Process for making custom joint replacements

Computer controlled apparatus for developing bone contour data of a bone structure internal to a body comprising:

• CT scanner means for developing CT scan data corresponding to the bone structure and surrounding tissue, said CT scan data including radiological density values for discrete points of said bone structure and surrounding tissue in each scan of said CT scan data;
• memory means for storing said developed CT scan data;
• first computer means for using said stored CT scan data and deriving a radiological density gradient value for said discrete points with respect to neighboring points in each scan;
• second computer means for deriving the contour of said outer surface of the bone structure using the radiological density values and the radiological density gradient values and developing bone outer contour data;
• comparison means for comparing the changes in contour circumference and area defining a contour shape factor of consecutively derived contours of said outer surface;
• selection means for selecting a derived contour of said outer surface having a higher value of contour shape factor corresponding to a more accurately derived contour;
• and
• third computer means for deriving the contour of said inner surface of the bone structure using said developed bone outer contour data and said density values and developing bone inner contour data.