Case Control Study
Copyright ©The Author(s) 2016. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Orthop. Jan 18, 2016; 7(1): 61-68
Published online Jan 18, 2016. doi: 10.5312/wjo.v7.i1.61
Patient specific guides for total knee arthroplasty are ready for primetime
Martijn GM Schotanus, Bert Boonen, Nanne P Kort
Martijn GM Schotanus, Bert Boonen, Nanne P Kort, Department of Orthopaedic Surgery, Zuyderland Medical Centre, 6162 BG Sittard-Geleen, The Netherlands
Author contributions: Schotanus MGM designed the study, gathered and analysed all the data, wrote the initial draft of the manuscript, managed and performed the study; Boonen B ensured the accuracy of the data and the analysis and gave critical revisions related to important intellectual content of the manuscript; Kort NP designed the study, revised the manuscript and gave final approval of the version of the article to be published.
Institutional review board statement: The study was reviewed and approved by the Institutional Review Board (METC Atrium-Orbis-Zuyd, Heerlen, the Netherlands) file name 13-N-09.
Informed consent statement: All patients gave informed consent prior to the study enrolment.
Conflict-of-interest statement: Dr. Nanne P Kort is a consultant on the PSG technique for Biomet, Europe. The other authors declare that they have no conflict of interest.
Data sharing statement: No additional data are available.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Martijn GM Schotanus, MSc, Research Manager, Department of Orthopaedic Surgery, Zuyderland Medical Centre, location Dr. H vd Hoffplein 1, 6162 BG Sittard-Geleen, The Netherlands. martijnschotanus@hotmail.com
Telephone: +31-88-4597433 Fax: +31-88-4597986
Received: February 11, 2015
Peer-review started: February 12, 2015
First decision: June 18, 2015
Revised: October 22, 2015
Accepted: November 17, 2015
Article in press: November 25, 2015
Published online: January 18, 2016

Abstract

AIM: To present the radiological results of total knee arthroplasty (TKA) with use of patient specific matched guides (PSG) from different manufacturer in patients suffering from severe osteoarthritis of the knee joint.

METHODS: This study describes the results of 57 knees operated with 4 different PSG systems and a group operated with conventional instrumentation (n = 60) by a single surgeon. The PSG systems were compared with each other and subdivided into cut- and pin PSG. The biomechanical axis [hip-knee-ankle angle (HKA)], varus/valgus of the femur [frontal femoral component (FFC)] and tibia (frontal tibial component) component, flexion/extension of the femur [flexion/extension of the femur component (LFC)] and posterior slope of the tibia [lateral tibial component (LTC)] component were evaluated on long-leg standing and lateral X-rays. A percentage of > 3° deviation was seen as an outlier.

RESULTS: The inter class correlation coefficient (ICC) revealed that radiographic measurements between both assessors were reliable (ICC > 0.8). Fisher exact test was used to test differences of proportions. The percentage of outliers of the HKA-axis was comparable between both the PSG and conventional groups (12.28% vs 18.33%, P < 0.424) and the cut- and pin PSG groups (14.3% vs 10.3%, P < 1.00). The percentage of outliers of the FFC (0% vs 18.33%, P < 0.000), LFC (15.78% vs 58.33%, P < 0.000) and LTC (15.78% vs 41.67%, P < 0.033) were significant different in favour of the PSG group. There were no significant differences regarding the outliers between the individual PSG systems and the PSG group subdivided into cut- and pin PSG.

CONCLUSION: PSG for TKA show significant less outliers compared to the conventional technique. These single surgeon results suggest that PSG are ready for primetime.

Key Words: Total knee arthroplasty, Patient specific matched guides, Patient matched instruments, Single surgeon, Alignment, Conventional instruments, Cutting guides, Pin guides

Core tip: Total knee arthroplasty (TKA) is one of the most successful and commonly performed surgical procedure for the treatment of severe knee osteoarthritis with excellent 15-20 years survivorships. This article provides an analysis on patient specific matched guides (PSG) between different manufacturers and the conventional technique and between pin- and cutting guides for TKA. In addition, we compared our results with previous studies (level 1 evidence), which are generally unambiguous, and show no radiological difference. However, in this trial, we do see difference in favour of the PSG technique.


