scholarly journals In Vitro Testing of 2 Adjustable-Loop Cortical Suspensory Fixation Systems Versus Interference Screw for Anterior Cruciate Ligament Reconstruction

2021 ◽  
Vol 9 (9) ◽  
pp. 232596712110316
Author(s):  
Gerardo L. Garcés ◽  
Oscar Martel ◽  
Alejandro Yánez ◽  
Ignacio Manchado-Herrera ◽  
Luci M. Motta
Keyword(s):  
Anterior Cruciate Ligament ◽  
Acl Reconstruction ◽  
Failure Load ◽  
Cruciate Ligament ◽  
Interference Screw ◽  
Yield Load ◽  
Ultimate Failure Load ◽  
Significant Difference ◽  
Ultimate Failure ◽  
Anterior Cruciate

Background: It is not clear whether the mechanical strength of adjustable-loop suspension devices (ALDs) in anterior cruciate ligament (ACL) reconstruction is device dependent and if these constructs are different from those of an interference screw. Purpose: To compare the biomechanical differences of 2 types of ALDs versus an interference screw. Study Design: Controlled laboratory study. Methods: ACL reconstruction was performed on porcine femurs and bovine extensor tendons with 3 types of fixation devices: interference screw, UltraButton (UB) ALD, and TightRope (TR) ALD (n = 10 for each). In addition to specimen testing, isolated testing of the 2 ALDs was performed. The loading protocol consisted of 3 stages: preload (static 150 N load for 5 minutes), cyclic load (50-250 N at 1 Hz for 1000 cycles), and load to failure (crosshead speed 50 mm/min). Displacement at different cycles, ultimate failure load, yield load, stiffness, and failure mode were recorded. Results: In specimen testing, displacement of the ALDs at the 1000th cycle was similar (3.42 ± 1.34 mm for TR and 3.39 ± 0.92 mm for UB), but both were significantly lower than that of the interference screw (7.54 ± 3.18 mm) ( P < .001 for both). The yield load of the UB (547 ± 173 N) was higher than that of the TR (420 ± 72 N) ( P = .033) or the interference screw (386 ± 51 N; P = .013), with no significant difference between the latter 2. In isolated device testing, the ultimate failure load of the TR (862 ± 64 N) was significantly lower than that of the UB (1879 ± 126 N) ( P < .001). Conclusion: Both ALDs showed significantly less displacement in cyclic loading at ultimate failure than the interference screw. The yield load of the UB was significantly higher than that of the other 2. The ultimate failure occurred at a significantly higher load for UB than it did for TR in isolated device testing. Clinical Relevance: Both UB and TR provided stronger fixation than an interference screw. Although difficult to assess, intrinsic differences in the mechanical properties of these ALDs may affect clinical outcomes.

Biomechanical Performance of Metallic and Bioabsorbable Interference Screw for Tibial Graft Fixation in ACL Reconstruction

2013 ◽  
Author(s):  
Ari Digiacomo Ocampo Moré ◽  
André Luiz Almeida Pizzolatti ◽  
Eduardo Fancello ◽  
Carlos Rodrigo de Mello Roesler
Keyword(s):  
Cyclic Loading ◽  
Acl Reconstruction ◽  
Failure Load ◽  
Mechanical Performance ◽  
Cruciate Ligament ◽  
Interference Screw ◽  
Bioabsorbable Screw ◽  
Bioabsorbable Interference Screw ◽  
Ultimate Failure ◽  
Anterior Cruciate

Background: The interference screw is widely used to fix the graft in the tibial portion in anterior cruciate ligament (ACL) reconstruction. However, there is no evidence of what type of screws, if metallic or bioabsorbable, have the better mechanical performance. Methods: Twenty porcine tibias, 10 for metallic and 10 for bioabsorbable screw, were submitted to cyclic loading between 50 N to 250 N for 1000 cycles at 1 Hz. For devices that not failed during cyclic loading, a tensile test to failure was performed at strain rate of 50 mm/min. Results: There were no differences in the stiffness and ultimate failure load between metallic and bioabsorbable screw. Conclusion: There is no difference in biomechanical performance between metallic and bioabsorbable screw.

scholarly journals Whether Sutures Reduce the Graft Laceration Caused by Interference Screw in Anterior Cruciate Ligament Reconstruction a Biomechanical Study in Vitro

