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Original Research |
1 Division of Musculoskeletal Radiology, Department of Radiology, Massachusetts
General Hospital and Harvard Medical School, 55 Fruit St., YAW 6048, Boston,
MA 02114.
2 Tesla Medicina Diagnostica, Pelotas, Rio Grande do Sul, Brazil.
Received November 11, 2008;
accepted after revision December 15, 2008.
Address correspondence to M. Torriani
(mtorriani{at}hms.harvard.edu).
Abstract
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MATERIALS AND METHODS. We reviewed MR images of 12 hips in nine patients with hip pain and abnormal MR signal intensity of the quadratus femoris muscle. Using axial MR images, two musculoskeletal radiologists measured the ischiofemoral and quadratus femoris spaces. We also examined changes to muscles and tendons for the presence of edema and tears. Data were compared with 11 hips in 10 control subjects. Statistical analyses determined interobserver variability and differences between groups.
RESULTS. Subjects with an abnormal quadratus femoris muscle were all women 30-71 years old (mean age, 53 years) and had significantly narrower ischiofemoral spaces when compared with control subjects (13 ± 5 vs 23 ± 8 mm, respectively; p = 0.002). The quadratus femoris space was significantly narrower in affected subjects (7 ± 3 vs 12 ± 4 mm; p = 0.002). Abnormalities of the quadratus femoris muscle included edema (100%), partial tear (33%), and fatty infiltration (8%). The hamstring tendons of affected subjects showed evidence of edema (50%) and partial tears (25%).
CONCLUSION. Ischiofemoral impingement may represent a cause of hip pain and should be considered in cases with MR signal abnormality of quadratus femoris muscle.
Keywords: femur • impingement • ischium • lesser trochanter • quadratus femoris muscle
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Impingement between the ischium and femur was first suggested in three patients with prior hip surgery who obtained pain relief after lesser trochanter excision [3]. In a recent case report, Patti et al. [4] described MRI findings of ischiofemoral narrowing and impingement in a patient with hip pain and no history of surgery. The dominant findings were congenital narrowing of the space between the ischial tuberosity and lesser trochanter with abnormal MR signal intensity of the quadratus femoris muscle.
The purpose of our study was to describe the MRI findings of ischiofemoral impingement in patients with hip pain and abnormal MR signal intensity of the quadratus femoris muscle.
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Control subjects were selected from the same database, searched between 2006 and 2008. We selected dedicated hip MR examinations performed to rule out fracture after a fall, with no evidence of fracture, marrow edema, or soft-tissue abnormality. This was accomplished by searching history fields with terms including "fall" and "fracture" and subsequently reviewing the impression for the absence of abnormalities. Exclusion criteria for control subjects included male sex (because the cohort of affected subjects was made up entirely of women), large-field-of-view pelvic MRI examination, and discrepancy between the original report and case review by the authors. Data on subject age, sex, history, and duration and side of symptoms were collected. When available, management and follow-up notes were tabulated.
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Hip MRI was performed on a 1.5-T scanner, using a phased-array coil and the following parameters: coronal T1-weighted (700/18; NEX, 3; matrix, 192 x 320; slice thickness, 4 mm; FOV, 16 cm), axial FSE proton density-weighted (1,900/25; NEX, 4; matrix, 192 x 384; slice thickness, 4 mm; FOV, 16 cm), axial FSE fat-suppressed T2-weighted (5,000/50; NEX, 3; matrix, 192 x 384; slice thickness, 4 mm; FOV, 16 cm), coronal FSE fat-suppressed T2-weighted (5,000/50; NEX, 3; matrix, 192 x 384; slice thickness, 4 mm; FOV, 16 cm), and sagittal FSE fat-suppressed proton density-weighted (2,850/20; NEX, 2; matrix, 192 x 320; slice thickness, 4 mm; FOV, 36 cm) sequences. A coronal FSE inversion recovery pulse sequence was performed with the body coil using 4,000/48; NEX, 2; matrix, 192 x 320; slice thickness, 4 mm; and FOV, 36 cm. Contrast-enhanced pulse sequences were not performed.
