No difference in postoperative patient satisfaction rates between mechanical and kinematic alignment total knee arthroplasty: A systematic review

Abstract Purpose The purpose of this systematic review was to compare patient satisfaction patient‐reported outcomes (PROMs) levels after mechanically aligned (MA) and kinematically aligned (KA) total knee arthroplasty (TKA). Methods A systematic literature search following PRISMA guidelines was conducted on PubMed, Embase, Medline and Scopus to identify potentially relevant articles for this review, published from the beginning of March 2013 until the end of October 2023. Only articles reporting satisfaction after KA TKA, MA TKA or both were included, which use valid and reliable tools for the evaluation and reporting of satisfaction after TKA. Title, authors, year of publication, study design, level of evidence, follow‐up period, patients' demographic data, sample size, type of satisfaction score, postoperative satisfaction score, postoperative alignment, statistical significance, as well as other variables, were extracted for analysis. An Agency for Healthcare Research and Quality's (AHRQ) design‐specific scale was used for assessing randomized control trials (RCTs). The nonrandomized control trials were evaluated by using the Joanna Briggs Institute's (JBI) Critical Appraisal Tool. The Newcastle‐Ottawa Scale (NOS) was also used to assess cohort studies, while case series were evaluated using the NIH Quality Assessment Tool for Case Series Studies. Results The initial search identified 316 studies, of which 178 were considered for screening. Eleven studies completely fulfilled the inclusion criteria, including one RCT, five nonrandomized control trials/quasi‐experiments, three case series, and two cohort studies. The total number of patients recruited for MA TKA was 1740. Conversely, 497 patients were enrolled for KA TKA. Five studies used the visual analogue scale (VAS) for assessing postoperative patient satisfaction, four used the Knee Society Score (KSS) 2011 version and two Likert‐based types of scores. Overall, the highest mean satisfaction score of KSS 2011 was 31.5 ± 6.6 in the MA group, and 29.8 ± 80 in the KA group in four studies. All of them showed high postoperative patient satisfaction rates for both MA and KA TKA, but with no statistically significant difference between them (p > 0.05). Conclusion Both mechanically aligned total knee arthroplasty, as well as kinematically aligned total knee arthroplasty led to high rates of postoperative patient satisfaction, with no statistically significant differences between them. Level of Evidence Level III, systematic review.


INTRODUCTION
Postoperative restoration of a neutral limb alignment has been the primary goal of conventional total knee arthroplasty (TKA) over the past two decades [28].The mechanical alignment (MA) philosophy emphasizes the importance of a mechanically aligned knee, as the implanted femoral and tibial TKA components should be perpendicular to the mechanical axis of the limb [28].This, in turn, leads to a more balanced loading and thus increases components' survival [28,36].However, this alignment philosophy does not respect the anatomical joint line orientation and phenotypes of the native knee and, therefore, alters surrounding soft tissues' tension [36].Additionally, MA does not restore the individual knee kinematics [12].The rates of residual knee symptoms and patient dissatisfaction after MA TKA have been reported to be as high as 50% and 20%, respectively [23].Furthermore, changing the native alignment could play a significant role in postoperative patient satisfaction levels and patientreported outcomes (PROMs) [23].However, recently, the preferred alignment philosophy in TKA has shifted from a systematic approach toward a more personalized one in search of higher functionality and patient satisfaction [2,16,34].In this regard, kinematic alignment (KA) has gained significant momentum, as it conceptually aims to restore the alignment and kinematics of the native prearthritic knee [19].
Nonetheless, given the still high dissatisfaction rate after present TKAs (10%-20%), and the current widespread use of both alignment strategies, the need to identify any possible influence of the chosen alignment strategy over patient satisfaction levels, which particularly leads to a better postoperative patient satisfaction score becomes apparent [4,6].To better understand the patient's perspective, the analysis of PROMs and patient satisfaction is crucial [5].Some of the most used PROMs for achieving satisfaction after TKA are Visual Analogue Scales (VAS), the new Knee Society Knee Scoring System (KSS 2011) and Likert-Scale [11,15].Therefore, the aim of this systematic review is to compare patient satisfaction PROMs after MA and KA TKA.The hypothesis of this study is that the alignment strategy does influence patient satisfaction levels after TKA and KA TKA produces superior postoperative satisfaction levels when compared to MA TKA.

