Abstract
Aims
The Coronal Plane Alignment of the Knee (CPAK) classification has been developed to predict individual variations in inherent knee alignment. The impact of preoperative and postoperative CPAK classification phenotype on the postoperative clinical outcomes of total knee arthroplasty (TKA) remains elusive. This study aimed to examine the effect of postoperative CPAK classification phenotypes (I to IX), and their pre- to postoperative changes on patient-reported outcome measures (PROMs).
Methods
A questionnaire was administered to 340 patients (422 knees) who underwent primary TKA for osteoarthritis (OA) between September 2013 and June 2019. A total of 231 patients (284 knees) responded. The Knee Society Score 2011 (KSS 2011), Knee injury and Osteoarthritis Outcome Score-12 (KOOS-12), and Forgotten Joint Score-12 (FJS-12) were used to assess clinical outcomes. Using preoperative and postoperative anteroposterior full-leg radiographs, the arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO) were calculated and classified based on the CPAK classification. To investigate the impact on PROMs, multivariable regression analyses using stepwise selection were conducted, considering factors such as age at surgery, time since surgery, BMI, sex, implant use, postoperative aHKA classification, JLO classification, and changes in aHKA and JLO classifications from preoperative to postoperative.
Results
The preoperative and postoperative CPAK classifications were predominantly phenotype I (155 knees; 55%) and phenotype V (73 knees; 26%), respectively. The change in the preoperative to postoperative aHKA classification was a significant negative predictive factor for KOOS-12 and FJS-12, while postoperative apex proximal JLO was a significant negative predictive factor for KSS 2011 and KOOS-12.
Conclusion
In primary TKA for OA, preoperative and postoperative CPAK phenotypes were associated with PROMs. Alteration in varus/valgus alignment from preoperative to postoperative was recognized as a negative predictive factor for both KOOS-12 and FJS-12. Moreover, the postoperative apex proximal JLO was identified as a negative factor for KSS 2011 and KOOS-12. Determining the target alignment for each preoperative phenotype with reproducibility could improve PROMs.
Cite this article: Bone Joint J 2024;106-B(10):1059–1066.
Take home message
Maintaining consistent varus/valgus alignment from pre- to postoperative stages and avoiding postoperative apex proximal joint line obliquity are crucial for improving patient-reported outcomes in total knee arthroplasty.
This finding underlines the importance of tailored preoperative planning based on the Coronal Plane Alignment of the Knee classification.
Introduction
Total knee arthroplasty (TKA) has demonstrated a long-term success rate of approximately 96%.1 However, patient satisfaction has remained at approximately 80%.2 Traditionally, the surgical approach for TKA has utilized a mechanical alignment method, targeting a hip-knee-ankle angle (HKAA) of 0° (neutral alignment).3 Neutral alignment is believed to reduce mechanical imbalance between the medial and lateral aspects of the knee joint, thereby reducing polyethylene wear and loosening.4 However, because this neutral alignment is not always the patient’s specific native anatomical alignment,5 there is potential to create physiological imbalance in the soft-tissues. There is an ongoing debate regarding the optimal alignment to improve overall patient satisfaction.3 In the kinematic alignment method,6-8 which aims to replicate each patient’s inherent anatomical alignment, opinions vary, with some reports indicating improved clinical outcomes compared to the mechanical alignment method,9,10 whereas others suggest no statistically significant differences.11-13
The Coronal Plane Alignment of the Knee (CPAK) classification has been proposed to predict individual variations in inherent alignment.14,15 This system allows for a classification based solely on a full-leg radiograph, categorizing knee joint varus/valgus and joint line obliquity (JLO) into three types. Using combinations of these categories, a classification from phenotype I to IX is derived (Figure 1). In the Asian population, there is a higher prevalence of varus alignment, resulting in a frequent classification into varus alignment in the CPAK classification.16 To address this bias, the modified CPAK classification has been proposed.17 This classification widens the range of neutral alignment of the varus/valgus and joint line compared with the original CPAK classification. There are only limited reports on the impact of pre- and postoperative changes in the original and modified CPAK classifications on patient-reported outcome measures (PROMs).18,19
Fig. 1
Diagram of the Coronal Plane Alignment of the Knee classification, developed by MacDessi et al.14 aHKA, arithmetic hip-knee-ankle angle; JLO, joint line obliquity; LDFA, lateral distal femoral angle; MPTA, medial proximal tibial angle.
