scholarly journals Effects of Sex and Fatigue on Biomechanical Measures During the Drop-Jump Task in Children

2017 ◽  
Vol 5 (1) ◽  
pp. 232596711667964 ◽  
Author(s):  
Kristín Briem ◽  
Kolbrún Vala Jónsdóttir ◽  
Árni Árnason ◽  
Þórarinn Sveinsson
Keyword(s):  
Knee Flexion ◽  
Female Athletes ◽  
Cruciate Ligament ◽  
Pearson Correlation ◽  
Reaction Force ◽  
Acl Injury ◽  
Initial Contact ◽  
Drop Jump ◽  
Increased Risk ◽  
Movement Strategies

Background: Female athletes have a higher rate of anterior cruciate ligament (ACL) injury than males from adolescence and into maturity, which is suggested to result from sex-specific changes in dynamic movement patterns with maturation. Few studies have studied movement strategies and response to fatigue in children. Purpose: To evaluate the effect of fatigue on biomechanical variables associated with increased risk for ACL injury during a drop-jump (DJ) performance in children. Study Design: Controlled laboratory study. Methods: A total of 116 children (mean age, 10.4 years) were recruited from local sports clubs and performed 5 repetitions of a DJ task before and after a fatigue protocol. Kinematic and kinetic data from initial contact (IC) to the first peak vertical ground reaction force (vGRF) were analyzed for both limbs, including limb and fatigue as within-subject factors for analyses between boys and girls. Pearson correlation coefficients were calculated to identify associations between variables of interest. Results: Girls demonstrated greater peak vGRF values than boys (by 8.1%; P < .05), there were greater peak vGRF values for the right limb than the left (by 6.2%; P < .001), and fatigue led to slightly greater values ( P < .05). Although weak, the correlation between peak vGRF values and knee flexion excursion was stronger for girls ( r = –0.20) than boys ( r = –0.08) ( P < .006). Fatigue resulted in greater knee flexion angles at IC and less excursion during landing, more so for girls (by 6.1° vs 1.4°; interaction, P < .001), although the knee flexion moment was generally lowered by fatigue ( P < .001). Limb asymmetry in knee flexion moments was more pronounced for boys than for girls (interaction, P < .05), contrary to that seen in frontal plane knee moments, where asymmetry was much greater in girls than boys (interaction, P < .001). Conclusion: Even as young athletes, girls and boys seem to adopt dissimilar movement strategies and are differently affected by fatigue. Clinical Relevance: Injury prevention programs should be considered at an earlier age in an effort to lower the risk of ACL injury in athletes.

Preliminary Evaluation of Knee Kinetics in Female Athletes on Hormonal Contraceptives

2019 ◽  
Vol 41 (02) ◽  
pp. 113-118
Author(s):  
Gabrielle Gilmer ◽  
Gretchen D. Oliver
Keyword(s):  
Injury Risk ◽  
Female Athletes ◽  
Cruciate Ligament ◽  
Reaction Force ◽  
Acl Injury ◽  
Hormonal Contraceptives ◽  
Preliminary Evaluation ◽  
Knee Valgus ◽  
Time Points ◽  
Acl Injury Risk

AbstractRecently, an emphasis has been placed on understanding how ovarian sex hormones and hormonal contraceptives affect risk for anterior cruciate ligament (ACL) injury. The literature presents large discrepancies in whether or not hormonal contraceptives affect ACL injury risk; therefore, the purpose of this study was to evaluate whether vertical ground reaction force (GRF) and knee valgus force are different between athletes who do and do not use hormonal contraceptives. Twenty-two female athletes volunteered to participate and were divided into two groups based on their answers to a health history questionnaire: those who use hormonal contraceptives and those who do not. Participants performed a drop vertical jump (DVJ) and single leg crossover dropdown (SCD) at two different time points in their menstrual cycle (pre-ovulatory phase and mid-luteal phase). Kinetic data were collected at 1000 Hz. Independent samples t-tests revealed no significant differences between groups in vertical GRF and knee valgus force at both time points. Findings from this study suggest that hormonal contraceptives do not elicit detectable changes in vertical GRF and knee valgus force. Ultimately, this calls for further studies on the relationship between hormones and ACL injury risk and physicians to consider hormonal screening in addition to neuromuscular and biomechanical screening.

scholarly journals Individuals With an Anterior Cruciate Ligament–Reconstructed Knee Display Atypical Whole Body Movement Strategies but Normal Knee Robustness During Side-Hop Landings: A Finite Helical Axis Analysis

