Anterior Cruciate Ligament Injury In Female Athletes Research Articles

Primary Anterior Cruciate Ligament Injury: Extrinsic and Intrinsic Risk Factors.

Anterior cruciate ligament (ACL) injuries continue to increase in incidence despite extensive research into prevention strategies. Many extrinsic and intrinsic risk factors for sustaining ACL injuries have been identified and continue to be investigated. Extrinsic risk factors for ACL injury relate to the athlete's environment, such as the shoe-surface interaction, weather conditions, and sport played. Intrinsic risk factors relate to the athlete's sex, hormones, knee anatomy, landing and pivoting biomechanics, and neuromuscular control. Recent research has highlighted the role of the bony morphology of the proximal tibia and distal femur on primary ACL injury risk, as well as the risk for ACL graft failure. Sex differences in bony and ligamentous morphology of the knee, neuromuscular control, and hormonal factors, such as serum relaxin levels and variations within the menstrual cycle, have been correlated with a higher risk of noncontact primary ACL injuries in female athletes compared with male athletes.

Immediate Effect of a Kinesiotape Bandage on Knee Mechanics during Functional Tests in Female Rugby and Football Athletes: A Pilot Study

Background: Some bandages with Kinesiotape have demonstrated some potential as means of prevention for Anterior Cruciate Ligament (ACL) injury in men. Objective: The main objective of this pilot study was to observe if a Kinesiotape bandage at the knee could potentially have an immediate preventive effect against ACL injuries by improving proprioception and balance and reducing knee valgus and anterior translation of the tibia during certain functional tests in female athletes. Materials and Methods: A cross-over clinical trial including 10 female athletes (football and rugby) was conducted, where the two lower limbs of the 10 participants (n = 20) were randomly assigned to the intervention group (IG) or to the control group (CG). A Kinesiotape bandage was placed on one knee with a tension of 75% (IG, n = 10) and another bandage on the other knee with a tension of 10% (CG, n = 10), as a placebo. Ultrasound assessment and functional tests were performed before (T1) and after (T2) bandaging according to group assignment. A videographic analysis was carried out with the ImageJ Software version 2.0. Results: A statistically significant reduction in knee valgus was observed in the Lateral Step Down test in the IG, compared to the CG (p < 0.05; η2p = 0.26) (IG-T1: 151.40 ± 11.04°; IG-T2: 157.10 ± 10.18°; versus CG-T1: 156.96 ± 5.44°; CG-T2: 158.68 ± 6.12°). In the other tests, no significant differences were found in terms of time × group interaction. Conclusions: A Kinesiotape bandage was able to reduce knee valgus in a functional test compared to a placebo bandage but was not more effective at reducing the anterior translation of the tibia or improving balance or proprioception. Based on these results, it could have a modest preventive effect against an ACL injury in female athletes.

The Relationship Between Isometric Hip Strength and Incidence of Noncontact Anterior Cruciate Ligament Injuries in Female Athletes: A Critically Appraised Topic

Clinical Scenario: Noncontact anterior cruciate ligament (ACL) injuries are prevalent among athletes in multiplanar sports, especially females. Hip strength may contribute to the incidence of these injuries due to dynamic movement patterns at the knee. Clinical Question: Does hip strength impact the incidence of noncontact ACL injuries in female athletes? Summary of Key Findings: A literature search was conducted on the relationship between hip strength and noncontact ACLs. Three prospective studies measuring isometric hip strength and recording the number of noncontact ACL injuries that occurred within a time period were included. One study demonstrated lower isometric hip adductor-to-abductor ratio was associated with noncontact ACL injuries. Two studies demonstrated those with noncontact ACL injuries had greater isometric hip abduction strength. Clinical Bottom Line: Evidence suggests that greater isometric hip strength and low hip adductor-to-abductor strength ratio may be a risk factor that is associated with noncontact ACL injuries in females. Future research should investigate the impact of hip strength on the incidence of noncontact ACL injuries, across all genders. Strength of Recommendation: Based on the Center of Evidence-Based Medicine, these studies provide Level 3 evidence that hip strength is associated with the risk of noncontact ACL injuries in females.

Anterior cruciate ligament injuries in female athletes: risk factors and strategies for prevention.

