Background: Several studies have documented that the size of the
osteonecrotic lesion in the femoral head is an essential parameter in
determining prognosis and treatment. There are several methods currently
available to measure lesion size, but no general agreement as to which is most
useful. In the present study, three different radiographic methods for
determining lesion size were evaluated and compared.
Methods: Anteroposterior and lateral radiographs of forty-two hips
with osteonecrosis were examined. The extent of osteonecrotic involvement of
the femoral head was determined through the use of three different methods:
the volume of necrosis by quantitative digital image analysis, and the angular
measurements described by Kerboul et al. and Koo and Kim. Graphs were
constructed to demonstrate these relationships.
Results: Volumetric measurement appeared to be the most reliable.
There was only a rough correlation with angular measurements. Several sources
of error were noted when simple angular measurements of irregular,
three-dimensional lesions were used. The Kerboul method routinely
overestimated lesion size and designated 81% of the lesions as
"large." The modified Koo and Kim method provided a more even
distribution of lesion size and correlated with volumetric measurements in 74%
of hips (thirty-one of forty-two hips).
Conclusions: Quantitative volumetric measurements appear to be the
most reliable method to measure the true size of a three-dimensional
osteonecrotic lesion of the femoral head. Volumetric measurement is more
accurate than angular measurement and can be performed easily with modern
technology. Angular measurements, although somewhat simpler to use than
volumetric measurements, may provide only a rough estimate of lesion size,
partly due to the considerable differences in outline or location of the
necrotic segments. Nevertheless, determination of lesion size must be part of
a comprehensive system of staging of this disease, which includes the
evaluation of other parameters, such as the extent and degree of articular
surface involvement and the status of the hip joint and the acetabulum.
Level of Evidence: Diagnostic Level III. See Instructions
to Authors on
jbjs.org for a
complete description of levels of evidence.