ischiofemoral impingement

Ischiofemoral impingement refers to the impingement of soft tissues between the ischial tuberosity and lesser trochanter of the femur.

Clinical presentation

Ischiofemoral impingement is a rare cause of buttock pain, groin pain, or a snapping hip .


Females are more affected than males. Ischiofemoral narrowing may be bilateral but symptoms may only be unilateral .


Narrowing of ischiofemoral space and quadratus femoris space or the distance between the ischial tuberosity and lesser trochanter of the femur predisposes to symptomatic ischiofemoral impingement, primarily affecting the quadratus femoris muscle manifesting with muscle belly edema in the acute setting and fatty degeneration in chronic cases. It can also lead to tears of the common hamstring tendon.


There are numerous causes for narrowing of the ischiofemoral and quadratus femoris space including :

Radiographic features

Plain radiograph

A recent study suggested ischiofemoral impingement is likely in patients with chronic pelvic pain if the ischiofemoral space is <2 cm or <1.9 cm on supine and standing pelvic x-rays, respectively. It warrants further investigation by pelvic MRI .


The main finding in the acute case is muscle edema of the quadratus femoris muscle, in some cases with concomitant adventitious bursitis .

In chronic situations of impingement, there will be fatty infiltration and atrophy of the quadratus femoris muscle and sometimes tears of the hamstring musculature at their common insertion site .

In addition, the ischiofemoral and quadratus femoris spaces can be measured, they are, however difficult to standardize due to leg positioning :

  • T1
    • ischiofemoral space is measured on an axial T1 sequence
      • shortest distance between medial cortex lesser trochanter and lateral cortex ischial tuberosity
      • cut-off: ≤15 mm (sensitivity 77%, specificity 81%, accuracy 74%) 
    • quadratus femoris space is measured on an axial T1 sequence
      • smallest distance for the passage of quadratus femoris between the posteromedial iliopsoas tendon or ischial tuberosity and the superolateral hamstring tendons
      • cut-off: ≤10 mm (sensitivity 79%, specificity 74%, accuracy 77%)
    • fatty atrophy of quadratus femoris may be present
  • STIR/T2 FS
    • quadratus femoris muscle belly edema and/or tears
    • muscle belly edema may extend to the hamstrings and/or iliopsoas muscles

History and etymology

Ischiofemoral impingement was first described as a cause for hip pain by K A Johnson in 1977 .