The medial quadriceps expansion is the contribution of the vastus medialis obliquus (VMO) and the medial patellar retinaculum to the extensor mechanism medial retinaculum. It runs from the medial quadriceps tendon and the medial patella to the medial tibial surface, blending with the medial collateral ligament superficially. The medial patellofemoral ligament (MPFL) is the deepest and most important component of the medial retinaculum, running from the medial patella to the medial femoral epicondyle.
| Location | Medial side of the front of the knee, beside the patella |
|---|---|
| Boundaries |
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Holds the patella against lateral displacement and helps keep it centred in the trochlear groove.
The medial quadriceps expansion is the primary medial restraint to lateral patellar dislocation: when the medial retinaculum and MPFL tear in an acute patellar dislocation, the medial expansion is disrupted. In recurrent patellar instability, the MPFL component of the medial expansion is reconstructed with a graft from the medial femoral epicondyle to the medial patella edge. VMO strengthening exercises target the medial expansion to dynamically stabilise the patella, and are the first-line treatment for patellofemoral pain syndrome.
Lateral patellar dislocation tears the medial quadriceps expansion including the MPFL from the medial patellar margin, producing acute medial knee pain and haemarthrosis; MRI confirms the MPFL avulsion from the patella bone marrow oedema pattern, and recurrent instability from MPFL failure is treated by anatomic MPFL reconstruction with gracilis or semitendinosus graft.
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