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Simulation of Coupled Bone Healing and Implant Degradation

In a recent doctoral project, we were able to develop a first preliminary model that can also be used to simulate the gradual resobtion of a degradable bone implant. To simplify matters, the degradation is modeled as a gradual, controlled volume loss of the implant. The implant surface is shifted inwards in an iterative loop over time depending on local mechanical and biological factors (surface tracking). The first results could be presented at a conference [Pietsch 2018a].

The first very promising simulation results of this model for five different cases of rotationally symmetrical (the axis of symmetry is on the left edge of the healing area) fusion implants made of a resorbable material can be seen in the picture (right). An axial load is transferred from the upper to the lower bone plate via the implant and leads to different straining and thus different stimulation of cartilage and bone growth. The model shows that a successful bone fusion depends very much on the degradation kinetik and the design of the cages mikrostructure. In any case, the model impressively shows the potential as a valuable tool for developing and optimizing degradable bone implants.

Regarding the Interface-Capturing Approach:

  • [Pietsch 2018b]  Pietsch M, F Niemeyer, U Simon, A Ignatius, K Urban:  Modelling the fracture-healing process as a moving-interface problem using an interface-capturing approach. Computer methods in biomechanics and biomedical engineering 21 (8), 512-520, https://doi.org/10.1080/10255842.2018.1487554, 2018
  • [Pietsch 2019]  Pietsch, Martin: Modelling the fracture healing process with interface capturing techniques. Open Access Repositorium der Universität Ulm. Dissertation, http://dx.doi.org/10.18725/OPARU-11273, 2019

Regarding the simulation of degradable bone implants coupled with bone healing:

  • [Pietsch 2018a]  M Pietsch, F Niemeyer, K Urban, A Ignatius, U Simon: Including the Implant Degradation Process in a Fracture Healing Model. In Proc: 8th World Congress of Biomechanics, Dublin, Oral-0586, 2018

 

Results of an axisymmetrical simulation for the case of a degradable fusion implant material (red) in a bone defect (blue) between two bone fragments (orange) with axial load. Implant degradation and new bone formation (gray) for five different implants (a - e). The time course can be seen from left to right (unit = day). Without any implant and therefore with excessive stretching (a) or with a permanent implant with stiff bridging lamellae (b) and therefore stress shielding, new bone formation does not occur. When using an degradable cage (c), bone formation occurs, but only late and incomplete. A pseudarthrosis forms with layers of cartilage (light blue) in the remaining gap. Cases (d) and even better (e) show an optimized implant design for which continuous bone formation resulting in a complete bone fusion is being predicted.