The effects of wear particles on artificial hip joints are well documented. Aseptic loosening has been demonstrated to be dependent on both particle numbers and particle size. This study investigated the effects of stem material and surface finish on particles produced at the stem/cement interface in cemented artificial hips. Three commonly used implant materials of different hardness were investigated: cobalt chrome, the hardest of the three materials, stainless steel and titanium alloy which was the softest material tested.

The surfaces of three femoral stems with different surface finishes were measured and used as templates; the Exeter which is highly polished, the Charnley which is moderately rough and the Capital which is very rough. Test plates were manufactured in each material and with each surface finish making 9 sets of plates in all.

The plates were opposed to cement pins (CMW) in a sliding wear tester. The volume of debris produced was calculated from measurements of the pins pre- and post-test. The debris was collected, filtered and examined under the electron microscope, which allowed particle sizes of a representative sample of debris to be measured. From this mean particle size was calculated.

Volume of debris: for all three materials the roughest surface produced the greatest volume of debris and the smoothest surface the least. For any given surface finish the softest material produced the greatest volume of debris and the hardest material the least.

Size of particles: for all three materials the roughest surfaces produced the largest particles and the smoothest surface the smallest particles. For any given surface finish the hardest material produced the smallest particles and the softest material produced the largest particles.

Particulate debris has been demonstrated to have a major role in the aseptic loosening of artificial joints. Biological activity is stimulated by particles of size 0.1 to 10 microns with maximum affect being seen in particles of approximately 0.5 microns. This study investigated the particle size of wear debris produced at the stem/cement interface in cemented artificial hips comparing different materials and surface finishes of the stem.

Materials and Methods: The stem surfaces of three cemented femoral prostheses with different surfaces were used as templates, one smooth (Exeter, How-medica), one slightly rough (Elite, DePuy) and one very rough (Capital, 3M). Three commonly used implant materials were compared, cobalt chrome, stainless steel and titanium alloy.

Test plates were manufactured in each material and with each of the three surface finishes.

The plates were opposed to cement pins in a sliding wear tester. The debris produced was collected, filtered and examined under an electron microscope. Representative samples of particles produced by each test series were measured and aspect ratios calculated.

Plates were also measured pre and post test to ensure no significant change in surface roughness during testing.

Results: Each of the materials demonstrated an increase in mean particle size with increasing roughness of the test surfaces. This was more marked for titanium alloy than for cobalt chrome.

For any given surface roughness the size of particles produced was smallest for the hardest material (cobalt chrome) and largest for the softest material (titanium alloy).

Conclusion: The majority of particles produced were within the biologically active range. Particle size of debris was related to surface roughness with rougher surfaces producing larger particles. Harder materials produced smaller particles than softer materials and more particles in the biologically active range.