Primary Arthroplasty
Total Knee Arthroplasty in Patients With Extra-Articular
Deformity: Restoration of Mechanical Alignment Using
Accelerometer-Based Navigation System
Fabrizio Matassi, MD, Andrea Cozzi Lepri, MD, Matteo Innocenti, MD
*,
Luigi Zanna, MD, Roberto Civinini, MD, Massimo Innocenti, MD
University of Florence, Orthopaedic Clinic CTO, Florence, Italya r t i c l e i n f o
Article history:
Received 20 September 2018 Received in revised form 27 December 2018 Accepted 31 December 2018 Available online 5 January 2019 Keywords: extra-articular deformities knee arthroplasty computer assisted accelerometer mechanical alignment
a b s t r a c t
Background: Total knee arthroplasty (TKA) in patients with post-traumatic extra-articular deformity (EAD) is difficult to manage using conventional instrumentation techniques. In this study, we evaluate whether accelerometer navigation system can be a valuable option to make accurate bone resections and restore the neutral mechanical axis in complex TKA patients with EAD.
Methods: From May 2015 to June 2017, 18 consecutive TKA were performed in 18 patients with knee osteoarthritis with associated EAD. An accelerometer-based navigation system was used to guide tibial and femoral resection in the coronal and sagittal plane. Postoperative lower limb alignment in coronal plane and component position in coronal and sagittal plane was measured through full-leg weight-bearing X-ray. Clinical score were recorded using the Knee Society Score at thefinal follow-up. Results: The mean hip-knee-ankle angle was 0.9± 1.4varus alignment. The coronal alignment of the femoral component was 89.2± 1.9, and the coronal alignment of the tibial component was 89.4± 2.1. The sagittal alignment of the femoral component was 93.2± 1.9, and the sagittal alignment of the tibial component was 84.4± 3.1. At thefinal follow-up, the Knee Society Score was 89 points (range, 82-100), and the functional score was 86.7 points (range, 60-100). No intraoperative and postoperative surgical complications were reported using this technology.
Conclusion: Accelerometer-based navigation is accurate in achieving neutral mechanical alignment and optimal implant position after TKA in patients with EAD. This system should be considered a valuable option to the more complex technique of computer navigation or robotic surgery.
© 2019 Elsevier Inc. All rights reserved.
Total knee arthroplasty (TKA) is a successful procedure that improves function, increases the range of motion, and relieves pain
from knee osteoarthritis [1,2]. The outcome of this procedure is
strictly correlated with postoperative lower limb alignment and
component position[3e5].
To obtain a neutrally aligned lower limb with component
posi-tioned within 3from mechanical axis (MA) is the primary goal of
TKA because it was supposed to reduce the risk of abnormal wear,
premature loosening, and early implant failure [6,7]. However,
recent studies have questioned the importance of mechanical
alignment in TKA reporting good outcomes with pain relief for those patients with constitutional varus that still have a varus lower
limb alignment after TKA [8]. To date, it is unknown whether
alteration of component alignment from MA will compromise implant survival, and for this reason, most of the surgeons still aim to obtain a neutral lower limb alignment after TKA.
When osteoarthritis is combined with a femoral or tibial extra-articular deformity (EAD), performing a TKA and restoring neutral mechanical axes can make the surgery challenging. Femoral or tibial deformity from previous trauma or surgery may compromise the use of conventional intramedullary instrumentation for TKA because of the distortion of the bony canal or the presence of hardware (Every type of metallic or other material devices used in the previous sur-geries taken for trauma surgery/sports surgery etc.). In these cases, many systems can support the surgeon to obtain the desired component position and alignment according to MA such as
No author associated with this paper has disclosed any potential or pertinent conflicts which may be perceived to have impending conflict with this work. For full disclosure statements refer tohttps://doi.org/10.1016/j.arth.2018.12.042.
* Reprint requests: Matteo Innocenti, MD, University of Florence, Orthopaedic Clinic CTO, Largo Palagi 1, 50139 Florence, Italy.
