Kevin R. Ford

Biomechanical Measures of Neuromuscular Control and Valgus Loading of the Knee Predict Anterior Cruciate Ligament Injury Risk in Female Athletes A Prospective Study

Background Female athletes participating in high-risk sports suffer anterior cruciate ligament injury at a 4- to 6-fold greater rate than do male athletes. Hypothesis Prescreened female athletes with subsequent anterior cruciate ligament injury will demonstrate decreased neuromuscular control and increased valgus joint loading, predicting anterior cruciate ligament injury risk. Study Design Cohort study; Level of evidence, 2. Methods There were 205 female athletes in the high-risk sports of soccer, basketball, and volleyball prospectively measured for neuromuscular control using 3-dimensional kinematics (joint angles) and joint loads using kinetics (joint moments) during a jump-landing task. Analysis of variance as well as linear and logistic regression were used to isolate predictors of risk in athletes who subsequently ruptured the anterior cruciate ligament. Results Nine athletes had a confirmed anterior cruciate ligament rupture; these 9 had significantly different knee posture and loading compared to the 196 who did not have anterior cruciate ligament rupture. Knee abduction angle (P <. 05) at landing was 8° greater in anterior cruciate ligament-injured than in uninjured athletes. Anterior cruciate ligament-injured athletes had a 2.5 times greater knee abduction moment (P <. 001) and 20% higher ground reaction force (P <. 05), whereas stance time was 16% shorter; hence, increased motion, force, and moments occurred more quickly. Knee abduction moment predicted anterior cruciate ligament injury status with 73% specificity and 78% sensitivity; dynamic valgus measures showed a predictive r2 of 0.88. Conclusion Knee motion and knee loading during a landing task are predictors of anterior cruciate ligament injury risk in female athletes. Clinical Relevance Female athletes with increased dynamic valgus and high abduction loads are at increased risk of anterior cruciate ligament injury. The methods developed may be used to monitor neuromuscular control of the knee joint and may help develop simpler measures of neuromuscular control that can be used to direct female athletes to more effective, targeted interventions.

Valgus Knee Motion during Landing in High School Female and Male Basketball Players

PURPOSEnThe purpose of this study was to utilize three-dimensional kinematic (motion) analysis to determine whether gender differences existed in knee valgus kinematics in high school basketball athletes when performing a landing maneuver. The hypothesis of this study was that female athletes would demonstrate greater valgus knee motion (ligament dominance) and greater side-to-side (leg dominance) differences in valgus knee angle at landing. These differences in valgus knee motion may be indicative of decreased dynamic knee joint control in female athletes.nnnMETHODSnEighty-one high school basketball players, 47 female and 34 male, volunteered to participate in this study. Valgus knee motion and varus-valgus angles during a drop vertical jump (DVJ) were calculated for each subject. The DVJ maneuver consisted of dropping off of a box, landing and immediately performing a maximum vertical jump. The first landing phase was used for the analysis.nnnRESULTSnFemale athletes landed with greater total valgus knee motion and a greater maximum valgus knee angle than male athletes. Female athletes had significant differences between their dominant and nondominant side in maximum valgus knee angle.nnnCONCLUSIONnThe absence of dynamic knee joint stability may be responsible for increased rates of knee injury in females but is not normally measured in athletes before participation. No method for accurate and practical screening and identification of athletes at increased risk of ACL injury is currently available to target those individuals that would benefit from neuromuscular training before sports participation. Prevention of female ACL injury from five times to equal the rate of males would allow tens of thousands of young females to avoid the potentially devastating effects of ACL injury on their athletic careers.

Anterior Cruciate Ligament Injuries in Female Athletes Part 1, Mechanisms and Risk Factors

The mechanism underlying gender disparity in anterior cruciate ligament injury risk is likely multifactorial in nature. Several theories have been proposed to explain the mechanisms underlying the gender difference in anterior cruciate ligament injury rates. These theories include the intrinsic variables of anatomical, hormonal, neuromuscular, and biomechanical differences between genders and extrinsic variables. Identification of both extrinsic and intrinsic risk factors associated with the anterior cruciate ligament injury mechanism may provide direction for targeted prophylactic treatment to high-risk individuals.

Neuromuscular training improves performance and lower-extremity biomechanics in female athletes.

The purpose of this study was to examine the effects of a comprehensive neuromuscular training program on measures of performance and lower-extremity movement biomechanics in female athletes. The hypothesis was that significant improvements in measures of performance would be demonstrated concomitant with improved biomechanical measures related to anterior cruciate ligament injury risk. Forty-one female basketball, soccer, and volleyball players (age, 15.3 ± 0.9 years; weight, 64.8 ± 9.96 kg; height, 171.2 ± 7.21 cm) underwent 6 weeks of training that included 4 main components (plyometric and movement, core strengthening and balance, resistance training, and speed training). Twelve age-, height-, and weight-matched controls underwent the same testing protocol twice 6 weeks apart. Trained athletes demonstrated increased predicted 1 repetition maximum squat (92%) and bench press (20%). Right and left single-leg hop distance increased 10.39 cm and 8.53 cm, respectively, and vertical jump also increased from 39.9 ± 0.9 cm to 43.2 ± 1.1 cm with training. Speed in a 9.1-m sprint improved from 1.80 ± 0.02 seconds to 1.73 ± 0.01 seconds. Pre- and posttest 3-dimensional motion analysis demonstrated increased knee flexion-extension range of motion during the landing phase of a vertical jump (right, 71.9 ± 1.48 to 76.9 ± 1.48; left, 71.3 ± 1.58 to 77.3 ± 1.48). Training decreased knee valgus (28%) and varus (38%) torques. Control subjects did not demonstrate significant alterations during the 6-week interval. The results of this study support the hypothesis that the combination of multiple-injury prevention-training components into a comprehensive program improves measures of performance and movement biomechanics.

