Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs

2019 ◽  
Vol 47 (6) ◽  
pp. 1376-1384 ◽  
Author(s):  
Frank R. Noyes ◽  
Lauren E. Huser ◽  
Brad Ashman ◽  
Michael Palmer
Keyword(s):  
Patellar Tendon ◽  
Pivot Shift ◽  
Cruciate Ligament ◽  
Anterior Tibial Translation ◽  
Acl Graft ◽  
Flexion Extension ◽  
Anterior Tibial ◽  
Tibial Translation ◽  
Bone Patellar Tendon ◽  
Anterior Posterior

Background: Anterior cruciate ligament (ACL) graft conditioning protocols to decrease postoperative increases in anterior tibial translation and pivot-shift instability have not been established. Purpose: To determine what ACL graft conditioning protocols should be performed at surgery to decrease postoperative graft elongation after ACL reconstruction. Study Design: Controlled laboratory study. Methods: A 6 degrees of freedom robotic simulator evaluated 3 ACL graft constructs in 7 cadaver knees for a total of 19 graft specimens. Knees were tested before and after ACL sectioning and after ACL graft conditioning protocols before reconstruction. The ACL grafts consisted of a 6-strand semitendinosus-gracilis TightRope, bone–patellar tendon–bone TightRope, and bone–patellar tendon–bone with interference screws. Two graft conditioning protocols were used: (1) graft board tensioning (20 minutes, 80 N) and (2) cyclic conditioning (5°-120° of flexion, 90-N anterior tibial load) after graft reconstruction to determine the number of cycles needed to obtain a steady state with no graft elongation. After conditioning, the grafts were cycled a second time under anterior-posterior loading (100 N, 25° of flexion) and under pivot-shift loading (100 N anterior, 5-N·m internal rotation, 7 N·m valgus) to verify that the ACL flexion-extension conditioning protocol was effective. Results: Graft board tensioning did not produce a steady-state graft. Major increases in anterior tibial translation occurred in the flexion-extension graft-loading protocol at 25° of flexion (mean ± SD: semitendinosus-gracilis TightRope, 3.4 ± 1.1 mm; bone–patellar tendon–bone TightRope, 3.2 ± 1.0 mm; bone–patellar tendon–bone with interference screws, 2.4 ± 1.5 mm). The second method of graft conditioning (40 cycles, 5°-120° of flexion, 90-N anterior load) produced a stable conditioned state for all grafts, as the anterior translations of the anterior-posterior and pivot-shift cycles were statistically equivalent ( P < .05, 1-20 cycles). Conclusion: ACL graft board conditioning protocols are not effective, leading to deleterious ACL graft elongations after reconstruction. A secondary ACL graft conditioning protocol of 40 flexion-extension cycles under 90-N graft loading was required for a well-conditioned graft, preventing further elongation and restoring normal anterior-posterior and pivot-shift translations. Clinical Relevance: There is a combined need for graft board tensioning and robust cyclic ACL graft loading before final graft fixation to restore knee stability.

scholarly journals Lateral Extra-Articular Tenodesis Reduces ACL Graft Force Under Multiplanar Torques Simulationg Pivot Shit

2020 ◽  
Vol 8 (7_suppl6) ◽  
pp. 2325967120S0035
Author(s):  
Niv Marom ◽  
Herve Ouanezar ◽  
hamidreza jahandar ◽  
Zaid Zayyad ◽  
Thomas Fraychineaud ◽  
...  
Keyword(s):  
Pivot Shift ◽  
Knee Kinematics ◽  
Lateral Compartment ◽  
Anterior Tibial Translation ◽  
Acl Graft ◽  
Anterior Tibial ◽  
Text Figure ◽  
Force Reduction ◽  
Tibial Translation ◽  
Intact Knee

