Mechanisms of noncontact anterior cruciate ligament injury

Anterior cruciate ligament prevention strategies: are they effective in young athletes - current concepts and review of literature

PURPOSE OF REVIEW

Participation in sports is on the rise, with young athletes training year round and specializing at earlier ages, predisposing them to sports-related injuries. Once thought to be rare, injuries of the anterior cruciate ligament (ACL) are being seen with a greater frequency in the paediatric population. Numerous preventive training programmes have been developed. The purpose of this review is to discuss risk factors and the effectiveness of preventive programmes in the young athlete.

RECENT FINDINGS

Most ACL prevention programmes take a multifaceted approach, targeting dynamic neuromuscular and proprioceptive deficits. Focus often lies on noncontact mechanisms of injury, jump and landing techniques, and improving movement patterns during pivoting, cutting and change in direction. However, the effectiveness of these programmes in skeletally immature athletes needs to be evaluated.

SUMMARY

Early specialization and increased demand for peak performance at a time of major physiological change, lack of physical fitness and neuromuscular deficits have contributed to an increase in ACL injuries in young athletes. Various preventive training programmes have been developed, but their effectiveness is debatable. We encourage young athletes to partake in preseason training programmes focused on strengthening, neuromuscular and proprioceptive training units under the appropriate supervision of qualified personnel.

Real-time feedback on knee abduction moment does not improve frontal-plane knee mechanics during jump landings

Excessive knee abduction loading is a contributing factor to anterior cruciate ligament (ACL) injury risk. The purpose of this study was to determine whether a double-leg landing training program with real-time visual feedback improves frontal-plane mechanics during double- and single-leg landings. Knee abduction angles and moments and vertical ground reaction forces (GRF) of 21 recreationally active women were quantified for double- and single-leg landings before and after the training program. This program consisted of two sessions of double-leg jump landings with real-time visual feedback on knee abduction moments for the experimental group and without real-time feedback for the control group. No significant differences were found between training groups. In comparison with pre-training data, peak knee abduction moments decreased 12% post-training for both double- and single-leg landings; whereas peak vertical GRF decreased 8% post-training for double-leg landings only, irrespective of training group. Real-time feedback on knee abduction moments, therefore, did not significantly improve frontal-plane knee mechanics during landings. The effect of the training program on knee abduction moments, however, transferred from the double-leg landings (simple task) to single-leg landings (more complex task). Consequently, ACL injury prevention efforts may not need to focus on complex tasks during which injury occurs.

Functional knee brace use effect on peak vertical ground reaction forces during drop jump landing

PURPOSE

The aim of the study was to investigate the landing strategies used by non-injured athletes while wearing functional knee braces (FKB, BR condition) during a drop jump task compared with non-injured, non-braced (NBR condition) subjects and also to ascertain whether accommodation to a FKB was possible by non-injured BR subjects.

METHODS

Twenty-three healthy male provincial and national basketball and field hockey athletes (age, 19.4 ± 3.0 years) were tested. Each subject was provided with a custom-fitted FKB. Five NBR testing sessions were performed over 3 days followed by five BR testing sessions also over 3 days, for a total of 17.5 h of testing per condition. Each subject performed eight trials of the drop jump task during each testing session per condition. Single-leg peak vertical ground reaction forces (PVGRF) and the time to PVGRF were recorded for each NBR and BR trail.

RESULTS

The BR group mean PVGRF at landing was significantly lower (1,628 ± 405 N, 2.1 ± 0.5 BW versus 1,715 ± 403 N, 2.2 ± 0.5 BW, F (1,22) = 6.83, P = 0.01) compared with NBR subjects, respectively. The group mean time to PVGRF was not statistically longer during the BR condition (F (1,22) = 0.967, P = 0.3). Further, an accommodation trend was noted as percent performance difference decreased with continued FKB use.

CONCLUSIONS

The significantly lower group mean PVGRF while using a FKB could keep traumatic forces from reaching the ACL until the active neuromuscular restraints are activated to provide protection to the knee joint ligaments. Also, accommodation to FKB is possible after approximately 14.0 h of brace use. The results of this paper will assist clinicians in providing information to their patients regarding a FKB ability to offer protection to an ACL-deficient knee or to address concerns about early muscle fatigue, energy expenditure, heart rate, and decrease in performance level.

LEVEL OF EVIDENCE

Prospective study, Level I.

Cruciate ligament loading during common knee rehabilitation exercises

Cruciate ligament injuries are common and may lead to dysfunction if not rehabilitated. Understanding how to progress anterior cruciate ligament and posterior cruciate ligament loading, early after injury or reconstruction, helps clinicians prescribe rehabilitation exercises in a safe manner to enhance recovery. Commonly prescribed therapeutic exercises include both weight-bearing exercise and non-weight-bearing exercise. This review was written to summarize and provide an update on the available literature on cruciate ligament loading during commonly used therapeutic exercises. In general, weight-bearing exercise produces smaller loads on the anterior cruciate ligament and posterior cruciate ligament compared with non-weight-bearing exercise. The anterior cruciate ligament is loaded less at higher knee angles (i.e. 50-100 degrees). Squatting and lunging with a more forward trunk tilt and moving the resistance pad proximally on the leg during the seated knee extension unloads the anterior cruciate ligament. The posterior cruciate ligament is less loaded at lower knee angles (i.e. 0-50 degrees), and may be progressed from level ground walking to a one-leg squat, lunges, wall squat, leg press, and the two-leg squat (from smallest to greatest). Exercise type and technique variation affect cruciate ligament loading, such that the clinician may prescribe therapeutic exercises to progress ligament loading safely, while ensuring optimal recovery of the musculoskeletal system.

Lower body stiffness and muscle activity differences between female dancers and basketball players during drop jumps

Background:

Anterior cruciate ligament (ACL) injuries often occur during landing, with female athletes at higher injury risk than male athletes. Interestingly, female dancers have lower ACL injury rates than do female athletes in general.

Hypothesis:

Female dancers will have earlier and greater lower extremity muscle activity and higher sagittal knee joint and leg stiffness than will female basketball players.

Study Design:

Cross-sectional group comparison.

Methods:

Fifty-five healthy female athletes (35 dancers, 20 basketball players) performed 5 double-leg drop jumps from a 45-cm box. Surface electromyography (onsets and amplitudes; prelanding and postlanding) was recorded from the lateral gastrocnemius, medial and lateral hamstrings, lateral quadriceps muscles with a 3-dimensional electromagnetic tracking system, and forceplates recording biomechanics (leg spring stiffness and knee joint stiffness).

Results:

Compared with basketball players, dancers had greater leg spring stiffness (P = 0.047) but similar knee joint stiffness (P = 0.44). Although no significant differences were observed in overall muscle onset times (P = 0.22) or activation amplitudes (prelanding, P = 0.60; postlanding, P = 0.78), small to moderate effect sizes (ESs) suggest trends in dancers toward earlier (ES = 0.53) and higher medial hamstrings activation pre- (ES = 0.55) and post- (ES = 0.41) landing and lower lateral quadriceps (ES = 0.30) and higher gastrocnemius (ES = 0.33) postlanding muscle activation.

Conclusions:

In dancers, the higher leg spring stiffness and trends toward higher hamstrings prelanding and postlanding, as well as lower quadriceps and higher gastrocnemius activation postlanding with similar knee joint stiffness, indicate lower extremity neuromechanical differences across other joints.

