Possible ischiofemoral impingement

[Xue Heng]

Hi, Steve.
This patient was a 68-year-old female, with right lower limb pain and numbness.
The clinician considered the diagnosis of Piriformis syndrome, and refered sciatic nerve ultrasound.
Although we find bilateral sciatic nerve with similar dimention, ischiofemoral pace dimension of the symptomatic side (right side) was obvious more narrow than the left side (1.9cm vs 2.9cm).
Can we reach the diagnosis of ischiofemoral impingement?
Is there any diagnostic criteria for the disease? Or any dynamic test?
Is enlarged sciatic nerve a necessity for the diagnosis?
And can we observe enlarged Quadratus femoris, similar to MRI?
Thank you very much, Steve. You are a great teacher.

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[Stephen Bird]

Hi Xue,

Nice lateral thinking,

I agree the ischiofemoral space is quite asymmetrical in your patient.

Ultrasound is less sensitive than MRI for this diagnosis as the MRI looks for oedema in the quadrates femoris muscle which is not easily seen with ultrasound so MRI is the more sensitive test.

But we can still make an assessment with ultrasound.

I perform what is known as a “tick tock” test where the patient is prone and the knee is flexed to 90 degrees. Then swing the lower lex internally and externally which produces internal and external rotation of the hip. Scan at the level of the quadrates femoris and you can observe what happens to the muscle and the sciatic nerve which sits immediately on top of the muscle. If it is normal you will see Quad Fem stretch nicely and then contract nicely and the nerve will simply slide on top of it. If there is ischiofemoral impingement you will see the lesser trochanter of the femur almost bump into the ischial tuberosity and the quad fem and the sciatic nerve will be compressed.

Sometimes I see the quad fem getting compressed and the sciatic nerve is expelled from the space as the lesser trochanter and the ischial tuberosity approach each other.

I think sometimes you see sciatic nerve oedema and other times I don’t.

Steve.

[Xue Heng]

Thank you for teaching me the dynamic test for ischiofemoral impingement.
Next time I would perform the test when IFI is suspected.

[Stephen Bird]

Nice one Xue.

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