Patellofemoral instability

Written by Dr Sheila Strover on March 14, 2025

In patellofemoral instabilty the patella (kneecap) changes its relationship to the groove of the femur bone (thighbone) and may partially or fully de-rail.

Illustration showing the patella riding up its underlying groove, but still retained by its walls.
In subluxation the kneecap may feel uncomfortably about to come right out of the underlying groove, but then it pops back into place.
Illustration showing patella dislocated right out of its underlying groove.
With dislocation the kneecap comes right out of its groove, creating a painful and ugly deformity. In some cases it pops back but it other cases it stays like that and the person cannot straighten the knee without help.

What constitutes patellar instability?

Patellar instability is a continuum. Patients may progress from one level of instability to another:

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Structural causes of patellar instability

Factors which contribute to an unstable kneecap include one or more of -

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Management of patellofemoral instability

Not every patient will be managed the same - the management depends on the underlying factors that led to the instability.

Treatment plans should be based on the identification of contributing anatomical factors and tailored to each individual patient.

Véronique Drapeau-Zgoralski et al

A-Z Keywords

Patellar dislocation, Patellar subluxation, Trochlear groove

Primer - 2019 - All about dislocation of the patella

Contributions by experts -

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