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The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis
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Orthopaedics & Traumatology: Surgery & Research xxx (2017) xxx–xxx
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Original article
The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis C. Rivière a,∗ , F. Iranpour a , S. Harris a , E. Auvinet a , A. Aframian a , P. Chabrand b , J. Cobb a a b
Department of joint replacement, the MSK Lab, Charing Cross Campus, Laboratory Block, Fulham Palace Rd, W6 8RP London, UK Institut des sciences du mouvement, université Aix-Marseille, 171, avenue de Luminy, 13009 Marseille, France
a r t i c l e
i n f o
Article history: Received 28 January 2017 Accepted 23 June 2017 Keywords: Total Knee Arthroplasty Kinematic alignment Reproducibility Positioning Reliability Cylindrical axis
a b s t r a c t Introduction: Kinematic alignment (KA) technique is an alternative technique for positioning a TKA, which aims a patient-specific implant positioning in order to reproduce the pre-arthritic knee anatomy. Because reliability in implant positioning is of interest to obtain reproducible good functional results, our study tests the hypothesis that the medial and lateral distal and posterior positions of the planned and surgically implanted kinematically aligned femoral component are similar. Methods: Preoperative knee magnetic resonance imaging (MRI) and postoperative knee computed ® tomography (CT) of 13 patients implanted with a KA Persona TKA (Zimmer, Warsaw, USA) using ® manual instrumentation (kinematically-aligned TKA procedure pack , Zimmer Biomet, Warsaw, USA) were segmented to create 3D femoral models. The kinematic alignment position of the femoral component was planned on the 3D model created from the preoperative MRI. Differences in the positions of the planned and surgically implanted kinematically-aligned femoral component were determined with in-house analysis software. Results: The average differences between the medial and lateral distal and posterior positions of the planned and surgically implanted kinematically-aligned femoral component were inferior to 1 mm and no statistically significant. In terms of variability, 62% (8/13) of performed implants matched all four positions within 1.5 mm, and the maximum difference was 3 mm. Conclusion: In this small series, intraoperative kinematic positioning of the femoral component with the specific manual instrumentation closely matched the planned position, which suggests that this technique reliably aligned the flexion-extension axis of the femoral component to the cylindrical axis. Level of evidence: Level 3. © 2017 Elsevier Masson SAS. All rights reserved.
1. Introduction Knee osteoarthritis (OA) is a growing socio-economic burden because of the ageing population and the epidemic of obesity. It is projected that by 2030, patients younger than 65 years of age will make up the majority of patients undergoing knee arthroplasty in the USA, with up to one million performed annually [1]. For decades, a stable knee with a neutral mechanically axis lower limb alignment has been one of the primary goals of TKA because it was believed to be important for successful clinical outcomes and implant survivorship [1–3]. The joint line is made perpendicular to the neutral mechanical axis of the limb and the femoral component is expected to be frontally and axially aligned with the trans-epicondylar axis
∗ Corresponding author. E-mail address: [email protected] (C. Rivière).
(TEA), which then becomes the flexion-extension axis of the knee [4]. Mechanical alignment does not restore the patient-specific alignment (constitutional anatomy) but an average positioning of the prosthetic knee, which aims at reducing the adduction moment arm and distributes the load more evenly on the tibial compartments, thus potentially reducing instability, polyethylene wear and implant loosening. This average approach to alignment does not account for the variations in anatomy between patients [5]. For these reasons, the conventional MA technique has been recently challenged by a new alternative technique, namely kinematic alignment (KA), aiming at reproducing the constitutional tibiofemoral tridimensional alignment and knee laxity [6–14]. Kinematically-aligned TKA is a surgical technique that targets the restoration of the native alignment of the limb, and of the native orientation of the tibiofemoral joint line [15–20]. Kinematic alignment has gained interest because two randomized trials and a national multi-centre study showed that patients treated with kinematic
http://dx.doi.org/10.1016/j.otsr.2017.06.016 1877-0568/© 2017 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: Rivière C, et al. The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis. Orthop Traumatol Surg Res (2017), http://dx.doi.org/10.1016/j.otsr.2017.06.016
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ARTICLE IN PRESS C. Rivière et al. / Orthopaedics & Traumatology: Surgery & Research xxx (2017) xxx–xxx
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alignment reported significantly better pain relief, function, flexion, and a more normal feeling knee than patients treated with mechanical alignment [15,16,19], whereas two other randomized trials showed similar clinical outcomes between kinematic alignment and mechanical alignment [20,21]. Bone cuts in KA technique can be performed using manual instrumentation [13,22], patient specific instrumentation (PSI) [18], and navigation (CAS) [11] with each option having different advantages and drawbacks. Tibial implant rotational positioning with KA technique has been shown to be highly reproducible with the use of conventional instrumentation [22], but there is no data regarding the one for the femoral implant. Because implant-positioning reproducibility is important to reach reproducible good outcomes, our study aims at testing the hypothesis that the medial and lateral distal and posterior positions of the planned and surgically implanted kinematically-aligned femoral component are similar. 2. Methods Anonymised preoperative magnetic resonance imaging (MRI) scans and postoperative computer tomographic (CT) scans of ® 13 patients having received a kinematically-aligned TKA (Persona , Zimmer, Warsaw, USA) for end-stage tibiofemoral osteoarthritis (Ahlbäck > 2) were selected for study. TKA were implanted by using the specific manual instrumentation (kinematically-aligned TKA procedure pack, Zimmer Biomet, Warsaw, USA). Because the imaging studies and clinical data were anonymised, their use was not subject to approval by our institutional review board. Preoperative knee MRIs and postoperative knee CT-scans were segmented to create 3D femoral models. Bone and cartilage were segmented on the MRI while bone and implant were segmented on ® the CT-scan. A set of Persona femoral implants (Zimmer, Warsaw, USA) was laser scanned (C-track 780 3D laser scanner, Creaform, Quebec, Canada) to create 3D femoral implant models. In-house planning software was then used to simulate a kinematic alignment
