With the passing of Title IX in 1972, there has been exponential growth in the participation of females in women sports (250,000 in 1972 to over 3,000,000 in 2004) (Silvers, 2009). Mirroring the tremendous growth in women sports has been an ACL injury phenomenon.
The focus in recent years from the sports medicine community is on understanding the risk factors involved in these injuries and putting programs into place to reduce the risk of ACL injuries.
According to an epidemiological study conducted by physical therapist Holly Silvers, M.PT., Director of Research at the Santa Monica Orthopaedic and Sports Medicine Research Foundation, females between the ages of 14 and 20 are in a high risk group for ACL injuries with an injury incidence of 2 to 10 times greater than their male peers (Practical Applications in Sports Medicine Conference, May, 2009).
Mechanism of Injury for Non-Contact ACL Injuries
An interesting fact of this injury phenomenon is that 70% of the ACL injuries are non-contact injuries. This means that the athlete was alone on the field or the court and suffered the injury without any opponents involved. The mechanism of injury included:
- Hyperextension
- Pivot
- Landing in extension
- One step-stop deceleration
Athletes described the injury mechanism as an “unexpected” move on the field that resulted in the ACL tear and then collapse of the athlete. This suggests that the muscles within the knee, thigh, and hip were not able to correct and withstand the “unexpected” movement and corresponding forces placed on the knee.
According to Silver’s research, there are four general risk factors when looking at the female athlete. These included anatomy, hormones, environmental conditions (cleats, field conditions), and biomechanics. Silver’s research has focused on the biomechanical risk factors.
Biomechanical Factors Unique to Females
Silver’s studied the running and landing patterns of females. Using the biomechanical research lab, the research documented specific differences in the biomechanics of female running and landing patterns off of a jump box.
One of the primary findings was that the hamstring muscle group in females activated more slowly than their male peers with female’s hamstrings firing at only 55.2% at initial contact whereas the male’s hamstrings were firing at 71.8% at initial contact. This is significant because the hamstring muscle group in effect performs the same role as the ACL in preventing anterior movement of the tibia on the femur. If the hamstring muscle group is weak, then the ACL is compromised.
Silver also looked at the biomechanical landing patterns of females off of a jump box. Females with weak quadriceps, hamstring, and hip musculature initially landed on two feet, but then proceeded to have an inward bowing of both knees as the athlete absorbed the landing forces prior to correcting and returning to a standing position. This “inward bowing of the knees” is a distinct biomechanical pattern that is seen in female athletes at risk for ACL injuries.
ACL Prevention Project
Out of this research came the Santa Monica ACL Prevention Project. It is known as the PEP Program (Prevent Injury and Enhance Performance). The program was designed as a 15 minute warm-up (agility, strengthening, plyometric, and flexibility exercises) to be easily incorporated into any team’s warm-up.
Initial research documented a significant decrease in ACL injuries in NCAA female athletes that had used this program (American Journal of Sports Medicine, August, 2008). There is currently a five year study funded by the National Institute of Health to document the effectiveness of the PEP program over time.
Coaches and professionals working with young women athletes need to understand the phenomenon of ACL injuries in females, research ACL prevention programs that are documented to be effective, and incorporate those prevention programs into their own warm-up to reduce the incidence of ACL injury to their athletes.
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