Download Radial MRI of the hip with moderate osteoarthritis

Radial MRI of the hip with moderate
osteoarthritis
Motoyuki Horii, Toshikazu Kubo, Yasusuke Hirasawa
From Kyoto Prefectural University of Medicine, Kyoto, Japan
e carried out radial MRI in 30 hips with
moderate osteoarthritis and in ten normal hips.
On a scout view containing the entire acetabular rim,
12 vertical radial slices were set at 15° intervals.
Different appearances were observed in different parts
of the joint. In the weight-bearing portion, from 45°
anterosuperior to 45° posterosuperior, ‘attenuation’
(n = 16) and ‘disappearance’ (n = 25) were observed as
abnormalities of the labrum with ‘capsular stripping’
(n = 29) and ‘extraosseous high signal lesion’ (n = 27)
as capsular abnormalities, seen more often in the
anterosuperior portion. In all 12 planes there were
osteophytes on the acetabular edge (n = 24), femoral
head (n = 22) and/or at the central acetabulum (n = 6),
a bone cyst on the acetabulum (n = 18) and/or the
femoral head (n = 9), irregularity of the articular
cartilage (n = 30), and an effusion (n = 28). Our
findings indicate that radial MRI may be a useful
non-invasive diagnostic method for demonstrating
pathology in moderate osteoarthritis of the hip.
W
J Bone Joint Surg [Br] 2000;82-B:364-8.
Received 15 February 1999; Accepted after revision 3 September 1999
Involvement of the labrum of the acetabulum in osteoarthritis (OA) of the hip, termed the acetabular rim syn1
2
drome in dysplastic hips or an inverted acetabular labrum
as a cause of primary OA, has attracted some attention.
3
4
Arthrography and/or arthroscopy have been used in the
evaluation of abnormalities of the labrum, but these methods
are invasive and provide limited images of the hip. MRI is
non-invasive and can clearly depict morphological and qual5
itative changes in any direction. We have previously reported a method using MRI to depict the entire acetabular rim
M. Horii, MD, Assistant Professor
T. Kubo, MD, Associate Professor
Y. Hirasawa, MD, Professor and Chairman
Department of Orthopaedic Surgery, Kyoto Prefectural University of
Medicine, Kawaramachi-Hirokoji, Kamigyo-ku, Kyoto 602-8566, Japan.
Correspondence should be sent to Dr T. Kubo.
©2000 British Editorial Society of Bone and Joint Surgery
0301-620X/00/39923 $2.00
364
by determining radial sections centred on the mid-point of
6,7
the acetabulum.
With this technique we have now
obtained radial MR scans of patients with moderate OA
because of dysplasia, in whom conventional radiographs
depicted ‘marked narrowing of the joint space’, and examined abnormalities of the acetabular rim including the labrum in the weight-bearing portion.
Patients and Methods
We studied 24 patients (30 hips) with moderate OA whose
conventional anteroposterior radiographs showed marked
narrowing, but not obliteration, of the joint space. There
were two men (two hips) aged 21 and 40 years and 22
women (28 hips) with a mean age of 45 years (29 to 57).
8
The mean acetabular Sharp angle was 47.7 ± 4.3° and the
9
mean centre-edge angle of Wiberg was 11.0 ± 12.2°.
Ten other hips, eight in four healthy volunteers aged
from 23 to 35 years and two in patients with unilateral nontraumatic osteonecrosis of the femoral head, were examined as a control group.
For MRI we used a superconducting MR 1.5 Tesla
imager (SMT-100X; Shimadzu, Kyoto, Japan) with an offcentre zoom technique and a local surface coil as a receiver
antenna. The field of view was set at 20 cm and the matrix
at 256 256. T2-weighted radial images with a section
thickness of 4 mm were obtained at 15° intervals using the
STAGE method (TR, 500 ms; TE, 20 ms; flip angle,
10,11
30°)
in approximately four minutes. For this radial
imaging, the scout view was determined as the section
which included the entire acetabular rim, after adjustment
of the anterior open angle and the slope of the acetabulum,
and the epicentre as the mid-point of the acetabulum (Fig.
