Paper # 188: Can You Achieve Anatomic Femoral Tunnel Placement with Transtibial Anterior Cruciate Ligament Reconstruction Using Smaller Tunnel Sizes?

ABSTRACTS Abstract: Introduction: Femoral tunnel can be made with transtibial or transportal technique in ACL reconstruction. Transportal technique has the advantages in positioning the femoral tunnel independent of tibial tunnel. However, the transportal technique needs deep knee flexion and it results in limited arthroscopic view and short femoral tunnel. Transtibial technique has the advantages of more adequate femoral tunnel length compared with that of transportal technique. However, the position of femoral tunnel is largely affected by the position of the tibial tunnel. It has been considered it is very difficult to have more anatomically located femoral tunnel with conventional transtibial technique. We have modified the conventional transtibial technique. In this study, we tried to evaluate the position and the length of potential femoral tunnel and the obliquity of graft in single bundle ACL reconstruction using the modified transtibial technique and compare them with those of the transportal technique. Methods: In this retrospective matched paired study, we compared 20 knees of modified transtibial technique(mTT) with 20 knees of transportal technique(TP). In mTT group, the tibial tunnel was started from the area superior to pes anserinus and anterior to medial collateral ligament, and the femoral tunnel was made through the tibial tunnel at 90°of knee flexion while applying an anterior drawer and varus force on the proximal tibia. The position and the length of potential femoral tunnel and the obliquity of reconstructed graft were measured on postoperative radiograph and 3 D computed tomography(CT). Quadrant method has been used for the evaluation of femoral tunnel position. The length of potential femoral tunnel was measured as the length from the beginning of femoral tunnel to lateral cortex of lateral femoral condyle in the direction of femoral tunnel on 3D-CT using OnDemand 3DTM AAP(version 1.0) program. Results: The angles between femoral and tibia tunnel were 6.7° ⫾ 5.0° in mTT group and 9.9° ⫾ 6.0° in TP group(p⫽0.069). The positions of the anterior border of the femoral tunnel measured as the percentage of the length of the condyles along the Blumensaat line from the front were 72.5 ⫾ 6.4% in mTT and 68.8 ⫾ 6.5% in TP group(p⬎0.05). The coronal angles between the joint line and the graft determined on CT were 67.1° ⫾ 6.7° in mTT and 68.4° ⫾ 6.7 ° in TP group(p⬎0.05). The sagittal angles between the joint line and the graft on CT were 62.6° ⫾ 7.0°, 65.6° ⫾ 9.2° respectively(p⬎0.05). The angles between the femoral tunnel and anteroposterior axis of the distal femur, which connects the deepest part of the patellar groove and the center of the intercondylar notch, measured on the axial view of CT were 38.6° ⫾ 7.9° in mTT and 47.2° ⫾ 9.6° in TP group

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(p⬍0.01). With the quadrant method, deep-shallow positions of femoral tunnel were 35.0 ⫾ 4.5% in mTT and 30.8 ⫾ 4.8% in TP group (p⬍0.01) and high-low positions were 24.6 ⫾ 6.1% in mTT and 27.4 ⫾ 8.1% in TP group (p⬎0.05). The mean distance of deep-shallow position between the femoral tunnels of mTT and TP groups was 1.8mm. The lengths of potential femoral tunnel were 38.3 ⫾ 4.4 mm in mTT and 34.3 ⫾ 2.8 mm in TP group(p⫽0.001). Conclusion: With our modified transtibial technique, the position of femoral tunnel and obliquity of reconstructed graft were similar with those of transportal technique, and the lengths of potential femoral tunnel were longer than those of transportal technique. The femoral tunnels were slightly shallower than those of transportal technique, however, the distances between femoral tunnels of two groups were not long enough to make an effect on obliquity of the reconstructed graft. Paper # 188: Can You Achieve Anatomic Femoral Tunnel Placement with Transtibial Anterior Cruciate Ligament Reconstruction Using Smaller Tunnel Sizes? VASILI KARAS, BS, USA JOSEPH BARKER, MD, USA ERIC STRAUSS, MD, USA KEVIN MCGILL, MPH, USA MATTHEW T. PROVENCHER, MD, USA BERNARD R. BACH JR, MD, USA NIKHIL N. VERMA, MD, USA · Rush University Medical Center, Chicago, IL, USA Summary: Using a transtibial drilling technique for hamstring ACL reconstruction results in non-anatomic femoral tunnels that are superior and slightly posterior to the native femoral insertion. Abstract: Objective: The purpose of this study is to evaluate whether anatomic femoral tunnels could be achieved with transtibial ACL reconstruction using smaller tunnel sizes. We hypothesized that the smaller tibial tunnel utilized for hamstring ACL reconstruction would result in non-anatomic femoral tunnel placement. Methods: Seven cadaveric knees fixed at 90 degrees of flexion were dissected to expose the centers of the native femoral and tibial ACL insertions. Using a standardized tibial starting point based on previous studies evaluating transtibial femoral drilling using 11mm tunnels, tibial tunnels were drilled to the center of the tibial insertion using a 7 mm reamer. Next, using a 6 mm over the top

