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The minimum clinically important difference for the Japanese version of the new Knee Society Score (2011KSS) after total knee arthroplasty
Journal of Orthopaedic Science 24 (2019) 1053e1057
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Journal of Orthopaedic Science journal homepage: http://www.elsevier.com/locate/jos
Original Article
The minimum clinically important difference for the Japanese version of the new Knee Society Score (2011KSS) after total knee arthroplasty* Kohei Nishitani a, *, Yosuke Yamamoto b, Moritoshi Furu a, Shinichi Kuriyama a, Shinichiro Nakamura a, Hiromu Ito a, Shunichi Fukuhara b, Shuichi Matsuda a a b
Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Shogoin-Kawahara-Cho, Sakyo, Kyoto, 606-8507, Japan Department of Healthcare Epidemiology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-Cho, Sakyo, Kyoto, 606-8507, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 April 2019 Received in revised form 30 July 2019 Accepted 3 September 2019 Available online 19 September 2019
Background: The new Knee Society Score (2011KSS) has been used to evaluate post-operative outcomes after total knee arthroplasty (TKA). However, there is no minimum clinically important difference (MCID) for 2011KSS. The purpose of this study is to define MCID of 2011KSS after TKA. Methods: Patients who underwent primary TKA for primary knee osteoarthritis between April 2012 and December 2016 were included in the study. The Japanese version of 2011KSS and original Knee Society Score (OKSS) were recorded preoperatively and at one-year postoperatively. With improvement in pain score of OKSS as an anchor, an anchor-based approach was used to identify the MCID of 2011KSS. The improvement in pain of OKSS was classified into 5 categories. The MCID was determined using a linear regression analysis of delta 2011KSS against improvement in the category of pain in OKSS. The MCID for 2011KSS expectation was not calculated because the items of pre- and post-operative questionnaires were different. Results: Five hundred and twenty-two cases were enrolled (age: 74.8 ± 7.3 years, female: 80.0%). After 1year follow-up, 344 TKAs were finally included (age: 74.6 ± 7.1 years, female: 77.9%). Linear regression analyses showed that MCID for 2011KSS was 1.9 (95% confidential interval (CI): 1.3e2.5) in symptom, 2.2 (95%CI: 1.4e2.9) in satisfaction, and 4.1 (95%CI: 2.5e5.7) in functional activities. Conclusions: MCID for 2011KSS was successfully calculated. These MCID values make the 2011KSS a more efficient tool for evaluating the physical activities of the populations of patients undergoing TKA. These MCID values can also be used to calculate sample size to evaluate the power of a study in designing clinical studies. © 2019 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
1. Introduction
* The location where this study performed: Department of Orthopaedic Surgery, Kyoto University Hospital, 54 Shogoin-Kawahara-Cho, Sakyo, Kyoto, Japan, 6068507; Department of Orthopaedic Surgery, Kyoto City Hospital, 1-2 Mibuhigashi Takadacho, Nakagyo, Kyoto, Japan; Department of Orthopaedic Surgery, Nishi-Kobe medical center, 5-7-7-1 Keyakidai, Nishi-ku, Kobe, Japan; Department of Orthopaedic Surgery, Seirei-Mikatahara Hospital, 3453 Mikatahara-cho, Kita-ku, Hamamatsu, Japan. * Corresponding author. E-mail addresses: [email protected] (K. Nishitani), yamamoto.yosuke. [email protected] (Y. Yamamoto), [email protected] (M. Furu), kuriyama@ kuhp.kyoto-u.ac.jp (S. Kuriyama), [email protected] (S. Nakamura), [email protected] (H. Ito), [email protected] (S. Fukuhara), [email protected] (S. Matsuda).
Total knee arthroplasty (TKA) is one of the most promising surgical treatments for pain relief and improved quality of life for patients with end-stage knee osteoarthritis (OA). To evaluate the outcomes of knee and hip arthroplasties, the American Association of Hip and Knee Surgeons has recommended the use of patient reported outcome measures (PROMs) [1]. Numerous validated PROMs are available to assess the outcomes of TKA, including the Medical Outcomes study Short Form (SF)- 36 [2], SF-12 [3], Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) [4], Knee injury and Osteoarthritis Outcome Score (KOOS) [5], and the Oxford knee score (OKS) [6]. As a classical and mostly objective scoring system, the original Knee Society Score (OKSS) is one of the
https://doi.org/10.1016/j.jos.2019.09.001 0949-2658/© 2019 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
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most popular methods to evaluate outcomes after TKA. However, nowadays OKSS has been challenged in its utility and validity for patients whose demands, expectations, and functional requirements are different from those of previous generations [7]. As a new PROM, the new Knee Society Score (2011KSS) was published in 2012 and has been validated to better characterize the expectations, satisfaction, and physical activities of the younger and more diverse population of patients undergoing TKA [7,8]. With 2011KSS, the internal properties and responses of each patient can be captured in every domain of the subjective score, including symptoms, satisfaction, and expectation. Various kind of activities, including essential activities, higher-level activities, and discretionary/recreational activities are also evaluated by 2011KSS [8]. The 2011KSS has been translated into multiple languages and validated [9e11]. Since then, a variety of studies have used it to evaluate the clinical outcomes and improvement after TKA [12e18], and more recently, the usefulness of 2011KSS has been further validated based on its low ceiling effect and greater responsiveness compared with the WOMAC, SF-12, and OKSS [19]. Recently, the concept of the minimum clinically important difference (MCID) has been emphasized to define the smallest amount by which an outcome must change