The adapters of modular prostheses are the structural components mostly likely to fail during the use of prostheses because of the high forces and moments occurring during the human gait. In this study, structural performance of a modular uniaxial leg adapter during gait is analysed utilizing computer software. By analysing the results, the relevant product was redesigned in order to prevent possible failures. Subsequently, the developed modular uniaxial leg adapter was tested in accordance with ISO 10328 in order to ensure the safety of the design. Further, the test results are compared with a finite element analysis to evaluate the performance of the numerical analysis.