This paper, in one hand, investigates the clinically tolerable, and therefore admissible, volume of ultra-high-molecular-weight polyethylene (UHMWPE) wear in total knee arthroplasties (TKAs) through an extensive literature review. On the other hand, the paper evaluates whether the existing numerical wear models can reliably predict TKA wear volumes and whether the estimated results for a given TKA geometry are credible enough to classify the implant’s osteolysis risk as low, medium, or high. Based on the findings of the first part, three clinically meaningful linear wear rate thresholds have been established from current orthopaedic and tribological literature: below 0.05 mm/year (low osteolysis risk), 0.05–0.1 mm/year (medium risk), and above 0.1 mm/year (high risk). By the use of typical tibial insert contact areas, a lower and upper level have been determined (12.5–37.5 mm³/year or million cycle), which range covers most TKA designs. From the outcomes of the second part, the Archard-based wear formulations, implemented in Finite Element Models (FEM) and Multibody Dynamics models (MBD), showed good agreement with experimental knee simulator data under ISO 14243-1 loading, confirming that numerical models validity and the investigated TKAs reliability for long-term use. This summary demonstrated that (a) the available FEM and MBD models coupled with different wear equations can reliably predict TKA wear volumes (b) the less sophisticated MBD model is also capable to estimate global wear propagation, therefore to decide the implant’s osteolysis risk.