The stabilisation of bone fragments during surgical fracture treatment substantially impacts the healing process. The osteosynthesis, which a surgeon can directly control, determines the mechanical situation at the fracture site. Groups at the Julius Wolff Institute, among others, have shown that a mechanical stimulus can improve tissue regeneration while mechanical overloading may disrupt it. In addition, factors such as patient anatomy, activity level, and fracture geometry influence the mechanical conditions at the fracture site (internal kinematics, interfragmentary movement) and thus also directly affect tissue regeneration. A well‐controlled mechanical loading of the fracture site is an essential stimulus and driver of bone healing, yet local interfragmentary kinematics has not been directly investigated or even measured in human patients.

We are aiming at assessing the ranges of interfragmentary motion occurring in humans and to stratify beneficial versus detrimental interfragmentary motion by determining the threshold of critical straining in fracture patients. These results will allow a confirmation of the validity of large animal studies and tissue differentiation in in silico models. This project will also lay the foundation for validated recommendations on fracture fixation in humans (e.g. plate working length, plate position, screw positioning) and pave the way for personalised fracture treatment.

Current state of research

It is known from animal experiments that a certain level of compression of fracture fragments can enhance healing while shear movement delays regeneration. Currently, there is no or only limited data available to verify if the findings derived from large animals are also valid and directly transferable to humans. How local mechanical conditions at the fracture site in humans can be controlled by intra‐operative and post‐operative means is so far largely unknown. Only recently, gait analysis combined with in silico musculoskeletal modelling allows for prediction of the subject‐specific musculoskeletal loading conditions. While such data exists in total joint replacement patients, measurements of the mechanical conditions at fracture sites have so far not been realized for larger groups of human fracture patients.

Factors affecting the deformation (strain) of the tissue in the fracture gap

Factors affecting the deformation of the tissue in the fracture gap (compression and shear).

 

Interfragmentary movement

Over the last two decades, Zachow and his group at ZIB have established advanced methods for 3D anatomy reconstruction from medical image data for model‐guided therapy planning and biomechanical research. While 3D image acquisition methods like computed tomography (CT) and magnetic resonance imaging (MRI) are increasing in availability, conventional 2D X‐ray images are often still the standard for diagnosis and treatment planning in orthopaedics. However, precise analyses of local mechanical conditions do require an evaluation based on 3D geometry. Among others, model‐to‐image registration techniques using statistical shape and intensity models have been developed to reconstruct 3D anatomical structures from 2D X‐ray images. This in vivo imaging technology has been already employed in multiple studies by Zachow and Trepczynski, which showed that 3D‐reconstructions of joint movements and implant positions are possible and will now be extended to movements of bone fragments at the fracture gap (dynamic X‐rays) under physiological loading.

Reconstruction of 3D geometry and implant position from two X‐rays

Reconstruction of 3D geometry and implant position from two X‐rays.