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'.