To investigate roughness effect in spine implant, a contact model is offered in this paper. The contact surfaces are modeled macroscopically as semi-spherical containing micro-scale roughness. A minimum mean surface separation between two rough surfaces is defined and related to contact force. This is accomplished through a statistical account of elastic and plastic micro contact at the surface roughness scale and the subsequent integration of micron level events to obtain macro level expectation of force as a function of mean surface separation. Contact force - minimum separation relation facilitates the derivation of hysteretic energy loss during a load-unload event. It is found that the surface high plasticity index yields more energy per cycle. Using the force-minimum surface separation in a dynamic interaction of the implant, approximate leads to the prediction of contact natural frequencies and damping ratio of the implant. These characteristics along with energy loss in implant affect implant's performance and durability.