of femoral implant model on the preoperative MRI, using the same femoral implant size as the one used intra-operatively. Femoral implant was positioned flush with healthy cartilage on the unworn tibiofemoral compartment, and 2-mm distal or posterior to the subchondral condylar bone when cartilage was worn out on the degenerated tibiofemoral compartment. Femoral implant models were also overlaid on the femoral CT model to replicate, in silico, the alignment of the implant on the postoperative bone. This enabled reproduction in the computer model the features of the implant lost due to CT metal artefacts, thus improving the shape accuracy of the femoral component (Fig. 1). The CT and MRI data were co-registered using Artec 3D software (Artec3D, Palo Alto, Ca, USA). A section of the femoral shaft unaffected by metal artefacts from the implants was used to register the preoperative MRI and postoperative CT 3D models to the same coordinate geometry (Fig. 2). The femoral shaft was chosen as it is an area unmodified by surgery. This technique confers precision to < 1 mm error (unpublished data). The laser scanned overlaid implant was maintained in space while the registered preoperative MRI based model, with femoral implant planned on it, was substituted for the CT-based model, thus keeping the same implant to bone alignment on the preoperative images as was derived from the postoperative data. In-house software enabled a comparison of prosthetic articular surfaces between the planned and performed femoral implant (Fig. 2). The software made measurements by revolving around the cylindrical axis, which was identified by selecting multiple points on the flexion facets of the medial and lateral femoral condyles, that is the femoral articular surfaces contacting the tibia when knee flexes. Spheres were automatically fitted to the selected points, and a line drawn between their centres represented the cylindrical axis. Because KA technique aims at aligning femoral component with the cylindrical axis (or transcondylar axis) and therefore restoring the distal femoral joint line obliquity in frontal and axial planes, we paid specific attention to the restoration of the most distal and
Fig. 1. Overlaying femoral implant model on postoperative femoral model.
Fig. 2. Overlay of the preoperative planned implant (grey) and the postoperative performed implant (blue). The in-house analysis software enables a comparison of their articular surfaces. Cutting plane for measurement revolves around cylindrical axis (*). Planes at 0◦ , 90◦ , and 180◦ of revolving are illustrated.
Please cite this article in press as: Rivière C, et al. The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis. Orthop Traumatol Surg Res (2017), http://dx.doi.org/10.1016/j.otsr.2017.06.016
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Table 1 Differences for every case between planned and performed implant positioning for the four condylar points of interest. Cases
Medial condyle – distal point (mm)
Lateral condyle – distal point (mm)
Medial condyle – posterior point (mm)
Lateral condyle – posterior point (mm)
1 2 3 4 5 6 7 8 9 10 11 12 13 Mean SD
−0.6 −3 0 −2 −2.5 −0.5 −3 0.9 −1.2 0.1 1 0.4 0 −0.80 1.41
−2.5 −0.7 0 0.2 −1.3 −0.6 −1.3 −0.8 −1.5 −1.5 0.3 −0.5 0 −0.78 0.82
−1.4 −1.4 0 −1.8 −2.4 −0.5 −1.9 0.1 −0.9 −1 −0.1 0.4 0 −0.84 0.90
−2.6 −0.6 0 −1.8 −1.6 −1.3 −2.3 0.3 −1 −0.3 −1 −0.1 0 −0.95 0.93
posterior points of both condyles. The most distal and posterior condylar points were located at 70◦ and 180◦ of the revolving process, respectively. Regarding the most distal and posterior points of both condyles, we also defined the number and proportion of performed implants having more than 1.5-mm difference with the planned implant, as there is 1.8◦ of extension lost per millimetre of under resection of the distal femoral condyle and an underresection of 1.5 mm would reduce the passive knee extension by an average of 3◦ [23]. 2.1. Statistical analysis Raw data was adjusted so that right and left knees were comparable. Paired t-tests were conducted for the medial and lateral distal and posterior positions to determine differences between the planned and surgically implanted kinematically-aligned femoral component. A level of significance (P-value) of 0.05 was selected. Results are expressed as mean (SD, min to max). Negative value indicated under-stuffing of the planned implant by the performed ® implant. All statistical tests used IBM SPSS Statistics V22.0 (IBM Corp., Armonk, NY, USA). 3. Results Results for every case are presented in Table 1. The average differences between planned and surgically implanted femoral component were respectively −0.8 mm (1.4, −3 to 1) for the distal medial position, −0.8 mm (0.8, −1.5 to 0.2) for the distal lateral position, −0.8 mm (0.9, −2.4 to 0.4) for the posterior medial position, and −0.9 mm (0.9, −2.3 to 0.3) for the posterior lateral position. There were no statistically significant differences for the medial and lateral distal and posterior positions between the planned and surgically implanted kinematically-aligned femoral component. Two of 13 surgically implanted femoral components perfectly matched the plan, 5 and 8 of 13 matched all points within ±1 mm, and ±1.5 mm, respectively. The maximum difference was 3 mm. When a difference existed of > 1.5 mm, the surgically implanted femoral component was within the planned position resulting in under-stuffing. Figs. 3 and 4 illustrate the worst and best cases, respectively. 4. Discussion Kinematically-aligned TKA is a new surgical technique that targets the restoration of the native alignment of the limb, and of the native orientation of the tibiofemoral joint line [15–20]. Reproducibility in implant positioning is important to reach reproducible
