Ischiofemoral impingement is mainly congenital although it was first described in patients with total hip arthroplasty or femoral osteotomy by Johnson in 1977 [1]. Other studies have shown that the impingement occurs in athletes and non-athletes and is more common in women than in men. It occurs mostly in the fifth decade and is bilateral in one third of patients [2–4].

Ischiofemoral narrowing is the main cause of impingement and may be result from trauma or tumoral disorders. Nevertheless, a case of a 17-year-old girl with post-traumatic ischiofemoral narrowing without any fracture but with an audible snapping was reported by Ali et al.; she required resection of the lesser trochanter [5]. A traumatic cause may not be uncovered; it is important to remember that the onset of symptoms is usually progressive and has a positional cause [6, 7] (Fig. 25.2).

We report a case of ischiofemoral impingement in its classical presentation. Ischiofemoral narrowing leads to compression of the quadratus femoris muscle and progressive onset of hip pain. Snapping is a less common finding and was absent in this case. Clinical examination is often normal although pain may be reproduced by a combination of extension, adduction and external rotation of the hip [1, 4].

X-rays are often normal or may show secondary causes such as post-traumatic deformities or tumors involving the lesser trochanter or the ischium [8]. Sclerosis or cystic changes of the lesser trochanter have also been described [9]. Ischiofemoral narrowing cannot be assessed on radiographs.

CT or MRI are more reliable to assess the distance between the lesser trochanter and the ischial tuberosity. Torriani et al. showed that the mean distance was 13 +/- 5 mm in patients with ischiofemoral impingement and 23 +/- 8 mm in a control group [10]. Care should be taken when assessing this measurement because it depends on the degree of the internal or external rotation of the hip. A study on MRI assessment of ischiofemoral impingement by Tosun et al. showed that the ischiofemoral space (distance between the lateral cortex of the ischial tuberosity and medial cortex of the lesser trochanter), quadratus femoris space and muscle volume values of the patient group were significantly lower than those of controls. Measurements of the hamstring tendon area and inclination angle (angle between the long axis of the femoral neck and the long axis of the femoral shaft on coronal T1-weighted images) in the patient group were also significantly higher than in controls. The quadratus femoris muscle fatty replacement grades were significantly higher in the patient group than in the control group [2].

MRI is the most useful imaging modality to diagnose ischiofemoral impingement because it allows assessment of the quadratus femoris within the ischiofemoral space. This muscle emerges from the lateral edge of the ischial tuberosity, proximal to the hamstring tendons and inserts on the intertrochanteric crest of the proximal femur. It is innervated by a small branch of the sacral plexus [11]. Its proximity with this latter may explain why ischiofemoral impingement can cause pain with distal radiation.