ACL Injury in Female Athletes
Preventing anterior knee (ACL) pain in young female athletes start with understanding the primary causes that place females at risk for a number of acute and chronic knee injuries. Evidence is now showing that anatomical and hormonal differences in females may be one of the primary causes placing females at risk for knee injuries.
While girls and young women have gained significant ground in opportunities for participating and competing in sports, the increase in the numbers of young women competing in sports have also revealed an alarming increase in the rate of both acute injuries and chronic anterior knee pain. Unfortunately, the numbers of knee injuries in girls have statistically risen far above those seen in their male peers (Green, J., 2010).
While researchers are continuing to study the possible causes that may correlate to an increase risk of injury in young women, a number of factors specific to female anatomy and development have risen to the top of the list. As these factors are better understood, researchers can then develop specific programs to help reduce the risk of injuries.
Female Hip and Knee Anatomy
Although many young girls are experiencing pain in their knees, the root of some of the problems may actually originate in the pelvis/hip structure. More and more sports medicine specialists are now focusing on the pelvis/hip as one means of reducing the incidence of knee pain.
According to the authors of Women’s Health and Fitness Guide (2006), the female pelvis has a number of differences as compared to the male pelvis for the purpose of accommodating childbirth. The differences include a pelvis cavity that is shallower, wider, and more circular resulting in hip joints that are smaller and more forward facing along with an increase in anterior pelvic tilt (forward tilt of the top of the pelvis).
The forward tilt of the pelvis along with the more forward facing hip joint can predispose female athletes towards the femur being positioned with more of an inward angle and internal rotation as compared to the average male. It is this increased angle of the femur as compared to the vertical placement of the tibia that can be a source of chronic anterior knee pain.
If the core, hip, and thigh muscles are not strong enough to compensate for the increased angle of the femur to the tibia, the female athlete may be at a higher risk for patellofemoral syndrome (chronic anterior knee pain).
While anatomical structures are one part of the equation, the problems do not stop there. Add to the anatomical equation the differences in development (skeletal muscle, bone, and differences in hormones) and one can understand why there has been such an increase in knee injuries in young girls.
Prior to puberty, both males and females have approximately the same rate of knee injuries. However, during and after puberty, the statistics change significantly. So what happens in females during and after puberty that may increase their risk for knee injuries?
As males go through puberty, their musculoskeletal systems change dramatically with both an increase in the height and density of their skeletal system with a corresponding increase in muscle mass and strength. The dramatic increase in muscle mass and strength seen in males is directly related to the hormone testosterone.
Testosterone is a key component in keeping knees healthy in young males because as their skeletal systems increase in size, there is an increased strength correlation seen in their muscular system. The increase seen in their muscle strength and size is proportional to the changes seen in their skeletal system.
In other words, as a young males’ skeletal system grows, their muscles’ strength and size develop at a pace to keep up with their increased mass and skeletal growth. For example, the muscles of the quadriceps and hamstring increase in size and strength in correlation to the growth of the femur.
However, although females do have a small amount of the hormone testosterone in their bodies, the amount is not significant enough to have an effect on the size and strength of their muscles. So as the females’ skeletal system changes in height and density, their corresponding muscles do not increase in strength and mass at the same rate as a male’s muscles would.
Another factor is that while young men tend to gain lean muscle mass and lose body fat during puberty because of the hormone testosterone, girls will not only not gain lean muscle mass at the same proportion as boys, but the girls will also gain body fat increasing their total body mass (Kettles, M., Cole, C., & Wright, B., 2006).
Moving through puberty for young girls can significantly increase their body mass without a corresponding increase in lean muscle mass to effectively move and stabilize their bodies and joints. This may be the key factor affecting the knee injury rate in young females.
Any weakness in the hip and thigh muscles will correspond to problems in the knee including anterior knee pain or patellofemoral syndrome as well as the high incidence of anterior cruciate ligament tears.
Understanding this information is crucial to knowing how to effectively prevent many knee injuries in female athletes. All coaches working with young female athletes need to incorporate strength training for the core muscles, hip and pelvis, and thigh muscle groups.
How Can a Female Athlete tell if she is at Risk for Knee Injuries?
One simple test that all coaches can have their athletes perform is a two-legged jump test. An athlete with strong core, hip, and thigh muscles will land a two-legged jump with both knees and femurs parallel as she absorbs the landing and then returns to a standing position. An athlete with a muscle weakness will land the jump with an inward rotation of one or both femurs resulting in her knees buckling inwards towards each other.
To perform the test, place the athlete on a small step or bleacher about twelve inches in height. Have the athlete perform a vertical jump off of the step and have her land with two feet. No instruction should be given to the athlete as to what the coach is looking for. The coach should be positioned in front of the athlete to be able to watch the position of the knee throughout the jump and landing.
Athletes whose knees buckle inward should be identified as at risk athletes and then be placed on a strength training program specifically for core, hip, and thigh muscles. Training should include proper technique, balance training, strengthening and low intensity jump training with specific instruction on landing softly, bending the knees upon landing, and controlling knee position throughout the training (Green, J., 2010).
Female athletes with identifiable muscle weaknesses should not be allowed or asked to perform high intensity plyometric jump training (box jumps). These types of exercises could cause injury in these athletes.
Jump training for these athletes should be initiated with two foot jumps from a stable ground surface. Vertical jumps are sufficient to start with for this type of training. As these athletes progress (control their knee position) and increase in strength, they may then progress to low box jump training (with a box no more than 12 inches in height).
Importance of Balance Training to Prevent Knee Injuries
Balance training simply means having the athlete balance on progressively more unstable surfaces on one leg while increasing the difficulty of the exercise. The purpose of this exercise is to increase the stability of the athlete’s hip, knee and ankle musculature.
Traditional strength training focuses on the muscles on one side of the extremity (i.e., knee extension works the quadriceps muscle group). Stability exercises work to increase the strength and neuromuscular firing of the muscles all around the joint.
Stability exercises work all of the muscles surrounding all of the lower extremity joints (hip, knee, and ankle). This type of exercise is beneficial for working multiple joints at one time.
Stability exercises should be progressive in nature. The athlete should only proceed to the next level when she can balance successfully for thirty seconds without losing her balance. As in all exercises, the athlete should maintain a slightly bent knee, neutral pelvis, and tight core throughout the exercise.
An effective balance training progression may include:
1. Single-leg stand on stable surface (floor), eyes open
2. Single-leg stand on stable surface, eyes closed
3. Single-leg stand on stable surface raising height of knee, eyes open
4. Single-leg stand on stable surface rotating knee left to right, eyes open
5. Single-leg stand on stable surface catching and throwing a ball
6. Single-leg stand on unstable surface, eyes open
7. Single-leg stand on unstable surface, eyes closed
8. Single-leg stand on unstable surface catching and throwing a ball
A number of pieces of equipment can be used to create an unstable surface including a Dynadisc, ½ foam roll, balance board, rocker board, and proprioception board. All of these pieces are specifically designed to increase the difficulty level of balancing.
Understanding the factors that may predispose female athletes to both acute and chronic knee injuries can help prevent these injuries. Athletes with weak core, hip, and knee musculature can be identified early and coaches can incorporate proper instruction as well as strength, power, and balance training into existing female sports programs.
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- Green, J. (November 16, 2010). Flexible fitness: Preventing adolescent knee pain, injury. Metrowest Daily News. Gatehouse News Service. (Accessed at www.metrowestdailynews.com on November 17, 2010).
- Kettles, M., Cole, C. & Wright, B. (2006). Women’s Health and Fitness Guide. Human Kinetics: Champaign, IL.
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