The objectives of this study were to examine the effect of postoperative CPAK classification phenotypes (I to IX), and their pre- to postoperative changes on PROMs, and determine which is more beneficial at predicting improvement in PROMs, either the original CPAK or the modified CPAK classification. We hypothesized that there would be no difference in PROMs between cases where varus/valgus alignment did not change pre- to postoperatively and cases that achieved neutral alignment, and that postoperative apex proximal joint line orientation would lead to a decline in PROMs.
Methods
Patients
This retrospective cohort study was conducted in accordance with the STROBE statement,20 and was approved by our facility’s Institutional Review Board (IRB number 2020-425).
This study included patients undergoing primary TKA using two implants for osteoarthritis (OA) at our institution between September 2013 and June 2019. Of the 358 patients with 448 knees, seven patients (eight knees) who underwent revision surgery due to infection and 11 patients (18 knees) who died were excluded. Questionnaires were sent in April 2021 to 340 patients (422 knees) who met the inclusion criteria; 231 patients (284 knees) responded, constituting a response rate of 68% (Figure 2).
Fig. 2
Flow diagram of patient selection for the analyses. TKA, total knee arthroplasty.
Surgical procedure
All operations were performed using the medial parapatellar approach, and a mechanical alignment method, without navigation. The Persona PS (Zimmer Biomet, USA) and Journey II BCS (Smith & Nephew, USA) cemented prostheses were used. All cases underwent patellar resurfacing.
Radiological assessment
Weightbearing anteroposterior full-leg radiographs were obtained preoperatively and postoperatively in accordance with previous studies.21,22 The medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) were measured. The MPTA was defined as the medial angle formed between the tibial mechanical axis and the joint line of the proximal tibia, and the LDFA was defined as the lateral angle formed between the femoral mechanical axis and the joint line of the distal femur.14 From these two parameters, the arithmetic hip-knee-ankle angle (aHKA: MPTA – LDFA) as an indicator of varus or valgus alignment and JLO (MPTA + LDFA) as an indicator of joint surface slope were calculated. Varus or valgus alignment was categorized as aHKA < -2° for varus, -2° ≤ aHKA ≤ 2° for neutral, and aHKA > 2° for valgus. JLO was classified as JLO < 177° for apex distal, 177° ≤ JLO ≤ 183° for neutral, and JLO > 183° for apex proximal. Based on these criteria, cases were categorized into nine phenotypes.14 Further classification was performed using the modified CPAK classification, which was designed to classify diverse knee joints, especially in Asian patients, who tend to have greater varus alignment.17 In this modified classification, aHKA calculation remained the same, categorizing aHKA < -3° as varus, -3 to 3° as neutral, and ≥ 3° as valgus. The modified JLO was calculated as 90° - 0.5(LDFA + MPTA) and was classified as apex proximal for -3° or below, neutral for -3 ° to 3°, and apex distal for 3° or more.17
Outcomes
To assess PROMs, the Knee Society Score 2011 (KSS 2011) was used as an indicator of symptoms, satisfaction, expectations, and activity levels.23,24 Knee injury and Osteoarthritis Outcome Score-12 (KOOS-12) was used to evaluate symptoms, pain, daily living, sports, and quality of life.25 Forgotten Joint Score-12 (FJS-12) was used to measure the extent to which patients were aware of their knees during daily activities.26
Statistical analysis
Continuous data are presented as means and SD. Statistical analyses were conducted using R software (R Foundation for Statistical Computing, Austria) and JMP Pro 16.0 (SAS Institute, USA), with a significance level set at p < 0.05. Given that the data did not exhibit a completely random missing pattern, multiple imputations were implemented using the mice 3.13.0 package (van Buuren S and Groothuis-Oudshoorn K, Netherlands), incorporating predictive mean matching.27 To investigate the impact on PROMs, multivariable regression analyses using stepwise selection were conducted, considering factors such as age at surgery, time interval since surgery, BMI, sex, implant use, postoperative aHKA classification, JLO classification, and changes in aHKA and JLO classifications from preoperative to postoperative. Variables were added or removed based on a significance threshold of p < 0.2 in the analyses. As there were nine factors used in the multivariable analyses, a sample size of 135 or more was deemed necessary. In this study, the sample size was 284, which was considered sufficient.