Objectives: Utilization of lateral extra-articular tenodesis (LET) in conjunction with anterior cruciate ligament reconstruction (ACLR) has increased in recent years, however, the biomechanical impact of LET, when performed with contemporary techniques, on both load sharing between the ACL graft and the LET and on knee kinematics is not completely clear. The purpose of this study was to quantify the effect of LET performed with ACLR, in the presence of a compromised anterolateral tissues, on (1) forces carried by the ACL graft and the LET and (2) knee kinematics, during simulated pivot shift. Methods: manipulator equipped with a six-axis force-torque sensor. The robot applied multiplanar torques simulating two types of pivot shift (PS) subluxing the lateral compartment at 15° and 30° of knee flexion. The following loading combinations were applied: (PS1) 8 Nm of valgus and 4 Nm of internal rotation torques; (PS2) 100 N compression force, 8 Nm valgus torque, 2 Nm internal rotation torque, and 30 N anterior force. Anteroposterior (AP) translation in the lateral compartment of the knee was recorded in the following states: ACL intact, sectioned, reconstructed and, finally, after sectioning the anterolateral ligament (ALL) and kaplan fibers and performing a LET. ACLR was performed utilizing a bone-patellar tendon-bone autograft, via medial parapatellar arthrotomy. LET was performed using a modified lemaire technique with a metal staple femoral fixation at 60° of flexion in neutral rotation. Resultant forces carried by the ACL graft and LET at the peak applied load in all tested conditions were determined utilizing the principle of superposition and serial sectioning. Results: Under both simulated pivot shift types and at both flexion angles the ACL force decreased with the addition of a LET, with the least force reduction of 39% for PS2 at 15° (p=0.01) and the most force reduction of 80% for PS1 at 30° (p<0.001). While decreasing ACL force, the LET carried at least 43% of the force carried by the ACL graft when tested without LET for PS2 at 15° and 91% of the force carried by the ACL graft at most, for PS1 at 30° (Table 1). For both combinations of multiplananr torques and at both flexion angles, the anterior tibial translation in the lateral compartment decreased for the ACLR+LET knee compared to the intact knee (5.3mm and 7.6mm decrease, for PS1 15° and 30° respectively, p<0.001; 4.4mm p=0.005 and 7.6mm p<0.001, for PS2 15° and 30°, respectively). (Figure 2). Conclusion: During a simulated pivot shift, LET shields the ACL graft from loading. This effect was greatest at 30° of flexion with an 80% drop in ACL graft force. While some shielding of load from the ACL graft can be beneficial, a more significant reduction in the load of the ACL graft may potentially be detrimental to the graft remodeling, maturation and function. The optimal load sharing pattern for improved clinical outcomes is not well understood and merit further investigation. In addition, LET also decreases anterior tibial translation in the lateral compartment to less than that of the intact knee, which represents overconstraint of the lateral compartment. These findings may support the purported “protective” effect of LET on the ACL graft and its important role in stabilizing the lateral compartment in the setting of combined ACL and anterolateral structures deficiency. The influence of overconstraint of the lateral compartment with LET warrants further biomechanical and clinical evaluation. [Table: see text][Figure: see text][Figure: see text]

scholarly journals Patient-Reported and Quantitative Outcomes of Anatomic Anterior Cruciate Ligament Reconstruction With Hamstring Tendon Autografts

2020 ◽  
Vol 8 (7) ◽  
pp. 232596712092615
Author(s):  
Theresa Diermeier ◽  
Sean J. Meredith ◽  
James J. Irrgang ◽  
Stefano Zaffagnini ◽  
Ryosuke Kuroda ◽  
...  
Keyword(s):  
Pivot Shift ◽  
Cruciate Ligament ◽  
Pivot Shift Test ◽  
Anterior Tibial Translation ◽  
Time Zero ◽  
Patient Reported ◽  
Anterior Tibial ◽  
Tibial Acceleration ◽  
Tibial Translation

