The vastus medialis is the most medial quadriceps head, its distal oblique fibres forming the VMO that is the only muscle pulling the patella medially. It preferentially atrophies after knee pain or injury faster than the other quadriceps heads, making it the primary rehabilitation target in any knee condition. Its visible teardrop shape on the inner thigh just above the knee is a useful indicator of quad symmetry.
| Origin | Lower intertrochanteric line, medial lip of the linea aspera, medial supracondylar line, and medial intermuscular septum |
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| Insertion | Medial border of the patella and patellar tendon to the tibial tuberosity |
| Nerve Supply | Femoral nerve (L2, L3, L4) |
| Blood Supply | Femoral artery |
| Actions | Extension of the knee; Medial stabilisation of the patella, particularly through the oblique VMO fibres in the last 30 degrees of extension |
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The VMO fires primarily in the final 30 degrees of knee extension where patellar tracking is most dependent on active muscle control rather than the bony trochlear groove, making it critical for pain-free terminal extension.
VMO atrophy is detectable clinically by comparing the teardrop bulk above the medial patella between sides. Selective VMO strengthening using terminal knee extension, step-downs, and Spanish squats is a cornerstone of patellofemoral pain rehabilitation. The VMO is also a critical post-operative target after ACL reconstruction, where quadriceps inhibition is profound and VMO recovery determines return-to-sport timing.
The VMO forms the visible teardrop-shaped muscle belly on the medial lower thigh just proximal to the medial patella border, best appreciated in lean individuals during the last 30 degrees of a straight leg raise.
VMO weakness relative to the vastus lateralis allowing lateral patellar maltracking, producing peripatellar pain with stairs, squatting, and prolonged sitting that is managed with targeted VMO and hip strengthening.