Contents lists available atScienceDirect
The Journal of Arthroplasty
j o u rn a l h o m e p a g e : w w w . a r t h r o p l a s t y j o u r n a l . o r g
https://doi.org/10.1016/j.arth.2018.12.042
computer-assisted surgery (CAS)[9e16], robotic surgery (RS)[17,18],
patient-specific instrumentation (PSI)[19e21], or the use of
extra-medullary guide[22,23]. However, there are many concerns such as
the learning curve required, expensive procedure, requirement of preoperative imaging (computed tomography [CT] scans or magnetic resonance imaging [MRI], longer operative time, extra pin sites, and
difficulties with sensitive optical instrumentations regarding the use
of this technology
Recently, some smart, easy, and cheap new navigation systems have been introduced in TKA using accelerometer portable compo-nents designed to improve component position and alignment. One of these systems is the i-ASSIST Knee Surgical Assistance for Total Knee
Arthroplasty (Zimmer Inc, Warsaw, IN)[24,25]. This device provides
intraoperative matching of bone cuts and overall alignment at each surgical step using an internal position-sensing technology integrated into microelectronic pods that attach to the standard cutting blocks. This technology allows positioning of the cutting blocks according to MA, avoiding violation of the intramedullary canal. Some recent studies have reported good clinical outcomes and reduction in out-liers for component position in coronal and sagittal planes using
accelerometer navigation system for TKA[26e29]. However, no study
published in literature reported the accuracy of this new navigation system in TKA in knee osteoarthritis associated with EAD.
The purpose of this study was to evaluate whether accelerometer navigation system can be a valuable option for TKA in post-traumatic knee osteoarthritis with femoral or tibial EAD. Our hypothesis is that this new technology enables the surgeon to make accurate bone re-sections and restore the neutral MA in complex TKA with EAD where conventional intramedullary instrumentation could not be used. Materials and Methods
Patient Selection
Between May 2015 and June 2017, 18 consecutive patients (18 knees) with osteoarthritis of the knee associated with EAD were who had undergone TKA with the i-ASSIST navigation system were selected. Patients were included in this prospective study after approval from our institutional review board. The inclusion criterion was severe osteoarthritis of the knee requiring TKA associated to EAD. The EAD had to be an angular deformity in the middle or distal third of the femur or in the proximal or middle third of the tibia without involvement of the articular surface and following the Wang's criteria
[30]. Exclusion criteria included active infection, severe ipsilateral hip
osteoarthritis, neurological disorders, and deformity in coronal plane
greater than 20in the femur and 30in the tibial bone that required
corrective osteotomy combined with TKA.
Our study cohort consisted of 9 males and 9 females, with an
average age of 63.7± 2.3 (mean ± standard deviation). The mean
body mass index was 28.6± 1.3. All deformities had resulted from
fracture malunions. Seven patients had a tibial EAD, 9 had a femoral EAD, and two had a combined deformity in the femur and tibia. Surgical Technique
All the surgeries were performed by the same surgeon through a medial parapatellar approach without eversion of the patella.
Pneumatic tourniquet was applied on the upper thigh, inflated
during the bone cut and released after the cement had set, to allow hemostasis before wound closure. Thirty minutes preoperatively and 30 minutes postoperatively, a tranexamic acid intravenous infusion (1 mg/kg) was administrated. A measured resection technique was used, followed by an adequate balance of the soft
tissues. The surgical workflow follows the standard method for TKA
in which each bone was resected independently and according to
the rules of MA alignment. The i-ASSIST system for TKA was used in all cases to guide both proximal tibial and distal femoral resections. This system provides disposable electronic pods that attach onto the cutting blocks. These pods contain accelerometer or gyroscopes that allow registration and provides real-time information to the surgeon for proper position of the resection instruments.
