Predicting clinical outcome of fracture fixation - A biomechanical study based on retrospective clinical data

Bone fracture healing is a complex and multifaceted process. Several factors affect the development of new callus such as fixation type, configuration, fracture characteristics and patient’s related factors. This study aims to deeper understand the influence of fracture fixation on bone healing processes. The thesis was subdivided into three main parts, assessing the objective from different perspectives. Firstly, validation of the mRUST scoring system was conducted, revealing its utility in evaluating fracture healing stages via Intraclass Correlation Coefficients between ratings from multiple clinicians, but also highlighting limitations such as visual impairment and bias due to absolute fracture stability conditions. The second research focused on evaluating callus density and size development and healing progress, correlating findings with finite element model simulations. Results indicate how callus development is influenced by bone type and fixation system, with femur cases producing larger and denser callus than tibia. Furthermore, plate fixations produced more irregular callus than nail or nail+plate treatments. FE simulations supported theories of strain-dependency of fracture healing. However, limitations related to model idealization and lack of data were noted. Finally, joint loading analysis in instrumented total knee replacements revealed linear correlations between resultant joint force, body weight, and knee varus angle. While body weight stood out as primary factor in load transmission, varus angle enhanced correlations if combined with other variables. This proves how a large amount of physiological and mechanical factors influence the load transmission at joint level and consequently at the fracture and fixation level, affecting the new bone callus’ development.