Effect Of Cartilage Wear Of Medial Posterior Femoral Condyle On The Rotational Alignment Of Femoral Component During TKA

Objective: Preoperative CT and MRI clinical data of patients with varus knee osteoarthritis were retrospectively analyzed to preliminarily explore the cartilage wear of femoral posterior condyle in patients with varus knee osteoarthritis and the difference between CT and MRI measurements of femoral posterior condylar angle(PCA).Methods: A total of 71 patients with varus knee osteoarthritis(73 cases of varus osteoarthritic knees)were admitted to the Department of Osteoarthritis of the First Affiliated Hospital of Nanjing Medical University from November 2018 to February2020.We retrospectively analyzed patients’ preoperative lower-extremity CT data and MRI data of the involved knees.CT images were used to measure the PCA(PCA-CT);The PCA was also measured by MRI images(PCA-MRI)in the same way.Meanwhile,the cartilage thickness of the medial and lateral posterior condyles as well as the medial and lateral distal femoral condyles was measured using MRI images.The cartilage thickness of posterior condyles on specimens was also measured.Radiographic images of the knee joint were used to measure the mechanical lateral distal femoral angle(mLDFA)and the medial proximal tibial angle(MPTA)to exclude extraarticular deformities.SPSS statistical software was used for analysis of measured angles and cartilage thickness.Significant differences between cartilage thickness and angles were analyzed by paired t-test.The relationship between the PCA-CT minus PCA-MRI values and the cartilage thickness of lateral posterior condyle(CLPC)minus cartilage thickness of medial posterior condyle(CMPC)values was assessed using Pearson’s correlation coefficient.At the same time,the scatterplot of CLPC minus CMPC values versus cartilage thickness of lateral distal femoral condyle(CLDFC)minus cartilage thickness of medial distal femoral condyle(CMDFC)values was also presented to analyze the relationship between them.Results: The cartilage thickness of medial posterior condyle on specimens(CMPCs)was(1.9±0.6)mm,which was significantly thinner than that of lateral posterior condyle on specimens(CLPCs)(2.8±0.6)mm,and the difference between two groups was statistically significant(P<0.01).The cartilage thickness of medial posterior condyle measured by MRI(CMPCm)was(1.9±0.6)mm,which was significantly thinner than that of lateral posterior condyle measured by MRI(CLPCm)(2.8±0.5)mm.There was no statistical difference between two groups(P<0.01).The cartilage thickness of medial distal femoral condyle measured by MRI(CMDFCm)(1.3±0.4)mm was significantly thinner compared with that of lateral distal femoral condyle measured by MRI(CLDFCm)(2.5±0.4)mm.The two groups were not statistically significant(P<0.01).But there was no statistical difference between the cartilage thickness of medial and lateral posterior condyles measured by MRI and that measured on the specimens(P>0.05).The scatterplot of CLPC minus CMPC values versus CLDFC minus CMDFC values showed that the wear of cartilage on medial posterior condyle was more severe in patients with varus knee osteoarthritis.In the case of more severe wear of medial posterior condylar cartilage,PCA-CT(4.09±1.39)° was significantly larger than PCA-MRI(2.25±1.01)°,and the difference between them was statistically significant(P<0.01).Pearson correlation analysis results showed that when the cartilage thickness of medial posterior condyle more severely wore and 2mm thinner than that of the lateral posterior condyle,PCA-MRI would be nearly 3° smaller than that of PCA-CT.Conclusions: The wear of medial posterior condylar cartilage is common in varus knee osteoarthritis,and this pattern of cartilage wear has a significant effect on the rotational alignment of femoral component.PCA measured by MRI was significantly smaller than that measured by CT.Orthopedic surgeons must take this difference into account and use a variety of methods to obtain an optimizing femoral component position.