Background: The pivot-shift test has become more consistent and reliable and is a meaningful outcome measurement after anterior cruciate ligament reconstruction (ACLR). Purpose/Hypothesis: The purpose of this investigation was to assess patient-reported outcomes (PROs) and the quantitative pivot shift (QPS) preoperatively, at time zero immediately after anatomic ACLR, and after 24 months as well as the relationship between PROs and the QPS. It was hypothesized that anatomic ACLR would restore rotatory stability measured by the pivot-shift test and that QPS measurements would be positively correlated with PROs. Study Design: Cohort study; Level of evidence, 2. Methods: The ACL-injured and contralateral uninjured knees from 89 of 107 (83.2%) enrolled patients at 4 international centers were evaluated using a standardized pivot-shift test. Tibial acceleration was assessed with an inertial sensor, and lateral compartment translation was measured using an image analysis system preoperatively, at time zero immediately postoperatively, and at follow-up after 2 years. PROs were assessed at 12 and 24 months postoperatively with the International Knee Documentation Committee (IKDC) subjective knee form, Cincinnati Knee Rating System (CKRS), Marx activity rating scale, and activity of daily living score (ADLS). Results: The mean patient age at surgery was 27 years (range, 15-45 years). A positive pivot shift preoperatively (side-to-side difference in tibial acceleration, 2.6 ± 4.0 m/s2; side-to-side difference in anterior tibial translation, 2.0 ± 2.0 mm) was reduced at time zero postoperatively (side-to-side difference in tibial acceleration, –0.5 ± 1.3 m/s2; side-to-side difference in anterior tibial translation, –0.1 ± 1.0 mm). All PROs improved from preoperatively to final follow-up at 24 months: from 56.5 to 85.5 points for the IKDC ( P = .0001), from 28.8 to 32.4 points for the CKRS ( P = .04), from 11.2 to 7.9 points for the Marx ( P < .0001), and from 75.7 to 91.6 points for the ADLS ( P < .0001). Neither preoperative nor time zero postoperative rotatory laxity assessed by the pivot-shift test correlated with PROs at 24-month follow-up. A graft retear was observed in 4 patients (4.5%) within 2 years of follow-up. Conclusion: Anatomic ACLR resulted in significantly improved and acceptable PROs at 2-year follow-up and a low failure rate. Anatomic ACLR restored QPS measurements of anterior tibial translation and tibial acceleration to those of the contralateral knee immediately after surgery while still under anesthesia, but there was no correlation between the QPS preoperatively or at time zero after ACLR and PROs at 2-year follow-up.

Robotically Simulated Clinical Pivot Shift: A Better Tool for Analyzing ACL Reconstructions?

2013 ◽  
Author(s):  
R. W. Colbrunn ◽  
J. E. Dumpe ◽  
T. F. Bonner ◽  
J. D. Kolmodin ◽  
W. K. Barsoum ◽  
...  
Keyword(s):  
Acl Reconstruction ◽  
Pivot Shift ◽  
Cruciate Ligament ◽  
Anterior Tibial Translation ◽  
Anterior Tibial ◽  
Robotic Testing ◽  
Anterior Cruciate ◽  
Tibial Translation

A pivot shift is a useful exam for evaluating anterior cruciate ligament (ACL) reconstruction surgery. A positive result is a perceived “clunk” and is quantified by the kinematics that occur during the tibial reduction phase. In vitro evaluation of ACL reconstruction techniques includes robotic testing of cadaveric knees where the applied loads represent estimated in situ loads. Early understanding of the mechanism of the pivot shift has resulted in a simplified representation where static “rotary loads” (10Nm valgus torque, 5Nm internal tibial torque) are applied at a few discrete flexion angles, and changes in anterior tibial translation (ATT) are compared [1]. Building upon this work, and with advances in technology, we are now able to create a robotic test that is more like the clinical exam. Our hypothesis was that kinematics produced during the robotically simulated pivot shift would be similar to the clinical pivot shift but would be significantly different from the rotary loads method. The ability for a test to produce larger kinematic differences between native and deficient states may suggest a more robust methodology by which to evaluate the efficacy of ACL reconstructions.

scholarly journals Anterior and Rotational Knee Laxity Does Not Affect Patient-Reported Knee Function 2 Years After Anterior Cruciate Ligament Reconstruction

2019 ◽  
Vol 47 (9) ◽  
pp. 2077-2085 ◽  
Author(s):  
Robert Magnussen ◽  
Emily K. Reinke ◽  
Laura J. Huston ◽  
Jack T. Andrish ◽  
Charles L. Cox ◽  
...  
Keyword(s):  
Acl Reconstruction ◽  
Pivot Shift ◽  
Cruciate Ligament ◽  
Knee Laxity ◽  
Anterior Tibial Translation ◽  
Patient Reported ◽  
Anterior Tibial ◽  
Kt 1000 ◽  
Tibial Translation ◽  
Rotational Knee Laxity