For the femoral resection, a little spike was impacted for 2.5 to 3.5 cm at the MA entry point in the distal femur, and a sensor was attached to the jig. The center of the hip is registered through a “stop-and-go” movement with star configuration, and MA is detected. The distal femoral cutting block is then inserted, and the
resection is adjusted in coronal (varus/valgus) and sagittal (flexion
and extension) planes (Fig. 1). The distal femoral cut was planned
with respect to its MA at 0in the frontal plane and at 3offlexion
in the sagittal plane. After the cut was performed, a validation pod
was used to confirm the desired alignment and perform additional
resection if necessary. In one case, an additional resection to
in-crease the femoralflexion was performed at this stage.
For the proximal tibial resection, a registration of the MA of the tibia is performed with the electronic pods attached to an extra-medullary guide. The leg was then brought into abduction, adduction, and back to neutral to allow the digitizer to register the tibial MA and transfer it to the pods attached to the tibial resection guide. The tibial resection guide was then adjusted to correct the
coronal alignment and the slope (Fig. 2). The proximal tibial
resection was planned with respect to its MA at 0in the frontal
plane and at 5 of posterior slope in the sagittal plane. After
resection, the accuracy of alignment is validated, and any adjust-ments can be performed at this stage. In two cases, an additional resection was necessary to increase the tibial slope.
At the end of the procedure with trial components in place, soft tissue balancing was performed to achieve proper ligament tension in flexion and in extension. In 16 cases, a posterior-stabilized tibial insert was used, and in 2 cases, a constrained condylar knee was necessary to
increase stability of the knee because of largerflexion gap after
liga-ment balancing. Cefazoline was administered as preoperative pro-phylactic antibiotic therapy and discontinued after 48 h. All patients
were subjected to the same rehabilitation protocol from thefirst day.
Radiographic Evaluation
Preoperative and postoperative weight-bearing radiographs
(anteroposterior and lateral full-length hip-to-ankle films) were
Fig. 1. Femoral cutting block with sensor attached to adjustflexion/extension and varus/valgus position.
taken in the specialist outpatient clinic 1 month after the surgery. The coronal hip-to-ankle radiographs were taken with the patient standing and the knee in full extension and both malleoli placed 20 cm apart with the toes pointing forward according to the rule
described by Moreland et al[31].
The sagittal hip-to-ankle radiographs were taken with the pa-tient standing and the knee in full extension in one-legged stance and with the patients instructed to face laterally so the posterior edges of the medial and lateral femoral condyles were aligned
us-ing the method described by Minoda et al[32].
The preoperative and postoperative MA of the lower limb and femoral and tibial component alignment in coronal plane (varus/
valgus) and sagittal plane (flexion/extension) was measured using a
specialized software (Carestream Health, Rochester, NY) (Fig. 3).
Data were recorded to an accuracy of 0.1. All the measurements
were independently taken by 2 observers, and the results were analyzed for interobserver variability.
At coronal hip-to-ankle radiographs, points were placed at the center of the femoral head, the femoral intercondylar notch, the tibial
interspinous groove, and at the center of the tibial plafond. The line
between thefirst two points defined the femoral MA, and the line
between second two points defined the tibial MA. Three radiograph
measurements were performed on the coronal hip-to-ankle radio-graphs: (1) hip-knee-ankle (HKA) angle as the angle formed between a line from the center of the femoral head and the center of the knee and a line from the center of the knee and the center of the talus (where positive numbers indicate varus alignment and negative numbers indicate valgus alignment); (2) coronal femoral component angle as the lateral angle formed by the femoral component and the MA of the femur; (3) coronal tibial component angle as the medial angle formed by the tibial component and the MA of the tibia.
Two radiograph measurements were performed on the lateral knee radiographs: (1) sagittal femoral component angle as the anterior angle formed by the intersection of femoral component and the line of the mechanical axis of the femur; (2) sagittal tibial component angle as the posterior angle formed at the intersection between a line tangent to the tibial component and a line of the MA
of the tibia[33].
A clinical evaluation was conducted with a minimum follow-up of 6 months using the Knee Society Score (KSS) which is subdivided into a knee score that rates only the knee joint itself and a functional
score that rates the patient's ability to walk and climb stairs[34].
