Ischiofemoral Impingement

Normally the femur can rotate without contacting the ischium or proximal hamstring tendons. Abnormal contact between the ischium and femur is referred to as ischiofemoral impingement and can cause hip pain. The abnormal contact can be due to congenital narrowing of the space between the ischial tuberosity and lesser trochanter or be the result of abnormal positioning following hip arthroplasty.

Radiographs may reveal sclerosis and cystic change at the lesser trochanter and ischium. On MRI, one can see crowding of the fibers of the quadratus femoris muscle belly as it passes between the ischium or hamstring tendons and the posteromedial femur. Edema can also be seen, centered in the muscle belly at the site of maximal impingement.

The main differential consideration is quadratus femoris strain, which presents with edema along the distal myotendinous junction near the posteromedial aspect of the proximal femur.

Two spaces have been defined for the purposes of assessing the free rotation of the femur without contacting the ischium or proximal hamstring tendons. The ischiofemoral space is "the smallest distance between the lateral cortex of the ischial tuberosity and medial cortex of the lesser trochanter." The quadratus femoris space is "the smallest space between the superolateral surface of the hamstring tendons and the posteromedial surface of the iliopsoas tendon or lesser trochanter" (this delimits the space for passage of the quadratus femoris muscle). Unfortunately, these measurements depend on the degree of hip rotation during imaging, and the validity of exact numbers remains unclear.

References

• Kassarjian A, Tomas X, Cerezal L, Canga A, Llopis E. MRI of the quadratus femoris muscle: anatomic considerations and pathologic lesions. AJR Am J Roentgenol. 2011 Jul;197(1):170-4.
• Patti JW, Ouellette H, Bredella MA, Torriani M. Impingement of lesser trochanter on ischium as a potential cause for hip pain. Skeletal Radiol. 2008 Oct;37(10):939-41.
• Torriani M, Souto SC, Thomas BJ, Ouellette H, Bredella MA. Ischiofemoral impingement syndrome: an entity with hip pain and abnormalities of the quadratus femoris muscle. AJR Am J Roentgenol. 2009 Jul;193(1):186-90.