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Knee: J. Lützner, F. Krummenauer, C. Wolf, K.-P. Günther, and S. Kirschner Computer-assisted and conventional total knee replacement: A COMPARATIVE, PROSPECTIVE, RANDOMISED STUDY WITH RADIOLOGICAL AND CT EVALUATION J Bone Joint Surg Br 2008; 90-B: 1039-1044 [Abstract] [Full text] [PDF]

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Authors' reply:

Jörg Lützner, Frank Krummenauer, Klaus P. Günther, and Stephan Kirschner   (6 October 2008)

Computer-assisted and conventional total knee replacement

Jon V Clarke, Tom Nunn, Jason L.B. Roberts   (3 September 2008)

Authors' reply: 6 October 2008
Jörg Lützner, Orthopaedic surgeon University Hospital carl Gustav Carus, Dresden, Germany, Frank Krummenauer, Klaus P. Günther, and Stephan Kirschner Send letter to journal: Re: Authors' reply: Joerg.Luetzner{at}uniklinikum-dresden.de Jörg Lützner, et al.	Sir, We thank Mr Clarke and colleagues for their valuable comments on our paper. We completely agree that as long as the registration process for rotational alignment is similar in navigated and conventional total knee arthroplasty (TKA) no difference can be expected. Improvements of navigation systems could possibly solve this problem in the future. With regards to the coronal positioning there are several reasons which may contribute to why we were not able to show a statistical difference between navigated and conventional TKA. During surgery we tried to achieve a neutral mechanical axis at least within +/-3°. We therefore accepted a malposition of the femoral and tibial component of not more than 1.5° and a deviation of the mechanical axis of usually not more than 2°. In two cases of severe deformity we accepted a deviation of 3°. The intra-operative data from the navigation system, the mechanical axis of the CT-Scan and from the whole-leg standing radiograph showed notable differences. Therefore we used the whole-leg standing radiograph as a reference, as in most studies before. This is a serious limitation. Comparing the outcome of a very precise system such as computer-assisted navigation (error 0.5° to 1°)1 with a method such as the whole-leg standing radiograph with much greater possible inaccuracies2 remains an unsolved problem. The calculation of statistical power was done for rotational alignment of the tibial component, as we considered this to be an unsolved problem. Therefore it could be that the number of patients was simply too low to show a statistical significant difference. The percentage of 87.5% of navigated TKA within the accepted range of +/- 3° is comparable with most randomised studies, but the percentage of 82.5% conventional TKA within this range is higher than in most of these studies. The mentioned study from Chauhan et al3 reported 86% of the navigated TKA but only 71% of the conventional TKA within the +/-3° range. We also agree that working with a navigation system has a considerable learning effect and therefore influences the results of conventional TKA. The senior author (SK) had previous experience with another navigation system than that used in this study. Both operating surgeons (JL, SK) had performed at least 20 navigated TKA before this study. Finally, we think that computer-assisted navigation in TKA improves implant positioning in the coronal plane but not the rotational alignment at the current stage and is additionally a good tool for educational purposes. Nonetheless, its value with regards to clinical outcome is still unclear and it remains time-consuming. These criteria must be weighed against each other. J. LÜTZNER, MD, Orthopaedic Surgeon, F. KRUMMENAUER, PhD, K.-P. GÜNTHER, MD, S. KIRSCHNER, MD, University Hospital Carl Gustav Carus, Dresden, Germany. 1.Pitto RP, Graydon AJ, Bradley L, et al. Accuracy of a computer-assisted navigation system for total knee replacement. J Bone Joint Surg [Br] 2006;88-B:601-5. 2. Krackow KA, Pepe CL, Galloway EJ. A mathematical analysis of the effect of flexion and rotation on apparent varus/valgus alignment at the knee. Orthopedics 1990;13:861-8. 3. Chauhan SK, Scott RG, Breidahl W, Beaver R J. Computer-assisted knee arthroplasty versus a conventional jig-based technique: a randomised, prospective trial. J Bone Joint Surg [Br] 2004;86-B:372-7.
Computer-assisted and conventional total knee replacement 3 September 2008
Jon V Clarke, SpR Orthopaedics & Trauma Western Infirmary, Glasgow, UK, Tom Nunn, Jason L.B. Roberts Send letter to journal: Re: Computer-assisted and conventional total knee replacement jvclarke{at}doctors.org.uk Jon V Clarke, et al.	Sir, We read with interest the article by Lützner et al1 entitled ‘Computer-assisted and conventional total knee replacement: a comparative, prospective, randomised study with radiological and CT evaluation.’ This paper has highlighted the limitations of current image-free navigation systems for improving the rotational alignment of both femoral and tibial components during total knee arthroplasty (TKA). The fact remains that the registration process for navigated TKA relies on identification and palpation of the same landmarks as for conventional instrumentation. This is a particular problem for tibial rotation where there is less agreement as to the most suitable reference points.2 With regards to coronal positioning it is interesting to note that the navigated group did not provide any statistical benefit in terms of varus/valgus malalignment. In view of this we feel it would be valuable if the authors could supply the following information: firstly, how did the intra-operative post-implant alignment data, as supplied by the navigation system, compare with the follow-up CT and plain radiographic measurements? If the mechanical femoral-tibial angle intra-operatively was found to be outwith 3° of varus/valgus from the desired neutral axis during the trial of the implant was this position then accepted? An obvious potential advantage of computer-navigated systems is real-time intra-operative feedback which enables appropriate adjustments to be made, if necessary, to achieve the desired coronal alignment. Secondly, it has been reported by Stulberg et al3 that previous exposure to navigation can lead to improved coronal positioning with conventional instrumentation. To what extent were the authors ‘trained in navigation’ prior to the study, and do they consider this a possible contributing factor in their results? In light of previous randomised, controlled trials of this same system achieving statistically significant improvements in coronal alignment compared with traditional instrumentation techniques4 we feel this information would be useful with regards to why this was not achieved in this paper. This would possibly provide a more useful contribution to the ongoing computer-assisted orthopaedic surgery debate. J.V. CLARKE, MBChB, MRCS(Glas), T. NUNN, MBChB, MRCS(Ed), J.L.B. ROBERTS, FRCS(Tr & Orth), Western Infirmary, Glasgow, UK. 1. Lützner J, Krummenauer F, Wolf C, Günther K.-P, Kirschner S. Computer-assisted and conventional total knee replacement: a comparative, prospective, randomised study with radiological and CT evaluation. J Bone Joint Surg[Br] 2008;90-B:1039-44. 2. Cobb JP, Dixon H, Dandachli W, Iranpour F. The anatomical tibial axis: reliable rotational orientation in knee replacement. J Bone Joint Surg[Br] 2008;90-B:1032-8. 3. Stulberg SD, Yaffe MA, Koo SS. Computer-assisted surgery versus manual total knee athroplasty: a case-controlled study. J Bone Joint Surg[Am] 2006;88-A(Suppl 4):47-54. 4. Chauhan SK, Scott RG, Breidahl W, Beaver RJ. Computer-assisted knee arthroplasty versus a conventional jig-based technique. A randomised, prospective trial. J Bone Joint Surg[Br] 2004;86-B:372-7.