CMM–based procedure for polyethylene non-congruous unicompartmental knee prosthesis wear assessment

One of the most recent advances in knee replacement surgery is the Unicompartmental Knee Prosthesis that involves the substitution of only one compartment. Uncertainties on the survivorship of such design led to the improvement of pre-clinical mechanical simulation. To effectively support this market phase with clinically relevant wear data it is important to be able to accurately quantify it and the consequent knee prostheses functionality. The aim of the present study was to validate a coordinate-measuring machine (CMM)-based procedure to assess the wear of a commercially available, non-congruous UKP design after mechanical simulation; gravimetric quantification of material defeat produced, in fact, a reference wear value. The two methods are in good agreement (R2 = 0.73) even if CMM technique systematically overestimates the measured values. Material behavior has been monitored through out the test to be able to distinguish, within dimensional changes, permanent plastic deformations and creep contribution. In the case of simulator test mean linear and gravimetric wear rate were evaluated, respectively, 0.19 ± 0.02 mm and 0.86 ± 0.15 mg/Mc. Our findings encouraged further work on reliability and accuracy improvement.