to be meaningful to patients. The MCID corresponding to SF-12 [20] and SF-36 [21], WOMAC [21], KOOS [22], OKS [20], and OKSS [23] after TKA have been defined. The MCID of 2011KSS was not estimated in any previous study, and hence, the clinical significance of statistical improvements in 2011KSS after TKA is unclear. To this end, the purpose of this study was to define MCID of 2011KSS after TKA. 2. Patients and methods This study was approved by the ethics committee of our hospitals, and written informed consent was obtained from all participants. The inclusion criteria were consecutive patients who underwent primary TKA between April 2012 and December 2016 in four hospitals for primary OA and who consented for prospective data collection required for 2011KSS and OKSS. Patients who deceased within one year, had to undergo revision arthroplasty within one year, or withdrew their consent were excluded from the study. The surgery was basically performed using medial approach (medial parapatellar, mid vastus or sub-vastus) and standard measured resection technique, aiming mechanical alignment without a computer navigation system. The femoral component was basically aimed perpendicular to the mechanical axis of the femur with sulcus cut, and the tibial component was aimed perpendicular to the mechanical axis of the tibia for coronal alignment. For sagittal alignment, the femoral component was aligned to the distal anatomical axis of the femur, and the tibial component was aligned to the proximal mechanical axis of the tibia, with preserving a native posterior slope. The rotation of the femoral component was aimed parallel to the surgical epicondylar axis, and the rotation of the tibial component was decided according to the Akagi's line. Patellar was resurfaced in the majority of cases. The patients were asked to grade their symptoms (Maximum 25 points), satisfaction (Maximum 40 points), expectations (Maximum 15 points), and functional activities (Maximum 100 points) using the Japanese version of the 2011KSS. This version has undergone back-translation, and its reliability has been validated in patients who have undergone TKA [11]. For pre-operative 2011KSS and OKSS, patients filled in the Japanese version of the 2011KSS by themselves, one day prior to TKA. OKSS were also evaluated one day prior to TKA by physiotherapists who were unrelated to this study. To evaluate OKSS, the range of motion was measured with handheld goniometer by physiotherapists. The varus-valgus knee joint stability was examined at 30 degrees of
flexion, and antero-posterior stability was examined by anterior and posterior drawer test. 2.1. Statistics The characteristic data at baseline between included and excluded TKAs were compared using student t-test or Fisher's exact test, and p value of <0.05 was considered statistically significant. An anchor-based approach was used to identify the MCID for 2011KSS. The anchor used in this study was pain score of OKSS (50 points: none, 45 points: mild/occasional, 40 points: mild (stairs only), 30 points: mild (walking and stairs), 20 points: moderate-occasional, 10 points: moderate-continual, 0 point: severe). Each point of OKSS pain score was changed to rank-order: 50 points to 7, 45 points to 6, 40 points to 5, 30 points to 4, 20 points to 3, 10 points to 2 and 0 point to 1. Then, the change in the rank of pain of OKSS (One year rank of OKSS e preoperative rank of OKSS) was classified into 5 categories in accordance with cutoff points close to the quintiles of the target patients. The rise of more than or equal to 5 ranks was defined as an excellent improvement, the rise of 4 ranks as a very good improvement, the rise of 3 ranks as a good improvement, the rise of 2 ranks as a mild improvement, and a rise less than or equal to 1 rank as no or minor improvement. The MCID was determined using the slope of the linear regression analysis of delta 2011KSS (pre-operative 2011KSS e one-year 2011KSS) against improvement of the category of pain in KSS. The MCID of 2011KSS expectation was not calculated because pre- and postoperative questionnaires were different. Therefore, MCID of symptoms, satisfaction, and functional activities were independently calculated. Due to the lack of MCID for expectation, MCID of total 2011KSS was not defined. All analysis was performed using STATA 14.2 (StataCorp LC, College Station, TX, USA). 3. Results 3.1. Baseline characteristics Five hundred and twenty-two cases were enrolled in this study (age: 74.8 ± 7.3 years, female: 80.0%). Of these, relevant data was not available for 19 patients, and hence, a total of 503 subjects were available at baseline. During follow-up, 2 patients were excluded due to their deaths that were unrelated to the surgery, 1 patient was excluded owing to the need for revision arthroplasty because of an infection, 1 case was excluded owing to the need for revision because of distal femoral fracture. Moreover, at one-year, relevant data was not available for 155 cases and a total of 159 subjects (age: 75.0 ± 7.6 years, female: 84.9%) were excluded. Finally, 344 subjects who underwent TKAs who completed all scores were included (age: 74.6 ± 7.1 years, female: 77.9%) in the study (Fig. 1). The detail demographics of the patients are shown in Table 1, and no
Fig. 1. Flow diagram. Patient enrollment and exclusions are shown.
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Table 1 Characteristics of included and excluded TKAs at baseline.
Patient age (years) Sex, female (%) Body mass index Right or Left, right (%) Race Asian (%) Caucasian (%) Hip-knee-ankle angle (degrees) Varus or valgus deformity, varus (%)
344 TKAs included
178 TKAs excluded
P value
74.6 ± 7.1 77.9% 26.4 ± 4.1 50.9%
75.2 ± 7.6 84.3% 25.5 ± 5.0 50.0%
0.41a 0.11b 0.04a 0.85b 0.10b
99.7% 0.3% 9.5 ± 8.3 varus 89.8%
98.3% 1.7% 8.6 ± 10.3 varus 85.4%
0.27a 0.12b
TKA: total knee arthroplasty. a p value by student t-test. b p value by Fisher's exact test.
