Knee pain doesn't always have a physical injury that caused it and it may be caused by a problem in your lower back. The muscles around your knees are powered by nerves that originate in your lower spine. Irritation or compression of these nerves at their spinal origin causes symptoms commonly known as sciatica, which may include knee pain and weakness.
Knee pain may be a symptom of sciatica
Common knee symptoms that you may experience when you have sciatica may include:
A warm sensation, sharp pain, or dull ache in the front, side, and/or back of the knee
Inability to bear weight on the knee
Buckling/giving out of the knee
Weakness while extending the knee (attempting to straighten your leg)
When knee pain is a part of your sciatica symptoms, you may also experience pain in your buttock, thigh, calf, and foot. However, in some cases, sciatic pain may just affect the knee area. The pain will almost always affect one leg at a time, so knee pain in sciatica typically does not affect both knees together.
Sciatica is commonly caused by a problem that affects your lower back. These underlying conditions may affect your spinal discs, nerve roots, joints, or soft tissues, such as muscles. Examples of these might be:
If you have sciatica, a likely cause of your knee symptoms may be irritation and sometimes compression of the L4 spinal nerve root (L4 radiculopathy). Common causes for the compression of this nerve root are a herniated disc or spinal stenosis (where the spinal canal – the space here the nerve go down before exiting the relevant spinal segment) in your lower back.
When the L4 nerve root is affected, you may also experience pain in your thigh and calf.
Another possible cause for knee pain due to sciatica is tightness in your hamstrings, the group of muscles located at the back of your thigh. When your hamstrings are tight, the stability in your lower back is altered as the normal curvature of your lower spine changes, and stresses build up within your spinal joints. It can also be an indication that the gluteal muscles around the pelvis are not working efficiently.
These changes may cause lower back pain and stiffness, with radiating pain from your lower back into your knee and leg.
If your knee pain is caused due to sciatica, it is important to look at the underlying cause. Sciatica symptoms are commonly treated with a range of approaches. These can range from self-care, manual therapy including postural and movement assessment, exercise programmes, acupuncture and medical management. Medical treatments commonly include pain-relieving medications, guided physical therapy and exercise programs. Occasionally, chronic pain referral may be needed, but this is not common.
Knee pain that may mimic sciatica
Your knee pain may originate due to a nerve or joint injury other than the typical causes of sciatica but may feel like sciatic nerve pain. Two common examples are discussed below.
A lumbar herniated disc or lumbar spinal stenosis that causes compression of the L3 nerve root in the middle of the lumbar spine region may cause knee pain and weakness. You may also experience pain in the front of your thigh, side of your hip, and the groin region.
Patellofemoral stress syndrome
A sharp, burning sensation around the edges of your kneecap may be due to patellofemoral stress syndrome (runner’s knee), a condition where the kneecap (patella) is not aligned correctly and there is a muscle imbalance between muscles in the front and side of the thigh and often poor gluteal function. This then causes irritation as the kneecap ends up rubbing on the inside of the knee and causes pain.
While this condition typically does not cause pain in other regions, such as the thigh or calf, the hot, burning sensation in the knee along with the resulting weakness may be mistaken for sciatica.
If your knee pain does not subside with self-care, affects your activities of daily living, or worsens over time, consult an osteopath physio or your doctor. Several back problems that cause sciatica may also result in knee pain, so be sure to mention all your symptoms, which will help pinpoint the origin of the underlying cause.
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