good outcomes. We found the kinematic positioning of the femoral component with the specific manual instrumentation was fairly reliable with mean differences < 1 mm, 62% of implant (8/13) fitting the plan within 1.5 mm, and differences not exceeding 3 mm. Our hypothesis is confirmed. Unfortunately, there is no literature, we can compare our results with. By planning the femoral implant as detailed in our method section, the planned femoral component is likely to end up frontally and axially aligned with the cylindrical axis [24,25]. By deduction, the performed femoral component is therefore likely to be also frontally and axially aligned with the cylindrical axis. This is of primary importance as the proper alignment of the femoral implant with the three kinematic axes, which guides the knee kinematics, is the cornerstone of the KA technique in order to reach good functional outcomes. Indeed, because the patella and tibia flex and extend around the femur, so the prosthetic femoral surface has to best reproduce femoral condyles in order not to create any compromise between patellofemoral and tibiofemoral joints kinematics during advanced flexion. This reliability for femoral positioning is mainly explained by two main reasons: firstly, the cartilage thickness on both condyles is quite standard, similar and on average approximately 2 mm [26]. This eases the positioning of the femoral cutting guide by using on the worn out side a spacer of 2 mm thickness [13]. Secondly, bone cut thicknesses can be easily anticipated in KA technique, without any complex preoperative planning, because the sum “bone cut thickness plus cartilage wear (2 mm) plus kerf thickness (approximately 1 mm)” should equal the thickness of the implant. Therefore, bone cut measurement is paramount in KA technique in order to check quality and do correction(s) if needed [13,25]. KA technique reliably positions the femoral component (our data) and the tibial implant (rotational positioning) [22], and therefore seems to be a precise technique for proper implant alignment with the kinematic axis of the knee. This, plus the fact that KA technique is likely to prevent generation of undesirable uncorrectable frontal knee imbalance and distal lateral trochlea facet and femoral condyle overstuffing, might explain the good early functional outcomes of KA TKA [16,21,17,27,28]. We believe our results are not implant-specific and could be generalisable to other implant designs. Indeed, KA technique aims at matching the most distal and posterior condylar points between the implant and the native femur (after taking into account cartilage wear), and this is likely to independent of femoral implant design. However, our results apply only for femoral component implanted with a specific manual instrumentation for KA, which is currently only available for the implant selected in this study. A few limitations should be discussed that might affect the generalisation of the findings. First, the potential imprecision in every
Please cite this article in press as: Rivière C, et al. The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis. Orthop Traumatol Surg Res (2017), http://dx.doi.org/10.1016/j.otsr.2017.06.016
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Fig. 3. Worst case. Coloured map (A). Non-coloured map (B) with planned implant (grey) and performed implant (blue).
Fig. 4. Coloured map of the best case.
step of our methods might have potentially impacted the validity of our results. We overlaid femoral component models onto the CT models to compensate for the imprecision in generation of 3D prosthetic femoral models after segmentation as a result of metal implant artefacts (“bloom”). However, metal artefact also affected the accuracy of this overlay. Because we found an overall very small difference between planned and performed implants (mean difference < 1 mm), the imprecision bias from the multiple processing steps was probably low. Second, our study was based on osteoarthritic knees without significant bone loss, which probably made intra-operative implant positioning easier. However, because bone loss rarely occurs on the femoral condyle even in severely osteoarthritic knees, our results can probably be generalised to most osteoarthritic knees [26]. Third, with only 13 knees, our study is underpowered to find a significant difference between
planned and performed implants. Last, the technique to co-register CT and MRI scans has not been validated yet, and therefore might be inaccurate. However, our unpublished data have shown our technique confers a precision to < 1 mm error, and the fact we found small differences between planned and performed implants (with notably 2 perfect matching) suggests the precision of our technique of co-registration. Beside the potential imprecisions generated by our method, differences observed between planned and performed implants might be true and explained either by an imprecision in bone cuts (secondary to poor positioning of the cutting guide, motion of the guide while cutting, and poor fit of the saw in the cutting slot), or a poor impaction of final implant when cementing. Those differences are however small (mean < 1 mm) and are probably mainly represented by understuffing of the performed implant, which would therefore
Please cite this article in press as: Rivière C, et al. The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis. Orthop Traumatol Surg Res (2017), http://dx.doi.org/10.1016/j.otsr.2017.06.016
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lead to a risk of tibiofemoral instability. Fortunately, as KA technique is meant to be only a bone procedure (soft tissue envelope integrity respected) [13], surgeons could easily avoid this complication by fine-tuning the tibial cut.