Statistical Analysis
Statistical analysis was performed using SPSS statistics software (IBM, Armonk, NY). The quantitative parameters (radiographic con-trol angles) were evaluated with the calculation of the mean and standard deviations. Ultimately, the data from clinical evaluation analysis (KSS) was obtained using Student's t-test, taking P values of
less than .05 as statistically significant with a 95% confidence interval,
to assess the outcome of subjective evaluation. The interobserver reliability was calculated using an unrepeated two-way analysis of variance of the averages of the three measurements obtained by each of the two observers. For all measurements, the intraclass correlation
coefficient of intraobserver reliability was >0.90, whereas the
intra-class correlation coefficient of interobserver reliability was >0.85.
Fig. 2. Tibial cutting block with sensor attached to adjust slope and varus/valgus position.
Results
The mean HKA angle was corrected from a preoperative 7.8±
8.3varus alignment (range: 15.6 varus to 8.9 valgus) to
post-operative 0.9 ± 1.4 varus alignment (range: 2.2 varus to 1.6
valgus). The coronal alignment of the femoral component was 89.2
± 1.9(range 91.3-88.1), and the coronal alignment of the tibial
component was 89.4± 2.1(range: 87.3-91.2). The sagittal
align-ment of the femoral component was 93.2± 1.9(range: 90.4-97),
and the sagittal alignment of the tibial component was 84.4± 3.1
(range: 89.4-82.1) (Table 1).
At thefinal follow-up, the KSS improved from a preoperative
average of 46.8 points (range, 23-65) to 89 points (range, 82-100) (P < .05), and the functional score improved from 46 points (range,
35-90) to 86.7 points (range, 60-100) (P < .05) at the latest
evaluation.
No intraoperative and postoperative surgical complications were reported in this cohort. The mean tourniquet time was 62 minutes (range 55-64 minutes). No blood transfusion was necessary intraoperatively and postoperatively.
Discussion
Restoration of mechanical alignment with component posi-tioned perpendicular to MA is crucial to improve clinical outcomes and long-term implant survival. However, when knee osteoarthritis is combined with EAD, obtaining neutral alignment with proper
component position is a challenge with conventional instrumen-tation for TKA. In this study, we demonstrated that the accelerometer-based navigation system for TKA is a valuable option for patients with knee osteoarthritis and EAD to restore neutral mechanical alignment with optimal component position and good clinical outcomes.
Recently, some studies in literature reported a reduction of outliers in component position in coronal and sagittal plane using
portable accelerometer-based surgical navigation system
compared with standard technique for TKA[25e27,29]. In a recent
study of 159 patients by Ueyama et al [28], they concluded that
using an accelerometer-based portable navigation system
(KneeAlign2, OrthAlign Inc, Aliso Viejo, CA) lead to a decrease in the number of outliers of prosthetic alignment in coronal and sagittal planes without any increased complications or operation time. Goh et al compared the alignment accuracy between accelerometer-based navigation and CAS, and they found no differences in lower limb alignment and in position of the femoral component in
cor-onal and sagittal plane between the two groups[35].The purpose of
the present study was to investigate whether this system based on accelerometer navigation can be a valuable option to restore neutral alignment with optimal implant position in post-traumatic knee osteoarthritis with femoral or tibial EAD. To our knowledge,
this is thefirst study to analyze the accuracy of this new navigation
system in component position and lower limb alignment after TKA in patients with EAD.
The presence of a femoral and/or tibial EAD creates an abnormal anatomical axis with distorted bony landmarks, which makes
cor-rect component position and identification of MA difficult. Thus, in
these cases, conventional instrumentation technique with the use of intramedullary guide for bony resection is unreliable.
Staged surgical procedures, including osteotomy of the femur or
tibia[36], followed by traditional TKA, can be used to recreate the
correct MA. However, these multiple procedures increase the risk of complications such as increased rates of infection, devitalization of
the skin, and arthrofibrosis[37].
CAS is a suitable option in these cases because the system measures the MA of the lower limb irrespective of local landmarks. Some studies describe the use of navigation for TKA in knee
Table 1
Preoperative and Postoperative Lower Limb Alignment and Component Alignment After TKA.
