Influence of Graft Bending Angle on Femoral Tunnel Widening After Double-Bundle ACL Reconstruction: Comparison of Transportal and Outside-In Techniques

Background: Previous studies have suggested that increased mechanical stress due to acute graft bending angle (GBA) is associated with tunnel widening and graft failure after anterior cruciate ligament (ACL) reconstruction. Few studies have compared the GBA between the outside-in (OI) and the transportal (TP) techniques. Purpose: To evaluate the influence of GBA on clinical outcomes and tunnel widening after ACL reconstruction with OI versus TP technique. Study Design: Cohort study; Level of evidence, 3. Methods: Included in the study were 56 patients who underwent double-bundle ACL reconstruction (n = 28 in the OI group and n = 28 in the TP group). Clinical outcomes (Lysholm, International Knee Documentation Committee, Tegner score, and knee laxity) 1 year postoperatively were evaluated. Computed tomography scans at 5 days and 1 year postoperatively were used for imaging measurements, and the femoral tunnel was divided into the proximal third, middle, and aperture sections. The GBA and cross-sectional area (CSA) were measured using image analysis software and were compared between groups. A correlation analysis was performed to determine if the GBA affected clinical outcomes or tunnel widening. Results: No significant difference was observed in clinical outcomes between the groups. The GBA of both the anteromedial (AM) and posterolateral bundles were more acute in the OI group compared with the TP group ( P < .05). The CSA at the AM tunnel aperture increased significantly in the OI group (84.2% ± 64.3%) compared with the TP group (51.4% ± 36.7%) ( P = .04). However, there were no differences in the other sections. In the Pearson correlation test, GBA was not correlated with tunnel widening or clinical outcomes. Conclusion: Regardless of technique, the GBA did not have a significant influence on tunnel widening or clinical outcomes. Considering a wider AM tunnel aperture, a more proximal and posterior AM tunnel position might be appropriate with the OI technique.

Biomechanical Effects of Aspect Ratio of the Knee during Outside-In Anterior Cruciate Ligament Reconstruction Surgery

We analyzed tunnel length, graft bending angle, and stress of the graft according to tunnel entry position and aspect ratio (ASR: ratio of anteroposterior depth to mediolateral width) of the articular surface for the distal femur during single-bundle outside-in anterior cruciate ligament reconstruction (ACLR) surgery. We performed multiflexible body dynamic analyses with four ASR (98, 105, 111, and 117%) knee models. The various ASRs were associated with approximately 1 mm changes in tunnel length. The graft bending angle increased when the entry point was far from the lateral epicondyle and was larger when the ASR was smaller. The graft was at maximum stress, 117% ASR, when the tunnel entry point was near the lateral epicondyle. The maximum stress value at a 5 mm distance from the lateral epicondyle was 3.5 times higher than the 15 mm entry position, and the cases set to 111% and 105% ASR showed 1.9 times higher stress values when at a 5 mm distance compared with a 15 mm distance. In the case set at 98% ASR, the low-stress value showed a without-distance difference from the lateral epicondyle. Our results suggest that there is no relationship between the ASR and femoral tunnel length. A smaller ASR causes a higher graft bending angle, and a larger ASR causes greater stress in the graft.

Influence of femoral tunnel exit on the 3D graft bending angle in anterior cruciate ligament reconstruction

Purpose To quantify the influence of the femoral tunnel exit (FTE) on the graft bending angle (GBA) and GBA-excursion throughout a full range of motion (ROM) in single-bundle anterior cruciate ligament (ACL) reconstruction. Methods Three-dimensional (3D) surface models of five healthy knees were generated from a weight-bearing CT obtained throughout a full ROM (0, 30, 60, 90, 120°) and femoral and tibial ACL insertions were computed. The FTE was simulated for 16 predefined positions, referenced to the Blumensaat's line, for each patient throughout a full ROM (0, 30, 60, 90, 120°) resulting in a total of 400 simulations. 3D GBA was calculated between the 3D directional vector of the ACL and the femoral tunnel, while the intra-articular ACL insertions remained unchanged. For each simulation the 3D GBA, GBA-excursion, tunnel length and posterior tunnel blow-out were analysed. Results Overall, mean GBA decreased with increasing knee flexion for each FTE (p < 0.001). A more distal location of the FTE along the Blumensaat's line resulted in an increase of GBA and GBA-excursion of 8.5 ± 0.6° and 17.6 ± 1.1° /cm respectively (p < 0.001), while a more anterior location resulted in a change of GBA and GBA-excursion of -2.3 ± 0.6° /cm (+ 0.6 ± 0.4°/ cm from 0–60° flexion) and 9.8 ± 1.1 /cm respectively (p < 0.001). Mean tunnel length was 38.5 ± 5.2 mm (range 29.6–50.5). Posterior tunnel blow-out did not occur for any FTE. Conclusion Aiming for a more proximal and posterior FTE, with respect to Blumensaat’s line, reliably reduces GBA and GBA-excursion, while preserving adequate tunnel length. This might aid to reduce excessive graft stress at the femoral tunnel aperture, decrease femoral tunnel widening and promote graft-healing. Level of Evidence IV

