ABSTRACT Current designs of leg‐lengthening implants have faced serious failures due to inadequacies in the mechanical design. The failure typically is the result of fatigue induced by a combined loading condition with axial and shear components acting in the tubular body of the implant. One of the reasons leading to the failure is improper verification testing for the design of the fatigue limit. The current test standards for pre‐clinical design phases of nail implants are relatively straightforward and widely accepted yet cannot produce the three‐dimensional stress state representative of the anticipated operation in a patient during the consolidation phase. This work introduces a major improvement toward a method for verifying fatigue life of tubular as well as solid implants under combined torque, axial load, and bending. The report describes a new loading fixture, a calibration method, and compares the qualification results of finite element simulation analyses and experimental measurements during cyclic loading tests. The findings state that the fixture produces controlled multi‐axial loadings to study varied osteotomy locations, quasi‐static strength and fatigue of intramedullary implants at an intermediate, 2 Hz, cycle rate. © 2019 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 38:984‐995, 2020 Fatigue in intramedullary implants causes severe complications due to the failure of implants and related operation during the consolidation phase. This work succeeds in developing a test fixture and procedure for inducing three‐dimensional loading in order to define the fatigue life of an implant. The fatigue can be analyzed for various osteotomy locations and for various load spectra based on the estimates made for a patient or patient group. The fixture induces reliable loadings at cycle rates up to 2 Hz.