Dear Editor,

It was with great interest that we read the paper by Goyal et al. [1] entitled “Simultaneous single-stage versus two-staged bilateral total knee arthroplasty: a prospective comparative study” published in the July 2020 issue of International Orthopaedics. The authors concluded that SS BLTKA seems to be a logical choice if both knees have severe osteoarthritis, for there does not appear to be a difference in complication rates between the two groups. It is a valuable study. However, we think that there are some flaws and imperfections in their study.

  1. (1)

    Though a large number of patients presented in the outpatient department with severe bilateral knee arthritis, the pain scores in bilateral knees were not always the same. If the more severe knee took the TKA operation first, the pain in the contralateral knee would be relieved because of less weight-bearing in some patients. The contralateral operation for these patients may be postponed or even redundant, so the SS BLTKA may be overaggressive.

  2. (2)

    In the Table 1, the pre-operative variables assessing the osteoarthritis were objective indicators, such as Kellgren-Lawrence classification and deformity of knees, without functional and pain scores. The post-operative variables of functional outcome scores were subjective indicators and largely dependent on the symptoms. It was unknown whether they were comparable or not before operation. Thus, it would be better to include the pre-operative functional scores and postoperative residual deformity. In addition, the joint range of motion and X-ray assessment are suggested, for they are objective and meaningful variables to evaluate surgical benefits.

  3. (3)

    It has been reported that post-operative results between the first and the second knees receiving simultaneous SS BLTKA were different [2]. The circumstances differed in the two consecutive operations, as well as the state of surgeons and patients. Therefore, we hold the opinion that the variables should be documented separately in each knee in every patient.

  4. (4)

    The authors had thoughtfully taken into account the medical comorbidities, which were comparable in the two groups as was shown in Table 1. However, each comorbidity severity among the patients was too abstract and varied extensively. They should be divided into several subgroups like ASA grade and grade of osteoarthritis, especially the patients with hypertension or diabetes mellitus because of sufficient quantity.

  5. (5)

    Nowadays, the overall peri-operative complications of TKA are very low with the maturity of techniques. In this study, the patients with severe comorbidities were excluded, which made the complications much lower. Thus, the bias may exist and it is necessary to include more patients to assess the peri-operative complications.

In conclusion, it is not easy to demonstrate that SS BLTKA was as safe as TS BLTKA. Furthermore, more detailed data demonstrations and long-term complications, such as periprosthetic joint infection and aseptic prosthesis loosening, are needed to clarify this controversial topic.