When the NFL’s Injury and Safety Panel released a report last month citing an 88 percent higher frequency of ACL injuries for players on modern synthetic surfaces—like FieldTurf—even casual football fans took the news with little surprise.
In the short time that teams have been playing and practicing on surfaces like FieldTurf, the stigma of such grounds yielding a greater number of injuries to the lower extremities has already built in the popular conscious.
Given the high rate of ACL injury as a whole in college football—the Cleveland Clinic puts the probability at 16 percent during a four-year career—should universities be more cautious with plans to replace grass surfaces with artificial ones?
Schools that had long played on original AstroTurf surfaces leapt at the chance to replace such padded artificial playing fields with softer—yet still budget friendly—crumb rubber infill ones, citing an increase in player safety while still maintaining the cost-saving advantages over a grass field.
As dollars in athletic budgets have turned more scarce, many universities have started replacing grass fields—and their higher cost of maintenance—with infill surfaces whose only consistent upkeep involves repairing seams and replacing the infill pellets.
While the NFL study—which analyzed data from the 2002 to 2008 seasons—is far from definitive, it does beg a question that schools, parents, athletes, and conscientious fans should be voicing in the field surface debate:
What is the cost to the athletes?
The question is a loaded one and not easily addressed verbatim. The variant of causes between contact and non-contact, specific knee injury, age of injured, and even gender all have influence on how the discussion is framed.
Looking deeper into each of these causal factors is often complicated and counter-intuitive, but also a necessary first step in reaching intelligent consensus on the matter.
Contact Versus Non-Contact
In an article published in January of this year, Drs. Matthew Gammons and Evan Schwartz cite the number of incidences of ACL injury in the general population at roughly 200,000 per year. Of those, approximately 95,000 are ruptures of the tendon that require reconstructive surgery.
The article also cites a study by Dr. G.F. Hewson, Jr. for the American Journal of Sports Medicine concluding that a college football player has a 100-fold increase in likelihood for ACL injury when compared to the general population.
Most of the injuries—including those requiring surgery—are of the non-contact variety and have four main causes according to Dr. Guy Slowik, FCRS:
1. Planting and Cutting: The leg and body of the individual moving in one direction while the foot is planted firmly on the ground. Example: a running back making a cutback.
2. Straight Knee Landing: Occurs when the player’s foot—and corresponding weight—strikes the ground while the leg is straight and taut. Example: A receiver coming down after catching a pass.
3. One-Step-Stop Landing while Knee Hyper-extended: When the leg abruptly stops in an over-straightened position. Example: a place kicker’s plant leg. An interesting note in the NFL report was the claim that kickers are the most likely of NFL players to suffer ACL injury.
4. Pivoting and Sudden Deceleration: a combination of a rapid slow down with a plant and twist of the foot. Example: the “spin” move.
Specific Knee Injury
Of the two classes of ACL injuries mentioned above—while less frequent—the contact injury as it occurs in football is the most damaging due to the associated injuries inherent in a severe blow to the knee.
Most contact ACL injuries have complimenting ligament and meniscal tears which have greater long term affects on knee degeneration and stabilization.
The long-term success of an ACL-only reconstruction is often quoted as high as 95 percent with a six-to-nine month recovery time.
Surgeries requiring reconstruction of multiple ligaments in the knee are far less successful, with only 20 percent of patients ever reporting their knee heals to within 85 percent of pre-injury strength.
The reasons for this are not unknown. An ACL injury affects knee stabilization, specifically the ability of the knee joint to keep the tibia bone from sliding out in front of the femur. If the meniscal cartilage or collateral ligaments are also ruptured or strained, the knee looses stability at a geometric rate, not a linear one.
Put more simply, the ACL is responsible for about 90 percent of knee stabilization, but is physically incapable of supplanting the support provided by the PCL, MCL or LCL. If any of those ligaments are traumatized as well—which studies conclude happens over 60 percent of the time in a contact injury—the original amount of support the ACL provides is seldom realized.
Another study on NFL players appeared in the AJSM in November of last year supports this claim. Led by Dr. R.H. Brophy, a group of doctors examined the affects of ACL and meniscal reconstructions on the average length of an NFL player’s career.
The group found that players with only ACL reconstructions had similar number of years and games played when compared to players with no ACL surgeries. However, players that underwent reconstructive surgeries for the ACL in addition to another part of the knee had their careers and number of games played reduced by approximately 20 percent.
Age Of Patients With ACL Injuries
The problem with the studies mentioned above as they relate to the question of using modern synthetic playing surfaces for college football is that the subjects in those studies were all older than accepted developmental and growth stages.
Modern techniques for reconstructing the ACL involve drilling holes in the tibia and femur bones in the areas nearest the knee joint to place screws and bone plugs.
In adults, these areas are called the physis.
In children, they are called the growth plates.
Damage to growth plates in children can cause skeletal asymmetry, with bones growing at incorrect angles or not at all.
First quoted in the Pittsburgh Gazette , Dr. Freddie Fu tells the story of a consult he was requested on involving a 14-year-old boy approximately a year after the boy’s ACL construction:
The boy’s leg was 20 degrees out of position in the knee and a full two inches shorter than his other leg.
The most ominous part of what the NFL study concluded may not ever have affect on the game of college football. However, if the study is proven correct as more analysis is completed—given what we know about ACL injuries in children—should it not affect the use of infill surfaces at the youth level?
