Jan 29, 2015
Joint Efforts

A veteran orthopedic specialist and colleagues answer key questions on the risk factors for ACL injury, the most effective prevention methods, and the state of the science in ACL rehabilitation.

By Jeffrey Albaugh, Jared Friedman, Stephanie Cody, and Dr. Theodore Ganley

Jeffrey Albaugh, MS, PT, ATC, is Physical Therapy Team Leader at the Sports Medicine & Performance Center at Children’s Hospital of Philadelphia. Jared Friedman is a medical student at the Sackler School of Medicine of Tel Aviv University in Israel. Stephanie Cody is a Clinical Research Coordinator in the Division of Orthopaedics at Children’s Hospital of Philadelphia. Theodore Ganley, MD, is Director of the Sports Medicine Program and Sports Medicine & Performance Center at Children’s Hospital of Philadelphia.

Anterior cruciate ligament (ACL) rupture in young athletes has been a hot topic in the sports medicine community in recent years. That’s not surprising, as over 100,000 ACL injuries occur in the U.S. every year, with the highest incidence among individuals between the ages of 15 and 25. Today, more ACL reconstructions are performed on high school athletes than on any other age group.

Those figures highlight the fact that injury prevention, treatment protocols, and rehabilitation strategies for the ACL are more important than ever. In addition, it has long been known that female athletes have special risk factors for ACL injury, and girls’ and women’s participation in athletics has skyrocketed in the past generation.

In the 1950s, when Don O’Donoghue’s famous “unhappy triad” of ACL rupture, medial meniscus tear, and medial collateral ligament injury was first discussed in the sports community, it was known mainly as a football injury caused by tackles from the side. Today, ruptures of the ACL in younger athletes occur frequently in both recreational and organized sports, in contact and non-contact situations.

This article answers some of the most important questions regarding ACL injury in young athletes. We’ll explain who is most susceptible to these injuries, where, when, and why they occur, what can be done to prevent them, and how current surgical concepts and practices are being used to treat young athletes, specifically those who still have open growth plates.

Do males and females sustain ACL injuries at the same rate, and from the same sports?

Several broad-based surveillance studies have looked at males and females in the same sports, and their results have varied as to the amount of difference in overall injury rate and risk. But it is generally the case that females have a higher incidence of ACL injury than males in sports played by both genders. Most studies put females’ ACL injury risk somewhere in the range of four to eight times that of males participating in the same or comparable activities.

We have worked with our own athletic training team and colleagues to gather data and define reportable injuries at 15 high schools. In all, we looked at 5,500 athletes–an equal number of males and females–for a total of nearly 800,000 hours of athletic exposure.

We found significant differences in most sports, but not all. Specifically, females had higher injury rates than males in soccer, basketball, track, cross country, and softball (as compared to baseball). There was no statistically significant difference in the injury rate for tennis. Overall, the highest-risk sports for females were basketball and soccer, with the most frequently injured parts being the knee, tibia, and ankle.

What are the biomechanical risk factors for ACL injury?

There are many predisposing factors, and no single element is directly responsible for the inequity between genders. Differences in ligament laxity, hormonal influences, muscle firing patterns, landing strategies, and proprioceptive characteristics all play a role. Recently, there has been greater emphasis on evaluating physical characteristics and how they affect task performance in areas such as cutting and landing mechanics.

A few gender-specific anatomical factors contribute to biomechanical alignment differences. Females are more likely to exhibit genu valgum (a “knock-kneed” position), tibial torsion, and forefoot overpronation. Neuromuscular factors in muscle activation, joint proprioception, and strength often differ along gender lines as well. Together, these characteristics affect the way females perform pivoting, jumping, and landing tasks, and those activities are most often responsible for ACL injuries–especially those of the non-contact variety.

In terms of proper body alignment and landing mechanics, females are safest when landing with normal lordosis (the natural curvature of the cervical and lumbar spine), as well as a flexed hip and knee in neutral rotation without excessive abduction or adduction. Those who land in a balanced position, in which the knees stay well centered over the toes on a firm foot and ankle, are less susceptible to injury.

