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Kneecap instability

The kneecap instability or patellofemoral instability (PFI) is a knee disease that consists of its joint misalignment or dysplasia of the patella and it primarily affects young people. The disease occurs when the patella slips out of its trochlear groove (patellar dislocation), thus becoming unstable. The causes can be multiple, ranging from trauma to bone anomalies of the patella and the femur, alteration of the knee’s capsules and ligaments, or structural problems such as knee valgus, muscular hypotrophy, or joint hypermobility and pathologies of rotational problems of the lower limbs.

Age group

Patellar instability affects people between 14 and 25 years of age. It is rarely diagnosed in older people.

Anatomy of the patella

The patella is a protruding bone that resembles an inverted triangle. It is located at the front of the knee joint and ensures leg extension. It increases the efficiency of the quadriceps muscle while protecting the knee’s anatomical structures.


The first symptom is pain localized at the front of the knee. The pain tends to increase when playing sports that involve flexion and extension movements of the knees and after sitting for a long time, up till the knee stiffens and gets blocked. It can be associated with crackling or crunching noise and swelling. If the patella dislocates (comes out of place), it will cause a blockage of the knee joint and reduce mobility.

When should you call a doctor?

You should call a doctor if the pain persists or if you experience a sensation of instability in the patella and the knee swells.

Diagnostic tools

Given that many factors can cause the patella to be unstable, the tests for diagnosis must be precise. Radiology tests, Magnetic Resonance (MRI), or any examination to study the ligament and cartilage components, as well as Computed Tomography (CT) with a dedicated method called CT with Lionese protocol, are often required. This type of CT scan allows you to evaluate some anatomical parameters of the knee. These tests are crucial to establish the correct therapeutic path.

What to do in the meantime?

Limit high-contact sports and apply ice (without direct contact to skin) prior to a visit with a doctor. You may also use a knee brace with patella centring or functional bandages.

How to prevent patellar instability

Adequate athletic training for under-trained individuals can reduce, if not eliminate, the problem. It is necessary for those who already practice sports to get to the origin of the cause of pain and correct the postures causing the pain.

Conservative therapies

In the first event of kneecap dislocation, therapies are advised only if there are no osteochondral lesions inside the knee which could cause a blockage of the joint. In all other cases, alterations in the knee’s morphological and rotational parameters must be evaluated. Physiotherapy may only be crucial in some cases. To relieve pain, obtain anti-inflammatory medication, apply ice, perform muscle strengthening exercises and stretching as well as go through physiotherapy. If necessary, patients may use knee braces or insoles to support the knee.

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