Introduction
In the last decades, Total Knee Arthroplasty (TKA) has demonstrated to be a successful surgical procedure and the total number of implants has grown due to the increasing life expectancy. A TKA aims to restore the knee function, remove pain symptoms, and return to normal activity for the patient.
Different techniques have been proposed to improve surgical outcomes [1]. It has been shown that a mechanically aligned (MA) TKA improves the quality of life of patients with end-stage knee osteoarthritis (OA) [2].
The mechanical alignment technique for TKAs can be considered as a compromise. This type of implants aims to create a “biomechanically friendly prosthetic knee” by straightening the leg
and obtaining a joint line perpendicular to the mechanical axis of the lower limb [3] (Figure 1). If compared with total hip arthroplasty, a mechanically aligned TKA provides inferior functional outcomes and a relatively high prevalence of residual symptoms.
Clinical outcomes of MA-TKA are generally good but international arthroplasty registries in the United Kingdom, Canada, and New Zealand have shown that 20%-25% of patients are not fully satisfied [4-5-6]. Part of the responsibility could be due to the prosthesis alignment. In the general population, 98% of normal limbs do not have a neutral mechanical axis and 76% of them have a deviation greater than 3° of varus/valgus [7]. A recent study, using weight-bearing radiographs, showed that 32% of men and 17% of women had constitutional varus knees with a mechanical axis
Abstract
Introduction: This scoping review aims to analyze history, philosophy, surgical technique, and results of Kinematic Alignment (KA) in total knee arthroplasty (TKA). KA co-aligns the axes and joint lines of the components with the three «kinematic» axes and joint lines of the arthritic or native knee without placing restrictions on the pre-operative deformity and post-pre-operative correction.
Methods: A scoping review of the existing literature utilizing PubMed was performed in march 2020. 44 studies published in peer-reviewed journals over the last ten years in English were reviewed.
Results: The growing interest in KA is confirmed by the presence of several studies comparing MA and KA techniques reported in the literature. Many reviews and meta-analysis showed that the functional outcomes and flexion range of motion of the KA technique were similar or even better than ones of the mechanically aligned MA implants.
Conclusions: The KA TKA is an effective alternative method to MA TKA, striving to increase patients satisfaction after TKA. Multicenter RCTs with longer follow up and larger sample studies are needed to clarify its longevity and results.
Level of evidence: V.
Keywords: Kinematic alignment; Knee; Mechanical alignment; Outcome; Total knee arthroplasty.
Kinematic Alignment technique for Total Knee
Arthroplasty: a scoping review
Filippo Calanna
1, Riccardo Compagnoni
1,2, Paolo Ferrua
1,
Matteo Lo Duca
1, Pietro Randelli
1,21) Laboratory of Applied Biomechanics, Department of Biomedical Sciences for Health, Università degli Studi di Milano, Via Mangiagalli 31, 20133 Milan, Italy; 2) 1° Clinica Ortopedica, ASST Centro Specialistico Ortopedico Traumatologico Gaetano Pini-CTO, Piazza Cardinal Ferrari 1, 20122 Milan, Italy.
Corresponding author: Riccardo Compagnoni - Via Pini,3 20122 Milano - [email protected]
Archivesof MedicineAnd surgery ofthe universityof Mil An
Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
greater than 3° [8].
In 2006, Howell et al introduced the concept of Kinematic Alignment (KA) in TKA intending to reduce the prevalence of unexplained knee pain, stiffness and instability, improve knee kinematic, contact forces and the rate of recovery [9-10-11]. The KA technique could be considered as a resurfacing of the tibiofemoral joint that aims to restore the pre-arthritic articular characteristics of the bones and soft tissues. The result is, therefore, a prosthetic joint as similar as possible to the native one both in functional and mechanical characteristics. To obtain this result the mechanical and anatomical axis must be preserved as native [12].
The idea of a KA TKA was firstly proposed by the pioneering work of Hungerford, Kenna, and Krakow [13-14]. They invented the porous-coated anatomic (PCA) total knee system to reconstruct normal knee kinematics by performing the minimal articular surface replacement. KA attempts to replicate the kinematics of the knee by respecting the 3D anatomy of the tibiofemoral joint line (TJFL) and aligning the implants with the kinematic axis of the knee around which the tibia moves on the femur.
