A custom arthroplasty guide and a method of manufacturing such a guide are disclosed herein. The method of manufacturing the custom arthroplasty guide includes: a) generating medical imaging slices of the portion of the patient bone； b) identifying landmarks on bone boundaries in the medical imaging slices； c) providing model data including image data associated with a bone other than the patient bone； d) adjusting the model data to match the landmarks； e) using the adjusted model data to generate a three dimensional computer model of the portion of the patient bone； f) using the three dimensional computer model to generate design data associated with the custom arthroplasty guide； and g) using the design data in manufacturing the custom arthroplasty guide.
