AJR 2000; 174:1635-1637
© American Roentgen Ray Society
Dynamic MR Imaging of the Hip in Legg-Calvé-Perthes Disease
Comparison with Arthrography
Dominik Weishaupt1,
G. Ulrich Exner1,2,
Paul R. Hilfiker1 and
Juerg Hodler1,3
1
Institute of Diagnostic Radiology, University Hospital,
Rämistr. 100, 8091 Zurich, Switzerland.
2
Present Address: Department of Radiology, Orthopedic Surgery, Section of
Pediatric and Tumor Orthopedics, Orthopedic University Hospital Balgrist,
Forchstr. 340, 8008 Zurich, Switzerland.
3
Present Address: Department of Radiology, Orthopedic University Hospital
Balgrist, 8008 Zurich, Switzerland.
Received August 18, 1999;
accepted after revision November 1, 1999.
Address correspondence to J. Holder.
Introduction
Arthrography of the hip is important in tailoring treatment in
Legg-Calvé-Perthes disease
[1,2,3,4].
Hip arthrography in children with
Legg-Calvé-Perthes disease is used for dynamic
imaging to determine congruency and containment of the femoral head by the
acetabulum and to rule out "hinge" abduction
[1,
3,
5]. Hinge abduction means
failure of the femoral head to move medially in abduction, with blocking of
the severe flattened femoral head on the lateral acetabular margin
[3]. Because the primary goal
in treatment of Legg-Calvé-Perthes disease is
to improve containment and joint congruity
[6], information obtained from
hip arthrography may help in selecting candidates for periacetabular and
intertrochanteric osteotomy [1,
4,
5]. Detection of hinge
abduction is of paramount importance. Hinging must be relieved to assure
normal femoral development, which requires contact between the femoral head
and the normally formed acetabulum. This relief can frequently be accomplished
by appropriate surgery [3].
Furthermore, arthrography allows assessment of joint congruity when
immobilization during the process of epiphyseal healing is used as treatment
[4].
MR imaging is a valuable tool in the diagnosis of early or radiographically
occult Legg-Calvé-Perthes disease. It shows
the extent of epiphyseal involvement
[7]. However, dynamic
examination of the hip with MR imaging is hampered by the closed architecture
of conventional MR systems. With the increasing availability of
open-configuration MR systems, dynamic imaging of joints in various positions
has become feasible.
The purpose of this study was to compare arthrography with dynamic MR
imaging of the hip using a superconducting open-configuration system to
evaluate Legg-Calvé-Perthes disease.
Subjects and Methods
Ten hips of nine children (seven boys, two girls; age range, 7-9 years;
mean age, 7.8 years) who were referred for evaluation and treatment of
Legg-Calvé-Perthes disease were included in
the study. According to the Catterall classification
[5], two hips were in group II
(50% involvement of femoral head with sparing of the lateral border), five
hips were in group III (75% involvement of femoral head with lateral head
significantly involved and collapsed), and three hips were in group IV (total
femoral head involvement). In accordance with the guidelines of our hospital's
institutional review board, written informed consent was obtained from all
patients' parents. All 10 hips were examined with arthrography and dynamic MR
imaging. Arthrograms and MR images were obtained with the hips in neutral
position and in maximally abducted and maximally adducted positions. Abduction
and adduction were performed without internal or external rotation. However,
examinations in flexion were performed if extension osteotomy was considered
as a surgical option. These images were not used for further evaluation,
however.
MR imaging was performed with a 0.5-T super-conducting open-configuration
MR system (Signa SP; General Electric Medical Systems, Milwaukee, WI). No
sedation was used. Each patient was placed in the supine position with a
flexible radiofrequency coil strapped around the pelvis. The geometry of the
magnet permits unrestricted motion of the hip to the position required for
this examination. To maintain the relevant positions, the pelvis and the
examined leg were fixed with clear adhesive tape. To optimize compliance, an
accompanying adult, sitting or staying in the gap between the two magnet
rings, was allowed to attend MR imaging.
To evaluate an appropriate MR protocol, we used two different MR sequences.
Six hips in five children were imaged using a T2-weighted fast spin-echo
sequence with the following parameters: TR/TE, 5000/133; section thickness, 5
mm; interslice gap, 0.5 mm; acquisitions, two; and echo train length, eight.
Imaging time of this sequence was 5 min 20 sec. A spoiled three-dimensional
gradient-recalled echo sequence was chosen for four hips in four children.
Imaging parameters for this sequence were the following: 50/5; flip angle,
35°; section thickness, 2.5 mm; and acquisitions, two. Imaging time for
this sequence was 10 min 20 sec. Field of view for both sequences was 25 cm,
and image matrix was 256 x 192. MR imaging was performed in the coronal
plane for all hip positions.
Hip arthrography was performed under general anesthesia in the operating
room. Radiographs taken in the same positions as the MR images were obtained.
MR imaging and hip arthrography were both performed within 1 week of each
other.
Arthrographic and MR images were reviewed separately by two observers in
consensus. Images of all joint positions were available on either
arthrographic or MR data sets. Overall image quality for diagnostic purposes
on both MR images and arthrography was ranked as poor, acceptable, or good.
