Background: Aseptic loosening is often mentioned as the primary
reason for costly revision of total joint arthroplasties. Receptor activator
of nuclear factor-?B ligand (RANKL) appears to be a major factor in the
bone resorption observed in periprosthetic osteolysis. RANKL plays an
essential role in the recruitment, differentiation, and survival of the
osteoclasts implicated in periprosthetic osteolysis. This study was performed
in an effort to identify the cell type in the periprosthetic membrane
responsible for expression of RANKL.
Methods: Tissues harvested from osteolytic lesions in nine patients
undergoing total joint revision were serially sectioned for
immunohistochemical analysis. Intercellular adhesion molecule-1 (ICAM-1) and
prolyl 4-hydroxylase (5B5) antibodies were used to detect fibroblasts, and
anti-CD-163 (Ber-MAC3) was used to detect macrophages. In addition, antibodies
to osteoprotegerin (OPG), RANKL, and receptor activator of nuclear
factor-?B (RANK) were utilized. The binding pattern of these antibodies
was then viewed with confocal microscopy with the use of only secondary
antibodies as method controls.
Results: Histological analysis was confined to areas of the membrane
where cells were detected with use of Hoechst 34580 nuclear stain. In the
membrane specimens from all nine patients, diffuse RANKL staining was
localized to areas lacking cells and more intense staining was seen in areas
containing nucleated cells. There was strong colocalization between RANKL and
OPG, and there was weak but specific colocalization between RANKL and both 5B5
and ICAM-1. In contrast, there was complete separation of antibody staining of
Ber-MAC3 and RANKL, indicating only generalized overlap of the myeloid markers
with the RANKL.
Conclusions: RANKL expression was localized to cells that stained
positively for fibroblast markers. The data also indicated that there is an
intact RANKL/RANK/OPG system in the periprosthetic membrane that could
regulate focalized bone resorption in osteolysis.
Clinical Relevance: Identifying the cell types responsible for RANKL
production is critical to the development of a strategy to prevent