remarkable differences were observed between the two groups, except body mass index (BMI). Among these 344 included TKAs, cruciate substituting (CS) implant was used in 216 cases, posterior stabilizing (PS) was in 87 cases, cruciate retaining (CR) was in 36 cases, bi-cruciate retaining (BCR) was in 2 cases, constrained condylar knee (CCK) was in 2 cases, and bi-cruciate substituting (BCS) was in 1 case. One-year 2011KSS and OKSS was recorded in the same day at the nearest out-patient visit one year after TKA (372 ± 34 days). Except for scores pertaining to expectation, other scores such as OKSS, OKSS pain, OKSS-Function Score, and each 2011KSS improved one year after TKA (Table 2). 3.2. MCID According to the change in OKSS pain, there were 54 patients who characterized it as an excellent improvement, 74 patients as a very good improvement, 110 patients as a good improvement, 51 patients as a mild improvement, 25 patients as a minor improvement, and 30 patients as no improvement. A linear regression analysis showed that MCID for 2011KSS (Table 3) was calculated to 1.9 in symptom (Fig. 2), 2.2 in satisfaction (Fig. 3), and 4.1 in functional activities (Fig. 4). 4. Discussion In this paper, MCID of 2011KSS for patients who underwent TKA was determined using the pain score of OKSS as an anchor. Till date, MCID of 2011KSS was not determined in any previous study. In a previous study, 10 points for improvement in 2011KSS was used as a tentative of MCID for total 2011KSS [14] although there was no corroborating calculation on this value. In the present study, the MCID was determined as 1.9, 2.2, and 4.1 for symptom, satisfaction,
and functional activities, respectively. If patients showed improvement over MCID, this improvement can be considered real improvement. To date, MCID for other PROMs such as SF-12 [20], SF-36 [21], WOMAC [21], KOOS [22], and OKS [20] have been determined to evaluate the outcome of TKA. As a new PROM with MCID, 2011KSS would have a merit to possibly evaluate the symptom, satisfaction, and functional activities of patients, separately. These values may be used in further studies comparing groups using different methods or implants. Even if these studies showed the significant change of the score yielded (with p < 0.05), it would be insufficient for patients to feel a difference unless it is greater than MCID. MCID is also useful in power-analysis and sample size estimation of clinical studies in which 2011KSS is utilized. An increasing number of studies uses 2011KSS nowadays [12e18]. Significant improvements of 2011KSS are reported in several studies. Niki et al. reports 5.3 point better functional activities in 2011KSS in kinematically aligned TKA compared to mechanically aliened TKA [18], and Kawahara et al. reports 15.7 points better functional activities in 2011KSS in femoral component neutral position group compared to femoral component internal rotation group [12]. Nishio et al. reports an intraoperative medial pivot TKA of 8.0 points better in patient satisfaction and 10.5 points better functional activities in 2011KSS than non-medial pivot TKA using navigation system [13]. Tsukiyama reported 7.6 points better satisfaction score and 5.7 points better symptom in 2011KSS in medially tight flexion group than in medially loose group [16]. The above-mentioned improvements are more than the MCID in this study and can, therefore, be considered as clinically and statistically significant. In the study by Kuriyama et al. satisfaction showed a difference of 3.0 points between never noised group and noised group [15], and in the study conducted by Murakami et al. the
Table 2 Pre- and one-year post-operative scores.
OKSS-Knee Score (0e100) OKSS pain (0e50) OKSS-Function Score (0e100) 2011KSS symptom (0e25) 2011KSS satisfaction (0e40) 2011KSS expectation (3e15) 2011KSS functional activities (0e100)
Pre-operative
One-year post-operative
44.1 ± 18.8 0 (0.6%)e100 (0.3%) 21.5 ± 12.2 0 (10.8%)e50 (1.2%) 54.3 ± 25.2 0 (2.9%)e100 (2.9%) 7.8 ± 5.4 0 (8.4%)e25 (0.6%) 14.2 ± 5.8 0 (0.3%)e36 (0.3%) 13.4 ± 2.0 3 (0.3%)e15 (42%) 40.8 ± 18.6 0 (0.9%)e97 (0.3%)
87.6 ± 11.2 46 (0.3%)e100 (7.3%) 45.1 ± 7.4 10 (0.3%)e50 (48.0%) 78.6 ± 18.2 0 (1.2%)e100 (17.7%) 16.6 ± 6.9 0 (0.3%)e25 (19.5%) 25.9 ± 8.3 6 (0.3%)e40 (9.1%) 9.8 ± 2.9 3 (2.3%)e15 (10.5%) 63.1 ± 19.7 0 (0.3%)e99 (0.3%)
Scores are presented as mean ± standard deviation in upper row and minimum (% of respondent) e maximum (% of respondent) in lower row.
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Table 3 MCID of each 2011KSS.
2011KSS symptom (0e25) 2011KSS satisfaction (0e40) 2011KSS functional activities (0e100)
MCID
95% confidential interval
1.9 2.2 4.1
1.3e2.5 1.4e2.9 2.5e5.7
MCID: minimum clinically important difference, KSS: Knee Society Score.
difference in satisfaction was 3.1 points between cruciate-retaining and posterior-stabilized TKA [17]. Although there are no significant differences between groups in these studies, the differences were more than the MCID. In these studies, numbers of subjects were very small, and hence, there is a possibility of b error. To avoid b error, power analysis is important, and MCID, which evaluated in the present study, could be used for that purpose. The anchor of this study was the improvement in pain score of OKSS. In previous studies, satisfaction or improvement of patients was frequently used as an anchor [20,21,23]. The level of satisfaction or improvement was asked only once after surgery at one year or two years after surgery. This means that there is a risk of recall bias. To decrease this recall bias, the pain evaluation was performed twice (at two different time points) in this study, and the change of the pain score was used as an anchor. Since pain is one of the most important factors for the patients who underwent TKA [24,25], we believe that the change of pain is a critical factor for the patients which represents clinically meaningful differences. Furthermore, the validity of the MCID in this study was supported in light of distribution-based approach. Previous studies reported that MCID can range from 0.2 to 0.5 standard deviation (SD) of the sample [26,27]. In the present study, anchor-based MCID for symptom, satisfaction, and total activity showed 0.35 SD, 0.38 SD, and 0.22 SD, respectively. Therefore, all the MCID were acceptable from the aspect of distribution-based approach, supporting the robustness of our results. Although MCID was successfully determined in this study, this study has some limitations. First, MCID for expectation of 2011KSS was not calculated because of the differences between pre- and post-operative questionnaires in terms of questions and scoring. The difference was in the uniqueness of the subdomain of expectation. In the questionnaires, preoperative and postoperative questions and points of distribution were not identical. So, we could not determine the improvement of expectation by subtracting preoperative from postoperative expectation. For example, if a patient who underwent TKA had high expectations regarding postoperative pain relief, the preoperative subscore would be 5.