[10]
[11]
5. Conclusion [12]
In this small series, the use of manual instrumentation to kinematically position the femoral component is reliable. High reliability of coaligning the flexion-extension axis of the femoral component with the cylindrical axis, is probably one of the reasons explaining the findings of two randomized trials and a national multi-centre study, which showed that patients treated with kinematic alignment reported significantly better pain relief, function, flexion, and a more normal feeling knee than patients treated with mechanical alignment. Disclosure of interest S.J.H. and E.A. are funded by the Uren Foundation and by the Sackler Trust. A.A. is funded by ORUK. The authors declare that they have no competing interest. Outside the current study, Charles Rivière declares having been consultant for Depuy, and Justin Cobb declares being consultant for Biomet-Zimmer, Mathortho, and to perceive fees from Microport. References [1] Kurtz S, Ong K, Lau E, Mowat F, Halpern M. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007;89:780–5. [2] Le DH, Goodman SB, Maloney WJ, Huddleston JI. Current modes of failure in TKA: infection, instability, and stiffness predominate. Clin Orthop Relat Res 2014;472:2197–200. [3] Sharkey PF, Lichstein PM, Shen C, Tokarski AT, Parvizi J. Why are total knee arthroplasties failing today – has anything changed after 10 years? J Arthroplasty 2014;29:1774–8. [4] Whiteside LA. Soft tissue balancing: the knee. J Arthroplasty 2002;17:23–7. [5] Gromov K, Korchi M, Thomsen MG, Husted H, Troelsen A. What is the optimal alignment of the tibial and femoral components in knee arthroplasty? Acta Orthop 2014;85:480–7. [6] Bellemans J, Colyn W, Vandenneucker H, Victor J. The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res 2012;470:45–53. [7] Nam D, Shah RR, Nunley RM, Barrack RL. Evaluation of the 3-dimensional, weight-bearing orientation of the normal adult knee. J Arthroplasty 2014;29:906–11. [8] Deep K, Eachempati KK, Apsingi S. The dynamic nature of alignment and variations in normal knees. Bone Joint J 2015;97–B:498–502. [9] Roth JD, Howell SM, Hull ML. Native knee laxities at 0 degrees, 45 degrees, and 90 degrees of flexion and their relationship to the goal of the
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gap-balancing alignment method of total knee arthroplasty. J Bone Joint Surg Am 2015;97:1678–84. Vanlommel L, Vanlommel J, Claes S, Bellemans J. Slight undercorrection following total knee arthroplasty results in superior clinical outcomes in varus knees. Knee Surg Sports Traumatol Arthrosc 2013;21:2325–30. Hutt JR, LeBlanc MA, Masse V, Lavigne M, Vendittoli PA. Kinematic TKA using navigation: surgical technique and initial results. Orthop Traumatol Surg Res 2016;102:99–104. Hungerford DS, Kenna RV, Krackow KA. The porous-coated anatomic total knee. Orthop Clin North Am 1982;13:103–22. Howell SMRJD, Hull ML. Kinematic alignment in total knee arthroplasty. Definition, history, principle, surgical technique, and results of an alignment option for TKA. Arthropaedia 2014:44–53. Elkus M, Ranawat CS, Rasquinha VJ, Babhulkar S, Rossi R, Ranawat AS. Total knee arthroplasty for severe valgus deformity. Five to 14-year follow-up. J Bone Joint Surg Am 2004;86–A:2671–6. Calliess T, Bauer K, Stukenborg-Colsman C, Windhagen H, Budde S, Ettinger M. PSI kinematic versus non-PSI mechanical alignment in total knee arthroplasty: a prospective, randomized study. Knee Surg Sports Traumatol Arthrosc 2017;25:1743–8. Dossett HG, Estrada NA, Swartz GJ, LeFevre GW, Kwasman BG. A randomised controlled trial of kinematically and mechanically aligned total knee replacements: 2-year clinical results. Bone Joint J 2014;96–B:907–13. Howell SM, Papadopoulos S, Kuznik K, Ghaly LR, Hull ML. Does varus alignment adversely affect implant survival and function six years after kinematically aligned total knee arthroplasty? Int Orthop 2015;39:2117–24. Howell SM, Howell SJ, Kuznik KT, Cohen J, Hull ML. Does a kinematically aligned total knee arthroplasty restore function without failure regardless of alignment category? Clin Orthop Relat Res 2013;471:1000–7. Miller EJ, Pagnano MW, Kaufman KR. Tibiofemoral alignment in posterior stabilized total knee arthroplasty: static alignment does not predict dynamic tibial plateau loading. J Orthop Res 2014;32:1068–74. Ji HM, Han J, Jin DS, Seo H, Won YY. Kinematically aligned TKA can align knee joint line to horizontal. Knee Surg Sports Traumatol Arthrosc 2016;24:2436–41. Waterson HB, Clement ND, Eyres KS, Mandalia VI, Toms AD. The early outcome of kinematic versus mechanical alignment in total knee arthroplasty: a prospective randomised control trial. Bone Joint J 2016;98–B:1360–8. Nedopil AJ, Howell SM, Rudert M, Roth J, Hull ML. How frequent is rotational mismatch within 0 degrees ± 10 degrees in kinematically aligned total knee