Background: Although metaphyseal radiolucent changes are often seen
in patients with Legg-Calvé-Perthes disease, the pathogenesis of these
changes remains controversial. The purpose of the present study was to
determine the prevalence and histopathological characteristics of these
metaphyseal radiolucent changes in a piglet model of ischemic necrosis of the
capital femoral epiphysis.
Methods: Ischemic necrosis of the right femoral head was produced in
fifty piglets by surgically placing a ligature tightly around the femoral
neck. The contralateral, left hip of each animal was used as a control.
Radiographs and histological sections of the femoral heads were examined at
two, four, and eight weeks. The radiographs were used to measure the femoral
neck length in order to assess growth disturbance.
Results: Thirteen of the fifty animals were found to have
radiolucent changes in the proximal femoral metaphysis on the side of the
infarcted femoral head. These changes were observed in none of the twelve
animals that were evaluated at two weeks, in one of the fourteen animals that
were evaluated at four weeks, and in twelve of the twenty-four animals that
were evaluated at eight weeks. The radiolucent changes ranged from a focal
cystic lesion to a diffuse area of radiolucency around the proximal femoral
physis. Three distinct types of histological changes were observed in the
metaphysis. Type-I changes were characterized by focal thickening of the
physeal cartilage extending down into the metaphysis. Some of these lesions
demonstrated cystic degeneration of the thickened cartilage. Type-II changes
were characterized by central disruption of the physis and resorption and
replacement of the metaphyseal bone in the region by fibrovascular tissue.
Type-III changes were characterized by diffuse resorption of the physeal
cartilage and resorption of the adjacent metaphyseal and epiphyseal bone. The
mean femoral neck length on the infarcted side in animals with metaphyseal
radiolucent changes was significantly shorter than that in animals without
metaphyseal radiolucent changes (p = 0.02).
Conclusions: Metaphyseal radiolucent changes frequently were
observed in this piglet model at eight weeks after the induction of ischemia.
The metaphyseal radiolucent changes were associated with histopathological
lesions of the physis. The present study suggests that the presence of
metaphyseal lesions can result in a greater growth disturbance of the proximal
femoral physis than is seen in the absence of metaphyseal lesions.
Clinical Relevance: The present study supports the clinical
observation that the presence of diffuse metaphyseal radiolucent changes may
be associated with substantial growth disturbance of the proximal part of the
femur in patients with Legg-Calvé-Perthes disease. The study provides a
histopathological basis for proximal femoral physeal growth disturbance that
has not been clearly demonstrated in the past. These findings also may provide
a histopathological basis for the fluidfilled metaphyseal cysts that sometimes
are observed on the magnetic resonance imaging scans of these patients.