Over the past 20 years, there has been a steady increase of female participation in sports at both the high school and collegiate levels. This growth in participation has proven to be a valuable outlet for which females can develop, practice and demonstrate athletic abilities.
Compared to their male counterparts, however, female athletes have been statistically more prone to a certain type of injury. This injury is a particularly daunting hurdle that has the potential of blocking further athletic performance.
This hurdle, in the form of an ACL (anterior cruciate ligament) tear, can take six to eight months to recover from before the athlete is back on track. Unfortunately, it is a hurdle that appears to be disproportionately high in female athletic populations.
As early as the mid 1980s to the early 1990s, statistics have shown a gender-biased knee injury rate with females vs. males. These injury rates, documented by the NCAA, NATA and various independent studies, show a much higher injury rate at the knee in females compared to males competing in comparable sports.
One would think that injury to the ACL would necessitate some sort of traumatic contact with another athlete, such as in football or soccer. While contact ACL injuries are prevalent, many of these injuries occur in sports such as volleyball, basketball and gymnastics, which are typically thought of as no/low contact sports. This initially led many researchers, physicians and physical therapists to focus their attention on other factors that could be a contributing factor to non-contact ACL injuries.1
Knowing the Causes
Potential explanations for the cause of this higher injury rate were many and varied. Initially, attention was focused on female-specific biology. It was proposed that hormonal factors and fluctuating levels of estrogen before ovulation could affect ligament laxity and thus affect injury rate. Oral contraceptives were also studied to investigate their effects on ligament laxity and injury rates. It was suggested that such contraceptives could decrease ligament laxity and thereby decrease injury rate.2
Lower-extremity morphology or the shape, appearance or alignment of bone structures has continued to be an area of focus with female knee injuries. Theories have been proposed in which the width of a bony crevice at the lower end of the thigh bone (femoral intercondylar notch) can affect ligament stability and injury rate. The Q-angle, or the angle of the thigh muscle (quadriceps) pulling on the kneecap and lower leg bone, has also been researched.
Other researchers have focused extensively on discrepancies in strength or muscle imbalances in female athletes. Most studies focused on the strength of the two large muscle groups crossing the knee joint-the hamstrings and quadriceps.
The strength of these groups was compared in a ratio appropriately called the H/Q (hamstring/quadriceps) ratio. The premise of the investigations is that if one of these muscle groups were weaker than the other, the H/Q ratio would be affected. This would in turn affect the dynamic stability of the knee and make the knee more vulnerable to injury.
While the range of injury risks included hormones, contraceptives, female alignment/bone structure, muscle imbalances and joint/ligament laxity, they all had one thing in common. All of these studies focused on the effects of all these variables on one plane of motion-the sagittal plane.
This anterior-to-posterior (front-to-back) plane of motion was studied almost exclusively due to the ACL’s proposed biomechanical role at resisting shear force at the knee. While most all the studied injury risks had the real potential to contribute to knee injury, there was an underlying premise that ACL injuries occurred in only the sagittal plane of motion.
Studying the Biomechanics
Those working with athletes who sustained non-contact ACL injuries recognized that the mechanism of injury rarely occurred in exclusively the sagittal plane of motion. The review of a patient’s history and mechanism of injury often were more complex than that of an injury sustained in purely a sagittal plane.
Forces imposed upon the knee during non-contact injury typically involved multiple planes of motion. Studies soon began to look outside the somewhat tunnel vision of sagittal plane injury and began to investigate “multiplanar” involvement.
Studies emerged producing strong evidence that non-contact ACL injuries likely occur as a result of excess motion in the sagittal, frontal and/or transverse planes of motion.3 Injury to the ACL began to be looked upon in a much more dynamic, multidirectional fashion.
Video analysis of athletes who sustained an ACL injury proved to be a valuable biomechanical tool for the study of ACL injury. Review of these videos produced a common theme for those unfortunate athletes who sustained injury.
A majority of the athletes were prone to having their legs fall into a particularly vulnerable position, which has since acquired the phrase “dynamic valgus collapse” (DVC). This valgus collapse involves the movement of the leg/knee in multiple planes of motion.
The thigh bone (femur) falls and rotates in toward the opposite leg (adduction and internal rotation). The lower leg bones (tibia and fibula) rotate out (external rotation). All of this happens simultaneously while the knee bends and falls in (flexion with valgus force).
Think of the knee going into a knock-knee position (falling in) while the thigh bone rotates in and the lower leg bones rotate out. The result is an opposing twisting force meeting a collapsing-type force at the knee.
Video review of individuals who sustained an ACL injury during competitive sporting events has shown a gender-biased injury risk toward females. During basketball events, researchers found females to be more than five times more prone than males to dynamic valgus collapse.4
This valgus collapse was seen during cutting maneuvers, deceleration maneuvers, initial contact from jumping, semi-squat positions and push-off type motions in lateral maneuvers. Later studies confirmed this phenomenon of females having greater valgus collapse.5
How should physical therapists address this phenomenon of DVC? Since the mechanism of injury essentially involves a fault with movement, interventions typically involve neuromuscular re-education/control to correct the faulty movement pattern.
Depending on the patient/athlete at hand and the data obtained from your evaluation, there may be multiple causes for this neuromuscular deficiency.
Some patients may have a balance deficit in conjunction with poor core strength. They may in turn require a plan of care and home program tailored toward balance training, dynamic stabilization and perturbation exercises, as well as core/lumbar stabilization. Others may present with functional strength impairments or poor jumping technique. These patients may benefit from plyometric training and jump retraining/kinesthesia exercises.
The cause of the functional strength deficit needs to be addressed and may include proximal musculature such as the gluteus medius. This can help control eccentric hip adduction and internal rotation, both of which are components of dynamic valgus collapse. Training the quadriceps and hamstrings to co-contract with the more proximal hip musculature is also of vital importance.6
As with any plan of care, function should be a driving force, and exercises should be as sport-specific as possible. This may require varying degrees of agility training and/or endurance training, depending on the physical and metabolic demands of the sport at hand.
If a patient presents in your clinic with movement patterns similar to that noted with DVC, you may have the potential to prevent an unfortunate injury in the form of an ACL tear. If a patient has already had an ACL tear, retraining this impairment will do wonders for preventing further re-injury. This could in turn save a patient from a six- to eight-month hurdle blocking athletic participation.
1. Bernier, M. (2010). Injuries in Youth Sports. Instructional course lecture by MEDS PDN, p. 43-48.
2. Martineau, P. (2004). Clinical Journal of Sport Medicine, Vol. 14, 281-286.
3. Quatman, C., & Hewett, T. (2009). The ACL injury controversy: Is “valgus collapse” a sex-specific mechanism? British Journal of Sports Medicine, 43(5), 328-335.
4. Hewett, E., Bahr, R., et al. (2007). Mechanisms of anterior cruciate ligament injury in basketball: Video analysis. American Journal of Sports Medicine, 35, 359.
5. Barry, P., Boden, J., Torg, S., Knowles, S., & Hewett, T. (2009). Video analysis of anterior cruciate ligament injury. American Journal of Sports Medicine, 37, 252.
6. Van Ingen Schenau, G., Bobbert, M., & Rozendal, R. (1987). The unique action of bi-articular muscles in complex movements. Journal of Anatomy, 155, 1-5.
Ben Wiggin works at Huggins Hospital Back Bay Rehabilitation in Wolfeboro and Tamworth, NH. He is also one of the team therapists for student athletes at Brewster Academy in Wolfeboro, NH, dealing with the treatment and prevention of sport-specific injuries. He has clinical interest in orthopedics, sports rehabilitation and manual interventions.