Alignment Parameters Mean Range
Preoperative HKA angle 7.8± 8.3 15.6to 8.9
Postoperative HKA angle 0.9± 1.4 2.2to 1.6
Coronal femoral component angle (CFA) 89.2± 1.9 91.3-88.1
Coronal tibial component angle (CTA) 89.4± 2.1 87.3-91.2
Sagittal femoral component angle (SFA) 93.2± 1.9 90.4-97
Sagittal tibial component angle (STA) 84.4± 3.1 89.4-82.1
HKA, hip-knee-ankle.
Table 2
Summary of Studies Reporting Results of TKA in Patients With EAD.
Authors Years Nin TKA Surgical Techniques HKA Angle Clinical Results
Klein et al[9] 2006 5 CAS (Striker Navigation System) 0.6 (range 1.88 to 0.48) NA
Bottros et al[10]. 2008 9 CAS (Striker Navigation System) 1.3(range 2.5 to 0.2) Knee score: 92 (range 83-97), functional
score: 83 (range 60-100) Mullaji and Shetty[11]. 2009 40 CAS (Brainlab, Munich, Germany) 0.9(range 1.4-0.5) Knee score: 90.4 (range 80-95),
functional score: 84.9 (range 50-100) Kim et al[12]. 2010 4 CAS (Striker Navigation System) 0.3(range 0.5 to 1.2) Knee score: 95 (range 88-98), functional
score: 95 (range 90-100) Catani et al[13]. 2012 20 CAS (Striker Navigation System) 0.8(range 1 to 2) Knee score: 91.4 (range 81-97),
functional score: 85 (range 78-93) Xiao-Gang et al[22]. 2012 9 Intramedullary guide or extramedullary
guide or c-armfluoroscopy
1(range 4-0) HSS: 89.8 (range 81-96)
Shao et al[14]. 2012 12 CAS (Striker Navigation System) 0.9(range 2 to 0.5) Knee score: 94.9 (range 91-100) Functional score: 95.4 (range 90-100) Liu et al[16]. 2013 8 CAS (Striker Navigation System) 1.2(range 4.5 to 1.5) Knee score: 84 (range 77-94), functional
score: 87.50 (range 75-100) Rhee et al[15]. 2013 13 CAS (Medtronic Electromagnetic Knee
Navigation System Zimmer)
0.2(range 6 to 12) Knee score: 89.6 (range 80-97)
Thienpont et al[38]. 2013 10 5 Signature Biomet, 3 PSI Zimmer, 1 My Knee Medacta, 1 Hafez Guide
0.7 (range 3 to 1) Knee score: 91, functional Score: 92 Vasdev et al[23]. 2013 36 4 CAS, 32 conventional techniques 2(range 6 to 2) Knee score: 85 (range 35-95), functional
score 69.5 (range 0-90)
Current study 18 I-Assit Zimmer 0.9 (range 2.2 to 1.6) Knee score: 89 (range 82-100),
functional score: 86.7 (range 60-100) Positive value means varus alignment, and negative value, valgus alignment.
arthritis with EAD with good clinical results, appropriate bone cuts,
and soft tissue release[9e16]. (Table 2)
However, despite many encouraging data, CAS have some dis-advantages such as the use of trackers placed on the bone with transosseous pins that enhance the risk of weakening the anterior
cortex of femur and tibia and of additional bleeding [39,40].
Furthermore, the system requires a recording chamber for the signal, and the surgeon needs to observe the monitor during the whole procedure. Several studies underline the increased surgical times with CAS compared with conventional techniques and a learning curve of about 30 cases to overcome the delay in the
operating time[41,42].(Table 2).
Recently, a PSI technique using MRI or CT scan has been devel-oped to improve lower limb alignment and implant position in all three planes. The plastic disposable cutting blocks designed from MRI or CT images are intended to provide a more accurate align-ment, without any reference to anatomical mechanical axes or
violation of the intramedullary canal[19,20]. Thienpont et al[38]
investigated the use of this technology in 10 patients with EAD and found restoration of neutral alignment after TKA with femoral
and tibial component positioned within less than 3of deviation
from MA.
