Review Question - QID 218120

The patient has peri-acetabular osteolysis with well-fixed implants. Osteolysis occurs when very small debris particles (< 1 micron) stimulate macrophage activation.

Osteolysis represents a histiocytic response to particulate debris via a predictable cascade: (1) particulate debris formation (particles sized 0.1 to 1 micron), (2) macrophage-activated osteolysis, (3) prosthesis micromotion, (4) particulate debris dissemination. In step 2, activated macrophages propagate the osteolytic cascade by releasing cytokines, predominantly IL-1, IL-6, and TNF-alpha. TNF-alpha, in turn, causes an up-regulation of RANK/RANKL-mediated bone resorption.

Campbell, et al. published on a technique for isolating submicron-sized UHMWPE wear particles from the periprosthetic tissues of arthroplasty patients. The recovery of polyethylene particles, which have a density less than that of water (0.93-0.94 g/cm3), required new methods to be devised through a series of experiments with various reagents and separation techniques. They concluded that their devised method was reproducible, that particle morphology was very consistent, and that most particles were submicron in size.

McKellop, et al. published on the origin of submicron polyethylene wear debris in total hip arthroplasty. The authors noted that the polyethylene particles isolated from the serum lubricants of the wear tests and from the periprosthetic tissues were primarily submicron in size. They concluded that the submicron particles are the primary culprits associated with inflammatory periprosthetic bone loss in total hip replacement.

Maloney, et al. isolated wear particles from 35 membranes obtained from revision hip replacement procedures. The authors found that the mean size of the polyethylene particles was 0.5 micrometers, while the metal particles were a mean of 0.7 micrometers, as determined with scanning electron microscopy. They concluded that it is important for surgeons who perform joint-replacement operations to be cognizant of factors that may influence the production of wear debris and thus affect the fixation of the implant and limit the longevity of the reconstruction.

Figure 1 is an AP radiograph of the low AP pelvis showing a large peri-acetabular and trochanteric lytic lesions surrounding well-fixed total hip arthroplasty implants consistent with osteolysis.

Incorrect Answers:
Answers 1, 2, and 5: Osteolysis is a macrophage-driven process.
Answer 4: Macrophages are stimulated by very small particulate debris sized < 1 micron.