Development of a novel surgical planning tool for high tibial osteotomy and a musculoskeletal model to determine the changes in internal knee loading

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High Tibial Osteotomy (HTO) surgery is performed as a treatment for people who have osteoarthritis (OA) affecting one side of their knee. It realigns the joint to redistribute joint loading and relieve pain. It is used by some clinicians as a valuable joint preserving intervention for patients who are too young for a total knee replacement. It is also occasionally used in asymptomatic patients to prevent further mal-alignment of the knee. To prolong the life of the joint, the angle of joint alignment correction must be sufficient to reduce loads on the medial compartment, whilst not excessively loading the lateral compartment. In current clinical practice, the angle of correction is estimated from standing static x-rays. However, dynamic gait measurements, in particular the knee adduction moment, are reported to be more highly related to clinical outcome than measures of static knee alignment. The proposed research aims to develop a method to quantify the optimum correction angle, based on a patients preoperative gait biomechanics. If new methods of calculating the correction angle can be found that improve longevity of the joint, the procedure as a service may be adopted more widely. This proposal also aims to evaluate associated changes in the forces acting through the joint using models that consider the effects of muscle forces on the joint. A patient specific dynamic model from the University of Florida will be employed in this research. This model was developed to predict the changes in knee adduction moment following HTO surgery using pre-operative gait data and the angles of correction measured from standard long leg x-rays. This research will test whether optimised models, calibrated to each patient, can predict post-surgery knee adduction moments using HTO surgical parameters. This will be the first implementation of this software using pre and post-operative patient data. This software will be adapted to determine the changes in tibial geometry required to produce the optimum post-operative knee adduction moment. The ability to calculate the optimum angles of correction based on a patient's pre-operative gait will form the basis of a new clinical tool.As part of the proposed research, open-source software (OpenSim) will be employed to investigate changes in joint reaction forces following HTO surgery. A model will be adapted for this purpose. This will be the first implementation of a musculoskeletal model to investigate changes in joint reaction forces for patients undergoing HTO and will provide a basis for further development. Joint reaction forces calculated pre-operatively and how they change post-operatively will be compared to a healthy cohort. This will provide information on the changes in loading in the knee and thus the efficacy of HTO surgery in restoring normal knee joint loading. The end product of this research will be a new tool for bespoke surgical planning and outcome measures detailing the efficacy of HTO surgery. It will enhance the biomechanical understanding of HTO realignment and demonstrate the usefulness of dynamic measurements and musculoskeletal modelling.