Fig. 2. Linear regression to calculate 2011KSS symptom. The figure shows change of 2011KSS symptom with 95% confidential interval at 1 year according to the degree of pain improvement. The slope of the linear regression indicates the MCID of 2011KSS symptom.
Fig. 3. Linear regression to calculate 2011KSS satisfaction. The figure shows change of 2011KSS satisfaction with 95% confidential interval at 1 year according to the degree of pain improvement. The slope the linear regression indicates the MCID of 2011KSS satisfaction.
Then, if the patient's preoperative expectations in terms of pain relief were met after TKA, the subscore would be 3. In this case, even though pain relief was obtained after TKA, the score reduces after surgery. This complexity may itself be a limitation of 2011KSS, and hence, we decided not to determine the MCID for this parameter (2011KSS for expectation). Moreover, the total score of 2011KSS was not calculated either due to the unavailability of MCID for expectation score. Second, there were some missing data oneyear after TKA. Out of 503 TKAs at baseline, 159 cases (31.1%) did not complete the follow-up questionnaire, so we could not evaluate the data of the 1-year 2011KSS of the excluded patients. Although BMI was slightly but significantly higher in included group, we believe that there were no definitive differences between included and excluded populations at baseline, so the included cases may be considered as representative of the whole cohort. Third, MCID was calculated with one-year improvement of 2011KSS. In previous studies, MCID after TKA is determined at 6 months [21], one year [20,22], or two years [23] after surgery. If patients kept improving after TKA, it might be better to determine the MCID of longer durations to determine the maximum possible improvement after TKA. However, a numbers of studies report that the symptoms and functions stabilize by one-year after TKA [28,29]. That is why we decided to calculate MCID of 2011KSS using one-year improvement after TKA. Fourth, the Japanese version of 2011KSS had a minor difference in discretionary activities, in which ground golf and hiking was added since these are popular activities among Japanese
Fig. 4. Linear regression to calculate 2011KSS functional activities. The figure shows the change in 2011KSS functional activities with 95% confidential interval at 1 year according to the degree of pain improvement. The slope the linear regression indicates the MCID of 2011KSS functional activities.
K. Nishitani et al. / Journal of Orthopaedic Science 24 (2019) 1053e1057
people based on a previous survey [11]. Lastly, there is the COnesus based Standard for the selection of health status Measurement Instruments (COSMIN) checklist to assess the methodological quality of studies on measurement properties of health status measurement instruments [30]. Although this manuscript was compliant to the all items in the check list “Interpretability”, in which MCID was described, the 2011KSS on its own is not complaint to every item of the COSMIN checklist, for example minimum detectable change (MDC) was not calculated. Some more efforts are needed to fully compliant to the COSMIN checklist, to improve the validity of 2011KSS. In conclusion, the MCID of 2011KSS was successfully calculated as 1.9 in symptom, 2.2 in satisfaction, and 4.1 in functional activities. With these MCID, 2011KSS is a more efficient tool to evaluate the physical activities of the diverse populations of patients undergoing TKA. These MCID values can also be used to calculate sample size to ensure the power of a study in designing clinical studies. Conflict of interest Kyocera (Kyoto Japan) supports the prospective data acquisition in part. The department of KN, MF, SK, SN, HI and SM received a research grant from Kyocera. This company has no role in the design and conduct of the study, analysis of the data, the preparation of the manuscript or decision to submit the manuscript for the publication. Ethical statement This study was approved by the Ethics Committee of our hospitals and performed in accordance with the ethical standards in the Declaration of Helsinki. Acknowledgements We thank Drs. Masahiro Yoshida, Susumu Kamisato, Ichiro Nakayama, Yoshitomo Sano, Shinobu Tabata, Hironobu Bito, Shinnosuke Yamashita, Yoshihiro Ishihama, Takaaki Shirai, Chiaki Tanaka, Hiroshi Kanoe, Hiroshi Tada, Keiji Yoshida, Masatoshi Fujiwara, Kenichi Takaya, Kazutaka Masamoto, Kazuaki Morizane, Kazunari Nakai, Masanori Kobayashi, and Yoshihiro Sekimoto for helping with data collection. References [1] Lieberman JR. American association of hip and knee surgeons and outcome measures after total joint arthroplasty. J Arthroplast 2016 Jun;31(6):1137e8. [2] Jenkinson C, Coulter A, Wright L. Short form 36 (SF36) health survey questionnaire: normative data for adults of working age. BMJ 1993 May 29;306(6890):1437e40. [3] Hurst NP, Ruta DA, Kind P. Comparison of the MOS short form-12 (SF12) health status questionnaire with the SF36 in patients with rheumatoid arthritis. Br J Rheumatol 1998 Aug;37(8):862e9. [4] Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1988 Dec;15(12): 1833e40. [5] Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD. Knee injury and osteoarthritis outcome score (KOOS)edevelopment of a self-administered outcome measure. J Orthop Sport Phys Ther 1998 Aug;28(2):88e96. [6] Dawson J, Fitzpatrick R, Murray D, Carr A. Questionnaire on the perceptions of patients about total knee replacement. J Bone Joint Surg Br 1998 Jan;80(1): 63e9. [7] Scuderi GR, Bourne RB, Noble PC, Benjamin JB, Lonner JH, Scott WN. The new knee society knee scoring system. Clin Orthop Relat Res 2012 Jan;470(1): 3e19.