2020 ◽  
Vol 48 (5) ◽  
pp. 1117-1126 ◽  
Author(s):  
Jonas L. Markström ◽  
Helena Grip ◽  
Lina Schelin ◽  
Charlotte K. Häger
Keyword(s):  
Knee Flexion ◽  
Cruciate Ligament ◽  
Body Movement ◽  
Whole Body ◽  
Helical Axis ◽  
Initial Contact ◽  
Movement Strategies ◽  
Flexion Moment ◽  
Anterior Cruciate ◽  
Whole Body Movement

Background: Atypical knee joint biomechanics after anterior cruciate ligament reconstruction (ACLR) are common. It is, however, unclear whether knee robustness (ability to tolerate perturbation and maintain joint configuration) and whole body movement strategies are compromised after ACLR. Purpose: To investigate landing control after ACLR with regard to dynamic knee robustness and whole body movement strategies during sports-mimicking side hops, and to evaluate functional performance of hop tests and knee strength. Study Design: Controlled laboratory study. Methods: An 8-camera motion capture system and 2 synchronized force plates were used to calculate joint angles and moments during standardized rebound side-hop landings performed by 32 individuals with an ACL-reconstructed knee (ACLR group; median, 16.0 months after reconstruction with hamstring tendon graft [interquartile range, 35.2 months]) and 32 matched asymptomatic controls (CTRL). Dynamic knee robustness was quantified using a finite helical axis approach, providing discrete values quantifying divergence of knee joint movements from flexion-extension (higher relative frontal and/or transverse plane motion equaled lower robustness) during momentary helical rotation intervals of 10°. Multivariate analyses of movement strategies included trunk, hip, and knee angles at initial contact and during landing and hip and knee peak moments during landing, comparing ACLR and CTRL, as well as legs within groups. Results: Knee robustness was lower for the first 10° motion interval after initial contact and then successively stabilized for both groups and legs. When landing with the injured leg, the ACLR group, as compared with the contralateral leg and/or CTRL, demonstrated significantly greater flexion of the trunk, hip, and knee; greater hip flexion moment; less knee flexion moment; and smaller angle but greater moment of knee internal rotation. The ACLR group also had lower but acceptable hop and strength performances (ratios to noninjured leg >90%) except for knee flexion strength (12% deficit). Conclusion: Knee robustness was not affected by ACLR during side-hop landings, but alterations in movement strategies were seen for the trunk, hip, and knee, as well as long-term deficits in knee flexion strength. Clinical Relevance: Knee robustness is lowest immediately after landing for both the ACLR group and the CTRL and should be targeted in training to reduce knee injury risk. Assessment of movement strategies during side-hop landings after ACLR should consider a whole body approach.

scholarly journals Jump-Landing Biomechanics and Knee-Laxity Change Across the Menstrual Cycle in Women With Anterior Cruciate Ligament Reconstruction

2014 ◽  
Vol 49 (2) ◽  
pp. 154-162 ◽  
Author(s):  
David R. Bell ◽  
J. Troy Blackburn ◽  
Anthony C. Hackney ◽  
Stephen W. Marshall ◽  
Anthony I. Beutler ◽  
...  
Keyword(s):  
Menstrual Cycle ◽  
Cruciate Ligament ◽  
Reaction Force ◽  
Knee Laxity ◽  
Acl Injury ◽  
Initial Contact ◽  
Vertical Ground Reaction Force ◽  
Jump Landing ◽  
Anterior Knee Laxity ◽  
Anterior Cruciate

