Evaluation of the Zimmer PSI System for Total Knee Arthroplasty Using Computer Navigation

2013 ISAKOS ABSTRACTS e169

standing anteroposterior and lateral radiographs of theknee.Results: No significant differences were found betweengroups in terms of the coronal tibial component angle,89.86 � 2.48 degrees at bony landmark method, and89.85 � 2.21 degrees at conventional method. Posterior tiltof the tibial component was significantly smaller in thelandmark method than the conventional method(5.14 � 2.85� vs. 6.38 � 3.18�, respectively; P ¼ 0.007).The percentages of patients with a coronal tibial compo-nent angle over 3 degrees varus or valgus had no signifi-cant between two groups (18.1% vs. 12.4% respectively).The percentages of patients with a posterior tlt of the tibialcomponent over 10 degrees were significantly smaller inbony landmark method than the conventional method(1.3% vs. 8.25 % respectively; P¼0.04).Conclusion: Bony landmark method could provide betteraccuracy for posteror tibial slope compared witha conventional method. But, no difference could beobserved at coronal alignment compared with conven-tional method.

Paper #226: Evaluation of the Zimmer PSI System forTotal Knee Arthroplasty Using Computer NavigationMYLES RAPHAEL JAMES COOLICAN, FRACS, AUSTRALIA PRESENTINGAUTHOR

COREY J. SCHOLES, PHD, AUSTRALIA

VARUN SAHNI, MBBS, AUSTRALIA

SEBASTIEN LUSTIG, MD, PHD, FRANCEDAVID ANTHONY PARKER, MBBS, BMEDSCI, FRACS, AUSTRALIA $Sydney Orthopaedic Research Institute, Chatswood, NSW,Australia

SUMMARYThe aim of this study was to determine the efficacy of

patient-specific cutting blocks by comparing them tonavigation, the current gold standard.

ABSTRACT DATAIntroduction: Patient-matched instrumentation is advo-cated as the latest development in arthroplasty surgery.Custom-made cutting blocks created from preoperativeMRI scans have been proposed to achieve perfect align-ment of the lower limb in total knee arthroplasty (TKA)more efficiently than current methods. The aim of thisstudy was to determine the efficacy of patient-specificcutting blocks by comparing them to navigation, thecurrent gold standard.Method: Patients were recruited (N ¼25) to undergo theirtotal knee arthroplasty with a senior consultant surgeonusing imageless computer navigation in the standard fashion(Orthosoft, Zimmer USA). Each participant underwent pre-operative imaging comprising a full-length MRI, which wasused to produce an operative plan thatwas confirmed by thesurgeon prior to surgery. The plan was then used toconstruct cutting blocks specific to the patient’s anatomy(PSI, Zimmer, USA). During the arthroplasty procedure, theblocks were placed on the joint as per manufacturer’sinstructions and the computer navigation system was usedto evaluate the alignment of the cutting blocks. The blockswere assessed intraoperatively for the alignment in the

coronal and sagittal planes, as well as rotation, sizing andresection depth. The intraoperative results were comparedto the pre-operative plan and the differences analysed usingone-sample t-tests. The proportion of differences within +3�

was also calculated, as well as the prediction interval ofa single future measurement based on the data collected.Results: Significant differences were detected between theplanned alignment and the alignment verified intra-operatively with navigation for mean femoral coronalalignment (-0.6+1.0, p < 0.01) and femoral rotation(3.0+3.4, p <0.01), but not for femoral flexion (-0.6+1.6, p¼ 0.08). In contrast, tibial frontal alignment was notsignificantly different to the plan (-0.4+2.4, p ¼ 0.87),while the slope differed by 1.1� (+2.1, p ¼ 0.02). Thepercentage of the sample that fell within 3� of the planranged from 60% (femoral rotation) to 96% (femoralcoronal). Total virtual alignment in the coronal and sagittalplanes were not significantly different from zero. However,of the sample measured, 76% were within +3� in thecoronal plane and 80% in the sagittal plane. Importantly,99% prediction intervals ranged from 5.9� for femoralcoronal alignment to 15.8� for total sagittal alignment.Discussion & Conclusions: Although the results indicatethat the cutting blocks do not systematically over or under-estimate alignment compared to imageless computer navi-gation, the variability in the differences between measure-ments suggests they are not yet accurate for total kneearthroplasty. The results of this investigation comparefavourably to recent reports on other available systems,particularly for alignment in the sagittal plane. Howeverthere remains a high frequency of potential limb malalign-ment when compared with standard computer navigation.Further investigation is warranted to identify the source oferrors in the process and caution is recommended for routineclinical use without objective verification of alignment.

Paper #227: Early Experience With Visionaire PatientMatched Instrumentation in Total Knee Arthro-plasty NARAYANA PRASAD, FRCS (TR & ORTH), UNITED KINGDOM

PRESENTING AUTHOR

MARK LEWIS, FRCS (TR & ORTH), UNITED KINGDOM $ Royal GwentHospital, Newport, Wales, United Kingdom

SUMMARYA comparison of total knee replacement using patient

specific instrumentation with historical cohort in terms ofoperating time, length of stay and long leg alignment.

ABSTRACT DATAIntroduction: We aim to report the preliminary outcomeof Visionaire (Genesis 2, Smith and Nephew) patientmatched instruments in total knee arthroplasty in terms ofoperating time, hospital stay and post-operative alignmentin coronal plane. We also compared this with a historicalcohort of patients who had total knee arthroplasty usingthe same implant (Genesis 2 Smith and Nephew) withstandard instrumentation.Patients and Methods: Twenty-five patients wereincluded in the prospective study to have Visionaire (Genesis2, Smith and Nephew) patient matched instruments for totalknee replacement. All patients had pre-operative MRI scan