An Exploratory Assessment of Associations Between Serum Estrogen to Progesterone Ratio and Anterior Cruciate Ligament Size, Biomechanics, and T2* Relaxation Time in the Porcine Model.

ACL Research Retreat IX Summary Statement: The Pediatric Athlete, March 17-19, 2022; High Point, North Carolina.

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Objective: To critically assess the literature focused on sex-specific trajectories in physical characteristics associated with anterior cruciate ligament (ACL) injury risk by age and maturational stage.Data Sources: PubMed, CINHAL, Scopus, and SPORTDiscus databases were searched through December 2021.Study Selection: Longitudinal and cross-sectional studies of healthy 8- to 18-year-olds, stratified by sex and age or maturation on 1 measure of body composition, lower extremity strength, ACL size, joint laxity, knee-joint geometry, lower extremity alignment, balance, or lower extremity biomechanics were included.Data Extraction: Extracted data included study design, participant characteristics, maturational metrics, and outcome measures. We used random-effects meta-analyses to examine sex differences in trajectory over time. For each variable, standardized differences in means between sexes were calculated.Data Synthesis: The search yielded 216 primary and 22 secondary articles. Less fat-free mass, leg strength, and power and greater general joint laxity were evident in girls by 8 to 10 years of age and Tanner stage I. Sex differences in body composition, strength, power, general joint laxity, and balance were more evident by 11 to 13 years of age and when transitioning from the prepubertal to pubertal stages. Sex differences in ACL size (smaller in girls), anterior knee laxity and tibiofemoral angle (greater in girls), and higher-risk biomechanics (in girls) were observed at later ages and when transitioning from the pubertal to postpubertal stages. Inconsistent study designs and data reporting limited the number of included studies.Conclusions: Critical gaps remain in our knowledge and highlight the need to improve our understanding of the relative timing and tempo of ACL risk factor development.Context: The risk of anterior cruciate ligament (ACL) injury in female athletes increases throughout the stages of maturation. Previous evidence has indicated a lack of dynamic knee control during double-limb jump landings throughout maturation, yet the extent of biomechanical changes that occur throughout maturation during single-limb landings are not well understood. A maturational analysis of high-risk biomechanics during single-limb landings may elucidate and inform injury risk reduction efforts.Objective: To determine differences in single-limb landing biomechanics between pre-pubertal, pubertal, and post-pubertal female soccer players.Design: Cross-sectional (pre-testing component of a randomized controlled trial)Setting: Research biomechanics laboratoryPatients or Other Participants: 151 competitive female soccer playersIntervention(s): Participants were categorized based on percent of adult stature into pre-pubertal (PRE: <84% of adult stature, n=23), pubertal (PUB: 87%-94% of adult stature, n=36), and post-pubertal (POST: >94% of adult stature, n=92) maturational groups.Main Outcome Measure(s): All participants were instrumented for standard three-dimensional motion analysis and completed three trials of an ipsilateral single-limb hop and land over a 4-inch hurdle. Variables of interest included peak landing kinematics (hip flexion, hip adduction, hip internal rotation, knee flexion, knee abduction, ankle dorsiflexion) and peak landing external moments and ground reaction forces normalized to body mass (hip flexion, knee flexion, knee abduction, vertical ground reaction force). Multivariate analysis of variance (MANOVA) was used to compare the biomechanical variables of the dominant limb (preferred kicking limb) between maturational groups (α=0.05). Pearson's correlational analyses identified the relationship between the estimated percent of adult stature and lower extremity biomechanical variables.Results: There were significant differences in lower extremity kinematics (λ=0.79, p<0.001) and kinetics (λ=0.78, p<0.001) between maturational groups. POST landed in less hip internal rotation (POST: -0.3±5.4°) than PRE (3.8±7.0°, d= 0.67, p=0.008) and PUB (3.4±6.0°, d= 0.65, p=0.004), and greater knee abduction (POST: 5.1±4.8°) than PUB (2.4±3.4°, d= 0.66, p=0.009). POST also landed with vertical ground reaction forces 14% lower (POST: 3.20±0.76 xBW) than PRE (3.69±0.78 xBW, d= 0.62, p=0.01) and 13% lower than PUB (3.65±0.47 xBW, d= 0.73, p=0.005). Weak relationships were identified between the estimated percent of adult stature and peak hip internal rotation angle (r=-0.26) and vertical ground reaction force (r=-0.31).Conclusions: Post-pubertal female soccer players performed single-limb landings with lesser hip internal rotation, greater knee abduction, and lower vertical ground reaction forces. These findings are inconsistent with previous evidence that indicates higher risk movement strategies in post-pubertal athletes. The single-limb landing over a standardized hurdle height may not provide a comprehensive biomechanical picture for which to assign injury risk profiles.Context: Researchers have identified modifiable biomechanical anterior cruciate ligament (ACL) injury risk factors in laboratory settings with change of direction tasks. To preserve athlete-environment relationship, it has been advocated to assess movement strategies on the field rather than only in the laboratory. However, the kinematic differences between laboratory and on-field settings have never been investigated.Objective: To investigate