Anterior cruciate ligament (ACL) injuries are among the most common and debilitating knee injuries in professional athletes with an incidence in females up to eight-times higher than their male counterparts. ACL injuries can be career-threatening and are associated with increased risk of developing knee osteoarthritis in future life. The increased risk of ACL injury in females has been attributed to various anatomical, developmental, neuromuscular, and hormonal factors. Anatomical and hormonal factors have been identified and investigated as significant contributors including osseous anatomy, ligament laxity, and hamstring muscular recruitment. Postural stability and impact absorption are associated with the stabilizing effort and stress on the ACL during sport activity, increasing the risk of noncontact pivot injury. Female patients have smaller diameter hamstring autografts than males, which may predispose to increased risk of re-rupture following ACL reconstruction and to an increased risk of chondral and meniscal injuries. The addition of an extra-articular tenodesis can reduce the risk of failure; therefore, it should routinely be considered in young elite athletes. Prevention programs target key aspects of training including plyometrics, strengthening, balance, endurance and stability, and neuromuscular training, reducing the risk of ACL injuries in female athletes by up to 90%. Sex disparities in access to training facilities may also play an important role in the risk of ACL injuries between males and females. Similarly, football boots, pitches quality, and football size and weight should be considered and tailored around females' characteristics. Finally, high levels of personal and sport-related stress have been shown to increase the risk of ACL injury which may be related to alterations in attention and coordination, together with increased muscular tension, and compromise the return to sport after ACL injury. Further investigations are still necessary to better understand and address the risk factors involved in ACL injuries in female athletes.

Is the Use of Oral Contraceptive Beneficial to Female Athletes in the Prevention of Anterior Cruciate Ligament Injury?

Research has shown that women are 2 to 9 times more likely to sustain an anterior cruciate ligament (ACL) injury than men. The increased risk of ACL injuries in females can be attributed to several factors including anatomical, hormonal, biomechanical, and neuromuscular variations. Previous literature found that female hormones such as relaxin, progestin, and estrogen play a role in ligamentous laxity within the female ACL. Oral contraceptives (OC) regulate these hormones by inhibiting the spike of estrogen and progestin during the menstrual cycle. The aims of this study were to investigate the influence of female hormone concentrations on the ACL and to determine if OC can reduce the risk of ACL injuries in female athletes. We hypothesize that OC will have an effect on reducing the incidence of ACL injuries in female athletes. Articles were retrieved from Google Scholar and PubMed databases. A systematic review was conducted and ranked using the Oxford Levels of Evidence. The result revealed there are variations in the ranking of literature based on the Oxford Levels of Evidence. The evidence reveals that OC may have an inhibitory effect on relaxin receptors within the female ACL and could be recommended as a preventive measure for ACL ligamentous injury. Further research is needed to determine the causal effect of oral contraceptives on ACL prevention.

Post COVID-19 Anterior Cruciate Ligament (ACL) Tear in Twin Sisters After Re-starting Professional Futsal Exercises: A ‎Case Report

Awareness of the long-term COVID-19 complications is of significant importance in reducing its morbidity through the implementation of timely interventional programs. In this study, we report an anterior cruciate ligament (ACL) tear in athlete identical twin sisters almost 2 months after the COVID-19 infection. The patients had 15 years of professional futsal experience and showed no obvious risk factors for an ACL tear, such as familial history, abnormal menstruation, oral contraceptive consumption, reduced intercondylar notch, or increased tibial slope. However, they experienced a non-contact complete ACL tear within 1 month of re-participation in professional exercise after the COVID-19 infection. Both patients reported a sense of muscle weakness during the COVID-19 recovery period, and ligamentous laxity was obvious according to the clinical examination and the Beighton criteria. This report shows persistent muscle weakness after the COVID-19 infection that could increase the risk of ACL injury in female athletes and suggests taking a prophylactic rehabilitating program to prevent its catastrophic consequences.

Medio-Lateral Hamstring Muscle Activity in Unilateral vs.Bilateral Strength Exercises in Female Team Handball Players - A Cross-Sectional Study.