arthroplasty? Orthopedics 2013;36:e1515–20. Smith CK, Chen JA, Howell SM, Hull ML. An in vivo study of the effect of distal femoral resection on passive knee extension. J Arthroplasty 2010;25:1137–42. Howell SM, Howell SJ, Hull ML. Assessment of the radii of the medial and lateral femoral condyles in varus and valgus knees with osteoarthritis. J Bone Joint Surg Am 2010;92:98–104. Howell SM. Kinematic alignment in total knee arthroplasty. In: Scott N, editor. Insall & Scott surgery of the knee. 2011. p. 1255–69. Nam D, Lin KM, Howell SM, Hull ML. Femoral bone and cartilage wear is predictable at 0 degrees and 90 degrees in the osteoarthritic knee treated with total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2014;22:2975–81. Calliess T, Bauer K, Stukenborg-Colsman C, Windhagen H, Budde S, Ettinger M. PSI kinematic versus non-PSI mechanical alignment in total knee arthroplasty: a prospective, randomized study. Knee Surg Sports Traumatol Arthrosc 2016;25:1743–8. Young SW, Walker ML, Bayan A, et al., The Chitranjan S. Ranawat award: no difference in 2-year functional outcomes using kinematic versus mechanical alignment in TKA: a randomized controlled clinical trial. Clin Orthop Relat Res 2017;475:9–20.
Please cite this article in press as: Rivière C, et al. The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis. Orthop Traumatol Surg Res (2017), http://dx.doi.org/10.1016/j.otsr.2017.06.016
ARTICLE IN PRESS
OTSR-1818; No. of Pages 5
Orthopaedics & Traumatology: Surgery & Research xxx (2017) xxx–xxx
Available online at
ScienceDirect www.sciencedirect.com
Original article
The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis C. Rivière a,∗ , F. Iranpour a , S. Harris a , E. Auvinet a , A. Aframian a , P. Chabrand b , J. Cobb a a b
Department of joint replacement, the MSK Lab, Charing Cross Campus, Laboratory Block, Fulham Palace Rd, W6 8RP London, UK Institut des sciences du mouvement, université Aix-Marseille, 171, avenue de Luminy, 13009 Marseille, France
a r t i c l e
i n f o
Article history: Received 28 January 2017 Accepted 23 June 2017 Keywords: Total Knee Arthroplasty Kinematic alignment Reproducibility Positioning Reliability Cylindrical axis
a b s t r a c t Introduction: Kinematic alignment (KA) technique is an alternative technique for positioning a TKA, which aims a patient-specific implant positioning in order to reproduce the pre-arthritic knee anatomy. Because reliability in implant positioning is of interest to obtain reproducible good functional results, our study tests the hypothesis that the medial and lateral distal and posterior positions of the planned and surgically implanted kinematically aligned femoral component are similar. Methods: Preoperative knee magnetic resonance imaging (MRI) and postoperative knee computed ® tomography (CT) of 13 patients implanted with a KA Persona TKA (Zimmer, Warsaw, USA) using ® manual instrumentation (kinematically-aligned TKA procedure pack , Zimmer Biomet, Warsaw, USA) were segmented to create 3D femoral models. The kinematic alignment position of the femoral component was planned on the 3D model created from the preoperative MRI. Differences in the positions of the planned and surgically implanted kinematically-aligned femoral component were determined with in-house analysis software. Results: The average differences between the medial and lateral distal and posterior positions of the planned and surgically implanted kinematically-aligned femoral component were inferior to 1 mm and no statistically significant. In terms of variability, 62% (8/13) of performed implants matched all four positions within 1.5 mm, and the maximum difference was 3 mm. Conclusion: In this small series, intraoperative kinematic positioning of the femoral component with the specific manual instrumentation closely matched the planned position, which suggests that this technique reliably aligned the flexion-extension axis of the femoral component to the cylindrical axis. Level of evidence: Level 3. © 2017 Elsevier Masson SAS. All rights reserved.
1. Introduction Knee osteoarthritis (OA) is a growing socio-economic burden because of the ageing population and the epidemic of obesity. It is projected that by 2030, patients younger than 65 years of age will make up the majority of patients undergoing knee arthroplasty in the USA, with up to one million performed annually [1]. For decades, a stable knee with a neutral mechanically axis lower limb alignment has been one of the primary goals of TKA because it was believed to be important for successful clinical outcomes and implant survivorship [1–3]. The joint line is made perpendicular to the neutral mechanical axis of the limb and the femoral component is expected to be frontally and axially aligned with the trans-epicondylar axis
∗ Corresponding author. E-mail address: [email protected] (C. Rivière).