the knee kinematics of female soccer players during agility movements performed both in laboratory and in soccer field environments.Design: Observational.Setting: Research laboratory and field.Patients or Other Participants: Twenty healthy female soccer players (14.9 ± 0.9 years, height 167.9 ± 4.8 cm, mass 56.4 ± 7.3 kg) participated.Intervention(s): Unanticipated sidestep cutting tasks with the dominant leg (towards the non-dominant leg) were collected both in the laboratory and on the field. In the laboratory, the players used a 5m approach run followed by a 1-foot landing and a 40°-50° change of direction followed by running through a gate 5m away. On-field tasks were recorded during a game performed as part of their regular training session. Kinematics were collected through wearable inertial sensors (Xsens Technologies, Enschede, The Netherlands). One-way ANOVA was used to compare knee joint kinematics between the conditions, with level of significance set at p<.05. Waveform consistency was investigated through Pearson's correlation coefficient and standardized z-score vector.Main Outcome Measure(s): For both conditions, 3D joint angles were defined using the Euler sequence ZXY and exported from the Xsens software (Xsens MVN Analyze 2020.0.1) to a customized Matlab (The MathWorks 2019a, Natick, Massachusetts, US) script. The ultimate foot contact before the change of direction was used and data were processed in a time-normalized interval from 50ms prior to the initial contact (0%) to 25ms after (100%). For the field, 40°-50° changes of direction were extracted for comparison with the laboratory condition.Results: On-field agility yielded vastly different knee kinematics compared to lab agility. At initial contact, the average knee flexion angle on-field was 31.96° - 36.92° versus 19.47° - 21.15° in the laboratory (p=.004). For the frontal plane at initial contact, we found -1.08° - -2.31° knee abduction in the field and 0.29° - 0.67° knee adduction in the laboratory (p=.007). The peak knee angles in frontal and sagittal planes were comparable among the two conditions. Waveform correlation was poor-to-excellent between laboratory and field (r: 0.20-1.00).Conclusions: Movement strategies used for changes of direction tasks in the laboratory were different from the on-field movement strategies in young female soccer players. This could be attributed to the differences in the environment and support the need for on-field injury risk screening.Context: Increased knee extensor moments relative to hip extensor moments during landing have been proposed as a risk factor for ACL injury in females. Diminished strength of the hip extensors relative to the knee extensors has been shown to predict an increased knee-hip extensor moment ratio during the deceleration phase of landing.Objective: To determine if decreased strength of the hip extensors relative to the knee extensors predicts re-injury in females who have returned to sport following ACL reconstruction (ACLR). Design: Retrospective, case-controlSetting: Patient clinicIntervention(s): Maximum isometric strength of the hip and knee extensors was measured using a motor-driven dynamometer (BTE Primus; BTE) as part of return to sport testing following ACLR. Patients were contacted to participate in an online survey concerning their return to sport and ACL injury status at least 12 months following testing.Patients or Other Participants: 345 females post ACLR who had previously undergone baseline strength testing were surveyed. The survey response rate was 54%. Respondents who sustained an ipsilateral ACL re-injury (non-contact) within 36 months of returning to sport were considered as cases.Main Outcome Measure(s): Twelve cases (14-22 years) were identified and matched with 2-4 non-injured controls (n = 41) based on sport level, athletic exposures, age, and graft type. Peak isometric strength for the hip and knee extensors was identified for each case and control from patient records. The hip-knee extensor strength ratio was calculated by dividing the peak strength of the hip extensors by the knee extensors (expressed as percentage). Logistic regression was performed to determine if the hip-knee extensor strength ratio predicted ACL re-injury, adjusted for known confounders (athletic exposures, age, graft type, months ACLR to return to sport). Receiver operator characteristic (ROC) curve analysis was conducted to determine the cutoff for the hip-knee extensor strength ratio that distinguished between high-risk and low-risk outcomes.Results: Cases had a lower hip-knee extensor strength ratio compared to controls (0.83 ± 0.16 vs. 0.98 ± 0.17, p = 0.007). The hip-knee extensor strength ratio significantly predicted ACL re-injury (p = 0.036, adjusted OR = 0.944, 95% CI: 0.894, 0.996). For every 1% increase in the hip-knee extensor strength ratio, there was 5.6% lower odds of re-injury. ROC curve analysis revealed an area under the curve of 74.8% [95% CI: 58.7%, 90.9%] (p=0.010), indicating fair prediction accuracy. The cutoff for the hip-knee extensor strength ratio to define high risk was <= 97.1% (sensitivity: 91.7%, specificity: 51.2%).Conclusions: Female athletes with a lower hip-knee extensor strength ratio following ACLR are at greater risk of ACL re-injury (ipsilateral limb). These results suggest that return to sport testing to assess risk for ACL re-injury should consider the inclusion of hip and knee extensor strength.Context: Upwards of 30% of youth athletes sustain a repeat anterior cruciate ligament (ACL) injury after ACL reconstruction. While specific risk factors for re-injury and predictive models exist, these models are: 1) Limited in scope, failing to consider the large number of variables