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Letters to the Editor

References 1. Stronach BM, Pelt CE, Erickson J, et al. Patient specific total knee arthroplasty required frequent surgeon-directed changes. Clin Orthop Relat Res 2013;471:169. 2. Lee GC, Lotke PA. Can surgeons predict what makes a good TKA? Intraoperative surgeon impression of TKA quality does not correlate with Knee Society scores. Clin Orthop Relat Res 2012;470:159.

We believe that there is a place for PSI in specific cases (eg posttraumatic, heavily deformed femurs, where no IM guide can be used). But there is no added value for the standard TKA. Also the clinical results are—so far—NOT better! It is our duty, as a researcher, to investigate if results are better with a newer technology, not to assume that it is! Sincerely yours, Bart Vundelinckx, MD.

Answer to Letter to the Editor, concerning

B. Vundelinckx, MD Resident Orthopaedic Surgery and Traumatology Care To Move, AZ Nikolaas, Sint-Niklaas, Belgium Reprint requests: B. Vundelinckx, MD Berenbroekstraat 29, 3600 Genk, Belgium

Functional and Radiographic Short-Term Outcome Evaluation of the Visionaire System®, a Patient Matched Instrumentation System for Total Knee Arthroplasty

Dear Mrs./Mr. With great interest we have read the comments in the Letter to the Editor concerning our article about Patient Specific Instrumentation. First, we would like to ask if it would be possible to have the name of the author of the Letter to the Editor. It would be more polite if it would not be anonymous. It is stated that post-operative X-ray images are not an accurate measurement tool. However, the pre-operative planning is done, based on an MRI of the knee AND a full leg standing X-ray film. This same, standardized full leg X-ray is used to evaluate the overall mechanical axis and its deviation from the pre-operative plan. As this is done with the leg in a standardized position, the same way as used for the pre-operative planning, we believe that this is an accurate measurement tool for post-operative overall alignment evaluation of the leg. For the tibial slope however, a standardized lateral X-ray was used instead of a full leg lateral view. This was done for cost-saving reasons. Of course, in perspective of costs and irradiation, it would not be possible to include a post-operative full leg MRI of CT of the leg. Moreover, this kind of examination is never performed in our hospital. The outcome results were indeed compared to the pre-operative planning: there was a standard pre-operative planning of mechanical alignment of the leg of 0° (hip–knee–ankle) in the frontal view and a 3° tibial slope. The outcome results of both study groups were compared to this standard planning. In Table 6 of our study, it can be seen that the deviation of the actual versus the planned femoral angle was measured. Rotation of the femoral component however was not measured, as no CT-scans were taken post-operatively. It was the aim of our study to compare if the traditional or the PSI technique would give results, closest to the pre-operatively planned values. These results were clearly given in our study. It is stated that comparing postoperative results with the preoperative plan is not the same as evaluating surgical outcome. Of course this is true. But in our study, BOTH were done, independently! OF COURSE all preoperative plans were created and validated by the surgeon himself. The radiographic outcomes were compared versus the pre-operative plans and compared between both groups. Also, the functional outcome results were compared between both groups, to evaluate whether traditional instrumentation or PSI scored better, independently from the radiographic outcome. In your last paragraph, you assume that, by using modern technologies, the problem of 20–30% of dissatisfied patients after TKA would be solved! This looks very naive! The aim of studies like ours and the others you mentioned is to investigate if we can get to better results using those techniques. Of course, not every new technology will lead to better results! And if these new technologies are more expensive or more time consuming, their existence has to be questioned.

K. De Mulder, MD Consultant Surgeon Orthopaedic Surgery and Traumatology Care To Move, AZ Nikolaas, Sint-Niklaas, Belgium J. De Schepper, MD Consultant Surgeon Orthopaedic Surgery and Traumatology Care To Move, AZ Nikolaas, Sint-Niklaas, Belgium G. Van Esbroeck, MD Consultant Surgeon Orthopaedic Surgery and Traumatology Care To Move, AZ Nikolaas, Sint-Niklaas, Belgium

http://dx.doi.org/10.1016/j.arth.2014.11.027

Evaluation of Patient Specific Instruments. To measure is to know!

To the Editor: With great interest we have read a series of 7 articles regarding Patient Specific Instrumentation (PSI) published in the Journal of Arthroplasty (4 in 2013 and 3 in 2014) [1–7]. We were however surprised to read the conclusions drawn from these studies and suspect a fundamental flaw. In essence, the goal of PSI is to offer a consistent and accurate solution for positioning of the components in Total Knee Arthroplasty (TKA) as planned preoperatively. The expected result is fewer outliers and a smaller tolerance on surgical implant position variability. Inherent to this technology is that every patient is treated with a personalized preoperative plan. The patient specific instrument is designed to transfer that plan to the patient’s anatomy in the operating room. The intended output of the surgery is a postoperative result identical to the preoperative plan. The deviation between both needs to be studied. The observation that we made however, is that the cited papers go about this comparison in the wrong way. To avoid comparing apples and oranges, two criteria must be satisfied. First, an accurate measurement tool should be used. Second, the postoperative result should be compared to the actual preoperative plan. Both criteria are explained in more detail hereafter. There is consensus amongst clinicians that a postoperative X-ray image does not qualify as an accurate measurement tool. On the one hand, the intra and inter observer variability of measuring on an X-ray image is very large as compared to an MRI or CT image [8,9]. On the other hand, an X-ray image is highly dependent of the imaging angle. A small angular difference in imaging position can result in large differences in postoperative measurements. For a measurement of the flexion angle of an implant for example, it is crucial that this is done in the

