High-Turnover Periprosthetic Bone Remodeling and Immature Bone Formation Around Loose Cemented Total Hip Joints

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Abstract
Aseptic loosening and periprosthetic osteolysis are the major problems awaiting solution in total hip surgery. The clinical investigation focused on the analysis of periprosthetic bone remodeling to clarify one important key event in the cascade of periprosthetic connective tissue weakening and osteolysis around loose artificial hip joints. Twelve acetabular bone samples adjacent to granulomatous synovial‐like membrane of loose hip prosthesis were retrieved at revision surgery and processed for Villanueva bone staining for morphological observation and bone histomorphometric analysis. Eight well‐fixed bony samples were used as control. Although osteoclastic surface and eroded surface by osteoclasts were evident in the periprosthetic bone from loose hip joints (p = 0.003 and p = 0.027), increased osteoid/low‐mineralized bone matrix (p < 0.001) and osteoid width (p < 0.001) also were significant findings in structural analysis. In addition, not only elevated mineral apposition rate (MAR; p = 0.044) but also increased mineralizing surface (p = 0.044) and bone formation rate (BFR; p = 0.002) in loose periprosthetic bones were shown in dynamic data analysis. These results were confirmed by precise morphological observation by confocal laser scanning microscopy. Active coupling of bone formation and resorption and increased osteocytes with abundant bone canalicular projections were found in combined with the presence of immature bone matrices (osteoid and low‐mineralized bone areas) in periprosthetic bones from loose hip joints. These results indicated that active osteoclastic bone resorption and/or defective bone formation are coupled with monocyte/macrophage‐mediated foreign body‐type granuloma in the synovial‐like interface membrane of loose hip joints. Thus, this unique high‐turnover periprosthetic bone remodeling with bad bone quality probably is caused by the result of cellular host response combined with inappropriate cyclic mechanical loading. The fragile periprosthetic bone may contribute to hip prosthesis loosening.