Anterior Cruciate Ligament Injury Risk Research Articles

Preliminary Evaluation of Knee Kinetics in Female Athletes on Hormonal Contraceptives.

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

Recurrent Anterior Cruciate Ligament Tears in the National Football League: A Case-Control Study.

Background:Anterior cruciate ligament (ACL) injuries are common in American football players. The risk of subsequent ACL reinjury to either the ipsilateral or the contralateral knee in National Football League (NFL) draftees with a history of successful ACL reconstruction before entering the NFL remains unknown.Hypothesis:NFL athletes with a history of successful ACL reconstruction before being drafted will likely demonstrate increased risk of subsequent ACL injury when compared with a control cohort consisting of players of similar positions and draft class.Study Design:Cohort study; Level of evidence, 3.Methods:Detailed orthopaedic evaluations of NFL Combine participants from 2006 to 2012 were obtained to identify players entering the NFL draft with a history of successful ACL reconstruction. A control cohort was created in a 2:1 ratio, consisting of players matched by position and draft class.Results:Of the 2016 players invited to the NFL Combine during the study period, 100 met the inclusion criteria. A total of 26 subsequent ACL reinjuries (12 ipsilateral, 14 contralateral) occurred in 25 players (25%) while playing in the NFL, with injuries occurring at a mean of 22.1 months after the NFL draft. In comparison, 18 of the 200 (9%) carefully matched cohort players without history of prior ACL injury sustained a new ACL injury during this time period (P < .001).Conclusion:NFL athletes with a history of successful ACL reconstruction before being drafted into the NFL have a significantly higher rate of subsequent ACL reinjury while playing in the NFL when compared with a carefully matched cohort of players without a history of prior ACL injury.

Difference in leg asymmetry between female collegiate athletes and recreational athletes during drop vertical jump

BackgroundNeuromuscular imbalance will lead to loading asymmetry in sporting activities. This asymmetry is related to leg dominance, which has been associated with increased risk of anterior cruciate ligament (ACL) injury. Therefore, potential biomechanical differences between legs are important. However, little attention has been paid to the biomechanical details of leg dominance. The purpose of the present study was to clarify the relationship between leg dominance and knee biomechanics in females with different activity level during dynamic athletic tasks.MethodsA total of 23 female collegiate (mean age = 19.6 ± 1.4 years, mean body mass index = 21.5 ± 0.9) and 19 recreational athletes (mean age = 20.7 ± 1.1 years, mean body mass index = 20.5 ± 1.7) were enrolled. Tegner activity scores of the collegiate and recreational athletes were 9 and 7, respectively. Knee kinematic and kinetic asymmetries between the dominant (DL) and non-dominant (NDL) legs during the landing phase of drop vertical jump (DVJ) were assessed using three-dimensional motion analysis in collegiate and recreational athletes separately. Statistical comparison was done using two-tailed paired t test between DL and NDL in each athlete.ResultsThe peak knee abduction angle was significantly larger on the DL than on the NDL in collegiate athletes. Knee abduction angle at initial contact (IC), peak knee abduction angle, knee internal rotation angle at IC, and peak knee internal rotation angle were significantly larger on the NDL than on the DL in recreational athletes. Moreover, peak knee abduction moment within 40 ms from IC was larger on the NDL than on the DL in recreational athletes, while the moment was not significantly different in collegiate athletes.ConclusionsFrom the present study, the relationship between leg dominance and knee biomechanics was totally different in females with different activity level. Specifically, asymmetry of the knee abduction angle between limbs was opposite between female recreational and collegiate athletes. According to previous literatures, abduction and internal rotation angles as well as abduction moment were key issues for mechanism of non-contact ACL injury. Therefore, the NDL in female recreational athletes was associated with increased risk of ACL injury.

