THE RELATIONSHIP BETWEEN HAMSTRING MUSCULO-ARTICULAR STIFFNESS AND LOWER-EXTREMITY BODY COMPOSITION

The purpose of this study was to compare hamstring musculo-articular stiffness (MAS) and lower extremity (LE) body composition in the dominant (D) and non-dominant (ND) legs of men and women, and then to examine relationships between MAS and LE body composition while controlling for sex. No differences in MAS or LE body composition were found between D and ND legs in either sex. Males demonstrated greater MAS and LE % lean mass (%LM) than females, while females had greater LE % fat mass (%FM) than males. The combination of sex and %FM explained ~60% of the variance in MAS, while ~31% of the variance could be attributed to sex alone. Findings suggest that between-sex differences may potentially mask relationships between MAS and the factors influencing this measure, highlighting the need for future sex-stratified designs

HAMSTRING STIFFNESS IS RELATED TO ANTERIOR TIBIAL TRANSLATION WHEN TRANSITIONING FROM NON-WEIGHT BEARING TO WEIGHT BEARING

Anterior tibial translation (ATT) loads the anterior cruciate ligament (ACL) as the knee transitions from non-weight bearing (NWB) to weight bearing (WB). Therefore, any factors able to effectively reduce ATT during initial WB would theoretically reduce ACL loading. This study evaluated the extent to which hamstring musculo-articular stiffness (KHAM) is associated with ATT as the knee transitions from NWB to WB in 10 healthy females (19.9 ± 1.5 yrs, 1.65 ± 0.06 m, 62.3 ± 6.3 kg). Linear regression revealed that KHAM predicted 48.6% of the variance in ATT (R2 = .486, p = .025), with higher KHAM being associated with less ATT. KHAM is modifiable through training, and thus may be an important factor to consider from ACL injury prevention and rehabilitation perspectives

The differential effects of fatigue on reflex response timing and amplitude in males and females

We examined the effects of fatigue on patellar tendon reflex responses in males and females. A spring-loaded reflex hammer elicited a standardized tendon tap with the knee positioned in an isokinetic dynamometer and flexed to 85°. We recorded vastus lateralis activity (SEMG) and knee extension force production at the distal tibia (force transducer). Reflex trials were performed before and after (immediate, 2, 4, and 6 min) an isokinetic fatigue protocol to 50% MVC (90°/s). For each event, pre-motor time (PMT), electromechanical delay (EMD), and total motor time (TMT) were obtained, as well as EMG amplitude (EMGamp), time to peak EMG (EMGtpk), peak force amplitude (Famp), time to peak force (Ftpk), EMG:force ratio (E:F), and rate of force production (Frate=N/ms). TMT increased significantly in females following fatigue, while males showed no change. The increased TMT was due to an increased EMD with fatigue, while PMT was unaffected. EMGamp and Famp were somewhat diminished in females yet significantly augmented in males following fatigue, likely accounting for the differential changes in EMD noted. Results suggest males and females may respond differently to isokinetic fatigue, with males having a greater capacity to compensate for contraction force failure when responding to mechanical perturbations

Anatomic Alignment, Menstrual Cycle Phase, and The Risk of Anterior Cruciate Ligament Injury

The fundamental basis for knee trauma prevention research is that injuries occur in patterns reflecting the underlying causes. Understanding the underlying causes or risk factors for one of the more severe sport-related knee injuries, an anterior cruciate ligament (ACL) disruption, is important for developing intervention strategies, identifying those at increased risk of this injury, and allowing targeted interventions. The risk factors for ACL injury have been considered either internal or external to an individual. In the following review, we focus on what is known about 2 categories of internal risk factors: an athlete's anatomy and menstrual cycle phase

Effects of Pronated and Supinated Foot Postures on Static and Dynamic Postural Stability