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ABSTRACTS

guide positioned as close as possible to the anatomic femoral insertion on the lateral wall, femoral tunnels were drilled with the 7 mm reamer. For each tunnel, the location and geometry relative to the native insertion site was evaluated using a NextEngine 3D scanner. Results: The reamed tibial tunnel occupied 41.3% (⫾ 4.5) of the native tibial insertion. Transtibial drilling resulted in femoral tunnels that were superior and slightly posterior compared to the native femoral insertion. The femoral tunnel had a mean overlap of 36.3% (⫾ 6.2) with the femoral insertion, located 2.7 mm (⫾ 0.4) from the posterior wall and 1.6 mm (⫾ 0.3) from the roof of the notch. Conclusions: During hamstring ACL reconstructions, the constraints imposed by a coupled drilling technique and smaller tibial tunnel results in non-anatomic femoral tunnels that are superior and slightly posterior to the native femoral insertion.

Paper # 189: Pitfall in ACL Reconstruction Using a Medial Portal Approach: Penetration of the Second Femoral Cortex MIRCO HERBORT, MD, GERMANY STEFFEN ROSSLENBROICH, MD, GERMANY WOLF PETERSEN, MD, PROF., GERMANY MICHAEL JOHANNES RASCHKE, PROFESSOR, GERMANY THORE ZANTOP, MD, GERMANY · University of Muenster, Muenster, NRW, GERMANY Summary: Biomechanical investigation of the primary stability of ACL reconstruction after penetration of the second femoral cortex. Abstract: Introduction: Tunnel placement for ACL reconstruction with cortical flip buttons implies the risk of accidentally perforating the lateral cortex with a drill of larger diameter than the intended 4.5 mm. Especially by using a medial portal approach the risk of accidental perforation of the lateral cortex is increased because of the shorter femoral tunnel length. This clinical pitfall has several issues when using a cortical fixation technique. Aim of the current study was to evaluate the structural properties after penetration of the lateral femoral cortex using different sized drill sizes. We hypothesized that a penetration of the second cortex using 7, 8 and 9 mm drill diameters result in significantly lower structural properties compared to a 4.5mm penetration (conventional technique). Furthermore we hypothesize that after perforation of the lateral cortex with a tunnel diameter of 7, 8 and 9 mm a hybrid fixation using a size matching inter-

ference screw increased the low structural properties significantly. Methods: In 100 porcine femurs ACL reconstruction using a medial portal approach were performed. Subsequently the constructs were mounted in a custom made fixation and a cryofixation clamp and were cyclically loaded by a uniaxial material testing machine ZWICK/ROELL Z005 (Zwick, GmbH und Co. KG, Ulm, Germany). In the control group, a penetration of the second cortex was performed with a 4.5 mm diameter drill (10 mm to a 9 mm blind ending graft tunnel. To simulate a situation with perforation of the lateral cortex a tunnel with a continuous diameter of 5mm, 5.5 mm , 6 mm, 7 mm, 8 mm and 9 mm has been drilled in the other groups. In the first part of the study the grafts have been fixed for reconstruction by a cortical fixation using a 1 mm Ethibond suture and a flip button (FlippTack, Karl Storz, Tuttlingen/Germany). In the second part of the study, a hybrid fixation with an additional interference screw (MegaFix, KARLSTORZ, GmbH & Co. KG, Tuttlingen, Germany) matching the size of the tunnel diameter has been performed in the groups with a tunnel diameter of 7 mm to 9 mm. (Fig.1) During biomechanical testing every construct has been loaded cyclically 1000 times between 50 and 250 N with a displacement rate of 200mm/min. After surviving cyclic testing all constructs were loaded to failure. The tested groups were compared regarding different parameters such as number of survived cycles, stiffness, maximum load, yield load, elongation after 1000 cycles and modes of failure. Statistical analyses were performed using the Kolmogorow-Smirnow Test and the Mann-Whitney U Test (p ⬍ 0.05). Results: The control group without perforation of the femoral cortex survived the cycling testing protocol and mean elongation after 1000 cycles was 4.3 (⫾0.8) mm. Groups with a continuous tunnel diameter of 5mm, 5.5mm and 6 mm (cortical fixation) survived the cycling testing procedure without failure and showed a mean elongation of 4.4 (⫾2.2) mm, 5.1 (⫾1.6) mm and 3.75 (⫾0,6) mm, respetively (p⬎0.05 to control group). In the 7mm, 8mm and 9 mm tunnel group the constructs did not survive the cyclic testings. All fixations failed by “pullin” of the button into the larger tunnel. In the hybrid fixation group using an interference screw fixation and cortical fixation, the reconstruction evaluating a 7,8 and 9mm penetration survived the cyclic protocol. Ultimate failure tests in the control group showed a stiffness of 114.9 (⫾27.7) N/mm, yield load of 492.1 (⫾28.7) N and a mean maximum load of 670.8 (⫾104.1) N. In the 7, 8 and 9 mm tunnel group (cortical fixation) none of the constructs could be loaded to failure. Recon-