Citation: Schotanus MG, Boonen B, Kort NP. Patient specific guides for total knee arthroplasty are ready for primetime. World J Orthop 2016; 7(1): 61-68
INTRODUCTION

Total knee arthroplasty (TKA) has been developed significantly over the last decades. Many changes have been made to improve both survival and functioning. A good postoperative biomechanical axis is one of the key elements for a good implant survival. Malalignment is associated with poor implant survivorship[1-4]. Several studies reported results of postoperative malalignment using conventional intramedullary alignment rods in TKA[5-9]. Computer navigation was introduced to cope with malalignment and instability in conventionally placed prostheses[10]. These days, revolutionary changes within the elective knee arthroplasty have taken place due to industry driven interventions[11]. Patient specific matched guides (PSG) for TKA is a relatively new technique to align the knee prosthesis, using 3D rapid prototyped disposable cut or pin guides that fits on the native anatomy of the individual patient[12,13]. This perioperative guiding technique eliminates the use of intra- and extra medullar rods to make bony resections. Previous published results on PSG suggest this to be a good alternative to conventional instrumentation with comparable results, improved radiological outcome and reduced operation time and blood loss[7,13-23].

This prospective study on PSG between different manufacturers and conventional technique for the implantation of TKA was designed to address the following research questions: Is there a significant difference in outliers in alignment in the frontal and lateral plane between PSG and conventional TKA, secondly between the four individual different PSG systems and thirdly between cut- and pin PSG? We hypothesise that there will be fewer outliers with PSG TKA compared to conventional TKA without differences between different PSG systems and cut- and pin PSG.

MATERIALS AND METHODS

Patients were operated for TKA with PSG systems from 4 different manufactures (Table 1). In daily practice the TKA system and PSG from the company Biomet is used. Between May 2013 and April 2014, 60 consecutive patients with debilitating osteoarthritis (OA) of the knee joint, who were eligible for primary TKA were included (Figure 1). Patients who were not eligible to undergo magnetic resonance imaging (MRI) due to metal artefacts around the knee joint from previous surgery, claustrophobia, movement artefacts during MRI scanning time, pigmented villonodular synovitis, implanted electronic devices and patients that refused to consent were excluded. TKA surgery was done using PSG and consisted of guides from 4 different TKA suppliers (Table 1). The conventional TKA group consisted of 60 patients who were randomly selected from a cohort (n≥ 500) as a comparison group. We did not match patients (e.g., body mass index, gender, age and severity of OA) to avoid selection bias.

Table 1 Different industries with brand names, guide type, implant name and scanning modality.
Dupuy-SynthesSmith and NephewZimmerBiomet
PSGTrumatchVisionairePSISignature
GuidesCutCutPinPin
ImplantSigma CRGenesis IINexGenVanguard CR
Imaging protocolCT1MRI2CT or MRI1CT or MRI1
Figure 1
Figure 1 Anterior-posterior radiograph of a left knee of a female patient. A: Preoperative severe osteoarthritis; B: Postoperative with the Sigma CR, total knee arthroplasty (Depuy) in situ.

All patients gave informed consent to participate in this prospective study and were operated by a senior knee orthopaedic surgeon (NK) with extensive experience with PSG[15,16]. Patients were not blinded to the type of alignment method used. Three patients were excluded from the study and therefore did not receive the intervention as planned. A flowchart of the study design is shown in Figure 2. There were no significant differences in baseline demographics, as summarized in Table 2.

Table 2 Baseline demographics per alignment method, n (%).
TrumatchVisionairePSISignatureConventionalP value
Number of patients1513141560
Mean age, yr (range)72 (57-90)72 (63-82) 69 (52-86)68 (56-74)65 (50-83)0.097
Male6 (40)7 (54)7 (50)7 (47)34 (57)0.967
Mean BMI (range)30 (23-36)30 (23-37) 30 (26-36)30 (23-38)28 (21-37)0.373
Severity OA
Moderate13 (87)11 (85)13 (93)14 (93)53 (88)0.991
Severe2 (13)2 (15)1 (7)1 (7)7 (12)0.959
Figure 2
Figure 2 Flowchart study design. PSI: Patient-specific instrument; MRI: Magnetic resonance imaging.

