Expression of parathyroid hormone related protein in the tissue around loosened hip prostheses.

OBJECTIVE To investigate the eventual presence and cellular source ofparathyroid hormone related protein (PTHrP) in the synovial-like interface membrane from aseptic loosening of total hip replacement (THR). METHODS A polyclonal rabbit antiserum to the amino-terminal peptide of human PTHrP was used to stain 10 interface membrane samples from loose THR and 10 synovial tissue samples from hip osteoarthritis (OA). Quantitative microscopic assessment was done with a computer-assisted image analysis system. Western blotting was applied to verify the presence of PTHrP in both tissue samples. Double immunofluorescence labelling aimed to reveal the cellular sources of PTHrP. RESULTS Immunoreactive PTHrP was found in all interface membrane and OA synovial tissue samples. The number of PTHrP positive cells in interface membrane was much higher than in OA synovial tissue. Positive cells were most commonly seen in the lining-like layers and sublining area of interface membrane. Double immunofluorescence labelling showed that most macrophages and fibroblasts in interface membrane were PTHrP positive. Western blotting revealed the 24-25 KD bands in both tissue samples. CONCLUSIONS PTHrP expression is upregulated in interface membrane around loosened hip prostheses. Locally accumulated PTHrP may contribute to periprosthetic osteolysis and aseptic loosening of THR through its direct effects on bone, or indirectly via the induction of inflammatory mediators.