Clinical Relevance:

Female dancers may have lower extremity neuromechanics that are different from those of basketball players during drop jumps. If dancers use ACL-protective strategies during activity, then their training routines should be further investigated to improve ACL injury prevention programs.

A musculoskeletal modeling approach for estimating anterior cruciate ligament strains and knee anterior-posterior shear forces in stop-jumps performed by young recreational female athletes

The central goal of this study was to contribute to the advancements being made in determining the underlying causes of anterior cruciate ligament (ACL) injuries. ACL injuries are frequently incurred by recreational and professional young female athletes during non-contact impact activities in sports like volleyball and basketball. This musculoskeletal-neuromuscular study investigated stop-jumps and factors related to ACL injury like knee valgus and internal-external moment loads, knee anterior-posterior (AP) shear forces, ACL strains and internal forces. Motion capture data was obtained from the landing phase of stop-jumps performed by eleven young recreational female athletes and electromyography (EMG) data collected from quadriceps, hamstring and gastrocnimius muscles which were then compared to numerically estimated activations. Numerical simulation tools used were Inverse Kinematics, Computed Muscle Control and Forward Dynamics and the knee modeled as a six degree of freedom joint. Results showed averaged peak strains of 12.2 ± 4.1% in the right and 11.9 ± 3.0% in the left ACL. Averaged peak knee AP shear forces were 482.3 ± 65.7 N for the right and 430.0 ± 52.4 N for the left knees, approximately equal to 0.7-0.8 times body weight across both knees. A lack of symmetry was observed between the knees for valgus angles (p < 0.04), valgus moments (p < 0.001) and muscle activations (p < 0.001), all of which can be detrimental to ACL stability during impact activities. Comparisons between recorded EMG data and estimated muscle activations show the relation between electrical signal and muscle depolarization. In summary, this study outlines a musculoskeletal simulation approach that provides numerical estimations for a number of variables associated with ACL injuries in female athletes performing stop-jumps.

Tibial plateau geometry influences lower extremity biomechanics during landing

BACKGROUND

Intersubject differences in lateral and medial posterior tibial plateau slope, coronal tibial slope (CTS), and medial tibial plateau depth (MTD) may influence one's susceptibility for anterior cruciate ligament (ACL) injury. Understanding how these structural characteristics influence hip and knee joint biomechanics during weightbearing activity may advance our understanding of how tibial plateau geometry influences one's injury risk potential. Purpose/

HYPOTHESES

To determine the extent to which tibial plateau geometry is associated with frontal and transverse plane hip and knee joint biomechanics during the initial landing phase of a double-legged drop landing. Greater lateral tibial slope combined with lower medial/lateral tibial slope ratio would predict greater tibial internal rotation motion and moments. Lower CTS would predict greater hip adduction and knee valgus motion and reduced internal peak varus moments. These associations would be stronger when combined with a shallower MTD.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Magnetic resonance scans of the knee were obtained on 23 female participants who were also assessed for hip and knee joint biomechanics during the initial landing phase of double-legged drop jumps.

RESULTS

Once controlling for the respective initial hip flexion or initial knee flexion angle at ground contact, lower CTS consistently predicted greater initial and peak hip adduction and knee valgus angles (R (2) range, .212-.427, P < .027). Greater coronal and lateral tibial slope predicted greater hip internal rotation (femur relative to pelvis) at initial contact (R (2) = .504) and greater CTS and lower medial/lateral tibial slope ratio predicted greater knee internal rotation (tibia relative to femur) excursions (R (2) = .594, P = .001). Joint geometry was not associated with hip or knee peak joint moments.

CONCLUSION

These data confirm substantial intersubject differences in tibial condylar geometry that are associated with intersubject differences in hip and knee motion patterns when landing from a jump.

CLINICAL RELEVANCE

The current findings may partially explain a female's greater likelihood of demonstrating combined motion patterns of knee valgus and external rotation during landing. Although tibial geometry cannot be modified through training, these associations suggest that tibial geometry may have a substantial influence on tibiofemoral joint biomechanics when the knee is subjected to external loads and deserves further study in our understanding of ACL injury.

Variation of Anatomical and Physiological Parameters that Affect Estimates of ACL Loading During Drop Landing

BACKGROUND

Anterior cruciate ligament (ACL) loading during drop landing has been recently studied with a sagittal plane knee model developed by Kernozek and Ragan using mean anatomical and physiological parameters obtained from cadaveric and clinical data. It is unknown how estimates in ACL load may be altered due to variations in anatomical and physiological parameters used from other research.

METHODS

USING THE SAME MODEL, THESE PARAMETERS WERE SYSTEMATICALLY VARIED, INCLUDING: tibial slope, moment arms of the patellar tendon, hamstring, and gastrocnemius at the knee and ankle, patellar tendon and hamstring line of force, ACL stiffness, and nonlinear muscle activation parameters. To determine the sensitivity of the model to changes in these parameters, each was varied independently by ±5% and by ranges reported in the literature. Changes in maximum ACL load and shear force components of the patellar tendon, hamstring, and tibio-femoral contact force were calculated from drop landing data of 21 subjects.

RESULTS

The variation in ACL load during drop landing from its nominal value was largest (-100% to 176%) when extremes in reported tibial slope values were utilized. Variation in the next most important parameter, patellar tendon line of force, affected ACL load by -72% to 88%.

CONCLUSION

Variations in tibial slope and patellar tendon line of force had the greatest influence on estimated ACL loading during drop landing. Differences in these parameters between subjects may be just as important to ACL loading as the kinematic and kinetic performance differences observed in landing.

Sex-dimorphic landing mechanics and their role within the noncontact ACL injury mechanism: evidence, limitations and directions

Anterior cruciate ligament (ACL) injuries continue to present in epidemic-like proportions, carrying significant short- and longer-term debilitative effects. With females suffering these injuries at a higher rate than males, an abundance of research focuses on delineating the sex-specific nature of the underlying injury mechanism. Examinations of sex-dimorphic lower-limb landing mechanics are common since such factors are readily screenable and modifiable. The purpose of this paper was to critically review the published literature that currently exists in this area to gain greater insight into the aetiology of ACL injuries in females and males. Using strict search criteria, 31 articles investigating sex-based differences in explicit knee and/or hip landing biomechanical variables exhibited during vertical landings were selected and subsequently examined. Study outcomes did not support the generally accepted view that significant sex-based differences exist in lower-limb landing mechanics. In fact, a lack of agreement was evident in the literature for the majority of variables examined, with no sex differences evident when consensus was reached. The one exception was that women were typically found to land with greater peak knee abduction angles than males. Considering knee abduction increases ACL loading and prospectively predicts female ACL injury risk, its contribution to sex-specific injury mechanisms and resultant injury rates seems plausible. As for the lack of consensus observed for most variables, it may arise from study-based variations in test populations and landing tasks, in conjunction with the limited ability to accurately measure lower-limb mechanics via standard motion capture methods. Regardless, laboratory-based comparisons of male and female landing mechanics do not appear sufficient to elucidate causes of injury and their potential sex-specificity. Sex-specific in vivo joint mechanical data, if collected accurately, may be more beneficial when used to drive models (e.g., cadaveric and computational) that can additionally quantify the resultant ACL load response. Without these steps, sex-dimorphic landing mechanics data will play a limited role in identifying the aetiology of ACL injuries in women and men.