According to Howell et al [12] three kinematics axes can be identified: first, the transverse axis in the femur located in the center of a circle inscribed in the femoral condyles, around which the tibia flexes and extends, [15]; second, the transverse axis in the femur parallel to the patella axis and to the first transverse femoral axis, around which the patella flexes and extends [16]; and third, the longitudinal axis in the tibia lying perpendicular to the previous axes, around which the tibia internally and externally rotates on the femur [17] (Figure 2). Following these premises, KA is not considered an adjustment of the MA technique but a new surgical technique with nothing in common with the MA alignment except the sagittal positioning of the femoral component.
KA TKA has three main assumptions that have to be considered; firstly, the bone wear is predictable in the osteoarthritic knee with a varus-valgus deformity. The distal femoral cartilage wear to
bone averages 1.9 mm while the posterior condyle wear is negligible. In the varus osteoarthritic knee, cartilage wear is generally confined to the distal medial condyle, compared to the valgus knee in which the worn part is more frequently located in the distal lateral condyle [18]; secondly, the asymmetry between the radii of the medial and lateral femoral condyles in varus and valgus knees with end-stage osteoarthritis is about 0.2 mm, which is small enough to be considered clinically unimportant when aligning a total knee prosthesis [19]; third, the varus-valgus and internal-external rotational laxities of the knee are greater at 90° than at 0° of flexion, creating a tight rectangular space when the knee is in extension and slack trapezoidal space, with more laxity laterally than medially, when the knee is in flexion [20].
KA technique can be performed using surgical navigation, patient-specific instrumentation, robotics but also with standard instrumentation [21]. Considering the growing interest in Kinematically aligned TKA in the last years [22-23-24-25]. The study aims to describe the KA surgical technique, showing the main results and limitations, performing a scoping review of current literature.
Surgical Technique
According to Howell et al, the supine position and the parapatellar median approach are used [21]. The surgical technique begins by using an offset caliper to measure the anterior-posterior offset of the anterior tibia from the distal medial femur at 90° of flexion of the knee.
To perform the femoral cuts the prediction of cartilage wear is mandatory. Once the knee is fully exposed the locations of cartilage wear are assessed on the distal femur. A ring curette is used to remove every partially worn cartilage to bone. The flexion-extension position of the femoral component is set by using a rod 8-10 cm long through a hole drilled parallel to the anterior surface of the distal femur and perpendicular to the distal articular surface, positioning the starting hole midway between the top of the intercondylar notch
and the anterior cortex of the femur. A disposable distal referencing guide that compensates for 2 mm of cartilage wear on the worn condyle is used to set the varus-valgus rotation and proximal-distal translation of the femoral component. Furthermore, a posterior referencing guide is placed in contact with the posterior femoral condyles at 90° degrees of flexion. The anterior-posterior translation and the internal-external rotation are set by placing the posterior referencing guide at 0° of rotation. The positioning of the posterior referencing guide rarely requires correction because the posterior femoral condyle worn is irrelevant. Both the distal and posterior femoral cuts must be equal to the condylar thickness of the femoral component after compensating for cartilage wear and kerf [12-26]. For the placement of the tibial component, an extramedullary tibial guide is used. The varus-valgus tibial cut is set by lateral translation of the slider at the ankle until the saw slot is parallel to the tibial articular surface. Later, to perform the flexion-extension tibial cut is mandatory to place the angel wing parallel to the slope of the medial joint line. The proximal-distal tibial cut is set by adjusting the level of the saw slot until the 8 mm tibial resection gauge is in contact with the center of the base of the tibial spine in an area with intact cartilage [26-27].
The knee is flexed to 90°. The tightest fitting spacer block is inserted between the femur and the tibia. The tibia is re-cut using the 2-mm re-cut guide when the flexion space is too tight for the tightest spacer. The spacer is internally and externally rotated with the knee in 90° of flexion and the relative tightness between the medial and the lateral compartments is assessed. It must be confirmed that the spacer fits tighter in the medial compartment, fits looser in the lateral compartment, and pivots about the medial compartment, which restores a trapezoidal flexion space like the native knee [28]. Afterward, the knee is placed in full extension. The spacer is re-inserted. The soft tissues are retracted and the varus-valgus laxity between the femoral and tibial resection is checked. It must be confirmed that the varus-valgus laxity is negligible and that the difference in the gaps between the medial
and lateral compartments is within 0/0.5 mm. If the lateral compartment is 2 mm tighter, the tibia must be re-cut using the 2° valgus re-cut guide. Otherwise is medial compartment is 2 mm tighter, the tibia must be re-cut using the 2° varus re-cut guide.