Background: While a primary goal of anterior cruciate ligament (ACL) reconstruction is to reduce pathologically increased anterior and rotational knee laxity, the relationship between knee laxity after ACL reconstruction and patient-reported knee function remains unclear. Hypothesis: There would be no significant correlation between the degree of residual anterior and rotational knee laxity and patient-reported outcomes (PROs) 2 years after primary ACL reconstruction. Study Design: Cross-sectional study; Level of evidence, 3. Methods: From a prospective multicenter nested cohort of patients, 433 patients younger than 36 years of age injured in sports with no history of concomitant ligament surgery, revision ACL surgery, or surgery of the contralateral knee were identified and evaluated at a minimum 2 years after primary ACL reconstruction. Each patient underwent Lachman and pivot-shift evaluation as well as a KT-1000 arthrometer assessment along with Knee injury and Osteoarthritis Outcome Score and subjective International Knee Documentation Committee (IKDC) scores. A proportional odds logistic regression model was used to predict each 2-year PRO score, controlling for preoperative score, age, sex, body mass index, smoking, Marx activity score, education, subsequent surgery, meniscal and cartilage status, graft type, and range of motion asymmetry. Measures of knee laxity were independently added to each model to determine correlation with PROs. Results: Side-to-side manual Lachman differences were IKDC A in 246 (57%) patients, IKDC B in 183 (42%) patients, and IKDC C in 4 (<1%) patients. Pivot-shift was classified as IKDC A in 209 (48%) patients, IKDC B in 183 (42%) patients, and IKDC C in 11 (2.5%) patients. The mean side-to-side KT-1000 difference was 2.0 ± 2.6 mm. No significant correlations were noted between pivot-shift or anterior tibial translation as assessed by Lachman or KT-1000 and any PRO. All predicted differences in PROs based on IKDC A versus B pivot-shift and anterior tibial translation were less than 4 points. Conclusion: Neither the presence of IKDC A versus B pivot-shift nor increased anterior tibial translation of up to 6 mm is associated with clinically relevant decreases in PROs 2 years after ACL reconstruction.

scholarly journals Effect of Fatigue on Functional Stability of the Knee: Particularities of Female Handball Players

2019 ◽  
Vol 40 (07) ◽  
pp. 468-476 ◽  
Author(s):  
Timothée Gillot ◽  
Maxime L'Hermette ◽  
Typhanie Garnier ◽  
Claire Tourny-Chollet
Keyword(s):  
Cruciate Ligament ◽  
Joint Laxity ◽  
Ligament Injury ◽  
Anterior Tibial Translation ◽  
Knee Stability ◽  
Load Curve ◽  
Fatigue Protocol ◽  
Flexion Extension ◽  
Anterior Tibial ◽  
Tibial Translation

AbstractThe risk of anterior cruciate ligament injury in female handball players is high. Fatigue of active stabilizers and increases in joint laxity are often mentioned in the literature as causal factors. However, no studies have been carried out on this population. Our objective is to determine the effect of muscle fatigue on active and passive knee stability in female handball players. This prospective study assessed tibiofemoral joint laxity, as well as hamstring and quadriceps strength, before (Tinitial), during and 3 min after (Tfinal) an isokinetic fatigue protocol (25 repetitions of knee flexion / extension at 180°.s−1). Laxity values (slope of the displacement-load curve and anterior tibial translation) were measured using a GNRB-Rotab® arthrometer; torque values were measured at specific joint angles and peak muscle torque using an isokinetic dynamometer. Nineteen women (20.9±2.4 years, 62.0±4.9 kg, 166±5 cm) were included. Normalized peak torque decreased significantly between the first three and last three repetitions of the fatigue protocol (p<0.0001, ES=3.2 and 3.2). Slope of the displacement-load curve and anterior tibial translation, functional and conventional ratios did not change significantly between Tinitial and Tfinal. Active and passive markers of knee stability were not altered by a fatigue protocol in female handball players, suggesting these players have a large capacity for recovery. These results suggest that muscle strengthening to prevent ACL injury in female handball players may be inappropriate.Level of evidence: Level 2b, Prospective Cohort.

scholarly journals Copers and Noncopers Use Different Landing Techniques to Limit Anterior Tibial Translation After Anterior Cruciate Ligament Reconstruction