What strains the anterior cruciate ligament during a pivot landing?

BACKGROUND

The relative contributions of an axial tibial torque and frontal plane moment to anterior cruciate ligament (ACL) strain during pivot landings are unknown.

HYPOTHESIS

The peak normalized relative strain in the anteromedial (AM) bundle of the ACL is affected by the direction of the axial tibial torque but not by the direction of the frontal plane moment applied concurrently during a simulated jump landing.

STUDY DESIGN

Controlled and descriptive laboratory studies.

METHODS

Fifteen adult male knees with pretensioned knee muscle-tendon unit forces were loaded under a simulated pivot landing test. Compression, flexion moment, internal or external tibial torque, and knee varus or valgus moment were simultaneously applied to the distal tibia while recording the 3D knee loads and tibiofemoral kinematics. The AM-ACL relative strain was measured using a 3-mm differential variable reluctance transducer. The results were analyzed using nonparametric Wilcoxon signed-rank tests. A 3D dynamic biomechanical knee model was developed using ADAMS and validated to help interpret the experimental results.

RESULTS

The mean (SD) peak AM-ACL relative strain was 192% greater (P < .001) under the internal tibial torque combined with a knee varus or valgus moment (7.0% [3.9%] and 7.0% [4.1%], respectively) than under external tibial torque with the same moments (2.4% [2.5%] and 2.4% [3.2%], respectively). The knee valgus moment augmented the AM-ACL strain due to the slope of the tibial plateau inducing mechanical coupling (ie, internal tibial rotation and knee valgus moment); this augmentation occurred before medial knee joint space opening.

CONCLUSION

An internal tibial torque combined with a knee valgus moment is the worst-case ACL loading condition. However, it is the internal tibial torque that primarily causes large ACL strain.

CLINICAL RELEVANCE

Limiting the maximum coefficient of friction between the shoe and playing surface should limit the peak internal tibial torque that can be applied to the knee during jump landings, thereby reducing peak ACL strain and the risk for noncontact injury.

An unusual mechanism for injury of the anterior cruciate ligament in figure skating

A 20-year-old competitive figure skater presented with an acute disabling knee injury that occurred in the overhead, non-weight-bearing knee during the performance of a Biellmann spin. Examination and magnetic resonance imaging confirmed the diagnosis of a complete anterior cruciate ligament (ACL) tear. To our knowledge, no previous cases of acute injury of the ACL sustained during the execution of a Biellmann spin have been reported. The ACL injury we report is unique because it occurred without the blade contacting the ice. The mechanism of injury has some features that are similar to those of other noncontact ACL injuries, with the addition of centrifugal force as a potential contributor to the injury.

Valgus plus internal rotation moments increase anterior cruciate ligament strain more than either alone

PURPOSE

To test the influence of combined knee valgus and internal tibial rotation moment on anterior cruciate ligament (ACL) strain during single-leg landing. We tested the following hypotheses: the combination of the valgus and internal rotation moments observed during single-leg landing produces a higher ACL strain than either moment applied individually, the combined rotational moments at the physiological levels observed could theoretically increase strain in the ACL high enough to rupture the ACL, and the location of the peak contact force was at the posterior-lateral side for combined loading.

METHODS

The study was conducted by applying in vivo human loading data to a validated simulation model of the three-dimensional dynamic knee joint to predict ACL strains.

RESULTS

The peak ACL strain increased nonlinearly when either applied valgus moment or internal rotation moment was increased in the model. When the two rotational moments were applied individually, neither caused ACL strain >0.077. However, when applied in combination, the two rotational moments had a much larger effect, and the predicted peak ACL strain increased up to 0.105. During landing, the peak contact force occurred at the posterior-lateral side of the tibial cartilage in the model when the combined maximum valgus moment and tibial internal rotation moments were applied.

CONCLUSIONS

Combined knee valgus and internal rotation moments increases ACL strain more than either alone. The combination of a valgus and internal rotational moment at magnitudes that occurs in vivo during landing can cause ACL strains that may be high enough to cause ACL rupture. This predicted high ACL strain and the contact force location suggest that combined valgus and internal tibial rotational moments during single-leg landing are relevant to ACL injuries.

Objective criteria for return to athletics after anterior cruciate ligament reconstruction and subsequent reinjury rates: a systematic review

OBJECTIVE

To review anterior cruciate ligament (ACL) clinical studies to assess the objective functional criteria used to determine when patients can return to athletics postoperatively, and to determine the rates of reinjury to either knee when these criteria are applied.

METHODS

A literature search was conducted using the Medline database. The inclusionary criteria were the English language, publication between April 2001 and April 2011, original clinical trials, all levels of evidence, primary ACL reconstruction, skeletal maturity, minimum 2 years of follow-up, and ≥1 objective test used to allow release to sports activities. The exclusionary criteria were revision ACL reconstructions or dislocated knees; studies that specifically excluded patients with ACL graft failure or reinjuries; major concomitant procedures such as high tibial osteotomy, meniscus allograft, other knee ligament reconstructions; and case reports, abstracts, review articles, and technical notes.

RESULTS

Three objective criteria were used to allow release to sports activities. The most common were lower extremity muscle strength, followed by lower limb symmetry, and knee examination parameters of range of knee motion and effusion. Twelve studies listed 1 criterion for release to sports, 8 studies listed 2 criteria, and 1 study recommended 3 criteria. Failure rates of the ACL reconstructions ranged from 0% to 3% in 7 studies, from 4% to 6% in 6 studies, from 7% to 10% in 4 studies, and from 14% to 24% in 4 studies. There were no injuries in the contralateral ACL in 14 studies (67%); in the other 7 studies, contralateral injury was reported in 2% to 15% of patients.

CONCLUSIONS

Few objective functional criteria are used to determine when patients return to unrestricted sports activities. Clinically feasible recommendations are made for measurement of muscle strength, lower limb symmetry, lower limb neuromuscular control, and ligament function in patients who desire to return to athletics after ACL reconstruction. Future studies are required to determine whether the demonstration of normal lower limb function before return to sports is effective in reducing reinjury rates.

Cartilage pressure distributions provide a footprint to define female anterior cruciate ligament injury mechanisms

BACKGROUND

Bone bruises located on the lateral femoral condyle and posterolateral tibia are commonly associated with anterior cruciate ligament (ACL) injuries and may contribute to the high risk for knee osteoarthritis after ACL injury. The resultant footprint (location) of a bone bruise after ACL injury provides evidence of the inciting injury mechanism. Purpose/

HYPOTHESIS

(1) To analyze tibial and femoral articular cartilage pressure distributions during normal landing and injury simulations, and (2) to evaluate ACL strains for conditions that lead to articular cartilage pressure distributions similar to bone bruise patterns associated with ACL injury. The hypothesis was that combined knee abduction and anterior tibial translation injury simulations would demonstrate peak articular cartilage pressure distributions in the lateral femoral condyle and posterolateral tibia. The corollary hypothesis was that combined knee abduction and anterior tibial translation injury conditions would result in the highest ACL strains.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Prospective biomechanical data from athletes who subsequently suffered ACL injuries after testing (n = 9) and uninjured teammates (n = 390) were used as baseline input data for finite element model comparisons.

