1. Introduction Patient specific positioning guides (PSPGs) in TKA are based on MRI or CT data. Preoperatively, knee component positions can be visualized in 3-dimensional reconstructed images. Software allows anticipation of component position. From software planning PSPGs are manufactured and those PSPGs represent intra-operative component alignment Aim To investigate the correlation between pre-operative planning of component positioning and the post-operative achieved alignment with PSPG technique. Patients First 42 TKA (Vanguard® Complete Knee System, Biomet) with PSPG technique (Signature™, Materialise) Methods - CT measurement of component position according Perth protocol - Compared CT measurements with softwareplan obtained from MRI - 2 independent observers Femoral component angle: 3 planes Tibial component angle: 2 planes Measurements in the axial plane were not performed: intraoperative tibial rotation was in most cases obtained by extra-medullary guide. Results Intra-class correlation (ICC) between observer 1 and observer 2 Target angle: pre-operative planned alignment from Signature software. Mean, SD and Range of post-operative CT measurements Conclusion In our study postoperative knee component positioning is not consistent with preoperative software planning. Correlation between pre-operative planning and post-operative position of components in TKA with PSPG Justin AMJ van leeuwen¹, Stephan M Röhrl², Bjarne Grøgaard², Finnur Snorrason³ ¹Dep. of Orthopaedic Surgery, Betanien Hospital Skien, Norway ²Dep. of Orthopaedic Surgery, Oslo University Hospital, Norway ³Dep. of Orthopaedic Surgery, Vestre Viken Drammen, Norway 25 TKAs at Telemark Hospital, SkienPeriod: 2009-2010 17 TKAs at Oslo University HospitalPeriod: 2010-2011 CT Measurements: Component Angles ICC Femur Coronal0.75 Femur Sagittal0.93 Femur Axial0.46 Tibia Coronal0.89 Tibia Sagittal0.91 Component AngleTargetMeanSDRange Femur Coronal (valgus- / varus +) 0.0 1.2 1.6 -1.7 – 4.5 Sagittal (flexion- / extension+)-2.8-4.4 3.9-17.3 – 2.5 Axial (Internal rot- / external rot+) 0.0 0.5 0.1 -2.9 – 4.3 Tibia Coronal (valgus- / varus +) 0.0 0.5 2.4 -3.6 – 7.3 Sagittal (flexion- / extension+)-3.0-3.7 2.3 -8.8 – 2.4 Discussion Mean values of post-operative measurements are close to pre- operative software planning, but we found a considerable spread. Possible explanations might be error levels in pre-operative wrong identification of landmarks from MRI and/or different identification of bony landmarks on CT and intra-operative errors. There might be a learning curve in using PSPGs. Time gap between PSPG manufacturing and intra-operative use can theoretically provide a less proper fit due to slight change of anatomy in a progressive osteoarthritis. It is uncertain whether this inconsistency is of clinical relevance. More data is necessary to prove any benefit of PSPG compared to existing procedures for TKA. -Victor J, Van Doninck D, Labey L, Innocenti B, Parizel PM, Bellemans J: How precise can bony landmarks be determined on a CT scan of the knee? The Knee 2009, 16(5):358-365. -Chareancholvanich K, Narkbunnam R, Pornrattanamaneewong C: A prospective randomised controlled study of patient-specific cutting guides compared with conventional instrumentation in total knee replacement. The bone & joint journal 2013, 95-B(3):354-359. -Boonen B, Schotanus MG, Kort NP: Preliminary experience with the patient-specific templating total knee arthroplasty. Acta orthopaedica 2012, 83(4):387-393. Justin van Leeuwen E-mail: jusdep@online.no