Stabilization of the patella

Published by Professor Etienne Cavaignac, an Orthopaedic surgeon specializing in knee and sports traumatology

Written by Professor Etienne Cavaignac


The stabilization of the patella is practiced by an intervention consisting in replacing the damaged ligament, generally in charge of maintaining the patella in its place.


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There are several causes of patellar instability, although the patients are often young and athletic. Stabilization of the patella is performed by replacing the injured ligament, which is usually responsible for holding the patella in its socket. The patella moves out of place, causing severe pain and preventing the flexion-extension activity of the leg.

The patella: a useful little bone

The patella is the small pebble-shaped bone on the front of the knee. It is also called the patella. It is positioned in a small housing located at the head of the femur and called the trochlea.

Ligaments and tendons hold it in place. In particular, an important ligament is attached to the femur and the patella, right in the middle; it is the medial patellofemoral ligament (MPFL).

The patella allows all movements of flexion and extension of the leg and all actions related to mobility (walking, running, change of position, sitting/standing/lying, etc.). It is an essential stabilizer of the patella and prevents it from dislocating. It is therefore very much in demand daily.

Patellar instability: causes

This pathology is not related to age. It often affects young and athletic patients who practice an activity that requires a lot of knee flexion (skiing, soccer, etc.).

Hyperlaxed people (whose joint movements are naturally too great), mainly adolescents and women, may also be affected. A bone abnormality of the femur, the patella, or a defect in the axis of the leg can also cause this instability.

This joint deformation is called patellofemoral dysplasia (femur and patella). Another possible cause of instability is that the patella is placed too high in the joint, and in this case, it engages with difficulty in the trochlea.

Patellar instability: symptoms and consequences

Occasionally, the kneecap may come out of its socket and move to the side of the femur, outside the knee. This is called a dislocation of the patella. This very painful pathology is also disabling, as it prevents specific movements in everyday life.

If this dislocation is repeated at least twice, it is called patellar instability. Very painful, this instability prevents walking and flexion or extension movements of the leg (stairs, sloping ground, change of sitting/standing position, etc.) The knee locks are stiff, do not function well, or makes a clicking noise. At rest, the patient may feel very temporary relief. In addition to pain and displacement of the patella, bleeding and swelling may indicate damage to the patellofemoral ligament that holds it in place.

To diagnose, the doctor performs a clinical examination, palpation, and flexion-extension movements to localize the pain and verify that the patella is unstable. X-rays, scans, and arthroscans will be performed in addition if necessary.

Depending on the results and the abnormalities observed, an adapted treatment is proposed in order to stabilize the patella.

Stabilization of the patella

This surgery aims to prevent the patella from dislocating (coming out) on the lateral side of the knee. In all cases, the injured medial patellofemoral ligament, which no longer fulfills its function of preventing the patella from coming out of its socket, will be reconstructed.

The tendon of the gracilis muscle (inner thigh muscle) will then be used to replace this damaged ligament. After removing a piece of this tendon through a small incision in the thigh, the surgeon will attach it to the kneecap and the inner part of the femur.

Depending on the case, an osteotomy of the tibial tuberositý may be performed. This involves the surgeon detaching the area of the tibia around where the tendon inserts to replace it in the desired location, thus changing the direction the extensor apparatus will take. Therefore, during flexion-extension movements, the patella will no longer have this tendency to leave the trochlea because the tendon will be in the right place to hold it.

The healing of the gracilis muscle, from which the surgeon will have removed a piece, is generally simple and quick. This operation, performed on an outpatient basis, takes about 20 minutes. The patient can therefore get up the same day.

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