RESULTS

Peak articular pressures that occurred on the posterolateral tibia and lateral femoral condyle were demonstrated for injury conditions that had a baseline knee abduction angle of 5°. Combined planar injury conditions of abduction/anterior tibial translation, anterior tibial translation/internal tibial rotation, or anterior tibial translation/external tibial rotation or isolated anterior tibial translation, external tibial rotation, or internal tibial rotation resulted in peak pressures in the posterolateral tibia and lateral femur. The highest ACL strains occurred during the combined abduction/anterior tibial translation condition in the group that had a baseline knee abduction angle of 5°.

CONCLUSION

The results of this study support a valgus collapse as the major ACL injury mechanism that results from tibial abduction rotations combined with anterior tibial translation or external or internal tibial rotations.

CLINICAL RELEVANCE

Reduction of large multiplanar knee motions that include abduction, anterior translation, and internal/external tibial motions may reduce the risk for ACL injuries and associated bone bruises. In particular, prevention of an abduction knee posture during initial contact of the foot with the ground may help prevent ACL injury.

Is noncontact ACL injury associated with the posterior tibial and meniscal slope?

BACKGROUND

The risk of noncontact ACL injury reportedly is increased in patients with a greater posterior tibial slope (PTS), but clinical data are inconsistent. It is unclear whether the medial and lateral PTSs have a different impact on this connection. It also is unknown whether the meniscal slope (MS) is associated with ACL injury.

PATIENTS/METHODS

Using MRI, we compared the medial and lateral PTSs and MSs separately in 55 matched pairs of patients with isolated noncontact ACL injuries and a control group.

RESULTS

Neither the PTS nor the relative difference between the medial and lateral PTSs differed between groups. In contrast, the lateral MS was greater with ACL injuries: 2.0° versus -2.7° in males with and without ACL injury and 1.7° versus -0.9 in females. Uninjured females had a greater PTS than males: 4.9° versus 3.0° in females and males medially, respectively; 5.7° versus 4.0° lateral.

CONCLUSIONS

There is no obvious link between the medial or lateral PTSs and ACL injury, and there is no obvious link between the relative difference in the medial and lateral PTSs and noncontact ACL injury. However, a greater lateral MS may indicate a greater risk of injury. The PTS can differ between the genders but the average difference is small.

LEVEL OF EVIDENCE

Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Timing of lower extremity frontal plane motion differs between female and male athletes during a landing task

BACKGROUND

Female athletes are at a greater risk for noncontact anterior cruciate ligament injuries than male athletes. Gender differences in frontal plane kinematics (hip adduction, knee valgus, and ankle eversion) and temporal relationships that make up the components of dynamic knee valgus may explain this discrepancy.

HYPOTHESIS

The authors hypothesized that women would reach peak frontal plane kinematic values earlier during landing compared with their male counterparts.

STUDY DESIGN

Controlled laboratory study.

METHODS

Hip, knee, and ankle 3-dimensional kinematics were measured using high-speed motion capture in 10 National Collegiate Athletic Association Division I female athletes and 10 male practice squad athletes during a drop-jump landing. Independent t tests were used to analyze each dependent variable to identify differences between genders.

RESULTS

Maximum hip adduction, knee valgus, and ankle eversion occurred earlier in women than in men (mean differences 33.7% of stance [95% CI, 20.2%-47.2%], 41.7% [95% CI, 31.5%-51.6%], 16.5% of stance [95% CI, 7.3%-25.6%], respectively). Maximum hip adduction and knee valgus occurred before maximum knee flexion in women and after in men (mean differences 0.11 seconds [95% CI, 0.05-0.18 seconds], 0.19 seconds [95% CI, 0.13-0.25 seconds], respectively). Maximum ankle eversion occurred earlier in women than in men (mean difference 0.06 seconds [95% CI, 0.01-0.11 seconds]). There was a significant difference between genders for angular velocity of knee valgus (mean difference = 25.53 deg/sec [95% CI, 8.30-42.77 deg/sec]).

CONCLUSION

Frontal plane kinematic temporal relationships at the hip, knee, and ankle differ between genders. The components of dynamic knee valgus peak during the deceleration phase in women and during the acceleration phase in men during a drop-jump landing. These data suggest that men and women employ a completely different kinematic landing/jumping strategy and that women land and collapse very rapidly into valgus compared with their male counterparts.

CLINICAL RELEVANCE

The differences in timing of the components of dynamic knee valgus between women and men may contribute to the increased risk of noncontact anterior cruciate ligament injuries in female athletes. There may be implications for neuromuscular reeducation training in those at risk for anterior cruciate ligament injury so the components of dynamic valgus occur later in the landing phase of jumping.

Mechanisms of anterior cruciate ligament injury in World Cup alpine skiing: a systematic video analysis of 20 cases

BACKGROUND

There is limited insight into the mechanisms of anterior cruciate ligament injuries in alpine skiing, particularly among professional ski racers.

PURPOSE

This study was undertaken to qualitatively describe the mechanisms of anterior cruciate ligament injury in World Cup alpine skiing.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Twenty cases of anterior cruciate ligament injuries reported through the International Ski Federation Injury Surveillance System for 3 consecutive World Cup seasons (2006-2009) were obtained on video. Seven international experts in the field of skiing biomechanics and sports medicine related to alpine skiing performed visual analyses of each case to describe the injury mechanisms in detail (skiing situation, skier behavior, biomechanical characteristics).

RESULTS

Three main categories of injury mechanisms were identified: slip-catch, landing back-weighted, and dynamic snowplow. The slip-catch mechanism accounted for half of the cases (n = 10), and all these injuries occurred during turning, without or before falling. The skier lost pressure on the outer ski, and while extending the outer knee to regain grip, the inside edge of the outer ski caught abruptly in the snow, forcing the knee into internal rotation and valgus. The same loading pattern was observed for the dynamic snowplow (n = 3). The landing back-weighted category included cases (n = 4) where the skier was out of balance backward in flight after a jump and landed on the ski tails with nearly extended knees. The suggested loading mechanism was a combination of tibiofemoral compression, boot-induced anterior drawer, and quadriceps anterior drawer.

CONCLUSION

Based on this video analysis of 20 injury situations, the main mechanism of anterior cruciate ligament injury in World Cup alpine skiing appeared to be a slip-catch situation where the outer ski catches the inside edge, forcing the outer knee into internal rotation and valgus. A similar loading pattern was observed for the dynamic snowplow. Injury prevention efforts should focus on the slip-catch mechanism and the dynamic snowplow.

Effect of a high intensity quadriceps fatigue protocol on knee joint mechanics and muscle activation during gait in young adults

The purpose of this study was to determine the effect of impaired quadriceps function on knee joint biomechanics and neuromuscular function during gait. Surface electromyograms, three-dimensional motion and ground reaction forces were collected during gait before and after 20 healthy adults completed a high intensity quadriceps fatigue protocol. Pattern recognition techniques were utilized to examine changes in amplitude and temporal characteristics of all gait variables. The fatigue protocol resulted in decreased knee extensor torque generation and quadriceps median power frequencies for 18 of 20 participants (p < 0.05). The gait data from these 18 participants was analyzed. The knee external rotation angle increased (p < 0.05), the net external flexion and external rotation moments decreased (p < 0.05), and the net external adduction moment increased (p < 0.05). Post-fatigue changes in periarticular muscle activation patterns were consistent with the biomechanical changes, but were not significantly altered. Even for this low demand task of walking the knee motion and loading characteristics were altered following a high intensity fatigue protocol in a manner that may place the knee joint at greater risk for joint pathology and injury.

