Anatomic versus Low Tibial Tunnel in Double-Bundle Posterior Cruciate Ligament Reconstruction: Clinical and Radiologic Outcomes with a Minimum 2-Year Follow-Up.

There is currently no consensus on the optimal placement of the tibial tunnel for double-bundle posterior cruciate ligament (PCL) reconstruction. The purpose of this study was to compare the clinical and radiologic outcomes of double-bundle PCL reconstruction utilizing anatomic versus low tibial tunnels. We conducted a retrospective cohort study involving patients who underwent double-bundle PCL reconstruction between Jan 2019 and Jan 2022, with a minimum follow-up of 2 years (n = 36). Based on the tibial tunnel position on postoperative computed tomography, patients were categorized into two groups: anatomic placement (group A; n = 18) and low tunnel placement (group L; n = 18). We compared the range of motion, stability test, complications, and side-to-side differences in tibial posterior translation using kneeling stress radiography between the two groups. There were no significant differences between the groups regarding clinical outcomes or complication rates. No significant differences in the posterior drawer test and side-to-side difference on kneeling stress radiography (2.5 ± 1.2 mm in group A vs. 3.7 ± 2.0 mm in group L; p = 0.346). In conclusion, the main findings of this study indicate that both anatomic tunnel and low tibial tunnel placements in double-bundle PCL reconstruction demonstrated comparable and satisfactory clinical and radiologic outcomes, with similar overall complication rates at the 2-year follow-up.

Influence of the Tibial Tunnel Angle and Posterior Tibial Slope on "Killer Turn" during Posterior Cruciate Ligament Reconstruction: A Three-Dimensional Finite Element Analysis.

This study aimed to evaluate the influence of various posterior tibial slopes (PTSs) and tibial tunnel angles (TTAs) on "killer turn" in posterior cruciate ligament (PCL) reconstruction by using three-dimensional finite element analysis (FEA). The study models were created using computed tomography images of a healthy young Asian male. Using SolidWorks, PCL grafts and tibial bone tunnels at different tibial drilling angles (30°, 45°, 60°) were developed. Anterior opening wedge high tibial osteotomy (aOW-HTO) was performed to evaluate the influence of the PTS (+8°, +4°, native, -4°, -8°). An FEA was performed utilizing the ANSYS software program. In the same PTS model, the peak of the equivalent Von Mises stress in PCL grafts decreased as the angle of the TTA increased. In the same TTA model, the peak of the Von Mises in PCL grafts decreased as the PTS angle increased. The "high-contact stress area" (contact stress greater than 10 MPa) was diminished when the TTA and PTS were increased. aOW-HTO was used to steepen the PTS, and a larger TTA may reduce the stress at the "killer turn" during PCL reconstruction. In conclusion, the study findings suggest that using aOW-HTO to steepen the PTS and a larger TTA may reduce the stress at the "killer turn" during PCL reconstruction. The usefulness and safety of this surgical procedure need to be evaluated in future clinical studies.

3D Killer Turn Angle in Transtibial Posterior Cruciate Ligament Reconstruction Is Determined by the Graft Turning Angle both in the Sagittal and Coronal Planes.

OBJECTIVE: During the transtibial posterior cruciate ligament (PCL) reconstruction, surgeons commonly pay more attention to the graft turning angle in the sagittal plane (GASP), but the graft turning angle in the coronal plane (GACP) is always neglected. This study hypothesized that the three-dimensional (3D) killer turn angle was determined by both the GASP and GACP, and aimed to quantitively analyze the effects of the GASP and GACP on the 3D killer turn angle. METHODS: This was an in-vitro computer simulation study of transtibial PCL reconstruction using 3D knee models. Patients with knee injuries who were CT scanned were selected from the CT database (April 2019 to January 2021) at a local hospital for reviewing. A total of 60 3D knees were simulated based on the knees' CT data. The femoral and tibial PCL attachment were located on the 3D knee model using the Rhinoceros software. The tibial tunnels were simulated based on different GASP and GACP. The effects of the GASP and GACP on the 3D killer turn angle were quantitatively analyzed. One-way analysis of variance was used to compare the outcomes in different groups. The regression analysis was performed to identify variables of the GASP and GACP which significantly affected 3D killer turn angle. RESULTS: The 3D killer turn angle showed a significant proportional relationship not only with the GASP (r2 > 0.868, P < 0.001), but also with the GACP (r2 > 0.467, P < 0.001). Every 10° change of the GACP caused 2.8° to 4.4° change of the 3D killer turn angle, whereas every 10° change of the GASP caused 6.4° to 9.2° change of the 3D killer turn angle. CONCLUSIONS: The 3D killer turn angle was significantly affected by both the GASP and GACP. During the transtibial PCL reconstruction, the proximal anterolateral tibial tunnel approach could increase the 3D killer turn angle more obviously compared with the most distal anteromedial tibial tunnel approach. To minimize the killer turn effect, both the GASP and GACP were required to be considered to increase.

