Female athletes suffer a disproportionate number of knee injuries in running and cutting sports compared to their male counterparts of the same age. The medical community has done considerable research on the reasons for this increase of knee injuries in females, and whether the number can be reduced. Knee injuries in female athletes range from slight sprains and bone contusions to more severe anterior cruciate ligament (ACL) injuries and meniscal tears, which often require surgery. These types of injuries can cause over a year of missed time from competitive play, and significant expense through the surgical and rehabilitation process.
Knee injuries can be divided into two categories: contact and non-contact injuries. In contact injuries, the impact of a collision results in the injury. This type of injury is often inevitable based on the force of the collision, and the difference between male and female athletes is often negligible. However, non-contact injuries tell a different story. These injuries occur when the athlete hurts their knee without being contacted by another athlete. It has been found that females are four to eight times more susceptible to sustain non-contact knee injuries than males.
Why the disparity? Research divides the risk of athlete’s injury into two factors—intrinsic and extrinsic. Intrinsic factors are essentially a person’s genetics. As it relates to knee injury risk, these factors would include the athlete’s Q-angle (hip to knee angle), their hormonal cycle, and foot-type. Extrinsic factors are external things an athlete could change in order to become more or less successful. Females tend to put more stress on the ligaments of their knee rather than rely on the supporting musculature which is also weaker than the males.
Intrinsic factors are inherent to a person and are difficult to change or alter. For example, females have a wider hip to knee ratio, on average, than males. This increased angle may put the knee in a more compromising position when jumping, landing, or pivoting. Also, ample research has been done on the hormonal cycle of females and its correlation to knee injuries. It is intuitive that when a female athlete produces more of the hormone relaxin, there is an increase in joint laxity and a decrease in joint stability. This decrease in joint stability may put the knee more at risk to exceed its limit, causing injury. A flatter foot has been shown to aid in driving the knee more inward when squatting and landing. So, to combat this problem, the use of an over the counter orthotic device may help decrease that inward acceleration of the foot and knee which causes injury.
Female athletes have four common components in the mechanism of non-contact knee injuries. Females tend to land with their knees pointed inward, with a straighter knee, with their weight mostly or all on one foot, or with their trunk tilted outside of their center of mass. These mechanisms are controlled by the extrinsic factors of the female athletes themselves. After puberty, females typically gain increased strength in their quadriceps in the front of their legs at a disproportionate rate to the strength of their hamstrings and glute muscles in the back of their legs. This disparity in strength is accentuated by the hamstrings and glutes firing later than the quadriceps during jumping and landing movements. The combination of weaker muscles and delayed firing causes the knee to be pulled forward and inward, putting it at risk for injury.
Women usually rely more on their ligaments to stabilize the knee rather than the supporting muscles. This can lead to the knee being thrown backward into hyperextension and an injury to the ACL and/or menisci. Females also tend to be more one-legged dominant than males, with one leg stronger than the other. All of these factors are magnified by their tendency to land in a position with knees facing inward and rotating while being in a straighter position. This is attributed to having less spatial awareness (compared to males) of where their trunk is in space, causing body weight to be unequally distributed over the lower body.
After puberty, males typically gain more power and strength that is proportionate to their size. This helps control their bigger and longer body. Females, without extra training, tend to have a greater fat to muscle ratio without an increase in strength and power to control their longer body. This compounds with the other risk factors to jeopardize female athlete knee health. With less trunk control, disproportionate muscle strength, and the mechanical inclination to land in a compromising position, it is much more likely for a female athlete to sustain a knee injury.
What can we do?
Females in the at-risk category of 12-22 years of age have been shown to benefit greatly from training to correct these factors. Training programs have been found to be up to 80% successful in reducing non-contact ACL injuries. Some injuries are inevitable, but with proper training, the injury rate is significantly reduced. The focus of this type of training is to improve the female athlete’s ability, technique, strength, and balance, the extrinsic factors that greatly reduce knee injury.
If you would like to learn more about how to prevent or treat knee injuries contact Foothills Sports Medicine, your Phoenix physical therapy experts, for more details!