Influence of Foot-Landing Positions at Initial Contact on Knee Flexion Angles for Single-Leg Drop Landings

ABSTRACTPurpose: Small knee flexion angles are associated with increased non-contact anterior cruciate ligament (ACL) injury risks. The purpose of this study was to provide insights into how ankle plantar flexion angles influenced knee flexion angles at initial contact during single-leg drop landings. Method: Thirteen male recreational basketball players performed single-leg drop landings from a 30-cm high platform using three randomized foot-landing positions (natural, fore-foot, and flat-foot). A motion capture system and a force plate were used to measure lower extremity kinematics and vertical ground reaction force (VGRF). A one-way repeated measures Analysis of Variance and the Friedman test were conducted (α = .05). Results: Foot-landing position had a significant effect on knee flexion angles at initial contact (p < .001). As compared to flat-foot landings (18° (SD 5°), significantly smaller knee flexion angles were found for natural (mean 12° (SD 5°), p = .004) and fore-foot landings (mean 12° (SD 3°), p = .001). There was however significantly smaller knee flexion range of motion in flat-foot landings (mean 42° (SD 3°), as compared to natural landings (mean 48° (SD 4°) (p < .001). Flat-foot landings also resulted in a 1.4 times higher maximum VGRF than fore-foot landings (p < .001) and 1.3 times higher than natural landings (p = .005). Conclusions: Natural and fore-foot landings are better for force absorption but are associated with smaller knee flexion angles at initial contact. These findings have important implications for non-contact ACL injuries.

The Effect of Oral Contraceptive Hormones on Anterior Cruciate Ligament Strength

Background: Women are 2 to 9 times more likely to experience an anterior cruciate ligament (ACL) injury than men. Various hormones including relaxin, progesterone, and estrogen influence ACL strength. Oral contraceptives (OCs) alter these hormone levels; however, studies have yet to comprehensively compare different OCs’ effects on the ACL. Hypothesis: OCs with increased progestin-to-estrogen ratios will (1) increase ACL collagen expression, (2) decrease ACL matrix metalloproteinase expression, and (3) increase ACL strength. Study Design: Controlled laboratory study. Methods: Untreated female rats were compared with rats treated with 1 of 5 clinically used OCs: norethindrone (NE) only, NE plus ethinylestradiol (EE), etynodiol diacetate (ED) plus EE, norgestimate (NG) plus EE, and drospirenone (DS) plus EE. Doses were scaled from human doses to account for differences in bioavailability and body weight, and OCs were administered daily via oral gavage for 4 rat estrous cycles (20 days). A total of 36 rats were then sacrificed (6 rats/group). ACLs underwent biomechanical testing to assess ACL strength, stiffness, and maximum load before failure. ACL specimens were also isolated for quantitative real-time polymerase chain reaction analysis to assess collagen, matrix metalloproteinase, and relaxin receptor–1 expression. Results: While the primary structural property of interest (ACL maximum load before failure) was not significantly improved by OC treatment, the main material property of interest (ACL strength) in rats treated with NE only, DS + EE, ED + EE, and NE + EE was significantly increased compared with untreated controls (P = .001, P = .004, P = .004, and P = .04, respectively). The order from strongest to weakest ACLs, which was also the same order as the highest to lowest progestin-to-estrogen ratios, was groups treated with NE only, DS + EE, ED + EE, NE + EE, and lastly NG + EE. Higher ratio formulations also increased the expression of type I collagen (P = .02) and decreased the expression of matrix metalloproteinase–1 (P = .04). Conclusion: OC formulations with higher progestin-to-estrogen ratios may be more protective for the ACL than formulations with lower ratios. Clinical Relevance: OC formulations with high progestin-to-estrogen ratios may benefit female athletes by reducing their ACL injury risk by decreasing the effects of relaxin on the ACL.

Late Activation of the Vastus Medialis in Determining the Risk of Anterior Cruciate Ligament Injury in Soccer Players.

Activation time of the quadriceps is important in determining injury risk in professional soccer players. To compare the activation time of the quadriceps and hamstrings muscles during a movement that puts stress on anterior cruciate ligament (ACL) to assess the risk of ACL injury. Case series. University laboratory for movement analysis. Twenty (10 males and 10 females) professional soccer players. An inertial sensor and 4 electrodes positioned on the quadriceps and hamstrings muscles were used for the surface electromyography. The athlete resting on 1 leg dropped, from a 32-cm-high platform, on the suspended foot (testing leg), without jumping or lowering his center of gravity and maintaining single-leg landing for 5 seconds. Using a software, it is possible to calculate the activation time of the rectus femoris, vastus medialis (VM), biceps femoris, and semimembranosus muscles before ground contact. To evaluate the activation times of the rectus femoris, VM, biceps femoris, and semitendinosus muscles before ground contact in comparison with the range of normality calculated by the manufacturer. All male soccer players demonstrated a low risk related to the correct activation of all the examined muscles, while female soccer players demonstrated delayed activation of the VM. Delayed activation of the VM registered in females determines an increase in anterior shear force, which is an important risk factor for incurring an ACL injury. This testing protocol becomes adequate for the screening of high-risk athletes and for targeting interventions to specific imbalances that may increase injury risk.