related to re-injury, 2) Overly simplistic, overlooking the interaction amongst variables, 3) Too broad, identifying risk factors within a group context and 4) non-actionable, utilizing risk factors that cannot be altered in recovery.Objective: The goal of this study was to develop an ACL re-injury prediction model capable of evaluating each patient's individual risk, identifying modifiable risk factors and ranking these factors on the order of importance and ability to be modified.Design: Retrospective database study of 432 patients (mean age 15.0, Female 50.7%) who underwent ACL reconstruction. This dataset represented a targeted extraction from a larger dataset and had a reinjury rate of 30%.Setting: The dataset included variables across the following categories: Demographics, injury information, family history of ACL injury, surgical variables, rehabilitation & performance testing and re-injury information.Intervention(s): Machine learning (ML) techniques leveraging clinician domain knowledge were utilized to develop a model capable of determining a patient's risk for repeat ACL injury. Two highly experienced surgeons and a physical therapist independently assessed risk factors and ranked their contribution to injury and ability to be modified during recovery. These classifications were integrated into the modeling, allowing clinician expertise to improve upon standard ML methodologies. After patient risk classification, the model ranks the most significant risk factors according to impact and ease of modification.Main Outcome Measure(s): Multiple weighting methods and hyperparameter schemes were evaluated to obtain the highest accuracy classifying patients into high, medium or low risk categories, and weighting of modifiable risk factors. Model accuracy was determined using a 5-fold cross validation process over a 20% holdout dataset. An a-priori goal of classifying double the rate of re-injury across the entire dataset into high-risk patients (54%) and half this rate (13.5%) into low-risk.Results: The final model included 23 modifiable variables represented mostly by performance factors (e.g. normalized quad peak torque, quad/hamstring strength ratio, hop testing performance or time to return to sports). The model adjusts risk factor weight on a case-by-case basis. Performance goals were achieved with ACL re-tear rates of 58% in high-risk and 7% in low-risk categories, with sensitivity of 89% and specificity of 66% and verified within the cross-validation process.Conclusions: This ACL-Reinjury Risk Prediction Model can improve clinical care through accurate risk stratification and identification of patient specific modifiable risk factors, that can inform ongoing reinjury reduction or rehabilitation programs. Continued improvements in model accuracy will incorporate additional features, developing more intelligent labeling functions and adding confidence metrics.Context: The high incidence of anterior cruciate ligament (ACL) injuries in young female soccer players compared to their male counterparts has led to a large body of work aimed at reducing injury.Objective: To determine the effects of neuromuscular training using biomechanical biofeedback in order to reduce the risk of ACL injuries in adolescent female athletes.Design: Randomized controlled clinical trial; Level of evidence, 1.Setting: Research laboratoryPatients or Other Participants: 150 (age:13.3±2.2yrs; height: 156.1±10.6cm; mass:50.2±11.3kg) female soccer players.Intervention(s): A prospective, randomized, active comparator, open blinded, end-point trial was conducted. Participants were randomized into one of three study arms where each received neuromuscular training plus 1) sham biofeedback as an active control (NMT), 2) knee-focused biofeedback (NMT+K), and 3) hip-focused biofeedback (NMT+H).Main Outcome Measure(s): Each participant completed a pre-intervention baseline session and a post-intervention session to determine knee abduction moment (KAM) during a double leg drop vertical jump (DVJ) and an unplanned single leg cutting task at discrete time points and at specific time points during the stance phase. Athletic exposures and ACL injuries were tracked weekly for six months following the post-test session.Results: 140 participants (93.3%) completed the 6-week intervention and post-test. No ACL injuries were reported among any of the intervention groups six months following post-testing. Peak KAM was significantly improved in all three intervention groups from baseline to the post-test during the drop vertical jump (NMT: baseline -21.4Nm [95% CI: -25.4, -17.4], post -16.6Nm [95% CI: -19.7, -13.5], p=0.001, d=-0.48; NMT+K baseline -19.5Nm [95% CI: -23.2, -15.8], post -14.6Nm [95% CI: -17.6, -11.7], p=0.003, d=-0.42; NMT+H baseline -22.2Nm [95% CI: -26.9, -17.8]; post -17.6Nm [95% CI: -21.1, -14.1], p=0.002, d=-0.45). The primary outcome in this RCT, peak KAM, had mean improvement of 22.7% from baseline to post-testing which did not differ between groups during the DVJ (p>0.05). However, statistically significant differences in peak KAM during the unanticipated cutting task were only found in the NMT+H intervention group (NMT: baseline -25.0Nm [95% CI: -30.4, -19.6], post -25.0Nm [95% CI: -29.6, -20.5], p=0.49, d=004; NMT+K baseline -23.6m [95% CI: -28.9, -18.3], post -22.8Nm [95% CI: -28.0, -17.6], p=0.377, d=-0.05; NMT+H baseline -29.5Nm [95% CI: -35.3, -23.8]; post -22.9Nm [95% CI: -27.8, -18.0], p=0.003, d=-0.44).Conclusions: While female soccer players involved in neuromuscular training programs regardless of intervention group exhibit significant improvements in KAM during a double leg landing, those that engage in hip-focused biofeedback compared to knee-focused or sham