Rationale and implementation of anterior cruciate ligament injury prevention warm-up programs in female athletes

The sex disparity in anterior cruciate ligament (ACL) injury risk and the subsequent adverse effects on knee joint health, psychosocial well-being, and financial costs incurred have produced a surge in research on risk factors and interventions designed to decrease this disparity and overall incidence. Biomechanical and neuromuscular differences have been identified throughout the trunk and lower extremity that may increase noncontact ACL injury risk in female athletes. Evidence demonstrates that many risk factors are modifiable with intervention programs and that athletic performance measures can be enhanced. No universally accepted ACL injury prevention program currently exists, and injury prevention programs are diverse. Anterior cruciate ligament injury prevention programs introduced in a warm-up format offer multiple benefits, primarily, improved compliance based on improved practicality of implementation. However, drawbacks of warm-up style formats also exist, most notably that a lack of equipment and resources may preclude measurable improvements in athletic performance that foster improved compliance among participants. The purpose of this review is to analyze the current literature researching possible biomechanical and neuromuscular risk factors in noncontact ACL injury in female athletes and the most effective means of implementing critical elements of a program to decrease ACL injury risk in female athletes while improving athletic performance. Hip and hamstring training, core stabilization, plyometrics, balance, agility, neuromuscular training with video and verbal feedback to modify technique, and stretching appear to be essential components of these programs. Further research is critical to determine ideal training program volume, intensity, duration, and frequency.

Whole body, long-axis rotational training improves lower extremity neuromuscular control during single leg lateral drop landing and stabilization

BACKGROUND

Poor neuromuscular control during sports activities is associated with non-contact lower extremity injuries. This study evaluated the efficacy of progressive resistance, whole body, long-axis rotational training to improve lower extremity neuromuscular control during a single leg lateral drop landing and stabilization.

METHODS

Thirty-six healthy subjects were randomly assigned to either Training or Control groups. Electromyographic, ground reaction force, and kinematic data were collected from three pre-test, post-test trials. Independent sample t-tests with Bonferroni corrections for multiple comparisons were used to compare group mean change differences (P≤0.05/21≤0.0023).

FINDINGS

Training group gluteus maximus and gluteus medius neuromuscular efficiency improved 35.7% and 31.7%, respectively. Training group composite vertical-anteroposterior-mediolateral ground reaction force stabilization timing occurred 1.35s earlier. Training group knee flexion angle at landing increased by 3.5°. Training group time period between the initial two peak frontal plane knee displacements following landing increased by 0.17s. Training group peak hip and knee flexion velocity were 21.2°/s and 20.1°/s slower, respectively. Time period between the initial two peak frontal plane knee displacements following landing and peak hip flexion velocity mean change differences displayed a strong relationship in the Training group (r(2)=0.77, P=0.0001) suggesting improved dynamic frontal plane knee control as peak hip flexion velocity decreased.

INTERPRETATION

This study identified electromyographic, kinematic, and ground reaction force evidence that device training improved lower extremity neuromuscular control during single leg lateral drop landing and stabilization. Further studies with other populations are indicated.

Joint laxity is related to lower extremity energetics during a drop jump landing

PURPOSE

To examine the relationships between anterior knee laxity (AKL), genu recurvatum (GR), and general joint laxity (GJL) with sagittal plane energetics in males and females during a drop jump task.

METHODS

A total of 68 females and 50 males were measured for AKL, GR, and GJL and were instrumented to obtain neuromuscular and biomechanical data on their dominant limb during the initial landing phase of a 45-cm drop jump. Multiple linear regressions determined the extent to which the three joint laxity variables combined to predict hip, knee, and ankle work absorption and stiffness. Associations between joint laxity and joint kinematics, joint kinetics, and muscle activation amplitudes were also investigated to further interpret significant relationships.

RESULTS

Higher AKL and GJL and lower GR combined to predict greater knee work absorption (R2 = 0.210, P = 0.002) and stiffness (R2 = 0.127, P = 0.033) and lower ankle stiffness (R2 = 0.115, P = 0.048) in females. These associations were modulated through greater peak knee extensor moments and flexion angles, lower hamstring activation, and lower ankle extensor moments. In males, joint laxity had little impact on knee energetics, but a significant association was observed between greater GJL and decreased ankle stiffness (R2 = 0.209, P = 0.012), a product of both greater peak ankle flexion and decreased ankle extensor moment.

CONCLUSIONS

Females with greater AKL and GJL and lower GR demonstrated a landing strategy that increased work absorption and stiffness about the knee, whereas females with greater GR demonstrated a landing style that reduced knee work absorption and stiffness. The findings suggest that AKL, GR, and GJL may represent distinct risk factors and support the need to consider more comprehensive laxity profiles as they relate to knee joint function and anterior cruciate ligament injury risk.

Variations in varus/valgus and internal/external rotational knee laxity and stiffness across the menstrual cycle

Cyclic variations in genu recurvatum (GR), general joint laxity (GJL), varus-valgus (VV), and internal-external (IER) rotational laxities and stiffnesses were examined in 64 females and 43 males at two time points during the females' menstrual cycle [days of minimum (T1) and maximum (T2) anterior knee laxity (AKL)]. Cyclic increases in AKL (9.5%), GR (37.5%), and GJL (13.6%) were observed in females but not males from T1 to T2 (p < 0.001). Cyclic increases in VV and IER laxity were negligible (1.5-3.2%, p > 0.320). Females compared to males had lower overall VV stiffness at T2 (F 37% <M) vs. T1 (F 26.9% <M; p = 0.011), but no difference across time points for IER stiffness (p = 0.452). Across both time points, females had consistently greater VV (30.2%) and IER (20%) laxity and less VV (32.5%) and IER (24.3%) incremental stiffness (p < 0.001). Low-to-moderate associations were observed between AKL, GR, and GJL with VV and IER laxities and stiffnesses in females as measured at T1 and the change in values from T1 to T2. Whether these findings reflect ligament-specific responses to hormone changes, or implicate changes in injury risk potential across the menstrual cycle requires further study.

A 'plane' explanation of anterior cruciate ligament injury mechanisms: a systematic review

Although intrinsic and extrinsic risk factors for anterior cruciate ligament (ACL) injury have been explored extensively, the factors surrounding the inciting event and the biomechanical mechanisms underlying ACL injury remain elusive. This systematic review summarizes all the relevant data and clarifies the strengths and weaknesses of the literature regarding ACL injury mechanisms. The hypothesis is that most ACL injuries do not occur via solely sagittal, frontal or transverse plane mechanisms. Electronic database literature searches of PubMed MEDLINE (1966-2008), CINAHL (1982-2008) and SportDiscus (1985-2008) were used for the systematic review to identify any studies in the literature that examined ACL injury mechanisms. Methodological approaches that describe and evaluate ACL injury mechanisms included athlete interviews, arthroscopic studies, clinical imaging and physical exam tests, video analysis, cadaveric studies, laboratory tests (motion analysis, electromyography) and mathematical modelling studies. One hundred and ninety-eight studies associated with ACL injury mechanisms were identified and provided evidence regarding plane of injury, with evidence supporting sagittal, frontal and/or transverse plane mechanisms of injury. Collectively, the studies indicate that it is highly probable that ACL injuries are more likely to occur during multi-planar rather than single-planar mechanisms of injury.