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Journal of Orthopaedic Science journal homepage: http://www.elsevier.com/locate/jos
Original Article
The minimum clinically important difference for the Japanese version of the new Knee Society Score (2011KSS) after total knee arthroplasty* Kohei Nishitani a, *, Yosuke Yamamoto b, Moritoshi Furu a, Shinichi Kuriyama a, Shinichiro Nakamura a, Hiromu Ito a, Shunichi Fukuhara b, Shuichi Matsuda a a b
Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Shogoin-Kawahara-Cho, Sakyo, Kyoto, 606-8507, Japan Department of Healthcare Epidemiology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-Cho, Sakyo, Kyoto, 606-8507, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 April 2019 Received in revised form 30 July 2019 Accepted 3 September 2019 Available online 19 September 2019
Background: The new Knee Society Score (2011KSS) has been used to evaluate post-operative outcomes after total knee arthroplasty (TKA). However, there is no minimum clinically important difference (MCID) for 2011KSS. The purpose of this study is to define MCID of 2011KSS after TKA. Methods: Patients who underwent primary TKA for primary knee osteoarthritis between April 2012 and December 2016 were included in the study. The Japanese version of 2011KSS and original Knee Society Score (OKSS) were recorded preoperatively and at one-year postoperatively. With improvement in pain score of OKSS as an anchor, an anchor-based approach was used to identify the MCID of 2011KSS. The improvement in pain of OKSS was classified into 5 categories. The MCID was determined using a linear regression analysis of delta 2011KSS against improvement in the category of pain in OKSS. The MCID for 2011KSS expectation was not calculated because the items of pre- and post-operative questionnaires were different. Results: Five hundred and twenty-two cases were enrolled (age: 74.8 ± 7.3 years, female: 80.0%). After 1year follow-up, 344 TKAs were finally included (age: 74.6 ± 7.1 years, female: 77.9%). Linear regression analyses showed that MCID for 2011KSS was 1.9 (95% confidential interval (CI): 1.3e2.5) in symptom, 2.2 (95%CI: 1.4e2.9) in satisfaction, and 4.1 (95%CI: 2.5e5.7) in functional activities. Conclusions: MCID for 2011KSS was successfully calculated. These MCID values make the 2011KSS a more efficient tool for evaluating the physical activities of the populations of patients undergoing TKA. These MCID values can also be used to calculate sample size to evaluate the power of a study in designing clinical studies. © 2019 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
1. Introduction
* The location where this study performed: Department of Orthopaedic Surgery, Kyoto University Hospital, 54 Shogoin-Kawahara-Cho, Sakyo, Kyoto, Japan, 6068507; Department of Orthopaedic Surgery, Kyoto City Hospital, 1-2 Mibuhigashi Takadacho, Nakagyo, Kyoto, Japan; Department of Orthopaedic Surgery, Nishi-Kobe medical center, 5-7-7-1 Keyakidai, Nishi-ku, Kobe, Japan; Department of Orthopaedic Surgery, Seirei-Mikatahara Hospital, 3453 Mikatahara-cho, Kita-ku, Hamamatsu, Japan. * Corresponding author. E-mail addresses: [email protected] (K. Nishitani), yamamoto.yosuke. [email protected] (Y. Yamamoto), [email protected] (M. Furu), kuriyama@ kuhp.kyoto-u.ac.jp (S. Kuriyama), [email protected] (S. Nakamura), [email protected] (H. Ito), [email protected] (S. Fukuhara), [email protected] (S. Matsuda).
Total knee arthroplasty (TKA) is one of the most promising surgical treatments for pain relief and improved quality of life for patients with end-stage knee osteoarthritis (OA). To evaluate the outcomes of knee and hip arthroplasties, the American Association of Hip and Knee Surgeons has recommended the use of patient reported outcome measures (PROMs) [1]. Numerous validated PROMs are available to assess the outcomes of TKA, including the Medical Outcomes study Short Form (SF)- 36 [2], SF-12 [3], Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) [4], Knee injury and Osteoarthritis Outcome Score (KOOS) [5], and the Oxford knee score (OKS) [6]. As a classical and mostly objective scoring system, the original Knee Society Score (OKSS) is one of the
https://doi.org/10.1016/j.jos.2019.09.001 0949-2658/© 2019 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
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most popular methods to evaluate outcomes after TKA. However, nowadays OKSS has been challenged in its utility and validity for patients whose demands, expectations, and functional requirements are different from those of previous generations [7]. As a new PROM, the new Knee Society Score (2011KSS) was published in 2012 and has been validated to better characterize the expectations, satisfaction, and physical activities of the younger and more diverse population of patients undergoing TKA [7,8]. With 2011KSS, the internal properties and responses of each patient can be captured in every domain of the subjective score, including symptoms, satisfaction, and expectation. Various kind of activities, including essential activities, higher-level activities, and discretionary/recreational activities are also evaluated by 2011KSS [8]. The 2011KSS has been translated into multiple languages and validated [9e11]. Since then, a variety of studies have used it to evaluate the clinical outcomes and improvement after TKA [12e18], and more recently, the usefulness of 2011KSS has been further validated based on its low ceiling effect and greater responsiveness compared with the WOMAC, SF-12, and OKSS [19]. Recently, the concept of the minimum clinically important difference (MCID) has been emphasized to define the smallest amount by which an outcome must change to be meaningful to patients. The MCID corresponding to SF-12 [20] and SF-36 [21], WOMAC [21], KOOS [22], OKS [20], and