Osteoarthritis of the knee often includes bilateral involvement and requires TKA, but choosing staged or simultaneous bilateral TKA is still controversial. Studies have shown that simultaneous bilateral TKA is an effective treatment for patients with osteoarthritis, and it reduces hospital expense and recovery time [4,5,6,7, 29]. Whether there are satisfaction level differences with the first and second knees in the early stage after simultaneous bilateral TKA is still unknown. In our research, one of the important findings is that there is better satisfaction with the second knee in the early stage after simultaneous bilateral TKA. We found that the second knee had higher satisfaction VAS and lower pain VAS, drainage volume, and swelling compared with the first knee.
Bullens et al.  reported that the satisfaction VAS scores provided additional information about subjective outcomes after TKA and were lower in the first knee than the second knee. Satisfaction VAS scores mirrored patient satisfaction and results from the objective parameters.
In fact, surgeons have different methods for using TXA and tourniquets during simultaneous bilateral TKA, which may affect patient satisfaction with both knees in the postoperative period. Many methods have been used in simultaneous bilateral TKA to reduce blood transfusion and blood loss and shorten operation time and time under anesthesia, such as the use of TXA and tourniquets. However, the different dosages and timing of TXA in TKA can affect pain, knee swelling, and knee function, and tourniquets may also contribute to pain  and worse knee function [26, 27]. Therefore, whether TXA and tourniquets in simultaneous bilateral TKA affected pain, knee swelling, and knee function are still unknown.
Furthermore, the optimal dosage and timing of TXA in TKA remain undetermined. TXA (10 mg/kg) was given intravenously to reduce perioperative blood loss . A fixed dose of TXA for patients undergoing simultaneous bilateral TKA was also effective and safe in reducing total blood loss and allogeneic blood transfusion needs without any additional thromboembolic risk .
However, there has been no report of drainage volume differences in simultaneous bilateral TKA. Our records showed that the average drainage volume in the first knee was less than that in the second one, which may be due to the timing of TXA between the completion of the prosthesis installation and closing the incision for the first-side TKA. Additionally, there is less published research available for drainage volume, which was statistically significantly different in both knees after simultaneous bilateral TKA.
Multiple boluses of TXA (3 and 6 h after surgery) without a tourniquet can reduce pain and knee swelling and lead to better knee function compared with single boluses before skin incision . However, the TXA used in our study was provided between the completion of the prosthesis installation and closing the incision. Therefore, it would affect the first knee by providing TXA when the right tourniquet was released to accompany the blood congestion in the first knee. We know that the half-period of TXA is 2 h and the peak time is 3 h after injection. Therefore, the first knee had more time with TXA in our procedure, especially after the left limb blood flow was removed. Therefore, the timing of TXA administration may be one of the reasons for the decreased mean drainage volume in the first knee compared to the second knee, resulting in the different amounts of swelling in both knees.
Moreover, a previous study reported that the control of swelling could reduce pain and improve the rapid rehabilitation of the knee after surgery . Noble et al.  also suggested that improvements in the results of TKA would prevent the knees from swelling. Therefore, in our study, we found that the swelling of the first knee was higher than that of the second after surgery, which may have led to higher pain VAS scores and the lower satisfaction in the first knee.
A tourniquet release after wound closure was used to reduce the duration of the TKA procedure and to avoid the possible risks of extended anesthesia in simultaneous bilateral TKA as previously reported . A tourniquet was used to reduce perioperative blood loss in TKA with many other advantages, such as clean and dry visualization of the surgical field [22,23,24,25]. However, the current evidence is not enough to indicate that tourniquet release before wound closure is superior to its release after wound closure in cemented TKA . Moreover, tourniquets commonly used in TKA may contribute to pain  and worse knee function [26, 27]. A meta-analysis showed that TKA with a tourniquet might hinder patients’ early postoperative rehabilitation exercises . Furthermore, limb swelling and knee joint pain may affect the use time of a tourniquet in TKA . Tai et al.  reported that there were no significant differences in swelling defined as the circumference of the limb between the tourniquet and no-tourniquet areas, but the time spent using the tourniquet was 52.5 ± 10 min, which may have minimally affected the knee. In our surgery, the time spent using the tourniquet was 85.3 ± 11.3 min in the first-side TKA and 84.4 ± 10.2 min in the second side. However, we used an unsterile tourniquet, which was released after the first knee surgery was performed but not removed from the limb until the end of the bilateral TKA. This action might have affected the blood deposit in the vein and resulted in swelling, especially due to the fragility of the imbalanced condition after the surgery.
Currently, there is a type of sterile tourniquet that can be released when the surgery is completed, which may help to reduce the satisfaction level difference of patients in the early stage of simultaneous bilateral total knee arthroplasty.
There are some limitations to this research study. First, the correlation among patient satisfaction, leg swelling, and the patients’ pain was not examined. Second, we did not use ultrasonography to confirm whether the swelling was due to the DVT. However, the patients had no signs or symptoms of thromboembolism, so it was not a routine check. Furthermore, the long-term clinical outcomes of both knees will be followed in the future.