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.

Collagen type type II destruction was studied after induction of experimental OA by ACL-transection in the rat. Damage was investigated by analysis of type II collagen neoepitope expression. Cleavage of type II collagen by collagenases (MMP’s) was detected by the Col2-3/4C-short antibody and collagen denaturation by Col2-3/4m. Rats were sacrificed after 2, 7, 14, 28 and 70 days. Immunostaining was performed using the Col2-3/4C (Collagenase-cleavage site) or the Col2-3/4m antibody (denatured type II collagen).

The first changes after the ACL-transsection were chondrocyte death at the margins of the articular cartilage of both tibia and femur. At day seven a pannus-like tissue protruded from the synovial tissue over the dead cartilage. Underneath the pannus-like tissue a marked staining for the collagenase-cleavage site was observed. The dead cartilage was replaced by fibrocartilage within 4 weeks after which the staining for the collagenase cleavage neoepitope had completely disappeared.

In contrast with the peripheral cartilage, in the central part of the medial tibia and femur dead chondrocytes were found on week 2 until the last time point examined, which was not replaced by fibrocartilage in this timespan. In these areas, loss of proteoglycans, fibrillation of superficial cartilage and staining for denatured type II collagen was found. Both cartilage damage and staining for denatured collagen increased with time. Only light collagenase cleavage site staining was observed on all time points in this central location.

OA in rats after ACL-transsection can be divided in two stages. An early phase lasting about 4 weeks, in which chondrocyte remodelling of the dead cartilage follows death at the cartilage margins. In this phase marked degradation of type II collagen by collagenases occurs. The second phase, characterised by cartilage damage in the central tibia and femur, shows increased staining for denatured type II collagen but little staining for the collagenase cleavage neoepitope.

Type I and II collagen-based scaffolds, with and without attached chondroitine sulphate (CS), were implanted without additional chondrocytes into full-thickness defects in the trochlea of young adult rabbits. We hypothesise that the chemical composition of the matrix will have a direct effect on the speed of repopulation and the phenotypic expression of the subchondral repair cells.

Evaluation of the repair process was performed with routine histology and with two quantitative histological grading systems, four and twelve weeks after implantation.

Four weeks after implantation, type I collagenous scaffolds were completely filled with a cartilage-like repair tissue. By contrast, type II collagenous scaffolds showed a superficial zone of cartilaginous tissue, and in many defects chondrocyte-like cells at the interface of the implant material with the subchondral bone. In collagen type II filled lesions larger areas of the scaffolds were completely devoid of repair tissue. Control defects showed a repair reaction that was very similar to that observed in defects filled with a type I scaffold.

After 12 weeks, the subchondral defect was largely replaced by bone and the differences between the scaffolds were less pronounced. The quantitative blind score of the sections confirmed that the scores of the control defect and of the collagen type I based scaffolds were slightly higher as compared to the type II based scaffolds. Irrespective of the type of scaffold, there was a trend that the scaffolds with CS scored slightly higher than those without CS.

We conclude that different types of scaffold induce different repair reactions. Collagen types I based scaffolds seem superior to guide progenitor cells from a subchondral origin into the defect. Repair cells in collagen type II based scaffolds seem to assume a chondrocyte-like phenotype, which could have a negative effect on the mobility of the repair cells.