With the first cases described in 1977, ischiofemoral impingement (IFI) is a relatively recently discovered and less known potential cause of hip pain caused by compression on the quadratus femoris muscle (QFM).1-10 These first patients, who were treated with surgical excision of the lesser trochanter, experienced symptom improvement in all 3 cases.5,7 The most widely accepted diagnostic criteria use a combination of clinical and imaging findings.1-10 Criteria most often cited in the literature include isolated edema-like signal in the QFM on magnetic resonance imaging (MRI) and ipsilateral hip pain without a known cause, such as recent trauma or infection.4,5 All studies describe QFM compression occurring as the muscle passes between the lesser trochanter of the femur and the origin of the ischial tuberosity/hamstring tendons.1-10
Several authors have sought to improve diagnostic accuracy by providing various measurements to quantify the probability of impingement.5,7,9 Although groups have proposed different thresholds, our institution currently uses values reported by Tosun and colleagues5 because theirs is the most robust sample size to date and included 50 patients with IFI.7,9 Although 5 different measurements were proposed, 2 are more commonly cited. The first is the ischiofemoral space (IFS), which is the most narrow distance between the cortex of the lesser trochanter and the cortex of the ischial tuberosity. This space should normally be greater than 1.8 cm.5 The second measurement is called the quadratus femoris space (QFS) and is the most narrow distance between the hamstring tendons and either the iliopsoas tendon or the cortex of the lesser trochanter. The QFS should normally be greater than 1.0 cm.5 However, because these measurements may depend on the hip position during imaging, full-range-of-motion (FROM) MRI may increase diagnostic yield. At our institution, patients are usually imaged supine in neutral position (with respect to internal or external rotation).
In this article, we briefly review IFI, provide an example of how FROM MRI can improve diagnostic accuracy, describe our FROM protocol, and propose an expanded definition of the impingement criteria. The patient provided written informed consent for print and electronic publication of the case details and images.
Full–Range-of-Motion MRI Technique
A 58-year-old woman with no surgical history or diagnosed inflammatory arthropathy presented to the department of physical medicine and rehabilitation with left-buttock pain radiating down the left thigh. Despite nonsurgical management with nonsteroidal anti-inflammatory medication, exercise therapy, use of a transcutaneous electrical nerve stimulator unit, and oral corticosteroid therapy, the pain continued. The patient was referred for MRI, and routine static imaging of the pelvis was performed. Although edema-like signal was present in both QFMs (Figure 1), left more than right, the measurement of the QFS and IFS did not meet all criteria for narrowing as described in previous studies. On the symptomatic left side, the IFS measured 1.5 cm and the QFS measured 1.4 cm (Figure 2). On the same side, the distance between the cortex of the greater trochanter and the cortex of the ischial tuberosity, proposed adapted IFS, measured 1.4 cm, and the distance between the cortex of the greater trochanter and the hamstring tendons origin, proposed adapted QFS, measured 1.1 cm (Figure 3). However, because of the isolated QFM edema, refractory buttock and thigh pain, and exclusion of other diagnoses (such as labral tear, bone marrow edema/stress reaction in the hip, or MRI findings of sciatic neuropathy), we determined that the patient needed evaluation of the QFS and the IFS through a full range of motion. The patient returned for the FROM MRI 16 days after the initial static MRI.
Our FROM MRI was performed on a Magnetom Skyra 3 Tesla magnet (Seimens Healthcare Global, Munich, Germany), using a body array 18-channel coil and a table spine coil. In a supine position, the patient’s imaging started with the hip in extension, adduction, and approximately 20º of internal rotation. During imaging acquisition, the patient was maintained in adduction and extension while the hip was passively externally rotated (Figure 3). A technologist assisted the patient in maintaining the position through a 60º arc of external rotation, while an axial-gradient echo sequence was used to obtain sequential images through the entire arc. Selected parameters are listed in the Table. Acquisition of the arc of motion in the axial plane requires approximately 3 minutes per hip to generate between 8 and 10 images.
With the patient’s hip in internal rotation, narrowing between the ischium or hamstring tendons and the lesser trochanter did not meet all of the criteria described by Tosun and colleagues5 or Torriani and colleagues.7 However, when the patient shifted into external rotation, the distance between the ischial tuberosity and the greater trochanter, and between the hamstring tendons origin and the greater trochanter, significantly narrowed. The adapted IFS decreased from 3.4 cm to 1.5 cm, and the adapted QFS decreased from 3.2 cm to 0.9 cm, accounting for a 54% and 72% reduction of the adapted IFS and QFS, respectively, with maximum external rotation (Figures 4, 5).