Letters to the Editor

sagittal plane. Every deviation in imaging angle from this sagittal plane will skew the results. Therefore results based on an X-ray study should be interpreted with care. It is probable that the investigated postoperative deviation is masked by the inaccuracy of the measurement tool. The second criterion is that the postoperative result must always be compared to the actual preoperative plan. For PSI this plan is derived from bony landmarks indicated on an MRI or CT image. Some researchers however compare this plan with a postoperative X-ray image [1,3,4,6,7] or perform an analysis based on computer-assisted surgery (CAS) or navigation [2]. On this X-ray image or in the CAS system a newly planned outcome is created, independent of the original plan, and used to evaluate the postoperative result. We disagree that this approach allows a quantitative comparison with the preoperatively planned outcome, because these postoperative or intraoperative plans will most likely be different from the preoperative plan. We would also like to draw attention to the fact that comparing postoperative results with the preoperative plan is not the same as evaluating surgical outcome. The former can be attributed almost entirely to the patient specific instruments, for the latter another factor comes into play: the quality of the preoperative plan. By being offered advanced planning software, orthopedics is entering the second machine age. Surgeons who want to improve their results should embrace the computer software and use it as an extension of their brains. Every patient has his own specific knee and soft tissue sleeve [9,10]. Therefore surgeons must carefully design and check each preoperative plan, change it if necessary and validate it personally just like they would do intra operatively using conventional surgery. Just accepting default settings reduces surgeons to cook book surgeons. Surprisingly, the cited papers do not mention whether the preoperative plan was validated by the surgeon himself. Hence no distinction is made between the role of PSI and the role of the envisioned preoperative plan. This is fundamentally wrong. In addition, we want to emphasize that each PSI system is different and that an evaluation of one system cannot be extrapolated to others. Numerous studies report that 20%-30% of patients continue to endure knee pain or have problems after TKA with standard instruments. By now the pioneering days of TKA should have ended. Such a high patient dissatisfaction rate must no longer be tolerated. Therefore we should embrace the technologies that are being offered to us and not discard them based on dubious quantitative data. It is imperative that the performance

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of the available technologies is evaluated in an objective and correct way. This is only possible if the correct techniques are used to report on the link between pre-operative planning and postoperative results. Hendrik P. Delport, MD, PhD Ortho-Expert, Sint-Niklaas, Belgium August de Boeckstraat,1 B-9100 Sint-Niklaas, Belgium Jos Vander Sloten, PhD Faculty of Engineering Science, Section of Biomechanics, Chairman Leuven Medical Technology Centre, University of Leuven, Belgium

http://dx.doi.org/10.1016/j.arth.2014.11.026

References 1. Hamilton WG, Parks NL, Saxena A. Patient-Specific Instrumentation does not shorten surgical time: A prospective, Randomized Trial. J Arthroplast 2013;28(1):96. 2. Lustig S, Scholes CJ, Oussedik SI, et al. Unsatisfactory accuracy as determined by Computer Navigation of VISIONAIRE Patient-Specific Instrumentation for Total Knee Arthroplasty. J Arthroplast 2013;28:469. 3. Vundelinckx BJ, Bruckers L, De Mulder K, et al. Functional and Radiographic ShortTerm Outcome Evaluation of the Visionaire System, a Patient-Matched Instrumentation System for Total Knee Arthroplasty. J Arthroplast 2013;28:946. 4. Barrett W, Hoeffel D, Dalury D, et al. In-Vivo Alignment Comparing Patient Specific Instrumentation with both Conventional and Computer Assisted Surgery (CAS) Instrumentation in Total Knee Arthroplasty. J Arthroplast 2014;29:343. 5. Voleti PB, Hamula J, Baldwin KD, et al. Current Data do not support Routine Use of Patient-Specific Instrumentation in Total Knee Arthroplasty. J Arthroplast 2014; 29(9):1709. 6. Lionberger DR, Crocker CL, Chen V. Patient Specific Instrumentation. J Arthroplast 2014;29(9):1699. 7. Stronach BM, Pelt CE, Erickson JA, et al. Patient-Specific Instrumentation in Total Knee Arthroplasty Provides No Improvement in Component Alignment. J Arthroplast 2014; 29(9):1705. 8. Hirschmann MT, Konala P, Amsler F, et al. The position and orientation of total knee replacement components: a comparison of conventional radiographs, transverse 2DCT slices and 3D-CT reconstruction. J Bone Joint Surg (Br) 2011;93:629. 9. Victor J, Van Doninck D, Labey L, et al. How precise can bony landmarks be determined on a CT scan of the knee? Knee 2009;16:358. 10. Delport H, Labey L, Innocenti B, et al. Restoration of constitutional alignment in TKA leads to more physiological strains in the collateral ligaments. Knee Surg Sports Traumatol Arthrosc 2014. http://dx.doi.org/10.1007/s00167-0142971-z.

Evaluation of Patient Specific Instruments. To measure is to know!

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