OKSS [23] after TKA have been defined. The MCID of 2011KSS was not estimated in any previous study, and hence, the clinical significance of statistical improvements in 2011KSS after TKA is unclear. To this end, the purpose of this study was to define MCID of 2011KSS after TKA. 2. Patients and methods This study was approved by the ethics committee of our hospitals, and written informed consent was obtained from all participants. The inclusion criteria were consecutive patients who underwent primary TKA between April 2012 and December 2016 in four hospitals for primary OA and who consented for prospective data collection required for 2011KSS and OKSS. Patients who deceased within one year, had to undergo revision arthroplasty within one year, or withdrew their consent were excluded from the study. The surgery was basically performed using medial approach (medial parapatellar, mid vastus or sub-vastus) and standard measured resection technique, aiming mechanical alignment without a computer navigation system. The femoral component was basically aimed perpendicular to the mechanical axis of the femur with sulcus cut, and the tibial component was aimed perpendicular to the mechanical axis of the tibia for coronal alignment. For sagittal alignment, the femoral component was aligned to the distal anatomical axis of the femur, and the tibial component was aligned to the proximal mechanical axis of the tibia, with preserving a native posterior slope. The rotation of the femoral component was aimed parallel to the surgical epicondylar axis, and the rotation of the tibial component was decided according to the Akagi's line. Patellar was resurfaced in the majority of cases. The patients were asked to grade their symptoms (Maximum 25 points), satisfaction (Maximum 40 points), expectations (Maximum 15 points), and functional activities (Maximum 100 points) using the Japanese version of the 2011KSS. This version has undergone back-translation, and its reliability has been validated in patients who have undergone TKA [11]. For pre-operative 2011KSS and OKSS, patients filled in the Japanese version of the 2011KSS by themselves, one day prior to TKA. OKSS were also evaluated one day prior to TKA by physiotherapists who were unrelated to this study. To evaluate OKSS, the range of motion was measured with handheld goniometer by physiotherapists. The varus-valgus knee joint stability was examined at 30 degrees of
flexion, and antero-posterior stability was examined by anterior and posterior drawer test. 2.1. Statistics The characteristic data at baseline between included and excluded TKAs were compared using student t-test or Fisher's exact test, and p value of <0.05 was considered statistically significant. An anchor-based approach was used to identify the MCID for 2011KSS. The anchor used in this study was pain score of OKSS (50 points: none, 45 points: mild/occasional, 40 points: mild (stairs only), 30 points: mild (walking and stairs), 20 points: moderate-occasional, 10 points: moderate-continual, 0 point: severe). Each point of OKSS pain score was changed to rank-order: 50 points to 7, 45 points to 6, 40 points to 5, 30 points to 4, 20 points to 3, 10 points to 2 and 0 point to 1. Then, the change in the rank of pain of OKSS (One year rank of OKSS e preoperative rank of OKSS) was classified into 5 categories in accordance with cutoff points close to the quintiles of the target patients. The rise of more than or equal to 5 ranks was defined as an excellent improvement, the rise of 4 ranks as a very good improvement, the rise of 3 ranks as a good improvement, the rise of 2 ranks as a mild improvement, and a rise less than or equal to 1 rank as no or minor improvement. The MCID was determined using the slope of the linear regression analysis of delta 2011KSS (pre-operative 2011KSS e one-year 2011KSS) against improvement of the category of pain in KSS. The MCID of 2011KSS expectation was not calculated because pre- and postoperative questionnaires were different. Therefore, MCID of symptoms, satisfaction, and functional activities were independently calculated. Due to the lack of MCID for expectation, MCID of total 2011KSS was not defined. All analysis was performed using STATA 14.2 (StataCorp LC, College Station, TX, USA). 3. Results 3.1. Baseline characteristics Five hundred and twenty-two cases were enrolled in this study (age: 74.8 ± 7.3 years, female: 80.0%). Of these, relevant data was not available for 19 patients, and hence, a total of 503 subjects were available at baseline. During follow-up, 2 patients were excluded due to their deaths that were unrelated to the surgery, 1 patient was excluded owing to the need for revision arthroplasty because of an infection, 1 case was excluded owing to the need for revision because of distal femoral fracture. Moreover, at one-year, relevant data was not available for 155 cases and a total of 159 subjects (age: 75.0 ± 7.6 years, female: 84.9%) were excluded. Finally, 344 subjects who underwent TKAs who completed all scores were included (age: 74.6 ± 7.1 years, female: 77.9%) in the study (Fig. 1). The detail demographics of the patients are shown in Table 1, and no
Fig. 1. Flow diagram. Patient enrollment and exclusions are shown.
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Table 1 Characteristics of included and excluded TKAs at baseline.
Patient age (years) Sex, female (%) Body mass index Right or Left, right (%) Race Asian (%) Caucasian (%) Hip-knee-ankle angle (degrees) Varus or valgus deformity, varus (%)
344 TKAs included
178 TKAs excluded
P value
74.6 ± 7.1 77.9% 26.4 ± 4.1 50.9%
75.2 ± 7.6 84.3% 25.5 ± 5.0 50.0%
0.41a 0.11b 0.04a 0.85b 0.10b
99.7% 0.3% 9.5 ± 8.3 varus 89.8%
98.3% 1.7% 8.6 ± 10.3 varus 85.4%
0.27a 0.12b
TKA: total knee arthroplasty. a p value by student t-test. b p value by Fisher's exact test.