METHODS
A systematic literature search following PRISMA guidelines was conducted on PubMed, Embase, Medline and Scopus to identify potentially relevant articles for this review, published from the beginning of March 2013 until the end of October 2023.Mesh terms such as "alignment technique," "total knee arthroplasty," and "dissatisfaction" were used for building a search strategy in each database accordingly.A detailed description of the search strategy can be found in File S1.The study protocol was registered with PROSPERO (CRD42023492219).
Identified studies have been imported into Covi-dence® (Veritas Health Innovation Ltd) and removal of duplicates has been automatically performed.Two authors independently underwent title and abstract screening.The same two authors have performed fulltext analysis.In case of disagreement/uncertainty, a third author was consulted.The selection was based on the following inclusion criteria: full-text clinical studies in English, published in peer-reviewed journals, which use valid and reliable tools for the evaluation and reporting of satisfaction after TKA.Only articles reporting satisfaction after KA TKA (unrestricted), MA TKA or both were included.All preprints, abstract-only studies, protocols, literature reviews, meta-analyses, expert opinion articles, book chapters, surgical technique studies, and studies pertaining to restricted or inverse KA alignment, unicondylar knee arthroplasty (UKA), patellofemoral arthroplasty (PFA), or revision total knee arthroplasty (rTKA), were excluded.Studies with unavailable numeric data (graphical only) were also excluded.

Data extraction
Title, authors, year of publication, study design, level of evidence, follow-up period, patient's demographic data, sample size, type of satisfaction score, preoperative, and/or postoperative satisfaction score, postoperative alignment, statistical significance, as well as other variables, were extracted for analysis.

Quality assessment
All included studies were assessed for their quality according to the study design.In this review, an Agency for Healthcare Research and Quality (AHRQ) designspecific scale for randomized control trials (RCTs) [35] (Table 1).The nonrandomized control trials were assessed by using the Joanna Briggs Institute's (JBI) Critical Appraisal Tool [14] (Table 2).The Newcastle-Ottawa Scale (NOS) was also used to assess cohort studies [30] (Table 3), and case series were evaluated by using the NIH Quality Assessment Tool [20] (Table 4).

Statistical analysis
The heterogeneity of included studies and different tools used for outcome measures precluded a meta-analysis.Therefore, continuous variables were defined by using descriptive statistics such as means, standard deviations and percentages.The quality assessment was performed for all the content used in this systematic review.
Four studies used 2011 KSS for assessing satisfaction [24,25,31,33], while five studies have used VAS [1,3,7,8,32].In all the included studies, the method of satisfaction assessment was clearly mentioned in the methodology section.All details regarding the use of satisfaction assessment tools are presented in Table 6.

Association between satisfaction score and alignment target
Out of all included studies, only three mentioned the preoperative satisfaction score [24,31,33] (Table 6).Of the four studies, which used KSS 2011, two compared satisfaction between MA and KA, while the other two reported satisfaction in only MA or KA groups individually.Overall, the highest mean satisfaction score of KSS 2011 was 31.5 ± 6.6 in the MA group, and 29.8 ± 80 in the KA group [24,25,31,32].The two studies, which compared satisfaction scores in KSS 2011 between MA and KA, did not report any statistically significant differences between the groups [24,25].
Five studies which used VAS reported satisfaction mean/median and standard deviation/interquartile range, except Blyth et al. [3].Among these five studies, three reported these outcomes after MA TKA [1,7,14] and two after KA TKA [8,32].The reported results indicate that the satisfaction scores after MA and KA TKA are equally high, displaying no relation to the chosen alignment technique.
TA B L E 1 Quality assessment criteria for randomized control trials (RCTs).

Quality assessment
Blyth et al. [2] Was the allocation sequence generated adequately?Yes Was the allocation of treatment adequately concealed?

Yes
Did researchers rule out any unintended exposure that might bias results?

