[Measurement of the tibial alignment after total knee replacement without the extramedullary cutting guide]

To evaluate the accuracy and analysis of the influencing factors of the tibia prosthetic coronal alignment after total knee arthroplasty without tibia extramedullary cutting guide.

In the study, 76 patients (96 knees) who had primary total knee arthroplasty in Peking University First Hospital from February 2012 to April 2016 were selected retrospectively. All of the cases were performed by the same experienced orthopedic surgeon team. The patients were divided into 2 groups randomly: tibia cutting without guide group and tibia cutting with extramedullary guide group. Lower extremity standard anterior and posterior X-ray films of the knees were taken before and after surgery, and the anatomical tibial angle (AT), the posterior slope angle (PSA) before and after surgery, the tibia component angle (TCA) were measured in the X-ray films. We also recorded the beginning and finishing time of the operation, the operation sequence of the day respectively at the same time. The data were analyzed by correlation analysis, t test and chi square test between the two groups.

The age, gender, body mass index, AT/PSA before the surgery and TCA/PSA after the surgery of the two groups were no significant differences (P>0.05). The rate of 90-TCA≥ 3° was 31.5% (17 knees) and 31% (12 knees) respectively, there were no significant differences (P=0.956) between the two groups. The postoperative TCA of two groups was not correlated with age, gender, body mass index (BMI), operation side (P>0.05), there was also no correlation between the postoperative TCA and the start time of the operation, the whole operation time, and the operation sequence of the day (P>0.05). The two groups were divided into subgroups according to 90-AT before the operation (0°≤90-AT<3°, 3°≤90-AT<5°, 5°≤90-AT<8°, 90-AT≥8°), and there was no difference among them. But we found there was a much higher rate of 90-TCA<3° in the group without cutting guide than the group with extramedullary guide when 90-AT≥8° before the surgery (the rates were 71.4 % and 42.9%, P<0.05).

There is no significant difference of the tibia prosthetic coronal alignment accuracy between the tibia cutting without guide and the traditional extramedullary guided bone cutting by experienced surgeons. Only if when patients already have suffered severe malformation of knee joint (90-AT≥8°) before the operation, tibia cutting without cutting guide is more effective to rectify the tibia prosthetic coronal alignment.