Relationship Between Product Demand, Tibial Polyethylene Insert Shelf Age, and Total Knee Arthroplasty Survival : Retrospective Review of Total Knees of One Design

Shelf aging of γ-irradiated–in–air polyethylene tibial components has been associated with increased articular surface wear and an elevated risk for revision. Nine hundred fifty cruciate-retaining inserts of one design were implanted between 1987 and 1996 (shelf age, 1.0 ± 1.2 years). Less frequently used inserts (smallest/largest sizes, thicker thicknesses, supplemental articular constraint) had longer shelf ages (means ranged from 1.2 to 2.6 years). Survival analysis showed that shelf age (P < .01) and γ-sterilization in air (P = .01) elevated the risk for revision. Surgeons must remain attentive to identify the shelf-aged γ-irradiated–in–air polyethylene tibial component while following designs from the era when this sterilization method was used. Recognition is expedited by understanding how shelf life is related to product demand and can be of aid when diagnosing the painful knee.