Abstract
A total knee arthroplasty system offers more distal femoral implant anterior–posterior
(AP) sizes than its predecessor. The purpose of this study is to investigate the impact
of increased size availability on an implant system's ability to reproduce the AP
dimension of the native distal femur. We measured 200 cadaveric femora with the AP-sizing
guides of Zimmer (Warsaw, IN) NexGen (8 sizes) and Zimmer Persona (12 sizes) total
knee arthroplasty systems. We defined “size deviation” as the difference in the AP
dimension between the anatomic size of the native femur and the closest implant size.
We defined satisfactory reproduction of distal femoral dimensions as < 1 mm difference
between the implant and native femur size. The NexGen system was associated with a
mean 0.46 mm greater implant size deviation than Persona (p < 0.001). When using a 1 mm size deviation as a cutoff for satisfactory replication
of the native distal femoral anatomy, 85/200 specimens (42.5%) were a poor fit by
NexGen, but a satisfactory fit by Persona. Only 1/200 specimens (0.5%) was a poor
fit by Persona, but a satisfactory fit by NexGen (p < 0.001). The novel knee system with 12 versus 8 sizes reproduces the AP dimension
of the native distal femur more closely than its predecessor. Further study is needed
to determine the clinical impact of these differences.
Keywords
total knee arthroplasty - cadaveric study - implant sizing - implant personalization