Results
Table I represents the patients’ characteristics and postoperative PROMs. At the time of surgery, the mean age was 74.0 years (SD 8.0), with 198 (238 knees) female and 33 (46 knees) male patients. The Persona PS and Journey II BCS prostheses were used in 150 and 134 knees, respectively. Before surgery, by the CPAK classification, phenotype I was the most common (155 knees; 55%), followed by phenotypes IV (45 knees; 16%) and II (38 knees; 13%) (Figure 3). After surgery, phenotype V was the most prevalent at 73 knees (26%), followed by II and IV at 45 knees (16%), and VI at 39 knees (14%) (Figure 4).
Table I.
Patient characteristics and postoperative patient-reported outcomes.
| Variable | Data |
|---|---|
| Patients, n | 231 |
| Knees, n | 284 |
| Mean age at surgery, yrs (SD) | 74.0 (8.0) |
| Sex, n of knees | |
| Female | 238 |
| Male | 46 |
| Mean BMI, kg/m² (SD) | 26.7 (4.4) |
| Kellgren-Lawrence grade, n of knees | |
| 3 | 89 |
| 4 | 195 |
| Mean postoperative time interval to response, mths (SD) | 55 (24) |
| Implant, n | |
| Persona PS | 150 |
| Journey II BCS | 134 |
| Mean PROM (SD) | |
| KSS 2011* | 127 (33) |
| KOOS-12† | 71 (20) |
| FJS-12† | 50 (26) |
-
*
0 to 180.
-
†
0 to 100.
-
FJS-12, Forgotten Joint Score-12; KOOS-12, Knee injury and Osteoarthritis Outcome Score-12; KSS 2011, Knee Society Score 2011; PROM, patient-reported outcome measure.
Fig. 3
Preoperative Coronal Plane Alignment of the Knee classification. aHKA, arithmetic hip-knee-ankle angle; JLO, joint line obliquity; LDFA, lateral distal femoral angle; MPTA, medial proximal tibial angle.
Fig. 4
Postoperative Coronal Plane Alignment of the Knee classification. aHKA, arithmetic hip-knee-ankle angle; JLO, joint line obliquity; LDFA, lateral distal femoral angle; MPTA, medial proximal tibial angle.
The mean values for KSS 2011, KOOS-12, and FJS-12 were 127 (SD 33), 71 (SD 20), and 50 (SD 26), respectively. Representative cases are shown in Figure 5.
Fig. 5
Pre- and postoperative weightbearing anteroposterior full-leg radiographs of representative cases. a) Preoperative Coronal Plane Alignment of the Knee (CPAK) classification: phenotype I (varus/apex distal); postoperative CPAK classification: phenotype IV (varus/neutral). This case did not show any negative factors, including change in pre- to postoperative arithmetic hip-knee-ankle angle (aHKA) classification or postoperative apex proximal joint line obliquity (JLO). b) Preoperative CPAK classification: phenotype II (neutral/apex distal); postoperative CPAK classification: phenotype V (neutral/neutral). This case did not show any negative factors, including change in pre- to postoperative aHKA classification or postoperative apex proximal JLO. c) Preoperative CPAK classification: phenotype I (varus/apex distal); postoperative CPAK classification: phenotype V (neutral/neutral). This case showed a negative factor: change in pre- to postoperative aHKA classification. d) Preoperative CPAK classification: phenotype I (varus/apex distal); postoperative CPAK classification: phenotype VII (varus/apex proximal). This case showed a negative factor: postoperative apex proximal JLO.
Multivariable regression analyses using stepwise selection showed that female sex (p = 0.005) and postoperative apex proximal JLO (p < 0.001) were significant negative factors for KSS 2011. For KOOS-12, significant negative factors included postoperative apex proximal JLO (p = 0.010) and changes in varus/valgus alignment from pre- to postoperative aHKA (Table II). Female sex (p = 0.003), Persona PS (p = 0.006), and changes in varus/valgus alignment in the pre- to postoperative aHKA (p = 0.005) were negative factors for FJS-12 (Table III).
Table II.
