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Knee dislocations are comparatively rare, but serious injuries. Not to be confused with patellar subluxations (where the patella of the knee disassociates itself from the groove at the end of the thigh bone), a knee dislocation is typically caused by an intensive injury to the knee, resulting in a complete break of connection between the thigh bone (femur) and the shin bone (tibia).
Though most commonly regarded as a sports-related injury, a knee dislocation can also occur in high-speed car crashes or even by misstepping and falling down a hole. In order to better understand knee dislocations in their entirety, we must look at the symptoms, causes as well as the treatment in such injuries.
A typical instance of knee dislocation can be identified by the swelling at the knee joint, the accompanying intense pain as well as the inability to move the knee. While in some cases the knee dislocation might reduce spontaneously within some time of the injury or even be physically reduced by someone, a knee dislocation that is unreduced appears as a significantly deformed knee to the observers.
Often the patient reports hearing of a slight popping sound at the time of sustaining the injury. With the pain being diffused with palpation and the range of motion of the knee being severely compromised, strength testing is not advisable.
When not done under medical supervision, strength testing of the affected knee by the patient himself or his well-meaning caregivers can lead to further neurovascular damage. With significant trauma imparted to the ligaments and soft tissues of the knees, any unnecessary additional trauma is best avoided.
The knee owes its strength to the combined action of many muscles, ligaments and tendons. While the knee is well-equipped to effectively handle valgus as well as varus forces, in addition to maintaining its rotational ability, a knee displacement occurs. The main mechanism of injury (MOI) is when there is forced hyperextension of the knee. This happens at the time of injuries sustained in motor vehicle accidents or caused by collisions between players in high-energy sports such as soccer, rugby or football.
While road accidents and sports injuries are the more commonly seen causes, a knee displacement can also be caused by the inadvertent hyperextension caused by stepping into or falling down a hole. It is this sudden forced hyperextension that leads to the displacement of the tibia (shin bone) from the femur (thigh bone).
Morbid obesity can also be a cause of knee dislocation. With the enormous amount of stress - often ranging between 2 to 4 times of the normal body weight - placed on the muscles and joints of the body, there are times when the knee just gives up, so to speak.
In morbidly obese patients, a knee displacement can occur by the simple act of getting up while seated or just by moving around.
As per Kennedy , there are five main types of knee dislocations.
1. Anterior - Most common kind of knee dislocation, seen in as many as 40% of all such cases.
2. Posterior - Accounting for 30% of such injuries, posterior knee displacements are usually associated with the typical 'dashboard injuries' sustained on the highways and with a sudden fall on a knee that was already in the flexed position.
3. Lateral - About 18% of all knee displacement injuries are caused by the varus/valgus stress on the knee.
4. Medial - Amounting to 4% of knee displacements, medial knee dislocations are also caused by the varus/valgus stress.
5. Rotary - Rarest of them all, such injuries are caused by rotary forces and amount to about 5% of knee dislocation injuries.
The above-mentioned classification system developed by Kennedy was not considered to be very practical as knee displacement injuries are spontaneously reduced and their assessment is hampered by the lack of radiographic clues. Subsequently, Schenck came up with an anatomical classification that was based on the patterns made by the damage to the ligaments. The classification by Schenck was later modified by Wascher.
Knee dislocations can also be classified into the two broad categories
• High-velocity - Such kind of knee dislocations are generally sustained by a sudden and extreme force on the knee, as seen in car accidents. Such dislocations lead to extensive damage to the knee and the soft tissue. In high-velocity knee displacements, the risk of neurovascular damage is also quite high.
• Low-velocity - These are usually seen as sports-related injuries. As compared to the high-velocity knee displacement injuries, such low-velocity knee dislocations cause a significantly lower overall damage to the knee.
The treatment for the knee displacement depends on the kind of injury sustained, as well as the age and the medical history of the patient concerned.
Proper assessment of the injury sustained is vital for suitable treatment to be given. With the spontaneous reduction of the knee dislocation before the patient reaches the medical examiner, it is fairly common for the injury to be underestimated. With the knee dislocation being significantly reduced, the medical examiner can overlook neurovascular signs and misjudge the extent of the injury.
As soon as the injury has been sustained, immediate first aid involves placing the knee in a splint either in extension or in the most comfortable position possible. After this, the patient should be moved to the emergency room without further delay. Once in the emergency room, the medical examiner should assess the knee dislocation which can be significantly reduced by that time. The knee dislocation should then be reduced - either by closed reduction or open reduction.
Post-reduction treatment takes into account a variety of factors, and can be of two kinds.
• Conservative treatment
This treatment is given when the knee joint feels somewhat stable after the reduction, or if the patient is advanced in age or has a sedentary lifestyle. A conservative treatment involves immobilization, which can be anywhere between the range of 3 weeks to 10 weeks. Usually, the average time period for immobilization is 5.5 weeks , anything beyond that leads to residual stiffness in the knee concerned.
• Surgical treatment
Active patients require surgical treatment. The help of magnetic resonance imaging (MRI) and arthroscopy is taken to ascertain whether surgical treatment should involve repair or reconstruction, and to what extent.
As compared to repairs, reconstructions are the much better alternative, providing better results in the long run. Surgical treatment involves the placement of allografts, which are preferred for many reasons - reduced post-operative stiffness and pain, lesser incisions, reduced tourniquet time and elimination of graft site morbidity.
Following the treatment, rehabilitation is determined by the type of ligaments injured as well as the method of treatment given. A patient with a knee dislocation requires a long program for rehabilitation, with a return to complete activity occurring not before 9 to 12 months from the injury. In the conservative treatment, mild rehabilitation can be commenced immediately in the period of immobilization.
Regardless of repair or reconstruction being opted for, an athlete who has undergone surgical treatment for knee dislocation will most likely be unable to perform at par with his performance before the injury.
Despite swift medical attention being provided to the patient, many serious complications can occur. The most serious complication of a knee dislocation is that of vascular damage. If vascular damage is not treated for over 8 hours after the injury, the risk of amputation is as high as 86%. With vascular damage being treated within the crucial 8 hours after the injury, the risk of amputation is 11%.
Other serious complications that can occur from knee dislocation are deep venous thrombosis and acute compartment syndrome. In order to rule out all the complications - vascular damage, deep venous thrombosis, acute compartment syndrome - it is essential to closely monitor the neurovascular signs of the patient, regardless of whether there is a spontaneous reduction or no reduction. Certain post-treatment complications can be post-traumatic arthritis, loss of motion and persistent instability.
Knee dislocation requires proper evaluation by the medical examiner, followed by suitable treatment and a comprehensive rehabilitation program as a follow-up to treatment. While a patient with low-velocity knee dislocation can expect to return to normal activity eventually, an athlete with a high-velocity injury would be wrong to expect to give the same performance as before his injury.
-  Henrichs A. (2004). A review of knee dislocations.Journal of athletic training, 39(4), 365-369.
-  McKee, L., Ibrahim, M. S., Lawrence, T., Pengas, I. P., & Khan, W. S. (2014). Current concepts in acute knee dislocation: the missed diagnosis?.The open orthopaedics journal, 8, 162-167.
-  Hussin, P., Mawardi, M., & Ab Halim, A. H. (2016). A rare variant of knee dislocation.Il Giornale di chirurgia, 37(2), 71-73.