remarkable differences were observed between the two groups, except body mass index (BMI). Among these 344 included TKAs, cruciate substituting (CS) implant was used in 216 cases, posterior stabilizing (PS) was in 87 cases, cruciate retaining (CR) was in 36 cases, bi-cruciate retaining (BCR) was in 2 cases, constrained condylar knee (CCK) was in 2 cases, and bi-cruciate substituting (BCS) was in 1 case. One-year 2011KSS and OKSS was recorded in the same day at the nearest out-patient visit one year after TKA (372 ± 34 days). Except for scores pertaining to expectation, other scores such as OKSS, OKSS pain, OKSS-Function Score, and each 2011KSS improved one year after TKA (Table 2). 3.2. MCID According to the change in OKSS pain, there were 54 patients who characterized it as an excellent improvement, 74 patients as a very good improvement, 110 patients as a good improvement, 51 patients as a mild improvement, 25 patients as a minor improvement, and 30 patients as no improvement. A linear regression analysis showed that MCID for 2011KSS (Table 3) was calculated to 1.9 in symptom (Fig. 2), 2.2 in satisfaction (Fig. 3), and 4.1 in functional activities (Fig. 4). 4. Discussion In this paper, MCID of 2011KSS for patients who underwent TKA was determined using the pain score of OKSS as an anchor. Till date, MCID of 2011KSS was not determined in any previous study. In a previous study, 10 points for improvement in 2011KSS was used as a tentative of MCID for total 2011KSS [14] although there was no corroborating calculation on this value. In the present study, the MCID was determined as 1.9, 2.2, and 4.1 for symptom, satisfaction,
and functional activities, respectively. If patients showed improvement over MCID, this improvement can be considered real improvement. To date, MCID for other PROMs such as SF-12 [20], SF-36 [21], WOMAC [21], KOOS [22], and OKS [20] have been determined to evaluate the outcome of TKA. As a new PROM with MCID, 2011KSS would have a merit to possibly evaluate the symptom, satisfaction, and functional activities of patients, separately. These values may be used in further studies comparing groups using different methods or implants. Even if these studies showed the significant change of the score yielded (with p < 0.05), it would be insufficient for patients to feel a difference unless it is greater than MCID. MCID is also useful in power-analysis and sample size estimation of clinical studies in which 2011KSS is utilized. An increasing number of studies uses 2011KSS nowadays [12e18]. Significant improvements of 2011KSS are reported in several studies. Niki et al. reports 5.3 point better functional activities in 2011KSS in kinematically aligned TKA compared to mechanically aliened TKA [18], and Kawahara et al. reports 15.7 points better functional activities in 2011KSS in femoral component neutral position group compared to femoral component internal rotation group [12]. Nishio et al. reports an intraoperative medial pivot TKA of 8.0 points better in patient satisfaction and 10.5 points better functional activities in 2011KSS than non-medial pivot TKA using navigation system [13]. Tsukiyama reported 7.6 points better satisfaction score and 5.7 points better symptom in 2011KSS in medially tight flexion group than in medially loose group [16]. The above-mentioned improvements are more than the MCID in this study and can, therefore, be considered as clinically and statistically significant. In the study by Kuriyama et al. satisfaction showed a difference of 3.0 points between never noised group and noised group [15], and in the study conducted by Murakami et al. the
Table 2 Pre- and one-year post-operative scores.
OKSS-Knee Score (0e100) OKSS pain (0e50) OKSS-Function Score (0e100) 2011KSS symptom (0e25) 2011KSS satisfaction (0e40) 2011KSS expectation (3e15) 2011KSS functional activities (0e100)
Pre-operative
One-year post-operative
44.1 ± 18.8 0 (0.6%)e100 (0.3%) 21.5 ± 12.2 0 (10.8%)e50 (1.2%) 54.3 ± 25.2 0 (2.9%)e100 (2.9%) 7.8 ± 5.4 0 (8.4%)e25 (0.6%) 14.2 ± 5.8 0 (0.3%)e36 (0.3%) 13.4 ± 2.0 3 (0.3%)e15 (42%) 40.8 ± 18.6 0 (0.9%)e97 (0.3%)
87.6 ± 11.2 46 (0.3%)e100 (7.3%) 45.1 ± 7.4 10 (0.3%)e50 (48.0%) 78.6 ± 18.2 0 (1.2%)e100 (17.7%) 16.6 ± 6.9 0 (0.3%)e25 (19.5%) 25.9 ± 8.3 6 (0.3%)e40 (9.1%) 9.8 ± 2.9 3 (2.3%)e15 (10.5%) 63.1 ± 19.7 0 (0.3%)e99 (0.3%)
Scores are presented as mean ± standard deviation in upper row and minimum (% of respondent) e maximum (% of respondent) in lower row.
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Table 3 MCID of each 2011KSS.
2011KSS symptom (0e25) 2011KSS satisfaction (0e40) 2011KSS functional activities (0e100)
MCID
95% confidential interval
1.9 2.2 4.1
1.3e2.5 1.4e2.9 2.5e5.7
MCID: minimum clinically important difference, KSS: Knee Society Score.
difference in satisfaction was 3.1 points between cruciate-retaining and posterior-stabilized TKA [17]. Although there are no significant differences between groups in these studies, the differences were more than the MCID. In these studies, numbers of subjects were very small, and hence, there is a possibility of b error. To avoid b error, power analysis is important, and MCID, which evaluated in the present study, could be used for that purpose. The anchor of this study was the improvement in pain score of OKSS. In previous studies, satisfaction or improvement of patients was frequently used as an anchor [20,21,23]. The level of satisfaction or improvement was asked only once after surgery at one year or two years after surgery. This means that there is a risk of recall bias. To decrease this recall bias, the pain evaluation was performed twice (at two different time points) in this study, and the change of the pain score was used as an anchor. Since pain is one of the most important factors for the patients who underwent TKA [24,25], we believe that the change of pain is a critical factor for the patients which represents clinically meaningful differences. Furthermore, the validity of the MCID in this study was supported in light of distribution-based approach. Previous studies reported that MCID can range from 0.2 to 0.5 standard deviation (SD) of the sample [26,27]. In the present study, anchor-based MCID for symptom, satisfaction, and total activity showed 0.35 SD, 0.38 SD, and 0.22 SD, respectively. Therefore, all the MCID were acceptable from the aspect of distribution-based approach, supporting the robustness of our results. Although MCID was successfully determined in this study, this study has some limitations. First, MCID for expectation of 2011KSS was not calculated because of the differences between pre- and post-operative questionnaires in terms of questions and scoring. The difference was in the uniqueness of the subdomain of expectation. In the questionnaires, preoperative and postoperative questions and points of distribution were not identical. So, we could not determine the improvement of expectation by subtracting preoperative from postoperative expectation. For example, if a patient who underwent TKA had high expectations regarding postoperative pain relief, the preoperative subscore would be 5.
