The stabilisation of bone fragments during surgical fracture treatment substantially impacts the healing process. Researchers at the Julius Wolff Institute have shown that 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 and thus also directly affect bone tissue regeneration. A well‐controlled mechanical loading of the fracture site is an essential stimulus and driver of the bone healing. However, local interfragmentary kinematics have not yet been directly investigated or even measured in human patients.

 

Current State of Research

It is known from animal experiments that a certain level of compression in the fracture site can enhance healing while shear movement delays it. Currently, there is no data available to verify if the findings derived from large animals are also valid for humans. How the local mechanical conditions at the fracture site can be controlled by bone fixation plate (osteosynthesis) is so far also largely unknown. Only recently, gait analysis combined with in-silico musculoskeletal modelling allowed 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 mechanical conditions in the fracture gap (compression and shear stress).

 

Project Goals

We are aiming to assess local interfragmentary motion occurring in human patients and stratify beneficial versus detrimental factors by determining the threshold of critical straining in fracture sites. These results will allow a confirmation of the validity of animal studies and tissue deformation in in-silico models. This project will also lay the ground 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.

 

Geometry Reconstruction

Over the last two decades, our group at ZIB has established advanced methods for 3D anatomy reconstruction from medical images 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, 2D images do not provide sufficient information for complete analysis of local mechanical conditions, which requires an evaluation based on complete 3D geometry of the bone fracture.

Imaging test setup and the resulting X-ray images.

 

To tackle this issue, special registration techniques have already been developed that use statistical shape and intensity models (SSIMs) to reconstruct 3D anatomical structures from 2D X‐ray images. These techniques have already been employed in multiple studies, 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 realistic loading conditions.

Reconstruction of 3D geometry and implant position from 2D bi-planar X‐rays.