The vastus intermedius muscle can cause and contribute pain down the front of the thigh and knees. Pain increases when walking up an incline or stairs.
The vastus medialis can cause and contribute to pain on the inside of the knee and front of the thigh. Dysfunction in this muscle will cause your knee to buckle. It is one of the four quadriceps muscles.
The rectus femoris muscle contributes to knee and thigh pain. It also contributes to restless leg syndrome and "knee bugs".
The gastrocnemius muscle is a prime contributor to pain in the back of the knee. It can contribute to lower leg, ankle, and arch pain.
The soleus muscle can cause and contribute to pain in the heel, ankle and back of the knee. It can also cause pain in the low back on the same side of the affected leg. Dysfunction of the soleus muscle can also contribute to swelling in the foot and ankle. Occasionally a trigger point at the bottom and outside of the muscle can contribute to pain in the jaw and side of the head.