PSG and the conventional TKA surgery are extensively described in previous published studies[15,16]. Preoperative, a virtual 3 dimensional plan was made based on the imaging protocols of the different manufacturers (Table 1). Preferred component position of the prosthesis was planned to obtain a neutral biomechanical axis [hip-knee-ankle angle (HKA)] and position of the femoral [frontal femoral component (FFC)] and tibial [frontal tibial component (FTC)] components in the frontal plane. All settings during planning in the lateral plane were similar for all PSG systems: Femoral component flexion [flexion/extension of the femur component (LFC)] and tibial component posterior slope [lateral tibial component (LTC)] were set at 3°. The final approval of settings was done by the operating surgeon (NK). After approval, the disposable cut or pin guides (Table 1) for perioperative alignment were manufactured and used during surgery. A midline approach was used and a cemented prosthesis implemented in all cases (Table 1). The guides were designed to make contact with osteophytes and therefore it was not allowed to remove these prior to the bony cuts. The same procedure was performed in the conventional group, except for the standard conventional rods for femur and tibia with the same implant as the Signature group (Vanguard Complete Knee System, Biomet, Warsaw, INC). Conventional rods were used to align the position of the cutting blocks: LFC and LTC were set at 0°.

All patients received a multimodal pain protocol including spinal or general anesthesia and local infiltration analgesia without a drain and urine catheter. Postoperative procedures were the same in all TKA patients. Patients followed an enhanced recovery pathway and received subcutaneous thromboprophylaxis (Fondaparinux) once daily for 35 d, starting on the evening on the first postoperative day.

Preoperative approved planning for the femur and tibia component were compared with the postoperative achieved alignment of each component on radiographs. HKA-axis and implant position were measured with a calibrated protocol on digital images on a PACS system[15,16]. HKA angle was evaluated on standardized 1-year postoperative frontal long-leg standing X-rays. Varus/valgus position of the FFC and FTC perpendicular to the HKA angle were measured on the same frontal radiographs. Flexion/extension of the LFC, measured from the anterior femoral cortex and posterior or anterior slope of the LTC measured from the posterior cortex of the tibia, were evaluated on 1-year postoperative lateral radiographs. Deviations of > 3° between preoperative planned HKA-axis (sum of FFC and FTC) and individual components (FFC, FTC, LFC and LTC) compared to the postoperative achieved alignment on radiographs, were considered as outliers. Mean values, SD and percentages of > 3° deviation of the preoperative planned alignment and postoperative alignment were first compared between the complete PSG group and the conventional group and all PSG groups were compared with each other. A comparison between cut- and pin guides was also made (Table 1).

Ethical approval

This study was approved by the institutional review board (IRB Atrium-Orbis Zuyd Heerlen, the Netherlands; IRB-nr.13N09), registered online at the Dutch Trial Register (NTR4739) and was performed in compliance with the Helsinki Declaration of 1975, as revised in 2000. All patients were informed and they consented to providing data for anonymous use.

Statistical analysis

Statistical Package for the Social Sciences V17.0 (SPSS, Inc., Chicago, IL) for Windows was used. All radiographic evaluation was performed once for each radiograph, performed by 2 independent assessors (MS and SH). Inter class correlation coefficient (ICC) was calculated to check for inter observer reliability. An ICC ≥ 0.7 was considered as good correlation. Statistically significant differences for radiographs were analyzed with a one-way ANOVA. The Bonferroni method for correcting for multiple comparisons was used to reduce the chances of obtaining false-positive results (type I errors). Fisher exact test was used to test differences of proportions. P-value was considered to be statistically significant at P≤ 0.05 for all statistical analyses.

RESULTS

Of the 120 patients included, 3 patients could not be scanned with MRI and were operated with use of computed tomography (CT)-based PSG (Signature, Biomet). Baseline demographics are shown in Table 2. All guides fitted well during the time of operation, there were no conversions to conventional instrumentation. All radiographic measurements of both observers were reliable and ICC’s were excellent (Table 3).