Measurement Technique and Qualitative Parameters
Measurements were obtained using the length tool in Osirix software version
3.2.1 (free software available at
www.osirix-viewer.com/index.html)
as follows (Fig. 1):
ischiofemoral space, the smallest distance between the lateral cortex of the
ischial tuberosity and medial cortex of the lesser trochanter; and quadratus
femoris space, the smallest space for passage of the quadratus femoris muscle
delimited by the superolateral surface of the hamstring tendons and the
posteromedial surface of the iliopsoas tendon or lesser trochanter. Two
musculoskeletal radiologists with 12 and 5 years of experience independently
performed the measurements on three contiguous axial FSE proton
density-weighted images through the lesser trochanter. The presence of a
normal or abnormal quadratus femoris muscle precluded investigators from being
blind to disease status. From each group of three measurements, the smallest
ischiofemoral and quadratus femoris spaces were averaged across investigators
and used for statistical analyses.
All MR examinations were evaluated for qualitative changes by consensus of
two musculoskeletal radiologists with 12 and 5 years of experience. In
affected subjects, edema of the quadratus femoris muscle, iliopsoas tendon,
and hamstring tendon attachment was tabulated as mild, moderate, and severe
(increased T2 signal intensity [SI] affecting < 50% of the structure, 
50% limited to the structure, and 50% extending to surrounding soft
tissues, respectively). Partial tears were defined as the presence of focal
fluidlike increased T2 SI within muscle or tendon, and full-thickness tears
were defined as fluidlike increased T2 SI with complete structure
discontinuity. Bone marrow edema and intervening bursalike fluid collections
were categorized as present or absent. In control subjects, MR examinations
were reviewed to confirm the absence of fracture, bone marrow edema, or
soft-tissue abnormality. Additional imaging studies (hip radiographs and CT
scans) obtained at the time of MR examinations were reviewed for the presence
of bone abnormalities by consensus of two musculoskeletal radiologists with 12
and 5 years of experience.
Statistical Analyses
One-way analysis of variance Student's t tests and pairwise
correlations were performed with JMP, version 7.0, software (SAS Institute).
Receiver operating characteristic (ROC) curves (to determine optimal threshold
values) and Bland-Altman analyses (for interobserver repro ducibility) were
calculated using MedCalc, version 9.2.1.0, software (MedCalc). Values for
p less than 0.05 were considered to indicate significant differences.
All measurements were expressed in millimeters ± SD.
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Ten control subjects were identified, of whom one underwent bilateral hip MRI. All subjects had no evidence of fracture, bone marrow edema, or soft-tissue abnormality. No subjects were excluded. Therefore, a total of 10 subjects were in the control group (n = 11 hips).
Clinical Information and Imaging Studies
All affected subjects were women between 30 and 71 years old (mean age, 53
years) who presented with hip pain. In four subjects (4/9, 44%), pain varied
in duration between 3 months and 10 years. In the remaining five subjects
(5/9, 56%), the duration of symptoms was not specified. Bilateral
abnormalities of the quadratus femoris muscle were present in three subjects:
two had unilateral pain (Fig.
2), and one had moderate pain in the right and mild pain in the
left hip.
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Three subjects (3/9, 33%) had pain radiating to the ipsilateral lower extremity. Five subjects (5/9, 56%) had a history of chronic back pain for which two underwent laminectomies. One subject (1/9, 11%) was referred for a snapping sensation in the symptomatic hip.
One subject underwent a CT-guided steroid injection of the left quadratus femoris muscle, with relief of symptoms for 1 week, and was subsequently treated with physical therapy. Another subject received a steroid injection of the hip joint with significant pain relief for 1 month and was subsequently treated with physical therapy and activity modification. Four subjects were treated with non-steroidal antiinflammatory drugs or opiates, with no follow-up data available. Three subjects had no data regarding management. No subjects underwent surgical intervention.
