Patellofemoral Instability

In the normal knee, kneecap moves up and down in the femoral groove as the knee bends and straightens. Altered anatomy and biomechanics of the patellofemoral joint result in abnormal forces that can result in the kneecap popping out of place. For example, if the groove is shallow or the kneecap small and high, it may not engage in the groove and could slide off resulting in partial or complete dislocation. A dislocation can also occur in an entirely normal knee during a traumatic event such as a fall or sporting injury.


The two common causes of instability are developmental and traumatic. This means that the way we are made could play a large part in determining whether we suffer with instability. All the causes mentioned before can also be responsible for instability although the majority of the severe cases have an underlying anatomical cause for example a shallow groove or a high kneecap.


There may have been some pre-existing symptoms such as pain in the front of the knee that worsened with activity, occasional stiffness and/or swelling and creaking or cracking sounds during movement. With instability, the knee may not be able support the body weight during walking or activities like dancing. It can buckle and give way, resulting in pain or even a fall. The kneecap can partially of completely dislocate.


In cases where there is a complete dislocation of the kneecap, the first step is to return the kneecap to its proper place in the femoral groove. Sometimes, this happens spontaneously. Other times, the kneecap needs to be gently manipulated back in place.

In cases where there is a sensation of instability or partial dislocation, the initial treatment is non-surgical with physiotherapy and exercises to stretch and strengthen the musculature around the kneecap. Cycling is often recommended as part of the rehab with an aim to return to normal activities within 1 to 3 months.

A complete dislocation often damages the cartilage on the underside of the kneecap and it may rupture a ligament (MPFL) on the inner aspect of the knee. The damaged kneecap cartilage can lead to additional pain and if torn off, can become a loose body floating inside the knee.

In recurrent or chronic cases of instability where non-operative measures have failed to improve the symptoms, surgery is considered to realign tendons and tighten ligaments to keep the kneecap in the groove or to release tight tissues that pull the kneecap off track.


Most people get better with simple non-surgical treatments although it may take 4-6 months for full recovery. Surgical treatment may be considered in patients with persisting symptoms despite the non-operative measures mentioned above.

Surgical treatments include:

1. Arthroscopy

This is keyhole surgery where fragments of damaged kneecap cartilage can be removed through a couple of small incision on either side of the kneecap. This is usually a day case procedure and the patient can walk out of the hospital on the same day.

2. Lateral Release

This could be done as a keyhole or an open procedure. The aim is to release the tight soft tissue structures on the outer aspect of the knee that pull the kneecap off track.

3. Realignment

In patients with malaligment problems the knee is opened the position of the kneecap is changed to realign it with the femoral groove. This reduces the abnormal pressure on cartilage of the kneecap and the supporting structures around the front of the knee.

4. MPFL Reconstruction

This is the Medial Patellofemoral Ligament located on the inner aspect of the knee. In certain circumstances where the kneecap has dislocated as result of a traumatic event, the repair/reconstruction of this ligament can restore kneecap stability.

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