Importance of trabecular anisotropy in finite element predictions of patellar strain after Total Knee Arthroplasty

- Aim of study was to estimate effect of isotropy/anisotropy on patellar strain after Total Knee Arthroplasty.
- We compared finite element results of 17 patellae, in physiological loading.
- Compared to anisotropy, isotropy overestimated stain up to 4 times.
- This strain difference was maximum with low density patellae.

Patellar fracture and anterior knee pain remain major complications after Total Knee Arthroplasty (TKA). Patient-specific finite element (FE) models should help improve understanding of these complications through estimation of joint and bone mechanics. However, sensitivity of predictions on modeling techniques and approaches is not fully investigated. In particular, the importance of patellar bone anisotropy, usually omitted in FE models, on strain prediction is still unknown. The objective of this study was thus to estimate the influence of modeling patellar trabecular anisotropy on prediction of patellar strain in TKA models.We compared FE-derived strain predictions with isotopic and anisotropic material properties using 17 validated FE models of the patella after TKA. We considered both non-resurfaced and resurfaced patellae, in a load-bearing TKA joint. We evaluated and compared the bone volume above a strain threshold and, in addition, estimated if the difference in isotopic and anisotropic predictions was consistent between patellae of different average bone volume fraction.Compared to the anisotropic reference, the isotropic prediction of strained volume was 3.7 ± 1.8 times higher for non-resurfaced patellae and 1.5 ± 0.4 times for resurfaced patellae. This difference was higher for patellae with lower average bone volume fraction.This study indicates that strain predictions acquired via isotropic patellar FE models should be interpreted with caution, especially when patellae of different average bone volume fraction are compared.