By failing to prepare, you are preparing your anterior cruciate ligament to fail.

There is strong evidence linking an athlete's movement technique during sidestepping with anterior cruciate ligament (ACL) injury risk. However, it is unclear how these injuriouspostures are influenced by prior movement. We aim to describe preparatory trunk and thigh kinematics at toe-off of the penultimate-step and flight-phase angular momenta, and explore their associations with frontal-plane risk factors during unplanned sidestepping maneuvers. We analyzed kinematic and kinetic data of 33 male Australian Football players performing unplanned sidestepping tasks (103 trials). Linear mixed models tested for reliable associations between ACL injury risk during weight acceptance of the execution-step, with preparatory kinematics and angular momenta of the trunk and thigh during the penultimate-step. Multi-planar flight-phase trunk momenta along with hip abduction angle at penultimate-step toe-off were significantly associated with peak knee valgus moments during the execution-step (R2 =.21, P<.01). Execution-step trunk lateral flexion was significantly predicted by frontal and sagittal-plane preparatory trunk positioning at toe-off of the penultimate-step (R2 =.44, P<.01). Multi-planar flight-phase trunk momenta as well as multi-planar trunk and hip positioning at penultimate-step toe-offwere associated with hip abduction during the execution-step (R2 =.53, P<.01). Preparatory positioning of the trunk and hip, along with flight-phase trunk momentum adjusting this positioning are linked to known ACL injury risk factors. We recommendthat during the penultimate-step athletes maintain an upright trunk, as well as minimize frontal-plane trunk momentum and transverse-plane trunk momentum toward the sidestep direction to reduce risk of ACL injury during unplanned sidesteps.

Decreased Postural Control in Patients Undergoing Anterior Cruciate Ligament Reconstruction Compared to Healthy Controls.

Patients with anterior cruciate ligament (ACL) tears are likely to have deficient dynamic postural stability compared with healthy sex- and age-matched controls. To test the hypothesis that patients undergoing ACL reconstruction have decreased dynamic postural stability compared with matched healthy controls. Prospective case-control study. Orthopedic sports medicine and physical therapy clinics. Patients aged 20 years and younger with an ACL tear scheduled for reconstruction were enrolled prospectively. Controls were recruited from local high schools and colleges via flyers. Patients underwent double-stance dynamic postural stability testing prior to surgery, recording time to failure and dynamic motion analysis (DMA) scores. Patients were then matched with healthy controls. Demographics, time to failure, and DMA scores were compared between groups. A total of 19 females and 12 males with ACL tears were matched with controls. Individuals with ACL tears were more active (Marx activity score: 15.7 [1.0] vs 10.8 [4.9], P < .001); had shorter times until test failure (84.4 [15.8] vs 99.5 [14.5]s, P < .001); and had higher (worse) DMA scores (627 [147] vs 481 [132], P < .001), indicating less dynamic postural stability. Six patients with ACL deficiency (1 male and 5 females) demonstrated lower (better) DMA scores than their controls, and another 7 (4 males and 3 females) were within 20% of controls. Patients undergoing ACL reconstruction had worse global dynamic postural stability compared with well-matched controls. This may represent the effect of the ACL injury or preexisting deficits that contributed to the injury itself. These differences should be studied further to evaluate their relevance to ACL injury risk, rehabilitation, and return to play.