biofeedback exhibit decreased KAM during an unanticipated cutting maneuver. Neuromuscular training programs that aim to modify the high-risk biomechanics associated with ACL injury may benefit from targeting the underlying components of injury, such as underutilization of hip musculature during dynamic sport related movements.Context: Neuromuscular training (NMT) programs have been shown to modify high-risk biomechanics and ACL injury risk. However, it is unknown which neuromuscular factors are modified following the completion of NMT programs. Hip strength has been suggested to be an important factor in ACL injury risk and is commonly emphasized in NMT programs. Understanding the immediate effects and retention of hip strength following a NMT program will provide insight into the effectiveness of NMT programs in reducing ACL injury risk.Objective: To examine the increase and retention of isokinetic hip strength in female adolescent soccer players following a neuromuscular training (NMT) program.Design: Prospective cohort study.Setting: Research laboratory.Patients or Other Participants: 126 adolescent female soccer players (age=13.2±2.1yrs, height=156.4±10.2cm, mass=49.9±11.0kg) were included in this subgroup analysis that completed all isokinetic hip strength assessments.Intervention(s): Participants volunteered to complete 6 consecutive weeks of a neuromuscular training (NMT) program with a frequency of 3 times a week. The NMT program included progressive exercises that included components of lower extremity strengthening, plyometrics, and core strengthening. Using an isokinetic dynamometer, 5 repetitions of isokinetic concentric (CON) and eccentric (ECC) hip extension (HEXT) torque were measured at 60 deg•s−1 bilaterally prior to (PRE) and following (POST) the NMT program. Retention (RET) of hip strength was assessed 6-months following the completion of the NMT program.Main Outcome Measure(s): The average peak torque (Nm) of the middle 3 repetitions for CON and ECC HEXT strength measures of the right and left limb during each testing session were used for analyses. Separate repeated measures ANOVAs were used to compare differences in HEXT strength between PRE, POST, and RET. Post-hoc pairwise comparisons with Bonferroni correction were performed when appropriate.Results: HEXT strength (CON, ECC) were significantly different between testing sessions. Specifically, POST right (146.9±48.3 Nm, 150.0±57.9 Nm) and left (147.4±47.7 Nm, 144.2±52.7 Nm) were greater than PRE right (138.8±44.0 Nm, P=0.007; 139.6±56.5 Nm, P= 0.026) and left (138.4±45.0 Nm, P=0.009; 139.4±56.2 Nm, P=0.035). RET right (130.2±48.8 Nm, 133.5±50.2 Nm) and left (131.9±46.2 Nm. 133.2±50.2 Nm) were less than POST (Prange= <0.001-0.007). However, neither right or left HEXT strength were different between PRE and RET (Prange=0.094-0.203).Conclusions: In female adolescent soccer players, increases in isokinetic HEXT strength were observed immediately following a 6-week NMT program. However, the increases in hip strength were not retained 6-months following the completion of the NMT program. While the immediate increases in hip strength may contribute to the effectiveness of NMT programs in reducing ACL injury risk, these positive changes appear to decrease over time. This suggests that adolescent athletes may need to continuously engage in NMT programs to maintain the immediate observed increases in hip strength.Context: Despite decades of research and innovation, primary and secondary ACL injury rates remain high. Traditional injury prevention programs focus on biomechanical-related outcomes, neglecting to maximize more cognitively-driven processes that capitalize on motor learning principles. The advent of virtual reality technology allows for seamless integration of targeted motor learning strategies into injury prevention regimens, which may lead to improved acquisition and retention of safe movement patterns.Objective: Determine the efficacy of a brief virtual-reality intervention to deliver specific motor learning of support or for retention of safe frontal plane We that and in greater improvements compared to a control repeated motion analysis laboratoryPatients or Other Participants: included participants cm, cm, kg) who frontal plane inclusion history of lower extremity or lower extremity injury for six months to data the final was Participants were to one of three groups or such that the ratio was across groups. All participants virtual reality that an plane Participants were to the 5 of 8 on the left The group their prior to each The group received positive biofeedback in the of when kinematics within Outcome Measure(s): Participants were for three-dimensional motion and completed repetitions of left leg Peak frontal plane and angles were measured before and immediately following the changes were assessed with A for time indicated that all groups increased hip adduction control by time revealed that the control group greater increases in knee abduction compared to and and that greater in ipsilateral compared to and control Hip adduction in all Despite and groups baseline knee the control group was through in ipsilateral of motor learning to the effects of increased and to athletes during increases and the motor learning on the timing of to movement The effects of on the of sidestep cutting a task that is highly related with ACL injury risk, are To investigate the of on was that the group more after the training than the Randomized controlled Research laboratory.Patients or Other Participants: healthy sport athletes years, cm, kg) were from on participants were to the or 1 and participants performed trials as and retention of three randomized an task and two in which participants