Mechanisms of the anterior cruciate ligament injury in sports activities: a twenty-year clinical research of 1,700 athletes

The mechanisms of anterior cruciate ligament (ACL) injuries are still inconclusive from an epidemiological standpoint. An epidemiological approach in a large sample group over an appropriate period of years will be necessary to enhance the current knowledge of the ACL injury mechanism. The objective of the study was to investigate the ACL injury occurrence in a large sample over twenty years and demonstrate the relationships between the ACL injury occurrence and the dynamic knee alignment at the time of the injury. We investigated the activity, the injury mechanism, and the dynamic knee alignment at the time of the injury in 1,718 patients diagnosed as having the ACL injuries. Regarding the activity at the time of the injury, "competition "was the most common, accounting for about half of all the injuries. The current result also showed that the noncontact injury was the most common, which was observed especially in many female athletes. Finally, the dynamic alignment of "Knee-in & Toe- out "(i.e. dynamic knee valgus) was the most common, accounting for about half. These results enhance our understanding of the ACL injury mechanism and may be used to guide future injury prevention strategies. Key pointsWe investigated the situation of ACL injury occurrence, especially dynamic alignments at the time of injury, in 1,718 patients who had visited our institution for surgery and physical therapy for twenty years.Our epidemiological study of the large patient group revealed that "knee-in & toe-out "alignment was the most frequently seen at the time of the ACL injury.From an epidemiological standpoint, we need to pay much attention to avoiding "Knee-in & Toe-out "alignment during sports activities.

Single leg jumping neuromuscular control is improved following whole body, long-axis rotational training

Improved lower extremity neuromuscular control during sports may decrease injury risk. This prospective study evaluated progressive resistance, whole body, long-axis rotational training on the Ground Force 360 device. Our hypothesis was that device training would improve lower extremity neuromuscular control based on previous reports of kinematic, ground reaction force (GRF) or electromyographic (EMG) evidence of safer or more efficient dynamic knee stability during jumping. Thirty-six healthy subjects were randomly assigned to either training (Group 1) or control (Group 2) groups. Using a pre-test, post-test study design data were collected from three SLVJ trials. Unpaired t-tests with adjustments for multiple comparisons were used to evaluate group mean change differences (P≤0.05/25≤0.002). During propulsion Group 1 standardized EMG amplitude mean change differences for gluteus maximus (-21.8% vs. +17.4%), gluteus medius (-28.6% vs. +15.0%), rectus femoris (-27.1% vs. +11.2%), vastus medialis (-20.2% vs. +9.1%), and medial hamstrings (-38.3% vs. +30.3%) differed from Group 2. During landing Group 1 standardized EMG amplitude mean change differences for gluteus maximus (-32.9% vs. +11.1%) and rectus femoris (-33.3% vs. +29.0%) also differed from Group 2. Group 1 peak propulsion vertical GRF (+0.24N/kg vs. -0.46N/kg) and landing GRF stabilization timing (-0.68 vs. +0.05s) mean change differences differed from Group 2. Group 1 mean hip (-16.3 vs. +7.8°/s) and knee (-21.4 vs. +18.5°/s) flexion velocity mean change differences also differed from Group 2. Improved lower extremity neuromuscular efficiency, increased peak propulsive vertical GRF, decreased mean hip and knee flexion velocities during landing, and earlier landing stabilization timing in the training group suggests improved lower extremity neuromuscular control.

Developing a 6-DOF robot to investigate multi-axis ACL injuries under valgus loading coupled with tibia internal rotation

Anterior cruciate ligament (ACL) injuries have become more common in recent years as more young people participate in risky sporting activities [1]. Most ACL injuries occur as a result of noncontact mechanisms. Previous in vitro studies of ACL strain have found significant increases in ACL strain primarily with anterior directed force on the tibia relative to the femur and with internal rotation and often with valgus torque [2,3]. However, there remains significant controversy over the mechanisms of ACL failure and the forces on the knee that lead to injury. Some studies have also shown that isolated valgus loading may not load the ACL strongly. The goal of this study was to investigate the mechanism underlying valgus-related ACL injuries. An improved understanding of ACL failure may lead to improved ACL injury prevention programs. A novel 6 degrees of freedom (DOF) knee driving robot was developed in this study with a unique multi-axis simultaneous torque/position control. It was found that pure valgus torque caused a torque that internally rotated the tibia and thus increased ACL strain markedly, which may be an important mechanism underlying the rather common seemingly valgus-related ACL injuries.

The effect of isolated popliteus tendon complex injury on graft force in anterior cruciate ligament reconstructed knees

Failure to diagnose injury to the posterolateral structures has been found to increase the forces experienced by the anterior cruciate ligament (ACL) and ACL grafts which may cause their subsequent failure. An isolated injury to the popliteus complex (PC) consisting of the popliteus tendon and popliteofibular ligament is not uncommon. Therefore, the purpose of this study was to discover if an isolated injury to the PC can significantly affect the forces experienced by the ACL graft under external loading conditions. We hypothesised that, under external tibial torque, the ACL graft will experience a significant increase in force, in knees with PC injury compared to the intact PC condition. Under varus tibial torque (10 N m), we observed minimal changes in the varus tibial rotation due to isolated sectioning of the PC in an ACL reconstructed knee (P > 0.05). Consequently, no significant increase in the ACL graft force was observed under varus tibial torque. In contrast, sectioning the PC resulted in a significant increase in the external tibial rotation compared to the intact PC knee condition under the external rotational tibial torque (5 N m) at all flexion angles (P < 0.05). These changes in kinematics under external tibial torque were manifested as elevated ACL graft forces at all selected flexion angles (P < 0.05). Prompt diagnosis of isolated PC injury and its treatment are warranted to prevent potential failure of ACL reconstruction.

Extent and distribution of tibial osteochondral disruption during simulated landing impact with axial tibial rotation restraint

Post-traumatic knee osteochondral injuries are often coupled with anterior cruciate ligament (ACL) injury mechanisms during landing. However, it is not well understood whether restraining axial tibial rotation during landing would influence the extent and distribution of osteochondral disruption. Using ski landing as an example, this study subjected knee specimens to simulated landing impact without and with axial tibial rotation restraint, and investigated the extent and distribution of osteochondral disruption at the tibial plateau. Twenty-one porcine knee specimens were randomly divided into three test conditions, namely: (1) control, (2) impact only (I), and 3) impact with restraint (IR). Simulated landing impact was applied to the specimens based on a single 10 Hz haversine. Osteochondral explants were obtained from anterior, middle and posterior regions of medial and lateral tibial compartments. The extent of cartilage and trabecular disruption in these explants was examined based on histology, SEM and microCT. Only specimens in unrestrained condition incurred ACL failure upon impact. Restraining axial tibial rotation during simulated impact generally inflicted cartilage damage and deformation, and further caused trabecular disruption. Axial tibial rotation restraint did not necessarily restrict anterior tibial translation, as indicated by the presence of relative posterior femoral translation and osteochondral disruption at anterior-posterior tibial regions. While the results obtained in the current study may not be completely translatable to human models, there is likelihood that restraining axial tibial rotation during landing may help to prevent ACL failure, but will also induce osteochondral disruption in most tibial regions.