Criteria evaluated on both arthrography and MR images included sphericity of
the femoral head [8],
irregularity of the cartilaginous articular surfaces
[1], presence of a hinge
abduction [3], and
identification of best position and fit of the femoral head by the acetabulum
(containment) [1]. Containment
is considered present when the femoral head is located completely in the
acetabular socket. Good containment reduces the pressure on the lateral
segment of the epiphyseal femoral cartilage and maintains sphericity of the
femoral head during development
[6].
Results
Dynamic MR imaging was well tolerated by all nine children. MR examination
was completed in a single session without sedation for each patient. Although
resolution of images obtained in open-configuration MR imaging is usually
inferior to images obtained on a conventional MR scanner, all MR images were
of diagnostic quality. Using the T2-weighted fast spin-echo sequence, image
quality of all 18 MR image data sets (six hips with three different positions)
was rated as good. Using the gradient-recalled echo sequence, observers rated
11 of 15 MR image data sets as good. The remaining four of 15 data sets in two
different patients were rated as acceptable because of motion artifacts. All
ten hips were non-spheric with flattening of the superior aspect of the
cartilaginous aspect of the femoral head on both arthrograms and MR images
(Fig.
1A,1B,1C,1D).
In all children, pooling of the joint fluid could be observed in the empty
space that formed between the flattened segment of the articular surface of
the epiphysis and the acetabulum. MR imaging was as efficient as arthrography
in showing irregularities of the capital articular surface that was almost
always located at the point of the weight-bearing area. In severe flattening
and protrusion of the femoral head, abduction leads to hinging of the head on
the lateral acetabular margin (Fig.
2A,2B).
MR imaging showed hinge abduction where it was visible on arthrography in all
eight hips of eight children. Complete agreement about the position of best
containment was found between arthrography and MR findings.
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Fig. 1A. —7-year-old boy with
Legg-Calvé-Perthes Catterall
[6] group III disease.
Arthrogram (A) and dynamic T2-weighted fast spin-echo MR image (TR/TE,
5000/133) (B) taken in neutral position show overgrowth of femoral head
and aspheric flattened subluxated femoral head. Note pooling of contrast
material and joint fluid (arrow), respectively, indicating
incongruency of articular surfaces.
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Fig. 1B. —7-year-old boy with
Legg-Calvé-Perthes Catterall
[6] group III disease.
Arthrogram (A) and dynamic T2-weighted fast spin-echo MR image (TR/TE,
5000/133) (B) taken in neutral position show overgrowth of femoral head
and aspheric flattened subluxated femoral head. Note pooling of contrast
material and joint fluid (arrow), respectively, indicating
incongruency of articular surfaces.
|
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Fig. 1C. —7-year-old boy with
Legg-Calvé-Perthes Catterall
[6] group III disease.
Arthrogram (C) and corresponding MR image (D) obtained in
adducted position show containment evidence by fact that femoral head is
centered within acetabulum.
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Fig. 1D. —7-year-old boy with
Legg-Calvé-Perthes Catterall
[6] group III disease.
Arthrogram (C) and corresponding MR image (D) obtained in
adducted position show containment evidenced by fact that femoral head is
centered within acetabulum.
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Fig. 2A. —9-year-old boy with
Legg-Calvé-Perthes Catterall
[5] group IV disease and hinge
abduction. Arthrogram (A) and gradient-recalled echo MR image (TR/TE,
50/5; flip angle, 30°) (B) were obtained in abduction. Note medial
pooling of contrast and joint fluid (arrows), respectively.
Subluxated superolateral part of femoral head blocks at acetabular edge
(open arrows).
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Fig. 2B. —9-year-old boy with
Legg-Calvé-Perthes Catterall
[5] group IV disease and hinge
abduction. Arthrogram (A) and gradient-recalled echo MR image (TR/TE,
50/5; flip angle, 30°) (B) were obtained in abduction. Note medial
pooling of contrast and joint fluid (arrows), respectively.
Subluxated superolateral part of femoral head blocks at acetabular edge
(open arrows).
|
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Discussion
Dynamic MR imaging of the hip in children with
Legg-Calvé-Perthes disease using an
open-configuration imager allows accurate assessment of the containment and
congruity in various positions without exposing the patient to the side
effects of irradiation and intraarticular injections. The excellent definition
of the cartilaginous acetabulum and femoral head allows assessment of
irregularity of the articular cartilage, which is important prognostically
[3].
In our series, all dynamic MR imaging was been performed without prior
sedation or need for general anesthesia. Although lack of need for sedation
was not a criterion for selection, no examination had to be cancelled because
of noncompliance.
Both sequences used in this investigation (T2-weighted fast spin-echo and
gradient-recalled echo sequence) are adequate. However, because of the shorter
imaging time and fewer motion artifacts, the fast spin-echo sequence may be
preferable.
Dynamic MR imaging of the hip appears to be a feasible noninvasive
alternative to arthrography in patients with
Legg-Calvé-Perthes disease in planning surgery
or evaluating the optimal position of the femoral head for immobilization. Our
preliminary study of 10 hips in nine patients showed promising results.
However, the statistical power of our study was limited, and further studies
to assess interobserver reliability are required.
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Introduction
Subjects and Methods
