The KSS-2011 total score, joint perception, and EQ-5D scores were significantly lower in the revision TKA cohort (approximately 74%, 79%, and 79%, respectively) than those in the primary TKA cohort. The expectation domain of KSS-2011 and surgical satisfaction were not significantly different between the cohorts. Multivariate analyses revealed that infection and RHK were significant factors of lower KSS-2011 scores following revision TKA.
In recent years, PROMs have become increasingly important. Although there are many reports of implant survival as an outcome, even after revision TKA [1, 2], it does not always reflect patient functional outcomes or satisfaction [12]. In this study on propensity-score-matched comparisons of PROMs after revision and primary TKAs, revision TKA scored significantly lower on KSS-2011, joint perception, and EQ-5D (approximately 80% than those with primary TKA), which was similar to a previous report on EQ-5D [13]. This study revealed that 75% of patients were satisfied with their surgery, which is consistent with the findings of a previous study [25].
According to previous studies on joint perception in primary TKA, 20–39% of patients perceived a natural joint, 12–17% perceived an artificial joint with no limitations, 36–48% perceived an artificial joint with minor limitations, 13–14% perceived an artificial joint with major limitations, and 0–1% perceived a non-functional joint for an average joint perception score of 3.4–3.8 [5, 31]. In this study, the mean score of joint perception was 3.8 for primary TKA, which is similar to those reported in previous studies, and the mean score for revision TKA was 3.0, just under 80% of primary TKA.
There was no significant difference between the cohorts in terms of surgical satisfaction and expectations in KSS-2011. Therefore, the level of satisfaction with the surgery and those who felt that their satisfaction was better than their preoperative expectations were at the same level as those in primary TKA. Consistent with our findings, previous studies have demonstrated that preoperative knee function scores were lower before revision TKA, especially in cases of infection or RHK [10, 17, 18]. Although the degree of postoperative improvement was not investigated in this study, it is possible that the patients had a lower preoperative function but comparable levels of improvement, which resulted in comparable levels of fulfillment of expectations and surgical satisfaction.
Regarding the indications for revision, two previous reports used a physician-oriented assessment and demonstrated that knee joint function was lower or nearly the same between the knees with and without infection [14, 15]; however, the results in this study revealed that the infection group scored significantly lower on KSS-2011, while the surgical satisfaction was comparable. In aseptic revision TKA, multiple surgeries and instability have been reported to worsen postoperative pain and scores [24]. We believe that the preoperative decline in knee joint function due to multiple surgeries and second-stage septic revision of TKA may have influenced the results.
Previous studies have reported that instability predicts lower functional postoperative improvement [24] and that aseptic loosening tends to have a better score, while instability tends to have a lower postoperative outcome than loosening [27]. However, in this study, the infection group had a significantly lower KSS-2011, but no significant differences were identified for other reasons for revision because the main goal of surgery is not necessarily to improve the joint function but to treat predefined problems, such as infection.
In terms of the implant type, previous reports have indicated that patients with RHK both before and after revision TKA have lower knee joint function [16, 23]. However, the scores were significantly lower in KSS-2011 and joint perception in this study, which may also be due to the preoperative knee joint dysfunction.
Our study had a few limitations. First, the study design was retrospective, which makes it susceptible to potential bias. Therefore, we attempted to reduce the bias and matched the cohorts using a propensity-score matching method. Particularly, the follow-up period was 6.2 ± 3.7 years in the revision cohort and 3.8 ± 1.8 years in the primary group. All patients were followed up for > 1 year, and it is unlikely that PROMs scores would fluctuate due to insufficient follow-up. A recent meta-analysis revealed no difference in PROMs following TKA between 12 and 24 months of follow-up [30]. Second, the study lacked a physician-oriented evaluation regarding the range of motion and radiographic assessments at the final follow-up. Further investigations, including physician-oriented evaluations, should be performed in addition to patient-oriented evaluations.