Anterior Cruciate Ligament Injuries in Female Athletes Part 2, A Meta-analysis of Neuromuscular Interventions Aimed at Injury Prevention

Female athletes have a 4 to 6 times higher incidence of anterior cruciate ligament injury than do male athletes participating in the same landing and pivoting sports. This greater risk of anterior cruciate ligament injury, coupled with a geometric increase in participation (doubling each decade), has led to a significant rise in anterior cruciate ligament injuries in female athletes. The gender gap in anterior cruciate ligament injury, combined with evidence that the underpinnings of this serious health problem are neuromuscular in nature, leads to the development of neuromuscular interventions designed to prevent injury. A systematic review of the published literature yielded 6 published interventions targeted toward anterior cruciate ligament injury prevention in female athletes. Four of 6 significantly reduced knee injury incidence, and 3 of 6 significantly reduced anterior cruciate ligament injury incidence in female athletes. A meta-analysis of these 6 studies demonstrates a significant effect of neuromuscular training programs on anterior cruciate ligament injury incidence in female athletes (test for overall effect, Z = 4.31, P< .0001). Examination of the similarities and differences between the training regimens gives insight into the development of more effective and efficient interventions. The purpose of this “Current Concepts” review is to highlight the relative effectiveness of these interventions in reducing anterior cruciate ligament injury rates and to evaluate the common training components between the training studies. In addition, the level of rigor of these interventions, the costs and the difficulty of implementation, the compliance with these interventions, and the performance benefits are discussed. This review summarizes conclusions based on evidence from the common components of the various interventions to discuss their potential to reduce anterior cruciate ligament injury risk and assess their potential for combined use in more effective and efficient intervention protocols.

Biomechanical measures during landing and postural stability predict second anterior cruciate ligament injury after anterior cruciate ligament reconstruction and return to sport.

Background Athletes who return to sport participation after anterior cruciate ligament reconstruction (ACLR) have a higher risk of a second anterior cruciate ligament injury (either reinjury or contralateral injury) compared with non—anterior cruciate ligament— injured athletes. Hypotheses Prospective measures of neuromuscular control and postural stability after ACLR will predict relative increased risk for a second anterior cruciate ligament injury. Study Design Cohort study (prognosis); Level of evidence, 2. Methods Fifty-six athletes underwent a prospective biomechanical screening after ACLR using 3-dimensional motion analysis during a drop vertical jump maneuver and postural stability assessment before return to pivoting and cutting sports. After the initial test session, each subject was followed for 12 months for occurrence of a second anterior cruciate ligament injury. Lower extremity joint kinematics, kinetics, and postural stability were assessed and analyzed. Analysis of variance and logistic regression were used to identify predictors of a second anterior cruciate ligament injury. Results Thirteen athletes suffered a subsequent second anterior cruciate ligament injury. Transverse plane hip kinetics and frontal plane knee kinematics during landing, sagittal plane knee moments at landing, and deficits in postural stability predicted a second injury in this population (C statistic = 0.94) with excellent sensitivity (0.92) and specificity (0.88). Specific predictive parameters included an increase in total frontal plane (valgus) movement, greater asymmetry in internal knee extensor moment at initial contact, and a deficit in single-leg postural stability of the involved limb, as measured by the Biodex stability system. Hip rotation moment independently predicted second anterior cruciate ligament injury (C = 0.81) with high sensitivity (0.77) and specificity (0.81). Conclusion Altered neuromuscular control of the hip and knee during a dynamic landing task and postural stability deficits after ACLR are predictors of a second anterior cruciate ligament injury after an athlete is released to return to sport.

Decrease in Neuromuscular Control About the Knee with Maturation in Female Athletes

BACKGROUNDnCompared with male athletes, female athletes demonstrate increased dynamic valgus angulation of the knee during landing from a jump, although prior to maturation male and female athletes have similar forces and motions about the knee when they land from a jump. Our hypothesis was that musculoskeletal changes that accompany maturation result in poor neuromuscular control of the knee joint in female athletes.nnnMETHODSnOne hundred and eighty-one middle-school and high-school soccer and basketball players-100 girls and eighty-one boys-participated in the study. Dynamic control of the knee joint was measured kinematically by assessing medial knee motion and the lower-extremity valgus angle and was measured kinetically by assessing knee joint torques; the values were then compared between female and male athletes according to maturational stage. Lower-extremity bone length was measured with three-dimensional kinematic analysis.nnnRESULTSnFollowing the onset of maturation, the female athletes landed with greater total medial motion of the knees and a greater maximum lower-extremity valgus angle than did the male athletes. The girls also demonstrated decreased flexor torques compared with the boys as well as a significant difference between the maximum valgus angles of their dominant and nondominant lower extremities after maturation.nnnCONCLUSIONSnAfter girls mature, they land from a jump differently than do boys, as measured kinematically and kinetically.