Municipalities are constructing and replacing youth fields with modern synthetic surfaces for much the same reason as the universities: It makes financial sense.
More kids are involved in sport than ever, and we all are well aware of the benefits children derive from being involved in athletics. With the risks involved in ACL reconstruction in still-growing children, many orthopedic surgeons are recommending that patients wait until they have approached or reached skeletal maturity to have the surgery.
Literally, that can mean a wait of three or four years during which time that young athlete is doing very little athletic.
There are non-surgical alternatives to ACL repair, but rehabilitation times are often twice that of reconstructed surgeries, and studies have shown a greater risk for long-term degenerative issues.
Moreover, non-surgical therapies often require the patient to choose a lesser activity level than the one enjoyed before the injury. While it is likely the person could jog—which requires a lower level of knee stabilization—high-impact and lateral sports are abandoned.
Gender Differences in ACL Injuries
Surprisingly, football players do not have the highest probability of ACL injury: female athletes competing in soccer or basketball are five times as likely to have a severe ACL injury then male football players.
If you think about the odd statistic from the NFL report stating that kickers are the most susceptible to ACL injury, then break down their kicking motion—deceleration, plant and kick—it is easy to understand why soccer with its higher repetition of the same motion results in so many injuries.
But the rates of ACL injury for female soccer players are also much higher than their male counterparts. In fact, rates of ACL injuries in female athletes are higher than males across the board.
There are few studies that have compiled enough data to offer definitive answers. Most of the answers given by medical practitioners still fall into the category of theory. That said, there is evidence hinting at probable causes:
1. The intercondylar notch is the groove in the femur through which the ACL passes, and has been found to be smaller in women than men. The ACL itself is also smaller.
2. The “Q Angle” refers to the angle of the femur as it approaches the knee from the hips. Anatomically, women have a wider pelvic base which causes a greater angle of descent and places more pressure on the medial aspect of the knee.
3. In men, the hamstrings play the primary role in keeping the tibia from moving forward in conjunction with the ACL; in women, the quadriceps is primary.
4. Women—although this is changing—tend to focus on one sport earlier in their careers than male athletes. Each sport uses and strengthens a different core group of muscles. Over use of a particular muscle group—especially when combined with limited development of other muscular groups—increases atrophy and prohibits rejuvenation.
5. There is a neuromuscular difference in reaction times between men and women that is thought to be a mitigating factor in sports related injuries.
There are more, but of the studies reviewed, these are the most accepted.
While the probability of ACL injury in female athletes has limited direct affect on the game of college football, it is a large part of the debate when considering the use of modern synthetic surfaces.
Additionally, the high frequency has put women’s athletic training at the forefront of preventative measures for ACL injury.
Strength programs that focus on the hamstrings and quads, lower body isometrics and even teaching proper jumping and landing technique are all programs that gained popularity in women’s sports training much earlier than they did in male athletics.
Dr. L.R. Roniger led a study published in the Journal of Biomechanics which dealt specifically with the benefits of specialized ACL training in young athletes. Roniger and his colleagues cited two training programs that—in combination—helped reduce the frequency of knee ligament injury:
1. A specialized program that focused on strengthening the knee, and
2. A larger program that focused on overall muscular development and agility of the entire lower body.
If we are to take the NFL study at face value and accept that modern synthetic playing surfaces increase the likelihood of ACL injuries, then the training programs that have been developed by women’s soccer and basketball teams to help curb injuries of this type should soon find their way to the football field.
At the very least, players, parents and coaches should be aware of the risks that playing on such surfaces entail, and of how to keep athletes best prepared to avoid injury.
Proper training is obviously the most important aspect to injury prevention, but things as simple as proper footwear affect injury rates as well. According to Dr. Gammons, “over-cleating” increases the coefficient of friction and yields a higher incidence of ACL injuries.
As athletes and coaches seek any advantage to increase performance, many turn to shoes that have large, tapered cleats around the periphery because those—they are told by manufacturers—are specifically designed to give the player the most traction.
The manufacturers are not misleading: Cleats of this type do just what they are intended to.
It just happens to be a medical fact that such cleats are the worst thing an athlete could wear on infill surfaces if they want to stay injury free.
A Little 'Give and Let Give'
Manufacturers of FieldTurf and its competitors are quick to point out the modeling flaws of the NFL report. They are right; there were conclusions drawn that can be challenged by statistical analysts.
But this is not a courtroom where a case can be tossed on a technicality, and nothing in the structure of the NFL study jeopardizes their larger consensus that playing on newer artificial surfaces increases the risk for ACL injury.
More than that, debating the metrics of the study completely misses the greater intent of what the panel—led by NY Jets Orthopedist Dr. Elliot Hershman—wanted teams, coaches and players to know:
There is a difference between grass and Field Turf, and failure to recognize and prepare for that difference is likely to get you hurt.
There are not enough studies completed to decide on fact whether or not modern synthetic surfaces are truly the root cause for the increase of ACL injuries seen in contemporary sports, much less college football.
But there are plenty of studies that show that treating such surfaces as though they play and react in the same manner as natural grass can soon put you on the operating table.
Natural grass is the safest playing surface because it will give—just a bit—when pushed.
Hopefully, coaches, parents, and athletes will learn that, in trying to get the best out of artificial turfs, the turfs are more likely to get the best of the athlete.
Jeb Williamson covers Ole Miss Football as a Featured Columnist for the Bleacher Report. He appreciates and welcomes all comments. Click here to visit a list of other articles.