Some researchers believe that females are in greater jeopardy of landing in dangerous positions because of alignment and rotational features. These include greater adduction and internal rotation at the upper leg, a less flexed and more valgus knee position with external rotation at the lower leg, and an unbalanced foot and ankle. Many of these risk factors can be addressed through specialized training and instruction.

Can ACL injury prevention programs truly improve performance and decrease injury risk for young athletes?

Over the past few years, there has been increased focus on ACL injury prevention programs, and several sports medicine specialists have designed programs for younger athletes. Studies have shown that participating in a well-designed preventive training program significantly decreases the risk of ACL injuries in all athletes, and females in particular. In addition, these programs have led to significant improvements in strength, neuromuscular firing patterns, and overall performance.

Some such programs are designed for use off the field in a strength training facility, group conditioning program, or rehabilitation setting. Some are best suited for an athlete’s off-season, while others focus on the warmup time before a team’s practice or workout. These warmup-based programs may be the most effective, because they are much easier to implement across an entire team.

A typical injury-prevention warmup plan involves a 15 to 20 minute program conducted prior to each practice to prepare the athletes for physical activity. It targets specific muscle groups, movement patterns, and previously determined risk factors that predispose athletes to knee injuries.

Traditional off-the-field ACL prevention programs have already been proven to increase strength and improve performance. To see whether a warmup-based program could produce similar positive results, we have completed research on a pre-practice program for female high school soccer players designed at the Children’s Hospital of Philadelphia Sports Medicine & Performance Center.

The program we studied consisted of a 15-minute session incorporating basic warmup activities, stretching, strengthening, and plyometric training. It included running and side shuffles, coupled with dynamic stretching to maximize flexibility of muscle groups crossing multiple joints in a single exercise. The strengthening portion consisted of an initial phase of double-leg squats, side lunges, and double-leg bridges on a ball, and a progression phase that incorporated single-leg squats, alternating lunges, and a single-leg bridge on a ball. The plyometric work included an initial phase of squat jumps, double-leg cone hops, and jump-and-sticks, as well as a progression phase that incorporated lunge jumps, single-leg cone hops, and a single-leg bounding exercise. (To learn more about this program, see the “Resources” below.”)

Our results supported the effectiveness of the program. Using pre- and post-isokinetic (Biodex) assessment in conjunction with a functional hop-testing and subjective drop-jump screening, we found that athletes who completed this program showed improvement in every area we examined, which included:

Strength Measures: • Quadriceps peak torque at 180 and 300 degrees per second • Hamstring peak torque at 180 and 300 degrees per second • Quad/hamstring and quad/body weight peak torque ratios

Performance Measures: • Vertical jump (unilateral) • Vertical jump (bilateral) • Triple hop • Drop jump screen

Based on this information, it’s clear that such a program can be highly valuable for high school-age athletes in terms of both performance enhancement and injury prevention. And with the promise of performance gains serving as a powerful motivator, these programs should be easy to implement in practically any setting.

Besides preventive use, specialized warmups can also be effective in the late phases of rehabilitation programs after an ACL tear or other knee injury. Restoring range of motion, strength, balance, and function are the standard goals of rehab, and a targeted warmup can advance those objectives while reducing the risk of reinjury. In addition, continued participation in such a program after return to play will assist with maintenance of lower-extremity strength and neuromuscular control.

What are the risks and benefits of delaying ACL reconstruction in young athletes with open growth plates?

Pediatric patients who sustain an ACL rupture are frequently given a long period in which to fully regain their range of motion, strength, balance, and function. The conventional wisdom has been that delaying surgery, sometimes even for several years, is a sound strategy because it can allow the patient to reach full skeletal maturity before undergoing the procedure.

Physicians need to balance the risks of surgical stabilization at a young age against the alternative, which typically includes a program of knee bracing and long-term activity restriction. It’s true that early ACL reconstruction risks damaging open growth plates and inducing growth disturbances, but delaying ACL reconstruction can cause severe knee instability and subsequent intra-articular damage to the cartilage surfaces and meniscus tissue.

