Pain on outside of knee radiating down leg

What causes pain on outside of knee radiating down leg?

Pain on outside of knee radiating down the leg can have many causes, but the most common cause is iliotibial band syndrome.

If you have ITB, the iliotibial band which spans from the hip to the shin bone gets inflamed near the knee. This inflammation results in the radiating pain you feel.

Other causes for radiating knee pain include eslipped capital femoral epiphysis (the fracture of the growth plate between the head and neck of the femur), nerve entrapment at the knee, and referred pain from the spine. As ITB is the most common cause, this will be the focus of this article.

ITB injury overview.
ITB injury overview.

Most common cause: iliotibial band syndrome

Iliotibial band injury is the most common injury which causes knee pain radiating downwards. This injury often happens during running, cycling, hiking and squatting.

Signs and symptoms of the ITB

Iliotibial band injury can have many kind of symptoms, but it usually consists of stinging pain just above the knee, and swelling of the tissue on the outer side of the knee. It usually takes some time for the pain to build up after you started your activity, and again some time to stop. The pain is the worst when your foot hits the ground or when you twist your knee. The pain can be present above or bellow the knee too. Stabilizing braces can help to an extent with this problem.

Causes of the ITB - your training habits

The most common cause for ITB are plain and simply wrong training habits. Yoga can be especially harmful, if you just started and keep forcing the lotus posture.

Other training errors include running on a banked surface, for example the side of the road; not warming up enough; running too much downhill or uphill, and cycling with your toes pointing inwards.

Causes continued - abnormalities in your leg/feet anatomy

From the point of view of abnormalities, the most common one is the tightness of the iliotibial band itself. Other causes include having high or low arches, striking the ground too hard with your feet, having bowlegs or legs with different lengths.

Even more causes - muscle imbalance

Muscle imbalances can cause many joint issues (when it comes to the knee, the patella is especially sensitive to muscle imbalances). Iliotibial band injury can be worsened if you have weak hip abductor or multifidus muscles, or uneven stretching of the band in your legs - just think of sitting cross-legged.

Anatomy of the ITB

The ilotibial band stretches from the outside of the pelvis to just bellow the knee. It stabilizes the knee during running, and while doing it's job it keeps moving from behind the femur to the front of the femur.

This causes constant rubbing between the tissues, which combines with the overuse caused by running, and leads to an inflammation.

Diagnosing the ITB injury

An ITB injury is usually diagnosed using the Noble compression: the doctor places his or her hand on the area where the ITB moves over, and asks you to move your knee from 90 degree flexed to fully extended. If you feel pain during this movement you have an ITB injury.

Treating an IT band injury - just use RICE

Fortunately the iliotibial band responds well to the usual combination of rest, ice, compression and elevation. Physiotherapy can help restore the full range of motion and strengthen the IT band to prevent further injury.

To learn more about ITB syndrome, check Physioworks' page on the subject.

SCFE X-ray.
SCFE X-ray.

Cause #2 for pain on the outside of the knee radiating down the leg - slipped capital femoral epiphysis

The slipped capital femoral epiphysis, also known as SCFE is actually a fracture, it only has a strange name.

It happens when the growth plate which sits between the head of the femur and the neck of the femur breaks and slips. This usually causes groin pain, but the pain can radiate to the knee and the thigh too.

The slipped capital femoral epiphysis is the most common hip problem in grown-ups.

The pain is usually worsening progressively, and in the end the best you'll be able to do is limping. Overstraining your hips will result in even further slipping which will worsen the pain too.

Signs and symptoms of a SCFE

The SCFE usually causes groin pain, but in some cases only thigh or knee pain is felt, as the obturator nerve channels the pain to a different location.

The most obvious sign of the SCFE is a waddling gait, combined with a decreased range of motion - range of rotation, flexion and abduction are all decreased.

If the SCFE is not treated, it may lead to death of the femoral head (a hip replacement will be needed), hip osteoarthritis, abnormal gait and chronic pain.

Treating the SCFE

SCFE is usually treated with a surgery as soon as possible: two pins are drilled into the femoral head through the femoral neck. These pins keep the head fixed while it heals, and stay in the patient for the rest of his or her life.

Until the surgery the patient should remain strictly in bed to prevent further slippage, as this could lead to bone necrosis and would make a hip replacement necessary.

After pinning the patient will be able to use his/her hip as before the injury. Regular checkups will be necessary to look for signs of bone necrosis.

For more details on the SCFE, check Medscape's article.

Peroneal nerve location behind the knee.
Peroneal nerve location behind the knee.

Cause #3 for radiating knee pain: peroneal nerve entrapment

If you have peroneal nerve entrapment, a bone or a tendon compresses the peroneal nerve. This can lead to either sensory problems, as the nerve becomes incapable of transmitting the sensory information to the brain (so a part of your leg bellow your knee will become less sensitive), or this can lead to motor problems, if the trapped nerve can't transfer your brain's command to your leg.