(TEA), which then becomes the flexion-extension axis of the knee [4]. Mechanical alignment does not restore the patient-specific alignment (constitutional anatomy) but an average positioning of the prosthetic knee, which aims at reducing the adduction moment arm and distributes the load more evenly on the tibial compartments, thus potentially reducing instability, polyethylene wear and implant loosening. This average approach to alignment does not account for the variations in anatomy between patients [5]. For these reasons, the conventional MA technique has been recently challenged by a new alternative technique, namely kinematic alignment (KA), aiming at reproducing the constitutional tibiofemoral tridimensional alignment and knee laxity [6–14]. Kinematically-aligned TKA is a surgical technique that targets the restoration of the native alignment of the limb, and of the native orientation of the tibiofemoral joint line [15–20]. Kinematic alignment has gained interest because two randomized trials and a national multi-centre study showed that patients treated with kinematic
http://dx.doi.org/10.1016/j.otsr.2017.06.016 1877-0568/© 2017 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: Rivière C, et al. The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis. Orthop Traumatol Surg Res (2017), http://dx.doi.org/10.1016/j.otsr.2017.06.016
G Model OTSR-1818; No. of Pages 5
ARTICLE IN PRESS C. Rivière et al. / Orthopaedics & Traumatology: Surgery & Research xxx (2017) xxx–xxx
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alignment reported significantly better pain relief, function, flexion, and a more normal feeling knee than patients treated with mechanical alignment [15,16,19], whereas two other randomized trials showed similar clinical outcomes between kinematic alignment and mechanical alignment [20,21]. Bone cuts in KA technique can be performed using manual instrumentation [13,22], patient specific instrumentation (PSI) [18], and navigation (CAS) [11] with each option having different advantages and drawbacks. Tibial implant rotational positioning with KA technique has been shown to be highly reproducible with the use of conventional instrumentation [22], but there is no data regarding the one for the femoral implant. Because implant-positioning reproducibility is important to reach reproducible good outcomes, our study aims at testing the hypothesis that the medial and lateral distal and posterior positions of the planned and surgically implanted kinematically-aligned femoral component are similar. 2. Methods Anonymised preoperative magnetic resonance imaging (MRI) scans and postoperative computer tomographic (CT) scans of ® 13 patients having received a kinematically-aligned TKA (Persona , Zimmer, Warsaw, USA) for end-stage tibiofemoral osteoarthritis (Ahlbäck > 2) were selected for study. TKA were implanted by using the specific manual instrumentation (kinematically-aligned TKA procedure pack, Zimmer Biomet, Warsaw, USA). Because the imaging studies and clinical data were anonymised, their use was not subject to approval by our institutional review board. Preoperative knee MRIs and postoperative knee CT-scans were segmented to create 3D femoral models. Bone and cartilage were segmented on the MRI while bone and implant were segmented on ® the CT-scan. A set of Persona femoral implants (Zimmer, Warsaw, USA) was laser scanned (C-track 780 3D laser scanner, Creaform, Quebec, Canada) to create 3D femoral implant models. In-house planning software was then used to simulate a kinematic alignment
of femoral implant model on the preoperative MRI, using the same femoral implant size as the one used intra-operatively. Femoral implant was positioned flush with healthy cartilage on the unworn tibiofemoral compartment, and 2-mm distal or posterior to the subchondral condylar bone when cartilage was worn out on the degenerated tibiofemoral compartment. Femoral implant models were also overlaid on the femoral CT model to replicate, in silico, the alignment of the implant on the postoperative bone. This enabled reproduction in the computer model the features of the implant lost due to CT metal artefacts, thus improving the shape accuracy of the femoral component (Fig. 1). The CT and MRI data were co-registered using Artec 3D software (Artec3D, Palo Alto, Ca, USA). A section of the femoral shaft unaffected by metal artefacts from the implants was used to register the preoperative MRI and postoperative CT 3D models to the same coordinate geometry (Fig. 2). The femoral shaft was chosen as it is an area unmodified by surgery. This technique confers precision to < 1 mm error (unpublished data). The laser scanned overlaid implant was maintained in space while the registered preoperative MRI based model, with femoral implant planned on it, was substituted for the CT-based model, thus keeping the same implant to bone alignment on the preoperative images as was derived from the postoperative data. In-house software enabled a comparison of prosthetic articular surfaces between the planned and performed femoral implant (Fig. 2). The software made measurements by revolving around the cylindrical axis, which was identified by selecting multiple points on the flexion facets of the medial and lateral femoral condyles, that is the femoral articular surfaces contacting the tibia when knee flexes. Spheres were automatically fitted to the selected points, and a line drawn between their centres represented the cylindrical axis. Because KA technique aims at aligning femoral component with the cylindrical axis (or transcondylar axis) and therefore restoring the distal femoral joint line obliquity in frontal and axial planes, we paid specific attention to the restoration of the most distal and
Fig. 1. Overlaying femoral implant model on postoperative femoral model.