Tibial acceleration variability during consecutive gait cycles is influenced by the menstrual cycle

BACKGROUND

The relationship between the phases of the menstrual cycle and injury risk remains unclear. Neuromuscular function may be compromised during menstruation, which could result in reduced cyclicality of movement patterns. We hypothesize that mediolateral (varus/valgus) knee acceleration during running gait will possess increased variability during menstruation when compared to approximately ovulation in women who do not take the monophasic oral contraceptive pill (MOCP).

METHODS

Thirty-six women (18 MOCP users: MOCP group and 18 non-pill users: NP group) performed six-minute treadmill running trials at 10 km h(-1) with an accelerometer fixed to the proximal tibia. Trials were performed at menstruation and approximately equal ovulation (for the MOCP group at a similar stage of the cycle) in a randomized order. The cyclicality of gross mediolateral tibial acceleration during 15 consecutive strides was assessed using combined wavelet and autocorrelation analysis. Longitudinal and anteroposterior accelerations were also examined. Repeated measures analysis of variance (ANOVA) tests were performed to assess differences at each stage of the menstrual cycle (alpha=0.05).

FINDINGS

Gross mediolateral acceleration in the NP group had significantly (P=0.022) increased variability at the time of menstruation compared to approximately equal ovulation, and was also significantly (P=0.011) more variable than the MOCP group at the corresponding time point. No significant difference was observed for any measure in the MOCP group.

INTERPRETATION

Increased variability in the NP users at menstruation may be a result of compromised motor control strategies. This provides further evidence of variability in performance and motor control during menstruation, and may have implications for a female athlete's risk of injury.

The effect of fatigue on landing biomechanics in single-leg drop landings

OBJECTIVE

To examine the effects of fatigue on landing biomechanics in single-leg drop landings.

DESIGN

Quasi-experimental.

SETTING

Controlled research laboratory.

PARTICIPANTS

Twenty-four healthy individuals (12 women and 12 men).

INTERVENTIONS

Participants performed 3 single-leg drop landings from a height of 0.36 m before and after a fatiguing protocol.

MAIN OUTCOME MEASURES

Sagittal ankle flexion, sagittal knee flexion, and frontal knee valgus angles (degrees) at initial ground contact; vertical ground reaction forces (N); and time to stabilization (TTS) were compared between sexes and before (pre) and after (post) the fatiguing protocol.

RESULTS

After fatigue, participants landed with greater knee flexion [P = 0.001; pre 142.58 (14.35) degrees; post 136.12 (14.48) degrees] and ankle plantar flexion [P = 0.012; pre 79.04 (6.96) degrees; post 80.78 (6.13) degrees], and higher peak vertical ground reaction forces (P = 0.002; pre 2202.5 (536.29) N to post 2537.86 (469.66) N] but did not show changes in frontal knee angles [P = 0.815; pre, 7.94 (3.74) degrees; post, 8.08 (4.33) degrees]. Participants had higher anterior-posterior TTS [P = 0.021; pre 1.73 (0.53) seconds to post 1.93 (0.53) seconds] and vertical TTS [P = 0.002; pre 0.65 (0.24) seconds to post 0.93 (0.37) seconds] with a significant interaction noted in medial-lateral TTS [P = 0.043; pre 1.49 (0.64) seconds to post 1.61 (0.67) seconds]. No significant sex differences existed across any of the examined variables.

CONCLUSIONS

When landing after fatigue, participants had greater knee and ankle flexion angles at initial contact, had greater peak ground reaction forces, and required longer times to stabilize the body after landing, regardless of sex. Overall, fatigue clearly affects lower body biomechanics during single-leg landings. Whether these changes actually increase injury risk during activity warrants further investigation.

Increasing pre-activation of the quadriceps muscle protects the anterior cruciate ligament during the landing phase of a jump: an in vitro simulation

We hypothesize that application of an unopposed quadriceps force coupled with an impulsive ground reaction force may induce anterior cruciate ligament (ACL) injury. This situation is similar to landing from a jump if only the quadriceps muscle is active; an unlikely but presumably dangerous circumstance. The purpose of this study was to test our hypothesis using in vitro simulation of jump landing. A jump-landing simulator was utilized. Nine cadaveric knees were tested at an initial flexion angle of 20 degrees . Each ACL was instrumented with a differential variable reluctance transducer (DVRT). Quadriceps pre-activation forces (QPFs) ranging from 25N to 700N were applied to each knee, followed by an impulsive ground reaction force produced by a carriage-mounted drop weight (7kg) that impulsively drove the ankle upward. ACL strain was monitored before landing due to application of QPF (pre-activation strain) and at landing due to application of the ground reaction force (landing strain). No ACLs were injured. Pre-activation strains exhibited a positive correlation with QPF (r=0.674, p<0.001) while landing strains showed a negative correlation (r=-0.235, p=0.032). Total ACL strain (pre-activation+landing strain) showed no correlation with QPF (r=0.023, p=0.428). Our findings indicate that elevated QPF increases pre-activation strain but reduces the landing strain and is therefore protective post-landing. Overall, there is a complete lack of correlation between "total" ACL strain and QPF suggesting that the total strain in the ACL is independent of the QPF under the simulated conditions.

A case-control study of anterior cruciate ligament volume, tibial plateau slopes and intercondylar notch dimensions in ACL-injured knees

The role played by anatomical factors in ACL injury remains elusive. In this study, objective methods were used to characterize ACL volume, tibial slopes and notch geometry from ACL-injured and matched-control subjects. The study tested four hypotheses: (1) the medial tibial plateau slope is steeper posteriorly in the injured group compared to the non-injured group, (2) the lateral tibial plateau slope is steeper posteriorly in the injured group compared to the non-injured group, (3) the femoral intercondylar notch dimensions are smaller in the injured group compared to the non-injured group and (4) the ACL volume, tibial plateau slopes and intercondylar notch dimensions are all independent of each other. Fifty-four subjects were divided into two groups, those who had suffered a non-contact ACL injury and those who still had two healthy ACLs, matched to the injured subjects by gender, age, height and weight. The lateral tibial plateaus in the uninjured contralateral knees of the injured subjects had a significantly steeper posterior slope (1.8 degrees vs. -0.3 degrees ), a factor that potentially contributed to the ACL injury in the opposite knee. The intercondylar notch dimensions were found to be smaller in the injured subjects, potentially putting the ACL at risk of impingement, and intercondylar notch volume was correlated to ACL volume (r=0.58). Discriminant analysis showed that the notch width at the inlet was the best single predictor of ACL injury.

Anterior cruciate ligament-deficient potential copers and noncopers reveal different isokinetic quadriceps strength profiles in the early stage after injury

BACKGROUND

Isokinetic muscle strength testing using the peak torque value is the most frequently included quadriceps muscle strength measurement for anterior cruciate ligament (ACL)-injured subjects. PURPOSE AND HYPOTHESES: The purpose of this study was to investigate quadriceps muscle performance during the whole isokinetic curve in subjects with ACL deficiency classified as potential copers or noncopers and to investigate whether these curve profiles were associated with single-legged hop performance. We hypothesized that quadriceps muscle torque at other knee flexion angles than peak torque would give more information about quadriceps muscle strength deficits. Furthermore, we hypothesized that there would be significant torque differences between potential copers and noncopers and a significant relationship between angle-specific torque values and single-legged hop performance.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Seventy-six individuals with a complete unilateral ACL rupture within the last 3 months were included. The subjects were classified as potential copers and noncopers. Isokinetic quadriceps muscle tests were performed at 60 deg/s. Mean torque values were calculated for peak torque as well as for specific knee flexion angles. The 1-legged hop and the 6-m timed hop tests were included, and symmetry indices were used.

