The local concentration of Ca(2+) correlates with BMP7 expression and osseointegration in patients with total hip arthroplasty

BACKGROUND: A successful osseointegration of total hip arthroplasty (THA) relies on the interplay of implant surface and bone marrow microenvironment. This study was undertaken to investigate the impact of perioperative biochemical molecules (Ca(2+), Mg(2+), Zn(2+), VD, PTH) on the bone marrow osteogenetic factors (BMP2, BMP7, Stro-1(+) cells) in the metaphyseal region of the femoral head, and further on the bone mineral density (BMD) of Gruen R3. METHODS: Bone marrow aspirates were obtained from the discarded metaphysis region of the femoral head in 51 patients with THA. Flow cytometry was used to measure the Stro-1(+) expressing cells. ELISA was used to measure the concentrations of bone morphologic proteins (BMP2 and BMP7) and the content of TRACP5b in serum. TRAP staining was used to detect the osteoclast activity in the hip joint. The perioperative concentrations of the biochemical molecules above were measured by radioimmunoassay. The BMD of Gruen zone R3 was examined at 6 months after THA, using dual-energy X-ray absorptiometry (DEXA). RESULTS: Our data demonstrated that the concentration of Ca(2+) was positively correlated with BMP7 expression, and with the postoperative BMD of Gruen zone R3. However, the concentration of Mg(2+) had little impact on the R3 BMD, although it was negatively correlated with the expression of BMP7. Osteoclast activity in hip joint tissue of patients with femoral neck fractures was increased. Compared with the patients before THA, the levels of TRACP5b in serum of patients after THA were decreased. The data also suggested that the other biochemical molecules, such as Zn(2+), VD, and PTH, were not significantly correlated with any bone marrow osteogenetic factors (BMP2, BMP7, Stro-1(+) cells). The postoperative R3 BMD of patients of different gender and age had no significant difference. CONCLUSIONS: These results indicate the local concentration of Ca(2+) may be an indicator for the prognosis of THA patients.