Co-creation of a sport-specific anterior cruciate ligament injury risk reduction program for women: A concept mapping approach

ObjectivesTo engage physiotherapists experienced in female elite sport and athletes to co-create a sport-specific anterior cruciate ligament (ACL) injury risk reduction program. DesignConcept Mapping. MethodsThe Concept Systems Global MAX™ web platform was used to collect and analyse data from 27 context and content experts (22 physiotherapists, 5 athletes). Participants brainstormed statements representing the critical elements that should be included in an ACL injury risk reduction program for women playing elite Australian Football (AF). ResultsTwenty-two participants brainstormed 56 statements that were synthesised and edited to 62 statements. Statements were sorted into clusters by twenty-three participants and rated on importance and feasibility using six-point scales. Multidimensional scaling and cluster analysis identified a 5-cluster solution as follows: Football-specific preparation (15 statements); Movement skills (17 statements); Strength and conditioning (15 statements); Individual preparation (7 statements); and Education (8 statements). Calculation of mean ratings for each cluster and statement identified the Movement skills cluster as most important (mean=3.61 out of 5) and the Football-specific preparation cluster as most feasible (3.75 out of 5). By contrast, the Individual preparation cluster was rated the least important (mean=2.9 out of 5), and the least feasible (3.12 out of 5), to include in the program. ConclusionsThe five clusters of critical elements to include in an ACL injury risk reduction program for women playing elite AF, in order of most to least importance were: movement skills, football-specific preparation, education, strength and conditioning and individual preparation.

Risk of Secondary ACL Injury in Adolescents Prescribed Functional Bracing After ACL Reconstruction.

Background:There is a high incidence of a secondary anterior cruciate ligament (ACL) injury in unbraced adolescent athletes. Little is known about the effect of functional bracing with regard to the risk of secondary ACL injuries among adolescents.Hypothesis:Our primary hypothesis was that adolescents would have a high rate of secondary ACL injury even with brace use. A secondary hypothesis was that the reinjury rate with brace use would be lower than that of a historical control group of unbraced patients.Study Design:Case series; Level of evidence, 4.Methods:A group of 219 patients (age <20 years at surgery) who underwent ACL reconstruction and were prescribed postoperative functional bracing during cutting and pivoting sports for 2 years after surgery completed a survey regarding reinjury to either knee. Rates of knee injuries following ACL reconstruction were calculated and compared with those reported in a similar unbraced cohort. The effect of demographic and anatomic factors on risk of secondary ACL injuries was also investigated.Results:The overall follow-up rate was 65% (142/219) at a mean 5.6 years after surgery. In the braced cohort, the overall graft retear rate was 10%, with the highest retear rates observed in male patients 17 years of age and younger (18%). The overall contralateral ACL injury and combined (graft or contralateral ACL) secondary injury rates were 13% and 23%, respectively, with female patients younger than 18 years having the highest contralateral and combined injury rates (17% and 26%, respectively). Younger age (odds ratio [OR], 0.70; P = .021), family history of ACL injury (OR, 2.81; P = .015), and higher lateral tibial slope (OR, 1.25; P = .016) were associated with increased risk of secondary knee injury in the braced cohort. Compared with the unbraced cohort, the braced cohort had a lower overall graft retear rate (P = .028), a lower graft retear rate in patients younger than 18 years (P = .012), lower early graft retear rate (within the first year after surgery) (P = .011), and lower early graft retear rate in subjects younger than 18 years (P = .003).Conclusion:Postoperative use of functional bracing can result in reduced risk of graft retear and no change in contralateral injury rates. Clinicians may want to consider the use of postoperative functional bracing in adolescent patients.

Increased Radiographic Posterior Tibial Slope Is Associated With Subsequent Injury Following Revision Anterior Cruciate Ligament Reconstruction.

