A joint prosthesis and/or trial implant alignment system 10 for intraoperatively assisting an alignment during a surgical procedure comprising patient-specific pre-operative data 14 forming a three-dimensional image 14 containing bone structure 32 and a predetermined alignment of the joint prosthesis and/or trial implant 12. The system comprises a patient imaging device 16 for intraoperatively imaging in two dimensions an operative area of the patient； and patient-specific intraoperative data 18 which forms a two-dimensional image 18 showing bone structure 32 and a real-time position of the joint prosthesis and/or trial implant 12. A registration means 20 registers the intraoperative data 18 and pre-operative data 14 based on geometry of bone structure 32 and/or joint prosthesis and/or trial implant 12. A display device 22 displays an output of the registration means 20, enabling a visual indication of real-time alignment relative to the predetermined alignment. The registering means may comprise contouring determination or landmark designation means. Methods for determining and monitoring implant alignment are also provided.