Table 3 Inter observer correlation coefficients.
HKAFFCFTCLFCLTC
Inter CC0.8110.8790.8830.8500.943

With regard to the individual components, percentage of outliers of the FFC (P < 0.000), LFC (P < 0.000) and LTC (P < 0.05) were significantly different in favour of the PSG group (Table 4). Regarding the individual different PSG systems, the mean (SD) HKA-axis (P < 0.000), the FFC (P < 0.000) and LTC (P < 0.000) alignment were significantly different (Table 5). The PSG group subdivided into cut- and pin PSG showed significant difference regarding the mean FFC (P < 0.022) and the LTC (P < 0.009) alignment (Table 6).

Table 4 Mean (SD) values and amount of patients and percentages of outliers of > 3˚ deviation of the planned alignment and postoperative alignment compared between the patient specific matched guides and the conventional group, n (%).
OutliersPSGConventionalP value
HKA outliers7 (12.28)11 (18.33)0.424
Mean (SD)179.49 (2.24)178.54 (2.27)0.015
FFC outliers0 (0)11 (18.33)0.000
Mean (SD)89.44 (1.73)88.03 (1.73)0.000
FTC outliers1 (1.75)0 (0)1.000
Mean (SD)89.87 (1.32)90.37 (1.38)0.058
LFC outliers9 (15.78)35 (58.33)0.000
Mean (SD)86.09 (2.86)86.04 (3.14)0.314
LTC outliers9 (15.78)25 (41.67)0.033
Mean (SD)92.86 (2.64)87.43 (2.63)0.000
Table 5 Mean (SD) values and amount of patients and percentages of outliers of > 3˚ deviation of the planned alignment and postoperative alignment compared between the patient specific matched guides groups, n (%).
TrumatchVisionairePSISignatureP value
HKA outliers3 (20.00)1 (7.69)2 (14.28)1 (6.66)0.819
Mean (SD)178.5 (2.3)181.3 (1.6)180.6 (1.6)177.9 (1.8)0.000
FFC outliers00001.000
Mean (SD)89.9 (1.6)90.1 (1.5)89.9 (1.2)87.9 (1.8)0.000
FTC outliers001 (7.14)01.000
Mean (SD)89.3 (1.4)90.0 (1.2)89.9 (1.6)90.6 (1.3)0.081
LFC outliers2 (13.33)2 (15.38)1 (7.14)4 (26.66)0.663
Mean (SD)85.7 (1.6)85.4 (2.1)87.4 (1.9)85.8 (4.5)0.307
LTC outliers2 (13.33)4 (30.76)2 (14.28)1 (6.66)0.594
Mean (SD)92.7 (2.4)91.2 (3.0)94.8 (1.2)92.8 (2.7)0.000
Table 6 Mean (SD) values and amount of patients and percentages of outliers of > 3˚ deviation of the planned alignment and postoperative alignment compared between the cut (n = 28, Trumatch and Visionaire) and pin (n = 29, patient-specific instrument and signature) patient specific matched guides group, n (%).
Cut PSGPin PSGP value
HKA outliers4 (14.3)3 (10.3)1.000
Mean (SD)179.9 (2.4)179.3 (2.2)0.342
FFC outliers001.000
Mean (SD)90.0 (1.5)89.6 (1.8)0.022
FTC outliers01 (3.4)1.000
Mean (SD)89.6 (1.3)90.2 (1.5)0.115
LFC outliers4 (14.3)5 (17.21.000
Mean (SD)85.6 (1.8)86.6 (3.5)0.184
LTC outliers6 (21.4)3 (10.3)0.477
Mean (SD)92.0 (2.7)93.8 (2.3)0.009
DISCUSSION

