Patent ID: 7780677

Claim:
A method of obtaining preoperative information determining the position of an articular point of a knee joint between a femur and a tibia of a leg for guiding orthopaedic surgery on the knee joint, the knee joint comprising a patella and medial and lateral epicondyles, the knee joint being located between a hip joint and an ankle joint, the hip joint and the ankle joint located at respective ends of said femur and said tibia, said method comprising the steps of: fixing a first marker to a portion of said leg comprising said femur; fixing a second marker to a portion of said leg comprising said tibia; identifying the positions of said first and second markers in space using a measuring device; palpating said patella using a third marker; identifying the position of said patella using said measuring device to measure the position of said third marker in space during said patella palpating step; determining the position of a femur articular point using a data processing system comprising a microprocessor adapted to receive signals corresponding to positional data of the markers from the measuring device; defining mathematically a femoral axis extending between said femur articular point and said patella using said data processing system; palpating said medial and lateral epicondyles using said third marker; identifying the positions of said epicondyles using said measuring device to measure the position of said third marker in space during said epicondyle palpating step; defining mathematically, using said data processing system, a plane substantially perpendicular to said femoral axis and at substantially equal respective rectangular distances to the positions of said medial and lateral epicondyles, the intersection of said plane and said femoral axis being an initial estimate of said articular point of said knee joint; defining a region in said plane having a predetermined size, said region including said initial estimate of said articular point of said knee joint; determining the position of an articular point of said tibia at said ankle joint; moving said tibia articular point relatively to said femur by rotating said tibia about said knee joint; identifying a multiplicity of different positions of said tibia articular point using said measuring device to measure the positions of said first and second markers during said motion of said tibia articular point; determining mathematically, using said data processing system, one point among a multiplicity of points within said region for which the position is substantially invariant for each of said positions of said tibia articular point, said one point being said articular point of said knee joint; and using the position of said articular point of said knee joint to guide an orthopaedic surgical procedure.