Coronal alignment in total knee arthroplasty: a review

Journal of Orthopaedics and Traumatology Matassi et al. Journal of Orthopaedics and Traumatology (2023) 24:24 https://doi.org/10.1186/s10195-023-00702-w Open Access REVIEW ARTICLE Coronal alignment in total knee arthroplasty: a review F. Matassi1, F. Pettinari1*, F. Frasconà1, M. Innocenti1 and R. Civinini1 Abstract Total knee arthroplasty (TKA) alignment has recently become a hot topic in the orthopedics arthroplasty literature. Coronal plane alignment especially has gained increasing attention since it is considered a cornerstone for improved clinical outcomes. Various alignment techniques have been described, but none proved to be optimal and there is a lack of general consensus on which alignment provides best results. The aim of this narrative review is to describe the different types of coronal alignments in TKA, correctly defining the main principles and terms. Keywords Total knee arthroplasty, TKA, Coronal alignment, Knee alignment, Robotic surgery, Personalized alignment Introduction Coronal alignment in total knee arthroplasty (TKA) has gained increasing attention since considered a cornerstone to improve clinical outcomes. To overcome the problem of patient dissatisfaction and perception of “unnatural knee” after TKA, different alignment options and philosophies have been described with the purpose to better reproduce knee anatomy and kinematics. Nowadays different principles and surgical techniques have been described that can be classified in three main categories [1] (Fig.1, Table 1): (1) Systematic alignment, which includes mechanical alignment (MA) [2–5] and anatomic alignment (AA) [7] with the goals to restore neutral alignment with hip–knee–ankle axis (HKA) of 180° for all patients independently from preoperative alignment; (2) Patient-specific alignment such as kinematic alignment (KA) [13] that aims to maintain the native limb alignment and joint line inclination; *Correspondence: F. Pettinari 1 Orthopedic Clinic, AOU Careggi, University of Florence, Florence, Italy (3) Hybrid alignment such as restricted kinematic alignment (rKA) [24, 25], inverse kinematic alignment (iKA) [23–25], adjusted mechanical alignment (aMA) [28–32], and functional alignment (FA) [35, 36] with the aim to restore the coronal alignment within an HKA angle safe zone of 177° to 183°. To date there is no consensus on the optimal coronal alignment techniques, and further studies with larger samples and longer follow-ups are necessary to prove which technique has more benefits than others. However, beyond clinical studies what is unclear is a correct definition of terms in the plethora of names used for defining each type of alignment. The aim of this narrative review is to clarify the different types of coronal alignment in TKA with correct definition of the main principles. We believe this narrative will help readers and researchers have a more universal definition of terms facilitating comparable analysis and clinical studies. Mechanical alignment (MA) Principles Mechanical alignment in TKA was described by Ranawat and Insall in the 1970s and is the most commonly used in TKA with well-documented long-term results. The © The Author(s) 2023. 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/. Matassi et al. Journal of Orthopaedics and Traumatology (2023) 24:24 Page 2 of 8 Fig. 1 Various alignment techniques Table 1 Main key points in different coronal alignments philosophies Mechanical alignment (MA) Anatomic alignment (AA) Kinematic alignment (KA) Inverse kinematic alignment (iKA) Restricted kinematic alignment (iKA) Adjusted Functional mechanical alignment (FA) alignment (aMA) Distal femoral cuts 90° 93° Femoral resurfacing According to extension gap 90 ± 5° 90 ± 2° According to extension gap(± 3°) Proximal tibial cuts 90° 87° According to extension gap Tibial resurfacing restricted to 84° (varus) to 92° (valgus) 90 ± 5° 90° According to extension gap (± 3°) Femur external rotation to PCA 3° 0° Femoral resurfacing According to flexion gap According to flexion gap 3° According to flexion gap Overall alignment 0° (HKA) 0° Native alignment Slight undercorrection safe zone +6° varus to −3° valgus Slight undercorrection safe zone +6° varus to −3° valgus Slight undercorrection Slight undercorrection Ligament release Yes Yes No Minimal Minimal Minimal Minimal Type Systematic Systematic Patient specific Hybrid Hybrid Hybrid Hybrid principle of this type of alignment is to position both the femoral and tibial components perpendicular to the mechanical axis. This allows one to obtain, after proper ligament release, a hip–knee–ankle (HKA) angle of 180°. Neutral alignment guarantees symmetric balanced load distribution between the medial and lateral compartments that minimize wear and potential component loosening. This alignment introduced the “compromise of 3°” as the femoral component should be positioned with 3° of external rotation to balance flexion gaps with the extension gaps [2]. Clinical results The mechanical alignment has been considered the gold standard for decades, and many studies have reported satisfactory clinical outcomes and long-term survival of Matassi et al. Journal of Orthopaedics and Traumatology (2023) 24:24 Page 3 of 8 implants between 89% and 99% at 10 years and between 85% and 97% at 20 years of follow-up [2–4]. Clinical results [Oxford Knee Score (OKS), Western Ontario and McMaster University index (WOMAC), Knee Society Score (KSS), range of motion (ROM)] were considered excellent with improvement in all outcomes from preoperative to postoperative [5]. Preliminary studies have reported good clinical outcomes but with short-term follow-up. However, there is a lack of long-term data on implant survival that support the varus alignment of the tibial component [8, 9]. Criticisms However, recently many criticisms have been raised regarding this principle, with some studies showing that up to 20% of patients were dissatisfied after TKA. One of the reasons could be attributed to the fact that MA is a systematic alignment where all limbs are aligned to a neutral HKA axis independently of the preoperative a (...truncated)