Recoil-implantation of multiple radioisotopes towards wear rate measurements and particle tracing in rosthetic joints

This study demonstrates a new method of radioisotope labeling of ultra-high molecular weight polyethylene nserts in prosthetic joints for wear studies. The radioisotopes ⁹⁷Ru, ¹⁰⁰Pd, ¹⁰⁰Rh, and ¹⁰¹mRh are produced in fusion evaporation reactions induced by ¹²C ions in a ⁹²Zr target foil. The fusion products recoil-implant into ultra-high molecular weight polyethylene plugs, machined to fit into the surface of the inserts. During laboratory simulations of the oint motion, a wear rate of the labeled polyethylene may be measured and the pathways of wear debris particles can be raced by detecting characteristic gamma-rays. The concentration profiles of the radioisotopes extend effectively niformly from the polyethylene surface to a depth of about 4 μhe multiplicity of labeling and the use of several gamma-ray lines aids with avoiding systematic measurement uncertainties. Two polyethylene plugs were labeled and one was fitted into the surface of the tibial insert of a knee prosthesis, which had been worn in. Actuation over close to 00,000 cycles with a 900 N axial load and a 24°ion angle removed (14 ± 1) % of the gamma-ray activity from the plug. Most of this activity dispersed into the serum lubricant identifying this as the important debris pathway. Less than % activity was transferred to the femoral component of the prosthesis and the measured activity on the tibial tray was insignificant. Assuming uniform wear across the superior surface of the insert, a wear rate of (12 ± 3) mm3/Megacycle was determined. This is consistent with wear rate measurements under similar conditions using other techniques.