Understanding & Preventing ACL Injuries in Female Athletes: Current Biomechanics
by Rudy L. Paul, MS, PT, CSCS, USPTR
(with excerpts from Hewitt,TE et al in N Am J Sports Phys Ther. Dec 2010; 5(4): 234-251 & Wilk,KE et al, J Ath Training. 1999;34(2):177-193)
The current state of knowledge in the area of ACL injuries.
- Female volleyball athletes were ………………4X more likely to sustain ACL injuries versus male volleyball athletes
- Females sustain 6-8X more ACL tears versus males in the same sports
- Collegiate female basketball players were ….8X more likely to sustain ACL injuries versus male BB players.
- Female soccer players were …………………..6X more likely to sustain ACL injuries versus male soccer athletes.
Facts surrounding the Costs of ACL injuries:
- Cost: $27,000. to $35,000. per ACL injury for surgery & rehabilitation
- The ACL is the 2nd most commonly injured ligament in the knee (behind MCL via valgus stress)
- Resulting in over 200,000 ACL reconstruction surgeries performed per year.
- Potential loss of sports participation- (it takes 9-12 months or longer to fully rehab. from an ACL injury),
- decreased scholarship funding,
- lowered academic performance,
- long term disability, and
- significantly greater risk of later OA (osteoarthritis).
How Does it Happen?
- The Majority of ACL injuries occur from non-contact injuries…70%
- Mechanism of Injury is a Pivot Shift Injury: The athlete decelerates with twisting, pivoting, or a change of direction.
- Females are 6-8x more likely to suffer an ACL injury.
Video Sequences of female athletes that have actually suffered ACL injuries were examined and it appears there are…
Four Common Biomechanical Positions that were identified during the Mechanism of ACL injury videos….
As the at risk female athlete lands, her...
- knee buckles inward or moves towards the big toe (called genu valgum), or the
- injured knee is relatively straight when landing (called genu recurvatum, or hyperextension), or
- most, if not all of her body weight is on a single lower extremity when landing. Finally, upon landing, her
- torso or trunk is tilted laterally, or her center of body mass is well outside her base of foot support.
Mechanism underlying female ACL injuries is Multi-Factorial in Nature:
- Extrinsic Factors…(physical and visual disturbances, bracing, and shoe-surface interactions)
- Intrinsic Factors… (anatomic, hormonal, neuromuscular, and biomechanical differences between genders)
- Ligament Dominance
- Quadriceps Dominance
- Side-to-Side Dominance
- Trunk or Torso (Core Dysfunction) Dominance
What are the Four Major Intrinsic Factors that Contribute to Female ACL injuries?
Upon landing, the excessive ground reaction forces may be directed improperly through the ACL as opposed to the LE muscles and tendons. This may be due to the fact that females inherently exhibit wider hips.This leads to the poor alignment of the hips, knees, and feet. If the hip, knee and foot are not aligned properly so that the muscles and tendons are not in a position to effectively absorb the ground reaction forces (upwards of 3 to 5X body weight) then the ACL or other static knee components have to take on that task and they may tear or rupture. This tearing occurs , again because biomechanically females all have a wider pelvis and hips and their knees are in a more valgus (knock-kneed position) and their feet are usually more pronated (so arch collapses at impact). Unless these female athletes are aggressively strength trained to overcome these inherent biomechanical predispositions, they will likely sustain ACL injuries in their athletic careers. This poor alignment issue can easily be strength trained away especially if the foot, knee and hip positioning is corrected and neuromuscularly retrained during slow squatting movements.
Female athletes may be "overpowered" and possess quadriceps muscles that are too strong relative to their hamstrings and core musculature. When they impact the ground and/or pivot they may stress or stretch the ACL to excess and this is when the ACL ruptures or tears. Female athletes commonly demonstrate this significant muscle imbalance between the quadriceps & all of the other protective Posterior Chain Muscles. This imbalance includes the low back muscles, gluteals, hamstrings & calves. The hamstring muscles especially need at least 85% of the strength of the quadriceps in order to adequately protect the ACL from injury. With sport-specific, aggressive strengthening, this quadriceps dominance factor may be neutralized. Specialized training aimed at awakening the dormant low back, gluteals, hamstrings & calves can protect the female athlete's ACLs. Balancing the overpowering strength of the dominant quadriceps muscle group may help to significantly decrease the incidence of ACL injury.
(3)…Side-to-Side Leg Dominance…
Female athletes tend to have a favorite leg and they tend to be more one-leg dominant when compared to their male counterparts. When a female athlete tears her ACL, most if not all her weight is focused onto a single leg when landing or pivoting. When female athlete's legs are strength screened between (L) to (R) sides, the comparative muscle strength identifys which LE is weaker. Once this is determined and the introduction of specialized strength & conditioning training is implemented, then this leg dominance factor may be overcome and the female athlete may enjoy equal side-to-side lower extremity strength. Abolishing this side-to-side leg dominance through proper strengthening may significantly decrease the risk of ACL injury in female athletes.
(4)…Trunk or Torso (Core Dysfunction) Dominance…
Female athletes inherently possess significantly less 3-D proprioceptive control of their torso or trunk when they are airborne compared to their male counterparts. What this means is that when a female athlete jumps and is airborne they may experience a loss of conscious awareness via neural control of where their body position is in space for just a split second. Again, due to their anatomical variation, if their center of mass gets outside of their base of support (foot) when they impact the ground, then this is when they are at highest risk to rupture their ACL. However, if certain sport-specific tests are administered like those included in the sport-specific injury prevention screenings then this trunk dominance factor may be identified early. After identifying and isolating the extent of this problem, it may be adequately addressed as a physical deficit and abolished by introducing corrective strategies. There are certain neuromuscular and balance activities that can neutralize this problem and it can be largely obliterated and the risk of ACL injury significantly reduced.
So, is there any way to prevent ACL injuries in female athletes?
Yes, sports injury prevention programs designed by specially trained sports physical therapists have been shown to dramatically decrease the incidence of these severe ACL ligamentous injuries. Studies have shown that the ACL injury risk may be decreased by between 30 and 80 percent!
If you have any sports-specific training, sports testing, or injury questions…
Contact Rudy L. Paul, MS, PT, CSCS, USPTR Tennis Professional at RPM Physical Therapy & High Velocity Sports Performance Call….813-368-0398 Now!