Context: Of the individuals able to return to sport participation after an anterior cruciate ligament(ACL) injury, up to 25% will experience a second ACL injury. This population may be more sensitive to hormonal fluctuations, which may explain this high rate of second injury. Objective: To examine changes in 3-dimensional hip and knee kinematics and kinetics during a jump landing and to examine knee laxity across the menstrual cycle in women with histories of unilateral noncontact ACL injury. Design  Controlled laboratory study. Setting: Laboratory. Patients or Other Participants: A total of 20 women (age = 19.6 ± 1.3 years, height = 168.6 ± 5.3 cm, mass = 66.2 ± 9.1 kg) with unilateral, noncontact ACL injuries. Intervention(s) Participants completed a jump-landing task and knee-laxity assessment 3 to 5 days after the onset of menses and within 3 days of a positive ovulation test. Main Outcome Measure(s): Kinematics in the uninjured limb at initial contact with the ground during a jump landing, peak kinematics and kinetics during the loading phase of landing, anterior knee laxity via the KT-1000, peak vertical ground reaction force, and blood hormone concentrations (estradiol-β-17, progesterone, free testosterone). Results: At ovulation, estradiol-β-17 (t = −2.9, P = .009), progesterone (t = −3.4, P = .003), and anterior knee laxity (t = −2.3, P = .03) increased, and participants presented with greater knee-valgus moment (Z = −2.6, P = .01) and femoral internal rotation (t = −2.1, P = .047). However, during the menses test session, participants landed harder (greater peak vertical ground reaction force; t = 2.2, P = .04), with the tibia internally rotated at initial contact (t = 2.8, P = .01) and greater hip internal-rotation moment (Z = −2.4, P = .02). No other changes were observed across the menstrual cycle. Conclusions Knee and hip mechanics in both phases of the menstrual cycle represented a greater potential risk of ACL loading. Observed changes in landing mechanics may explain why the risk of second ACL injury is elevated in this population.

Knee Valgus during Drop Jumps in National Collegiate Athletic Association Division I Female Athletes

2007 ◽  
Vol 36 (2) ◽  
pp. 285-289 ◽  
Author(s):  
Michael Joseph ◽  
David Tiberio ◽  
Jennifer L. Baird ◽  
Thomas H. Trojian ◽  
Jeffrey M. Anderson ◽  
...  
Keyword(s):  
National Collegiate Athletic Association ◽  
Female Athletes ◽  
Cruciate Ligament ◽  
Division I ◽  
Ligament Injury ◽  
Initial Contact ◽  
Knee Valgus ◽  
Drop Jump ◽  
Maximum Angle ◽  
Anterior Cruciate

Background Female athletes land from a jump with greater knee valgus and ankle pronation/eversion. Excessive valgus and pronation have been linked to risk of anterior cruciate ligament injury. A medially posted orthosis decreases component motions of knee valgus such as foot pronation/eversion and tibial internal rotation. Hypothesis We hypothesized a medial post would decrease knee valgus and ankle pronation/eversion during drop-jump landings in NCAA-I female athletes. Study Design Controlled laboratory study. Methods Knee and ankle 3-dimensional kinematics were measured using high-speed motion capture in 10 National Collegiate Athletic Association Division I female athletes during a drop-jump landing with and without a medial post. Analysis of variance was used to determine differences in posting condition, t tests were used to determine dominant-nondominant differences, and the Pearson correlation coefficient was used to determine relationships between variables. Results Significant differences were found for all measures in the posted condition. A medial post decreased knee valgus at initial contact (1.24°, P< .01) and maximum angle (1.21 °, P< .01). The post also decreased ankle pronation/eversion at initial contact (0.77°, P < .01) and maximum angle (0.95°, P = .039). Conclusion The authors have demonstrated a significant decrease in knee valgus and ankle pronation/eversion during a drop jump with a medial post placed in the athletes’ shoes. Clinical Relevance A medial post may be a potential means to decrease risk of anterior cruciate ligament injury.

scholarly journals Sagittal Plane Hip, Knee, and Ankle Biomechanics and the Risk of Anterior Cruciate Ligament Injury: A Prospective Study

2017 ◽  
Vol 5 (12) ◽  
pp. 232596711774548 ◽  
Author(s):  
Mari Leppänen ◽  
Kati Pasanen ◽  
Tron Krosshaug ◽  
Pekka Kannus ◽  
Tommi Vasankari ◽  
...  
Keyword(s):  
Knee Flexion ◽  
Sagittal Plane ◽  
Cruciate Ligament ◽  
Acl Injury ◽  
Young Female ◽  
Roc Curve Analysis ◽  
Acl Injuries ◽  
Increased Risk ◽  
Flexion Moment ◽  
Hip Flexion