2021 ◽  
Author(s):  
Yuanjun Teng ◽  
Lijun Da ◽  
Xiaohui Zhang ◽  
Hong Wang ◽  
Hua Han ◽  
...  
Keyword(s):  
Anterior Cruciate Ligament ◽  
Acl Reconstruction ◽  
Cruciate Ligament ◽  
Interference Screw ◽  
Biomechanical Study ◽  
Protective Effects ◽  
Mineral Density ◽  
Interference Screws ◽  
Anterior Cruciate

Abstract Background: Interference screw is commonly used for graft fixation in anterior cruciate ligament (ACL) reconstruction However, previous studies h a d reported that the insertion of interference screws significantly caused graft laceration . The purpose of this study was to determine whether sutures reduce d the graft laceration from the insertion of interference screws in ACL reconstruction. Methods: Porcine tibias and bovine extensor tendons were used for establishing a knee model of ACL reconstruction in vitro . The ends of grafts were sutured using three different sutures, including the bioabsorbable, Ethibond and ultra high molecular weight polyethylene (UHMWPE) sutures Poly ether ether ketone (PEEK) interference screw s w ere used fortibial fixation Biomechanical tests were performed to investigate the protective effects of different sutures on grafts Results : All prepared tendons and bone specimens showed similar characteristics (length, weight, and pre tension of the tendons, tibial bone mineral density) among all groups ( P 0.05). The biomechanical test s demonstrated that PEEK interference screw s significantly caused the graft laceration P 0.05). However, all sutures (the bioabsorbable, Ethibond and UHMWPE sutures) did not reduce the graft laceration in ACL reconstruction P 0.05). Conclusions : PEEK interference screw s significantly weakened the biomechanical properties of grafts during tibial fixation in ACL reconstruction. Absorbable Ethibond and UHMWPE sutures did not provide protective effects on grafts during ACL reconstruction.

scholarly journals Performance of the PROMIS in Patients After Anterior Cruciate Ligament Reconstruction

2018 ◽  
Vol 6 (5) ◽  
pp. 232596711877450 ◽  
Author(s):  
Elizabeth J. Scott ◽  
Robert Westermann ◽  
Nathalie A. Glass ◽  
Carolyn Hettrich ◽  
Brian R. Wolf ◽  
...  
Keyword(s):  
Anterior Cruciate Ligament ◽  
Physical Function ◽  
Acl Reconstruction ◽  
Cruciate Ligament ◽  
Sf 36 ◽  
Significant Difference ◽  
Patient Reported ◽  
Floor Effects ◽  
Anterior Cruciate ◽  
Pro Instruments

Background: The Patient-Reported Outcomes Measurement Information System (PROMIS) is designed to advance patient-reported outcome (PRO) instruments by utilizing question banks for major health domains. Purpose: To compare the responsiveness and construct validity of the PROMIS physical function computer adaptive test (PF CAT) with current PRO instruments for patients before and up to 2 years after anterior cruciate ligament (ACL) reconstruction. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: Initially, 157 patients completed the PROMIS PF CAT, Short Form–36 Health Survey (SF-36 physical function [PF] and general health [GH]), Marx Activity Rating Scale (MARS), Knee injury and Osteoarthritis Outcome Score (KOOS activities of daily living [ADL], sport, and quality of life [QOL]), and EuroQol–5 dimensions questionnaire (EQ-5D) at 6 weeks, 6 months, and 2 years after ACL reconstruction. Correlations between instruments, ceiling and floor effects, effect sizes (Cohen d), and standardized response means to describe responsiveness were evaluated. Subgroup analyses compared participants with and without additional arthroscopic procedures using linear mixed models. Results: At baseline, 6 weeks, and 6 months, the PROMIS PF CAT showed excellent or excellent-good correlations with the SF-36 PF ( r = 0.75-0.80, P < .01), KOOS-ADL ( r = 0.63-0.70, P < .01), and KOOS-sport ( r = 0.32-0.69, P < .01); excellent-good correlation with the EQ-5D ( r = 0.60-0.71, P < .01); and good correlation with the KOOS-QOL ( r = 0.52-0.58, P < .01). As expected, there were poor correlations with the MARS ( r = 0.00-0.24, P < .01) and SF-36 GH ( r = 0.16-0.34, P < .01 ). At 2 years, the PROMIS PF CAT showed good to excellent correlations with all PRO instruments ( r = 0.42-0.72, P < .01), including the MARS ( r = 0.42, P < .01), indicating frequent return to preinjury function. The PROMIS PF CAT had the fewest ceiling or floor effects of all instruments tested, and patients answered, on average, 4 questions. There was no significant difference in baseline physical function scores between subgroups; at follow-up, all groups showed improvements in scores that were not statistically different. Conclusion: The PROMIS PF CAT is a valid tool to assess outcomes after ACL reconstruction up to 2 years after surgery, demonstrating the highest responsiveness to change with the fewest ceiling and floor effects and a low time burden among all instruments tested. The PROMIS PF CAT is a beneficial alternative for assessing physical function in adults before and after ACL reconstruction.

