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Patella Problems & Instability

Other popular names

Who does it affect?

Anyone.  In some patients this tendency is greater than others due to their own individual body shape and bony anatomy.  In others it may be due to injury.

Why does it happen?

Disorders of the patello-femoral joint, that is the articulation between the undersurface of the patella and the front of the femur (the trochlea groove), are very common.

They can be broadly divided into two groups – patella instability and pain.  Patella instability is where the patella dislocates or subluxes (partially dislocates).

In everyone the pull of the quadriceps muscles tends to pull the patella laterally.  Some patients are pre-disposed to subluxation or dislocation and can dislocate their patella for the first time with less severe, and for some patients, even trivial trauma.  Some patients without such a pre-disposition can sustain a more severe injury that causes the patella to dislocate.

When a patella dislocates for the first time, it causes a rupture or stretching of a ligament on the inside of the knee called the medial patello-femoral ligament (MPFL).  This ligament normally is the primary restraint preventing lateral dislocation of the patella.

After a dislocation this ligament remains stretched and no longer restrains the patella resulting in an increased risk of further dislocations/subluxations.
The overall risk of having further episodes of patella instability is in the order of 50%, although the individual risk varies enormously depending on the pre-disposing factors present.


A combination of pain, swelling, instability and tenderness which may be localised or extended depending upon the injury.


The diagnosis is often clear with a knowledge of lateral dislocation of the patella followed by marked pain and swelling. On examination there is tenderness over the stretched MPFL.

After the pain and swelling of the acute injury has settled, abnormal lateral movement of the patella is often apparent and patients are often very apprehensive when the patella is moved laterally (patella apprehension).

An MRI scan is occasionally used to confirm the diagnosis and to identify any other injuries in the acutely painful and swollen knee following a dislocation.

Non-surgical treatment

All patients need a period of rest and rehabilitation following the acute injury.  This should include a program of physiotherapy to regain a full range of movement and improve muscle function around the knee.

Many patients are able to prevent further episodes of subluxation or dislocation by performing exercises taught though a physiotherapy programme aimed at improving the ability of the quadriceps, in particular, the function of the VMO (vastus medialis obliquitis) muscles to prevent patella dislocation.

Unfortunately some patients continue to experience patella instability symptoms despite a properly performed exercise programme and these patients can require surgery to prevent further episodes of dislocation.

Surgical treatment

Surgery is most commonly in the form of a medial patello-femoral ligament (MPFL) reconstruction but can also involve realignment of the patello-femoral joint with an osteotomy of tibial tuberosity to alter the angle of pull of the quadriceps tendon and sometimes more complex operations.

MPFL Reconstruction surgery involves a general or spinal anaesthetic as a day case or overnight stay. The aim of the operation is to rebuild the torn Medial patello-femoral ligament using the hamstring tendon along the same principles as an ACL reconstruction.

The procedure is usually performed using arthroscopic assistance and is aimed at replacing the deficient ACL with a graft ligament to stabilise the knee. The semitendinosus hamstring tendon is normally used as the graft to form the new ligament. This graft is taken through a small incision (4cm approximately) over the inner aspect of the shin just below the knee.

The tendon is passed through drill holes in the femur and patella so that it lies in the same position as the medial patello-femoral ligament.  This requires further small incisions over the femur and inner aspect of the patella. It is held in place with a screw or similar device in the femur and patella.

Post-surgery rehabilitation

MPFL reconstruction is performed as a Day Case or with an overnight stay.  All patients will need someone to take them home.

The anaesthetic will wear off after approximately 6 hours.  Simple analgesia (pain killers) usually controls the pain and should be started before the anaesthetic has worn off. 

Patients need to use crutches for the first 2 weeks following surgery although they can fully weight-bear - the crutches are mainly to prevent falls until good muscle control has been regained to the leg.


The large bandage around the knee is normally removed 24-48 hours after surgery and a tubigrip may be used to supply gentle compression to reduce post-operative swelling.

The sterile dressings on the wounds  may be replaced with clean waterproof dressings.  

Return to normal routine

Bathing and showering

The wounds should be kept clean and dry until the wound has sealed. Showering is fine and the waterproof dressings can be changed afterwards. Bathing is best avoided until the wounds are sealed, typically 10 days after surgery.

In summary, whilst the wounds are wet - keep them dry and when the wounds are dry, you can get them wet!


Surgery is followed by a prolonged course of physiotherapy. This requires a commitment to undertake this rehabilitation in order to achieve the best possible result (at least half an hour per day for 6 months).  It is vitally important to stay within the post-operative activity restrictions an physiotherapy guidelines to avoid damaging stretching your reconstructed ligament.

Return to work

The timing of your return to work depends on the type of work and your access, however, the following is a general guide:


When you can walk without crutches or a limp and be in control of your vehicle (about 4-6 weeks).


This procedure recreates an ‘anatomic’ MPFL and is effective in preventing further dislocation in more than 90% of patients.  MPFL reconstruction is a reliable operation, however, there is a small risk of problems or complications with any surgery.

These risks include:

All these risks are uncommon and in total, the chance of being worse off in the long term is about or less than 1%.

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