2021 ◽  
Vol 9 (4) ◽  
pp. 232596712199806
Author(s):  
Michèle N.J. Keizer ◽  
Egbert Otten ◽  
Chantal M.I. Beijersbergen ◽  
Reinoud W. Brouwer ◽  
Juha M. Hijmans
Keyword(s):  
Ligament Reconstruction ◽  
Cruciate Ligament ◽  
Anterior Tibial Translation ◽  
Return To Sports ◽  
Beighton Score ◽  
Positive Correlation ◽  
Anterior Tibial ◽  
Flexion Moment ◽  
Anterior Cruciate ◽  
Tibial Translation

Background: At 1 year after anterior cruciate ligament reconstruction (ACLR), two-thirds of patients manage to return to sports (copers), whereas one-third of patients do not return to sports (noncopers). Copers and noncopers have different muscle activation patterns, and noncopers may not be able to control dynamic anterior tibial translation (ATTd) as well as copers. Purpose/Hypothesis: To investigate whether (1) there is a positive correlation between passive ATT (ATTp; ie, general joint laxity) and ATTd during jump landing, (2) whether ATTd is moderated by muscle activating patterns, and (3) whether there is a difference in moderating ATTd between copers and noncopers. We hypothesized that patients who have undergone ACLR compensate for ATTd by developing muscle strategies that are more effective in copers compared with noncopers. Study Design: Controlled laboratory study. Methods: A total of 40 patients who underwent unilateral ACLR performed 10 single-leg hops for distance with both legs. Lower body kinematic and kinetic data were measured using a motion-capture system, and ATTd was determined with an embedded method. Muscle activity was measured using electromyographic signals. Bilateral ATTp was measured using a KT-1000 arthrometer. In addition, the Beighton score was obtained. Results: There was no significant correlation between ATTp and ATTd in copers; however, there was a positive correlation between ATTp and ATTd in the operated knee of noncopers. There was a positive correlation between the Beighton score and ATTp as well as between the Beighton score and ATTd in both copers and noncopers in the operated knee. Copers showed a negative correlation between ATTd and gastrocnemius activity in their operated leg during landing. Noncopers showed a positive correlation between ATTd and knee flexion moment in their operated knee during landing. Conclusion: Copers used increased gastrocnemius activity to reduce ATTd, whereas noncopers moderated ATTd by generating a smaller knee flexion moment. Clinical Relevance: This study showed that copers used different landing techniques than noncopers. Patients who returned to sports after ACLR had sufficient plantar flexor activation to limit ATTd.

scholarly journals Computer-Assisted System in Stress Radiography for Anterior Cruciate Ligament Injury with Correspondent Evaluation of Relevant Diagnostic Factors

Diagnostics ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 419
Author(s):  
Chien-Kuo Wang ◽  
Liang-Ching Lin ◽  
Yung-Nien Sun ◽  
Cheng-Shih Lai ◽  
Chia-Hui Chen ◽  
...  
Keyword(s):  
Diagnostic Accuracy ◽  
Cruciate Ligament ◽  
Anterior Tibial Translation ◽  
Computer Assisted ◽  
Time Interval ◽  
Stress Radiography ◽  
Factors Affecting ◽  
Anterior Tibial ◽  
Anterior Cruciate ◽  
Tibial Translation

We sought to design a computer-assisted system measuring the anterior tibial translation in stress radiography, evaluate its diagnostic performance for an anterior cruciate ligament (ACL) tear, and assess factors affecting the diagnostic accuracy. Retrospective research for patients with both knee stress radiography and magnetic resonance imaging (MRI) at our institution was performed. A complete ACL rupture was confirmed on an MRI. The anterior tibial translations with four different methods were measured in 249 patients by the designed algorithm. The diagnostic accuracy of each method in patients with all successful measurements was evaluated. Univariate logistic regression analysis for factors affecting diagnostic accuracy of method four was performed. In the inclusive 249 patients, 177 patients (129 with completely torn ACLs) were available for analysis. Mean anterior tibial translations were significantly increased in the patients with a completely torn ACL by all four methods, with diagnostic accuracies ranging from 66.7% to 75.1%. The diagnostic accuracy of method four was negatively associated with the time interval between stress radiography and MRI as well as force-joint distance on stress view, and not significantly associated with age, gender, flexion angle, intercondylar distance, and force-joint angle. A computer-assisted system measuring the anterior tibial translation in stress radiography showed acceptable diagnostic performance of complete ACL injury. A shorter time interval between stress radiography and MRI as well as shorter force-joint distance were associated with higher diagnostic accuracy.