1). In this technique, all 12 planes cross the acetabular rim
vertically, and 24 images of the rim (each plane includes
two parts on the rim) are depicted. Of the 24 images, the
most superior position was named mid-superior; the portions anterior to it were anterosuperior 15°, 30° and 45° and
those posterior to it posterosuperior 15°, 30° and 45°. We
looked for abnormalities of the acetabular rim, in particular
of the labrum and the labral and capsular attachments, by
monitoring those seven positions of the weight-bearing part
of the joint in a range of 90° centred on the mid-superior
portion. The anterior inferior iliac spine appeared in the
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RADIAL MRI OF THE HIP WITH MODERATE OSTEOARTHRITIS
365
Fig. 1
Scout view for the radial planes were
obtained a) by setting the image vertical to the inclination of the acetabulum
on the coronal section, b) by correcting
the anterior open angle on the slices
obtained in a), and c) by correcting the
acetabular inclination on the slices obtained in b). In d) planes were set
radially centred on the geometrical
centre of the acetabulum on the scout
view, which is parallel to a plane including the entire acetabular rim.
Fig. 2a
Fig. 2b
Fig. 2c
Radial MR scans of a normal hip showing a) the anterosuperior 30° portion, b) the mid-superior portion, and c) the posterosuperior 30° portion.
In this normal subject the acetabular labrum (arrowed) was clearly depicted as a homogeneous area of low signal intensity, the shape of which
was slightly different in the anterior and posterior portions. The joint capsule is located adjacent to the base of acetabular labrum, and attached
to the acetabular rim.
plane of anterosuperior 30°. All 12 planes were examined
for bone abnormalities (e.g., osteophytes or bone cysts),
thinning of the articular cartilage, and the presence of
synovial fluid.
Results
The appearance of a normal hip is shown in Figure 2. The
labrum is clearly depicted as a homogeneous area of low
signal intensity. Its shape is slightly different in the anterior
and posterior portions. The joint capsule is found adjacent
VOL. 82-B, NO. 3, APRIL 2000
to the base of the labrum attached to the acetabular rim.
In the images of patients with moderate OA, there were
several abnormalities when compared with normal hips.
These varied according to the plane of imaging. Often more
than one abnormality was found within a joint. In the
labrum there were ‘attentuation’ abnormalities in 16 hips
(53%) and ‘disappearance’ in 25 (83%) (Figs 3 and 4). The
incidence of these two abnormalities was markedly higher
in the anterosuperior images than in both the mid-superior
and posterosuperior images (Table I). Abnormalities in the
capsule were capsular stripping (29 joints, 97%), seen as a
366
M. HORII, T. KUBO, Y. HIRASAWA
Fig. 3a
Fig. 3b
Fig. 3c
Fig. 3d
The left hip of a 53-year-old woman showing a) an anterosuperior 30° MR scan, b) a mid-superior MR scan, c) a posterosuperior 30° MR scan and d)
a conventional radiograph. In the anterosuperior 30° and mid-superior images the acetabular labrum is obscure, and capsular stripping and marked
thinning of the articular cartilage are observed. An extraosseous high-signal lesion is seen in the anterosuperior 30° scan and small osteophytes also
appear on the acetabular rim. In the posterosuperior 30° scan, the acetabular labrum shows a moderate increase in signal intensity (Cp, capsule; HL,
extraosseous high-signal lesion; St, capsular stripping; FH, femoral head; Lb, acetabular labrum; O, osteophyte).
Table I. The number of hips shown to have labral abnormalities in the weight-bearing part after
MRI
Anterosuperior
Attenuation
Disappearance
Without these abnormalities
Posterosuperior
45°
30°
15°
Mid-superior
3
4
10
23
21
13
5
2
2
1
4
5
7
22
23
28
29
3
15°
30°
45°
5
0
0
Table II. The number of hips with capsular and associated abnormalities in the weight-bearing part
after MRI. Both abnormalities were found in some joints
Anterosuperior
Capsular stripping
Extraosseous high-signal lesion
Posterosuperior
45°
30°
15°
Mid-superior
15°
30°
45°
7
20
25
12
3
3
0
16
22
24
17
9
4
0
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RADIAL MRI OF THE HIP WITH MODERATE OSTEOARTHRITIS
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Fig. 4a
Fig. 4b
Fig. 4c
Fig. 4d
The left hip of a 41-year-old woman showing a) an anterosuperior 30° MR scan, b) a mid-superior MR scan, c) a posterosuperior 30° MR scan and d)
a conventional radiograph. In each scan, the acetabular labrum is obscure, and there is capsular stripping. An extraosseous high-signal lesion is depicted
clearly as a triangular form in the mid-superior image, and also found in the anterosuperior 30° image. The images clearly depict an osteophyte on the
central acetabulum (b and c) and on the head of the femur (a and b), a bone cyst on the acetabulum (a), and joint effusion (a, b and c) (BC, bone cyst;
Cp, joint capsule; HL, extraosseous high-signal lesion; St, capsular stripping; Ef, joint effusion; FH, femoral head; O, osteophyte.)
step between the articular surface and the capsule, and
extraosseous high-signal-intensity lesions (27 joints, 90%),
located outside the initial confines of the joint (Table II). In
addition to these changes, many patients had bone changes
such as osteophytes (Figs 3 and 4) and bone cysts (Fig. 4).
