Modelling and simulation of alternative designs for the femur–implant interface of Journey patellofemoral prosthesis

Abstract

The implantation of conventional patellofemoral arthroplasty solutions has been identified as a source of later femur weakness, which is associated with bone resorption and stress-shielding effect. In this work, the Journey PFJ® arthroplasty system, of Smith & Nephew (UK), is investigated. The purpose is to evaluate the structural effects of different femoral components on the bone–implant interface. The finite element method is used to evaluate the influence of the geometry and stiffness of alternative implants, for post-implantation and long-term scenarios. Firstly, the original bone–femur interface of Journey PFJ®, with four fixation pins, was modelled. Secondly, four alternative models were developed: (i) model with two pins; (ii) model without pins; (iii) model with new pin design; (iv) model with increased thickness. The behaviour of the five models was evaluated and compared. Validation against experimental data was also performed. Results showed that the elastic strain is two to three times lower on bone areas close to the pins, in the post-implantation scenario, which is most likely due to a stress-shielding effect. In a long-term scenario, bone rupture by fatigue may occur, associated with an increase in elastic strains. This effect is particularly noticed in the implants supported by fixation pins. In addition, contact analyses evidenced that implant stability is best promoted without fixation pins. Such outcomes suggest that the alternative implant without fixation pins on the bone–femur interface can improve the protection of the femur after patellofemoral arthroplasty, assuming good cement fixation throughout the implant’s lifetime.

Design and Analysis of Porous Functionally Graded Femoral Prostheses with Improved Stress Shielding

“…This is a common process which is regarded as "stress shielding" [5,6]. The stress shielding of the prosthesis leads to the reduction of the strength of the cortical structure of the bone, and it can also cause aseptic loosening, which is one of the main reasons for failure of THRs [7,8]. There are many studies conducted to identify an appropriate material for fabricating prostheses and minimizing the stress shielding.…”

Modern Patellofemoral Arthroplasty

“…Heyse et al showed that the tibiofemoral compartments can be evaluated with MRI after PFA, thus enabling a diagnosis of tibiofemoral disease progression to be made if it is unclear clinically and on plain radiographs. Some concern has been raised regarding stress shielding and reduced bone density of the femur after PFA implantation 99 ; design modifications have been suggested to reduce this occurrence 100 . However, the clinical significance of this is unclear, and most PFAs can be revised using primary TKA implants with no concerns around fixation or need for increased constraint 101-103 .…”

In Silico Optimization of Femoral Fixator Position and Configuration by Parametric CAD Model

“…Structural analysis has often been used to compare the suitability of various fixation devices for a certain fracture type, e.g. [7,8,9,10,11,12]. Parametric studies or optimization procedures have been employed to find the optimal configuration and position of an existing fixation device [13,14,15,16,17] or to optimize the shape and dimensions of a new one (e.g.…”