Introduction : The reason why heterotopic ossification develops after total hip arthroplasty is still not known, but it is assumed that inflammatory reaction is the major driving force. In literature little is known about the cytokine levels at the site of surgery, most measurements are done in serum. This study was conducted to investigate if the levels of different pro- en anti-inflammatory cytokines are measurable in drainage fluid and, when measurable, whether we can find a difference in cytokine concentration between one and six hours postoperatively.

Materials and methods: Samples from the drainage system in 30 consecutive patients undergoing primairy total hip replacement were collected at one and six hours after closure of the wound. GM-CSF, G-CSF, IFN-γ, TNF, MCP-1, IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13 and MIP-1beta levels were measured in the drainage fluids.

Results: Measurable levels of all cytokines studied were found, except for IL-17. A significant elevation of almost all cytokines was observed between the sample after one hour and six hours postoperatively. The elevation was significant for all cytokines except IL-10 and MIP-1b. We found a strong correlation between the different pro-inflammatory cytokines. Levels are much higher than previously shown levels in serum. When computing the IL-6 to IL-10 ratio, this ratio increased from 304 (SD 256) to 12357 (SD 6788) (p< 0,000), which shows an increased predominance of the pro-inflammatory interleukines when comparing the measurements after one and six hours respectively.

Conclusion: Detectable levels of numerous cytokines can be measured in drainage fluid post-operatively. The levels of most cytokines in drainage fluid are higher in samples taken six hours after surgery as compared to samples taken after one hour. Further studies are needed to detect the relation between these cytokine concentrations and the heterotopic bone formation.