Research advances in tibial insertion of posterior cruciate ligament and location of tibial tunnel / 中华创伤骨科杂志

Posterior cruciate ligament (PCL) plays an important role in maintaining the stability of knee. PCL injury is often accompanied by serious axial and rotational instability, and severe PCL injury is likely to be combined with injuries to the anterior cruciate ligament, medial collateral ligament and other tissues which are often repaired by necessary posterior cruciate ligament reconstruction (PCLR) to restore their physiological functions. However, PCLR research is not as common as the research into the anterior cruciate ligament reconstruction, not only due to controversies in the anatomy and mechanics of PCL but also due to a higher failure rate and more complications following PCLR. This situation is closely related to the anatomical characteristics of the PCL tibial insertion. The present review deals with the anatomy, mechanics and clinical research of the PCL tibial insertion in order to provide more references for PCLR operators.

Lower Tibial Tunnel Placement in Isolated Posterior Cruciate Ligament Reconstruction: Clinical Outcomes and Quantitative Radiological Analysis of the Killer Turn.

BACKGROUND: The "killer turn" effect after posterior cruciate ligament (PCL) reconstruction is a problem that can lead to graft laxity or failure. Solutions for this situation are currently lacking. PURPOSE: To evaluate the clinical outcomes of a modified procedure for PCL reconstruction and quantify the killer turn using 3-dimensional (3D) computed tomography (CT). STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A total of 15 patients underwent modified PCL reconstruction with the tibial aperture below the center of the PCL footprint. Next, 2 virtual tibial tunnels with anatomic and proximal tibial apertures were created on 3D CT. All patients were assessed according to the Lysholm score, International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form, Tegner score, side-to-side difference (SSD) in tibial posterior translation using stress radiography, and 3D gait analysis. RESULTS: The modified tibial tunnel showed 2 significantly gentler turns (superior, 109.87° ± 10.12°; inferior, 151.25° ± 9.07°) compared with those reconstructed with anatomic (91.33° ± 7.28°; P < .001 for both comparisons) and proximal (99° ± 7.92°; P = .023 and P < .001, respectively) tibial apertures. The distance from the footprint to the tibial aperture was 16.49 ± 3.73 mm. All patient-reported outcome scores (mean ± SD) improved from pre- to postoperatively: Lysholm score, from 46.4 ± 18.87 to 83.47 ± 10.54 (P < .001); Tegner score, from 2.47 ± 1.85 to 6.07 ± 1.58 (P < .001); IKDC sports activities score, from 19 ± 9.90 to 33.07 ± 5.35 (P < .001); and IKDC knee symptoms score, from 17.87 ± 6.31 to 25.67 ± 3.66 (P < .001). The mean SSD improved from 9.15 ± 2.27 mm preoperatively to 4.20 ± 2.31 mm postoperatively (P < .001). The reconstructed knee showed significantly more adduction (by 1.642°), less flexion (by 1.285°), and more lateral translation (by 0.279 mm) than that of the intact knee (P < .001 for all). CONCLUSION: Lowering the tibial aperture during PCL reconstruction reduced the killer turn, and the clinical outcomes remained satisfactory. However, SSD and clinical outcomes were similar to those of previously described techniques using an anatomic tibial tunnel.

[The killer turn in the posterior cruciate ligament reconstruction: mechanism and improvement].

OBJECTIVE: To summarize the research progress of killer turn in posterior cruciate ligament (PCL) reconstruction. METHODS: The literature related to the killer turn in PCL reconstruction in recent years was searched and summarized. RESULTS: The recent studies show that the killer turn is considered to be the most critical cause of graft relaxation after PCL reconstruction. In clinic, this effect can be reduced by changing the fixation mode of bone tunnel, changing the orientation of bone tunnel, squeezing screw fixation, retaining the remnant, and grinding the bone at the exit of bone tunnel. But there is still a lack of long-term follow-up. CONCLUSION: There are still a lot of controversies on the improved strategies of the killer turn. More detailed basic researches focusing on biomechanics to further explore the mechanism of the reconstructed graft abrasion are needed.

The killer turn in the posterior cruciate ligament reconstruction: mechanism and improvement / 中国修复重建外科杂志

Objective: To summarize the research progress of killer turn in posterior cruciate ligament (PCL) reconstruction. Methods: The literature related to the killer turn in PCL reconstruction in recent years was searched and summarized. Results: The recent studies show that the killer turn is considered to be the most critical cause of graft relaxation after PCL reconstruction. In clinic, this effect can be reduced by changing the fixation mode of bone tunnel, changing the orientation of bone tunnel, squeezing screw fixation, retaining the remnant, and grinding the bone at the exit of bone tunnel. But there is still a lack of long-term follow-up. Conclusion: There are still a lot of controversies on the improved strategies of the killer turn. More detailed basic researches focusing on biomechanics to further explore the mechanism of the reconstructed graft abrasion are needed.

