Stress shielding, caused by the mismatch in stiffness between conventional solid metallic implants and human bone, can result in bone resorption and implant loosening, leading to revision surgeries. One potential solution to address this issue is the use of porous structures, which can reduce the stiffness mismatch between the implant and surrounding bone. However, such structures also present a challenge in terms of reduced fatigue strength. To investigate this issue, we conducted finite element simulations and experimental tests to examine the influence of unit cell geometry on the elastic modulus and fatigue life of Ti-6Al-4V lattice structures printed via Electron Beam Melting (EBM). We analyzed four different lattices, including two topology-optimized structures, Design 1, and Design 2 and two conventionally used Cube and Octahedron unit cells. Based on our failure analysis, we found that fatigue fracture predominantly occurred at nodal connectivity points due to stress concentration and was relatively insensitive to manufacturing defects. Fatigue life being a critical aspect of Implant design, this work also explored methods to improve the fatigue life of lattice structures. Both Design 1 and Octahedron lattices were subjected to Hot Isostatic Pressing (HIP). While HIP was effective in closing internal voids associated with EBM, the process resulted in a reduction in yield strength. Consequently, the absolute fatigue strength under the same load amplitude did not improve with HIP. However, the normalized fatigue strength of Design 1 and Octahedron increased from 0.4σy to 0.49 σy and 0.4σy to 0.52σy respectively .