BackgroundReduced activation of the hamstring muscles and specifically the medial semitendinosus muscle (ST) has been shown to be a risk factor for non-contact anterior cruciate ligament (ACL) injury. Specific hamstring strength exercises may show high ST activity, however the effect of unilateral vs. bilateral exercise execution on ST activation remains unknown.PurposeTo investigate selected lower limb strengthening exercises performed either unilaterally or bilaterally to identify 1) which exercise elicited the highest hamstring activation, 2) which exercise elicited the highest ST activation, and 3) to examine if unilateral exercise execution altered the medio-lateral hamstring activation pattern. Furthermore, the kinematic characteristics of each specific exercise and execution modality were determined to reveal possible causes for differences in medio-lateral hamstring activation between the different exercise conditions.Study designCross-sectional study.MethodsSingle-session repeated measures were obtained in a randomized manner. Twenty-three female elite team handball players were recruited. Hamstring electromyographic (EMG) activity and 3D kinematics were obtained during selected lower limb exercises (hip thrust, kettlebell swing, Romanian deadlift). Hamstring EMG activity, normalized to maximal voluntary contraction (MVC) (nEMG), and inter-muscular activation difference between the ST and lateral hamstring biceps femoris (BF) were compared across exercises using two-way repeated measures ANOVA.ResultsBilateral hip thrust demonstrated highest overall hamstring activity (68.9±16.6 %). Kettlebell swing (Δ13%-point, p<0.01) and Romanian deadlift (Δ20-24%-point, p<0.01) demonstrated greater ST-BF activation differences (Δ=ST-BF) in favor of ST compared to hip thrust (Δ2-7%). Positive correlations were observed between knee joint angle and ST activity in kettlebell swing and deadlift.ConclusionKettlebell swing, deadlift and hip thrust all produced high activation of the hamstring muscles. Kettlebell swing and both deadlift exercises were superior in activating ST over BF, favoring these exercises in the prevention of non-contact ACL injury in female athletes, which should be evaluated in future intervention studies.Level of evidence3

Analyze the Differential Rates of Anterior Cruciate Ligament Injuries Between Men and Women by Biomechanical Study of Single-Leg Landing in Badminton.

In female badminton players, certain landings are associated with injury to the anterior cruciate ligament (ACL). However, the kinematic and kinetic changes of the landing leg and the effects of risky posture on ACL injuries among female vs male badminton players are still unknown. We hypothesized that female players land with a significantly higher knee valgus angle and moment compared to male players during single-leg landings in badminton. Ten male and ten female badminton players were enrolled in this study. In the laboratory, these subjects performed back-stepping to the backhand side with a concurrent overhead stroke, a single-leg landing on the force plate, and a return to the starting position. The kinematic data in the stance phase were normalized ranging from 0% as initial contact to 100% as toe-off; and 0% as initial contact to 100% as maximum knee flexion in the impact phase. The knee valgus angle in female players was significantly higher in initial contact (5.06° ± 6.83° vs - 5.10° ± 4.30, p = .001) and maximal knee valgus angle (7.58° ± 9.54° vs - 3.93° ± 4.22°, p = .004) compared to male players. The knee valgus moment was significantly higher in male players than female players ( - 0.09 ± 0.12 vs 0.03 ± 0.10 N∙m/kg, p = .032) in initial contact during the impact phase. During landings, female badminton players had lower hip flexion angles, greater knee valgus angles, and greater ankle dorsiflexion angles. Female badminton players presented higher knee valgus angles but smaller knee valgus moments compared with male players during backward single-leg landings. The concomitant kinematic and kinetic changes of the hip, knee, and ankle joints also can play an important role in the higher incidence of ACL injury in female athletes. The online version contains supplementary material available at 10.1007/s43465-021-00421-6.

A Secondary Injury Prevention Program May Decrease Contralateral Anterior Cruciate Ligament Injuries in Female Athletes: 2-Year Injury Rates in the ACL-SPORTS Randomized Controlled Trial.

To determine whether the addition of perturbation training to a secondary injury prevention program reduces the rate of second anterior cruciate ligament (ACL) injury compared to the prevention program alone. Single-blinded randomized controlled trial. Thirty-nine female athletes who intended to return to cutting/pivoting sports were enrolled 3 to 9 months after primary anterior cruciate ligament reconstruction (ACLR). Athletes were randomized to receive a training program of either progressive strengthening, agility, plyometrics, and prevention (SAPP) (n = 20) or SAPP plus perturbation training (n = 19); each had 10 sessions over 5 weeks. Occurrence and side of second ACL injury were recorded for 2 years after primary ACLR. There were 9 second ACL injuries in the 2 years after ACLR. There was no statistically significant difference in rate or side of second ACL injury between the SAPP-plus-perturbation training and SAPP groups. Adding perturbation training to a secondary ACL injury prevention program did not affect the rate of second ACL injury in female athletes. J Orthop Sports Phys Ther 2020;50(9):523-530. Epub 1 Aug 2020. doi:10.2519/jospt.2020.9407.

