Decreased stress shielding with poly-ether-ether-ketone tibial implant for total knee arthroplasty - A preliminary study using finite element analysis

In total knee arthroplasty (TKA), the mechanical mismatch between cobalt-chromium (CoCr) alloy tibial implant and bone has been implicated in stress shielding and subsequent implant failure and bone resorption. This study investigates the biomechanical advantages of poly-ether-ether-ketone (PEEK) tibial implant, which exhibit properties analogous to those of the surrounding bone. A finite element analysis (FEA) was employed to assess and compare the biomechanical performances of PEEK and CoCr tibial implants in patients with and without osteoporosis. Four FEA models were constructed with PEEK and CoCr alloy implants in normal and osteoporotic tibias. Based on previous literature and our clinical experience, stresses measurements were taken at 16 points on the tibial plateau and 8 points on the two surfaces which were 10 mm and 20 mm apart from the tibial plateau, with specific regions quantified for stress shielding. The results showed significant differences in stress distribution between PEEK and CoCr implants. The PEEK implants exhibited higher equivalent stresses on the tibial plateau in all models (normal bone: 0.22 ± 0.07 MPa vs. 0.13 ± 0.06 MPa, p < 0.01; osteoporotic bone: 0.39 ± 0.06 MPa vs. 0.17 ± 0.07 MPa, p < 0.01). In non-osteoporotic models, the mean equivalent stresses on proximal tibial surfaces were similarly elevated for PEEK implants (0.29 ± 0.13 MPa vs. 0.21 ± 0.08 MPa, p = 0.02). The CoCr implants demonstrated more stress shielding across all measured regions (tibial plateau: 23.47% vs. 2.73%; surface 1: 15.93% vs. 1.37%; surface 2: 10.71% vs. 6.56%). These disparities were even more pronounced in osteoporotic models in the CoCr group (tibial plateau: 32.50% vs. 8.36%). The maximum equivalent stresses on the tibial plateau further supported this trend (normal bone: 1.02 MPa vs. 0.52 MPa; osteoporotic bone: 1.43 MPa vs. 0.67 MPa). These data confirm the hypothesis that a PEEK tibial implant can reduce peri-prosthetic stress shielding, suggesting that PEEK implants have the capability to distribute loads more uniformly and maintain a closer approximation to physiological conditions.