The Effects of Plyometric Versus Dynamic Stabilization and Balance Training on Lower Extremity Biomechanics

Background Neuromuscular training that includes both plyometric and dynamic stabilization/balance exercises alters movement biomechanics and reduces ACL injury risk in female athletes. The biomechanical effects of plyometric and balance training utilized separately are unknown. Hypothesis A protocol that includes balance training without plyometric training will decrease coronal plane hip, knee, and ankle motions during landing, and plyometric training will not affect coronal plane measures. The corollary hypothesis was that plyometric and balance training effects on knee flexion are dependent on the movement task tested. Study Design Controlled laboratory study. Methods Eighteen high school female athletes participated in 18 training sessions during a 7-week period. The plyometric group (n= 8) performed maximum-effort jumping and cutting exercises, and the balance group (n = 10) used dynamic stabilization/ balance exercises during training. Lower extremity kinematics were measured during the drop vertical jump and the medial drop landing before and after training using 3D motion analysis techniques. Results During the drop vertical jump, both plyometric and balance training reduced initial contact (P= .002), maximum hip adduction angle (P= .015), and maximum ankle eversion angle (P= .020). During the medial drop landing, both groups decreased initial contact (P= .002) and maximum knee abduction angle (P= .038). Plyometric training increased initial contact knee flexion (P= .047) and maximum knee flexion (P= .031) during the drop vertical jump, whereas the balance training increased maximum knee flexion (P= .005) during the medial drop landing. Conclusion Both plyometric and balance training can reduce lower extremity valgus measures. Plyometric training affects sagittal plane kinematics primarily during a drop vertical jump, whereas balance training affects sagittal plane kinematics during single-legged drop landing. Clinical Relevance Both plyometric and dynamic stabilization/balance exercises should be included in injury-prevention protocols.

Gender Differences in the Kinematics of Unanticipated Cutting in Young Athletes

PURPOSEnAnterior cruciate ligament (ACL) injuries occur at a greater rate in adolescent females compared with males who participate in the same pivoting and jumping sports. The purpose of this study was to compare knee and ankle joint angles between males and females during an unanticipated cutting maneuver. The hypotheses were that female athletes would display increased knee abduction, increased ankle eversion and decreased knee flexion during the unanticipated cutting maneuver compared with males.nnnMETHODSnFifty-four male and 72 adolescent female middle and high school basketball players volunteered to participate in this study. Knee and ankle kinematics were calculated using three-dimensional motion analysis during a jump-stop unanticipated cut (JSUC) maneuver.nnnRESULTSnFemales exhibited greater knee abduction (valgus) angles compared with males. Gender differences were also found in maximum ankle eversion and maximum inversion during stance phase. No differences were found in knee flexion angles at initial contact or maximum.nnnCONCLUSIONnGender differences in knee and ankle kinematics in the frontal plane during cutting may help explain the gender differences in ACL injury rates. Implementation of dynamic neuromuscular training in young athletes with a focus on frontal plane motion may help prevent ACL injuries and their long-term debilitating effects.

The effects of plyometric vs. dynamic stabilization and balance training on power, balance, and landing force in female athletes.

Neuromuscular training protocols that include both plyometrics and dynamic balance exercises can significantly improve biomechanics and neuromuscular performance and reduce anterior cruciate ligament injury risk in female athletes. The purpose of this study was to compare the effects of plyometrics (PLYO) versus dynamic stabilization and balance training (BAL) on power, balance, strength, and landing force in female athletes. Either PLYO or BAL were included as a component of a dynamic neuromuscular training regimen that reduced measures related to ACL injury and increased measures of performance. Nineteen high school female athletes participated in training 3 times a week for 7 weeks. The PLYO (n = 8) group did not receive any dynamic balance exercises and the BAL (n = 11) group did not receive any maximum effort jumps during training. Pretraining vs. post-training measures of impact force and standard deviation of center of pressure (COP) were recorded during a single leg hop and hold. Subjects were also tested for training effects in strength (isokinetic and isoinertial) and power (vertical jump). The percent change from pretest to posttest in vertical ground reaction force was significantly different between the BAL and PLYO groups on the dominant side (p < 0.05). Both groups decreased their standard deviation of center of pressure (COP) during hop landings in the medial/lateral direction on their dominant side, which equalized pretested side to side differences. Both groups increased hamstrings strength and vertical jump. The results of this study suggest that both PLYO and BAL training are effective at increasing measures of neuromuscular power and control. A combination of PLYO and BAL training may further maximize the effectiveness of preseason training for female athletes.