The internal-external rotation of the tibial component is set regarding the major axis of the lateral tibial condyle or by using a so-called “kinematic tibial baseplate method”: an elliptically shaped boundary of the articular surface of the lateral tibial condyle is defined and the major axis is drawn. Two holes are drilled into the medial articular surface, parallel to the major axis of the lateral tibial condyle. Then, a line parallel to the drill holes is drawn to implant the score marks of tibial baseplate parallel to these lines, no matter of tibial plateau model.
Anterior-posterior slope and thickness of the tibial component are adjusted until the offset of the anterior tibia from the distal medial femoral condyle with the trial components matches the one at the time of exposure.
There are some particular considerations concerning the knee with an insufficient posterior cruciate ligament when performing kinematically aligned TKA. Managing a chronic posterior
cruciate ligament tear or insufficiency, three corrective actions can be performed.
The first method is to use a narrow version of a 2 mm larger posterior stabilized femoral component if the implant design allows it. The femoral component is cemented, filling the 2 mm gap between the posterior resection and the femoral component. This adjustment allows to maintain the level of the distal joint line and to compensate for the flexion gap. Otherwise, it is possible to use an ultra congruent liner, 2 mm thicker, overall in case of PCL insufficiency.
Results and Literature
A scoping review of the existing literature utilizing PubMed was performed in march 2020. 44 studies published in peer-reviewed journals over the last ten years in English were reviewed.
Many reviews and meta-analysis showed that the functional outcomes and flexion range of motion of the KA technique were better than those of the MA implants [22-23-24-25].
Yanghong Li et al analyzing six trials, involving 561 patients, found that the KA group achieved better performance in Womac score, knee function score, Oxford knee score, and range of flexion. Furthermore, they showed that the KA group had a shorter time of operation and a longer walk distance before discharge compared with the MA group.
Takahashi et al, analyzing 5 randomized controlled trials (RCT), demonstrated that KA components,
compared to MA, had more femoral valgus, tibial varus, and tibial slope.
Courtney et al highlighted that the cumulative survivorship at mean follow up of 37.9 months was 97.4% in KA TKA and the most common reasons for revision were patella-tracking problems in 8 patients (1.2%). No difference in the complication rate between the 229 kinematic and the 229 conventional TKA patients was found.
Xu et al analyzed 7 RCT studies and 1 retrospective observational study and showed that the functional outcomes and flexion range of motion were better in the KA technique. However, no significant differences between KA and MA groups regarding radiological outcomes, complications, and re-operation rates were found. Concerning the radiological findings, this study is in contrast with what Takahashi et al found. Probably this may be due to differences in the method of quantitative analysis because Takahashi analyzed both Dosset studies [2-29], while Xu included only the most complete one.
The improved functional outcomes reached with KA TKA may be related to native limb alignment and tibiofemoral articular restoration, without performing any ligament release. KA TKA seems to have better patient satisfaction and flexion than MA TKA because probably it does not change the angle and level of the joint line from native 16. KA has many short-term benefits but some concerns remain about the long term implant survivorship, particularly in the case of the varus or valgus outlier limb alignment [30-31].
Figure 2 - The Three Kinematic Axes of the Knee; the extension axis of the tibia is the green line, the flexion-extension axis of the patella is the magenta line and the internal-external axis of the tibia is the yellow line [28].
Howell et al evaluated 222 knees treated with KA TKA using patient-specific instrumentation (PSI) without any restrictions on the degree of preoperative varus, valgus, and flexion deformity [32] to determinate implant survivorship, the yearly rate of revision and function measured by OKS and WOMAC scores at 10 years. Furthermore, they wanted to deny the idea that the positioning of the tibial component, in varus or valgus outlier range, affects the implant survival and function. They found that the implant survival was 97.4% at 10 years and the yearly revision rate was 0.3%. The patients grouped in the varus and valgus outlier compared to those grouped in-range showed similar results.
One of the main goals of the KA is to restore the native left to right symmetry, the pre-arthritic alignment of the limb, and the joint line [26-33-34]. Moreover, measuring the difference in alignment of the limb and joint lines from desired targets is an important step to evaluate the success of the surgical technique.