Postoperative patient-reported outcomes concerning original Coronal Plane Alignment of the Knee classification.
| Outcome | Postoperative CPAK phenotype V | Others | p-value* | Cases avoiding CPAK negative factors† | Others | p-value* |
|---|---|---|---|---|---|---|
| Mean KSS 2011 (SD) | 128 (29) | 126 (34) | 0.994 | 131 (32) | 124 (33) | 0.030 |
| Mean KOOS-12 (SD) | 72 (18) | 71 (21) | 0.772 | 75 (21) | 69 (20) | 0.005 |
| Mean FJS-12 (SD) | 51 (25) | 50 (27) | 0.856 | 55 (27) | 48 (25) | 0.019 |
-
*
Mann-Whitney U test.
-
†
Cases avoiding postoperative apex proximal JLO and preoperative to postoperative aHKA classification changes.
-
aHKA, arithmetic hip-knee-ankle angle; CPAK, Coronal Plane Alignment of the Knee; FJS-12, Forgotten Joint Score-12; JLO, joint line obliquity; KOOS-12, Knee injury and Osteoarthritis Outcome Score-12; KSS 2011, Knee Society Score 2011.
Table III.
Multivariable analyses of patient-reported outcomes with original Coronal Plane Alignment of the Knee classification. The variables were selected using stepwise multiple regression analyses.
| Factor | Negative factor | β value (95% CI)* | p-value |
|---|---|---|---|
| KSS 2011 | |||
| Age at surgery | -0.40 (-0.87 to 0.06) | 0.088 | |
| Sex | Female | -7.2 (-12 to -2.1) | 0.005 |
| Pre- to postoperative aHKA† | -1.3 (-6.3 to 1.3) | 0.198 | |
| Postoperative JLO‡ | Apex proximal | -3.4 (-17 to -4.7) | < 0.001 |
| KOOS-12 | |||
| Sex | -1.8 (-6.1 to 0.3) | 0.075 | |
| Pre- to postoperative aHKA† | Change before and after surgery | -1.3 (-4.9 to -0.1) | 0.043 |
| Postoperative JLO‡ | Apex proximal | -2.6 (-9.3 to -1.3) | 0.010 |
| FJS-12 | |||
| Sex | Female | -3.0 (-10 to -2.2) | 0.003 |
| Implant | Persona PS | -5.3 (-9.1 to -1.5) | 0.006 |
| Pre- to postoperative aHKA† | Change before and after surgery | -4.4 (-7.4 to -1.3) | 0.005 |
| Postoperative JLO‡ | -3.2 (-7.1 to 0.7) | 0.108 |
-
*
β value is the standard regression coefficient.
-
†
aHKA = MPTA - LDFA (< -3°: varus; ≥ -3° and < 3°: neutral; > 3°: valgus.)
-
‡
JLO = MPTA + LDFA (< 177°: apex distal; ≥ 177° and < 183°: neutral; > 183°: apex proximal.)
-
aHKA, arithmetic hip-knee-ankle angle; FJS-12, Forgotten Joint Score-12; JLO, joint line obliquity; KOOS-12, Knee injury and Osteoarthritis Outcome Score-12; KSS 2011, Knee Society Score 2011.
Comparing postoperative CPAK V and other phenotypes, there were no significant differences observed in mean KSS 2011 (p = 0.994), KOOS-12 (p = 0.772), and FJS-12 (p = 0.856, all Mann-Whitney U test) between the two groups. In cases without changes in pre- to postoperative aHKA and avoiding postoperative apex proximal JLO, mean KSS 2011 (p = 0.030), KOOS-12 (p = 0.005), and FJS-12 (p = 0.019, all Mann-Whitney U test) were all significantly higher (Table II).
As additional verification, multivariable analyses using the modified CPAK classification were performed. For KSS 2011, older age (p = 0.046), female sex (p = 0.005), and postoperative apex proximal modified JLO (p = 0.010) were significant negative factors. Regarding KOOS-12, no significant negative factors were detected. For FJS-12, female sex (p = 0.005) and the use of Persona PS (p = 0.014) were significant negative factors (Table IV).
Table IV.