This industry driven technology proved to be safe, reproducible and easy to use. This leads to a commercial success compared to other computer-assisted technologies[11]. Although, published results on PSG are contrasted, even on level I  studies. Seven level  I  studies compared conventional instrumentation with PSG and compared different PSG manufacturers. None of them had measured a significant difference in outliers of HKA axis (Table 7). However, Pfitzner et al[24], recently published results comparing conventional instrumentation with CT and MRI based PSG from 2 different manufacturers, and between both PSG groups. They found a significant difference regarding the outliers in HKA-axis between MRI based PSG (Visionaire; 7%) and conventional instruments (43%), but no significant difference between CT based PSG and conventional instruments, neither between both PSG systems[24]. This was contrary to what Victor et al[25] found. They compared 4 different PSG systems with the conventional technique, operated by 4 surgeons, with more significant outliers for the FTC and LTC in favour of the intra- and extramedular technique (Table 7). Even between the 4 different PSG systems, percentages of outliers of > 3° deviation of the planned HKA and LFC angle were significantly different, ranging from 6% to 45% and 20% to 82%, respectively[25] (Table 7). Published level I percentages of outliers in the frontal and lateral plane for individual components for both femur and tibia vary and are inconclusive. Outliers of the FFC for the PSG are comparable or less than the conventional intramedular technique. Only 2 authors published significant differences in favour of the MRI based PSG[17,24]. This was in contrast to the FTC (Table 7). Most of the outcomes are comparable, however, 2 articles published significant better outcome with extramedular rods[25,26]. Only Ng et al[22] found significant better outcome with MRI based PSG for the tibia. LevelI results are very remarkable in regard to the LTC. These were significantly better with PSG than with conventional instrumentation (Table 7). Most notable are the significant differences that have been found with CT based PSG, which scored poorer outcome regarding to LTC outliers, ranging from 21% to 65%[19,25-27] (Table 7). A possible explanation for these outcomes can be the limitations in visualization and outlining of intra- articular cartilage in CT based 3D models[28-31]. Another explanation, based on our experience, is that CT based guides were more difficult to place on the bony surface compared to MRI based guides. Nevertheless, we did not reveal a significant difference between the MRI and CT PSG surgeries for HKA-axis and individual components for the different planes.

Table 7 Published level I studies with significant percentage of outliers of > 3˚ deviation between the patient specific matched guides and conventional intramedular and/or extramedular alignment method for hip-knee-ankle angle axis, frontal femoral component, frontal tibial component, flexion/extension of the femur component, lateral tibial component and axial rotation of the femur and/or tibia component controlled with postoperative X-ray (long-leg standing and/or lateral X-rays) and/or computed tomography.
Outliers (%) > 3° deviationPSG systemModalityConventionalControlSample sizeSignificant outliers (%)
femur/tibia(PSG/conventional)(PSG/conventional)
Boonen et al[16]SignatureMRIIntraX-ray90/90LFC (49/65)1
Chareancholvanich et al[17]PSIMRIIntra/ExtraX-ray and CT40/40FFC (0/18)1
Chotanaphuti et al[18]TruMatchCTIntra/ExtraX-ray and CT40/40NA
Hamilton et al[19]TruMatchScout CTIntra/ExtraX-ray26/26LTC (65/50)2
Ng et al[22] [Outliers (%) > 2° deviation]PSIMRIIntraCT51/27FTC (27/67)2, Femoral rotation (16/67)2, Tibial rotation (22/95)2
Pfitzner et al[24]TruMatchCTIntra/ExtraX-ray and CT(30/30)/30HKA (30/7/43)2
VisionaireMRI + X-rayFTC (13/3/23)1
Femoral rotation (1/13 /50)1
Victor et al[25]SignatureMRI, CTIntra/ExtraX-ray and CT(16/16/16/16)/64  FTC (15/3)1
TruMatchMRI + X-rayLTC (21/3)2
VisionaireMRIHKA (6/25/45/19)1, 3
PSILFC (62/20/20/56)2, 3
Kotela et al[26]SignatureCTIntra/ExtraX-ray49/46FTC (39/20)1
Woolson et al[27]TruMatchCTIntra/ExtraCT22/26LTC (32/8)1
Current studySignatureMRIIntraX-ray(15/13/14/15)/60FFC (022)2
TruMatchCTLFC (16/67)2
VisionaireMRI + X-rayLTC (16/42)1
PSIMRI

There may be some concerns regarding our radiological measurements. A wide variety of different analyses in the literature are used to objectively determine the postoperative position for both the femur and tibia implants (Table 7). Despite a good ICC for the evaluation of the frontal and lateral position of both femur and tibia implants, rotational alignment was not examined. Most of the literature use long-standing radiographs, except for 1 paper which used scout CT scan[17] and two used full-leg CT scans[22,27]. Postoperative evaluation on 3D-CT have shown to be a valuable tool to measure position and orientation of both the femur and tibia components and it is more accurate with significantly better femoral rotation alignment after use of PSG[18,22,32]. Unfortunately, a postoperative 3D-CT is not routinely performed in our clinic. On the other hand, plane radiographs are generally applicable for everyone.

