Download The Lesion Site and Morphological Characteristics of Transient

The Lesion Site and Morphological Characteristics of Transient Osteoporosis of the Hip
+1Yamaguchi R; 1Yamamoto T; 1Motomura G; 1Nakashima Y, 1Mawatari T, 1Ikemura S; 1Iwasaki K; 1Zhao G; 1Iwamoto Y
+1 Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, Japan
[email protected]
INTRODUCTION
Transient osteoporosis of the hip (TOH) is a rare disease seen in
pregnant women and middle-aged men. It is characterized clinically by
severe pain without an obvious antecedent cause. The radiologic
characteristics of the affected femoral head are focal loss of radiodensity
and a bone marrow edema pattern on MR imaging. Although several
possible causes have been reported such as transient ischemia of the
femoral bone, intermittent mechanical compression of the obturator
nerve or Sudeck atrophy, the precise etiology remains unknown. In a
recent study, very low signal intensity in bone marrow edema pattern on
T1-weighted MR images was proposed to represent subchondral fracture
line in TOH (1). However, there is no report regarding where in the
femoral head TOH occurs.
In the morphological abnormality of the hip joint, recent studies
have suggested that acetabular retroversion and proximal femoral
deformity are associated with joint degeneration in various disorders of
the hip (2). In TOH, these morphological abnormalities of the hip joint
have not been investigated.
The purpose of this radiological study was to evaluate the lesion
site and morphological characteristics of TOH. In addition, we
investigated the association between these site and characteristics of
TOH.
METHODS
During the 10 year period between Jan 2001 and Dec 2010, TOH
was diagnosed in 33 hip joints of 31 consecutive patients in our
institution. The patients comprised 25 men and 6 women, ages ranging
from 28 to 64 years old (mean age 46 years old). Two women were
pregnant when they developed symptoms. The diagnosis of TOH was
based on the following criteria: 1) hip pain that begins without any
history of antecedent infection or trauma; 2) radiographic
demineralization of the femoral head and/or neck; 3) decreased signal
intensity of bone marrow in the femur on T1-weighted MR images and
increased signal intensity relative to the intensity of normal bone
marrow on T2-weighted MR images (bone marrow edema pattern); and
4) spontaneous resolution of both the symptoms and radiographic
demineralization. The control group included 20 normal hip joints in 16
patients with osteoarthritis of the knee who had no history of hip joint
disease. The control subjects included 4 men and 12 women with an
average age of 76 years.
To evaluate the lesion site of TOH, the lowest signal intensity area
in T1-weighted MR images, where bone marrow edema had occurred,
were investigated. Femoral heads were divided into 4 regions with
parallel and perpendicular lines to the femoral neck which pass through
the center of the femoral head in coronal and axial images. The superior
(S) region, lateral (L) region, inferior (I) region and medial (M) region in
coronal images, the anterolateral (AL) region, anteromedial (AM) region,
posterolatelal (PL) region and posteromedial (PM) region in axial
images were included. In addition, sites of superior and inferior
acetabular edges in coronal images, anterior and posterior acetabular
edges in axial images were also investigated.
To assess morphological characteristics of the TOH and the
control groups in radiograph, the following factors were investigated
with plain radiographs of the hip: existence of coxa profunda, Sharp
angle, acetabular roof obliquity, center edge angle, acetabular head
index and existence of osteophyte at acetabular edge as acetabular
factors; existence of osseus bump at lateral head neck junction and
existence of liner indentation at anterior head neck junction as femoral
factors.
To compare acetabular anteversion angle between the TOH and
the control groups, axial T1-weighted MR images or CT images were
used. The alignment of the acetabular opening was defined by a line
drawn between the anterior and posterior edge. Lines drawn at the level
of the most proximal opening and the maximum diameter of the femoral
head were defined as the roof edge (RE) angle and the equatorial edge
(EE) angle, respectively. A previous study reported that the RE and EE
angles indicated retroversion of acetabulum at each level, and the arc
(EE-RE) angle indicated relative retroversion of acetabulum, which was
linked to cross over sign (3).
The chi-square test, Wilcoxon rank-sum test and TurkeyKraymer’s HSD test were used to compare the parameters among the
TOH and the control groups. Differences were defined as significant
when p was <0.05.
RESULTS
In coronal images, the lowest signal intensity areas were seen in
the S region of 30 hips (91%), M region of 1 hip (3%) and L region of 2
hips (6%). In axial images, these areas were seen in anterior (AM or AL)
region of 17 hips (52%), posterior (PM or PL) region of 9 (27%), and
both anterior and posterior regions of 7 hips (21%). All lesions were
seen contacting the articular surface. The concordance rates between the
site of the lowest signal intensity and acetabular edges were 31 hips
(94%) in coronal images including all of superior edge, and 32 hips
(97%) in axial images including 22 hips of anterior edge and 10 hips of
posterior edge.
In morphological evaluations of acetabular factors, center edge
angle, acetabular head index in the TOH group were significantly higher
than those in the control group (Table 1). In femoral factors, existence of
liner indentation at anterior head neck junction in the TOH group was
more frequent than that in the control group. In acetabular version
analysis, mean RE, EE angles in the TOH group were significantly
lower than those of the control group. The arc (EE-RE) angle in the
TOH group was significantly higher than that of the control group.
To investigate the association between the lesion site and the
morphological parameters, we categorized all hip joints into the
anterosuperior affected (AA; 17 hips, 52%) group, posterosuperior
affected (PA; 9, 27%) group and both affected (BA; 7, 21%) group.
Almost all parameters of each group differed from those of the control
group. In the multiple comparisons among affected groups, only the arc
(EE-RE) angle of AA group was significantly higher than those of the
PA and BA groups (17.8, 10.7 and 9.4, respectively).
CONCLUSION
TOH occurred in the superior portion of the femoral head
contacting the articular surface, and categorized into approximately half
of the anterosuperior affected group, 30 % of the posterosuperior
affected group and 20 % of both affected group. Almost all lesions were
concordant with the site of the acetabular edge. In the TOH group,
acetabular coverage toward the femoral head was relatively insufficient.
Acetabulums of the TOH group were totally and relatively retroverted,
especially the anterosuperior affected group was the most retroverted.
SIGNIFICANCE
The present study revealed the lesion site and morphological
characteristics of TOH, which helps to understand the etiology of TOH.
REFERENCES
1. Miyanishi K, et al. Skeletal Radiol. 2001;30:255-61.
2. Ezoe M, et al. J Bone Joint Surg Am. 2006;88:372-9.
3. Reynolds J, et al. J Bone Joint Surg Br. 1999;81:281-8.
Figure 1. Comparison in morphological characteristics between the
TOH and the control groups
Factors
Acetabular factors
Coxa profunda
Sharp angle
Acetabular roof obliquity
Center edge angle
Acetabular head index
Osteopyte of acetabular edge
Femoral factors
Lateral osseus bump
Anterior liner indentation
Anteversion angle
Roof edge angle (RE)
Equatorial edge angle (EE)
Arc angle (EE-RE)
Poster No. 0877 • ORS 2012 Annual Meeting
TOH group
Control group
P value
64%
36.5
2.6
34.6
83.0
9%
75%
36.1
4.8
43.6
88.1
0%
0.55
0.46
0.06
<0.0001
0.0073
0.28
15%
70%
5%
15%
0.39
0.0002
-0.1
13.9
14.0
14.2
21.4
7.3
<0.0001
<0.0001
0.0022