Conclusion
Two subcutaneous denosumab injections 6 months apart increase RANKL and depress TNFRSF9 after THA. This provides a possible explanation for the rebound effect on bone turnover markers as well as bone mineral density (BMD) upon withdrawal of denosumab. None of the other measured markers of inflammation was influenced by denosumab treatment.
Methods
Sixty-four patients operated with cementless THA were randomized to two doses of 60-mg denosumab or placebo 1-3 days and 6 months postoperatively. Serum samples were analyzed by a multiplex extension assay detecting 92 inflammation-related proteins. Bone turnover markers were assessed. Proteins were analyzed using linear mixed effect models. Validation of conspicuous findings was performed with ELISA.
Purpose
To evaluate whether denosumab, a human monoclonal antibody directed against receptor activator of nuclear factor kappa-B ligand (RANKL), modulates the inflammatory response after cementless total hip arthroplasty (THA) in patients with osteoarthritis of the hip.
Results
Two proteins were significantly affected by denosumab treatment: RANKL and tumor necrosis factor receptor super family member 9 (TNFRSF9). Serum levels of RANKL were more than twice as high in the denosumab than in the placebo group 3 months after surgery (ratio 2.10, p<0.001). Six and 12 months after surgery, the expression of RANKL was still elevated in the denosumab-treated group (ratios 1.50, p < 0.001; 1.47, p =0.002). The expression of TNFRSF9 was lower in the denosumab group at 3 months (ratio 0.68, p<0.001). In the denosumab group, concentrations of bone turnover markers were substantially reduced after 3 months, remained suppressed after 6 and 12 months, but increased above baseline at 24 months after surgery.