Background:Increased posterior tibial slope has been identified as a possible risk factor for injury to the anterior cruciate ligament (ACL) and has also been shown to be associated with ACL reconstruction graft failure. It is currently unknown whether increased posterior tibial slope is an additional risk factor for further injury in the context of revision ACL reconstruction.Purpose:To determine the relationship between posterior tibial slope and further ACL injury in patients who have already undergone revision ACL reconstruction.Study Design:Cohort study; Level of evidence, 3.Methods:A total of 330 eligible patients who had undergone revision ACL reconstruction between January 2007 and December 2015 were identified from a clinical database. The slope of the medial and lateral tibial plateaus was measured on perioperative lateral radiographs by 2 fellowship-trained orthopaedic surgeons using a digital software application. The number of subsequent ACL injuries (graft rupture or a contralateral injury to the native ACL) was determined at a minimum follow-up of 2 years (range, 2-8 years). Tibial slope measurements were compared between patients who sustained further ACL injury to either knee and those who did not.Results:There were 50 patients who sustained a third ACL injury: 24 of these injuries were to the knee that underwent revision ACL reconstruction, and 26 were to the contralateral knee. Medial and lateral slope values were significantly greater for the third-injury group compared with the no–third injury group (medial, 7.5° vs 6.3° [P = .01]; lateral, 13.6° vs 11.9° [P = .001]).Conclusion:Increased posterior tibial slope, as measured from lateral knee radiographs, was associated with increased risk of graft rupture and contralateral ACL injury after revision ACL reconstruction. This is consistent with the concept that increased posterior slope, particularly of the lateral tibial plateau, is an important risk factor for recurrent ACL injury.

Acute effects of preventive warm-up exercises on modifiable risk factors for anterior cruciate ligament injuries: a three-arm randomized-controlled crossover trial.

We aimed to compare the potential acute effects of single bouts of a classic prevention and a risk factor-focus training aiming to target modifiable anterior cruciate ligament (ACL) rupture risk factors and the impact of neuromuscular fatigue on relevant ACL rupture risk factors. Two preventive warm-up (standard and ACL rupture risk factor training) and one inactive arm were compared; each of these were followed by a standardized neuromuscular fatigue protocol. The assessments included two Trail making tests (TMT-A; TMT-B, time to complete), drop jump landings (knee separation distance, normalized at hip width), as well as unanticipated counter movement jump landings (time to stabilization and peak ground reaction force). We included 18 participants (25±2years). No differences were found between times and conditions for TMT (P>0.05). A significant time effect occurred in time to stabilization (F=2.6; P<0.05) and a significant time*baseline-value*jumping time interaction was seen in peak ground reaction force (F=3.1; P<0.05). No time effect was found for any knee separation distance (F=.1-2.4; P>0.05); but a significant time*baseline-value*jumping time interaction was seen at initial ground contact (F=2.8; P<0.05), and lowest point (F=4.2; P<0.01). Risk factor-focus and classic warm-up may not differ in their acute effects on modifiable functional ACL (re-)injury risks factors.

Return to Play and Long-term Participation in Pivoting Sports After Anterior Cruciate Ligament Reconstruction

Background: Rupture of the anterior cruciate ligament (ACL) is a common and feared injury among athletes because of its potential effect on further sports participation. Reported rates of return to pivoting sports after ACL reconstruction (ACLR) vary in the literature, and the long-term consequences of returning have rarely been studied. Purpose: To examine the rate and level of return to pivoting sports after ACLR, the duration of sports participation, and long-term consequences of returning to pivoting sports. Study Design: Cohort study; Level of evidence, 2. Methods: All primary ACLRs with a bone–patellar tendon–bone autograft between 1987 and 1994 (N = 234) in athletes participating in team handball, basketball, or soccer before injury were selected from a single-center quality database. A long-term evaluation (median, 25 years; range, 22-30 years) was performed using a questionnaire focusing on return to pivoting sports, the duration of sports activity after surgery, later contralateral ACL injuries, revision surgery, and knee replacement surgery. Participants were stratified into 2 groups depending on the time between injury and surgery (early, <24 months; late, ≥24 months). Results: A total of 93% of patients (n = 217) responded to the questionnaire. Although 83% of patients returned to pivoting sports after early ACLR, only 53% returned to preinjury level. Similar return-to-sport rates were observed in males and females (P > .05), but males had longer sports careers (median, 10 years; range, 1-23 years) than females (median, 4 years; range, 1-25 years; P < .001). The incidence of contralateral ACL injuries was 28% among athletes who returned to sports versus 4% among athletes who did not return (P = .017) after early ACLR. The pooled reinjury rate after return to preinjury level of sports was 41% (30%, contralateral injuries; 11%, revision surgery). The incidence of contralateral ACL injuries was 32% among females versus 23% among males (P > .05) and, for revision surgery, was 12% among females versus 7% among males (P > .05) after returning to sports. Having a late ACLR was associated with an increased risk of knee replacement surgery (9% vs 3%; P = .049) when compared with having an early ACLR. Conclusion: ACLR does not necessarily enable a return to preinjury sports participation. By returning to pivoting sports after ACLR, athletes are also facing a high risk of contralateral ACL injuries. Long-term evaluations in risk assessments after ACLR are important, as a significant number of subsequent ACL injuries occur later than the routine follow-up.