If a motor nerve gets compressed it could lead to muscle atrophy and gait problems.


For sensory nerve entrapment the most common symptoms are feeling of numbness at the affected area, pins-and-needles, ants crawling or feeling coldness.

A prolonged injury can lead to a prolonged healing time - up to 8 to 14 weeks.

This leads to a build up of fluid near the nerve which makes the symptoms even worse. A chronic injury can even lead to a continuous pain.

If you have motor nerve entrapment, you will gradually lose muscle strength. In short your leg just won't behave - your foot will drop and you will have a hard time walking.

Cramping is another common symptom of this injury - some muscle groups tend to cramp up if they do not get any input.

Cramping can be a symptom of other problems too, so do not assume you have nerve entrapment if your legs are cramping - see your doc and get a proper checkup.

Treating the nerve entrapment

In general, nerve entrapment is only treated if the symptoms are serious. The treatment consist of icing the location of the entrapment, taking anti-inflammatory drugs (NSAIDs typically) and resting the leg.

Serious cases may require a surgery to relieve the compression.

Peroneal nerve entrapment can also cause pain in the back of the knee and stiffness.

Cause #4 for radiating knee pain: referred pain from the lumbar spine

Finally, a nerve pinched in the spine can cause radiating pain in the knee.

This can happen because the nerve coming from the knee gets pinched in the spine. As the nerve normally transmits information from your knee, you will feel radiating knee pain, even though the problem is in your spine.

Exercises for the iliotibial band syndrome

Fortunately you can easily fix the iliotibial band syndrome with a few simple exercises. As this is the most common issue which can cause radiating pain, it's worth to pay extra attention to it.


Side leg raise.

Side leg raise

For side leg raise lie on your side with both of your legs straight. Slowly lift the leg on the upside to about 45 degrees, then lower it back again. Do 3 sets 30 repetitions for both sides.

If the exercises is too easy for you, use a resistance band between your ankles or knees.


Clam shell.

Clam shell

For clam shell lie on your side with your knees bent at 90 degrees, and your legs pulled up a bit. Keep your feet together and slowly open and close your legs as if it was a clamshell. Make sure you move your legs slowly and that your pelvis stays in place throughout the exercise. Do 3 sets of 30 reps on both sides.

You can use an exercise band between your knees to make it a bit harder.


Hip thrust/shoulder bridge.

Hip thrust

For hip thrusts just lie on your back with your arms on your sides, your feet on the floor and your knees bent at 90 degrees. Push your heels into the ground, and use your buttocks muscles to lift your pelvis from the floor. Keep lifting until your thighs and your torso line up. Slowly lower yourself then start again. Do 3 sets of 30 reps.

If you found this exercise too easy, keep only one of your legs planted on the floor and raise the other in the air. This will double the load on your buttocks muscles.


Side plank.

Side plank

For side plank lie on your side with your legs held straight, your elbow on the ground. Lift your pelvis off the ground and keep your weight on your feet and your elbow. Keep your torso and legs straight. This exercise works all the muscles and tendons on your lower side. Keep the position for 20 seconds, then slowly lower yourself down again. Do 5 reps for each side.


Side step/lateral walk.

Lateral walk with exercise band

For lateral walk get a medium-strength exercise band between your knees and go down to a half-squat. Walk with one leg to the side, then follow with the other. Do 5 steps to the left then 5 to the right. Repeat this exercise four times.


Pistol squat.

Pistol squat (advanced)

For the pistol squat stand on your leg with the other leg raised straight in front of you. Slowly lower yourself balancing on one leg, and straightening the other out in front of you. Go down as much as you are comfortable with then slowly raise your body back up. Do 3 sets of 10 reps for each leg.


ITB stretch.

ITB stretch

For ITB stretch, stand up and cross your legs. Slowly slide your hand down the side of your leg in the back. You should feel the outside of the front leg stretching.


Foam roller massage.

Foam roller massage

Lie down on your side, and place a 4 inch diameter foam roller at the middle of your thigh. Use your leg on the upper side and your arms to support yourself. Roll yourself up and down on the roller, covering the whole length of your thigh for knee to hipbone. Do this exercise for 5 minutes on both sides.


Glute stretch.

Glute stretch

For glute stretch lie on your back with your legs held straight. Bend one leg at the knee and move the knee up towards your opposite shoulder. Use your hands to pull the knee towards yourself to make your glutes stretch even more. Hold the position for 30 seconds, once for each leg.


Hip abduction.

Hip abduction

For hip abduction use a resistance band between your ankle and a fixed object. Pull your leg to the side working against the resistance band, keep your knee straight. Then let your leg slowly back to the starting position. Do 3 sets of 15 reps for each leg.

For a few more tips check out Prevention's article.