Injury to the ACL is one of the most common sporting knee injuries, occurring most commonly in dynamic team sports involving jumping and pivoting. As with any ligament injury, severity varies from partial to full thickness tears, with full thickness tears often associated with injury to other passive knee structures. Non-contact ruptures are the most common mechanism of injury, where the knee is exposed to high load valgus forces with the knee in external rotation and near full range of extension (see picture below). Contact injuries may also occur, however at a lower rate. Research has also found that Female athletes are 2-8 times more likely to injure their ACL, and with the success and rise in popularity of Women’s team sports in Australia, it is important to identify and prehabilitate athletes to prevent ACL injuries.
What is the ACL?
The ACL is one of 4 knee ligaments that provide passive stability to the knee joint. There are 2 parts to the ACL- the antero-medial and postero-medial aspects, both running obliquely from the femur to the tibia. The ACL provides approximately 85% of the resistance to anterior translation of the tibia on the femur (forwards movement of the lower leg on a stationary upper leg) and also has a major role in preventing tibial internal/femoral external rotation (lower leg rotating inwards/upper leg rotating outwards). When an injury does occur, 15% of all tears are partial compared to 85% of complete ruptures. Of these ACL ruptures, 25% have been reported as isolated injuries, with 75% occurring in combination with cartilaginous, meniscal or collateral ligament tears.
Why are Women more at risk of ACL injury?
Women are at greater risk of ACL injury due to the gender specific changes that occur at the onset of puberty. Due to the genetic bone structure, Females are predisposed to valgus forces at the knee due to their wider hips. It is also know that Female athletes are generally not as strong as their Male counterparts, who receive a dose of testosterone, ILGF and growth hormone during puberty that contributes to the increase in strength, and therefore dynamic knee stability.
Female athletes have also been found to adopt sub-optimal landing strategies that put greater stress on the ACL. Research has shown that females tend to land with:
- A more upright trunk with a quadriceps dominant pattern (less shock absorption from the hip muscles)
- Increased knee valgus
- Less and later gluteus medius activation
- Reduced hamstring strength compared to the quadriceps strength, increasing anterior tibial shear stress (the quadriceps tend to pull the lower leg forward at the knee joint)
How can we reduce the risk of injury?
A study has found that Female dancers did not show the same typical landing patterns as female athletes due to their early training of jumping and balance activities. This demonstrates the role of strengthening and neuromuscular control programs and the ability for Female athletes to improve their ability with training. A comprehensive rehabilitation program must address any strength, balance and control deficits that have been mentioned previously as a risk factor for injury.
A review of the evidence regarding the effectiveness of neuromuscular training programs in reducing ACL injuries in female athletes shows:
- Reduction of ACL injuries in female athletes following neuromuscular control training
- Programs that include proprioception and plyometric exercises may reduce the risk of ACL injuries (moderate evidence)
- Programs only implemented in season most likely do not reduce the incidence of ACL injuries (moderate evidence)
Before and after biomechanical correction
(http://strideseattle.com/who-needs-knees-why-acl-injury-prevention-matters/)
Written by Physiotherapist Jake Pemberton.
References
Arendt E,Dick R. Knee injuries patterns among men and women in collegiate basketball and soccer. NCAA data and review of literature. Am J Sports Med 995;23:694-701
Garrick JG, Requa RK. Anterior cruciate ligament injuries in men and women: how common are they? In: Griffin LY, ed. Prevention of noncontact ACL injuries. Rosemont,IL:American Academy Orthopaedic Surgeons,2001:1-10.
Agel J, Arendt E, Bershadsky B.Anterior cruciate ligament injury in national collegiate athletic association basketball and soccer: a 13 year review.Am J Sports Med 2005;33(4):524-30.
- Orishimo et al (2009). Comparison of landing biomechanics between male and female dancers and athletes. AJSM; 37
- Donnolly et al (2012). An Anterior Cruciate Ligament Injury Prevention Framework: Incorporating the Recent Evidence. Research in Sports Medicine; 20:239–262
- Dai et al (2012). Prevention of ACL Injury, Part II: Effects of ACL Injury Prevention Programs on Neuromuscular Risk Factors and Injury Rate. Research in Sports Medicine, 20:198–222
Images
http://thegamebeautiful.blogspot.com.au/2012/12/mechanisms-of-non-contact-acl-injuries.html
https://orthoinfo.aaos.org/en/diseases–conditions/anterior-cruciate-ligament-acl-injuries/