NON-CONTACT ACL INJURIES: UNDERSTANDING RISK FACTORS TO DEVELOP PREVENTION TECHNIQUES

Hannah BarberDecember 4th, 2013

NON-CONTACT ACL INJURIES: WHAT ARE THEY?

A non-contact ACL injury is a rupture or tear of the ACL not stemming from impact with another person or an object.

About 70% of ACL injuries are non-contact!

Sports that require certain types of movements put athletes at higher risk for injury, including:• Sidestep cutting

• Drop landing

• Pivoting

• Rapid changes in direction

NON-CONTACT ACL INJURIES: WHY ARE THEY IMPORTANT?

ACL injuries are important because they have several implications for the athlete who sustained them:

• They can lead to extended lay-off time for healing.

• They can contribute to higher instance of subsequent re-injury of the ligament.

• They can contribute to the development of chronic disease, such as osteoarthritis.

NON-CONTACT ACL INJURIES: CONTRIBUTORS TO RISK

There are several factors that can contribute to ACL injury risk:

• Neuromuscular factors

• Hormonal factors

• Genetic factors

• Anatomical or structural factors

NON-CONTACT ACL INJURIES: WHAT’S THE BIG DEAL?

Non-contact ACL injuries are an important area of study because:

• They’re extremely prevalent among professional and recreational athletes

• They are considered to be modifiable

CURRENT METHODS OF ACL INJURY STUDYIn-vivo laboratory-based methods

Longitudinal cohort studies

Currently, there is a pretty isolated focus on sex-dimorphism as a risk factor for ACL injury. Women have a significantly higher instance of injury than men.

DISADVANTAGES OF CURRENT METHODSExpensive and very time consuming

Disparities between sexes

Test “safe” movements

Don’t incorporate fatiguing and decision-making tasks

Unrealistic laboratory testing environments (i.e.- not on the field)

Can’t control all aspects of the neuromuscular profile

This means that researchers can’t accurately determine a cause and effect relationship between the “risk factors” they’ve identified and the actual injuries sustained.

IMPROVED METHODS FOR INJURY STUDY: Biomechanical modeling and simulation!!!

ADVANTAGES OF BIOMECHANICAL MODELINGFaster than cohort studies

Relatively inexpensive

Noninvasive

Improved prediction of injury risk

Potential for patient/subject-specific screening for injury risk

Allow control of all aspects of neuromuscular control

Allow study of injuries without exposing real people to injurious tasks/movements

LIMITATIONS OF BIOMECHANICAL MODELINGVery large optimization time. Depending on the scenario, it could take anywhere from 24 hours to 4 months.

Knee joint usually modeled as a simple hinge.

Muscle paths are measured with constant moment arms.

Often only simulate one type of potentially injurious task (side-step cutting, drop-landing, etc.)

ADVANCES IN MODELING

Researchers are beginning to include and evaluate several factors in their models:

• Fatiguing

• Decision-making

• Realistic lab environments

• Studies of actual injury events

One group has constructed a model that incorporates musculoskeletal movement and soft-tissue mechanics. These two aren’t usually put together.

RISK FACTORS IDENTIFIED

Greater knee valgus moment

Greater quadriceps muscle moment

Increased proximal anterior tibea shear force

Smaller knee flexion angles

Larger posterior ground reaction force

However! Researchers found that increased knee loading alone could not cause injury— large valgus and internal rotation knee joint torques are also necessary to sustain injury.

BETTER MODELING MEANS INJURY PREVENTION Why is biomechanical modeling so instrumental in injury prevention?

Helps identify risk factors for ACL injury

Allows coaches, trainers, and clinicians to develop training programs to teach athletes how to avoid injury.

Has potential for subject-specific simulation… This means more personalized injury-prevention technique development.

FUTURE DIRECTIONS

Development and validation of models for a more expansive list of tasks

Development of models based on video footage from actual injury situations

Develop and understand a cause-and-effect relationship between certain knee loads and neuromuscular profiles with ACL injuries

Further understanding of increased injury risk in females and better prevention techniques for female athletes