Multivariable analyses of patient-reported outcomes with modified Coronal Plane Alignment of the Knee. The variables were selected using stepwise multiple regression analyses.
| Factor | Negative factor | β value (95% CI)* | p-value |
|---|---|---|---|
| KSS 2011 | |||
| Age at surgery | Older age | -0.48 (-0.94 to 0.01) | 0.046 |
| Sex | Female | -7.3 (-12 to -2.3) | 0.005 |
| Implant | -5.3 (-6.7 to 0.8) | 0.128 | |
| Postoperative modified JLO† | Apex proximal | -13.3 (-23 to 3.2) | 0.010 |
| KOOS-12 | |||
| Age at surgery | -0.24 (-0.54 to 0.05) | 0.108 | |
| Sex | -2.9 (-6.1 to 0.35) | 0.081 | |
| Implant | -2.2 (-4.6 to 0.19) | 0.071 | |
| FJS-12 | |||
| Sex | Female | -5.9 (-10 to -1.8) | 0.005 |
| Implant | Persona PS | -3.8 (-6.8 to -0.8) | 0.014 |
| Pre- to postoperative modified aHKA‡ | -3.6 (-9.0 to 1.8) | 0.190 |
-
*
β value is the standard regression coefficient.
-
†
Modified JLO = 90° - 0.5(LDFA + MPTA) (< -3°: apex distal; ≥ -3° and < 3°: neutral; > 3°: apex proximal.)
-
‡
Modified aHKA = MPTA - LDFA (< -3°: varus; ≥ -3° and < 3°: neutral; > 3°: valgus.)
-
aHKA, arithmetic hip-knee-ankle angle; FJS-12, Forgotten Joint Score-12; JLO, joint line obliquity; KOOS-12, Knee injury and Osteoarthritis Outcome Score-12; KSS 2011, Knee Society Score 2011.
Discussion
This is the first study to examine the influence of postoperative CPAK classification phenotypes and their changes from pre- to postoperative on postoperative PROMs. We have demonstrated that changes in the preoperative to postoperative aHKA classification and postoperative JLO influenced the outcomes.
In our study, preoperative CPAK classification showed that phenotype I was the most prevalent (155 knees; 55%). In the initial report by MacDessi et al,14 who first proposed the CPAK classification, for cases of OA in Australian patients, phenotype II was the most common at 32.2%, and phenotype I was the second most common at 19.4%. In their investigation on the association between knee alignment and the onset of OA, Higano et al28 reported that varus alignment in the proximal tibia pre-existed before the onset of OA, and in patients with advanced OA, varus alignment was more common with statistical significance. A report by Toyooka et al,16 which investigated the preoperative CPAK classification phenotype in Japanese patients, indicated a high prevalence of varus deformity, with 53.8% classified as phenotype I, consistent with the results of our study. It has been suggested that in the Japanese population, varus alignment is common and often an innate alignment, and the higher prevalence of preoperative phenotype I in varus alignment may contribute to an increased susceptibility to the development of OA.
In our study, the postoperative CPAK classification, phenotypes II, V, and VIII, representing neutral alignment in varus/valgus, were the most prevalent, accounting for a total of 130 knees (46%). The mechanical alignment method was applied in all cases, yet the intended neutral alignment was not achieved in 154 knees (54%). In a study by Matsumoto et al,29 a postoperative HKAA deviation of 2° or more was measured in 11.4% of cases when using a robot-assisted surgery system, compared to 40% when employing manual instrumentation. Achieving the target alignment with manual instrumentation may be more challenging, suggesting that the use of computer-assisted navigation devices may be considered preferable in achieving target alignment.
Contrary to our initial assumption, the alteration in the aHKA classification before and after surgery was identified as a significant negative factor in KOOS-12 and FJS-12. Wan et al30 reported improved FJS-12 outcomes in knees with preoperative varus, in which postoperative alignment remained varus rather than achieving neutral alignment. Elkus et al31 reported favourable clinical outcomes in TKA for patients with valgus alignment, with a residual valgus of approximately 5° postoperatively. These findings are consistent with the results of this study. Altering the alignment of the varus/valgus preoperatively to postoperatively may lead to an increased imbalance in soft-tissue, potentially causing pain and discomfort due to instability.
As we hypothesized, the postoperative apex proximal JLO was identified as a significant negative predictive factor for both the KSS 2011 and FJS-12. Blakeney et al32 proposed that a postoperative apex distal joint line orientation was associated with better functional outcomes. Furthermore, Hungerford and Lennox33 reported an apex distal physiological slope of 3°. KSS 2011 focuses on activity rather than pain,23,24 FJS-12 addresses discomfort experienced during various activities,26 and KOOS-12 equally evaluates pain, physical activity, and quality of life.25 These characteristics support the findings of our study, suggesting that the apex proximal JLO influences the decline in KSS 2011 and FJS-12 scores, both of which place greater weight on functional scores compared with KOOS-12.