All control subjects were women between 24 and 95 years old (mean age, 67 years) with no significant difference in mean age when compared with affected subjects (p = 0.2). All subjects were imaged to rule out fracture after a fall, with a time to MRI between 1 and 60 days (mean, 15 days). Medical records indicated no history of hip pain before the fall.
Measurements and Qualitative Parameters
The results for comparison of measurements between groups and ROC cutoff
values to detect affected subjects are outlined in
Table 1. Affected subjects
showed significantly smaller ischiofemoral and quadratus femoris distances
when compared with control subjects. Combining both groups, there was
significant correlation between ischiofemoral and quadratus femoris
measurements (r = 0.88, p < 0.0001). Submillimeter mean
differences and strong correlation between observers suggested a high level of
measurement concordance. The mean interobserver difference for ischiofemoral
and quadratus femoris measurements was -0.5 and -0.4 mm, and 95% limits of
agreement were 2, -3 mm and 1, -2 mm, respectively. The correlation between
observers was r = 0.99, p < 0.0001 for ischiofemoral and
quadratus femoris measurements.
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Abnormalities of the quadratus femoris muscle (Figs. 3 and 4) included mild (5/12, 42%), moderate (2/12, 17%), and severe (5/12, 42%) edema. All cases showed diffuse abnormal SI as opposed to focal edema at the musculotendinous junction. Focal fatty infiltration of the quadratus femoris muscle was superimposed in one case of mild edema. Partial tears were noted in four (33%) of 12 cases. No full-thickness tears of the quadratus femoris muscle were seen.
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In a recent case report, Patti et al. [4] described a 43-year-old woman with no history of trauma or surgery who presented with chronic hip pain radiating to the knee. Radiographs and MR images showed severe ischiofemoral narrowing, edema of the quadratus femoris muscle, and cystic changes of the ischium [4]. Similar findings were mentioned in an article [2] in which edema of the quadratus femoris muscle was attributed to narrowing of the ischiofemoral space. However, measurements of the narrowed ischiofemoral space were not provided, and comparison with control subjects was not possible because of limited cohort size.
In an MRI study, O'Brien and Bui-Mansfield [5] described tears of the quadratus femoris muscle in a series of four women with hip pain. The most common (4/5, 80%) finding was edema or hemorrhage at the musculotendinous junction of the quadratus femoris muscle, with one full-thickness and three partial-thickness tears. In a subsequent article, the authors mentioned that their cases did not show narrowing of the ischiofemoral space [2]. Although details regarding hip positioning are unknown, the authors attributed their findings to musculotendinous injury because of resolution in follow-up imaging [2].
Our study suggests ischiofemoral impingement may be a cause of hip pain and abnormalities of the quadratus femoris muscle. The mean ischiofemoral and quadratus femoris spaces were significantly narrower in subjects with an abnormal quadratus femoris muscle, and the majority of affected subjects presented with ischiofemoral and quadratus femoris spaces below the threshold determined by ROC curve analyses. Although ischiofemoral impingement is unlikely to be the sole cause of quadratus femoris abnormalities, we believe our thresholds may help guide management in patients with hip pain and isolated changes of the quadratus femoris muscle. Taken together, our data suggest the cause for isolated quadratus femoris changes may be multifactorial, with ischiofemoral impingement representing a likely cause.
Three of our affected subjects were referred for pain radiating to the lower extremity. Although lower back pain was a frequent complaint in this cohort, it is possible that the proximity of the sciatic nerve to an abnormal quadratus femoris muscle may contribute to these symptoms [4]. One subject presented with a snapping sensation with motion of the hip, which may be similar to the crepitus and locking described in the case report by Patti et al. [4]. Although other syndromes may cause a snapping sensation at the hip, this symptom should lead to further investigation of the possibility of ischiofemoral impingement. If snapping occurs as a function of ischiofemoral impingement, it could be attributed to soft tissues interposed between the ischium and lesser trochanter, such as the quadratus femoris muscle, iliopsoas muscle, or hamstring tendons. Alternatively, it could be secondary to local bursitis. Of note, despite no evidence of ischiofemoral narrowing in the cases reported by O'Brien and Bui-Mansfield [5], two patients had a clinical diagnosis of snapping hip syndrome.