In Vivo Anterior Cruciate Ligament Deformation During a Single-Legged Jump Measured by Magnetic Resonance Imaging and High-Speed Biplanar Radiography

Background: The in vivo mechanics of the anterior cruciate ligament (ACL) and its bundles during dynamic activities are not completely understood. An improved understanding of how the ACL stabilizes the knee is likely to aid in the identification and prevention of injurious maneuvers. Purpose/Hypothesis: The purpose was to measure in vivo ACL strain during a single-legged jump through use of magnetic resonance imaging (MRI) and high-speed biplanar radiography. We hypothesized that ACL strain would increase with the knee near extension, and a peak in ACL strain would occur just before landing from the jump, potentially due to quadriceps contraction in anticipation of landing. Study Design: Descriptive laboratory study. Methods: Models of the femur, tibia, and ACL attachment sites of 8 male participants were generated from MRI scans through use of solid modeling. High-speed biplanar radiographs were obtained from these participants as they performed a single-legged jump. The bone models were registered to the biplanar radiographs, thereby reproducing the in vivo positions of the joint throughout the jump. ACL and bundle elongations were defined as the centroid to centroid distances between attachment sites for each knee position. ACL strain was defined as ACL length normalized to its length measured in the position of the knee at the time of MRI. Results: Peaks in ACL strain were observed before toe-off and 55 ± 35 milliseconds before initial ground contact. These peaks were associated with the knee positioned at low flexion angles. Mean ACL strain was inversely related to mean flexion angle (rho = −0.73, P < .001), such that ACL strain generally increased with knee extension throughout the jumping motion. ACL bundle lengths were significantly (rho > 0.85, P < .001) correlated with overall ACL length. Conclusion: These findings provide insight into how landing in extension can increase the risk of ACL injury. Specifically, this study shows that peak ACL strain can occur just before landing from a single-legged jump. Thus, when an individual lands on an extended knee, the ACL is relatively taut, which may make it particularly vulnerable to injury, especially in the presence of a movement perturbation or unanticipated change in landing strategy. Clinical Relevance: This study provides a novel measurement of dynamic ACL strain during an athletic maneuver and lends insight into how landing in extension can increase the likelihood of ACL failure.

A Comparison of the Hamstring to Quadriceps Activation Ratio in the Toe-in or Neutral Toe Position After Triple Jump Spikes in Female Volleyball Players

Background: Performing exercises or playing sports with an incorrect technique can cause musculoskeletal injuries. Objectives: The present study was conducted to compare the hamstring to quadriceps activation ratio when landing in a two-way spike in female volleyball players. Methods: In this cross-sectional study, 15 elite female volleyball players performed triple jump spikes (TJS) with their toe in and in a neutral ankle position. Electromyography (EMG) was used to measure the muscle activity of the biceps femoris, semitendinosus, vastus medialis and vastus lateralis in two phases before and after the initial contact. Data were analyzed using the Wilcoxon test at the significance level of P < 0.05. Results: The ratio of biceps femoris activity to vastus medialis (P = 0.04) and vastus lateralis (P = 0.04) activities in TJS with a toe-in ankle decreased significantly in the feed-back phase and the ratio of semitendinosus activity to vastus lateralis activity also decreased significantly in the feed-forward phase of TJS with a natural ankle angle (P = 0.02). Conclusions: A lower muscle activity ratio for biceps femoris to vastus lateralis and medialis in the toe-in position may lower hamstring muscle support from the anterior cruciate ligament (ACL) after landing, which might increase the risk of ACL injury when landing.