Fig. 2. Overlay of the preoperative planned implant (grey) and the postoperative performed implant (blue). The in-house analysis software enables a comparison of their articular surfaces. Cutting plane for measurement revolves around cylindrical axis (*). Planes at 0◦ , 90◦ , and 180◦ of revolving are illustrated.
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Table 1 Differences for every case between planned and performed implant positioning for the four condylar points of interest. Cases
Medial condyle – distal point (mm)
Lateral condyle – distal point (mm)
Medial condyle – posterior point (mm)
Lateral condyle – posterior point (mm)
1 2 3 4 5 6 7 8 9 10 11 12 13 Mean SD
−0.6 −3 0 −2 −2.5 −0.5 −3 0.9 −1.2 0.1 1 0.4 0 −0.80 1.41
−2.5 −0.7 0 0.2 −1.3 −0.6 −1.3 −0.8 −1.5 −1.5 0.3 −0.5 0 −0.78 0.82
−1.4 −1.4 0 −1.8 −2.4 −0.5 −1.9 0.1 −0.9 −1 −0.1 0.4 0 −0.84 0.90
−2.6 −0.6 0 −1.8 −1.6 −1.3 −2.3 0.3 −1 −0.3 −1 −0.1 0 −0.95 0.93
posterior points of both condyles. The most distal and posterior condylar points were located at 70◦ and 180◦ of the revolving process, respectively. Regarding the most distal and posterior points of both condyles, we also defined the number and proportion of performed implants having more than 1.5-mm difference with the planned implant, as there is 1.8◦ of extension lost per millimetre of under resection of the distal femoral condyle and an underresection of 1.5 mm would reduce the passive knee extension by an average of 3◦ [23]. 2.1. Statistical analysis Raw data was adjusted so that right and left knees were comparable. Paired t-tests were conducted for the medial and lateral distal and posterior positions to determine differences between the planned and surgically implanted kinematically-aligned femoral component. A level of significance (P-value) of 0.05 was selected. Results are expressed as mean (SD, min to max). Negative value indicated under-stuffing of the planned implant by the performed ® implant. All statistical tests used IBM SPSS Statistics V22.0 (IBM Corp., Armonk, NY, USA). 3. Results Results for every case are presented in Table 1. The average differences between planned and surgically implanted femoral component were respectively −0.8 mm (1.4, −3 to 1) for the distal medial position, −0.8 mm (0.8, −1.5 to 0.2) for the distal lateral position, −0.8 mm (0.9, −2.4 to 0.4) for the posterior medial position, and −0.9 mm (0.9, −2.3 to 0.3) for the posterior lateral position. There were no statistically significant differences for the medial and lateral distal and posterior positions between the planned and surgically implanted kinematically-aligned femoral component. Two of 13 surgically implanted femoral components perfectly matched the plan, 5 and 8 of 13 matched all points within ±1 mm, and ±1.5 mm, respectively. The maximum difference was 3 mm. When a difference existed of > 1.5 mm, the surgically implanted femoral component was within the planned position resulting in under-stuffing. Figs. 3 and 4 illustrate the worst and best cases, respectively. 4. Discussion Kinematically-aligned TKA is a new surgical technique that targets the restoration of the native alignment of the limb, and of the native orientation of the tibiofemoral joint line [15–20]. Reproducibility in implant positioning is important to reach reproducible
good outcomes. We found the kinematic positioning of the femoral component with the specific manual instrumentation was fairly reliable with mean differences < 1 mm, 62% of implant (8/13) fitting the plan within 1.5 mm, and differences not exceeding 3 mm. Our hypothesis is confirmed. Unfortunately, there is no literature, we can compare our results with. By planning the femoral implant as detailed in our method section, the planned femoral component is likely to end up frontally and axially aligned with the cylindrical axis [24,25]. By deduction, the performed femoral component is therefore likely to be also frontally and axially aligned with the cylindrical axis. This is of primary importance as the proper alignment of the femoral implant with the three kinematic axes, which guides the knee kinematics, is the cornerstone of the KA technique in order to reach good functional outcomes. Indeed, because the patella and tibia flex and extend around the femur, so the prosthetic femoral surface has to best reproduce femoral condyles in order not to create any compromise between patellofemoral and tibiofemoral joints kinematics during advanced flexion. This reliability for femoral positioning is mainly explained by two main reasons: firstly, the cartilage thickness on both condyles is quite standard, similar and on average approximately 2 mm [26]. This eases the positioning of the femoral cutting guide by using on the worn out side a spacer of 2 mm thickness [13]. Secondly, bone cut thicknesses can be easily anticipated in KA technique, without any complex preoperative planning, because the sum “bone cut thickness plus cartilage wear (2 mm) plus kerf thickness (approximately 1 mm)” should equal the thickness of the implant. Therefore, bone cut measurement is paramount in KA technique in order to check quality and do correction(s) if needed [13,25]. KA technique reliably positions the femoral component (our data) and the tibial implant (rotational positioning) [22], and therefore seems to be a precise technique for proper implant alignment with the kinematic axis of the knee. This, plus the fact that KA technique is likely to prevent generation of undesirable uncorrectable frontal knee imbalance and distal lateral trochlea facet and femoral condyle overstuffing, might explain the good early functional outcomes of KA TKA [16,21,17,27,28]. We believe our results are not implant-specific and could be generalisable to other implant designs. Indeed, KA technique aims at matching the most distal and posterior condylar points between the implant and the native femur (after taking into account cartilage wear), and this is likely to independent of femoral implant design. However, our results apply only for femoral component implanted with a specific manual instrumentation for KA, which is currently only available for the implant selected in this study. A few limitations should be discussed that might affect the generalisation of the findings. First, the potential imprecision in every
Please cite this article in press as: Rivière C, et al. The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis. Orthop Traumatol Surg Res (2017), http://dx.doi.org/10.1016/j.otsr.2017.06.016
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Fig. 3. Worst case. Coloured map (A). Non-coloured map (B) with planned implant (grey) and performed implant (blue).
