Measuring the femoral antetorsion angle γ of a human femur in particular on the basis of fluoroscopic images

A computer program embodied on a non-transitory computer readable medium for determining an antetorsion angle of a femur, said antetorsion angle γ being defined by an angle between

• a central axis through a femoral neck of said femur, said central axis running through a center of the femoral neck and parallel to a cortical surface of a proximal part of the femoral neck, and
• a posterior condyle axis, said posterior condyle axis connecting the most posterior points of the femoral condyles of the femur when the central axis through the femoral neck and the posterior condyle axis are projected onto a plane normal to the femoral shaft axis, wherein the femoral shaft axis is the central axis of the approximately cylindrically shaped shaft of the femur, the central axis of the cylindrical shaft being parallel to the most anterior tangent to the distal femur, and the femoral shaft axis also being perpendicular to the posterior condyle axis;
• said computer program comprising:
• (a) code that directs the capture of a first image of the posterior condyles of the femur such that the posterior condyles overlap laterally, wherein the posterior condyle axis is projected onto a point, and the normal to the image plane is parallel to the posterior condyle axis;
• (b) code that defines in the first image the most anterior tangent to the anterior cortex of the distal femur;
• (c) code that shifts said tangent parallel to itself until it includes the point of the posterior condyle axis in the first image, thereby determining a transcondylar plane;
• (d) code that determines a parallel to the femoral shaft axis in the first image;
• (e) code that directs the capture of a second image of the femoral neck of the femur such that the normal to the image plane of the second image encloses an angle β with the femoral shaft axis and an angle θ with the transcondylar plane;
• (f) code that defines in the second image the femoral neck axis enclosing an angle α′ with the transcondylar plane;
• and
• (g) code that calculates the antetorsion angle γ via the equation tan γ=tan α′/(cos β·cos θ).

A system for determining an antetorsion angle of a femur, said antetorsion angle γ being defined by an angle between

• a central axis through a femoral neck of said femur, said central axis running through a center of the femoral neck and parallel to a cortical surface of a proximal part of the femoral neck, and
• a posterior condyle axis, said posterior condyle axis connecting the most posterior points of the femoral condyles of the femur when the central axis through the femoral neck and the posterior condyle axis are projected onto a plane normal to the femoral shaft axis, wherein the femoral shaft axis is the central axis of the approximately cylindrically shaped shaft of the femur, the central axis of the cylindrical shaft being parallel to the most anterior tangent to the distal femur, and the femoral shaft axis also being perpendicular to the posterior condyle axis;
• said system comprising:
• a processor and memory;
• and
• logic stored in memory and executable by the processor, said logic including:
• (a) logic that directs the capture of a first image of the posterior condyles of the femur such that the posterior condyles overlap laterally, wherein the posterior condyle axis is projected onto a point, and the normal to the image plane is parallel to the posterior condyle axis;
• (b) logic that defines in the first image the most anterior tangent to the anterior cortex of the distal femur;
• (c) logic that shifts said tangent parallel to itself until it includes the point of the posterior condyle axis in the first image, thereby determining a transcondylar plane;
• (d) logic that determines a parallel to the femoral shaft axis in the first image;
• (e) logic that directs the capture of a second image of the femoral neck of the femur such that the normal to the image plane of the second image encloses an angle β with the femoral shaft axis and an angle θ with the transcondylar plane;
• (f) logic that defines in the second image the femoral neck axis enclosing an angle α′ with the transcondylar plane;
• and
• (g) logic that calculates the antetorsion angle γ via the equation tan γ=tan α′/(cos β·cos θ).