had to and or and a to the All participants received and were to the movement of the to the of their The group was to for after every trial during of 1) the Movement 2) and sagittal of the trial and 3) an external focus on to improve their The goal was to lower the The counterparts received after the trial on which their in the group had Outcome Measure(s): between groups and were with repeated measures with level of significance set at between groups were of at were higher compared to training and retention to the group improved during training which was in the and retention The group higher in and retention compared to training The group their improved during the retention the group to their baseline may benefit and could be considered as a to in ACL injury prevention the years, have injury prevention programs capable of reducing the rate of ACL injury. However, youth sport have been to these programs and injury rates to Previous studies have focused on the efficacy of during controlled conditions. research that factors impact the effectiveness of in Understanding and on and may be important for the and effectiveness of in youth To and the and of youth sport Sources: An database search was conducted in using and A of search prevention and were were limited to in studies were following a search for those Selection: with data were and studies were that did not injury prevention in sport were as were and and the studies and those which did not did not focus on the and only included of youth sport Extraction: studies from sport female not were to knowledge and were reported in the included of studies was not Synthesis: to lack of knowledge and lack of to to increase knowledge to positive that youth athletes are at high risk of injury and that reduce injury The identified this literature support the need for and to knowledge and support of youth sport for of the evidence in the 13 of the studies from the the focused on soccer and when sex of was the were The of such as the for Research and the will be in identifying that and developing to the of individual program increases risk of lower extremity injury, to the anterior cruciate ligament in neuromuscular control following

Given the relatively high risk of contralateral anterior cruciate ligament (ACL) injury in patients with ACL reconstruction (ACLR), there is a need to understand intrinsic risk factors that may contribute to contralateral injury. The ACLR group would have smaller ACL volume and a narrower femoral notch width than healthy individuals after accounting for relevant anthropometrics. Cross-sectional study. Level 3. Magnetic resonance imaging data of the left knee were obtained from uninjured (N = 11) and unilateral ACL-reconstructed (N = 10) active, female, collegiate-level recreational athletes. ACL volume was obtained from T2-weighted images. Femoral notch width and notch width index were measured from T1-weighted images. Independent-samples t tests examined differences in all measures between healthy and ACLR participants. The ACLR group had a smaller notch width index (0.22 ± 0.02 vs 0.25 ± 0.01; P = 0.004; effect size, 1.41) and ACL volume (25.6 ± 4.0 vs 32.6 ± 8.2 mm3/(kg·m)-1; P = 0.025; effect size, 1.08) after normalizing by body size. Only after normalizing for relevant anthropometrics, the contralateral ACLR limb had smaller ACL size and narrower relative femoral notch size than healthy individuals. These findings suggest that risk factor studies of ACL size and femoral notch size should account for relevant body size when determining their association with contralateral ACL injury. The present study shows that the method of the identified intrinsic risk factors for contralateral ACL injury could be used in future clinical screening settings.

A three-dimensional finite element model of the human anterior cruciate ligament: a computational analysis with experimental validation

The biomechanical function of the anteromedial (AM) and posterolateral (PL) bundles of the anterior cruciate ligament (ACL) remains controversial. Some studies report that the AM bundle stabilises the knee joint in anteroposterior (AP) translation and rotational movement (both internal and external) to the same extent as the PL bundle. Others conclude that the PL bundle is more important than the AM in controlling rotational movement. The objective of this randomised cohort study involving 60 patients (39 men and 21women) with a mean age of 32.9 years (18 to 53) was to evaluate the function of the AM and the PL bundles of the ACL in both AP and rotational movements of the knee joint after single-bundle and double-bundle ACL reconstruction using a computer navigation system. In the double-bundle group the patients were also randomised to have the AM or the PL bundle tensioned first, with knee laxity measured after each stage of reconstruction. All patients had isolated complete ACL tears, and the presence of a meniscal injury was the only supplementary pathology permitted for inclusion in the trial. The KT-1000 arthrometer was used to apply a constant load to evaluate the AP translation and the rolimeter was used to apply a constant rotational force. For the single-bundle group deviation was measured before and after ACL reconstruction. In the double-bundle group deviation was measured for the ACL-deficient, AM- or PL-reconstructed first conditions and for the total reconstruction. We found that the AM bundle in the double-bundle group controlled rotation as much as the single-bundle technique, and to a greater extent than the PL bundle in the double-bundle technique. The double-bundle technique increases AP translation and rotational stability in internal rotation more than the single-bundle technique.