Are Risk-Taking and Ski Helmet Use Associated with an ACL Injury in Recreational Alpine Skiing?

According to the risk compensation hypothesis, the use of a ski helmet might provide a false sense of security, resulting in a riskier behavior by skiing faster or more aggressively, which might lead to an increased injury risk. Injury of the anterior cruciate ligament (ACL) is a common diagnosis in downhill skiers. Thus, the aim of the study was to evaluate the potential impact of risk-taking and ski helmet use on ACL injury risk in recreational skiing. Eighty-two ACL injured and 446 uninjured skiers with a mean age of 37.3 ± 11.9 years (52% females) were surveyed during the winter season 2018/19 about age, sex, self-reported risk-taking behavior, self-reported skill level, perceived speed, and ski helmet use. Multiple regression analysis revealed that older age (OR: 1.3, 95% CI: 1.2–1.4), riskier behavior (OR: 5.4, 95% CI: 2.8–10.5), and lower skill level (OR: 6.7, 95% CI: 3.4–13.3) were found to be factors associated with ACL injury, while ski helmet use was not. In conclusion, no support for the risk compensation hypothesis was found with regard to ACL injuries. Therefore, we doubt that ski helmet use increases the risk for ACL injury and recommend wearing a ski helmet due to reported protective effects.

High Risk of Further Anterior Cruciate Ligament Injury in a 10-Year Follow-up Study of Anterior Cruciate Ligament-Reconstructed Soccer Players in the Swedish National Knee Ligament Registry

To follow up on soccer players 10years after a primary anterior cruciate ligament (ACL) reconstruction to find out how many players returned to play soccer, what influenced their decision, and if there are any differences in additional ACL injuries (graft failure and/or contralateral ACL injury) between those who returned to play and those who did not. The study cohort consists of 1661 soccer players from the Swedish National Knee Ligament Registry. A questionnaire was sent to each player regarding their return to play and additional knee injuries that may have occurred 10years after their primary ACL. The results are based on the 684 responders. Data such as age, sex, surgical procedural data, associated injuries, patient-reported outcome measures, and additional knee surgeries were collected from the registry. In this study, 51% returned to play soccer. For those who did not return to play, the primary reason was knee related (65.4% of the cases). The most common knee-related reasons for not returning were pain and/or instability (50%; n= 109), followed by fear of reinjury (32%; n= 69). Players who return to soccer have a significantly higher risk of additional ACL injury. Of the players who returned to play soccer, 28.7% (odds ratio [OR] 2.3, P < .001) had additional ACL injury, 9.7% (OR 2.9, P < .001) had a graft failure and 20.6% (OR 2.1, P < .001) had a contralateral ACL injury. Players that return to soccer have a significantly higher risk of sustaining further ACL injury. Only half of the soccer players return to play after ACL reconstruction, and in two-thirds of those who did not return, the reason was knee related. The high risk of sustaining additional knee injury is of serious concern to the player's future knee health and should be considered when deciding on a return to play. Level III retrospective case-control study.

Prior history of anterior cruciate ligament (ACL) reconstruction is associated with a greater risk of subsequent ACL injury in female collegiate athletes

ObjectivesThe risk of a subsequent anterior cruciate ligament (ACL) sprain is greater in high school aged female athletes with prior history of ACL reconstruction (ACLR) than in age-matched controls. The risk of a subsequent ACL injury in female collegiate athletes with prior ACLR is unknown. The primary purpose of this study was to determine the relative risk of a subsequent ACL injury in female collegiate athletes with prior ACLR when compared to age-matched controls. The secondary purpose of this study was to evaluate the ability of jump and hop tests to discriminate ACL injury risk. DesignProspective cohort. MethodsThree hundred and sixty female collegiate athletes (mean age 19.3 ± 1.4 years) representing the following sports: volleyball, soccer, and basketball were recruited.Subjects reported prior history of ACLR and standing long jump (SLJ) and single-leg hop (SLH) scores were collected during the preseason. Noncontact time-loss ACL and lower quadrant (i.e., low back and lower extremities) injuries were tracked by university athletic trainers. ResultsFemale collegiate athletes with a prior history of ACLR were 6 times (RR = 6.8 [95% CI: 1.4, 32.9] p-value = 0.007) more likely to experience an ACL injury than controls. Suboptimal performance on a battery of tests (SLJ ≤ 79% height, (B) SLH ≤ 69% height) was associated with a greater risk of lower quadrant injury (RR = 1.6 [95% CI: 1.1, 2.4] p-value = 0.028); however performance on these tests was not associated with ACL injury. ConclusionsFemale collegiate athletes should be screened for history of ACLR.

