Distal Femoral Morphology Analysis By An Ellipse Fitting Approach:the Relationship Between The Femoral Trochlea And The Femoral Condyle

Purpose:Distal femoral morphology(DFM)is not only critical for knee kinematics analysis,but also for the design of total knee arthroplasty(TKA)prosthesis.Especially in the sagittal position,the relationship between the femoral trochlea and the femoral condyle determines the anteroposterior dimension and the superoinferior dimension of the TKA femoral prosthesis.At present,almost all DFM analyses in the world are based on the circular theory,so for a long time,the design of TKA prostheses has not been significantly improved.In 20% of patients,the postoperative function of TKA is not satisfactory and it is considered to be related to the defects of the prosthesis design.In China,the key point is that China does not have any DFM measurement articles in the real sense.This has led to our country’s copying and drawing on foreign prosthesis design drawings for TKA prosthesis design.There is no independent TKA prosthesis for the Chinese people.Few studies reported the sagittal relationship between the femoral trochlea and condyle,and oftenwith contradictory results.We introduced an ellipse approach to express the shape of trochlea and condyle on MRI,and analyzed their relationship,and determined if there is a difference between male and female in TKA prosthesis and whether there is a correlation with the height parameter.Method:Fifty healthy right knees were sagittal-scanned by MRI at full extension(male was 25,and female was 25).The average age was27.8±3.5 in male and 24.2±0.8 in female.The scanning direction is at the coronal tangent to the distal femoral condyle,and is perpendicular to the transepicondylar axis(TEA)at the axial position.On the deepest trochlear groove slice,the articular surface was best-fitted by a circle.Based on the center of this circle,both medial and lateral trochleas were best-fitted by ellipses.On the distal-most slice of medial condyle,the articular surface was best-fitted by a horizontal ellipse.Based on the center of this ellipse,the lateral condyle was best-fitted by a rotational ellipse.The semi-major and semi-minor axes of the trochlear ellipse and the condylar ellipse constituted a rectangle that represented the relationship of the trochlea and condyle.Results:The anteroposterior dimension(l)of this rectangle was 12.33 ±1.41 mm,and the superoinferior dimension(w)was 7.21 ± 1.23 mm.The average tangent angle(θ)of the rectangle was 30.1o ± 2.6o.l,w,and θ had significant differences between males and females(all P ≤ 0.006),and had significant correlation with the magnitude of semi-major and semi-minor axes of all the ellipses(all P ≤ 0.019),as well as the height of subject(all P ≤ 0.001).Conclusion:The ellipse fitting approach can be used to analyze the relationship between the femoral trochlear and femoral condyle,and can be used as a new method to construct the TKA prosthetic articular surface.The relationship between the femoral tackle and the femoral condyle was significantly different between men and women,and there was a significant correlation with the subject’s height.Therefore,there is a difference between male and female TKA prosthesis,and there is a correlation with the height of the subject.