Evaluation of tibial tunnel placement in single case posterior cruciate ligament reconstruction: reducing the graft peak stress may increase posterior tibial translation.

BACKGROUND: The killer turn has been documented as the primary drawback of posterior cruciate ligament (PCL) reconstruction. Fanelli advocated placing the tibial tunnel outlet in the inferior lateral part of the PCL fovea to reduce the killer turn. This study aimed to confirm the validity of Fanelli's viewpoint regarding PCL reconstruction technique and to assess the specific Fanelli tunnel area on the inferior lateral part of the PCL fovea. METHODS: The geometrical data of the model were obtained by nuclear magnetic resonance (MRI) and computerized tomography (CT), with images taken from a healthy Chinese volunteer. The three-dimensional finite element model of the knee joint was established using Mimics, Geomagic Studio, 3-matic, and Ansys software. The finite analysis was performed after the material behavior, contact and boundary conditions, and loading were defined. The drawer tests were simulated with a posterior tibial load of 134 N at 0°, 30°, 60°, and 90° knee flexion. The PCL peak stress and tibial translation were recorded and compared among the 30 distinct tibial tunnel loci over a range of angles from 0° to 90°. RESULTS: In the area (Fanelli area, 5-20 mm inferior and 5-10 mm lateral to the PCL anatomical insertion), the lowest PCL peak stress in all sites with different flexion angles was lower than that of the PCL anatomical insertion site. The lowest PCL peak stress with different knee flexion angles was observed in the following location: 10 mm inferior and 5 mm lateral to the PCL anatomical insertion. In the Fanelli area, the tibial translations of three sites were lower and those of other sites were higher than that of the PCL anatomical insertion site. CONCLUSIONS: PCL reconstruction in the Fanelli area, especially 10 mm inferior and 5 mm lateral to the PCL anatomical insertion, could reduce the peak stress of the graft and may reduce the killer turn. However, whether the posterior stability of the knee is affected needs to be further studied.

What Role Does Low Bone Mineral Density Play in the "Killer Turn" Effect after Transtibial Posterior Cruciate Ligament Reconstruction?

OBJECTIVE: To explore the mechanism of the "killer turn", which is reported to be a reason for postoperative residual laxity after transtibial posterior cruciate ligament (PCL) reconstruction, in a low bone mineral density (BMD) condition. METHODS: A total of 80 skeletally mature female New Zealand white rabbits were included for biomechanical evaluation after transtibial PCL reconstructions. The subjects were equally divided into low BMD (n = 40) and control groups (n = 40). Rabbits in the low BMD group were treated with surgery and drug injection to establish an osteoporotic model. Rabbits in the control group received sham surgeries and no injection. All assignments were conducted randomly according to random numbers generated by a computer. All grafts were then subjected to biomechanical testing with an MTS model-858 Mini Bionix servohydraulic materials testing machine (MTS Systems, Minneapolis, Minnesota, USA). The experimental outcomes were the increment of total graft displacement, tunnel inlet enlargement, graft elongation, stiffness and failure load of the two groups, and the comparison between them. RESULTS: Among the 80 subjects, 1 subject of the low BMD group failed at the 30th cycle by proximal tibial fracture and 1 subject of the control group failed at the 20th cycle for the same reason. As a result, 39 subjects of the low BMD group and 39 subjects of the control group survived the cyclic loading test. Compared with the control group, the low BMD group demonstrated significantly larger total graft displacement ( P = 0.006) and tunnel inlet enlargement ( P = 0.041) than the control group. The number of subjects with less than 10% enlargement was significantly greater (57.1%) in the control group than in the low BMD group ( P = 0.004). In the load-to-failure test, 26 (66.7%) subjects in the low BMD group failed by proximal tibial fracture (around the tunnel), 6 (15.4%) at the mounting site, 5 (12.8%) at the fixation site, and only 2 (5.1%) failed at the "killer turn." In the control group, 20 (51.3%) failed at the "killer turn," 9 (23.1%) at the proximal tibia (around the tunnel), 5 (12.8%) at the mounting site, and 5 (12.8%) at the fixation site. There were significantly fewer failures (10.0%) at the "killer turn" ( P = 0.000) and 155.6% more for the para-tunnel fracture ( P = 0.000) in the low BMD group compared with the control group. CONCLUSIONS: The low BMD group demonstrated an inferior biomechanical outcome to the control group with the transtibial technique. With low BMD, the "killer turn" effect compromises the posterior tibial cortex by enlarging the tunnel inlet.