This single surgeon experience with different PSG manufacturers could raise questions about the general applicability. We had the opportunity to use different types of PSG and implants. Based on the experience with TKA, the use of PSG and a possible learning curve, implementation of a new implant system may be a potential bias in the outcome[25]. However, research is mostly performed by high-volume surgeons who probably easier adapt to a new surgical technique than low-volume surgeons or residents. PSG could be an added value in less experienced surgeons due to their simplicity[19]. On the other hand, we evaluated cut and pin PSG from different manufacturers with less outliers compared to the conventional group.

Our primary goal was to investigate the accuracy of alignment between conventional and PSG and between different PSG systems compared with published level I evidence. A comparison on perioperative and clinical outcome were not made, although there is a trend towards significant shorter operating time[16-18] and blood loss[16] with surgeries performed with PSG. However, published results on component sizing are inconclusive to come up with a statement[18,19,27].

Finally, even though this study was a consecutive series compared with a historical cohort and not a randomized trial, a potential criticism was the sample size and power of this study.

The present study illustrates that this simplified surgical technique for TKA is safe and effective with acceptable radiological outcome. The PSG group shows significantly less outliers compared to the conventional technique. Whether these differences are clinically relevant is questionable and should be investigated on the long term. Based on these single surgeon results, we conclude that PSG are ready for prime time.

ACKNOWLEDGMENTS

The authors want to thank Stef van Hoef for his work in measuring the alignment on digital long-leg standing and lateral radiographs. We also thank Dr. Rob Sollie from Flinders Medical Centre Adelaide, Australia, who served as external reader, and for his comments that greatly improved the manuscript.

COMMENTS
Background

Patients with knee osteoarthritis often results in debilitating function of the knee joint warranting a total knee arthroplasty (TKA). This study aims to present the radiological results of TKA with use of patient specific matched guides (PSG) from different manufacturer in patients suffering from severe osteoarthritis of the knee joint.

Research frontiers

Patients suffering from osteoarthritis of the knee joint can be operated with use of PSG for TKA from different manufacturer. TKA with PSG has concerns regarding accurate implant alignment and the long term survival of the TKA compared to the conventional instrumentation.

Innovations and breakthroughs

In this study, PSG for TKA from different manufacturer restored good biomechanical axis and individual implant alignment in patients suffering from moderate to severe osteoarthritis of the knee joint compared to conventional alignment.

Applications

To summarize, PSG from different manufacturer can be an added value in daily TKA practice in patients suffering from moderate to severe osteoarthritis of the knee joint compared to the conventional instrumentation for TKA.

Peer-review

The authors compared the accuracy of TKA using patient-specific instruments (PSIs) with that of TKA using the conventional technique. In addition, they compared the accuracy of 4 different manufactured PSI TKAs. In conclusion, TKA using PSIs was more accurate than TKA using the conventional method, and no difference in accuracy was found between the 4 different manufactured PSI TKAs. Regarding the PSI TKA that was recently developed, more research studies, including precision, cost, operation time, blood loss, radiation exposure, and long-term survival, should be conducted in order to examine if it confers more benefits to patients than the conventional TKA. The manuscript could add new information on PSI TKA regarding its accuracy.

