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Accuracy of Femoral Component Alignment Using Specimen MatchedCutting Blocks: An in Vitro Study.Carsten Tibesku - Sporthopaedicum Straubing - Straubing, GermanyDavid Mehl - Smith and Nephew Orthopaedics, Inc. - Memphis, USAPius Wong - European Centre for Knee Research, Smith & Nephew - Leuven, BelgiumBernardo Innocenti - Smith and Nephew - Leuven, Belgium*Luc Labey - Smith and Nephew - Leuven, BelgiumAbraham Salehi - Smith & Nephew, Inc. - Memphis, USA*Email: luc.labey@smith-nephew.comPurpose: Proper positioning of the components of a knee prosthesis for obtaining postoperativeknee joint alignment is vital to obtain good and long term performance of a kneereplacement. Although the reasons for failure of knee arthroplasty have not been studied indepth, the few studies that have been published claim that as much as 25% of knee replacementfailures are related to malpositioning or malalignment [x].The use of patient-matched cutting blocks is a recent development in orthopaedics. In contrastto the standard cutting blocks, they are designed to fit the individual anatomy based on 3Dmedical images. Thus, landmarks and reference axes can be identified with higher accuracy andprecision. Moreover, stable positioning of the blocks with respect to the defined axes is easierto achieve. Both may contribute to better alignment of the components.The objective of this study was to check the accuracy of femoral component orientation in acadaver study using specimen-matched cutting blocks in six specimens; first for a bicompartmentalreplacement, and then for a tri-compartmental replacement in the samespecimen.Materials and Methods: Frames with infrared reflective spherical markers were fixed to sixcadaveric femurs and helical CT scans were made. A bone surface reconstruction was createdand the relevant landmarks for describing alignment were marked using 3D visualisationsoftware (Mimics). The centres of the spherical markers were also determined. Based on thegeometry of the articular surface and the position of the landmarks, custom-made cutting blockswere designed. One cutting block was prepared to guide implantation of a bi-compartmentaldevice and another one to guide implantation of the femoral component of a total kneereplacement.The knee was opened and the custom-made cutting block for the bi-compartmental implant wasseated onto the surface. The block was used to make the anterior cut, after which it wasremoved and replaced with the conventional cutting block using the same pinning holes toensure the same axial rotational alignment. The other cuts were made using the conventionalcutting block and the bi-compartmental femoral component was implanted. Afterwards, asimilar procedure was used to make the extra cuts for the total knee component.The position of the components with respect to the reflective markers was measured by locatingthree reference points and “painting” the articular surface with a wand with reflective markers.The position of all marker spheres was continuously recorded with four infrared cameras andNexus software.Results: Average alignment for the bi-compartmental component in transverse and frontalplanes were 0.2° (standard deviation: 2.4°) and 0.4° (standard deviation: 2.8°), respectively.Average alignment for the tri-compartmental component in transverse and frontal planes were0.6° (standard deviation: 3.2°) and 0.9° (standard deviation: 5.5°), respectively.Conclusions: The specimen matched cutting blocks, designed based on CT scan data, achieveda similar level of alignment accuracy as reported for navigation systems.References: Austin et al., “Knee Failure Mechanisms After Total Knee Arthroplasty”,Techniques in Knee Surgery, 2004, pp 55-59file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]