RS is another valuable option to increase accuracy in alignment
and component position in standard TKA [43e45]. However, no
results are reported for patients with knee osteoarthritis associated
with EAD. Kim et al[46]investigated the role of RS in intra-articular
deformity in hemophilic arthropathy showing excellent accuracy of lower limb and component alignment. However, they concluded that factors such as high cost, additional preparation time, and longer operation time should be of main concern.
From ourfinding using the i-ASSIST Knee Surgical Assistance for
TKA in patients with EAD, the HKA angle was restored to 0.9± 1.4
from MA with optimal alignment of tibial and femoral component in coronal and sagittal plane.
This system is safe as no complications were recorded, and it is easy to use with no learning curve required or with no increased operating time. Accuracy on lower limb alignment and component position is comparable to the results provided from other studies in literature using CAS or PSI technology. This system guide distal femoral and proximal tibial resection and allow to obtain desired alignment and could be used independently of the prosthetic design.
Some limitations were identified and need to be considered
when interpreting these data. First, the relatively small series of this study is underpowered to detect meaningful clinical differ-ences or to permit subgroup analyses; nonetheless, we are dealing with TKA in patients with EAD, and this is one of the largest series reported in literature. Moreover, the main purpose of this study was
to suggest a novel technique to perform TKA in difficult and rare
situations such as in EAD.
Second, a control group with conventional techniques was not available for direct comparison to clearly demonstrate the advan-tages of accelerometer-based navigation technique. However, in this cohort of patients, the conventional technique with intra-medullary guide for femoral or tibial resection could not be used for ethical reasons and because of high risk of component malposition by the distortion of the bony canal or presence of hardware. A control group in which CAS, RS, or PSI or extramedullary guide was used could be an alternative for comparison, but the small number of patients in this cohort does not make it applicable. Our results were compared with other series reporting the use of other tech-niques to manage TKA with EAD.
Third, the rotation analysis of each EAD was not detected. This assessment requires a CT scan. However, the accelerometer-based navigation system provide alignment only in coronal and sagittal
plane without any information regarding the component position in the axial plane, and therefore, the axial alignment was manually decided for every patients and not analyzed in this study.
Conclusion
This study demonstrates that the i-ASSIST accelerometer-based navigation system is accurate in achieving neutral mechanical alignment and optimal implant position after TKA in patients with EAD. This system could be considered a valuable option to the computer navigation system to improve accuracy for resection guide without the disadvantages such as long operative time, ne-cessity of learning curve, high cost, and nene-cessity of preoperative imaging.
References
[1] Innocenti M, Matassi F, Carulli C, Nistri L, Civinini R. Oxidized zirconium femoral component for TKA: a follow-up note of a previous report at a min-imum of 10 years. Knee 2014;21:858e61.
[2] Matassi F, Paoli T, Civinini R, Carulli C, Innocenti M. Oxidized zirconium versus cobalt-chromium against the native patella in total knee arthroplasty: patel-lofemoral outcomes. Knee 2017;24:1160e5.
[3] Insall JN, Binazzi R, Soudry M, Mestriner LA. Total knee arthroplasty. Clin Orthop Relat Res 1985:13e22.
[4] Ranawat CS, Boachie-Adjei O. Survivorship analysis and results of total condylar knee arthroplasty. Eight- to 11-year follow-up period. Clin Orthop Relat Res 1988:6e13.
[5] Insall JN, Ranawat CS, Aglietti P, Shine J. A comparison of four models of total knee-replacement prostheses. J Bone Joint Surg Am 1976;58:754e65. [6] Jeffery RS, Morris RW, Denham RA. Coronal alignment after total knee
replacement. J Bone Joint Surg Br 1991;73:709e14.
[7] Lording T, Lustig S, Neyret P. Coronal alignment after total knee arthroplasty. EFORT Open Rev 2016;1:12e7.
[8] 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;470:45e53.
