Vastus medialis is the medial head of the quadriceps muscle.
What are the four heads of the quadriceps muscle?
The word 'quadriceps' means 'four heads'. The upper part of the quadriceps muscle has four distinct muscles which combine below into a common quadriceps tendon, which contains the patella, and continues as the patellar tendon:
- vastus lateralis
- vastus medialis
- vastus intermedius
- rectus femoris
Quote from peer-reviewed paper:
"The true insertion of the quadriceps femoris is into the tibial tubercle, but convention considers it as inserting into the patella....through the quadriceps tendon or the suprapatellar tendon....and the part distal to the [patella] is known as the patellar ligament...., patellar tendon, or infrapatellar tendon."
Citation: Waligora AC, Johanson NA, Hirsch BE. Clinical anatomy of the quadriceps femoris and extensor apparatus of the knee. Clin Orthop Relat Res. 2009 Dec;467(12):3297-306. doi: 10.1007/s11999-009-1052-y. Epub 2009 Aug 19. PMID: 19690926; PMCID: PMC2772911.
What is the VMO?
The VMO, or vastus medialis obliquus, is the bulky inner part of the vastus medialis just above the patella. It has oblique fibres, and is called the vastus medialis obliquus or VMO muscle. It has particular importance in stabilising the patella.
Peer-reviewed paperQuote from peer-reviewed paper:
"The most distal muscle fibers of the....[Vastus Medialis or]....VM often are referred to as the....[Vastus Medialis Obliquus or]....VMO....[but]....[t]here is controversy regarding whether the VMO is a separate muscle with separate innervation....The obliquely oriented fibers....contribute to medial patellar stability through their contribution to the superficial layer of the MPFL....[ie. Medial patellofemoral ligament]...."
Citation: Waligora AC, Johanson NA, Hirsch BE. Clinical anatomy of the quadriceps femoris and extensor apparatus of the knee. Clin Orthop Relat Res. 2009 Dec;467(12):3297-306. doi: 10.1007/s11999-009-1052-y. Epub 2009 Aug 19. PMID: 19690926; PMCID: PMC2772911.
What is the function of the vastus medialis muscle?
The vastus medialis controls knee extension but also stabilises the patella during weight bearing.
Peer-reviewed paperQuote from peer-reviewed paper:
"VMO activity was pronounced during the weight-bearing conditions, with increased medial and lateral knee movements. This suggests that the VM should not be considered simply as a knee extensor or as a muscle whose main role is to maintain normal patellar tracking."
Citation: Toumi H, Poumarat G, Benjamin M, Best TM, F'Guyer S, Fairclough J. New insights into the function of the vastus medialis with clinical implications. Med Sci Sports Exerc. 2007 Jul;39(7):1153-9. doi: 10.1249/01.mss.0b013e31804ec08d. Erratum in: Med Sci Sports Exerc. 2008 May;40(5):982. Best, Thomas [corrected to Best, Thomas M]. PMID: 17596784.