Fig. 2. Linear regression to calculate 2011KSS symptom. The figure shows change of 2011KSS symptom with 95% confidential interval at 1 year according to the degree of pain improvement. The slope of the linear regression indicates the MCID of 2011KSS symptom.
Fig. 3. Linear regression to calculate 2011KSS satisfaction. The figure shows change of 2011KSS satisfaction with 95% confidential interval at 1 year according to the degree of pain improvement. The slope the linear regression indicates the MCID of 2011KSS satisfaction.
Then, if the patient's preoperative expectations in terms of pain relief were met after TKA, the subscore would be 3. In this case, even though pain relief was obtained after TKA, the score reduces after surgery. This complexity may itself be a limitation of 2011KSS, and hence, we decided not to determine the MCID for this parameter (2011KSS for expectation). Moreover, the total score of 2011KSS was not calculated either due to the unavailability of MCID for expectation score. Second, there were some missing data oneyear after TKA. Out of 503 TKAs at baseline, 159 cases (31.1%) did not complete the follow-up questionnaire, so we could not evaluate the data of the 1-year 2011KSS of the excluded patients. Although BMI was slightly but significantly higher in included group, we believe that there were no definitive differences between included and excluded populations at baseline, so the included cases may be considered as representative of the whole cohort. Third, MCID was calculated with one-year improvement of 2011KSS. In previous studies, MCID after TKA is determined at 6 months [21], one year [20,22], or two years [23] after surgery. If patients kept improving after TKA, it might be better to determine the MCID of longer durations to determine the maximum possible improvement after TKA. However, a numbers of studies report that the symptoms and functions stabilize by one-year after TKA [28,29]. That is why we decided to calculate MCID of 2011KSS using one-year improvement after TKA. Fourth, the Japanese version of 2011KSS had a minor difference in discretionary activities, in which ground golf and hiking was added since these are popular activities among Japanese
Fig. 4. Linear regression to calculate 2011KSS functional activities. The figure shows the change in 2011KSS functional activities with 95% confidential interval at 1 year according to the degree of pain improvement. The slope the linear regression indicates the MCID of 2011KSS functional activities.
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people based on a previous survey [11]. Lastly, there is the COnesus based Standard for the selection of health status Measurement Instruments (COSMIN) checklist to assess the methodological quality of studies on measurement properties of health status measurement instruments [30]. Although this manuscript was compliant to the all items in the check list “Interpretability”, in which MCID was described, the 2011KSS on its own is not complaint to every item of the COSMIN checklist, for example minimum detectable change (MDC) was not calculated. Some more efforts are needed to fully compliant to the COSMIN checklist, to improve the validity of 2011KSS. In conclusion, the MCID of 2011KSS was successfully calculated as 1.9 in symptom, 2.2 in satisfaction, and 4.1 in functional activities. With these MCID, 2011KSS is a more efficient tool to evaluate the physical activities of the diverse populations of patients undergoing TKA. These MCID values can also be used to calculate sample size to ensure the power of a study in designing clinical studies. Conflict of interest Kyocera (Kyoto Japan) supports the prospective data acquisition in part. The department of KN, MF, SK, SN, HI and SM received a research grant from Kyocera. This company has no role in the design and conduct of the study, analysis of the data, the preparation of the manuscript or decision to submit the manuscript for the publication. Ethical statement This study was approved by the Ethics Committee of our hospitals and performed in accordance with the ethical standards in the Declaration of Helsinki. Acknowledgements We thank Drs. Masahiro Yoshida, Susumu Kamisato, Ichiro Nakayama, Yoshitomo Sano, Shinobu Tabata, Hironobu Bito, Shinnosuke Yamashita, Yoshihiro Ishihama, Takaaki Shirai, Chiaki Tanaka, Hiroshi Kanoe, Hiroshi Tada, Keiji Yoshida, Masatoshi Fujiwara, Kenichi Takaya, Kazutaka Masamoto, Kazuaki Morizane, Kazunari Nakai, Masanori Kobayashi, and Yoshihiro Sekimoto for helping with data collection. References [1] Lieberman JR. American association of hip and knee surgeons and outcome measures after total joint arthroplasty. J Arthroplast 2016 Jun;31(6):1137e8. [2] Jenkinson C, Coulter A, Wright L. Short form 36 (SF36) health survey questionnaire: normative data for adults of working age. BMJ 1993 May 29;306(6890):1437e40. [3] Hurst NP, Ruta DA, Kind P. Comparison of the MOS short form-12 (SF12) health status questionnaire with the SF36 in patients with rheumatoid arthritis. Br J Rheumatol 1998 Aug;37(8):862e9. [4] Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1988 Dec;15(12): 1833e40. [5] Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD. Knee injury and osteoarthritis outcome score (KOOS)edevelopment of a self-administered outcome measure. J Orthop Sport Phys Ther 1998 Aug;28(2):88e96. [6] Dawson J, Fitzpatrick R, Murray D, Carr A. Questionnaire on the perceptions of patients about total knee replacement. J Bone Joint Surg Br 1998 Jan;80(1): 63e9. [7] Scuderi GR, Bourne RB, Noble PC, Benjamin JB, Lonner JH, Scott WN. The new knee society knee scoring system. Clin Orthop Relat Res 2012 Jan;470(1): 3e19.
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