Kinematic alignment versus mechanical alignment in primary total knee arthroplasty: an updated meta-analysis of randomized controlled trials

Liu et al. Journal of Orthopaedic Surgery and Research https://doi.org/10.1186/s13018-022-03097-2 (2022) 17:201 RESEARCH ARTICLE Open Access Kinematic alignment versus mechanical alignment in primary total knee arthroplasty: an updated meta‑analysis of randomized controlled trials Binfeng Liu1,2,3, Chengyao Feng1,3 and Chao Tu1,3* Abstract Background: The purpose of this study was to perform an updated meta-analysis to compare the outcomes of kinematic alignment (KA) and mechanical alignment (MA) in patients undergoing total knee arthroplasty. Methods: PubMed, EMBASE, Web of Science, Google Scholar, and the Cochrane Library were systematically searched. Eligible randomized controlled trials regarding the clinical outcomes of patients undergoing total knee arthroplasty with KA and MA were included for the analysis. Results: A total of 1112 participants were included in this study, including 559 participants with KA and 553 patients with MA. This study revealed that the Western Ontario and McMaster Universities Osteoarthritis Index, Knee Society Score (knee and combined), and knee flexion range were better in the patients with kinematic alignment than in the mechanical alignment. In terms of radiological results, the femoral knee angle, mechanical medial proximal tibial angle, and joint line orientation angle were significantly different between the two techniques. Perioperatively, the walk distance before discharge was longer in the KA group than in the MA group. In contrast, other functional outcomes, radiological results, perioperative outcomes, and postoperative complication rates were similar in both the kinematic and mechanical alignment groups. Conclusions: The KA technique achieved better functional outcomes than the mechanical technique in terms of KSS (knee and combined), WOMAC scores, and knee flexion range. PROSPERO trial registration number CRD42021264519. Date registration: July 28, 2021. Keywords: Kinematic alignment, Mechanical alignment, Total knee arthroplasty, Total knee replacement, Metaanalysis Background Knee osteoarthritis (OA) is one of the most common degenerative joint diseases that impose a substantial socioeconomic burden on society and health care systems *Correspondence: 1 Department of Orthopaedics, The Second Xiangya Hospital, Central South University, Changsha 410011, Hunan, China Full list of author information is available at the end of the article [1]. The incidence of knee OA has significantly increased in recent decades due to the continuous increase in obesity and the aging population in the world [2]. Total knee arthroplasty (TKA) is the most effective treatment for end-stage knee OA, which can significantly alleviate pain and improve quality of life. Meanwhile, new technologies have further improved the clinical efficacy and safety of TKA, including novel concept implants, novel extramedullary guides, and computer-assisted surgery [3–5]. © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Liu et al. Journal of Orthopaedic Surgery and Research (2022) 17:201 Page 2 of 18 Cristian Aletto et al. revealed that computer-assisted TKA ensures good functional outcomes [3]. As a result, the number of patients undergoing TKA has steadily increased each year as these medical technologies continue to advance [6]. Previous studies claim that, by 2030, 3.8 million people will have undergone TKA each year [7]. The accurate restoration of knee alignment is essential to the success of TKA, which is vital for the recovery of the patient’s postoperative function and implant survival [8]. Currently, the alignment methods of the lower limbs used in TKA mainly include kinematic alignment (KA) and mechanical alignment (MA). MA is the traditional alignment method in TKA and has been used for more than 30 years. MA aims to create a neutral hip–knee–ankle angle (HKA) to restore the overall limb alignment to a neutral position [9]. From a mechanical perspective, MA can optimize load distribution in patients undergoing TKA and prolong prosthesis survival by reducing polyethylene wear and component loosening [10]. Previous studies have also reported that the MA technique can improve patient satisfaction and relieve pain [11]. For instance, navigation-assisted TKA can effectively replicate the neutral MA of the knee, thereby reducing alignment outliers [12]. However, it was reported that up to 25% of patients undergoing MA in TKA still have unsatisfactory outcomes [13, 14]. This may be due to abnormal touch kinematics caused by MA changing the limb axis of the knee, thus resulting in substandard patient satisfaction [15]. In contrast, the KA technique aims to restore the alignment and kinematics of the TKA implant, thus ensuring its match to the pre-osteoarthritis anatomy. Due to the disadvantages of MA, the clinical application of KA in TKA has become increasingly popular since Howell et al. introduced it in 2006 [16]. The KA technique was the preferential method to place the knee implant in a natural anatomical position, compensate for the tibia and femur rotation changes, and preserve the original soft-tissue envelope. It reduces the loosening of soft tissues and ligaments around the knee and achieves better physiological kinematics of the knee [17, 18]. To date, accumulating evidence has demonstrated that KA in TKA will also help patients achieve better functional outcomes and alleviate postoperative pain [13, 19, 20]. However, several limitations remain in this technique: Restoring natural varus can increase the contact stress between the tibiofemoral and patellofemoral joints, which may lead to an increased risk of early implant dysfunction and failure. Currently, no systematic evidence exists regarding whether the KA technique can attain similar or greater clinical outcomes than the classical MA technique in TKA. Although several randomized control trials (RCTs) and meta-analyses compared the clinical outcomes of KA and MA in T (...truncated)