Pace Setter : April 2024

Off The Road Column – The ACL

by Russ Ebbets, DC

If I were to invent a game for women where 10% of the participants, every year, tore their anterior cruciate ligament (ACL), a career ending injury for 60% of the participants, I have little doubt I would be vilified on social media, the subject of slam pieces by newsprint and probably forever associated with a lack of judgment, foresight or common sense. Part of the reasoning would no doubt include how my “creation” nullified or setback the advances women’s sports have made over the last 40 years. Further insults would include my chauvinistic attitude, a general lack of sensitivity and me leaving the toilet seat up! Fortunately, James Naismith, the inventor of basketball, was long gone before women began to play his sport in any numbers.

Classically, the ACL tear is not a track and field or running injury. The mechanism of injury, a quick turn with deceleration, is not a usual movement skill in any of the sport’s disciplines. That being said, I did have two female athletes suffer ACL tears in my coaching career. The first athlete tripped over a hurdle and landed awkwardly as she fell to the track. The second was a two sport star. In addition to being an excellent sprinter she was also a basketball forward. It was the basketball that tore the ACL. Her rehab was long and arduous and I never expected her to return. But due to her grit and persistence she did sprint again, although there were limitations.

In spite of our best efforts the sprinter lost a significant amount of flexion at the injured knee. In fact, she could not flex the knee enough to assume the conventional crouched sprinter’s start. What she could do was a plank position, move the uninjured leg first and essentially “pop up” into a running position. It was not ideal, looked odd, was less efficient and apparently “left her in the blocks,” but she was able to compete. And in truth, she did pretty well when allowed to use a running start for the 4x100m relay leg where she was a member of the team that set the college’s school record.

The ACL is found deep inside the knee and is one of the two cruciate ligaments. The cruciate ligaments criss-cross each other and limit the thigh bone’s (femur) ability to slide back and forth on the tibia (Figure 1). The ACL runs from the front of the tibia to the back of the femur. The posterior cruciate ligament (PCL) has an opposite insertion pattern from the back of the tibia to the front of the femur. What is problematic about this positioning is that the ACL is the more lateral ligament and wraps around the stronger PCL. This positioning combined with an excessive rotation at the knee can contribute to the tearing tendency seen in female athletes when there is a quick turn with deceleration.

To a lay person the knee is almost always seen as a hinge joint that moves back and forth, like the hinge of a door. A unique quality of the knee is that there is a degree of rotation that takes place with each step. The biomechanical term for this action is The Screw Home Mechanism. From a seated position, if one were to straighten the leg while palpating the front of the knee, one can feel a slight, maybe 5 degrees of external rotation of the tibia, in relation to the femur when the leg is extended. That is what happens to the leg with each heel strike of each forward step. As we move to mid-stance/weight bearing/foot pronation in the gait cycle the process reverses. The tibia internally rotates and the femur lags behind. That following or lagging behind of the femur stretches the ACL around the stronger PCL. The extreme actions of competitive sport or even a simple misstep, can snap the ACL if the stretching exceeds the elasticity of the ligament.

If the previously mentioned pronation is uncontrolled (the foot flops to the ground) or is excessive (due to a flat foot) these circumstances can also contribute to an excessive stretch and possible tear. Pronation can cause the problem from the bottom up. But ACL problems can also come from the “top down.” The Q angle (Figure 2) is a measurement made using the hip and knee landmarks to create a reproducible angle showing the relationship of the hip to the knee.

A wider pelvis in women (necessary for childbirth) creates a wider Q-angle and potentially an unstable weight distribution that can only minimally be addressed with improved fitness. Interestingly, women who ascend to the higher levels of sport often have what is called an android pelvis, a pelvis that is narrower and subsequently has a smaller Q-angle, producing less stress at the knee. 

So if all this biomechanical stuff is known, why is the ACL injury such a problem in many women’s athletic sports and not running?

I am confident few would argue with the anatomical causes of a torn ACL, but sport is a dynamic process with many, many moving parts that can contribute to a greater or lesser degree of the problem. Other causes may individually contribute to the injury or work in combination to create circumstances that predispose the injury. And the problem when discussing these “causes” is that some experts will agree while others are quick to dismiss what they don’t understand.

Past the anatomical causes I have long taught that a major reason why track and field does not have the ACL issues of ball sports is that runners are generally better conditioned. I realize such a statement will not make me popular, but it will not make me wrong either. Running leans towards being a year-round sport. Even a novice runner learns early that improvement requires months and months of dedicated effort. Seasonal sports (basketball, soccer, etc.) only require a 10-15 day pre-season in high school and no off-season work required in college. Granted the motivated athlete will do something to prepare for the coming season, but it is often fewer than most.