Miniplate Suture Button Augmentation for Soft Tissue Graft Tibial Fixation in Anterior Cruciate Ligament Reconstruction

2021 ◽  
Vol 104 (2) ◽  
pp. 277-285
Keyword(s):  
Anterior Cruciate Ligament ◽  
Acl Reconstruction ◽  
Cruciate Ligament ◽  
Interference Screw ◽  
Tibial Fixation ◽  
Suture Button ◽  
Soft Tissue Graft ◽  
Anterior Cruciate ◽  
Supplemental Fixation

Background: Anterior cruciate ligament (ACL) reconstruction requires reliable and rigid graft fixation. Tibial-sided fixation is frequently cited as the “weak point” of the femur-graft-tibia construct. Some authors have recommended supplemental fixation with a staple or screw suture to post improve the strength and stiffness of the fixation. However, with these fixations, there is a risk for symptomatic hardware. Miniplate is flatter than screw or staple and does not penetrate the bone when attached. It is used as a button for suspensory fixation to enhance interference screw tibial fixation. Objective: To evaluate the clinical outcomes of the miniplate suture button for supplemental soft tissue graft tibial fixation in ACL reconstruction. Materials and Methods: A retrospective study was carried out between August 2016 and December 2019. A total of 40 patients had undergone primary ACL reconstruction, performed with hamstring tendon grafts that were secured using a miniplate suture button for supplemental interference screw tibial fixation. A total of 18 patients were excluded, leaving 22 patients at 1-year follow-up. Results: At least 1-year follow-up, the remaining 22 patients had significant difference between preoperative and postoperative outcome of anterior drawer test, Lachman test and pivot shift test (p<0.05). Lysholm knee scores improved significantly from 54.0±12.53 to 90.04±5.38. However, 3 patients (13.6%) experienced symptomatic hardware pain and 3 patients (13.6%) tendered around the miniplate site. There were no radiographic changes in miniplate displacement, deformed or broken plate, and bony reaction around miniplate. Conclusion: The use of a miniplate suture button as a supplemental fixation showed adequate fixation strength and showed good results in postoperative manual ligament laxity test and functional scores at minimum 1-year follow-up. However, there is still symptomatic pain at the hardware site. Keywords: Anterior cruciate ligament reconstruction, Supplemental fixation, Suture button

Outcomes After Biologically Augmented Isolated Meniscal Repair With Marrow Venting Are Comparable With Those After Meniscal Repair With Concomitant Anterior Cruciate Ligament Reconstruction

2017 ◽  
Vol 45 (6) ◽  
pp. 1341-1348 ◽  
Author(s):  
Chase S. Dean ◽  
Jorge Chahla ◽  
Lauren M. Matheny ◽  
Justin J. Mitchell ◽  
Robert F. LaPrade
Keyword(s):  
Anterior Cruciate Ligament ◽  
Acl Reconstruction ◽  
Cruciate Ligament ◽  
Meniscal Repair ◽  
Intercondylar Notch ◽  
Inclusion Criteria ◽  
Significant Difference ◽  
Outcome Scores ◽  
Anterior Cruciate ◽  
Biological Augmentation

