This is an overview of the muscles that one comes across when reading about the knee.
Knee muscles from the front
The quadriceps muscles ('quads') dominate the front of the knee, and are the muscles making your 'lap'.
If you sit down and put your hands on your lap, then spread your fingers open - all of that muscle under your fingers are the bulky quadriceps.
This next illustration shows how the rectus femoris reaches all the way from the pelvis and hip to the tibia. The other heads originate on the femur. Physiotherapists tend to focus a lot of attention on the vastus medialis, especially at the lower end where the muscle fibres are more oblique. Here the muscle is referred to as the vastus medialis obliquus or VMO. Weakness in the VMO is considered to be a factor in failure to regain a good extension, although there is quite a lot of controversy about this.
'Quadriceps' means '4 heads' - the 'muscle' is actually four separate muscles that work together to straighten (extend) the knee. The muscles, quads tendon, patella, patellar tendon and the fibrous retinaculum at the sides of the patella are together called 'the extensor mechanism'.
The individual muscles heads of the quadriceps include:
- vastus lateralis
- vastus intermedius (underneath the rectus femoris, so you don't see it here)
- vastus medialis
- rectus femoris
At the lower end the rectus femoris attaches directly to the patella via the quads tendon, which itself attaches to the tibia via the patellar tendon. The area of attachment on the tibia is the tibial tubercle (or tibial tuberosity). The vastus medialis and lateralis are also linked to the patella, but this is via the lower end splaying out into a fibrous network called 'the retinaculum'.
Knee muscles from the back
This is an illustration of the back of a right knee.
The main muscles at the back of the knee are the hamstrings muscles at the back of the thigh and the gastrocnemius muscles at the back of the calf.
In the calf you can see the bulky gastrocnemius muscle. Under it lies the soleus muscle (not visible on image). The tendons of the two combine to form the strong Achilles tendon at the back of the ankle.
The long thin tendon of the semitendinosus muscle is frequently 'harvested' by the surgeon for use in cruciate ligament reconstruction. It is commonly referred to as one of -the 'pes' or 'pes anserinus' tendons (semitendinosus, gracilis, sartorius) which insert on the medial (inner) aspect of the tibia in a compound tendon which looks a bit like a goose's foot (hence the latin name 'pes anserinus').
The 'gracilis' muscle is another whose tendon is often used, together with that of semitendinosus, to make a replacement cruciate ligament.The gracilis muscle is, however from a different group of muscles known as the 'adductors' and is not technically a hamstrings muscle.