Knee-cap instability

The kneecap (patella) sits in the V shaped groove at the bottom of the femur (thigh bone). Some patients, especially young women, develop patellar instability in adolescence. Their patellae are more susceptible to dislocation due to either a bony abnormality of the femur, or due to laxity of the ligaments which stabilise it. These patients are often "loose jointed". When the kneecap (patella) dislocates the ligaments stabilising it may be stretched further and torn. The key stabilising ligament is the medial patello-femoral ligament or MPFL. If the MPFL is torn, this predisposes the kneecap to further dislocations and can cause significant damage to the cartilage lining the under-surface of the kneecap.


If an individual has normal anatomy but sustains a significant injury to the knee cap region, the MPFL can rupture and the knee cap can subsequently dislocate. These individuals are then at risk of having further knee-cap dislocations in the future. Each time this occurs there is significant pain, swelling and difficulty in walking. It also causes repeated damage to the under-surface of the knee-cap. If left untreated, this instability will cause arthritis to this part of the knee. It is therefore important to stabilise the knee cap either through surgical or non-surgical measures in order to reduce the risk of long-term damage to the knee. The most commonly performed operation to stabilise the knee cap is an MPFL Reconstruction

but the whole of the muscle and tendon arrangement on the front of the knee is assessed as sometimes surgery is needed to these structures.

Stable Knee Cap
X-ray of Normal Patellofemoral Joint

X-ray of the patellofemoral joint showing a normal, central position of the patella (knee-cap) in its groove.

Unstable Knee Cap
X-ray of Tilted Patello-femoral Joint

X-ray of the patello-femoral joint showing a patella (kneecap) which is tilted to one side and an empty groove.

Orthopaedic consultation
Key-hole  knee surgery
Mr Wilson carrying out knee arthroscopy surgery
Scrub team before ACL surgery