Fig. 4. Coloured map of the best case.
step of our methods might have potentially impacted the validity of our results. We overlaid femoral component models onto the CT models to compensate for the imprecision in generation of 3D prosthetic femoral models after segmentation as a result of metal implant artefacts (“bloom”). However, metal artefact also affected the accuracy of this overlay. Because we found an overall very small difference between planned and performed implants (mean difference < 1 mm), the imprecision bias from the multiple processing steps was probably low. Second, our study was based on osteoarthritic knees without significant bone loss, which probably made intra-operative implant positioning easier. However, because bone loss rarely occurs on the femoral condyle even in severely osteoarthritic knees, our results can probably be generalised to most osteoarthritic knees [26]. Third, with only 13 knees, our study is underpowered to find a significant difference between
planned and performed implants. Last, the technique to co-register CT and MRI scans has not been validated yet, and therefore might be inaccurate. However, our unpublished data have shown our technique confers a precision to < 1 mm error, and the fact we found small differences between planned and performed implants (with notably 2 perfect matching) suggests the precision of our technique of co-registration. Beside the potential imprecisions generated by our method, differences observed between planned and performed implants might be true and explained either by an imprecision in bone cuts (secondary to poor positioning of the cutting guide, motion of the guide while cutting, and poor fit of the saw in the cutting slot), or a poor impaction of final implant when cementing. Those differences are however small (mean < 1 mm) and are probably mainly represented by understuffing of the performed implant, which would therefore
Please cite this article in press as: Rivière C, et al. The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis. Orthop Traumatol Surg Res (2017), http://dx.doi.org/10.1016/j.otsr.2017.06.016
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lead to a risk of tibiofemoral instability. Fortunately, as KA technique is meant to be only a bone procedure (soft tissue envelope integrity respected) [13], surgeons could easily avoid this complication by fine-tuning the tibial cut.
[10]
[11]
5. Conclusion [12]
In this small series, the use of manual instrumentation to kinematically position the femoral component is reliable. High reliability of coaligning the flexion-extension axis of the femoral component with the cylindrical axis, is probably one of the reasons explaining the findings of two randomized trials and a national multi-centre study, which showed that patients treated with kinematic alignment reported significantly better pain relief, function, flexion, and a more normal feeling knee than patients treated with mechanical alignment. Disclosure of interest S.J.H. and E.A. are funded by the Uren Foundation and by the Sackler Trust. A.A. is funded by ORUK. The authors declare that they have no competing interest. Outside the current study, Charles Rivière declares having been consultant for Depuy, and Justin Cobb declares being consultant for Biomet-Zimmer, Mathortho, and to perceive fees from Microport. References [1] Kurtz S, Ong K, Lau E, Mowat F, Halpern M. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007;89:780–5. [2] Le DH, Goodman SB, Maloney WJ, Huddleston JI. Current modes of failure in TKA: infection, instability, and stiffness predominate. Clin Orthop Relat Res 2014;472:2197–200. [3] Sharkey PF, Lichstein PM, Shen C, Tokarski AT, Parvizi J. Why are total knee arthroplasties failing today – has anything changed after 10 years? J Arthroplasty 2014;29:1774–8. [4] Whiteside LA. Soft tissue balancing: the knee. J Arthroplasty 2002;17:23–7. [5] Gromov K, Korchi M, Thomsen MG, Husted H, Troelsen A. What is the optimal alignment of the tibial and femoral components in knee arthroplasty? Acta Orthop 2014;85:480–7. [6] Bellemans J, Colyn W, Vandenneucker H, Victor J. The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res 2012;470:45–53. [7] Nam D, Shah RR, Nunley RM, Barrack RL. Evaluation of the 3-dimensional, weight-bearing orientation of the normal adult knee. J Arthroplasty 2014;29:906–11. [8] Deep K, Eachempati KK, Apsingi S. The dynamic nature of alignment and variations in normal knees. Bone Joint J 2015;97–B:498–502. [9] Roth JD, Howell SM, Hull ML. Native knee laxities at 0 degrees, 45 degrees, and 90 degrees of flexion and their relationship to the goal of the
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Please cite this article in press as: Rivière C, et al. The kinematic alignment technique for TKA reliably aligns the femoral component with the cylindrical axis. Orthop Traumatol Surg Res (2017), http://dx.doi.org/10.1016/j.otsr.2017.06.016