A design for a biologically inspired knee prosthesis is presented. The design comes from using spring-driven devices in an antagonistic fashion to control both the position and stiffness of the knee joint. This work presents a proof-of-concept design that seeks to both develop an understanding of how to design and build a usable model and compare that physical model against a simulated model of the knee. The design was made in a pragmatic fashion and sources of error were mitigated during development. The final design following an intensive iterative design project allowed for quasi-static stiffness testing. The model was compared against simulated data. The model showed stiffening behavior and control over the position of the tibial component. It also showed a high amount of correlation to the simulated data. This holds promise for the future of the design, as it is proven to be feasible to build and simulations of optimized geometries can be trusted to yield valid data.