[9] Klein GR, Austin MS, Smith EB, Hozack WJ. Total knee arthroplasty using computer-assisted navigation in patients with deformities of the femur and tibia. J Arthroplasty 2006;21:284e8.
[10] Bottros J, Klika AK, Lee HH, Polousky J, Barsoum WK. The use of navigation in total knee arthroplasty for patients with extra-articular deformity. J Arthroplasty 2008;23:74e8.
[11] Mullaji A, Shetty GM. Computer-assisted total knee arthroplasty for arthritis with extra-articular deformity. J Arthroplasty 2009;24:1164e1169.e1. [12] Kim K, Ramteke AA, Bae DK. Navigation-assisted minimal invasive total knee
arthroplasty in patients with extra-articular femoral deformity. J Arthroplasty 2010;25:658.e17e22.
[13] Catani F, Digennaro V, Ensini A, Leardini A, Giannini S. Navigation-assisted total knee arthroplasty in knees with osteoarthritis due to extra-articular deformity. Knee Surg Sports Traumatol Arthrosc 2012;20:546e51. [14] Shao J, Zhang W, Jiang Y, Wang Q, Chen Y, Shen H, et al. Computer-navigated
TKA for the treatment of osteoarthritis associated with extra-articular femoral deformity. Orthopedics 2012;35:e794e9.
[15] Rhee SJ, Seo CH, Suh JT. Navigation-assisted total knee arthroplasty for pa-tients with extra-articular deformity. Knee Surg Relat Res 2013;25:194e201. [16] Liu Z, Pan X, Zhang X. Total knee arthroplasty using navigation system for severe osteoarthritis with extra-articular deformity. Eur J Orthop Surg Trau-matol 2013;23:93e6.
[17] Banerjee S, Cherian JJ, Elmallah RK, Jauregui JJ, Pierce TP, Mont MA. Robotic-assisted knee arthroplasty. Expert Rev Med Devices 2015;12:727e35. [18] Jacofsky DJ, Allen M. Robotics in arthroplasty: a comprehensive review.
J Arthroplasty 2016;31:2353e63.
[19] Lionberger DR, Crocker CL, Chen V. Patient specific instrumentation. J Arthroplasty 2014;29:1699e704.
[20] Mattei L, Pellegrino P, Calo M, Bistolfi A, Castoldi F. Patient specific instru-mentation in total knee arthroplasty: a state of the art. Ann Transl Med 2016;4:126.
[21] Stone AH, Sibia US, MacDonald JH. Functional outcomes and accuracy of patient-specific instruments for total knee arthroplasty. Surg Innov 2018;25: 470e5.
[22] Xiao-Gang Z, Shahzad K, Li C. One-stage total knee arthroplasty for patients with osteoarthritis of the knee and extra-articular deformity. Int Orthop 2012;36:2457e63.
[23] Vasdev A, Dahiya V, Tyagi V, Gupta H, Rajgopal A. Total knee arthroplasty in extra articular deformities: a series of 36 knees. Indian J Orthop 2013;47:35. [24] Chi-Kin L, Hok-Yin L, Yiu-Chung W, Yuk-Leung W. Total knee replacement with iASSIST navigation system. J Orthop Trauma Rehabil 2018;24:29e33.
[25] Kinney MC, Cidambi KR, Severns DL, Gonzales FB. Comparison of the iAssist handheld guidance system to conventional instruments for mechanical axis restoration in total knee arthroplasty. J Arthroplasty 2018;33:61e6. [26] Iorio R, Mazza D, Drogo P, Bolle G, Conteduca F, Redler A, et al. Clinical and
radiographic outcomes of an accelerometer-based system for the tibial resection in total knee arthroplasty. Int Orthop 2015;39:461e6.
[27] Fujimoto E, Sasashige Y, Nakata K, Yokota G, Omoto T, Ochi M. Technical considerations and accuracy improvement of accelerometer-based portable computer navigation for performing distal femoral resection in total knee arthroplasty. J Arthroplasty 2017;32:53e60.
