膝关节股骨远端截骨导板的旋转对截骨准确性的影响

The Influence of Rotation of Localizer on the Accuracy of Distal Femur Excision

目的:研究股骨远端截骨定位器械旋转对股骨远端截骨面的影响。方法:术中截骨验证:在外旋位时股骨远端截骨导板相对后倾;内旋位时股骨远端截骨导板相对前倾;股骨截骨导板的外翻角度则随着内外旋角度的增大而减小。据此建立数学模型计算:以髓内杆为旋转轴,标准位时股骨远端截骨导板与髓内杆在冠状面存在有角度A的外翻,而在矢状面上有角度B的前后倾。定义实际外翻角A’为实际的截骨面与髓内杆垂直面在冠状面上的夹角,实际前后倾角度B’为实际的截骨面与髓内杆垂直面之间在矢状面上的夹角,实际股骨远端截骨导板相对标准位的截骨导板旋转角度为C。通过数学模型计算实际外翻角A’和实际前后倾角度B’。结果:通过计算得出tan A’=tan A*cos C,sin B’=sin A/(1+cos2 A/tan2C)1/2(当C为正值时B’取正值,当C为负值时B’取负值)。当A取5°、6°或7°时,在30°股骨截骨导板的旋转偏差范围内,对实际的外翻角度的影响较小,在1°偏差以内。无论内外旋转,实际的外翻角度均小于设定的外翻角A;但对于实际的前后倾影响较大,当A取6°、旋转角度为30°时,前后倾的偏差约3°。结论:膝关节置换术中股骨远端截骨导板的旋转对截骨面的前后倾与外翻有较大的影响。

Objective To investigate the influence of rotation of localizer on the distal femur excision.Methods Valgus angle A’ was defined as the included angle of actual osteotomy plane and vertical plane of intramedullary rod on coronary plane,actual anterior-posterior dip angle B’ as the angle of actual osteotomy plane and vertical plane of intramedullary rod on sagittal plane,angle C as rotational angle of the osteotomy guide of distal femur relative to the standard position of osteotomy guide. A mathematical model was constructed and the angle of A’ and B’ was calculated. Results The calculation formula of the angles is as followed：A’ =tan A＊cos C and sin B’ =sin A/（1 ＋ cos2 A / tan2C）1/2（positive or negative value of B’ is coincidence with the C）. In the range of 30 degrees rotation deviation of angle C,the deviation of actual valgus angle is less than 1 degree（when A = 5,6 or 7 degrees）. Regardless of internal and external rotation,the actual valgus angle A’ is less than the set valgus angle A. However,when the rotation angle = 30 degrees,the actual retroversion or anteversion angle B’ is about 3 degrees（when A = 6 degrees）. Conclusions The rotation of the osteotomy guide during surgery affects significantly the valgus angle and anteversion/retroversion angle of the bone cut.