Background:High anterior knee laxity (AKL) has been prospectively identified as a risk factor for anterior cruciate ligament (ACL) injuries. Given that ACL morphometry and structural composition have the potential to influence ligamentous strength, understanding how these factors are associated with greater AKL is warranted.Hypothesis:Smaller ACL volumes combined with longer T2* relaxation times would collectively predict greater AKL.Study Design:Cross-sectional study; Level of evidence, 3.Methods:College-aged active male (n = 20) and female (n = 30) participants underwent magnetic resonance imaging (MRI) and AKL testing. T2-weighted MRI scans were used to assess ACL volumes, and T2* relaxation times were used to assess ACL structural composition. AKL was measured via a commercial knee arthrometer. Forward stepwise linear regression with sex and weight (first step; suppressor variables) as well as ACL volume and T2* relaxation time (second step; independent variables) was used to predict AKL (dependent variable).Results:After initially adjusting for sex and weight (R2 = 0.19; P = .006), smaller ACL volumes combined with longer T2* relaxation times collectively predicted greater AKL (R2 = 0.52; P < .001; R2Δ = 0.32; PΔ < .001). A smaller ACL volume was the primary predictor of greater AKL (R2Δ = 0.28; P < .001), with a longer T2* relaxation time trending toward a significant contribution to greater AKL (R2Δ = 0.04; P = .062). After adjusting for ACL volume and T2* relaxation time, sex (partial r = 0.05; P = .735) and weight (partial r = 0.05; P = .725) were no longer significant predictors.Conclusion:AKL was largely predicted by ACL volume and to a lesser extent by T2* relaxation time (and not a person’s sex and weight). These findings enhance our understanding of how AKL may be associated with a structurally weaker ACL. The current study presents initial evidence that AKL is a cost-effective and clinically accessible measure that shows us something about the structural composition of the ACL. As AKL has been consistently shown to be a risk factor for ACL injuries, work should be done to continue to investigate what AKL may tell a clinician about the structure and composition of the ACL.

Side-to-side differences in anterior cruciate ligament volume in healthy control subjects

Background:Little is known about sex-based differences in anterior cruciate ligament (ACL) tissue quality in vivo or the association of ACL size (ie, volume) and tissue quality (ie, normalized signal intensity on magnetic resonance imaging [MRI]) with knee anatomy.Hypothesis:We hypothesized that (1) women have smaller ACLs and greater ACL normalized signal intensity compared with men, and (2) ACL size and normalized signal intensity are associated with age, activity levels, body mass index (BMI), bicondylar width, intercondylar notch width, and posterior slope of the lateral tibial plateau.Study Design:Cross-sectional study; Level of evidence, 3.Methods:Knee MRI scans of 108 unique ACL-intact knees (19.7 ± 5.5 years, 62 women) were used to quantify the ACL signal intensity (normalized to cortical bone), ligament volume, mean cross-sectional area, and length. Independent t tests were used to compare the MRI-based ACL parameters between sexes. Univariate and multivariate linear regression analyses were used to investigate the associations between normalized signal intensity and size with age, activity levels, BMI, bicondylar width, notch width, and posterior slope of the lateral tibial plateau.Results:Compared with men, women had significantly smaller mean ACL volume (men vs women: 2028 ± 472 vs 1591 ± 405 mm3), cross-sectional area (49.4 ± 9.6 vs 41.5 ± 8.6 mm2), and length (40.8 ± 2.8 vs 38.1 ± 3.1 mm) (P < .001 for all), even after adjusting for BMI and bicondylar width. There was no difference in MRI signal intensity between men and women (1.15 ± 0.24 vs 1.12 ± 0.24, respectively; P = .555). BMI, bicondylar width, and intercondylar notch width were independently associated with a larger ACL (R2 > 0.16, P < .001). Younger age and steeper lateral tibial slope were independently associated with shorter ACL length (R2 > 0.03, P < .04). The combination of BMI and bicondylar width was predictive of ACL volume and mean cross-sectional area (R2 < 0.3). The combination of BMI, bicondylar width, and lateral tibial slope was predictive of ACL length (R2 = 0.39). Neither quantified patient characteristics nor anatomic variables were associated with signal intensity.Conclusion:Men had larger ACLs compared with women even after adjusting for BMI and knee size (bicondylar width). No sex difference was observed in signal intensity, suggesting no difference in tissue quality. The association of the intercondylar notch width and lateral tibial slope with ACL size suggests that the influence of these anatomic features on ACL injury risk may be partially explained by their effect on ACL size.Registration:NCT02292004 and NCT02664545 (ClinicalTrials.gov identifier).