Nedopil et al, evaluating 102 patients with KA TKA in one limb with post-operative scanograms, showed that caliper KA restored native left to right symmetry of the Hip-Knee-Ankle (HKA) angle, Distal Lateral Femoral Angle (DLFA) and Proximal Medial Tibial Angle (PMTA) within 0°+/- 3° in nearly all patients [35].
McClelland et al made a review of gait analysis following TKA and showed that the patients walked with a reduced range of motion and significant kinematic discrepancies compared to the normal controls [36]. Probably, this may be one of the main reasons why up to 20% of TKA patients are dissatisfied [6].
Blakeney et al, evaluating 18 KA TKA and 18 MA TKA with 3D knee kinematics analysis in a retrospective case-control study, showed that kinematic alignment group had no significant kinematics differences compared to healthy knees in sagittal plane range of motion, maximum flexion, abduction-adduction curves or knee external tibial rotation. In contrast, the mechanical alignment group demonstrated several significant differences compared to the healthy group [37].
There are some limitations to the KA TKA technique. First of all, considering that kinematic alignment has not been extensively performed worldwide, there could be some varus or valgus deformities that KA cannot correct. Secondly, to validate the short-term follow-up, results, and functional outcomes [22-23-24-25], long-term and larger sample studies are needed. Only one article showed long-term results [32] but it is published by a designer surgeon’s experience, which normally requires independent confirmation. This may be because designer surgeons tend to report lower failure rates and higher function than non-designer surgeons [38]. Thirdly, practitioners of MA have some concerns about the varus alignment of the tibial component, causing either polyethylene wear or catastrophic varus collapse of the tibia especially in obese patients [39-40]. However several authors reported a negligible incidence of varus failure at early and midterm follows up [2-29-3336]. These findings might be explained by Shelton et al, that showed as intra-operative forces in the medial and lateral tibial compartments after KA TKA without ligament release are close to the native knee and 3-6 times lower than after MA TKA with ligament release [41]. Niki et al showed that KA is a promising option especially for patients with large varus coronal bowing of the tibia because the adduction moment is reduced compared to MA TKA [42]. Moreover, several authors have shown that KA sets the joint line of the knee parallel to the floor both during single-leg and double-single-leg stance [36-43-44] that could be a reason for the low early and midterm implant failure rate.
Conclusion
Kinematic alignment is a resurfacing of the tibiofemoral joint aiming at restoring its pre-arthritic articular surfaces, soft tissue laxity, and native knee and limb alignment. The kinematically aligned TKA is an effective alternative method to mechanically aligned TKA, striving to increase patients satisfaction after TKA. Multicenter RCTs with longer follow up and larger sample studies
are needed to clarify its longevity and results. Declaration of interests: None declared. References
1. Rivière C, Lazic S, Boughton O, Wiart Y, Vïllet L, Cobb J. (2018) Current concepts for aligning knee implants: patient-specific or systematic? EFORT Open Rev. 3(1):1-6.
2. Dossett HG, Swartz GJ, Estrada NA, LeFevre GW, Kwasman BG. (2012) Kinematically versus mechanically aligned total knee arthroplasty. Orthopedics. 35(2):e160-9.
3. Rivière C, Iranpour F, Auvinet E, Howell S, Vendittoli PA, Cobb J, Parratte S. (2017) Alignment options for total knee arthroplasty: A systematic review. Orthop Traumatol Surg Res. 103(7):1047-1056.
4. New Zealand Orthopaedi Association. (2009) The New Zealand Joint Registry Ten-year Report: January 1999 to December 2008.
5. Baker PN, van der Meulen JH, Lewsey J, Gregg PJ (2007) National Joint Registry for England and Wales. The role of pain and function in determining patient satisfaction after total knee replacement. Data from the National Joint Registry for England and Wales. J Bone Joint Surg Br. 89(7):893-900.
6. Bourne RB, Chesworth BM, Davis AM, Mahomed NN, Charron KD. (2010) Patient satisfaction after total knee arthroplasty: who is satisfied and who is not? Clin Orthop Relat Res. 468(1):57-63.
7. Eckhoff DG, Bach JM, Spitzer VM, Reinig KD, Bagur MM, Baldini TH, Flannery NM. (2005) Three-dimensional mechanics, kinematics, and morphology of the knee viewed in virtual reality. J Bone Joint Surg Am. 87 Suppl 2:71-80.