Recent research has evaluated those risk factors and analyzed the results of different lengths of delay for ACL reconstruction. It was found that longer delays before surgical reconstruction after ligament injury (in particular delays of 12 weeks or more) were associated with further meniscal tears and chondral injuries in patients with open growth plates. These findings suggest that contrary to the common practice for many young patients with ACL rupture, it may be best to undergo prompt knee stabilization via surgical repair in order to prevent further injury and instability.

That advice isn’t universal, however. Non-operative management is still indicated when the patient’s physical, mental, or social situation precludes them from being able to fully understand or participate in rehabilitation. This is sometimes an issue for young patients, particularly if the nature of their injury suggests the rehab will be especially demanding. Non-operative treatment may also be best if a young athlete and his or her family clearly prefer activity restriction over surgical reconstruction and the risks and rehab requirements that come with it.

How do surgical approaches differ for younger patients as opposed to adolescents and adults?

Today’s surgical treatment for both the pre-pubescent and adolescent age groups includes procedures that avoid or cross the growth plate. For pre-pubescent patients, most surgeons are able to avoid the growth plates completely. For adolescents with closing growth plates, the surgery can be performed by creating tunnels across the plates, or physes, and placing a soft tissue graft at the growth plate level.

There are a few critical differences between the pre-adolescent and adolescent age groups from a physiological and anatomical standpoint. Pre-pubescent patients have considerably smaller knees, growth plates that undulate in the coronal and sagittal planes, and more future growth still to occur. In addition, younger children’s natural physiology simply makes some phases of rehabilitation more difficult, such as muscle activation and hypertrophy. Post-operative rehabilitation is also typically more challenging for this age group because patients are often less compliant.

Post-operative strength testing is beneficial for athletes of all ages, but it may be especially helpful for younger athletes, as it allows patients to see their progress as a process that’s hastening their return to athletics. This is important, because the return to play timeline for pre-adolescents is typically at least three months slower than for older adolescents.

Does preventive bracing help young athletes avoid ACL injury, and should bracing be utilized after surgery?

The effectiveness of bracing healthy knees to prevent ligament injuries, and its usefulness following ACL reconstruction, have been the subject of many orthopedic studies. However, the results do not provide a clear consensus to support or discourage preventive or post-surgical functional knee bracing in young athletes.

Though the literature remains controversial, orthopedic physicians most often prescribe functional knee bracing in the event of partial ACL ruptures or ACL-deficient knees in young athletes who have deferred or delayed reconstruction. Bracing is typically used in these instances in conjunction with patient education, activity modification, and an exercise program aimed at restoring function, motion, strength, and balance.

With regard to pediatric and adolescent athletes who have undergone ACL reconstruction, the decision to brace or not brace is generally made by a physician on an individual basis, accounting for factors ranging from the structural integrity of the reconstructed ligament to the sport that the athlete plays. Consideration is also given to the athlete’s response to rehabilitation, the intensity and physical demands of their desired activity level, and their psychological response to the injury and rehab.

The best available evidence doesn’t necessarily discount the possible benefits of bracing, so many orthopedic physicians and rehab specialists choose to brace young athletes in order to provide them with every tool at their disposal for safe return to athletic activity. But further research into the effects of functional knee bracing in young athletes is needed to address the possible psychological impact bracing may have, and also to compare the biomechanical effects of bracing in developing athletes as opposed to the effects on adults.


For details on the ACL injury prevention warmup program discussed in this article, which the authors found to be effective in reducing knee injuries, go to: www.chop.edu/service/sports-medicine-and-performance-center/home.html. To learn about another warmup program aimed at ACL injury prevention, the Prevent Injury and Enhance Performance (PEP) program, go to: www.Training-Conditioning.com Click on “Video Library,” then select “PEP: Warmup Program” from the menu at left.


To view full references related to this article, go to: www.Training-Conditioning.com/References.


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