Background: Meniscal repair in the setting of anterior cruciate ligament (ACL) reconstruction has demonstrated superior outcomes compared with isolated meniscal repair. Limited evidence exists for the effects of biological augmentation in isolated meniscal repair, particularly as compared with meniscal repair with concomitant ACL reconstruction. Purpose/Hypothesis: The purpose of this study was to compare the outcomes and survivorship of meniscal repair in 2 cohorts of patients: meniscal repair with biological augmentation using a marrow venting procedure (MVP) of the intercondylar notch, and meniscal repair with concomitant ACL reconstruction. We hypothesized that the clinical outcomes and survivorship of meniscal repair with concomitant ACL reconstruction would be improved compared with meniscal repair with biological augmentation. Study Design: Cohort study; Level of evidence, 3. Methods: Inclusion criteria were skeletally mature patients aged ≥16 years who underwent inside-out meniscal repair and either a concomitant MVP of the intercondylar notch or ACL reconstruction. Patients were excluded from this study if they were skeletally immature, underwent meniscus root or radial tear repair, or underwent meniscal repair with concurrent ligamentous reconstruction not limited to the ACL. At the preoperative evaluation and a minimum 2 years after the index meniscal repair procedure, patients were administered a subjective questionnaire. Differences in outcome scores, survivorship, and failure rates between the cohorts were assessed. Failure was defined as reoperation with meniscectomy or revision meniscal repair. Results: There were 109 patients (52 female, 57 male) who met the inclusion criteria for this study. There were 37 knees in cohort 1 (isolated meniscal repair plus MVP) and 72 knees in cohort 2 (meniscal repair plus ACL reconstruction). The failure status was known in 95 patients, and patient-reported outcome scores were obtained in 89 (82%) patients. Both cohorts demonstrated a significant improvement in all outcome scores, and there was no significant difference in any of the preoperative or postoperative outcome measures. The overall failure rate was 9.5% (9/95). There were 4 (12.9%) failures in cohort 1 and 5 failures (7.8%) in cohort 2, with no significant difference in failures between the cohorts ( P = .429). There was a significant association between failure and female sex ( P = .001). Conclusion: The most important finding in this study was that there was no difference in outcomes in meniscal repair performed with biological augmentation using an MVP versus that performed concomitantly with ACL reconstruction. The similar outcomes reported for meniscal repair with an MVP and meniscal repair with ACL reconstruction may be partly attributed to biological augmentation.

Surgical Management of Simultaneous Anterior Cruciate Ligament and Patellar Tendon Ruptures: A Systematic Review

2017 ◽  
Vol 31 (09) ◽  
pp. 875-883 ◽  
Author(s):  
Carlos Meheux ◽  
Robert Jack ◽  
Patrick McCulloch ◽  
David Lintner ◽  
Joshua Harris
Keyword(s):  
Systematic Review ◽  
Anterior Cruciate Ligament ◽  
Acl Reconstruction ◽  
Cruciate Ligament ◽  
Activity Level ◽  
Two Stage ◽  
One Stage ◽  
Significant Difference ◽  
Anterior Cruciate ◽  
The One

AbstractThis study performs a systematic review to determine (1) if a significant difference exists in return to preinjury activity level between one- and two-stage treatment of combined anterior cruciate ligament (ACL) and patellar tendon (PT) tears; and (2) if a significant difference exists in the number of postoperative complications between the two differing surgical treatment approaches. A systematic review was performed using Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines and registered on PROSPERO. MEDLINE, Cochrane Central Register of Controlled Trials, SCOPUS, and Sport Discus were searched for English language level I–IV evidence studies on either one- (simultaneous) or two-stage (sequential) surgical treatment of simultaneously sustained ipsilateral ACL and PT tears. The approach to initial evaluation, diagnosis, treatment, and outcomes were qualitatively analyzed. Methodological quality assessment of all included studies was completed using the Methodological Index for Non-randomized Studies (MINORS). The Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) tool was used to assess quality of evidence and provide strength of recommendation. Statistical analyses were done using Fischer's exact test. Eleven articles (18 patients; 83% males; mean age, 31.1 ± 10.1 years; mean follow-up, 2.2 ± 1.7 years; and mean MINORS 7.8/16) were analyzed. Eight patients had a one-stage procedure (primary PT repair and ACL reconstruction), and 10 patients underwent a two-stage procedure (primary PT repair first followed by ACL reconstruction) with mean 28 ± 45.7 weeks (5 weeks–3 years) between surgeries. The rate for return to preinjury activity level after surgery was not significantly different between one- (88%) and two-stage (100%) (p = 0.444). There was a significantly higher complication rate (p = 0.023) in the one-stage (stiffness, instability, and patella baja) versus two-stage surgery (no complications). There was no significant difference in return to preinjury activity level between one- and two-stage PT repair and ACL reconstruction. However, the one-stage combined surgery had a significantly higher complication rate compared with two-stage surgery. The level of evidence is IV.

