Association of joint awareness with satisfaction, knee function, and noise perception after total knee arthroplasty.

Background: Forgotten Joint Score-12 (FJS-12) measures the clinical outcomes focusing on joint awareness after surgery, such as total knee arthroplasty (TKA). The Knee Society Scoring System-2011 (KSS-2011) includes questionnaires for satisfaction, expectation, and functional activities. However, the relationship between FJS-12 and KSS-2011 has not been validated to our knowledge. In addition, some patients complain of noise after TKA. However, how the noise affects joint awareness and satisfaction has not been evaluated. The aim of this study is to clarify the relationship among FJS-12, KSS-2011 and the noise. Methods: Using the FJS-12 and KSS-2011, 295 knees from 225 patients who underwent TKA was retrospectively evaluated. Noise perception was evaluated by a questionnaire with five grades which is a method that follows the questionnaire form of FJS-12 “Are you aware of the noise of your artificial joint?” ; never, almost never, seldom, sometimes, mostly. The correlations among FJS-12, KSS-2011, and noise were analyzed. In addition, patients were divided into four groups based on the mechanism of their implant cruciate retaining, posterior stabilized, cruciate sacrificed, and bicruciate stabilized (BCS). FJS-12, KSS-2011, and noise were compared among the groups. Results: A strong correlation was observed between FJS-12 and the total score of KSS-2011 (0.70; P < 0.001). FJS-12 also was correlated with KSS-2011 subcategories for “symptoms,” “satisfaction,” and “standard activities” that these correlation coefficients were approximately 0.60. Noise was limited to have weak correlations with FJS-12 (0.28; P < 0.001) and KSS-2011 (0.20 P < 0.001). With comparison among the TKA mechanisms, BCS showed significantly better KSS-2011 and greater range of movement but worse noise scores. Conclusions: Joint awareness assessed

3 by FJS-12 was correlated strongly with KSS-2011 and associated with satisfaction, residual symptoms, and daily activities as assessed by KSS-2011 subscores. Noise perception had limited effect on joint awareness and clinical outcomes.

Background
Total knee arthroplasty (TKA) is a standard surgical treatment for advanced stage knee osteoarthritis [1]. Regarding the method used to evaluate its outcome, physician-derived scores had an important role in the past. However, an inconsistency was observed between physician-and patient-derived scores [2]. In addition, several reports show that patient satisfaction after TKA is not high [3][4][5].
Therefore, patient-reported outcome measures (PROMs), such as the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) [6], Knee Injury and Osteoarthritis Outcome Score (KOOS) [7], and Oxford Knee Score (OKS) [8], are used frequently to evaluate postoperative outcomes after TKA. The Knee Society also revised the evaluation method for TKA to PROMs in 2011, and it was launched as the Knee Society Scoring System 2011 (KSS-2011) [9] [10]. This scoring system includes questionnaires related to the category of satisfaction, which directly evaluates patient satisfaction after TKA. Furthermore, questionnaires about the condition of the knee when more active patients enjoy leisure activities and sports were included in addition to daily activities.
The Forgotten Joint Score-12 (FJS-12) is a PROM developed in 2012 [11]. Good joints are considered "no awareness," and the FJS-12 is useful to evaluate joint awareness. FJS-12 is correlated with PROMs associated with knee joints, such as WOMAC, KOOS, and OKS [11][12][13][14][15], and it is effective for evaluating outcomes after TKA. The FJS-12 has an advantage in that it has 12 questions and fewer ceiling and 4 floor effects. However, the relationship between FJS-12 and KSS-2011, which are the most recently developed PROMs used to evaluate postoperative TKA performance, has not been validated. In particular, because KSS-2011 is the only PROM that contains a "patient satisfaction" category, the relationship between FJS-12 and subcategories of KSS-2011 including "patient satisfaction" should be evaluated.
In addition, joint noise frequently occurs after TKA. Nam et al. [16] reported that noise after TKA is related to residual symptoms, whereas Kuriyama et al. [17] reported that noise was not correlated with patient satisfaction after TKA. Noise may be related to joint awareness after TKA. However, not enough information is available on whether the noise after TKA is related to patient-reported outcomes including joint awareness.
The aim of this study is to reveal how the joint awareness correlate with knee symptoms, functions, postoperative satisfaction, and noise perception after TKA. To assess this questions, the relationship between FJS-12 and KSS-2011, and the perception of noise was evaluated. Furthermore, the relationship between PROMs (FJS-12, KSS-2011, and noise perception) and factors, such as TKA mechanism and range of movement (ROM), was assessed.

