| Background：Total knee arthroplasty (TKA) is popularity regarded as aneffective treatment of late-stage osteoarthritis and other deformities of the kneejoint. Some researches of TKA had also provided evidences of long-termsuccess in treating severe knee diseases. However, there was still a high rate ofrevision operation undergone after primary TKA each year around the world.Some studies reported abnormal varus or valgus alignment may lead toloosening of the implants; also, if varus tilt of the tibial component was setmore than2degrees, the loosening rate of the implants will increase sharply.Therefore, the key to minimize the failure rate of TKA is to reestablish thenormal mechanical alignment of the knee joint with eliminating any abnormalvarus or valgus errors.In order to individualize the alignment for each single patient, somesurgeons prefer getting the valgus angle from a full-length X-ray radiographpreoperatively. However, since several imaging errors occurred in this method(images are not strictly frontal or sagittal, extension deficits, rotation betweenfemur and tibia), a general valgus angle created by experiences has beenselected by some other surgeons as a preferred option. Insall described aclassical way of placing the femoral component in7°of valgus in relation to theanatomical axis of the femur and placing the tibial component perpendicular tothe tibial shaft. Yet, the TKA surgery skills developed by Insall was based onthe anatomic structure of western ethnicity, and whether the surgicalexperiences in TKA are suitable for Chinese is still unclear. Although a5°valgus angle for people of Southern Chinese ethnicity was reported recently,because of an enormous population in China, more evidences should be obtained and a specific parameter system of Northern Chinese ethnicity shouldbe built.Objective：To establish a method for measuring the knee valgus anglewith anatomical and mechanical axes on three-dimensional reconstructionimaging. To obtain an estimated averaged valgus angle of Northern Chinesehealthy adults from statistical analyzing the valgus angles of80volunteers.Method: we chose160normal femurs in80cases of healthy adultvolunteers from lower extremities CT DICOM data, including40cases of maleand40cases of female adults. The ages for all the volunteers averaged24.6(range,19-29). The DICOM data were imported into Mimics10.0forthree-dimensional reconstruction of the femur. The deepest point in theintercondylar notch (point A) and the midpoint of the medullary cavity20cmabove the knee-joint line (point B) were noted on the3d models. Then, thereconstructed3d models were imported into Geomagic v12, and fitting thefemoral head with a sphere to obtain the center as the landmark of the femoralhead rotation center [point C]. Finally, the knee valgus angle was enclosed bythe distal femoral anatomical axis (line AB) and femoral mechanical axis (lineAC).Result: The average valgus angle is4.68±0.84degrees for all thevolunteers,4.91±0.84degrees for male volunteers,4.46±0.78degrees forfemale volunteers,4.70±0.83degrees for left side and4.67±0.85degrees forright side. There was no significant difference between left side and right sideof KVA; however according to the analysis, the averaged valgus angle of malevolunteers(4.91±0.84°) is a little bigger than that of the femaleones(4.46±0.78°), and a significant difference(P<0.05) was shown between thegenders.The KVA of right side showed a significant positive correlation(R2=0.576, p<0.001) with that of the left side. The relations between KVA and height as well as BMI of all the volunteers were not found to be statisticalrelated.Conclusion: The results indicate that choosing the valgus cut anglearound5other than7degrees may receive a better result in reestablishing thenatural mechanical alignment of lower extremity for Northern Chinese people.Preoperatively designing on3D-reconstruction imaging is a better methodcompare with doing that on the traditional full-length x-ray radiograph. |
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