Clinical Outcome of Fixed Versus Adjustable Loop Cortical Suspension Devices in Arthroscopic Anterior Cruciate Ligament Reconstruction

2020 ◽  
Vol 22 (3) ◽  
pp. 181-185
Author(s):  
Ramy Said Assaad Ahmed Mohamed ◽  
Mohamed Hossam El-Din El-Shafie ◽  
Mohamed Ahmed El-Sheikh
Keyword(s):  
Anterior Cruciate Ligament ◽  
Acl Reconstruction ◽  
Ligament Reconstruction ◽  
Cruciate Ligament ◽  
Loop Group ◽  
Lysholm Score ◽  
Graft Fixation ◽  
Cruciate Ligament Reconstruction ◽  
Significant Difference ◽  
Anterior Cruciate

Background. Anterior cruciate ligament (ACL) reconstruction has remained the gold standard for ACL injuries, especially for young individuals and athletes exposed to high level sporting activities aiming to return to their preinjury level of activity. Cortical suspensory femoral fixation is commonly performed for graft fixation to the femur in anterior cruciate ligament reconstruction using hamstring tendons. The aim of this study was to compare the clinical results of using fixed and adjustable loop cortical suspension devices in arthroscopic ACL reconstruction using the Lysholm Knee Scoring Scale after 12 months postoperatively. Material and methods. This study included a total of sixty patients who underwent transportal arthroscopic ACL reconstruction using a hamstring tendon autograft from November 2016 to December 2017. For femoral graft fixation, a fixed-length loop device was used in 30 patients (fixed-loop group) and an adjustable-length loop device was used in 30 patients (adjustable-loop group) randomly.For tibial graft fixation, interference screw was used for all patients. Results. The present study shows that there was no statistically significant difference between the two groups regarding the Lysholm score with highly statistically significant difference between preoperative and postoperative Lysholm score in each group separately. Conclusion. Both fixed loop and adjustable loop devices in ACL reconstruction provided good clinical outcomes but without significant statistical difference between both groups from the clinical point of view postoperatively using the Lysholm score.

scholarly journals Meniscal Repair with Concurrent Anterior Cruciate Ligament Reconstruction: Is ACL Graft Choice Predictive of Meniscal Repair Success?

2019 ◽  
Vol 7 (7_suppl5) ◽  
pp. 2325967119S0035
Author(s):  
Hytham S. Salem ◽  
Laura J. Huston ◽  
Alex Zajichek ◽  
Michelle Lora Wolcott ◽  
Eric C. McCarty ◽  
...  
Keyword(s):  
Anterior Cruciate Ligament ◽  
Acl Reconstruction ◽  
Cruciate Ligament ◽  
Meniscal Tear ◽  
Meniscal Repair ◽  
Acl Graft ◽  
Baseline Activity ◽  
Graft Choice ◽  
Significant Difference ◽  
Anterior Cruciate

