LIVRE JDG 2014

M. Bonnin

TKA (the contours of the implants is always

more than 2mm inside the bony contour) and

Oversized TKA (the TKA overhangs more than

2mm from the bony contours).

Analysis of DICOM images

DICOM images were analyzed with OsiriX®

software, with 3D multiplanar reconstructions.

From these raw images segmentation was done

withMimics®software (Materialize®, Leuven,

Belgium) in order to obtain three-dimensional

images. To improve the quality of the implants

visualization, the Stereo Litography files (STL)

of the implants were obtained from the

manufacturer, so that we can match with the

raw DICOM images (fig. 3).

Imaging of the PT in the

normal knee: The

“functional” tibial

plateau and the

“anatomic” tibial

plateau

In a normal knee, the PT crosses the postero-

superior surface of the tibial plateau, with a

maximum overlapping of 5.5mm (75mm

observed while the knee is fully extended

(fig. 4 and 5). This overlap decreases from 0° to

90° of flexion. In deep flexion, the PT remains

distant from tibial plateau.

Fig. 3: Three-dimensional reconstruction of the knee,

obtained from DICOM images after implantation of

the TKA. In this specimen, the prosthesis was

“normosized”. The PT crosses the posterolateral

corner of the plateaus. Reconstructions were made

with Mimics® software (Materialize®) with a fusion

of the STL files of the implant.

Fig. 4: This axial slice represents the standard tibial

cut made at 9mm from the top of the lateral

plateau. The contours of the tibia are circled in

green. The positions of the popliteus tendon on

each CT slice, from 9mm (circled in green) to 5mm

above the joint line level (JL) (orange) are projected

on this slice (i.e., 7.5mm distal to JL in red, 5mm

distal to JL in purple, 2.5mm in blue, JL level in

green and 2.5mm above JL in yellow). The PT

overlaps the reference cut in all the posterolateral

area. The maximum overlap zone in this specimen

was 7mm (black arrow). To avoid impingement, the

prothetic plateau should no overhang from the

yellow dotted line, which mark the limit of the

“functional” tibial plateau.