Retraction: Differences between the Craig’s test and computed tomography in measuring femoral anteversion in patients with anterior cruciate ligament injuries

[Purpose] This study aimed to compare the Craig’s test and computed tomography (CT) in measuring the femoral anteversion angle (FAA) in patients with anterior cruciate ligament (ACL) injuries. The relationship between the FAA measured on CT, and the range of axial rotation of the hip joint and muscle tightness around the hip joint was also investigated. [Participants and Methods] Twenty-six patients who received CT examination within 3 months after ACL reconstruction were enrolled in this study. The Craig’s test, internal and external rotation of the hip, the Ely test, Ober’s test, and FAA on the CT were assessed. [Results] The FAA on the Craig’s test and CT in female patients was 24.3 ± 3.9° and 23.0 ± 10.3°, respectively on the uninjured side and 25.0 ± 5.2° and 20.3 ± 11.2°, respectively on the injured side, indicating no significant correlation between the 2 measurement techniques. In contrast, the FAA on the CT was significantly correlated with the range of internal rotation of the hip, which was 40.5 ± 6.1° on the uninjured side and 37.8 ± 5.6° on the injured side. [Conclusion] The results suggest that measuring the internal hip rotation range rather than the Craig’s test, provides more reliable estimates of the magnitude of FAA, and may help to evaluate the risk of ACL injuries in female athletes.

The effect of leg dominance and landing height on ACL loading among female athletes

Female athletes are more prone to anterior cruciate ligament (ACL) injury. A neuromuscular imbalance called leg dominance may provide a biomechanical explanation. Therefore, the purpose of this study was to compare the side-to-side lower limb differences in movement patterns, muscle forces and ACL forces during a single-leg drop-landing task from two different heights. We hypothesized that there will be significant differences in lower limb movement patterns (kinematics), muscle forces and ACL loading between the dominant and non-dominant limbs. Further, we hypothesized that significant differences between limbs will be present when participants land from a greater drop-landing height. Eight recreational female participants performed dominant and non-dominant single-leg drop landings from 30 to 60cm. OpenSim software was used to develop participant-specific musculoskeletal models and to calculate muscle forces. We also predicted ACL loading using our previously established method. There were no significant differences between dominant and non-dominant leg landing except in ankle dorsiflexion and GMED muscle forces at peak GRF. Landing from a greater height resulted in significant differences among most kinetics and kinematics variables and ACL forces. Minimal differences in lower-limb muscle forces and ACL loading between the dominant and non-dominant legs during single-leg landing may suggest similar risk of injury across limbs in this cohort. Further research is required to confirm whether limb dominance may play an important role in the higher incidence of ACL injury in female athletes with larger and sport-specific cohorts.

Relationship between geometry of the extensor mechanism of the knee and risk of anterior cruciate ligament injury.

The complex inter-segmental forces that are developed across an extended knee by body weight and contraction of the quadriceps muscle group transmits an anteriorly directed force on the tibia that strain the anterior cruciate ligament (ACL). We hypothesized that a relationship exists between geometry of the knees extensor mechanism and the risk of sustaining a non-contact ACL injury. Geometry of the extensor mechanism was characterized using MRI scans of the knees of 88 subjects that suffered their first non-contact ACL injury and 88 matched control subjects with normal knees that were on the same team. The orientation of the patellar tendon axis was measured relative to the femoral flexion-extension axis to determine the extensor moment arm (EMA), and relative to tibial long axis to measure coronal patellar tendon angle (CPTA) and sagittal patellar tendon angle (SPTA). Associations between these parameters and ACL injury risk were tested with and without adjustment for flexion and internal rotation position of the tibia relative to the femur during MRI data acquisition. After adjustment for internal rotation position of the tibia relative to the femur there were no associations between EMA, CPTA, and SPTA and risk of suffering an ACL injury. However, increased internal rotation position of the tibia relative to the femur was significantly associated with increased risk of ACL injury in female athletes both in univariate analysis (Odds Ratio = 1.16 per degree of internal rotation of the tibia, p = 0.002), as well as after adjustment for EMA, CPTA, and SPTA.: © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:965-973, 2017.