RESULTS

The peak torque value did not identify the largest quadriceps muscle strength deficit. Rather, these were established at knee flexion angles of less than 40 degrees . There were significant differences in angle-specific torque values between potential copers and noncopers (P < .05). Moderate to strong associations were disclosed between angle-specific torque values and single-legged hop performance, but only for noncopers (r > or = .32-.58).

CONCLUSION

Angle-specific quadriceps muscle torque values of less than 40 degrees of knee flexion provide more information on the quadriceps strength deficits after ACL injury than the commonly used peak torque values. Interpretation of the isokinetic curve profiles seems to be of clinical importance for the evaluation of quadriceps muscle performance after ACL injury.

Expert versus novice interrater reliability and criterion validity of the landing error scoring system

CONTEXT

A clinical assessment tool that would allow for efficient large-group screening is needed to identify individuals potentially at risk for anterior cruciate ligament (ACL) injury.

OBJECTIVE

To assess the criterion validity of a jump-landing assessment tool compared with 3-dimensional (3D) motion analysis and evaluate interrater reliability across an expert vs novice rater using the Landing Error Scoring System (LESS).

DESIGN

Validity protocol.

SETTING

Controlled, laboratory.

PARTICIPANTS

Nineteen female (age 19.58 +/- .84 y, height 1.67 +/- .05 m, mass 63.66 +/- 10.11 kg) college soccer athletes volunteered.

MAIN OUTCOME MEASUREMENT

Interrater reliability between expert rater (5 y LESS experience) vs novice rater (no LESS experience). LESS scores across 13 items and total score. 3D lower extremity kinematics were reduced to dichotomous values to match LESS items.

INTERVENTIONS

Participants performed drop-box landings from a 30-cm height with standard video-camera and 3D kinematic assessment.

RESULTS

Intrarater item reliability, assessed by kappa correlation, between novice and experienced LESS raters ranged from moderate to excellent (kappa = .459-.875). Overall LESS score, assessed by intraclass correlation coefficient, was excellent (ICC(2,1) = .835, P < .001). Statistically significant phi correlation (P < .05) was found between rater and 3D scores for knee-valgus range of motion; however, percent agreement between expert rater and 3D scores revealed excellent agreement (range of 84-100%) for ankle flexion at initial contact, knee-flexion range of motion, trunk flexion at maximum knee flexion, and foot position at initial contact for both external and internal rotation of tibia. Moderate agreement was found between rater and 3D scores for trunk flexion at initial contact, stance width less than shoulder width, knee valgus at initial contact, and knee-valgus range of motion.

CONCLUSIONS

Our findings support moderate to excellent validity and excellent expert vs novice interrater reliability of the LESS to accurately assess 3D kinematic motion patterns. Future research should evaluate the efficacy of the LESS to assess individuals at risk for ACL injury.

The Effect of the Shoe-Surface Interface in the Development of Anterior Cruciate Ligament Strain

The shoe-surface interface has been implicated as a possible risk factor for anterior cruciate ligament (ACL) injuries. The purpose of this study is to develop a biomechanical, cadaveric model to evaluate the effect of various shoe-surface interfaces on ACL strain. There will be a significant difference in ACL strain between different shoe-surface combinations when a standardized rotational moment (a simulated cutting movement) is applied to an axially loaded lower extremity. The study design was a controlled laboratory study. Eight fresh-frozen cadaveric lower extremities were thawed and the femurs were potted with the knee in 30 deg of flexion. Each specimen was placed in a custom-made testing apparatus, which allowed axial loading and tibial rotation but prevented femoral rotation. For each specimen, a 500 N axial load and a 1.5 Nm internal rotation moment were placed for four different shoe-surface combinations: group I (AstroTurf-turf shoes), group II (modern playing turf-turf shoes), group III (modern playing turf-cleats), and group IV (natural grass-cleats). Maximum strain, initial axial force and moment, and maximum axial force and moment were calculated by a strain gauge and a six component force plate. The preliminary trials confirmed a linear relationship between strain and both the moment and the axial force for our testing configuration. In the experimental trials, the average maximum strain was 3.90, 3.19, 3.14, and 2.16 for groups I–IV, respectively. Group IV had significantly less maximum strain (p<0.05) than each of the other groups. This model can reproducibly create a detectable strain in the anteromedial bundle of the ACL in response to a given axial load and internal rotation moment. Within the elastic range of the stress-strain curve, the natural grass and cleat combination produced less strain in the ACL than the other combinations. The favorable biomechanical properties of the cleat-grass interface may result in fewer noncontact ACL injuries.

Distribution of injury mechanisms and related factors in ACL-injured female carving skiers

While ACL injury mechanisms in skiers using traditional skis are well studied, no study has yet investigated the distribution of injury mechanisms in carving skiers. In traditional skiers, the backward twisting fall seems to be the dominant injury mechanism, especially in female skiers. Female recreational skiers have a threefold higher risk to sustain an ACL injury than male skiers; therefore, it is important to determine if carving skis influence the distribution of injury mechanisms and the related frequencies of ACL injuries in female skiers. We investigated the frequencies of injury mechanisms and related factors in 65 ACL-injured female carving skiers by questionnaire. The forward twisting fall was the most reported ACL injury mechanism with about 51%, followed by the backward twisting fall within 29% of cases. Catching an edge of the ski (59 vs. 24%, P = 0.03) when executing turns (69 vs. 41%, P = 0.053) was a more frequent cause for forward twisting falls than for the other types of falling. While 29% of bindings released during a forward twisting fall, only 3.1% released during the remaining mechanisms. In contrast to traditional skiers, the forward twisting fall was the dominant injury mechanism in female carving skiers with ACL injury.

Prediction and prevention of musculoskeletal injury: a paradigm shift in methodology

Traditional methods employed to study musculoskeletal injury mechanisms and joint biomechanics utilise in vivo or in vitro techniques. The advent of new technology and improved methods has also given rise to in silico (computer modelling) techniques. Under the current research paradigm, in vivo, in vitro and in silico methods independently provide information regarding the mechanisms and prevention of musculoskeletal injury. However, individually, each of these methods has multiple, inherent limitations and is likely to provide incomplete answers about multifactorial, complex injury conditions. The purpose of this treatise is to review current methods used to study, understand, and prevent musculoskeletal injury and to develop new conceptual-methodological frameworks that may help create a paradigm shift in musculoskeletal injury prevention research. We term the fusion of these three techniques in simulacra amalgama, or simply in sim, meaning a "union of models done on the likeness of phenomena." Anterior cruciate ligament (ACL) injury will be employed as a model example for the utility and applicability of the proposed, synthesised approach. Shifting the current experimental paradigm to incorporate a multifaceted, multidisciplinary, integration of in vivo, in vitro and in silico methods into the proposed in sim approaches may provide a platform for a more comprehensive understanding of the relationships between complex joint biomechanics and observed injury mechanisms.