Extensor tendon injuries of the hand are common and potentially debilitating. The long-term objective of this research is to improve patient outcomes following extensor tendon injury. The first step towards this objective is to determine the effect of extensor tendon injury on patient function. Additional steps can then be taken to improve treatment and outcomes once the underlying causes of poor patient outcomes are known. The first step is the focus of this proposed work. Cadaveric experiments and mathematical modeling will be used to increase our understanding of the effect of extensor tendon injuries on hand function, and to improve treatments for extensor tendon injuries. In the cadaveric experiments the extensor tendons will be loaded to generate finger motion. Tendon excursion, tendon load, grip and finger rotation will be measured during these experiments. There will be two experimental groups with different patterns of extensor injury. Data collected from the first experimental group will be used to create mathematical models relating extensor tendon injury to finger function. The mathematical models will take simulated injury as an input and output finger motion and grip strength. An optimization procedure will be used to generate the models. Given the extensor tendon injury configuration in group one, the optimization will adjust the mathematical model parameters to minimize the difference between model output and group one data. These optimized mathematical models will then be given group two injury configurations as a system input. The accuracy of the mathematical models will be determined by comparing the model’s outputs to data collected from the second experimental group. The effect of extensor tendon injury on finger function will be determined using repeated measures analysis of variance. Accuracy of the mathematical models will be quantified using a similarity metric comparing the second group’s experimental data to the output of the mathematical models using group two’s set of simulated extensor injury.