Functional Performance Among Active Female Soccer Players After Unilateral Primary Anterior Cruciate Ligament Reconstruction Compared With Knee-Healthy Controls

Background: Good functional performance with limb symmetry is believed to be important to minimize the risk of injury after a return to pivoting and contact sports after anterior cruciate ligament reconstruction (ACLR). Purpose: This study aimed to investigate any side-to-side limb differences in functional performance and movement asymmetries in female soccer players with a primary unilateral anterior cruciate ligament (ACL)–reconstructed knee and to compare these players with knee-healthy controls from the same soccer teams. Study Design: Cross-sectional study; Level of evidence, 3. Methods: This study included 77 active female soccer players at a median of 18 months after ACLR (interquartile range [IQR], 14.5 months; range, 7-39 months) and 77 knee-healthy female soccer players. The mean age was 20.1 ± 2.3 years for players with an ACL-reconstructed knee and 19.5 ± 2.2 years for controls. We used a battery of tests to assess postural control (Star Excursion Balance Test) and hop performance (1-legged hop for distance, 5-jump test, and side hop). Movement asymmetries in the lower limbs and trunk were assessed with the drop vertical jump and the tuck jump using 2-dimensional analyses. Results: The reconstructed and uninvolved limbs did not differ in any of the tests. In the 5-jump test, players with an ACL-reconstructed knee performed worse than controls (mean 8.75 ± 1.05 m vs 9.09 ± 0.89 m; P = .034). On the drop vertical jump test, the ACL-reconstructed limb had significantly less knee valgus motion in the frontal plane (median 0.028 m [IQR, 0.049 m] vs 0.045 m [IQR, 0.043 m]; P = .004) and a lower probability of a high knee abduction moment (pKAM) (median 69.2% [IQR, 44.4%] vs 79.8% [IQR, 44.8%]; P = .043) compared with the control players’ matched limb (for leg dominance). Results showed that 9% to 49% of players in both groups performed outside recommended guidelines on the different tests. Only 14 players with an ACL-reconstructed knee (18%) and 15 controls (19%) had results that met the recommended guidelines for all 5 tests (P = .837). Conclusion: The reconstructed and uninvolved limbs did not differ, and players with an ACL-reconstructed knee and controls differed only minimally on the functional performance tests, indicating similar function. It is worth noting that many players with an ACL-reconstructed knee and controls had movement asymmetries and a high pKAM pattern, which have previously been associated with an increased risk for both primary and secondary ACL injury in female athletes.

Frontal plane comparison between drop jump and vertical jump: implications for the assessment of ACL risk of injury

The potential to use the vertical jump (VJ) to assess both athletic performance and risk of anterior cruciate ligament (ACL) injury could have widespread clinical implications since VJ is broadly used in high school, university, and professional sport settings. Although drop jump (DJ) and VJ observationally exhibit similar lower extremity mechanics, the extent to which VJ can also be used as screening tool for ACL injury risk has not been assessed. This study evaluated whether individuals exhibit similar knee joint frontal plane kinematic and kinetic patterns when performing VJs compared with DJs. Twenty-eight female collegiate athletes performed DJs and VJs. Paired t-tests indicated that peak knee valgus angles did not differ significantly between tasks (p = 0.419); however, peak knee internal adductor moments were significantly larger during the DJ vs. VJ (p < 0.001). Pearson correlations between the DJ and VJ revealed strong correlations for knee valgus angles (r = 0.93, p < 0.001) and for internal knee adductor moments (r = 0.82, p < 0.001). Our results provide grounds for investigating whether frontal plane knee mechanics during VJ can predict ACL injuries and thus can be used as an effective tool for the assessment of risk of ACL injury in female athletes.

Knee Laxity Variations in the Menstrual Cycle in Female Athletes Referred to the Orthopedic Clinic.

BackgroundAnterior cruciate ligament (ACL) rupture is the biggest concern for orthopedic surgeons who are involved in sports injuries, so most of ACL reconstruction surgeries are sports related. ACL injuries in female athletes are 2 - 8 times more common than male athletes in similar sport injuries.ObjectivesThe aim of this study was to compare knee laxity changes in the menstrual cycle in female athletes referred to the orthopedic clinic of Imam Khomeini hospital in the north of Iran, Sari, 2013.Patients and MethodsThe present descriptive study was conducted on 40 female athletes that were referred to the orthopedic clinic. Hormone levels, such as estrogen and progesterone were assessed by one laboratory in 3 phases of the menstrual cycle. We used Lachman test and anterior drawer test for knee laxity rate. The descriptive statistics were calculated as indices of central distribution of bonds (x ± SD) and relative frequency distribution was used for qualitative variables.ResultsThe results of the current study showed that there is no significant difference in ACL laxity in female athletes in three phases of menstrual cycle; namely menstruation time, ovulation time and mid-luteal phase.ConclusionsDespite numerous studies and research in the field of knee laxity and effects of female hormones, many researchers do not agree about the effect of female hormones on knee laxity. The current study also reported no relationship between female hormones and knee laxity, while statistics show fundamental difference between male and female athletes.

