Patellar instability


Patella is a bone found on the front of the knee, in the thigh muscle tendon ending (quadriceps). Quadriceps tendon is above the patella, toward the thigh, and the patellar tendon is attached toward the calf, below the patella. The fibrous layer covering the patella continues on these two tendons.

Patella has a protective role of the quadriceps tendon and it increases its leverage, thus its force on the tibia. Thus, patella removal leads to 30% loss of the quadriceps strength.

During flexion or extension, the patella slides up and down, and at the thighbone level it is at the front of the femoral groove called femural trochlea. Patella is above the trochlea when the knee is in extension. Knee flexion leads to engagement of the patella in the trochlea.

Patella is held mid-trochlea through multiple ligament attachments constituting the patellar wings. They are represented by triangular fibre blades originating on the lateral limits of the patella, ending on the femur (femoral condyle).

Patellar dislocation

Patella can dislocate, i.e. leave its normal place from the rest of the joint; it always dislocate outward. When the patella is dislocates, knee is completely blocked in flexion and patients experience acute pain.

This is an orthopaedic emergency; patella must be put in place and the repositioning is always done with the knee in extension. Sometimes repositioning happens spontaneously, by putting the knee in extension. This dislocation is accompanied by ligament injuries, often at the origin of residual patellar instability.


In a first step, patellar instability should be treated medically, even if examinations show that there are anatomical abnormalities.

Pain should be treated with painkillers and anti-inflammatory drugs, and especially with rehabilitation. In addition, in case of patellar dislocation, the first episode should always be treated correct. Good rehabilitation is essential because it can help avoid surgery.

First dislocationshould be treated by the emergency department with rehabilitation, followed by splint immobilization. It may be a plaster splint or a removable splint.

Knee puncture is not always useful. If the knee is very swollen, a puncture evacuating the haematoma could alleviate the pain, leading to a faster recovery of joint mobility.

Rehabilitation starts in about ten days

A good rehabilitation should include strengthening of the quadriceps muscles. Even if the internal vast muscle toning lost some interest, it insists, however, for a harmonious musculature of the quadriceps muscle. At the same time, we need to make stretches of the ischio-calf muscles, followed by a strengthening of those muscles.

After a knee sprain, I usually prescribe twenty sessions at a pace of three sessions a week. The number of sessions required varies on a case-by-case basis, depending on all reported injuries.

Rehabilitation exercises can be continued by patients outside the physical therapy sessions.

Resumption of sporting activity will be done gradually. We recommend cycling or swimming in the beginning, then a short round of footing.

In the resumption of activity, athletes will need to alternate running with walking. For example: at first, 10 minutes of running and 5 minutes of walking, then 10 minutes of running, progressively reaching 15 minutes of running and 5 minutes of walking….

Knee-protections are often used to resume activity.

Descriptionof some techniques used:

Severing of the external patellar ligament

Patella is maintained in the trochlear area by two ligaments. Sometimes, the external ligament is stronger and can be at the origin of an external displacement of the patella. Severing of this ligament allows patellar repositioning. This can be performed by open surgery or arthroscopic surgery.

I advocate a minimal approach via arthroscopy, with simple after-effects, patient leaving the hospital the same day.

Internal myoplasty

It means to strengthen the opposed ligament using the internal vast muscle, of which insertion is lowered to the patella.

Replacement of the medial patellofemural ligament (MPFL)

When this ligament opposite to the patellar external aileron is fully opened, we can consider its replacement often using a tendon graft from a muscle located on the internal side of the thigh. This is often accompanied by the severance of the external patellar ligament.

Transposition of the anterior tibial tuberosity

If the patella is defectively centred, we remove its tibial attachment (patellar tendon) with a bone fragment to allow a patellar re-centring. Sometimes additional actions are needed:  internal transposition, lowering or advancement. Tibialstrip so detached is fixed by screws which can then be removed.


In some patients, femoral trochlea is not hollow enough, favouring patellar instability (as a reminder, trochlea is on the front of the distal part of the femur and is a “rail” on which the patella slides during the knee flexion – extension).

Many techniques have been described to make the trochlea hollower; complementary actions are associated with this intervention.

Patellar dysplasia

Abnormal forms of the patella are too difficult to present here. When it comes to an injury to the cartilage, cartilage grafts can be performed. On the contrary, when dysplasia leads to a major femoral-patellar arthrosis, we propose partial femoral-patellar prosthesis.

Depending on the type of intervention, specific complications may be encountered. Certainly, when the surgical intervention is more complex, the risk of complications is higher.

Complications that can accompany these surgical interventions

We think of postoperative swelling, algodystrophy, phlebitis, infection, postoperative haematoma, instability relapse…


This is a complex pathology with multiple causes; choice of treatment and surgical indication will be decided after a thorough review. I

2018 - DuncaSKS. All Rights Reserved.