Excellence in Research:A Hybrid Transtibial Technique Combines the Strengths of theAnteromedial Portal and Transtibial Approaches: A Prospective Randomized Controlled Trial

Objectives: Improved biomechanical and clinical outcomes have been reported when femoral anterior cruciate ligament (ACL) tunnels are centered on the native footprint. The anteromedial (AM) portal technique achieves improved aperture position when compared to a transtibial (TT) approach but sacrifices technical ease and creates a shorter more acutely angulated tunnel. A hybrid transtibial technique (HTT) technique using medial portal guidance of a flexible transtibial guide wire without the need for knee hyperflexion may combine the strengths of both the AM and TT approaches. The authors hypothesized that this HTT technique would achieve anatomic femoral tunnel apertures similar to the AM technique, but with longer and less angulated femoral tunnels similar to a TT technique. Methods: A prospective randomized controlled trial was implemented where 30 consecutive patients with acute, primary ACL tears were randomized to receive a TT, AM or HTT technique for their reconstruction. A total of 46 patients were assessed for eligibility in the investigation (Figure 1). All patients underwent 3D CT scans of the operative knee 6 weeks postoperatively to characterize tunnel positions. Femoral and tibial tunnel aperture positions and tunnel lengths, as well as the graft bending angle in the sagittal and coronal plane were measured. Results: There were no significant differences between the patient demographics of the three groups. Tibial tunnel lengths and aperture positions were identical between the three groups. The AM portal and HTT techniques achieved identical femoral aperture positions in regards to both height (p=0.75) and depth (p=0.72). On the other hand, compared to the AM portal and HTT techniques, respectively, femoral apertures created by the TT technique were significantly higher (p<0.001 and p<0.001) and shallower (p=0.001 and p<0.001) in the notch. The average femoral tunnel lengths varied significantly between the three groups measuring 35.16 mm, 41.64 mm, and 54.13 mm for the AM, HTT and TT groups, respectively (p<0.001). Lastly, there were no differences between the average coronal (164.0 degrees versus 158.8 degrees, p=0.190) and sagittal (114.0 degrees versus 111.0 degrees, p=0.358) graft bending angles between the TT and HTT groups, respectively. By contrast, compared to the TT and HTT groups, respectively, the graft bending angles created with an AM technique were significantly more acutely angled in the coronal (146.3 degrees, p<0.001, p<0.006) and sagittal (100.5 degrees, p=0.014, p=0.013) planes. Conclusion: The HTT technique achieves femoral aperture positions equally as anatomic as an AM portal technique, but with longer and less acutely oriented grafts similar to a transtibial approach. These advantages will decrease the incidence of graft tunnel mismatch as well as reduce the amount of stress imparted onto the graft by avoiding an acute graft bending angle. As such, this hybrid approach may represent a beneficial combination of both transtibial and AM portal techniques.

Optimal Condition to Create Femoral Tunnel Considering Combined Influence of Knee Flexion and Transverse Drill Angle in Anatomical Single-Bundle ACL Reconstruction Using Medial Portal Technique: 3D Simulation Study

There has been no previous study using three-dimensional (3D) measurement on femoral tunnel characteristics according to the combined influence of various flexion angles of knee and transverse drill angles in single-bundle ACL reconstruction with transportal technique. The purpose of this study was to determine optimal condition of knee flexion angle and transverse drill angle to create secure femoral tunnel in single-bundle ACL reconstruction with transportal technique considering tunnel length, tunnel wall breakage, and graft bending angle. This study was conducted using simulation of 3D computed tomography of thirty subjects. Three variables of femoral tunnel changed according to combined influence of four flexion angles of knee and three transverse drill angles were measured: tunnel length, wall breakage, and graft bending angle. There was no case of short femoral tunnel less than 25 mm at 120° and 130° of flexion. There was no case of breakage of femoral tunnel at 120° of flexion with maximum transverse drill angle (MTA) and MTA-10° and at 130° of flexion. Considering effect on graft bending angle, decrease of flexion angle and transverse drill angle could be appropriate in creating femoral tunnel. Increased flexion angle and transverse drill angle secured femoral tunnel having sufficiently long length without wall breakage. However, avoiding excessive flexion angle and maximum transverse drill angle could be recommended because they tended to cause more acute graft bending angle.