Context: The foot is the most distal segment in the lower extremity chain and represents a relatively small base of support on which the body maintains balance (particularly in single-leg stance). Although it seems reasonable that even minor biomechanical alterations in the support surface may influence postural-control strategies, the implications of a hypermobile or hypomobile foot on balance have received little attention to date.Objective: To determine if supinated and pronated foot types influence measures of static and dynamic balance.Design: Participants were assigned to 1 of 3 groups depending on foot type, as defined by navicular-drop measures: pronated (=10 mm), neutral (5–9 mm), or supinated (=4 mm). Measures of static and dynamic balance were obtained for each participant and compared across groups.Setting: Sports medicine and athletic training research laboratory.Patients or Other Participants: Sixteen individuals with pronated (navicular drop = 13.0 ± 3.7 mm), neutral (navicular drop = 6.2 ± 1.1 mm), or supinated (navicular drop = 2.2 ± 1.7 mm) foot postures volunteered to participate in the study.Main Outcome Measure(s): We used the Chattecx Balance System to measure center of balance, stability index, and postural sway during static single-limb stance under eyes-open and eyes-closed conditions. Center of balance was defined as the point on the foot at which the body weight was equally distributed between the medial-lateral and anterior-posterior quadrants and was recorded in centimeters. Stability index was defined as the mean deviation in sway around the center of balance. Postural sway was expressed as the maximum sway distance recorded (cm) in the medial-lateral and anterior-posterior directions. The Star Excursion Balance Test was used to measure dynamic balance, which was reported as the reach distance (cm) in each of the 8 directions tested. The average of 3 trials of each measure was calculated and normalized to the subject's height.Results: We found no difference in center of balance or postural sway as a function of foot type. The stability index was greater in pronators than in supinators, but neither group was different from those with neutral foot types. Dynamic reach differed among groups but only in some directions. Generally, pronators reached farther in the anterior and anterior medial directions and supinators reached farther in the posterior and posterio-lateral directions. In the lateral direction, supinators reached farther than pronators but not farther than neutrals.Conclusions: Our results suggest that postural stability is affected by foot type under both static and dynamic conditions. These differences appear to be related to structural differences as opposed to differences in peripheral input. These effects should be considered when clinicians use such balance measures to assess injury deficits and recovery

Clinical and Instrumented Measurements of Hip Laxity and Their Associations With Knee Laxity and General Joint Laxity

Context: Hip-joint laxity may be a relevant anterior cruciate ligament injury risk factor. With no devices currently available to measure hip laxity, it is important to determine if clinical measurements sufficiently capture passive displacement of the hip.Objective: To examine agreement between hip internal-external–rotation range of motion measured clinically (HIERROM) versus internal-external–rotation laxity measured at a fixed load (HIERLAX) and to determine their relationships with knee laxity (anterior-posterior [KAPLAX], varus-valgus [KVVLAX], and internal-external rotation [KIERLAX]) and general joint laxity (GJL).Design: Cross-sectional study.Setting: Controlled research laboratory.Patients or Other Participants: Thirty-two healthy adults (16 women, 16 men; age = 25.56 ± 4.08 years, height = 170.94 ± 10.62 cm, weight = 68.86 ± 14.89 kg).Main Outcome Measure(s): Participants were measured for HIERROM, HIERLAX at 0° and 30° hip flexion (-10 Nm, 7 Nm), KAPLAX (-90 N to 133 N), KVVLAX (±10 Nm), KIERLAX (±5 Nm), and GJL. We calculated Pearson correlations and 95% limits of agreement between HIERROM and HIERLAX_0° and HIERLAX_30°. Correlation analyses examined the strength of associations between hip laxity, knee laxity, and GJL.Results: The HIERROM and HIERLAX had similar measurement precision and were strongly correlated (r > 0.78). However, HIERROM was systematically smaller in magnitude than HIERLAX at 0° (95% limits of agreement = 29.0° ± 22.3°) and 30° (21.4° ± 19.3°). The HIERROM (r = 0.51–0.66), HIERLAX_0° (r = 0.52–0.69) and HIERLAX_30° (r = 0.53–0.76) were similarly correlated with knee laxity measures and GJL. The combinations of KVVLAX and either HIERROM, HIERLAX_0°, or HIERLAX_30° (R2 range, 0.42–0.44) were the strongest predictors of GJL.Conclusions: Although HIERROM and HIERLAX differed in magnitude, they were measured with similar consistency and precision and were similarly correlated with knee laxity and GJL measures. Individuals with greater GJL also had greater hip laxity. These findings are relevant to clinicians and investigators conducting prospective risk factor studies, given the need for accessible, efficient, and low-cost alternatives for characterizing an individual's laxity profile

Multivariate Analysis of the Risk Factors for First-Time Noncontact ACL Injury in High School and College Athletes: A Prospective Cohort Study With a Nested, Matched Case-Control Analysis