8. Bellemans J, Colyn W, Vandenneucker H, Victor J. (2012) The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res. 470(1):45-53.
9. Howell SM, Kuznik K, Hull ML, Siston RA. (2008) Results of an initial experience with custom-fit positioning total knee arthroplasty in a series of 48 patients. Orthopedics. 31(9):857-63.
10. Howell SM, Hodapp EE, Kuznik K, Hull ML.
(2009) In vivo adduction and reverse axial rotation (external) of the tibial component can be minimized. Orthopedics. 32(5):319.
11. Howell SM, Rogers SL. (2009) Method for quantifying patient expectations and early recovery after total knee arthroplasty. Orthopedics. 32(12):884. 12. Howell SM, Hull ML. (2011) Kinamatic alignment in total knee arthroplasty. In: Norman Scott W. Insall and Scott Surgery of the knee (5th edition). London: Churcill Livingston, 1255-1269
13. Hungerford DS, Kenna RV, Krackow KA. (1982) The porous-coated anatomic total knee. Orthop Clin North Am. 13(1):103-22.
14. Nam D, Lin KM, Howell SM, Hull ML. (2014) Femoral bone and cartilage wear is predictable at 0° and 90° in the osteoarthritic knee treated with total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 22(12):2975-81.
15. Schiraldi M, Bonzanini G, Chirillo D, de Tullio V. (2016) Mechanical and kinematic alignment in total knee arthroplasty. Ann Transl Med. 4(7):130.
16. Howell SM, Howell SJ, Kuznik KT, Cohen J, Hull ML. (2013) Does a kinematically aligned total knee arthroplasty restore function without failure regardless of alignment category? Clin Orthop Relat Res. 471(3):1000-7.
17. Pickering S, Armstrong D. (2012) Focus on alignment in total knee replacement. J Bone Joint Surg. 18. Howell SM, Howell SJ, Hull ML. (2010) Assessment of the radii of the medial and lateral femoral condyles in varus and valgus knees with osteoarthritis. J Bone Joint Surg Am. 92(1):98-104.
19. Joshua D. Roth, Stephen M. Howell, MD, Maury L. Hull, PhD. (2014) Varus-valgus Laxity Of The Normal Knee At 0° And 90° Flexion: Implications In Gap-balancing TKA, ORS Annual Meeting
20. Roth JD, Howell SM, Hull ML. (2015) Native Knee Laxities at 0°, 45°, and 90° of Flexion and Their Relationship to the Goal of the Gap-Balancing Alignment Method of Total Knee Arthroplasty. J Bone Joint Surg Am. 97(20):1678-84.
21. Howell SM, Hull ML. (2014) Kinematic alignment in total knee arthroplasty. Definition, history, principle, surgical technique, and result of an alignment option for TKA. Arthropaedia 1:44-53.
22. Xu J, Cao JY, Luong JK, Negus JJ. (2019) Kinematic versus mechanical alignment for primary total knee
replacement: A systematic review and meta-analysis. J Orthop. 16(2):151-157.
23. Li Y, Wang S, Wang Y, Yang M. (2018) Does Kinematic Alignment Improve Short-Term Functional Outcomes after Total Knee Arthroplasty Compared with Mechanical Alignment? A Systematic Review and Meta-analysis. J Knee Surg. 31(1):78-86.
24. Takahashi T, Ansari J, Pandit HG. (2018) Kinematically Aligned Total Knee Arthroplasty or Mechanically Aligned Total Knee Arthroplasty. J Knee Surg. 31(10):999-1006.
25. Courtney PM, Lee GC. (2017) Early Outcomes of Kinematic Alignment in Primary Total Knee Arthroplasty: A Meta-Analysis of the Literature. J Arthroplasty. 32(6):2028-2032.e1.
26. Howell SM, Papadopoulos S, Kuznik KT, Hull ML. (2013) Accurate alignment and high function after kinematically aligned TKA performed with generic instruments. Knee Surg Sports Traumatol Arthrosc. 21(10):2271-80.
27. Nedopil AJ, Howell SM, Hull ML. (2016) Does Malrotation of the Tibial and Femoral Components Compromise Function in Kinematically Aligned Total Knee Arthroplasty? Orthop Clin North Am. 47(1):41-50.