No
Were participants analysed within the groups they were originally assigned to?

Yes
Was the length of follow-up different between the groups?

No
Were the outcome assessors blinded to the intervention or exposure status of participants?

Yes
Were the potential outcomes prespecified by the researchers?Are all pre-specified outcomes reported?

Yes
If attrition was a concern, were missing data handled appropriately?

Yes
Were outcomes assessed using valid and reliable measures across all study participants?

Yes
Judgement on the risk of bias?Low risk Note: Assessed using AHRQ design-specific scale.
| 3 of 10 Additionally, Khuangsirikul et al. [17] evaluated patient satisfaction after MA TKA by using a selfadministered patient satisfaction score.The overall satisfaction rate was almost 100%.Lastly, Koh et al. [18] reported patient satisfaction levels on a Likert-type scale adapted from the North American Spine Society Questionnaire.It showed 97.8% satisfied patients after MA TKA and just 90.3% after KA TKA.The findings did not, however, qualify as a statistically significant difference.

DISCUSSION
The most important findings of the present review were that both MA and KA TKA led to high postoperative patient satisfaction levels and that although the heterogeneity in used assessment tools was quite high, no statistically significant difference in patient satisfaction when comparing KA with MA TKA was observed.The general idea, in the current available literature mentions satisfaction rates from 80% to 100% after TKA procedures.However, the number of systematic reviews and/or meta-analyses focusing on comparing satisfaction scores between alignments and providing specific findings is rather low.The vast majority of studies are focused on reporting outcomes through compounded functional scores, which contain satisfaction subcomponents, but to a lesser extent, and more    Nonetheless, there are certain significant limitations to this systematic review.Firstly, the quality of the included studies is moderately low, as most of them are level III and IV studies.This review unrestricted KA to maintain homogeneity between groups.This may compromise the assessment of satisfaction for all types of KA TKA (restricted/inverse), which may impact the overall patient satisfaction.The comparison of patient satisfaction between two alignments was made for different implants due to heterogeneity in the published literature.Therefore, it was impossible to control confounding factors like differences in implant and post-operative rehabilitation.Furthermore, the reporting of satisfaction after TKA was highly variable in all studies, regardless to alignment, multiple scores and methodologies being used for patient satisfaction assessment.Therefore, performing a meta-analysis of the data for more concrete findings was not possible.Moreover, this review included studies from different cultural backgrounds.A previously published report indicated that cultural differences in the healthcare system might influence patient-reported satisfaction [14].This might also impact the comparative measures of satisfaction between all groups.However, considering the aim of the review, it was determined that it would be useful to evaluate the complete body of evidence published in the selected period, rather than to include only one particular geographic area.Nevertheless, further high quality level studies are required to more accurately and clearly assess and compare postoperative patient satisfaction between MA and KA TKA.Therefore, future efforts should be made to unify the reporting and assessing postoperative patient satisfaction methods after TKA through the use of dedicated and validated instruments.The validation of patient-centred instruments to measure satisfaction after TKA would not only improve the quality and assessment of satisfaction but also facilitate the comparison between alignments.
However, for this purpose, clinical studies need to include detailed information on knee phenotypes as it can be expected that some phenotypes are better off with different alignment philosophies and some are not [10,21,26,27].

CONCLUSION
Both mechanically aligned TKA, as well as kinematically aligned TKA led to high rates of postoperative patient satisfaction, but with no statistically significant differences between them.

F I G U R E 1
Flowchart of the study selection process according to the PRISMA 2020 statement: An updated guideline for reporting systematic reviews.| 5 of 10 TA B L E 2 Quality assessment criteria for nonrandomized control trials (RCTs).Is it clear in the study what is the 'cause' and what is the 'effect'?The Joanna Briggs Institute Critical Appraisal Tools for Use in JBI Systematic Reviews.
Note:TA B L E 3 Quality assessment criteria for Cohort study.Note: The Newcastle-Ottawa scale.TA B L E 4 Quality assessment criteria for case series.Note: Quality Assessment Tool for Case Series Studies.
Overview of selected studies.Overview of used instruments for satisfaction assessment.