THREE-DIMENSIONAL EVALUATION FOR KNEE JOINT MORPHOLOGY IN JAPANESE – ASSUMPTION OF CUTTING SURFACE OF FEMUR AND TIBIA IN TKA

Abstract

Objects: We have studied knee morphology using 3DCT considering the bone cutting surface in Total Knee Arthroplasty (TKA in Japan. Subjects were 50 knees in 49 with knee disorders, consisting of 20 knees in 20 men and 30 knees in 29 women. The age range was 16–77 year old (the mean age 52.2).

Method: The image of a patient’s knee joint was taken by three-dimensional perspective imaging device (SIEMENS, ARCADIS) before surgery, and it was structured with the three-dimensional computer software K.G.T, INTAGE Realia Professional to measure the knee joint configuration.

In the measured site with assumption of the bone cutting surface of the femur side in TKA, the valgus angle of femur was °to the bone axis and the maximum transverse diameter and the maximum anteroposterior diameter of the external condyle were measured at the femur side 8 mm proximal to the external condyle, and the tibial side was vertical to the bone axis and the maximum anteroposterior diameter of the internal and external condyles were measured at the tibial side 2 mm distal to the interior joint surface. The ratio of the anteroposterior diameter and the transverse diameter was computed by these measurements.

Result: The average measurements of the femur were 70.82mm of the transverse diameter, 51.2mm of the anteroposterior diameter, and 0.73 of the ratio of the anteroposterior diameter and the transverse diameter.

The average measurements of the tibia were 72.5mm of the transverse diameter, 54.4mm of the anteroposterior diameter of the interior condyle, 46.7mm of the anteroposterior diameter of the exterior condyle, and 0.75 and 0.64 of the ratio of the anteroposterior diameter and the transverse diameter of the interior and exterior condyles, respectively.

The measurements of the femur were bigger in any sites of men than women, and the transverse diameter was bigger, the anteroposterior diameter tended to be smaller.

The transverse diameter did not clearly correlate with the ratio of the anteroposterior diameter and the transverse diameter at the tibial side, and different correlations were shown between men and women respectively.

Discussion: At the femur side, a Japanese knee was flatter than a Westerner’s knee just like the previous reports in Japan. The knee is bigger, the knee tends to become flatter, and men are more likely to have the tendency than women.

At the tibia side, there were differences for correlation of the flat level between men and women, and it suggested the potential sex difference.

Conclusion: The measurement with 3DCT is easy-to-use, and the variation is small compared to an actual measurement value. We want to put it to use for implant design in references to these measurements for the future.