The vastus medialis oblique (VMO) refers specifically to the distal oblique fiber bundle of the vastus medialis muscle whose fibers run at 50-55 degrees to the quadriceps axis, inserting directly onto the medial patella. It is the principal dynamic medial patellar stabilizer in terminal knee extension. VMO atrophy or inhibition is associated with patellofemoral pain syndrome, patella alta, and patellar instability.
| Origin | Medial intermuscular septum and medial supracondylar ridge of the femur; the distal oblique fibers arise from the adductor magnus tendon |
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| Insertion | Medial border of the patella and the medial patellar retinaculum; the oblique fibers insert at 50-55 degrees to the quadriceps tendon axis |
| Nerve Supply | Femoral nerve (L2-L4) |
| Blood Supply | Descending genicular artery; medial superior genicular artery |
| Actions | Extends the knee; the oblique fibers specifically resist lateral patellar displacement by pulling the patella medially during terminal knee extension; provides the primary dynamic medial restraint to the patella in the last 10-15 degrees of extension |
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VMO strengthening is the cornerstone of conservative treatment for patellofemoral pain syndrome and patellar instability. Straight-leg raises, terminal knee extensions, and VMO-biased closed-chain exercises selectively activate the VMO. Biofeedback EMG training can improve VMO:VL activation ratio. After total knee arthroplasty, restoring VMO strength is essential for patellar tracking. The medial parapatellar TKA approach requires careful VMO repair to restore patellar stability post-operatively.
Reflex inhibition of the VMO in the presence of even small knee effusions allows the dominant vastus lateralis to lateralize the patella, worsening patellofemoral contact pressure; EMG-biofeedback-guided VMO training restores the VMO:VL timing ratio and reduces lateral patellar tilt in patellofemoral pain syndrome.
