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Knee disc

Kniescheibe
Kniescheibe

o be exact, the knee joint has 2 joints. It consists of the joint between the upper and lower leg bones and the joint between the knee disk and the thigh. Basically, both parts may be affected by damage or injury. The knee disk (patella) is important for transferring power from the thigh muscle to the lower leg. It centers the incoming muscle energy and bears weight with every extension of the knee or with stopping movements. Optimal function is possible only if the inner and outer ligaments center the knee disk in the sliding channel. If this function is disturbed, the knee disk joint becomes overloaded and pains develop. In some cases the result is knee disk instability with luxations.

Knee disc luxations
The sliding channel of the knee disk is quite flat. For this reason, the lateral tendon apparatus has great significance for stabilizing the patella. If the knee disk is dislocated (patellar luxation), these ligaments tear or at least become overstretched. A patellar luxation resulting from an accident occurs if direct trauma takes place that is strong enough to tear the patella out of its position. Much more frequently the knee disk moves out of the sliding channel without apparent trauma. This instability is therefore considered as caused naturally. The cause is a congenital weakness in the ligament or a flat sliding channel. A distinction is made between what is called the habitual patellar luxation and the purely traumatic patellar luxation. Initial treatment consists of repositioning the knee disk, the diagnostic clarification of accompanying damage (cartilage fractures), treatment of blood effusion with cooling and possibly with puncture, administering medications for reducing swelling and pain, and heparin for thrombosis prophylaxis. Early functional exercise treatment with partial load bearing is usually possible immediately. If there is no serious damage to the cartilage, the prognosis is good. In tears of the support apparatus of the knee disk, there may continue to be a chronic instability, which makes an operation necessary (see below regarding habitual patellar luxation).
 
Operating technique
In serious tears and primary instability of the patella, the operative reconstruction of the medial support apparatus is performed. This can occur through open suture of the binding tissue in the joint capsule. In most cases the torn joint capsule can be adapted once again into the knee disk with the use of arthroscopy and minimal incisions. Here too the prognosis is good.

Habitual patellar luxation
This is understood to mean the repeated and regular movement of the knee disk out of its sliding position, in which patients initially need only medical help. As time passes, they are usually in a position of themselves repositioning the knee disk. The causes of this instability depend on the physical structure. The constant, partial or complete movement out of the knee disk from its guidance is very limiting and painful; in addition, this instability over the long run usually leads to significant wearing away (arthrosis) of the knee disk joint. In essence, several causative factors come together here, such as elevation of the patella and flattening out of the sliding path at the thigh bone. As a rule, a concave channel exists here, it in which the patella is well centered and from which a perfect path is made. If there is significant flattening or even a convex shape of the entry of this channel, the patella tends to center itself very late or even to bypass this sliding path completely. Other disturbing factors are a strong knock knee axis of the knee joint and assorted rotation variants between the hip joint, the upper and lower knee joint, and the lower leg. The diagnostic clarification consists of a thoroughgoing clinical examination and an x-ray with assorted special projections of the knee disk. Intensive physical therapy, supported by taping and wearing an elastic knee cover, are possible as conservative measures.

Operating technique
Here the various unfavorable factors are corrected. A knee disk situated too high is corrected by moving the end of the tendon down to a normal position. This shifted bone graft is made stable with screws, and as a result functional physical therapy and partial load bearing become possible. In addition, the inner thigh muscle (vastus medialis) is shifted down so that its tension direction works more on the interior side of the knee. If there is strong smoothing and tongue-like extension of the sliding position upwards, this is operatively hollowed out until reaching an approximate anatomic form. In severe instabilities and in significant axial deviations and rotational errors, axis corrections (repositioning osteotomies) and rotation osteotomies may be necessary. However, this is seldom the case.

Rehabilitation
In most operations, the prognosis is good. The repeat rate is low. Operating treatment requires a short inpatient stay of several days. Further treatment for functioning begins early with partial load bearing for about 4 weeks. The length of physical therapy can be estimated at a total of 3-4 months.

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