The So-Called "Vastus Lateralis Obliquus" is the Most Distal Part of the Vastus Intermedius

The vastus lateralis (VL) has long been described as comprising a longitudinal part (vastus lateralis longus, VLL) and an oblique part (vastus lateralis obliquus, VLO), the latter inserting onto the superolateral border of the patella and traditionally regarded as a component of the VL that stabilizes the patella laterally. However, the anatomical relationship between the VLO and the remainder of the VL has never been rigorously defined, and electromyographic studies have independently regarded the muscle belly emerging at the distolateral thigh as the "superficial region of the vastus intermedius (VI)." To address this discrepancy, we re-examined the structure and innervation of the VLO in five thighs from five embalmed cadavers by gross dissection. The belly conventionally identified as the VLO was present in all specimens and inserted onto the superolateral patella. When the VLL was reflected, this belly was continuous with the VI, which arose broadly from the anterior surface of the femoral shaft; thus, the VLO was the most distal portion of the VI protruding lateral to the lateral border of the VL. Consistently, this region was supplied by the terminal twigs of the lateral branch of the VI (femoral nerve), whereas the branch to the VL did not reach it. We conclude that the so-called VLO is not part of the VL but the distal part of the VI. This reinterpretation reconciles the anatomical convention with electromyographic findings and has implications for anatomical nomenclature, interpretation of VI surface electromyography, and understanding the traction source in painful bipartite patella.