Pro-inflammatory and anti-inflammatory circulating cytokines and periprosthetic osteolysis

We investigated the circulating levels of the main cytokines involved in bone resorption (IL-1beta, IL-6, TNF-alpha), prostaglandins (PGE2) and metalloproteases (MMP-1), as possible early markers of osteolysis, in the serum of eight patients with periprosthetic osteolysis and ten patients without osteolysis. All had received a cementless hip prosthesis (ABG-1). We also assessed the serum levels of IL-1 and TGF-beta anti-inflammatory cytokines exerting protective effect on bone resorption. The mean serum levels of IL-1beta, IL-6, TNF-alpha, TGF-beta, MMP-1, and PGE2 in patients with periprosthetic osteolysis did not differ significantly from those of patients without osteolysis or from those of normal controls. IL-11 serum levels were not detectable at all in any of the patients, while they were detected within normal reference values in the control subjects (significant inverse correlation). We believe that circulating cytokines cannot be regarded as markers of osteolysis, a condition characterised by a local inflammation without systemic signs of inflammation. On the contrary, the undetectable levels of IL-11 in implanted patients could provide evidence for a lack of balance between pro- and anti-inflammatory cytokines in these patients.