28. Howell SM. (2019) Calipered Kinematically Aligned Total Knee Arthroplasty: An Accurate Technique That Improves Patient Outcomes and Implant Survival. Orthopedics. 42(3):126-135.
29. Courtney PM, Lee GC. (2017) Early Outcomes of Kinematic Alignment in Primary Total Knee Arthroplasty: A Meta-Analysis of the Literature. J Arthroplasty. 32(6):2028-2032.e1.
30. Bonner TJ, Eardley WG, Patterson P, Gregg PJ. (2019) The effect of post-operative mechanical axis alignment on the survival of primary total knee replacements after a follow-up of 15 years. J Bone Joint Surg Br. 93(9):1217-22.
31. Parratte S, Pagnano MW, Trousdale RT, Berry DJ. (2010) Effect of postoperative mechanical axis alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg Am. 92(12):2143-9.
32. Howell SM, Shelton TJ, Hull ML. (2018) Implant Survival and Function Ten Years After Kinematically Aligned Total Knee Arthroplasty. J Arthroplasty. 33(12):3678-3684.
33. Calliess T, Bauer K, Stukenborg-Colsman C, Windhagen H, Budde S, Ettinger M. (2017) PSI kinematic versus non-PSI mechanical alignment in total knee arthroplasty: a prospective, randomized study. Knee Surg Sports Traumatol Arthrosc. 25(6):1743-1748.
34. Howell SM, Papadopoulos S, Kuznik K, Ghaly LR, Hull ML. (2015) Does varus alignment adversely affect implant survival and function six years after kinematically aligned total knee arthroplasty? Int Orthop. 39(11):2117-24.
35. Nedopil AJ, Singh AK, Howell SM, Hull ML. (2018) Does Calipered Kinematically Aligned TKA Restore Native Left to Right Symmetry of the Lower Limb and Improve Function? J Arthroplasty. 33(2):398-406.
36. McClelland JA, Webster KE, Feller JA. (2007) Gait analysis of patients following total knee replacement: a systematic review. Knee. 14(4):253-63.
37. Blakeney W, Clément J, Desmeules F, Hagemeister N, Rivière C, Vendittoli PA. (2018) Kinematic alignment in total knee arthroplasty better reproduces normal gait than mechanical alignment. Knee Surg Sports Traumatol Arthrosc.
38. Labek G, Neumann D, Agreiter M, Schuh R, Böhler N. (2011) Impact of implant developers on published outcome and reproducibility of cohort-based clinical studies in arthroplasty. J Bone Joint Surg Am. 93 Suppl 3:55-61.
39. Baier C, Wolfsteiner J, Otto F, Zeman F, Renkawitz T, Springorum HR, Maderbacher G, Grifka J. (2017) Clinical, radiological and survivorship results after ten years comparing navigated and conventional total knee arthroplasty: a matched-pair analysis. Int Orthop. 41(10):2037-2044.
40. Fehring TK, Fehring KA, Anderson LA, Otero JE, Springer BD. (2017) Catastrophic Varus Collapse of the Tibia in Obese Total Knee Arthroplasty. J Arthroplasty. 32(5):1625-1629.
41. Shelton TJ, Nedopil AJ, Howell SM, Hull ML. (2017) Do varus or valgus outliers have higher forces in the medial or lateral compartments than those which are in-range after a kinematically aligned total knee arthroplasty? Bone Joint J. 99-B(10):1319-1328.
42. Niki Y, Nagura T, Nagai K, Kobayashi S, Harato K. (2018) Kinematically aligned total knee arthroplasty reduces knee adduction moment more than
mechanically aligned total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 26(6):1629-1635.
43. Hutt J, Massé V, Lavigne M, Vendittoli PA. (2016) Functional joint line obliquity after kinematic total knee arthroplasty. Int Orthop. 40(1):29-34.
44. Ji HM, Han J, Jin DS, Seo H, Won YY. (2012) Kinematically aligned TKA can align knee joint line to horizontal. Knee Surg Sports Traumatol Arthrosc. 4(8):2436-41.
![Figure 2 - The Three Kinematic Axes of the Knee; the flexion-extension axis of the tibia is the green line, the flexion- flexion-extension axis of the patella is the magenta line and the internal-external axis of the tibia is the yellow line [28].](https://thumb-eu.123doks.com/thumbv2/123dokorg/8420475.138177/4.892.99.795.69.337/figure-kinematic-flexion-extension-flexion-extension-internal-external.webp)
