Disruption of the scapholunate ligament can result in significant immediate and long-term disability. Of the available current acute and subacute treatment strategies for this disorder, the use of a solid screw to stabilize the scapholunate relationship has been proposed. However, subsequent carpal bone loss is an inherent risk to this technique. The goal of this study was to design a flexible orthopedic screw that can be placed between the scaphoid and lunate to restore more normal biomechanics without the risk of osteolysis. Several ideas were generated during the course of the study to create a moveable section in a bone screw implant. Designs that met the specifications and were promising from the manufacturing point of view were tested using finite element analysis. Some designs were prototyped and one of them was tested using a cadaver wrist. Every design concept revealed some positive and negative features in terms of manufacturing and functionality. It is promising in terms of fulfilling the design requirements, but prototyping the design was very difficult. In conclusion, it can be said that the invented flexible screw techniques are sufficient to hold the scaphoid and lunate together after the scapholunate ligament injury, to restore more normal wrist biomechanics.

As computational power has increased, computational modeling has become a very promising tool to model the biomechanics of complex joint systems. Musculoskeletal computational models have become more complex when compared to original iterations which utilized a number of simplifications. This thesis utilized a three-dimensional computational model of the wrist joint structure to investigate scapholunate kinematics. The model accurately represented the bony anatomy of the wrist and hand and represented soft tissue structures such as ligaments, tendons, and other surrounding tissues. Creation of the model was done using commercially available computer-aided design and medical image processing software, and utilized the rigid body modeling methodology. It was validated for scapholunate kinematics against a cadaver study and then utilized to investigate further measures and surgical procedures. The simulations performed by the model demonstrated an accurate anatomical response of wrist function. As better understanding of the biomechanics of the wrist joint is achieved, this model could prove to be an important tool to further investigate wrist mechanics.

Le poignet, complexe articulaire situé entre l'avant-bras et la main, est sujet aux traumatismes. Par exemple, une chute sur le poignet suite à la pratique d'un sport de glisse ou tout simplement dans un accident de la vie quotidienne peut entraîner une lésion du ligament scapho-lunaire. Cette lésion, difficile à diagnostiquer sur une simple radiographie, évolue toujours vers l'arthrose du poignet. Si le diagnostic est fait pendant la phase aigue, proche du traumatisme, la réparation du ligament ou des techniques conservatrices sur parties molles sont possibles. Si la lésion n'est pas détectée à temps, celle-ci engendre une instabilité du carpe évoluant vers l'arthrose.. A ce stade, des techniques plus radicales incluant des arthrodèses partielles ou totales sont bien connues. Cependant, ces techniques de fusion des os engendrent une perte conséquente de mobilité du poignet. L'objectif de la thèse est de définir une méthode de conception et le dimensionnement d'un implant dont le but est de rétablir la cinématique du carpe après une lésion ligamentaire. Ce dispositif devra remplacer la partie dorsale du ligament scapho-lunaire lorsque celui-ci n'est plus réparable et avant apparition de l'arthrose. / ScaphoLunate interosseous ligament (SLIL) lesion can occur when falling on an outstretched, pronated hand and lead to carpal instability. If SLIL tears are detected early, the ligament can be repaired. However, if the ligament is left untreated, SLIL instability can evolve into carpal arthritis called ScaphoLunate Advanced Collapse (SLAC). Well-known SLAC treatments include arthrodeses. These techniques modify the carpal kinematics and involve a range of motion (ROM) loss. Different prostheses are proposed for patients with arthritis. However, these prostheses do not make an acceptable compromise between the ROM allowed and their mechanical strength. This thesis presents an implant to replace the dorsal part of SLIL when the ligament is not repairable and before the apparition of SLAC. The implant must restore normal kinematics and the mechanical behavior of the carpus. Each step of its design is presented. Kinematic constraints of the implant were derived from measured bone displacements. Using a 3D best-fit method, their mean values and uncertainties were determined. The mechanical behavior of the implant was defined by SLIL stiffness and elongation. Strain energy of the native ligament was a characteristic relevant to the implant behavior design. Surgical and anatomical constraints lead to a small amount of space availaible; hence, the design was driven by strain energy distribution. Using an material capability index, the choice of suitable material is discussed. Finally, the implant design and its method are presented, which satisfy all previous constraints. FEA of the most critical case of kinematic constraints was performed to validate the proposed implant design.