Background: Stiff landings with less knee flexion and high vertical ground-reaction forces have been shown to be associated with an increased risk of anterior cruciate ligament (ACL) injury. The literature on the association between other sagittal plane measures and the risk of ACL injuries with a prospective study design is lacking. Purpose: To investigate the relationship between selected sagittal plane hip, knee, and ankle biomechanics and the risk of ACL injury in young female team-sport athletes. Study Design: Case-control study; Level of evidence, 3. Methods: A total of 171 female basketball and floorball athletes (age range, 12-21 years) participated in a vertical drop jump test using 3-dimensional motion analysis. All new ACL injuries, as well as match and training exposure data, were recorded for 1 to 3 years. Biomechanical variables, including hip and ankle flexion at initial contact (IC), hip and ankle ranges of motion (ROMs), and peak external knee and hip flexion moments, were selected for analysis. Cox regression models were used to calculate hazard ratios (HRs) with 95% CIs. The combined sensitivity and specificity of significant test variables were assessed using a receiver operating characteristic (ROC) curve analysis. Results: A total of 15 noncontact ACL injuries were recorded during follow-up (0.2 injuries/1000 player-hours). Of the variables investigated, landing with less hip flexion ROM (HR for each 10° increase in hip ROM, 0.61 [95% CI, 0.38-0.99]; P < .05) and a greater knee flexion moment (HR for each 10-N·m increase in knee moment, 1.21 [95% CI, 1.04-1.40]; P = .01) was significantly associated with an increased risk of ACL injury. Hip flexion at IC, ankle flexion at IC, ankle flexion ROM, and peak external hip flexion moment were not significantly associated with the risk of ACL injury. ROC curve analysis for significant variables showed an area under the curve of 0.6, indicating a poor combined sensitivity and specificity of the test. Conclusion: Landing with less hip flexion ROM and a greater peak external knee flexion moment was associated with an increased risk of ACL injury in young female team-sport players. Studies with larger populations are needed to confirm these findings and to determine the role of ankle flexion ROM as a risk factor for ACL injury. Increasing knee and hip flexion ROMs to produce soft landings might reduce knee loading and risk of ACL injury in young female athletes.

scholarly journals Sexual Dimorphisms in Anterior Cruciate Ligament Injury: A Current Concepts Review

2021 ◽  
Vol 9 (12) ◽  
pp. 232596712110253
Author(s):  
Tayt M. Ellison ◽  
Ilexa Flagstaff ◽  
Anthony E. Johnson
Keyword(s):  
Female Athletes ◽  
Cruciate Ligament ◽  
Acl Injury ◽  
Extrinsic Factors ◽  
Male Athletes ◽  
Acl Injuries ◽  
Sexual Dimorphisms ◽  
Increased Risk ◽  
Anterior Cruciate ◽  
Postsurgical Outcomes

Background: Although most anterior cruciate ligament (ACL) injuries occur in male athletes, female athletes are consistently observed to be at a higher risk for sports-specific ACL injury. Purpose: To provide a thorough review of what is known about the sexual dimorphisms in ACL injury to guide treatment and prevention strategies and future research. Study Design: Narrative review. Methods: We conducted a comprehensive literature search for ACL-related studies published between January 1982 and September 2017 to identify pertinent studies regarding ACL injury epidemiology, prevention strategies, treatment outcomes, and dimorphisms. By performing a broad ACL injury search, we initially identified 11,453 articles. After applying additional qualifiers, we retained articles if they were published in English after 1980 and focused on sex-specific differences in any of 8 different topics: sex-specific reporting, difference in sports, selective training, hormonal effects, genetics, neuromuscular and kinematic control, anatomic differences, and outcomes. Results: A total of 122 articles met the inclusion criteria. In sum, the literature review indicated that female athletes are at significantly higher risk for ACL injuries than are their male counterparts, but the exact reasons for this were not clear. Initial studies focused on intrinsic differences between the sexes, whereas recent studies have shifted to focus on extrinsic factors to explain the increased risk. It is likely both intrinsic and extrinsic factors contribute to this increased risk, but further study is needed. In addition to female patients having an increased risk for ACL injuries, they are less likely than are male patients to undergo reconstructive surgery, and they experience worse postsurgical outcomes. Despite this, reconstructive surgery remains the gold standard when knee stability, return to sports, and high functional outcome scores are the goal, but further research is needed to determine why there is disparity in surgical rates and what surgical techniques optimize postsurgical outcomes for female patients. Conclusion: Male athletes often predominated the research concerning ACL injury and treatment, and although sex-specific reporting is progressing, it has historically been deficient. ACL injuries, prevention techniques, and ACL reconstruction require further research to maximize the health potential of at-risk female athletes.

scholarly journals Instruction and Jump-Landing Kinematics in College-Aged Female Athletes Over Time

2013 ◽  
Vol 48 (2) ◽  
pp. 161-171 ◽  
Author(s):  
Jena Etnoyer ◽  
Nelson Cortes ◽  
Stacie I. Ringleb ◽  
Bonnie L. Van Lunen ◽  
James A. Onate
Keyword(s):  
Lower Extremity ◽  
Retention Test ◽  
Knee Flexion ◽  
Female Athletes ◽  
Initial Contact ◽  
Knee Valgus ◽  
Drop Jump ◽  
Jump Landing ◽  
Peak Knee ◽  
Hip Flexion