Background: Multivariate analysis that identifies the combination of risk factors associated with anterior cruciate ligament (ACL) trauma is important because it provides insight into whether a variable has a direct causal effect on risk or an indirect effect that is mediated by other variables. It can also reveal risk factors that might not be evident in univariate analyses; if a variable’s effect is moderated by other variables, its association with risk may be apparent only after adjustment for the other variables. Most important, multivariate analyses can identify combinations of risk factors that are more predictive of risk than individual risk factors.Hypothesis: A diverse combination of risk factors predispose athletes to first-time noncontact ACL injury, and these relationships are different for male and female athletes.Study Design: Case-control study; Level of evidence, 3.Methods: Athletes competing in organized sports at the high school and college levels participated in this study. Data from injured subjects (109 suffering an ACL injury) and matched controls (227 subjects) from the same athletic team were analyzed with multivariate conditional logistic regression to examine the effects of combinations of variables (demographic characteristics, joint laxity, lower extremity alignment, strength, and personality traits) on the risk of suffering their first ACL injury and to construct risk models.Results: For male athletes, increases in anterior-posterior displacement of the tibia relative to the femur (knee laxity), posterior knee stiffness, navicular drop, and a decrease in standing quadriceps angle were jointly predictive of suffering an ACL injury. For female athletes the combined effects of having a parent who had suffered an ACL injury and increases in anterior-posterior knee laxity and body mass index were predictive of ACL injury.Conclusion: Multivariate models provided more information about ACL injury risk than individual risk factors. Both male and female risk models included increased anterior-posterior knee laxity as a predictor of ACL injury but were otherwise dissimilar

Non-contact ACL injuries in female athletes: an International Olympic Committee current concepts statement

The incidence of anterior cruciate ligament (ACL) injury remains high in young athletes. Because female athletes have a much higher incidence of ACL injuries in sports such as basketball and team handball than male athletes, the IOC Medical Commission invited a multidisciplinary group of ACL expert clinicians and scientists to (1) review current evidence including data from the new Scandinavian ACL registries; (2) critically evaluate high-quality studies of injury mechanics; (3) consider the key elements of successful prevention programmes; (4) summarise clinical management including surgery and conservative management; and (5) identify areas for further research. Risk factors for female athletes suffering ACL injury include: (1) being in the preovulatory phase of the menstrual cycle compared with the postovulatory phase; (2) having decreased intercondylar notch width on plain radiography; and (3) developing increased knee abduction moment (a valgus intersegmental torque) during impact on landing. Well-designed injury prevention programmes reduce the risk of ACL for athletes, particularly women. These programmes attempt to alter dynamic loading of the tibiofemoral joint through neuromuscular and proprioceptive training. They emphasise proper landing and cutting techniques. This includes landing softly on the forefoot and rolling back to the rearfoot, engaging knee and hip flexion and, where possible, landing on two feet. Players are trained to avoid excessive dynamic valgus of the knee and to focus on the "knee over toe position" when cutting

Bilateral Asymmetries in Clinical Measures of Lower-Extremity Anatomic Characteristics

Objective: To quantify side-to-side differences in lower-extremity anatomic characteristics, and to compare the magnitude of left-right differences with the measurement error for each variable.Design: Descriptive.Setting: Applied neuromechanics research laboratory.Participants: One hundred healthy participants (50 male, 50 females).Assessment of Risk Factors: One examiner measured 14 anatomic characteristics on the left and right lower extremities. The value on the left was subtracted from value on the right, and 68% (±1 SD) and 95% (±1.96 SD) confidence intervals were constructed around the mean differences, respectively. These values were compared with the examiner's absolute measurement error for each measure.Main Outcome Measurements: Total leg length, pelvic angle, hip anteversion, standing and supine quadriceps angle, tibiofemoral angle, knee laxity, genu recurvatum, femur and tibia length, tibial torsion, rearfoot angle, and navicular drop.Results: Left-right differences in pelvic angle, tibial torsion, and navicular drop exceeded the measurement error in more than 32% of the cases. Five to thirty-two percent of the cases had left-right differences exceeding the measurement error for hip anteversion, standing and supine quadriceps angle, tibiofemoral angle, knee laxity, genu recurvatum, and femur length. Asymmetries in limb length were not observed.Conclusions: Bilateral asymmetries exist in many clinical alignment characteristics, indicating that measurements taken on one limb may not be representative of the contralateral limb. We recommend measuring both extremities when anatomic characteristics are included as part of preseason screenings and prospective study designs to ensure valid comparison