[28] Ueyama H, Minoda Y, Sugama R, Ohta Y, Yamamura K, Nakamura S, et al. An accelerometer-based portable navigation system improved prosthetic align-ment after total knee arthroplasty in 3D measurealign-ments. Knee Surg Sports Traumatol Arthrosc 2018;26:1e7.
[29] Kawaguchi K, Michishita K, Manabe T, Akasaka Y, Higuchi J. Comparison of an accelerometer-based portable navigation system, patient-specific instru-mentation, and conventional instrumentation for femoral alignment in total knee arthroplasty. Knee Surg Relat Res 2017;29:269e75.
[30] Wang J-W, Wang C-J. Total knee arthroplasty for arthritis of the knee with extra-articular deformity. J Bone Joint Surg Am 2002;84-A:1769e74. [31] Moreland JR, Bassett LW, Hanker GJ. Radiographic analysis of the axial
alignment of the lower extremity. J Bone Joint Surg Am 1987;69:745e9. [32] Minoda Y, Kobayashi A, Iwaki H, Sugama R, Iwakiri K, Kadoya Y, et al. Sagittal
alignment of the lower extremity while standing in Japanese male. Arch Orthop Trauma Surg 2008;128:435e42.
[33] Ewald FC. The Knee Society total knee arthroplasty roentgenographic evalu-ation and scoring system. Clin Orthop Relat Res 1989:9e12.
[34] Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989:13e4.
[35] Goh GS, Liow MHL, Tay DKJ, Lo NN, Yeo SJ, Tan MH. Accelerometer-based and computer-assisted navigation in total knee arthroplasty: a reduction in me-chanical axis outliers does not lead to improvement in functional outcomes or
quality of life when compared to conventional total knee arthroplasty. J Arthroplasty 2017;33:379e85.
[36] Demir B, €Ozkul B, Saygılı MS, Çetinkaya E, Akbulut D. Deformity correction with total knee arthroplasty for severe knee osteoarthritis accompanying extra-articular femoral deformity: the results are promising. Knee Surg Sports Traumatol Arthrosc 2018;26:3444e51.
[37] Papadopoulos EC, Parvizi J, Lai CH, Lewallen DG. Total knee arthroplasty following prior distal femoral fracture. Knee 2002;9:267e74.
[38] Thienpont E, Paternostre F, Pietsch M, Hafez M, Howell S. Total knee arthroplasty with patient-specific instruments improves function and re-stores limb alignment in patients with extra-articular deformity. Knee 2013;20:407e11.
[39] Kamara E, Berliner ZP, Hepinstall MS, Cooper HJ. Pin site complications associated with computer-assisted navigation in hip and knee arthroplasty. J Arthroplasty 2017;32:2842e6.
[40] Minoda Y, Watanabe K, Iwaki H, Takahashi S, Fukui M, Nakamura H. Theo-retical risk of anterior femoral cortex notching in total knee arthroplasty using a navigation system. J Arthroplasty 2013;28:1533e7.
[41] Jenny J-Y, Picard F. Learning navigatione learning with navigation. A review. SICOT J 2017;3:39.
[42] Jenny J-Y, Miehlke RK, Giurea A. Learning curve in navigated total knee replacement. A multi-centre study comparing experienced and beginner centres. Knee 2008;15:80e4.
[43] Siebert W, Mai S, Kober R, Heeckt PF. Technique andfirst clinical results of robot-assisted total knee replacement. Knee 2002;9:173e80.
[44] Bellemans J, Vandenneucker H, Vanlauwe J. Robot-assisted total knee arthroplasty. Clin Orthop Relat Res 2007;464:111e6.
[45] Kim S-M, Park Y-S, Ha C-W, Lim S-J, Moon Y-W. Robot-assisted implantation improves the precision of component position in minimally invasive TKA. Orthopedics 2012;35:e1334e9.
[46] Kim K-I, Kim D-K, Juh H-S, Khurana S, Rhyu K-H. Robot-assisted total knee arthroplasty in haemophilic arthropathy. Haemophilia 2016;22:446e52.
