الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Avascular necrosis (AVN) of the femoral head is an
increasingly common cause of musculoskeletal disability, and it
poses a major diagnostic and therapeutic challenge. Although
patients are initially asymptomatic, avascular necrosis of the
femoral head usually progresses to joint destruction, requiring
total hip replacement (THR), usually before the fifth decade.
In fact, 50% of patients with avascular necrosis experience
severe joint destruction as a result of deterioration and undergo a
major surgical procedure for treatment within 3 years of diagnosis.
Femoral head collapse usually occurs within 2 years after
development of hip pain.
The lack of level 1 evidence in the literature makes it
difficult to identify optimal treatment protocols to manage patients
with pre-collapse avascular necrosis of the femoral head, and early
intervention prior to collapse is critical to successful outcomes in
joint preserving procedures.
There have been a variety of traumatic and a traumatic
factors that have been identified as risk factors for osteonecrosis,
but the etiology and pathogenesis still remains unclear.
Summary & Conclusions
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Current osteonecrosis diagnosis is dependent upon plain
anteroposterior and frog-leg lateral radiographs of the hip,
followed by magnetic resonance imaging (MRI). Generally, the
first radiographic changes seen by radiograph will be cystic and
sclerotic changes in the femoral head. Although the diagnosis may
be made by radiograph, plain radiographs are generally
insufficient for early diagnosis, therefore MRI is considered the
most accurate benchmark.
MRI detects chemical changes in the bone marrow and
provides the doctor with a picture of affected area and bone
rebuilding process. In addition MRI may show diseased areas that
are not yet causing any symptoms.
High soft tissue contrast, the ability to image in multiple
planes, the ability to manipulate tissue contrast, and high
sensitivity to marrow based pathologic condition gives MRI
significant advantage over other imaging techniques.
The final outcome of the treatment for follow-up was directly
related to the size and the topography of the lesion. The
importance of the lesion size for outcome prediction was
recognized and several methods were proposed for lesion size
assessment.
Summary & Conclusions
105
Methods based on radiographs provide a rough assessment of
the lesion size. Several methods were based on MR imaging but
performing only 2D assessment, i.e. they estimate the area of the
lesion in the central slice, or the arc of involvement of the weightbearing
area. Some methods have been proposed for the
evaluation of the actual volume of the lesion.
Many studies associated the location of the necrotic lesion to
the risk of collapse; lesions that extend to the superolateral area of
the head are characterized by high risk of collapse. Hips that fail
usually have wide lesions extending beyond the lip of the
acetabulum. Femoral heads with lesions mainly located on the
medial area of the head retain a lateral supportive pillar of intact
bone that may act as a stress shield for the affected segment and
protects it from excessive loads. The absence of this pillar in hips
with wide lesions (extending in the supero-lateral segment of the
head) makes those hips susceptible to early collapse.
The loss of the spherical contour of the articular surface is a
key point at all classification systems, once has occurred the role
of prophylactic surgery is limited. MRI should be done for its high
specificity and sensitivity for early disease, according to the
findings the disease is classified under the above mentioned
criteria, the patient is going to benefit from a prophylactic surgery
if the size of the lesion is less than 30% of the femoral head this is
Summary & Conclusions
106
best measured using 3D MRI reconstruction from T1W coronal
images using special software and 3D finite element analysis these
two methods are reproducible and time saving also the location of
the lesion should be located medially and the necrotic lesion
should show signal characteristic that fall under Mitchel
classification A or B and surrounded with little or no edema,
although these last two criteria are supportive for the decision
making and not crucial as the size and location of the lesion