QUANTITATIVE ANALYSIS OF OSTEOLYSIS IN A SMALL ANIMAL MODEL OF ASEPTIC LOOSENING

Abstract

Background: The commonest cause of long term failure of total joint arthroplasty is aseptic loosening. As a result, many patients will require complex revision surgery that is not only technically challenging but associated with poorer results. Revisions procedures are also associated with higher morbidity and costs.

Aim: To quantify osteolysis in a small animal model of aseptic loosening. This model can then be utilised for screening therapeutic agents to inhibit aseptic loosening.

Materials and Methods: 7 time mated female mice were injected with radioactive calcium 45 on day 14 of gestation. The 52 offsprings were divided into 2 equal groups and subjected to either the implantation of clinically relevant ceramic particles or sham surgery into their femora. The non-operated femora were used as control. Animals were killed 4 weeks following surgery. Femora were retrieved, dissolved and radioactivity measured as outcome (CPM/mg = Counts Per Minute per milligram). A Linear mixed effects model was utilised to examine the difference in outcome between the 2 groups.

Results: The mean scintillation count for sham surgery was 388 CPM/mg compared to 449 CPM/mg in the control femora. The mean scintillation count for ceramic particles was 351 CPM/mg compared to 420 CPM/mg in the control femora. The mean effect on outcome of surgery with ceramic particles relative to sham surgery was estimated at 16.7 CPM/mg (95CI%: 0.9 to 32.5 CPM/mg; p = 0.025).

Conclusion: We have successfully shown that this model can quantify osteolysis. However, the difference detected between sham surgery and ceramic particles was biologically small displaying the inert properties of ceramic. Extending the post surgery interval might show a larger difference between sham surgery and ceramic particles and permit quantitative analysis of therapeutic agents to be screened to inhibit aseptic loosening.