Design Principles to Increase the Patient Specificity of High Tibial Osteotomy Fixation Devices

High stiffness fracture fixation devices inducing absolute stability, activate inefficient primary healing and stress shielding. Taking High Tibial Osteotomy as a representative example, review of the clinical literature and mapping the fracture healing process revealed two physically contradicting requirements, which are only partially met by current techniques. Stiffness of the fixation is required immediately after fracture, however in the remodelling phase this can cause stress shielding. Stability is required immediately after fracture, however in the ossification phase less stability is required to stimulate secondary (and more efficient) healing. This study evaluates the use of the TRIZ Inventive Design Principles to overcome these physical contradictions. Six designs concepts were evaluated, of which the Macro-Geometry stiffness modulated design was ranked the highest. This was achieved through spatial decomposition of the problem utilising the Inventive Principles of Asymmetry, Extraction and Local Quality. This study offer perspectives on how to increase the patient specificity of fixation utilising the increased topology freedom of design for additive manufacture (AM).