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Knee: Patellofemoral instability

Patellofemoral instability affects around 6 per 100,000 people, but when one looks at adolescent population, (10-17 yr olds) it affects around 29 per 100,000 people.

It is a spectrum of disorder and ranges from anterior knee pain, to subluxation of patella (knee cap coming out partially) to frank dislocation (knee cap coming out completely resulting in fall or instability).

It can be a result of trauma or it can develop over time due to several inherent risk factors.

Traumatic or acute patella dislocation can reduce itself spontaneously or may need a manual reduction by self or by a medical personnel (usually sports physio on the field or a paramedic or a doctor). The knee swells up usually due to bleeding and rupture of ligaments holding the patella in place (Medial patello-femoral ligament [MPFL]). The treatment for an acute 1st time patella dislocation is usually conservative and includes bracing, ice, rest, crutches and a physiotherapy programme aimed at building up a specific muscle group of quadriceps muscle called vastus medialis obliquus (VMO).

There is a small percentage of patients who will develop a recurrence. These could be due to poor healing of the ligamentous checkrein, or due to Anatomic Patellar instability factors (APIFs). T

These are pre-existing anatomic factors that may have resulted in the dislocation in the first place. These can include a shallow groove for the kneecap (Trochlear dysplasia), higher position of patella (patella alta), twisted knee cap and tibia (increased trochlear-tibial tuberosity distance)

Presence of these factors does not necessarily mean that all of these need correcting, but a careful judgement is needed in planning the surgery.

The gold standard of treatment for recurrent patello-femoral instability is MPFL reconstruction. This is usually done using one of the hamstring tendons from the patient (autograft) or a cadaveric tendon (allograft) or an artificial ligament (fibertape).

Additional surgery may be needed depending on APIFs.

The rehabilitation after surgery is very important too and the overall success of the surgery largely depends on the engagement with and adherence to a strict Physiotherapy protocol.

For more information and advice about Patellofemoral instability and MPFL reconstruction, click on

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