Objectives: The success rate of meniscal repair is known to increase with concurrent anterior cruciate ligament (ACL) reconstruction. However, the influence of ACL graft choice has not been described. The current study examines the effect of ACL graft choice on the outcome of meniscal repair performed in conjunction with ACL reconstruction (ACLR). Methods: Patients who underwent meniscal repair with concurrent primary ACLR were identified from a longitudinal, prospective cohort. Patient demographics and subjective outcome measures including the International Knee Documentation Committee (IKDC), Knee injury and Osteoarthritis Outcome Score (KOOS), and Marx activity rating scale were collected preoperatively. Arthroscopic assessment of meniscal tear characteristics and associated repair technique were recorded intraoperatively. Patients with subsequent repair failure, defined as any subsequent surgical procedure addressing the meniscus repaired at index surgery, were identified and operative notes were obtained in order to accurately classify pathology and treatment. A logistic regression model was built to assess the association of patient specific factors, ACL graft, baseline Marx activity level and meniscal tear laterality with the occurrence of repair failure at 6-year follow-up. Results: A total of 646 patients underwent ACLR with concurrent meniscal repair. Bone-patellar tendon-bone (BTB) and soft tissue (ST) autograft were used in 55.7% and 33.9% of cases, respectively, while allografts were utilized in the remaining cases. Table 1 summarizes the univariate analysis of each baseline variable. A total of 101 patients (15.6%) required subsequent surgery on the meniscus repaired at index surgery, including 89 meniscectomies (87 partial, 2 subtotal), 11 revision meniscal repairs, and 1 meniscus allograft transplantation. No statistically significant difference in meniscal repair failure rate was observed based on patient age, sex, BMI or smoking status. The odds of meniscal repair failure within 6 years of surgery for patients with only a lateral meniscal repair are 68% less than those with only a medial meniscal repair (CI: 41%, 83%; p<0.001). There is a statistically significant relationship between baseline Marx activity and the risk of subsequent meniscal repair, though it is nonlinear—patients with low or high baseline activity are at the highest risk of meniscal repair failure (CI: 1.05,1.31; p=0.004, Figure 1). The estimated odds of meniscal repair failure for BTB allograft, ST allograft, and ST autograft were 2.78 (CI: 0.84,9.19; p=0.09), 2.29 (CI: 0.97,5.45; p=0.06), and 1.42 (CI:0.87,2.32; p=0.16) times that of BTB autograft, respectively, although none proved statistically significant. Meniscal repair failure is associated with significantly lower 6-year scores for all KOOS components and the IKDC (p<0.001). However, there was no significant difference in MARX activity at 6-years (p=0.27). Conclusion: In the setting of primary ACLR, the risk of meniscal repair failure is increased with medial versus lateral meniscal repair. Patients with low or high baseline activity levels are also at an increased risk. ACL graft choice seems to have an effect on meniscal repair failure that approaches but does not reach statistical significance. A larger sample size may be required to accept the null hypothesis. [Table: see text][Figure: see text]

scholarly journals Effect of Geometry on the Fixation Strength of Anterior Cruciate Ligament Reconstruction Using BASHTI Technique

2020 ◽  
Author(s):  
Hadi Moeinnia ◽  
Amir Nourani ◽  
Amirhossein Borjali ◽  
Mahdi Mohseni ◽  
Narges Ghias ◽  
...  
Keyword(s):  
Anterior Cruciate Ligament ◽  
Acl Reconstruction ◽  
Failure Modes ◽  
Cruciate Ligament ◽  
Surface Strain ◽  
Fixation Strength ◽  
Pullout Load ◽  
Ultimate Failure ◽  
Anterior Cruciate ◽  
Cannulated Drill

AbstractThe goal of this study is to investigate the effects of tendon and cannulated drill bit diameter on the strength of the bone and site hold tendon inside (BASHTI) fixation technique for an anterior cruciate ligament (ACL) reconstruction. Bovine digital tendons and Sawbones blocks were used to mimic the ACL reconstruction. Mechanical strength of the specimens was measured using a cyclic loading continued by a single cycle pullout load until failure to simulate the real postsurgical loading conditions. Finally, failure modes of specimens and ultimate failure load were recorded. The maximum possible tendon surface strain (i.e., tendon compression [TC]) for tendon diameters of 6, 7, 8, and 9 mm were 0.73, 0.8, 0.7, and 0.65, respectively. Eighty per cent of the specimens with tendon diameter of 6 mm and 20% of specimens with tendon diameter of 7 mm failed on the torn tendon. All samples with larger tendon diameters (i.e., 8 and 9 mm) failed on the fixation slippage. The maximum fixation strength according to the most suitable core bones for 6, 7, 8, and 9 mm tendons were 148 ± 47 N (core 9.5 mm), 258 ± 66 N (core 9.5 mm), 386 ± 128 N (core 8.5 mm), and 348 ± 146 N (core 8.5 mm), respectively. The mode of tendon failure was significantly influenced by the tendon diameter. Also, an increase in TC raised the fixation strength for all tendon diameters; however, tendon over compression decreased the fixation strength for the 8 mm tendon group. Finally, an empirical equation was proposed to predict BASHTI fixation strength.

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