Hip Rotation as a Crucial Risk Factor for Anterior Cruciate Ligament Injury in Female Athletes

Non-contact anterior cruciate ligament (ACL) injuries occurs with a higher incidence in female athletes compared with males after the onset of puberty. One anatomical factor with clinically observable differences between males and females is lower extremity alignment. The knee joint valgus in the coronal plane, which is associated with ACL injury risk, is composed of rotation of the tibia around the stationary femur and hip rotation combined with knee flexion. However, knee abduction measurements require expensive biomechanical laboratories. Therefore, it is important to develop simple measurement methods of the anatomical and structural factors to determine female athletes at increased risk for ACL injury. PURPOSE: The purpose of this study was to prove the difference of hip rotation between female and male handball players with or without history of ACL injury. METHODS: Elite collegiate athletes on the varsity handball team (17 females and 24 males) were recruited. Whereas 8 females and 1 male had a history of ACL injury, there were 9 females and 23 males with no history of ACL injury. The 6 measures of hip joint motion (flexion, extension, abduction, adduction, external rotation, and internal rotation) and the 2 measures of knee joint motion (flexion and extension) were measured with the standard procedure using a goniometer. RESULTS:Table: No title available.*p<0.05 vs. female players with no ACL injury COCLUSION: Female handball players with a history of ACL injury had greater hip internal rotation with smaller hip external rotation, compared with the counterpart without history of ACL injury. Hip rotation, which can be readily measured by coaches, athletic trainers, physical therapists, and athletes, may be a crucial risk factor for ACL injury in female athletes.

ABCs of Evidence-based Anterior Cruciate Ligament Injury Prevention Strategies in Female Athletes.

Anterior cruciate ligament (ACL) injury is a major concern in physically active females. Although ACL reconstruction techniques have seen significant advances in recent years, risk associated with re-injury and future osteoarthritis remains a major concern. Thus, prevention of ACL injury is a logical step to protect and preserve healthy knee joints in young athletes. The current report aims to summarize a list of evidence-based prevention strategies to reduce ACL injury in female athletes. A list of six critical principles, which come from documented, large scale clinical trial studies and further analyses, were presented with ABC format including age, biomechanics, compliance, dosage, exercise, and feedback. Also, a grade for evidence and implications of future research is noted. Finally, in the conclusion section, importance of collaborative efforts from healthcare practitioners, researchers, and personnel associated with athletics is addressed.

Unstable Surface Improves Quadriceps:Hamstring Co-contraction for Anterior Cruciate Ligament Injury Prevention Strategies.

Background:Increasing quadriceps:hamstring muscular co-contraction at the knee may reduce the risk of anterior cruciate ligament (ACL) injury. The purpose of this investigation was to examine muscle activation in the quadriceps and hamstrings and peak kinematics of the knee, hip, and trunk when performing a single-leg drop (SLD) on to a Bosu ball (unstable surface) compared with on to the floor (stable surface).Hypotheses:(1) The SLD on an unstable surface would lower the quadriceps to hamstrings electromyographic (EMG) activation ratio (Q:H EMG activation ratio) compared with being performed on the floor. (2) Lower Q:H EMG activation ratio would be caused by a relative increase in hamstring activation, with no significant change in quadriceps activation.Study Design:Controlled laboratory study.Methods:Thirty-nine Division I National Collegiate Athletic Association (NCAA) female athletes performed 3 SLDs per leg onto a Bosu ball and onto the floor. Muscle activity of the vastus lateralis and lateral hamstrings were used to estimate peak quadriceps and hamstring activation, along with the Q:H EMG activation ratio. Kinematic measures at the knee, hip, and trunk were also estimated. Differences between landings were assessed using a 2-level analysis of variance (limb and surface).Results:The maximum Q:H EMG activation ratio was significantly reduced when athletes performed an SLD onto the Bosu ball (20%, P < 0.001) compared with the floor. Peak hamstring activity was higher when athletes landed on a Bosu ball (18% higher, P = 0.029) compared with when they landed on the floor.Conclusion:Compared with landing on the floor (a stable surface), landing on a Bosu ball (unstable surface) changed the athlete’s co-contraction at the knee and increased hamstring activity. However, landing on a Bosu ball also decreased the athlete’s knee flexion, which was an undesired effect.Clinical Relevance:These findings highlight the potential utility of unstable surfaces as a training tool to reduce the risk of ACL injury in female athletes.

