Correlation Between Tibial Plateau Varus And External Rotation Of Distal Femur In Patients With Medial Single Compartment Osteoarthritis

Objective: previous studies have found that greater varus of the tibial plateau is associated with increased external rotation of the femur during total knee arthroplasty.These studies suggest that the change of posterior condylar angle of the femur can be predicted by measuring the inversion angle of the tibial plateau by measuring the full-length X-ray film of the lower extremities in the standing position before operation.In order to further study the correlation between the two,the following studies were done.Methods: 36 patients with medial single chamber osteoarthritis were measured by standing lower limb full-length X-ray film and the angle of posterior condyle of femur was measured on the MRI of the affected knee and the inverted angle of the tibial plateau was measured by the full-length X-ray film of the lower limb in the standing position before operation.The correlation between the posterior condylar angle of the femur and the inverted angle of the tibial plateau was analyzed.The posterior condylar angle(PCA)defines the relative rotation angle between the posterior condylar axis and the supracondylar axis.The TPTS angle is defined as the proximal medial angle formed between the mechanical axis of the tibia and the knee joint line of the tibia between the forehead.Pearson correlation analysis was performed to test the correlation between TPTS and PCA.Results: 1.Data of 36 patients: the average age was 66.6 years(range 56 to 88years).The average TPTS angle was 3.90 °(SD1.43 °,range 0.68 °-6.18 °).The average PCA was 3.38 °(SD1.38 °,range from 0.10 °to 6.90 °).There was no correlation between TPTS angle and PCA(p < 0.61)(Table 1).2.According to the angle of TPTS,the patients were divided into two groups: TPTS ? 4 °mild varus group(n = 28)and TPTS > 4 °severe varus group(n = 14).In the mild varus group,the average TPTS angle was 2.80 °(SD 1.00 °),and the average PCA was 3.79 °(SD 1.29 °).In the severe varus group,the average TPTS angle was 5.41 °(SD 0.82 °),PCA 2.57 °(SD 1.22 °).There was significant difference in PCA between mild and severe varus group(p < 0.006)(Table 2).3.In order to study whether the degree of medial posterior condyle degeneration affects the correlation between TPTS and PCA in patients with medial single ventricular osteoarthritis,patients were divided into two groups according to the degree of medial posterior condyle degeneration.The wear of the medial posterior condyle of the femur was more severe in the second group(n <24).There was no significant difference in PCA between the two groups(p < 0.85),but there was significant difference in TPTS between the two groups(P < 0.02).(table3)Conclusion:This study does not support the conclusions of previous studies,and that the degree of tibial varus measured by the full-length X-ray film of the lower extremities in the standing position before operation can not predict the degree of rotation of the distal end of the femur.Therefore,we believe that the medial angle of the tibial plateau can not be used to predict the external rotation of the femoral prosthesis in patients with medial single ventricular osteoarthritis.