Devices and methods for surgery

A method of preparing a joint for a prosthesis in a patient comprising:

• registering, in a coordinate system, one or more optical head mounted displays worn by a surgeon or surgical assistant,
• obtaining one or more intra-operative measurements from the physical joint of the patient to determine one or more intra-operative coordinates,
• registering the one or more intra-operative coordinates from the physical joint of the patient in the coordinate system,
• generating a virtual surgical guide, wherein the virtual surgical guide is a three-dimensional digital representation corresponding to at least one portion of a physical surgical guide, a placement indicator of the physical surgical guide, or a combination thereof,
• determining a predetermined position and/or orientation of the virtual surgical guide based in part on the one or more intra-operative coordinates,
• displaying and superimposing the virtual surgical guide, using the one or more optical head mounted displays, onto the physical joint based at least in part on coordinates of the predetermined position of the virtual surgical guide, and
• aligning the physical surgical guide or a physical saw blade with the virtual surgical guide to guide a bone cut of the joint.