The purpose of this study was to reveal the correlation between the size of the native anterior cruciate ligament (ACL) footprint and the area of commonly used autografts using cadaveric knees. Twenty-Four non-paired human cadaver knees were used. The size of the femoral and tibial ACL footprints, length of Blumensaat's line, and the height and area of the lateral wall of the femoral intercondylar notch were photographed and measured with Image J software (National Institution of Health). Simulating an semitendinosus tendon (ST) graft, the ST was cut in half. The bigger half was regarded as the antero-medial (AM) bundle, and the remaining half was regarded as the postero-lateral (PL) bundle. Simulating an semitendinosus and gracilis (ST-G) graft, the bigger half of the ST and G was regarded as the AM bundle, and the smaller half of the ST was regarded as the PL bundle. Each graft diameter was measured, and the graft area was calculated. Simulating a bone-patella tendon-bone (BPTB) graft, a 10-mm wide BPTB graft was harvested and the area calculated. The sizes of the native femoral and tibial ACL footprints were 72.3 ± 24.4 and 134.1 ± 32.4 mm(2), respectively. The length of Blumensaat's line, and the height and area of the lateral wall of the femoral intercondylar notch were 29.5 ± 2.5 mm, 17.7 ± 2.3 mm, and 400.9 ± 62.6 mm(2), respectively. The average areas of the ST, ST-G, and BPTB graft were 52.7 ± 6.3, 64.7 ± 7.6, and 37.1 ± 7.5 mm(2). Both the height and the area of the lateral wall of the femoral intercondylar notch were significantly correlated with the femoral size of the ACL footprint (p = 0.007 and 0.008, respectively). However, no significant correlation was observed between ACL footprint size and autograft size. No significant correlation was observed between autograft size and the size of the lateral wall of the femoral intercondylar notch. In ACL reconstruction, if the reconstructed ACL size is determined by the harvested autograft size alone, native ACL size and anatomy are unlikely to be reproduced.

We aimed to measure lengths of both anteromedial (AM) and posterolateral (PL) bundles of anterior cruciate ligament (ACL) in flexion and extension, and analyse statistically. 20 knees of 10 human cadavers were studied in Republic of Turkey Ministry Of Justice Forensic Medicine Institute. All the subjects were male (100%). An anterior longitudinal incision was made and After passing subcutaneous tissue, knee joint was visualized with a medial parapatellar approach. Lengths of both AM and PL bundles of ACL in flexion and extension were measured in millimetres with flexible ruler scale. Data was analysed statistically. Wilcoxon test was used for statistical analysis. Mean age was 46.5 (32-62). A statistically significant difference was seen in lengths of both AM and PL bundles of ACL in flexion and extension (p<0.05). Difference in lengths of bundles of AM and PL in flexion and extension is statistically significant. Whereas, any statistical difference was not noted in comparison of length differences among bundles during flexion and extension (z=0.085, p=0.932). Difference in lengths’ of bundles of AM and PL in flexion and extension was seen statistically significant in our study. In single-bundle technique, only AM bundle of ACL is reconstructed. Besides, both AM and PL bundles of ACL are reconstructed in double-bundle technique. AM and PL bundles have distinct features and lengths in different flexion degrees. We emphasize to review this entity while determining reconstruction technique for ACL-deficient patients.

Background: There is controversy regarding the functional role of the posterolateral (PL) bundle of the anterior cruciate ligament (ACL). Purpose: To evaluate the in vivo function of the PL and anteromedial (AM) bundles of the ACL during anatomic double-bundle (DB) ACL reconstruction for acute, isolated ACL tears utilizing a computer navigation system to track intraoperative knee kinematics. Study Design: Controlled laboratory study. Methods: Fifteen patients with acute, isolated ACL tears who underwent anatomic DB ACL reconstruction formed the sample for this study. During surgery, knees were examined by a clinician preoperatively, after fixation of the PL bundle, and after fixation of both the PL and AM bundles. An image-free computer navigation system with custom-made software recorded the data during kinematic tests. The examination consisted of the Lachman and anterior drawer tests, internal-external rotation at 30° of knee flexion, and varus-valgus rotation at 30° of knee flexion. Paired Wilcoxon tests were performed to evaluate the effects of each bundle. The comparisons included ACL-deficient to PL bundle–reconstructed knees, ACL-deficient to DB ACL–reconstructed knees, and PL bundle–reconstructed to DB ACL–reconstructed knees. Significance was set at P < .017 to account for the multiple comparisons. Results: Fixation of the PL bundle significantly improved knee laxity during the Lachman and anterior drawer tests as well as internal-external rotation at 30° of knee flexion (P < .017 for all tests). The addition of the AM bundle further improved knee laxity during the Lachman and anterior drawer tests compared with PL bundle fixation as well as during varus-valgus rotation at 30° of knee flexion compared with ACL-deficient knees (P < .017 for all tests). Conclusion: This in vivo study demonstrates that isolated PL bundle reconstruction improves laxity in an ACL-deficient knee and that the addition of the AM bundle improves laxity parameters further. Clinical Relevance: Abnormal knee kinematics is known to be linked to the earlier onset of osteoarthritis and lower rates of return to sport. This study suggests that both the AM and PL bundles are important to stabilize ACL-deficient knees.

