Are you suffering from knee pain but have no history of trauma to the knee? Or can your doctor never seem to find a reason for your knee pain?
If this sounds like you, you might have referred to pain in your knee caused by something called sciatica.
How Spinal Pain Causes Knee Pain
The nerves that transmit sensations to the legs, like pain, originate in the spine.
Your spinal column is made up of small bones called vertebrae. In between the vertebrae are discs of tissue that cushion the individual bones and prevent the vertebrae from grinding together. When trauma occurs to the back, these discs can become injured. The disc tissue degenerates, thins, and sometimes becomes a bulging disc between the vertebrae.
When you have bulging or damaged discs, the spinal nerves can be pinched as they make their way from the spine and down to the areas of the legs that they are sending and receiving nerve signals to and from. Other problems that can cause this pressure on the nerves are bone spurs or arthritis.
If you are suffering from pain in your leg that is coming from an injury in your back (instead of an injury close to where it hurts on your leg), that is called “referred pain.”The specific nerves that transmit sensation to the knee originate in the second, third, and fourth lumbar vertebra. The lumbar vertebrae are the thickest, biggest vertebrae that sit in the low back and down to the buttocks area.
If you had a back injury that caused bulging discs, arthritis, or a bone spur in your back in the lumbar vertebrae area (at the small of the back, just above the buttocks), then you might have referred pain to the knee.
Even though it might feel like there is an injury near to your knee causing pain, if it’s referred from the spine, your nerves are sending signals that cause you to have pain in the legs that originate in the spine.
If you are having pain, weakness, tightness, or numbness in the thigh, hip, or knee, have a medical practitioner examine you to determine any neurological issues. The hip can also refer pain to those areas, as well as the lower back.
Common signs of referred leg pain include:
- Pain in the kneecap
- Tingling or numbness in the thigh
- Weakness in the hips or thighs
Referred Pain From Sciatica
Sciatica is pain, numbness, or tingling like pins and needles that originates in the low back, and may affect the buttocks, hips, upper legs, knees, and even the feet. Sciatica is a common cause of referred pain to the knee from the back. You won’t typically experience pain in both knees at once, but it is possible.
Common symptoms of sciatica that is referred to the knee:
- Sharp pain in and around the knee
- Dull ache around the knee
- Weakness when trying to extend the knee
- The burning sensation or warmth around the knee
- Buckling of the knee when walking
Besides your knee, you might experience similar symptoms in the buttocks, thigh, calf, or even all the way into the foot.
Common Causes of Sciatica
Sciatica is very common and has many potential causes.
Herniated or Slipped Lumbar Disc
Up to 90% of sciatica symptoms are found to be caused by issues with the disc in L3 or the third lumbar disc. When this disc herniates, it irritates one or more of the spinal nerve roots from L4 -- S3 (Lumbar 4 -- Sacrum 3), which together are referred to as the sciatic nerve. Herniation or slippage of the disc causes sciatica in two different ways.
Direct compression is one way a herniated lumbar disc can cause sciatica. After an injury that causes the lumbar discs to bulge or to leak the inner material that is the “cushion” inside of the disc, which is called herniation, it causes the nerves that exit between the vertebrae to become pinched or irritated.
Chemical inflammation is another way the sciatic nerve is irritated. When a disc bursts, or herniates, the soft, inner padding leaks out. This soft material is called hyaluronan. Hyaluronan contains acidic liquids that are capable of causing inflamed tissues all around the spinal nerves that form the sciatic nerve.
When the disc is slipped or herniated, it may affect one side, or the disc might be so damaged that there is pinching or inflammation on both sides of the vertebrae. Depending on how badly the disc is damaged, you may suffer from symptoms in one leg, or in both. Symptoms in both legs are more uncommon.
Lumbar Spinal Stenosis
A relatively common cause of back pain issues in older adults is spinal stenosis. This is a narrowing of the spinal canal, which holds the spinal cord and surrounding cerebrospinal fluid. A stenosis condition called lateral recess stenosis is possibly a common cause of sciatic pain in adults over 60.
Degeneration of Tissues
Degeneration of the tissues in the lumbar spine affects the bone tissue as well as the softer tissues. The facet joints sit posteriorly to the discs in the spinal column. When these joints become damaged or irritated from surrounding damage, they can leak synovial fluid that can cause inflammation of tissues, and scar, which increases the bulk of the joint.
When the bone tissue of the vertebrae is injured, it can lead to painful bony growths, called osteophytes and bone spurs. Any of these abnormal tissue masses can irritate the sciatic nerves and compress multiple nerve roots. When this is coupled with inflammation from leaking discs, the irritation to the nerve bundles can be significant.
Sciatica can be a difficult issue to treat. If you have had knee pain that has been referred from your lower back, you might have already experienced some confusion about what’s causing your pain.
Physical therapy by a licensed physical therapist is a common first-line treatment for back pain issues after a confirmed diagnosis from a physical exam. Building up the muscle tone around the spine is a necessary treatment for chronic back pain. PT, coupled with postural therapy, helps most people with this kind of issue find pain relief.
If pain is severe and doesn’t respond to more conservative treatment for long periods of time, people are very often referred to a pain clinic. They may also receive injections from their primary caregiver of steroid-based medication that is injected near the inflamed area around the spine that is causing pain.
Surgery (after scans like x-rays, CT, or an MRI) is usually only discussed after other treatment methods have failed to provide adequate pain control or resolve issues related to the spinal injury. In certain severe spinal injuries, surgery might be needed to stabilize the spine, or for other emergent reasons, immediately after trauma has occurred.
If you are receiving treatment for your back, and your knee problems do not seem to be resolving, you might need further testing to determine if the source of your pain might be from the hip or elsewhere.