Patient-Specific Instrumentation in Total Knee Arthroplasty Provides No Improvement in Component Alignment Benjamin M. Stronach, MD a , Christopher E. Pelt, MD b , Jill A. Erickson, PA b , Christopher L. Peters, MD b a Department of Orthopaedic Surgery, University of Mississippi Medical Center, Jackson, Mississippi b University of Utah, University Orthopaedic Center, Salt Lake City, Utah abstract article info Article history: Received 19 February 2014 Accepted 20 April 2014 Keywords: patient-specific instrumentation total knee arthroplasty femoral component alignment tibial component alignment MRI Improved component alignment in TKA remains a commonly cited benefit of MRI based patient-specific instrumentation (PSI). We hypothesized that PSI would lead to improved alignment versus traditional instrumentation (TI) during primary TKA. Fifty-eight knees (54 patients) that underwent TKA with PSI were compared to 62 knees that had previously undergone TKA with TI. Radiographs were evaluated for mechanical axis and alignment of the femoral and tibial components. Alignment was similar between the groups. However, the PSI group showed fewer knees in the target range for posterior tibial slope (PSI 38% vs. TI 61%, P = 0.01) in addition to a trend for fewer knees in target range for femoral flexion (PSI 40% vs. TI 56%, P = 0.07). This study demonstrated no improvement in overall alignment and perhaps a worsening of the tibial slope. © 2014 Elsevier Inc. All rights reserved. It is generally accepted that coronal alignment following total knee arthroplasty (TKA) should approximate the mechanical axis. A higher failure rate has been reported in knees that were not aligned in proximity to the mechanical axis [1–3]. However, this remains a topic of controversy with one recent report showing no increase in failure rate of knees falling outside the accepted range for appropriate alignment [4]. To achieve alignment, traditional instrumentation (TI) uses a series of jigs to provide bone resections when performing TKA. This has been the primary method of alignment since the advent of this surgery and was the only option available for guiding surgical resections until recently. Potential drawbacks of TI include instru- mentation of the femoral canal, the need for multiple surgical trays, human error with setting the guides, and the potential for inaccurate alignment based on surgeon technique. An entire industry has been developed to increase the accuracy of implant alignment to include the use of robotics and computer navigation. Computer navigation is an effective method for improving accuracy [5–9], but comes with potential problems [5,10–14] in comparison to TI that include pin site fracture and increased operative time. There has also been no proven benefit in terms of long-term patient outcomes with the use of this technology. The use of patient specific instrumentation (PSI) for knee arthroplasty is a novel technology aiming to increase the accuracy of component sizing, rotation and alignment without the associated risks of computer navigation. The potential benefits include: decreased operative time, decreased instrumentation, no intramedullary entry and increased accuracy of component alignment. Multiple manufac- turers offer this technology and there are variations in the methodology with each system. The algorithms used to render imaging and determine alignment remain proprietary, making comparisons be- tween products difficult. Initial reports on the use of PSI were conflicting with some supporting the technology [15–18] while others abandoned the use of PSI with concern for component mal-alignment [19]. Component alignment has been evaluated using several different systems and no advantage in alignment in comparison to traditional instrumentation or computer navigation has yet been shown [20–23]. Patient specific instrumentation is being provided by seven implant manufacturers and was used for an estimated 82,556 total knee arthroplasties worldwide in 2012 [24] despite no proven clinical benefit and minimal literature available to support its use. The purpose of this study was to evaluate the accuracy of implant alignment with the use of Biomet Signature (Biomet, Warsaw, IN, USA) MRI based PSI technology in comparison to TI for TKA in regards to sagittal and coronal implant alignment and overall mechanical axis. More specifically, we sought to compare the postoperative alignment of TKAs performed with PSI to TI in regards to overall mechanical alignment and sagittal and coronal alignment of the femoral and tibial components. We also compared the accuracy of PSI to TI for obtaining the surgeon's preferred implant alignment. Operative variables were recorded for both groups to include tourniquet time and estimated blood loss. The Journal of Arthroplasty 29 (2014) 1705–1708 Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained. This work was performed at the University of Utah, Salt Lake City, UT, USA. The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.04.025. Reprint requests: C. L. Peters, MD, University of Utah, University Orthopaedic Center, 590 Wakara Way, Salt Lake City, UT 84108. http://dx.doi.org/10.1016/j.arth.2014.04.025 0883-5403/© 2014 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org