Brian Schiff’s Blog

Why is it that athletes performing a movement they have done so many times suddenly tear their ACL?  We have been studying ACL injury and prevention for many years now, and despite our best efforts, we have not made marked progress in preventing the number of ACL injuries.  In addition to anatomical variants and perhaps some genetic predisposition, I feel that the earlier push for sports specialization in our society resulting in increased training/competition hours is a major factor.

The term ACL fatigue may or may not be familiar to you.  But in essence, this theory would suggest that after a certain number of impacts/loading, the ACL becomes weakened and less resistant to strain.  You could almost compare this to a pitcher who suffers an injury to his medial collateral ligament with too much throwing.

As someone who is consistently rehabbing athletes with ACL tears and screening athletes to assess injury risk, I am always interested in how we can keep people from suffering such a devastating non-contact injury. A recent article in the American Journal of Sports Medicine sought so assess ACL fatigue failure in relation to limited hip internal rotation with repeated pivot landings.

We already know that hip mobility is often an issue for our athletes.  Researchers at the University of Michigan sought to determine the effect of limited range of femoral internal rotation, sex, femoral-ACL attachment angle, and tibial eminence volume on in vitro ACL fatigue life during repetitive simulated single leg pivot landings.

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I had the pleasure of listening to Darin Padua, PhD, of UNC present some of his latest research on ACL injury prevention last week. He has been doing research for some time. One of his studies (JUMP ACL) in collaboration with the military and several others has looked at prospective data and injury occurrence among college age subjects.

Much of the research to date on injury prevention has been done by Timothy Hewett and his colleagues. It has concluded that drop landing with a valgus collapse (hip abduction/IR with valgus knee moment) is a risk factor for injury. Interstingly enough, despite that knowledge and the proliferation of prevention programs, Darin mentioned that overall these prevention programs have not slowed the rate of ACL tears in the last decade. Why is that?  He also relayed that much of what we know now is based on 15 total cases.

The Jump ACL Study in a nutshell lasted for 5 years at 3 different military academies:

N = 5,700 cadets with no prior ACL surgery

• Soccer players = 1,690
• Tested from 2005 to 2008
• 39% female; 25% NCAA athletes
• 14,653 person-years of follow-up

N = 113 incident ACL injuries

• Soccer players = 29
• Mean time from testing to injury = 3.1 yrs
• N = 92 one ACL injury; N = 11 two ACL injuries

Some data (will be published) he discussed based on his findings revealed the following about high risk profiles for ACL injury:

• Hip flexion > 40 degrees at landing = 1.76x increased risk
• Hip adduction plus knee valgus = 3x increased risk
• Hip adduction plus knee varus = 27x increased risk

He also mentioned that the high risk profile does not correspond to the ACL injury event profile of:

• Hip abduction
• Lateral trunk flexion
• Knee valgus collapse
• Small knee flexion
• Tibial ER/IR

In the end, he suggests we need to better understand who to target (high risk profile clients) and what to modify (injury event profile) so we can better customize injury prevention programs that optimize proper movement and meet the needs of each individual athlete.  He reminded us that using the uninjured side for comparison is insufficient as faulty movement patterns already likely existed contributing to the first ACL injury.

So, assessing movement continuously and striving for excellent movement quality is a MUST if we are going to both prevent initial ACL injuries and reduce the re-tear rates for our athletes we send back to play.  He reports that those at increased risk simply have bad biomechanics.  His message provides more weight to having an advanced algorithm to identify asymmetry, poor motor control and flawed movement patterns in order to effectively prescribe interventions to address these things.

At UNC they use a PRIME assessment.  I am excited to learn more about it and have referred one of my female higher level soccer players to their lab for assessment as I look at this return to play decision with her now that she is just past 7 months post-op.   I think the hip/core obviously play an important role as I see so much deficiency in my female patients recovering from injury.