Prevention of Anterior Cruciate Ligament Rupture in Female Athletes: A Systematic Review.

A number of reports have been published on the effectiveness and design of intervention programs for the prevention of rupture of the anterior cruciate ligament (ACL) in female athletes. The purpose of this study was to systematically review the literature to determine the effectiveness of neuromuscular training programs in preventing ACL injury in female athletes. A systematic review was performed with use of the PubMed, MEDLINE, Embase, and Cochrane Central Register of Controlled Trials databases. The search terms included "anterior cruciate ligament" and "ACL" combined with "prevention" and "intervention." The searches included material indexed by September 30, 2013. Data concerning study design, the characteristics of participants, the details of the neuromuscular programs, the types of sports, and number of ACL ruptures were extracted from the studies. Study heterogeneity was assessed with funnel plot and Egger regression methods. Pooled effects were calculated with use of a DerSimonian-Laird random-effects model. The number needed to treat was calculated on the basis of pooled incidence data. The risk of ACL rupture was 1.83 times higher for female athletes who did not participate in neuromuscular ACL-prevention training programs (odds ratio [OR], 1.83; 95% confidence interval [95% CI], 1.08 to 3.10; p = 0.02). In studies that focused exclusively on soccer, the risk of ACL rupture was 2.62 times higher for nonparticipating athletes (OR, 2.62; 95% CI, 1.59 to 4.32; p < 0.01). When the data were analyzed according to the timing of the intervention, no significant effects were found. In studies in which the program took place both preseason and in-season, the risk (odds ratio) of ACL rupture for nonparticipating athletes was 2.34 (95% CI, 0.82 to 6.7; p = 0.11). In studies in which the intervention took place in-season only, the risk (odds ratio) of ACL rupture for nonparticipating athletes was 1.25 (95% CI, 0.23 to 6.75; p = 0.8). The number needed to treat to prevent a single ACL rupture was 128.7 athletes. We found no significant heterogeneity among the included studies. The I value was 35.40% (p = 0.11). No significant publication bias was found in our included studies. The results of this systematic review and meta-analysis favor a protective effect of neuromuscular training programs on the risk of ACL rupture in female athletes. This protective effect is more pronounced in soccer players. Additional research is needed to design the optimal training program. Therapeutic Level II. See Instructions to Authors for a complete description of levels of evidence.

The Muscle Stretch Reflex throughout the Menstrual Cycle

The significant sex disparity in sports-related knee injuries may be due to underlying differences in motor control. Although the development of sex-specific movement patterns is likely multifactorial, this study specifically focuses on the potential modulatory role of sex hormones. This study aimed to investigate the muscle stretch reflex (MSR) across the menstrual cycle. We hypothesized that the MSR would fluctuate throughout the menstrual cycle and that the lowest response would correspond with peak concentrations of estrogen. Nineteen healthy women age 18-35 yr participated in this study: 8 eumenorrheic women and 11 women taking oral contraceptives. Serum estradiol and progesterone concentrations, anterior knee laxity (AKL), and the MSR response of the quadriceps muscles were measured three times during the menstrual cycle. The MSR response of the rectus femoris (RF) varied significantly across the menstrual cycle in both groups. Specifically, the RF MSR response was 2.4 times lower during the periovulatory phase when compared with the luteal phase (P = 0.007). The same trend was seen in the vastus medialis, but this did not reach statistical significance (P = 0.070). The MSR response of the vastus lateralis did not change significantly across the menstrual cycle (P = 0.494). A mixed model comparison did not show an association between endogenous concentrations of estradiol and progesterone, exposure to hormonal contraceptives or AKL, and the MSR response for any muscle. Our results demonstrate that the RF MSR response varies throughout the menstrual cycle with the lowest response around the time of ovulation. Additional research is needed to clarify the exact relationship between sex hormones, AKL, and MSR response and to determine the specific origin of the change along the monosynaptic reflex arc.