An osteophyte on the acetabular rim (Fig. 3) is difficult to
evaluate, but was found in 24 hips (80%). An osteophyte on
the head of the femur and in the central acetabulum (Fig. 4)
was clearly depicted, and found in 21 (70%) and six (20%)
hips, respectively. Bone cysts were seen quite clearly, and
found in the acetabulum of 18 hips (60%) and nine femoral
heads (30%).
It was difficult to distinguish clearly the articular cartilage of the acetabulum from that of the head of the femur,
but all joints examined showed some variation in the
VOL. 82-B, NO. 3, APRIL 2000
thickness of the cartilage. A joint effusion was found
around the femoral neck (Fig. 4) in 28 hips (93%).
Discussion
12
Radial MRI has been used in studies of the knee and
13
6,7
shoulder, but has been rarely used in the hip. A scout
view of radial imaging depicts the acetabular rim as a
circular form in one plane. Therefore vertical sections of
this plane which are radially determined using the ‘midpoint’ of the acetabulum as the epicentre, cross vertically
the tangent line on the rim. This minimises imaging artifacts induced by a partial volume effect. In the production
of radial section images there may be artifacts due to ‘cross
talk’ at the epicentre, but this is not an important problem
368
M. HORII, T. KUBO, Y. HIRASAWA
since the diameter of the acetabular rim in adults is more
than 4 cm. With the sequence parameters used in our study,
normal fibrous tissue (e.g., labrum) was depicted at low
signal intensities, and articular cartilage and joint effusion
11
at high signal intensities. In the normal hip the acetabular
labrum was depicted as an area of homogeneous low-signal
intensity.
Our findings of labral attenuation, labral disappearance,
capsular stripping, and extraosseous high-signal lesions in
patients with OA were not found in the normal hips. The
changes appeared mainly in the anterosuperior images in
the hips with OA, possibly because the anterosuperior parts
of the joint are the most susceptible to secondary arthritic
changes in dysplastic hips.
Disappearance of the acetabular labrum on the images
does not always represent pathological change. Variation in
signal intensity due to degeneration, with or without displacement, could make the labral image obscure, and this
condition was assessed as ‘disappearance’. Another possible reason for such ‘disappearance’ is the magic angle
14
phenomenon, a well-known artifact, which could occur,
even in a normal labrum, because of circumferentially
orientated collagen fibres. This phenomenon, however, was
not likely to be the major reason in our patients, because in
the normal hips no acetabular labra showed similar
‘disappearance’.
Extraosseous high signal lesions in the images were not
examined histologically, and their pathological counterpart
was not determined. If the capsule was stripped away from
its normal attachment and there was a joint effusion, we
would have expected to find MR signals for the fluid
outside the confines of the joint. Extraosseous high signal
lesions may reflect the combination of capsular stripping
and joint effusion.
Radial MRI also showed osteophytes and bone cysts.
They can usually be demonstrated by plane radiography or
15
CT. Radial MRI makes it easier to understand the location of the lesions.
Data are available from recent studies to compare MRI
findings with biochemical, gross pathological and histo16
logical results, and the use of contrast medium for imag5,16,17
ing.
There has also been an improvement in imaging
techniques. The usefulness of MRI in the evaluation of the
18
articular cartilage in OA of the hip has been reported.
With the sequence parameters used in our study, however,
both articular cartilage and a joint effusion showed high
signal and therefore the thickness of the cartilage was not
always shown accurately. In the gradient-echo sequence,
the strength of T1 saturation can be controlled by the flip
angle. Setting the flip angle at 90° makes the T1 saturation
11
strongest and decreases the signal intensity of an effusion.
This will allow cartilage to be distinguished from an effusion, although the depiction of the labrum may become
indistinct.
To differentiate the articular cartilage of the acetabulum
from that of the head of the femur, improvements in MRI
will be needed with a decreased field of view, increased
matrix and higher resolution of the images with short
imaging time. Radial MRI, which has a signal void area
caused by ‘cross talk’ around the epicentre, may not be the
best way to investigate the detail of changes in cartilage,
especially at the early stages of OA. By contrast, the
artifact induced by a partial volume effect can be ignored
on any planes obtained by radial MRI. Although it lacks
precision, we consider that radial MRI can be applied to the
evaluation of the irregularity of the articular cartilage in
moderate OA of the hip as well as to abnormalities of the
labrum and capsular insertion.
The authors do not choose to respond to the request for a conflict of
interest statement.
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