Context: Instruction can be used to alter the biomechanical movement patterns associated with anterior cruciate ligament (ACL) injuries. Objective: To determine the effects of instruction through combination (self and expert) feedback or self-feedback on lower extremity kinematics during the box–drop-jump task, running–stop-jump task, and sidestep-cutting maneuver over time in college-aged female athletes. Design: Randomized controlled clinical trial. Setting: Laboratory. Patients or Other Participants: Forty-three physically active women (age = 21.47 ± 1.55 years, height = 1.65 ± 0.08 m, mass = 63.78 ± 12.00 kg) with no history of ACL or lower extremity injuries or surgery in the 2 months before the study were assigned randomly to 3 groups: self-feedback (SE), combination feedback (CB), or control (CT). Intervention(s): Participants performed a box–drop-jump task for the pretest and then received feedback about their landing mechanics. After the intervention, they performed an immediate posttest of the box–drop-jump task and a running–stop-jump transfer test. Participants returned 1 month later for a retention test of each task and a sidestep-cutting maneuver. Kinematic data were collected with an 8-camera system sampled at 500 Hz. Main Outcome Measure(s): The independent variables were feedback group (3), test time (3), and task (3). The dependent variables were knee- and hip-flexion, knee-valgus, and hip- abduction kinematics at initial contact and at peak knee flexion. Results: For the box–drop-jump task, knee- and hip-flexion angles at initial contact were greater at the posttest than at the retention test (P &lt; .001). At peak knee flexion, hip flexion was greater at the posttest than at the pretest (P = .003) and was greater at the retention test than at the pretest (P = .04); knee valgus was greater at the retention test than at the pretest (P = .03) and posttest (P = .02). Peak knee flexion was greater for the CB than the SE group (P = .03) during the box–drop-jump task at posttest. For the running–stop-jump task at the posttest, the CB group had greater peak knee flexion than the SE and CT (P ≤ .05). Conclusions: Our results suggest that feedback involving a combination of self-feedback and expert video feedback with oral instruction effectively improved lower extremity kinematics during jump-landing tasks.

scholarly journals Effects of Lower Extremity Muscle Fatigue on Knee Loading During a Forward Drop Jump to a Vertical Jump in Female Athletes

2020 ◽  
Vol 72 (1) ◽  
pp. 5-13 ◽  
Author(s):  
Tzu Lin Wong ◽  
Chen Fu Huang ◽  
Po Chieh Chen
Keyword(s):  
Muscle Fatigue ◽  
Energy Absorption ◽  
Female Athletes ◽  
Inverse Dynamics ◽  
Cruciate Ligament ◽  
Vertical Jump ◽  
Reaction Force ◽  
Drop Jump ◽  
Shear Forces ◽  
Lower Extremity Muscle

AbstractThe aim of this study was to examine changes in the kinematic and kinetic parameters of female athletes performing a forward drop jump to a vertical jump under muscle fatigue condition. Twelve female college athletes performed a forward drop jump to a vertical jump with and without muscle fatigue conditions. A motion capture system and two AMTI force plates were used to synchronously collect kinematic and kinetic data. Inverse dynamics were implemented to calculate the participant’s joint loading, joint moment, and energy absorption. A paired sample t-test was used to compare statistical differences between pre-fatigue and post-fatigue conditions (α = .05). The forward trunk lean angle at initial foot contact, as well as the knee range of motion, total negative work and energy absorption contribution of the knee joint during the landing phase were significantly decreased under post-fatigue condition. The increased peak vertical ground reaction force and peak tibial anterior shear forces were also found under post-fatigue condition. These results indicated that muscle fatigue caused participants to change their original landing posture into stiff landing posture and decrease the energy absorption ability, which increased the tibial anterior shear forces. Therefore, female athletes should appropriately increase the knee flexion angle under muscle fatigue condition to reduce the risk of anterior cruciate ligament injuries.

scholarly journals EVALUATION OF SERUM RELAXIN CONCENTRATIONS AND KNEE VALGUS AFTER ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

