Tibial post wear in posterior-stabilized knee replacements is design-dependent

Abstract

Polyethylene tibial post wear in posterior-stabilized knee designs is a major problem. The Insall-Burstein II (IB PS II) reportedly has severe anterior wear of the post in retrieved implants. We hypothesized the more anterior placement in the IB PS II would be reflected in greater wear at the anterior face than the IB PS I. We examined 234 retrieved inserts using subjective scales to grade post damage and wear. Of the IB PS II inserts, 38% demonstrated severe wear compared with only 25% of IB PS I inserts. The most prevalent damage location for the IB PS II was the anterior face, whereas the IB PS I sustained wear mainly on the medial face. While the IB PS post was not designed to constrain posterior femoral displacement, our observations confirm contact in hyperextension or other paradoxic anterior tibial translation is common and design-dependent. Minimizing wear and damage through proper post placement and changes in implant design to anticipate contact on the anterior post should be considered for future posterior stabilized knee replacements. These changes cannot occur in isolation, however, because changes in post placement and design also depend on their relation to the shape and location of the tibial bearing surfaces.

Fig. 1A–B

Box plots for damage and wear scores for IB I and IB II. No statistical differences were found in (A) total damage or (B) total wear scores for all IB PS I versus all IB PS II components.

Fig. 2

Fractured post of IB II posterior stabilized tibial insert is shown. Complete fracture of the post was found on three IB II inserts and one IB I insert.

Fig. 3A–F

Damage patterns on medial and anterior faces of the tibial post on IB I and IB II retrieved inserts. Design, location, and length of implantation are identified for each figure. The dominant wear locations were on the medial face for the IB I inserts and on the anterior face for the IB II inserts. (A) IB I, medial, 4 years; (B) IB I, anterior, 2.9 years; (C) IB I, medial, 10.3 years; (D) IB II, anterior, 2.5 years; (E) IB II, anterior, 7 years; (F) IB II, anterior, 6.3 years.