions)
All procedures aim to restore the normal anatomy of the knee joint. During the operation, it is essential to repair the cartilage damage on the one hand and to remove any free bone or cartilage from the joint on the other. These removals can usually be carried out during arthroscopy of the knee as part of the diagnostic procedure. As a rule, soft-tissue surgery is primarily used when it is highly likely to lead to healing, and only in more extreme cases is bony correction methods (which, moreover, may only be used after growth has been completed).
For example, insall surgery is a pervasive operation. Here, the inner capsule apparatus is sutured tightly, and the ligament is gathered on the inside, which ultimately pulls the kneecap more towards the inside of the joint, making it much more difficult to luxate outwards.
MPFL reconstruction often occurs when the holding apparatus is damaged. In this procedure, the triangular ligament between the inside of the patella and the thigh (the Medial Patello-Femoral Ligament = MPFL) is replaced by a tendon that is previously obtained from the lower leg. This results in high stability. If necessary, both procedures can be combined with the so-called “lateral release.” This is characterized by the fact that the ligament structures on the outside of the patella are severed, which reduces the tendency of the patella to protrude outwards.
A bony measure is, for example, the tuberosity dislocation (surgery, according to Elmslie-Trilat). In this procedure, the point where the kneecap tendon attaches to the lower leg is moved further inwards.
As a result, the patella is located further inwards in its glide path and can no longer dislocate so easily.
However, there are many other possibilities for treating a patella dislocation surgically.
After the operation, however, the treatment phase is not yet complete. Depending on which procedure is chosen, the patient must still relieve the knee joint for a certain period and then undergo regular physiotherapy in order to ensure the correct position of the patella in the long term.
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Aftercare of the patella luxation
The follow-up treatment after a reconstruction operation for a patella dislocation consists of 4 phases.
The first phase begins during the hospital stay and includes the first week of post-operative care. Pain medication, cryotherapy, passive, and active-assisted physiotherapy using a movement splint and lymph drainage are used. Only 2-3 days after the operation, the knee remains immobile using a splint, after which the therapy mentioned above and a partial weight-bearing of approx. 50lb begin.
After the first week, the same therapy measures are continued outside the hospital, and physiotherapy is intensified. The partial weight-bearing is increased to half the body weight.
This is followed by phase 2 for a further two weeks, during which active physiotherapy with the full range of motion as required, strength and stretching exercises are performed, and full weight-bearing with orthosis is aimed for.
The following phase 3 includes four weeks of further increase in load and training intensity, as well as a full load without orthosis.
In phase 4, i.e., about three months after the operation, sports-specific training can be resumed without restriction (ball and contact sports; however, only after 9-12 months).
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Every patellar dislocation is a severe injury to the knee joint, often accompanied by permanent damage. For this reason, optimal follow-up treatment of the often still young patients is particularly important.
Even with ideal follow-up treatment of a patella luxation, damage to the cartilage sliding surface of the patella and thigh must be expected in the medium and long term. The highest goal must be to keep this damage as low as possible in order to ensure a long-term pain-free function of the knee joint.
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