Yonsei Med J.  2013 Jul;54(4):1006-1014. 10.3349/ymj.2013.54.4.1006.

Femoral Graft-Tunnel Angles in Posterior Cruciate Ligament Reconstruction: Analysis with 3-Dimensional Models and Cadaveric Experiments

• Kim SJ
• Chun YM
• Kim SH
• Moon HK
• Jang JW

• KMID: 2158238
• DOI: http://doi.org/10.3349/ymj.2013.54.4.1006

Abstract

PURPOSE
The purpose of this study was to compare four graft-tunnel angles (GTA), the femoral GTA formed by three different femoral tunneling techniques (the outside-in, a modified inside-out technique in the posterior sag position with knee hyperflexion, and the conventional inside-out technique) and the tibia GTA in 3-dimensional (3D) knee flexion models, as well as to examine the influence of femoral tunneling techniques on the contact pressure between the intra-articular aperture of the femoral tunnel and the graft.
MATERIALS AND METHODS
Twelve cadaveric knees were tested. Computed tomography scans were performed at different knee flexion angles (0degrees, 45degrees, 90degrees, and 120degrees). Femoral and tibial GTAs were measured at different knee flexion angles on the 3D knee models. Using pressure sensitive films, stress on the graft of the angulation of the femoral tunnel aperture was measured in posterior cruciate ligament reconstructed cadaveric knees.
RESULTS
Between 45degrees and 120degrees of knee flexion, there were no significant differences between the outside-in and modified inside-out techniques. However, the femoral GTA for the conventional inside-out technique was significantly less than that for the other two techniques (p<0.001). In cadaveric experiments using pressure-sensitive film, the maximum contact pressure for the modified inside-out and outside-in technique was significantly lower than that for the conventional inside-out technique (p=0.024 and p=0.017).
CONCLUSION
The conventional inside-out technique results in a significantly lesser GTA and higher stress at the intra-articular aperture of the femoral tunnel than the outside-in technique. However, the results for the modified inside-out technique are similar to those for the outside-in technique.

Keyword

Posterior cruciate ligament; reconstruction; graft-tunnel angle; 3-dimensional

MeSH Terms

Cadaver
Femur/radiography/surgery
Humans
*Imaging, Three-Dimensional
Knee Joint/surgery
Models, Anatomic
Posterior Cruciate Ligament/radiography/*surgery
Reconstructive Surgical Procedures/*methods
Tibia/radiography/surgery
Tomography, X-Ray Computed

Figure

• 

  Fig. 1 To construct 3-dimensional (3D) knee flexion models, the 3D images of the tibia at four different knee flexion angles (0°, 45°, 90°, and 120°) were registered for each specimen.

• 

  Fig. 2 (A) Three different guide pins (OI, the outside-in technique; IoM, the modified inside-out technique; IoC, the conventional inside-out technique) were passed through the center of the anterolateral bundle of the PCL. After removing all guide pins, each specimen was scanned and reconstructed. The reconstructed femoral (B) and tibial (C) images, which had intra-articular and outer cortical apertures made by guide pins (TI, intra-articular aperture of the anterolateral tibial tunnel; TO, outer cortical aperture of the anterolateral tibial tunnel), were separately registered into the previously obtained knee flexion model (D). (E) This method enabled us to make a 3D flexion model with constant apertures of the femoral and tibial tunnels that were made during surgery. PCL, posterior cruciate ligament; 3D, 3-dimensional.

• 

  Fig. 3 (A) To measure the femoral graft-tunnel angle, the datum plane including the intra- and extra-articular apertures of the femoral tunnel (FI and FO, respectively) and the intra-articular aperture of the tibial tunnel (TI) was chosen. (B) The femoral graft-tunnel angle was measured for each technique on an individual datum plane. (C) Images show 3D-measurements of the femoral critical corner angle and the tibial killer turn angle from an anteromedial view. 3D, 3-dimensional.

• 

  Fig. 4 Mounted on the specially designed jigs under 90° of knee flexion, the femur was forced to move downward (anterior direction) with a force of 150 N. The pressure sensitive thin film was inserted between the graft and the intra-articular aperture of the femoral tunnel.

• 

  Fig. 5 Angles were measured for the 3D models at different knee flexion angles: 0°, 45°, 90°, and 120° (mean±standard deviation). (A) For all three femoral tunneling techniques, the femoral graft-tunnel angle tended to decrease as knee flexion increased (*p<0.001). Conversely, the tibial graft-tunnel angle was lowest at 45° of knee flexion and it significantly increased as knee flexion increased between 45° and 120° (*p<0.001). (B) Between 45° and 120° of knee flexion, the femoral graft-tunnel angle for the conventional inside-out technique was significantly more acute than that for the other two techniques (*p<0.001). Also, the femoral graft-tunnel angle for the conventional inside-out technique was significantly more acute than the tibial killer turn angle at 120° of knee flexion (*p<0.001). 3D, 3-dimensional.

• 

  Fig. 6 (A) Scanned images (left rows) and converted images with the calibrated contact stress map (right rows) obtained from the pressure sensitive films for each technique. (B) The average and maximum contact pressure at the intra-articular aperture of the femoral tunnel for each technique. The values of the average and maximum contact pressure in the conventional inside-out group was significantly higher than that of the outside-in group (*p=0.012, †p=0.005) and the modified inside-out group (*p=0.012, ‡p=0.017). Error bars represent interquartile range.

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