IntroductionPatient 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

AimTo investigate the correlation between pre-operative planning of component positioning and the post-operative achieved alignment with PSPG technique.

PatientsFirst 42 TKA (Vanguard® Complete Knee System, Biomet) withPSPG 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 planesMeasurements 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

ConclusionIn 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, Skien Period: 2009-2010

17 TKAs at Oslo University Hospital Period: 2010-2011

CT Measurements: Component Angles

ICC

Femur Coronal 0.75

Femur Sagittal 0.93

Femur Axial 0.46

Tibia Coronal 0.89

Tibia Sagittal 0.91

Component Angle Target Mean SD Range

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

DiscussionMean 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