Chronic contact between the ischial tuberosity and lesser trochanter may lead to cystic changes; however, it is uncertain whether ischiofemoral impingement represents the cause [4]. Osseous changes were not identified in our subjects. With the hip in adduction, external rotation, and extension, the lesser trochanter and ischial tuberosity are about 2.0 cm apart [3]. This relationship allows the femur to rotate without contacting the ischial tuberosity or proximal hamstring tendons. In our affected subjects, ischiofemoral narrowing was likely congenital, with bilateral involvement present in 25%. Although beyond the scope of this study, the space between the ischium and femur could vary because of a larger cross-section of the femur at the level of the lesser trochanter, a congenital posteromedial position of the femur, or the lower ischiopubic ramus having an angle closer to the coronal plane. That all of our affected subjects were women suggests a potential relationship with the anatomy of the female pelvis. Besides having a greater width and smaller depth, the female pelvis is characterized by ischial tuberosities that are wider apart [6]. Although there is no known sex-related anatomic variability of the lesser trochanter, it is possible that women with prominence of this structure may be predisposed to ischiofemoral impingement. Other potential causes include valgus hip or a sessile osteochondroma [4]. Conversely, ischiofemoral narrowing may occur in several acquired conditions, such as intertrochanteric fractures or after valgus intertrochanteric osteotomy [3]. Degenerative arthritis may lead to superior and medial migration of the femur and narrowing of the ischiofemoral distance [3]. Further studies with dynamic imaging of the hip in several degrees of rotation may help to confirm the cause and associated findings of ischiofemoral impingement.
Some affected subjects in our study showed edema and tears affecting the hamstring tendons. Although no tears were seen involving the iliopsoas tendon, edema was seen surrounding its insertion in a few cases. Cases of severe changes to the quadratus femoris muscle were more likely to show edema surrounding the hamstring and iliopsoas tendon attachments. Whereas the cause for SI changes remains unknown, direct osseous impingement may play a significant role. However, adjacent inflammation, musculotendinous injury, unrelated enthesopathy, and overuse syndromes also may account for these findings [4]. Two patients presented with a bursalike formation surrounding the lesser trochanter, which may similarly reflect chronic impingement in the ischiofemoral space. Another patient with a 10-year history of hip pain presented with mild edema and focal fatty infiltration in the quadratus femoris, which may also point toward a chronic process. Our results also highlight the importance of identifying a narrow quadratus femoris space. Although quadratus femoris space narrowing occurred as a function of the ischiofemoral space, it is possible that anatomic variation at the origin of the hamstring tendons could lead to soft-tissue impingement on the quadratus femoris muscle without significantly narrowed ischiofemoral space.
Our study has limitations. Because of its retrospective nature, our search primarily identified cases with quadratus femoris muscle abnormalities. The majority presented narrowed ischiofemoral and quadratus femoris spaces; however, cases with narrowing but normal quadratus femoris were likely missed. Therefore, our series cannot establish a direct cause-and-effect relationship between these phenomena. It was not possible to confirm ischiofemoral impingement as the source of pain in affected subjects because no surgical correction was performed. However, there is currently no surgical procedure described in the literature for correction of ischiofemoral impingement. Another limitation was that although internal hip rotation was routinely performed in our MR examinations, it was not possible to prospectively ensure identical positioning throughout our cohort. This could lead to overestimation of ischiofemoral and quadratus femoris space narrowing in cases with some degree of external rotation. It is important to note that our threshold measures are more likely to be of value in subjects imaged using a similar protocol as described in our series. Finally, our control group was not composed of asymptomatic volunteers and contained a small number of subjects. However, the control subjects presented with hip pain after a fall with no evidence of prior symptoms.
Although ischiofemoral impingement requires further validation through more extensive case series with surgical correlation, the observations in our study may guide the investigation and management in a subset of patients with hip pain. In this population, evidence of isolated changes to the quadratus femoris muscle should prompt the radiologist to evaluate for narrowing between the lesser trochanter and ischium.
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