Clinical Tests Can Be Used to Screen for Second Anterior Cruciate Ligament Injury in Younger Patients Who Return to Sport.

Background:Younger athletes have high rates of second anterior cruciate ligament (ACL) injury. Return-to-sport criteria have been proposed to enable athletes to make a safe return, but they frequently lack validation. It is unclear whether commonly recorded clinical measures can help to identify high-risk athletes.Purpose:To explore the association between commonly recorded clinical outcome measures and second ACL injury in a young, active patient group.Study Design:Cohort study; Level of evidence, 2.Methods:Included in this study were 329 athletes (200 males, 129 females) younger than 20 years at the time of first primary ACL reconstruction surgery who had subsequently returned to sport participation. Clinical examination included range of knee motion (passive flexion and extension deficits), instrumented anterior knee laxity, and single- and triple-crossover hop for distance. Patients also completed the subjective International Knee Documentation Committee form. All measures were collected prospectively at a 12-month postoperative clinical review. Patients were evaluated for a minimum 3 years to determine the incidence of subsequent ACL injury.Results:A total of 95 patients (29%) sustained a second ACL injury following clinical assessment and return to sport. There were 50 graft ruptures and 45 contralateral ACL injuries. Patients with a flexion deficit of 5° had over 2 times the odds of sustaining a graft rupture (odds ratio, 2.3; P < .05), and patients with a side-to-side difference in anterior knee laxity of 3 mm or greater had over 2 times the odds of sustaining a contralateral ACL injury (odds ratio, 2.4; P < .05). Overall, 29% (94 of 329) of patients met the threshold for satisfactory function on all 6 clinical measures; these patients had a 33% reduction in the risk of sustaining a second ACL injury (P = .05) as compared with those who did not meet all clinical thresholds.Conclusion:Clinical measures of knee flexion and stability may have utility to screen for and identify patients who are at greater risk for a second ACL injury in an already high-risk group (ie, age and activity level).

EMG-Informed Musculoskeletal Modeling to Estimate Realistic Knee Anterior Shear Force During Drop Vertical Jump in Female Athletes.

The anterior cruciate ligament is the primary structural restraint to tibial anterior shear force. The anterior force occurring at the knee during landing contributes to anterior cruciate ligament injury risk, but it cannot be directly measured experimentally. The objective of this study was to develop electromyography-informed musculoskeletal simulations of the drop vertical jump motor task and assess the contribution of knee muscle forces to tibial anterior shear force. In this cross-sectional study, musculoskeletal simulations were used to estimate the muscle forces of thirteen female athletes performing a drop vertical jump using an electromyography-informed method. Muscle activation and knee loads that resulted from these simulations were compared to the results obtained with the more common approach of minimization of muscle effort (optimization-based method). Quadriceps-hamstrings and quadriceps-gastrocnemius co-contractions were progressively increased and their contribution to anterior shear force was quantified. The electromyography-informed method produced co-contraction indexes more consistent with electromyography data than the optimization-based method. The muscles that presented the largest contribution to peak anterior shear force were the gastrocnemii, likely from their wrapping around the posterior aspect of the tibia. The quadriceps-hamstring co-contraction provided a protective effect on the ACL and reduced peak anterior shear force by 292N with a co-contraction index increase of 25% from baseline (31%), whereas a quadriceps-gastrocnemius co-contraction index of 61% increased peak anterior shear force by 797N compared to baseline (42%). An increase in gastrocnemius contraction, which might be required to protect the ankle from the impact with the ground, produced a large quadriceps-gastrocnemius co-activation, increasing peak anterior shear force. A better understanding of each muscle's contribution to anterior shear force and, consequently, anterior cruciate ligament tension may inform subject-specific injury prevention programs and rehabilitation protocols.