Ligament instability in the knee

The knee is stabilised by ligaments in conjunction with muscles encompassing the joint. The ligaments must have a certain strength in order to ensure stabilisation and proper mobility in the joint.

Ligament weakness (laxity) may occur due to congenital or acquired factors. This frequently results in weakness of the joints. In case of a ligament rupture, stability in the joint may even be lost entirely.


Knee instablity is caused by congenital or acquired ligament weakness, with or without the involvement of other, stabilising structures (e.g. joint capsule, articular cartilage, menisci, muscular structures). This can lead to significant instablity in the knee joint.

The form of knee instability is generally defined by the number of affected ligament structures. The more ligaments are affected, the more unstable the knee joint will be. When the cruciate ligaments are affected, instabilities frequently result that allow more pronounced shifting of the lower leg to anterior and posterior. The cause of complex knee instability frequently lies in a combination of affected structures, e.g. the laxity of the interior cruciate ligaments, the collateral ligaments, the flaccid knee joint capsule and/or damage to the menisci.


Knee instability may result in a feeling of instability, actual instability, pain and irritation. At the outset, instability is expressed for example by uncertainty while walking or pain under increased strain. Knee instability can be confirmed or excluded by clinical tests.


Once knee instability has been confirmed by clinical test procedures, additional tests often follow in case of painful instability or restricted mobility. These include comparative leg length measurements, examination of the pelvis position and joint-specific tests, e.g. using imaging methods such as X-rays and MRT.


The therapy depends on the cause and severity of the instability. It may be conservative, i.e. without an operation, and/or with an operation. With conservative therapy, the treatment focus is on physiotherapy and stabilising orthoses.

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