Clearly his findings with hip adduction and varus as a big risk factor seem to indicate it could be a top down kinetic chain breakdown as well upon impact based on the risk profile.  Pelvic stability or the lack thereof seems to be significant, only NOT in the same manner we thought about it before based on previous research available.  Stay tuned, as we have lots more to learn about ACL injuries and how best to tailor our prevention efforts.

ACL injuries continue to proliferate among female athletes.  I am passionate about preventing them, and part of my professional mission is to study and evolve in my rehab and prevention training approaches all the time to stay on top.  I wanted to pass along some new information on a new screening tool just unveiled in the Strength and Conditioning Journal this month.

Before I reveal the screening and training tool, I want to take a moment and review what Timothy Hewett refers to as modifiable risk factors that contribute to injury risk based on his work:

1. Ligament Dominance – defined as an imbalance b/w neuromuscular and ligamentous control  of dynamic knee stability and it is visualized by loss of frontal plane control with landing and cutting
2. Quadriceps Dominance – defined as an imbalance between quad and hamstring strength, recruitment and coordination
3. Leg Dominance – defined as an imbalance between the two legs with respect to strength, coordination and control
4. Trunk Dominance ‘Core’ Dysfunction – defined as an imbalance b/w the inertial demands on the trunk and its ability to resist or control/resist it

Previously, Hewett has identified that high knee abduction moments are related to high LOAD on the knee and a major risk factor for ACL injury.  He and his colleagues have done extensive motion analysis in their lab in Cincinnati, OH.  As such, a drop landing test has been used as one tool to observe landing mechanics and assign some risk value to athletes competing in cutting and jumping sports.

In the current article (click here for the abstract) Meyer, Brent, Ford and Hewett unveil a new screening tool involving the tuck jump.  They propose that this tool is easier for the S & C coaches to do on the field and not only assess risk factors by way of observing technical flaws, but also use the tool as a training maneuver.

The idea is the subject will perform tuck jumps for 10 seconds consecutively while the observer makes notes on the following pre, mid and post jumping:

1. Lower extremity valgus at landing
2. Thighs do not reach parallel (peak height of jump)
3. Thighs not equal side-to-side (during flight)
4. Foot placement not shoulder width apart
5. Foot placement not parallel (front to back)
6. Foot contact timing not equal
7. Excessive landing contact noise
8. Pause b/w jumps
9. Technique declines prior to 10 seconds
10. Does not land in same footprint (excessive in flight motion)

Factors 1-3 refer to knee and thigh motion, 4-7 refer to foot position during landing and 8-10 refer to plyometric technique.  Coaches are instructed to grade the flaws if seen with check marks during the phases they are seen and use this as a guide for correction.  They may also use cameras in the frontal and sagittal plane to assist them.

My thoughts on this are:

• There is sound science behind the rationale for the test and modifiable risk factors
• There is a need for basic no-cost screening tools coaches can apply in their settings
• The tuck jump assessment will provide instant feedback on form and identify technical flaws that may indicate higher risk for injury
• The tuck jump is a higher demand plyo drill so I fear poor form may be as much to blame on inexperience and unrefined motor patterns as it is to just dominance patterns so we need to keep plyo training experience in mind when analyzing the screen results especially for beginners
• The tuck jump assessment does not really consider fundamental movement restrictions that may bias the form on one side if an asymmetry is present
• I still wonder how much ankle pronation impacts landing and whether we will see more research on this – there was a study done at ECU where they used orthotics and saw a reduction in ACL tears in their collegiate athletes so I have to wonder about this crucial element of the kinetic chain

In the end, we still lack many answers.  According to data published in the Journal of Athletic Training in 2006, non targeted neuromuscular training programs need to be applied to 89 female athletes to prevent 1 ACL tear.  So, we need to keep studying and applying science to our training, all the while critically questioning science and looking at our athletes holistically to find the best prevention strategies for each one individually and for at risk athletes as a whole.