The present disclosure relates to model-based surgical planning. One aspect of the present disclosure relates to a surgical planning tool that can be implemented on a computer to be used for model-based surgical planning. The surgical tool can determine a coordinate system related to gravity from a plurality of standing images of a joint of a patient. The coordinate system can be used to plan a patient-specific arthroplasty procedure. As such, the surgical planning can include orienting a model of an implant for the joint at an optimal location in the coordinate system based on a weighting between an edge loading value and an impingement value.