Polymer debris from the sliding wear of a rotating steel wheel on flat polyethylene was traced using the radioisotope indium-111 to identify wear debris pathways. The radioisotope was ion-implanted just below the surface of ultra-high molecular weight polyethylene samples at a mean implantation depth of 144 nm. The implantation fluence was 4 × 1012 ions/cm2 or less. Several samples were actuated by the rotating wheel with two different normal loads and varying actuation regimes in a water lubricant. The depths of the wear cavities in the polyethylene extend well below the shallow implantation depth. It is shown that the debris transport from the polyethylene sample to the wheel, the return of debris from the wheel to the sample, and the dispersion of debris to the water lubricant can be accurately traced and quantified using indium-111. During wear-in the debris exchange between sample and wheel quickly attains quasi-equilibrium, with a relatively small amount of debris dispersed into the water. Assuming a critical limit for the abrasion of the polymer, a wear model is presented which agrees with the measurements.