Abstract
Introduction:
Wear debris from articulating joint implants is inevitable. Small debris particles are phagocytosed by macrophages. Larger particles initiate the fusion of many macrophages into multi-nucleated giant cells for particle encasement. Macrophages are recruited into inflamed tissues from the circulating monocyte population. Approximately 10% of white blood cells are monocytes which after release from the bone marrow circulate for 2–3 days, before being recruited into tissues as inflammatory macrophages or undergoing apoptosis. Circulating MRP8/14 (S100A8/A9) is a measure of monocyte recruitment, part of the monocyte-endothelial docking complex, and shed during monocyte transmigration across the endothelium. The higher the S100A8/A9 the more monocytes being recruited giving an indirect measure of debris production.
Methods:
2114 blood samples were collected from arthroplasty patients with hip or knee osteoarthritis (primary, post-traumatic and secondary), 589 before their primary arthroplasty, 1187 patients > 1 year post-arthroplasty, 101 patients before revision for aseptic loosening and 237 patients >1 year post-revision. Plasma S100A8/A9 was measured using BMA Biomedicals Elisa kit, normal levels in health adults are 0.5–3 mg/ml. Joint specific scores, WOMAC knee or Oxford Hip adjusted to percent of maximum, together with SF-12 were completed.
Results:
Mean and S.D. plasma S100A8/A9 before a primary 4.89 + 3.12, >1 year post-surgery follow up 4.03 + 2.2, before revision 5.08 + 2.59 and >1 year post revision 3.89 + 1.94. Percent joint specific scores before a primary 40.33 + 15.75, >1 year post-surgery follow up 70.34 + 22.33, before revision 38.75 + 15.12 and >1 year post revision 53.88 + 22.02. SF-12 physical function scores before a primary 26.52 + 7.12, >1 year post-surgery follow up 35.76 + 11.50, before revision 24.71 + 6.47 and >1 year post revision 30.08 + 9.82. The pre-op primary to follow up S100A*/A9 fell p < 0.001 while both joint specific and SF-12 PCS improved p < 0.001. The pre-revision concentration of S100A8/A9 was significantly higher than routine follow up levels p < 0.001 while joint specific and SF-12 scores fell p < 0.001. S100A8/A9 correlates negatively with both scores p < 0.
Discussion:
Osteoarthritis demonstrates enhanced monocyte recruitment before primary surgery which is significantly reduced following arthroplasty. There is a detectable and significant increase in S100A8/A9 concentrations indicative of enhanced monocyte recruitment again before revision surgery.