2020 ◽  
Vol 8 (4_suppl3) ◽  
pp. 2325967120S0013
Author(s):  
Gabrielle G. Gilmer ◽  
Michael D. Roberts ◽  
Gretchen Oliver
Keyword(s):  
Anterior Cruciate Ligament ◽  
Health Outcomes ◽  
Luteal Phase ◽  
Female Athletes ◽  
Cruciate Ligament ◽  
Acl Injury ◽  
Knee Valgus ◽  
Increased Risk ◽  
Anterior Cruciate

Background: Athletes who sustain an anterior cruciate ligament (ACL) injury are more likely to develop adverse health outcomes, such as knee osteoarthritis, knee pain, and obesity. It is assumed that the long-term consequences of ACL reconstruction are caused by the reconstruction itself. Studies have observed that relaxin, a peptide hormone similar in structure to insulin, interferes with the structural integrity of the ACL and elicits long term effects on bone, joint, muscle, and tendon health. Given the known effects of relaxin, it is reasonable to wonder if relaxin contributes to the development of these long-term health outcomes, independently of the ACL injury. Hypothesis/Purpose: The purpose of this study was to evaluate knee valgus and serum relaxin concentrations (SRC) in athletes who have and have not sustained an ACL injury. It was hypothesized that athletes who previously tore their ACL would have higher SRC and more knee valgus than those who were injury free. Methods: Twenty-two female athletes participated. Participants were assigned to one of two groups: ACL injury (6.0 ± 3.3 years after surgery, N = 4) and injury free (N = 18). Kinematic data were collected at 100 Hz using The MotionMonitor. Participants performed a single leg squat (SLS), single leg crossover dropdown (SCD), and drop vertical jump (DVJ) at two different time points in their menstrual period: pre-ovulatory phase and mid-luteal phase. Blood samples were collected when SRC are measurable (mid-luteal phase), and SRC were determined using a Quantikine Human Relaxin-2 Immunoassay. Results: Independent samples t-tests revealed significant differences between those who tore their ACL and those who were injury free in SRC and knee valgus during the SLS in the mid luteal phase, DVJ in both phases, and SCD in both phases. Specifically, the participants who tore their ACL had significantly higher SRC and more knee valgus than those who did not tear their ACL. Conclusion: These findings suggest that a previous ACL injury could place one at an increased risk of re-tear and other adverse effects on their joints, muscles, and tendons. Thus, further investigating hormonal risk factors during long term monitoring of recovery is needed.

scholarly journals Rapid Posterior Tibial Reduction After Noncontact Anterior Cruciate Ligament Rupture: Mechanism Description From a Video Analysis

2020 ◽  
Vol 12 (5) ◽  
pp. 462-469 ◽  
Author(s):  
Alberto Grassi ◽  
Filippo Tosarelli ◽  
Piero Agostinone ◽  
Luca Macchiarola ◽  
Stefano Zaffagnini ◽  
...  
Keyword(s):  
Anterior Cruciate Ligament ◽  
Video Analysis ◽  
Knee Flexion ◽  
Cruciate Ligament ◽  
Acl Injury ◽  
Soccer Players ◽  
Initial Contact ◽  
Acl Injuries ◽  
Posterior Tibial ◽  
Anterior Cruciate

Background: The mechanisms of noncontact anterior cruciate ligament (ACL) injuries are an enormously debated topic in sports medicine; however, the late phases of injury have not yet been investigated. Hypothesis: A well-defined posterior tibial translation can be visualized with its timing and patterns of knee flexion after ACL injury. Study Design: Case series. Level of Evidence: Level 4. Methods: A total of 137 videos of ACL injuries in professional male football (soccer) players were screened for a sudden posterior tibial reduction (PTR) in the late phase of noncontact ACL injury mechanism. The suitable videos were analyzed using Kinovea software for sport video analysis. The time of initial contact of the foot with the ground, the foot lift, the start of tibial reduction, and the end of tibial reduction were assessed. Results: A total of 21 videos exhibited a clear posterior tibial reduction of 42 ± 11 ms, after an average of 229 ± 81 ms after initial contact. The tibial reduction occurred consistently within the first 50 to 60 ms after foot lift (55 ± 30 ms) and with the knee flexed between 45° and 90° (62%) or more than 90° (24%). Conclusion: A rapid posterior tibial reduction is consistently present in the late phases of noncontact ACL injuries in some male soccer players, with a consistent temporal relationship between foot lift from the ground and consistent degrees of knee flexion near or above 90°. Clinical Relevance: This study provides insight into the late phases of ACL injury. The described mechanism, although purely theoretical, could be responsible for commonly observed intra-articular lesions.

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