Biomechanics of the Human Triple-Bundle Anterior Cruciate Ligament

The Lateral Intercondylar Ridge-A Key to Anatomic Anterior Cruciate Ligament Reconstruction

As our techniques for anterior cruciate ligament reconstruction have evolved, our focus has drifted from anatomy. We believe that it is important to hearken back to anatomy and to fully understand normal anatomy so that we can try to restore it with anterior cruciate ligament reconstruction surgery. The results associated with current anterior cruciate ligament reconstruction techniques are adequate but not exceptional. A recent meta-analysis of the outcomes of anterior cruciate ligament reconstruction indicated that only 33% of patients who had reconstruction with hamstring tendon graft and 41% of those who had reconstruction with bone-patellar tendon-bone graft had normal outcomes according to the final International Knee Documentation Committee score1. There is clearly room for improvement, and we think that the keys to improvement will be based on anatomical anterior cruciate ligament reconstruction. In their paper entitled "Morphology of the Femoral Intercondylar Notch," Farrow et al. evaluate the anatomy of the lateral intercondylar notch in 200 cadaveric specimens. The authors' goal—namely, to perform a detailed study of the area where the anterior cruciate ligament attaches in order to provide more reliable guidance for femoral tunnel placement—is admirable. The authors note that the osseous ridge that Dr. Clancy termed the "resident's ridge" was present in 194 of the 200 specimens. They suggest renaming it the "lateral intercondylar ridge" on the basis of its anatomic location. In their discussion, Farrow et al. state that "it is likely that the lateral intercondylar ridge represents the anterior border of the femoral attachment of the anterior cruciate ligament," concurring with Hutchinson and Ash, who performed an earlier study of the lateral intercondylar wall anatomy2. Farrow et al. also describe an osseous ridge along the medial aspect of the intercondylar notch, which marks the posterior aspect of the posterior cruciate ligament attachment. We applaud the authors for the clinical relevance of their paper. Improper femoral tunnel placement is a common error in anterior cruciate ligament surgery, and the identification of consistent anatomic landmarks to assist in more accurate tunnel placement is critical. The authors draw attention to the clinically relevant point that most surgeons usually remove the "lateral intercondylar ridge" during notchplasty prior to placing the femoral tunnel. Unfortunately, notchplasty has become a routine step in anterior cruciate ligament surgery, obliterating the osseous and soft-tissue landmarks that outline the femoral attachment of the anterior cruciate ligament. We have found that placing the arthroscope in the anteromedial portal allows full visualization of the anterior cruciate ligament attachment site and makes notchplasty unnecessary in about 95% of cases. If, after identification of the soft-tissue and osseous landmarks of the insertion site and tunnel-marking, visualization is still limited by a narrow notch, notchplasty can then be performed. Initially, however, notchplasty should be avoided to allow preservation of these important landmarks that guide accurate tunnel placement. In our center, we have also performed detailed anatomic studies of the lateral intercondylar notch over the past two years. In addition to cadaveric dissection and fetal histologic analysis, we performed sixty arthroscopic dissections at the time of anterior cruciate ligament reconstruction to identify the osseous ridges and soft-tissue attachments of the anterior cruciate ligament bundles. Our findings support Farrow et al.'s conclusion that the "lateral intercondylar ridge" consistently marks the border of the anterior cruciate ligament attachment (the anterior border with the knee in extension and the superior border with the knee in 90° of flexion). We also discovered the existence of another ridge, the "lateral bifurcate ridge," which separates the anteromedial and posterolateral bundles of the anterior cruciate ligament at the femoral attachment. This ridge is prominent in many knees undergoing anterior cruciate ligament reconstruction, and we now use it as an anatomic landmark to guide the placement of individual anteromedial and posterolateral bundles during anterior cruciate ligament reconstruction. In addition to our cadaveric and arthroscopic dissections, we performed three-dimensional laser digitization of our specimens to study the topography of the anterior cruciate ligament attachment. We found that the topography is different when the anteromedial bundle attachment is compared with the posterolateral bundle attachment and that the two ridges described above are easily visible (Fig. 1). We also studied the anatomy of the medial aspect of the intercondylar notch and found the consistent presence of a ridge marking the posterior border of the posterior cruciate ligament attachment, which Farrow et al. also described. These ridges and changes in osseous topography may prove to be useful during navigation-assisted ligament reconstruction.Fig. 1: A three-dimensional laser digitization of the lateral intercondylar notch of a human cadaveric specimen in 90° of flexion. The large arrowheads point to the "lateral intercondylar ridge," which marks the superior border of the anterior cruciate ligament attachment with the knee in 90° of flexion. The small arrowheads point to the "lateral bifurcate ridge," which separates the anteromedial (AM) and posterolateral (PL) bundle femoral attachments.We have even observed the presence of prominent osseous ridges along the lateral intercondylar notch of the femur in many animals. For both humans and animals, we suspect that the ridges and variation in slope of the anterior cruciate ligament attachment exist because of osseous remodeling in response to stress from the ligament fibers, in accordance with Wolff's law. In summary, we congratulate Farrow et al. on the tremendous clinical relevance of their anatomic study. Our studies in Pittsburgh confirm the importance of the lateral intercondylar ridge as a landmark to guide accurate femoral tunnel placement during anterior cruciate ligament reconstruction. When treating fractures, reduction must come before fixation. Similarly, with anterior cruciate ligament reconstruction surgery, we believe that it is most important to restore the anatomy first and to consider graft choice and fixation methods later. ▪