Footnotes

P- Reviewer: Anand A, Ohishi T

S- Editor: Song XX L- Editor: A E- Editor: Li D

References
1.  Bargren JH, Blaha JD, Freeman MA. Alignment in total knee arthroplasty. Correlated biomechanical and clinical observations. Clin Orthop Relat Res. 1983;178-183.  [PubMed]  [DOI]
2.  Jeffery RS, Morris RW, Denham RA. Coronal alignment after total knee replacement. J Bone Joint Surg Br. 1991;73:709-714.  [PubMed]  [DOI]
3.  Lotke PA, Ecker ML. Influence of positioning of prosthesis in total knee replacement. J Bone Joint Surg Am. 1977;59:77-79.  [PubMed]  [DOI]
4.  Ritter MA, Faris PM, Keating EM, Meding JB. Postoperative alignment of total knee replacement. Its effect on survival. Clin Orthop Relat Res. 1994;153-156.  [PubMed]  [DOI]
5.  Bauwens K, Matthes G, Wich M, Gebhard F, Hanson B, Ekkernkamp A, Stengel D. Navigated total knee replacement. A meta-analysis. J Bone Joint Surg Am. 2007;89:261-269.  [PubMed]  [DOI]
6.  Haaker RG, Stockheim M, Kamp M, Proff G, Breitenfelder J, Ottersbach A. Computer-assisted navigation increases precision of component placement in total knee arthroplasty. Clin Orthop Relat Res. 2005;152-159.  [PubMed]  [DOI]
7.  Ng VY, DeClaire JH, Berend KR, Gulick BC, Lombardi AV. Improved accuracy of alignment with patient-specific positioning guides compared with manual instrumentation in TKA. Clin Orthop Relat Res. 2012;470:99-107.  [PubMed]  [DOI]
8.  Song EK, Seon JK, Park SJ, Jung WB, Park HW, Lee GW. Simultaneous bilateral total knee arthroplasty with robotic and conventional techniques: a prospective, randomized study. Knee Surg Sports Traumatol Arthrosc. 2011;19:1069-1076.  [PubMed]  [DOI]
9.  Song EK, Seon JK, Yim JH, Netravali NA, Bargar WL. Robotic-assisted TKA reduces postoperative alignment outliers and improves gap balance compared to conventional TKA. Clin Orthop Relat Res. 2013;471:118-126.  [PubMed]  [DOI]
10.  Beringer DC, Patel JJ, Bozic KJ. An overview of economic issues in computer-assisted total joint arthroplasty. Clin Orthop Relat Res. 2007;463:26-30.  [PubMed]  [DOI]
11.  Thienpont E, Bellemans J, Delport H, Van Overschelde P, Stuyts B, Brabants K, Victor J. Patient-specific instruments: industry’s innovation with a surgeon’s interest. Knee Surg Sports Traumatol Arthrosc. 2013;21:2227-2233.  [PubMed]  [DOI]
12.  Krishnan SP, Dawood A, Richards R, Henckel J, Hart AJ. A review of rapid prototyped surgical guides for patient-specific total knee replacement. J Bone Joint Surg Br. 2012;94:1457-1461.  [PubMed]  [DOI]
13.  Nam D, McArthur BA, Cross MB, Pearle AD, Mayman DJ, Haas SB. Patient-specific instrumentation in total knee arthroplasty: a review. J Knee Surg. 2012;25:213-219.  [PubMed]  [DOI]
14.  Barrack RL, Ruh EL, Williams BM, Ford AD, Foreman K, Nunley RM. Patient specific cutting blocks are currently of no proven value. J Bone Joint Surg Br. 2012;94:95-99.  [PubMed]  [DOI]
15.  Boonen B, Schotanus MG, Kort NP. Preliminary experience with the patient-specific templating total knee arthroplasty. Acta Orthop. 2012;83:387-393.  [PubMed]  [DOI]
16.  Boonen B, Schotanus MG, Kerens B, van der Weegen W, van Drumpt RA, Kort NP. Intra-operative results and radiological outcome of conventional and patient-specific surgery in total knee arthroplasty: a multicentre, randomised controlled trial. Knee Surg Sports Traumatol Arthrosc. 2013;21:2206-2212.  [PubMed]  [DOI]
17.  Chareancholvanich K, Narkbunnam R, Pornrattanamaneewong C. A prospective randomised controlled study of patient-specific cutting guides compared with conventional instrumentation in total knee replacement. Bone Joint J. 2013;95-B:354-359.  [PubMed]  [DOI]