Effect of Meniscocapsular and Meniscotibial Lesions in ACL-Deficient and ACL-Reconstructed Knees: A Biomechanical Study

2018 ◽  
Vol 46 (10) ◽  
pp. 2422-2431 ◽  
Author(s):  
Nicholas N. DePhillipo ◽  
Gilbert Moatshe ◽  
Alex Brady ◽  
Jorge Chahla ◽  
Zachary S. Aman ◽  
...  
Keyword(s):  
Internal Rotation ◽  
Medial Meniscus ◽  
Pivot Shift ◽  
External Rotation ◽  
Posterior Horn ◽  
Pivot Shift Test ◽  
Anterior Tibial Translation ◽  
Anterior Tibial ◽  
Tibial Translation ◽  
Acl Deficient

Background: Ramp lesions were initially defined as a tear of the peripheral attachment of the posterior horn of the medial meniscus at the meniscocapsular junction. The separate biomechanical roles of the meniscocapsular and meniscotibial attachments of the posterior medial meniscus have not been fully delineated. Purpose: To evaluate the biomechanical effects of meniscocapsular and meniscotibial lesions of the posterior medial meniscus in anterior cruciate ligament (ACL)–deficient and ACL-reconstructed knees and the effect of repair of ramp lesions. Study Design: Controlled laboratory study. Methods: Twelve matched pairs of human cadaveric knees were evaluated with a 6 degrees of freedom robotic system. All knees were subjected to an 88-N anterior tibial load, internal and external rotation torques of 5 N·m, and a simulated pivot-shift test of 10-N valgus force coupled with 5-N·m internal rotation. The paired knees were randomized to the cutting of either the meniscocapsular or the meniscotibial attachments after ACL reconstruction (ACLR). Eight comparisons of interest were chosen before data analysis was conducted. Data from the intact state were compared with data from the subsequent states. The following states were tested: intact (n = 24), ACL deficient (n = 24), ACL deficient with a meniscocapsular lesion (n = 12), ACL deficient with a meniscotibial lesion (n = 12), ACL deficient with both meniscocapsular and meniscotibial lesions (n = 24), ACLR with both meniscocapsular and meniscotibial lesions (n = 16), and ACLR with repair of both meniscocapsular and meniscotibial lesions (n = 16). All states were compared with the previous states. For the repair and reconstruction states, only the specimens that underwent repair were compared with their intact and sectioned states, thus excluding the specimens that did not undergo repair. Results: Cutting the meniscocapsular and meniscotibial attachments of the posterior horn of the medial meniscus significantly increased anterior tibial translation in ACL-deficient knees at 30° ( P ≤ .020) and 90° ( P < .005). Cutting both the meniscocapsular and meniscotibial attachments increased tibial internal (all P > .004) and external (all P < .001) rotation at all flexion angles in ACL-reconstructed knees. Reconstruction of the ACL in the presence of meniscocapsular and meniscotibial tears restored anterior tibial translation ( P > .053) but did not restore internal rotation ( P < .002), external rotation ( P < .002), and the pivot shift ( P < .05). To restore the pivot shift, an ACLR and a concurrent repair of the meniscocapsular and meniscotibial lesions were both necessary. Repairing the meniscocapsular and meniscotibial lesions after ACLR did not restore internal rotation and external rotation at angles >30°. Conclusion: Meniscocapsular and meniscotibial lesions of the posterior horn of the medial meniscus increased knee anterior tibial translation, internal and external rotation, and the pivot shift in ACL-deficient knees. The pivot shift was not restored with an isolated ACLR but was restored when performed concomitantly with a meniscocapsular and meniscotibial repair. However, the effect of this change was minimal; although statistical significance was found, the overall clinical significance remains unclear. The ramp lesion repair used in this study failed to restore internal rotation and external rotation at higher knee flexion angles. Further studies should examine improved meniscus repair techniques for root tears combined with ACLRs. Clinical Relevance: Meniscal ramp lesions should be repaired at the time of ACLR to avoid continued knee instability (anterior tibial translation) and to eliminate the pivot-shift phenomenon.

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