Methods
A total of 476 patients (598 knees) who underwent primary TKA from January 2007 to November 2017 at our hospital and related institutions and for whom ≥1 year had elapsed after TKA were enrolled in this study. After excluding patients who died or whose implants were removed due to loosening or infection, the questionnaire survey, including FJS-12 and KSS-2011, was mailed to 451 patients (566 knees). We  Table 1 shows the demographic data for subject characteristics.  Table 4 shows the correlation between FJS-12 and the subscores of KSS-2011 by category. A positive correlation was observed in all items, and correlation coefficients of approximately 0.60 were observed for "symptoms," "patient satisfaction," "functional activities," and "standard activities."

Results
Noise showed weak correlations with FJS-12 (0.28; P < 0.001) and KSS-2011 (0.20; P < 0.001). Age, BMI, and ROM had no effect on FJS-12, KSS-2011, and noise (Table   5). ("walking and standing," "standard activities," "advanced activities," and "discretional activities"), our study indicated a significant correlation between FJS-12 and standard activities. Therefore, joint awareness was influenced by the difficulty level of routine activities, such as walking on an uneven surface, turning or pivoting, climbing up or down stairs, rising from a low chair, and stepping to the side. FJS-12 is a simple questionnaire with only 12 items and has few ceiling and floor effects. Therefore, FJS-12 is a useful tool to evaluate residual symptoms, performance of daily activities, and patient satisfaction after TKA.
Noise was expected to be correlated with joint awareness. However, it had only a weak correlation with FJS-12 and KSS-2011. Although patients with TKA are aware of noise, some studies have shown that it has minimal influence on patient satisfaction if the functional aspects, such as ROM, are good [17]. This previous study was done with a TKA model using a unique tri-condylar mechanism. Therefore, the influence of noise perception on PROMs for patients with conventional TKA models needed to be elucidated. In the current study of TKA mechanisms, a significant difference was observed between KSS-2011 and postoperative ROM, and the BCS results were good. A significant difference was confirmed regarding noise, and the BCS score was the lowest. Nam et al. [16] reported that noise was recognized in 27% of the patients and the likelihood of noise generation was different among the TKA mechanisms; PS design was the greatest, followed by rotating-platform, sexspecific, and CR factors. Furthermore, patient-recognized noise reportedly was associated with residual symptoms, such as difficulty in getting in and out of cars, limp, stiffness, or swelling. The inconsistency between the previous studies and our study can be caused by how to assess the noise frequency. The previous studies categorized subjects into two groups according to with or without noise, while the current study used an ordinal scale. From our findings, even if noise was recognized, patient satisfaction postoperatively would be high if functions, such as the ROM, were good. Therefore, noise itself had a limited effect on joint function, overall satisfaction, and joint awareness after TKA.
The present study had several limitations. First, there was a question with a low response rate in FJS-12. As reported in previous studies [18] [19], the response rate for item 12 was particularly low. It may be reasonable to consider that some patients who underwent TKA were relatively inactive. However, FJS-12 has been confirmed to be valid with a few missing items [11].
Second, this was a retrospective cross-sectional study, and there were variations in the time when the answers for FJS-12 were collected. In fact, some studies have shown that the FJS-12 scores change over time [20]. The differences in questionnaire sampling time might have influenced the results. However, we recruited patients for whom at least 1 year had passed postoperatively.
Third, various TKA models had been used. Although the mechanisms can be categorized into four systems, several models remained within the same category.
Furthermore, preoperative patient conditions were not matched among the groups (Table 6). In fact, preoperative ROM was greater in BCS. Therefore, this study did not conclude that BCS was superior in clinical outcomes than any other TKA mechanisms. We did not attempt to investigate which mechanism had the best performance. The point of this analysis was to show that some TKA model exhibit greater noise generation while showing higher KSS-2011 score. Thus, this finding suggested that noise perception has a limited effect on clinical outcomes.
Lastly, the noise score used in this study has not been validated before. Because there is no score as a reference to evaluate the noise perception, the same questionnaire expression method as the FJS-12 was used to evaluate noise.

Ethics approval and consent to participate
This study was approved by the Medical Ethical Committee of the Tokyo Women's Medical University (approval number: 4681). The form of Informed consent in this study is opt-out.

Consent for publication
Not applicable.

Availability of data and materials
Data are attached to supplementary material as an Excel document. Figure 1 The graph shows the relationship between Forgotten Joint Score-12 (FJS-12) and the Knee So

Supplementary Files
This is a list of supplementary files associated with the primary manuscript. Click to download. Tables.pdf