18.  Chotanaphuti T, Wangwittayakul V, Khuangsirikul S, Foojareonyos T. The accuracy of component alignment in custom cutting blocks compared with conventional total knee arthroplasty instrumentation: prospective control trial. Knee. 2014;21:185-188.  [PubMed]  [DOI]
19.  Hamilton WG, Parks NL, Saxena A. Patient-specific instrumentation does not shorten surgical time: a prospective, randomized trial. J Arthroplasty. 2013;28:96-100.  [PubMed]  [DOI]
20.  Heyse TJ, Tibesku CO. Improved femoral component rotation in TKA using patient-specific instrumentation. Knee. 2014;21:268-271.  [PubMed]  [DOI]
21.  Koch PP, Müller D, Pisan M, Fucentese SF. Radiographic accuracy in TKA with a CT-based patient-specific cutting block technique. Knee Surg Sports Traumatol Arthrosc. 2013;21:2200-2205.  [PubMed]  [DOI]
22.  Ng VY, Arnott L, Li J, Hopkins R, Lewis J, Sutphen S, Nicholson L, Reader D, McShane MA. Comparison of custom to standard TKA instrumentation with computed tomography. Knee Surg Sports Traumatol Arthrosc. 2014;22:1833-1842.  [PubMed]  [DOI]
23.  Spencer BA, Mont MA, McGrath MS, Boyd B, Mitrick MF. Initial experience with custom-fit total knee replacement: intra-operative events and long-leg coronal alignment. Int Orthop. 2009;33:1571-1575.  [PubMed]  [DOI]
24.  Pfitzner T, Abdel MP, von Roth P, Perka C, Hommel H. Small improvements in mechanical axis alignment achieved with MRI versus CT-based patient-specific instruments in TKA: a randomized clinical trial. Clin Orthop Relat Res. 2014;472:2913-2922.  [PubMed]  [DOI]
25.  Victor J, Dujardin J, Vandenneucker H, Arnout N, Bellemans J. Patient-specific guides do not improve accuracy in total knee arthroplasty: a prospective randomized controlled trial. Clin Orthop Relat Res. 2014;472:263-271.  [PubMed]  [DOI]
26.  Kotela A, Kotela I. Patient-specific computed tomography based instrumentation in total knee arthroplasty: a prospective randomized controlled study. Int Orthop. 2014;38:2099-2107.  [PubMed]  [DOI]
27.  Woolson ST, Harris AH, Wagner DW, Giori NJ. Component alignment during total knee arthroplasty with use of standard or custom instrumentation: a randomized clinical trial using computed tomography for postoperative alignment measurement. J Bone Joint Surg Am. 2014;96:366-372.  [PubMed]  [DOI]
28.  Choi JY, Choi JH, Kim NK, Kim Y, Lee JK, Kim MK, Lee JH, Kim MJ. Analysis of errors in medical rapid prototyping models. Int J Oral Maxillofac Surg. 2002;31:23-32.  [PubMed]  [DOI]
29.  Duryea J, Neumann G, Brem MH, Koh W, Noorbakhsh F, Jackson RD, Yu J, Eaton CB, Lang P. Novel fast semi-automated software to segment cartilage for knee MR acquisitions. Osteoarthritis Cartilage. 2007;15:487-492.  [PubMed]  [DOI]
30.  Joffe JM, Nicoll SR, Richards R, Linney AD, Harris M. Validation of computer-assisted manufacture of titanium plates for cranioplasty. Int J Oral Maxillofac Surg. 1999;28:309-313.  [PubMed]  [DOI]
31.  Winder J, Bibb R. Medical rapid prototyping technologies: state of the art and current limitations for application in oral and maxillofacial surgery. J Oral Maxillofac Surg. 2005;63:1006-1015.  [PubMed]  [DOI]
32.  Hirschmann MT, Konala P, Amsler F, Iranpour F, Friederich NF, Cobb JP. The position and orientation of total knee replacement components: a comparison of conventional radiographs, transverse 2D-CT slices and 3D-CT reconstruction. J Bone Joint Surg Br. 2011;93:629-633.  [PubMed]  [DOI]