This lack of conditioning promotes a non-muscular weight gain. This is a touchy subject but the reality is that an increase of as little as 10 pounds of non-muscle weight (i.e. fat) does not improve propulsive ability, joint stability, or mitigate the forces of ground contact. What this deconditioned weight does is multiply the forces on already vulnerable tissues. And with this issue being a touchy, even a taboo subject, it gets swept under the rug, ignored and the ACLs keep tearing.

A lack of conditioning also points to a specific lack of preparation. The neural pathway from the head to the foot is the longest neural pathway in the body. It also takes the longest time to send and receive a signal. If this pathway is not challenged and developed with movement skills (foot placement, stop/start/turning strategies, etc.) the body will remain uncoordinated and characterized with sloppy movements. This development takes months, if not years, not the 10 days of a pre-season.

Further complicating the conditioning issue is the weak foot all athletes from industrialized nations have. We live in a hard level floor world with beautiful shoes to protect our feet, but these shoes function as a soft cast that lead to an atrophy of the muscles necessary for stabilization, movement and balance.

The surfaces for competition can also pose a problem. Over the last two decades there has been a concerted effort to move away from natural grass fields for ball sports. The proliferation of synthetic fields has even been a point of negotiation for the NFL Players Association. How an athletic shoe interacts with the contact surface can pose a significant threat to the ACL, particularly for a poorly conditioned athlete. If the “grip” of the shoe’s sole plate is too strong, the gliding pivot and turn can happen at the knee, not at ground level and the associated stress on the ACL can cause a tear.

Additionally, many ball sports involve a degree of contact. Running, essentially does not, but more on that later. Contact, whether intentional or accidental, challenges the body’s balance. Conscientious development of such qualities as core stability or reactive strength may be able to mitigate a sudden shift in balance. Once again, off-season or year-round conditioning should be able to prepare an athlete to withstand a sudden bump or push.

A final area is the woman’s monthly cycle issue. Some believe that at the midpoint (14^th day) of a woman’s cycle, hormonal release can predispose females to injury due to the ligamentous laxity caused by the hormonal release. If all this is true, there is not much that can be done past creating an awareness and monitoring those problematic days.

At the Rio Olympics American Abby D’Agostino Cooper was tripped and fell in the qualifying round of the 5000m. She tore her ACL. The contact was accidental, but it happened. She literally limped home and subsequently required surgery. It was an unfortunate incident for an otherwise exceptional career. Could this have been prevented? In this case, I doubt it. It was just the luck, or unluck of the draw. Fortunately, she has returned to form, placing 4^th at the US Olympic 5000m Trials for Tokyo and producing a sub 15 minute 5000m personal record.

So while runners ACL injuries are less frequent, they can happen. Many of the training models running coaches use could be easily adapted by the ball sport coaches that would directly benefit their athletes. The promotion of movement skills with a dynamic top to bottom warm-up is 10-15 minutes of time well spent. 

A second idea is the use of multiple sports exposures over the course of years. This would address the “off-season” fitness issue as sports participation would assume a more year-round nature. The early specialization/one sport athlete is part of the ACL problem and until that flawed mentality changes the ACL issue will remain.

Finally, some of the responsibility here must be shifted to the athlete. The age old common denominators of athletic success – perseverance, hard work and dedication remain the same. The idle distractions of video games, social media and cell phones are all just that – idle distractions. The pursuit of excellence cannot be a sometime thing. The will to prepare must always precede the will to succeed.

Whether you are an innovative thinker, an Olympic contender or a healthful wanderer we all are bound by the limitations of anatomy and the rules of biomechanics. The pursuit of our goals is a solo journey fraught with trials and tribulations that present with daily challenges that forge our mettle over a lifetime and career.

 

Figure 1 – Knee from the front. The ACL is the more lateral ligament and “wraps” around the PCL. A “quick turn with deceleration” may exceed the elastic qualities of the ligament.

 

 

 

 

Figure 2 – The quadriceps angle (Q Angle) for females is slightly larger than for males. This fact can contribute to instability at the knee.

 

 

 

 

Russ Ebbets, DC is a USATF Level 3 Coach and lectures nationally on sport and health related topics. He serves as editor of Track Coach, the technical journal for USATF. He is author of the novel Supernova on the famed running program at Villanova University and the sequel Time and Chance. His 2019 book, A Runner’s Guide, a collection of training tips and running articles was a 2019 Track and Field Writers of America Book of the Year finalist. A Runner’s Guide 2 was published in February 2023. Books are available from Amazon.com. He can be contacted at spinedoctor229@hotmail.com.

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