Patients with lower back pain will often complain of knee pain. The most common roots to be irritated are the L5 and S1 nerve roots which supply many muscles that cross the knee or insert near the knee. Therefore when muscles such as the hamstrings, gluteus maximus, adductor magnus and tensor fascia latae shorten due to spasm, knee pain can often be felt.
Knee pain will be more noticeable on extension (straightening) of the knee or with excessive bending or weight bearing on the knees such as in crawling or kneeling. If the muscles that bend the knee such as the hamstrings go into spasm, knee pain will be felt with knee extension. When the knee extensors such as the tensor fascia latae and the gluteus maximus (through its insertion into the iliotibial tract) shorten due to spasm, knee pain will be felt with knee flexion (bending).
Chief extensors of the knee are the quadriceps (vastus lateralis, vastus medialis, vastus intermedius and rectus femoris) muscles supplied by the femoral nerve (L2, L3, L4).
It is very important that treatments related to problems with knee extension should not be focussed only to treating the quadriceps muscles.
Nerve related muscle pain assessment causing knee pain should include assessment of the movements of the entire spine from the neck to the lower back, hips, knees and ankles.