FORD, K. R., G. D. MYER, and T. E. HEWETT. Valgus Knee Motion during Landing in High School Female and Male Basketball Players. Med. Sci. Sports Exerc., Vol. 35, No. 10, pp. 1745–1750, 2003.
Purpose: The 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.
Methods: Eighty-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.
Results: Female 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.
Conclusion: The 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.
The knee is one of the most commonly injured areas of the body in female athletes. Injuries to the knee can account for up to 91% of season ending injuries and 94% of injuries requiring surgery in female basketball players (5). Season ending knee injuries can occur at a rate as high as 1 in 10 athletes annually at the intercollegiate level, which can account for 15,000 female athletes lost each year to athletic participation (16,25). Anterior cruciate ligament (ACL) ruptures are debilitating, often season-ending, knee injuries in female athletes that occur at a higher rate than in male athletes. In a study on the incidence of injury in collegiate basketball, Malone et al. (21) reported the ACL injury incidence was approximately sixfold higher in female than male players. Numerous studies have found a similar four- to sixfold higher incidence of knee injuries in females compared with males participating in jumping and cutting sports (5,8,11,16,18). This higher incidence of injury, combined with the dramatic increase in female participation that has occurred since the inception of Title IX in 1972, has led to a geometric increase in the number of ACL injuries in female athletes over the last three decades. In 2002, there were 452,728 female participants in high school basketball in the United States (26). At a rate of approximately 1 in 65 ACL injuries per participant annually, approximately 7000 ACL ruptures occur in high school female basketball players in the United States on an annual basis (16,30).
Significant attention has focused on ACL research over the past two decades resulting in more than 2000 scientific articles published outlining injury incidence, mechanism, surgical repair techniques, rehabilitation, and prevention of injury to this important knee ligament (9). The focus on ACL injury, especially on injury mechanism and prevention, is warranted considering that the cost of reconstructing and rehabilitating the ACL in these athletes at a conservative cost of $17,000 per patient would amount to $119 million annually spent on female high school basketball players alone (16). This is in addition to the traumatic effect to these individuals of potential loss of entire seasons of sports participation, possible scholarship funding, and significantly lowered academic performance (10).
ACL injuries result from either a contact or noncontact mechanisms. Noncontact ACL injuries account for more than two thirds of ACL injuries (3,12,16,23). The noncontact mechanism usually involves a deceleration before a change of direction or landing with the knee between 20° and full extension (3,23). Powell and Barber-Foss (27) found that rebounding the basketball was the cause of the majority of injures to female basketball players.
The potential mechanisms underlying the injury rate differences between genders can be categorized into three basic theories: anatomical, hormonal, and biomechanical. The risk of an ACL injury is likely multifactorial with no single causative factor being solely responsible for the increased rate. Anatomical risk factors that have been proposed include increased Q-angle, narrower femoral notch, and increased hypermobility or laxity in female athletes. Few, if any, anatomical variables, however, has been directly correlated with an increased risk of noncontact ACL injury (12). Decreased ligament strength or altered strength or muscle recruitment due to cyclic changes in female hormones may be possible contributors to the increased injury rates in female athletes (14). The experimental findings regarding the influence of hormones on injury risk are limited and remain controversial.
The third possible mechanism responsible for the gender differences in knee injuries is biomechanical or neuromuscular imbalances in female athletes. Three neuromuscular deficits related to biomechanical or neuromuscular coordination include ligament dominance, quadriceps dominance, and leg dominance (15). Andrews and Axe (1) first introduced the concept of ligament dominance whereby the lower extremity musculature does not adequately absorb the forces during a sports maneuver resulting in excessive loading of the knee ligaments, especially the ACL, which resists anterior tibial translation and knee valgus. Ligament dominance often results in high ground reaction forces, valgus knee moments, and excessive knee valgus motion. Quadriceps dominance is an imbalance between the recruitment patterns of the knee flexors and extensors. Females tend to rely on their quadriceps over their hamstrings to produce dynamic knee stability during jumping and landing activities (17,18). Leg dominance is an imbalance between muscular strength and recruitment patterns on opposite limbs, with one side often demonstrating greater dynamic control (17,19). Over-reliance on one limb can put greater stress on that knee, whereas the weaker side might not be able to effectively absorb the high forces associated with sporting activities.
Young athletes participating in high school sports are of particular interest due in part to the increase in sport participation at the high school level and the relative lack of literature related to mechanisms of injury at this age. With close to 3 million female high school sport participants and basketball players making up the largest percentage of these participants, additional research should focus on this population and identify specific mechanisms of injury within this group (26). The 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.