Cases of postoperative CPAK type V and others showed no significant differences in PROMs. However, in cases where the factors identified as negative for CPAK were avoided, all PROMs showed a significant improvement of approximately 10%. This suggests that rather than aiming for mechanical alignment, it may be advisable to maintain the preoperative aHKA classification and avoid postoperative apex proximal JLO.
In multivariable analyses based on the modified CPAK classification, the postoperative apex proximal modified JLO was a significant negative factor for KSS 2011. However, no other significant factors related to modified CPAK were detected in these analyses. The modified CPAK classification sets the neutral range for varus/valgus at 0° ± 3°, while this is 0° ± 2° in the original CPAK classification. Preoperatively, there were many cases of significant varus, and those classified as varus in the CPAK classification were often classified as varus in the modified CPAK classification. However, there was a prevalence of mild varus postoperatively, leading to many cases in which the CPAK and modified CPAK classifications differed. To improve postoperative outcomes, planning based on the original CPAK classification rather than the modified CPAK classification may be more appropriate, even in Asian populations.
This study had several limitations. First, the postoperative time interval varied among patients. However, all cases were more than one year post surgery, and although the postoperative follow-up duration was included in the multivariable analyses, it was not a significant factor, and its impact was considered small. Second, only anteroposterior radiographs were evaluated and assessments in the sagittal and transverse planes were not conducted; this is because the primary aim of this study was to investigate the CPAK classification and coronal alignment specifically. Third, although the overall number of cases was sufficient for multivariable analyses, there were limited cases for certain phenotypes, potentially resulting in inadequate evaluations. Therefore, further studies with a larger number of cases for each phenotype are required.
In conclusion, in primary TKA for OA, the pre- and postoperative CPAK phenotype was associated with postoperative PROMs. The change in varus/valgus alignment before and after surgery was identified as a negative predictive factor for KOOS-12 and FJS-12. In addition, postoperative apex proximal JLO was a negative predictive factor for KSS 2011 and KOOS-12 scores. In cases where these negative factors were avoided, all PROMs showed a significant improvement. Determining the target alignment for each preoperative phenotype and achieving reproducibility could lead to improvements in PROMs.
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Author contributions
T. Konishi: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Resources, Visualization, Writing – original draft, Writing – review & editing
S. Hamai: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing
H. Tsushima: Investigation, Project administration, Resources, Writing – review & editing
S. Kawahara: Investigation, Resources, Writing – review & editing
Y. Akasaki: Investigation, Resources, Writing – review & editing
S. Yamate: Data curation, Methodology, Resources, Writing – review & editing
S. Ayukawa: Investigation, Resources, Writing – review & editing
Y. Nakashima: Investigation, Project administration, Resources, Supervision, Writing – review & editing
Funding statement
The authors disclose receipt of the following financial or material support for the research, authorship, and/or publication of this article: this study was supported by a grant from the Ogata Memorial Foundation, Inc. (No. 135) and the Medical Care Education Research, as reported by S. Hamai.
ICMJE COI statement
S. Hamai reports a grant from the Ogata Memorial Foundation, Inc. (No. 135) and the Medical Care Education Research, related to this study. Y. Nakashima reports research grants from Zimmer Biomet, not related to this study.
Data sharing
The data that support the findings for this study are available to other researchers from the corresponding author upon reasonable request.
Acknowledgements
The authors would like to thank Editage (www.editage.com) for the English language editing.
Ethical review statement
This study was approved by our Institutional Review Board (2020-425). This study was conducted in accordance with the principles of the Declaration of Helsinki.
Open access funding
The authors report that they received open access funding for their manuscript from The Medical Care Education Research.
Open access statement
This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives (CC BY-NC-ND 4.0) licence, which permits the copying and redistribution of the work only, and provided the original author and source are credited. See https://creativecommons.org/licenses/by-nc-nd/4.0/
Social media
Follow T. Konishi on X @EruKonishi
Follow S. Hamai on X @shamai0220
This article was primary edited by D. Johnstone.
