ACL Injury Prevention

Anterior cruciate ligament (ACL) tears are among the most common orthopaedic injuries in the United States. More than 100,000 ACL reconstructions are performed annually with the purpose of reestablishing knee stability and kinematics post-injury. The mechanism of injury can be either contact or noncontact, with approximately 70% of ACL tears secondary to noncontact injuries. Much of the modern-day ACL injury research focuses on ACL injury prevention and investigating how best to reduce this serious knee injury. Fitness professionals have a unique opportunity in assisting clients who may be at risk for ACL injury or have recovered for an ACL injury, as the client navigates preparation for their chosen sport or recreational activity. Fitness professionals are frequently already engaged with at-risk populations at their gyms, health clubs or training centers. Certain sports, such as soccer and basketball, have higher incidences of ACL injuries due to the frequent cutting, pivoting and decelerations required to play competitively. Gender is also believed to play a large role in the risk of ACL injury, especially in the athletic, adolescent population.

ACL prevention before an ACL injury, as well as prevention of a recurrence of an ACL injury is important to the long-standing health of the knee joint. If an athlete sustains a second ACL injury, researchers have demonstrated that patients undergoing a revision ACL reconstruction have significantly more chondral (cartilage) damage at the time of their second injury presentation (Mitchell JJ, et al. Primary versus revision anterior cruciate ligament reconstruction: patient demographics, radiographic findings, and associated lesions. Arthroscopy. 2017, Dec.7(17):S0749-8063.) Further, the prevalence of osteoarthritis after an ACL reconstruction significantly increases over time. Indicators correlated with the development of osteoarthritis included longer chronicity of ACL tear (longer time prior to ACL reconstruction) and an older age at the time of surgery (Cinque ME et al. Higher rates of osteoarthritis develop after anterior cruciate ligament surgery: an analysis of 4108 patients. Am J Sports Med. 2017. Sep. Epub ahead of print). Prompt referral to a physician if an ACL injury is suspected can positively impact the health of the athlete’s knee for the long-term.

ACL Injuries and Gender

Female athletes experience a higher incidence of ACL ruptures across multiple sports than their male peers. Many modifiable and non-modifiable risk factors influence the higher incidence in females. Non-modifiable factors include anatomic factors (smaller width of the intercondylar notch of the knee and a smaller ACL size in females, for example). Reproductive hormones are also hypothesized to play a role in gender and ACL injury, with research proposing that a shift in the levels of estrogen and progesterone impacting the susceptibility of an ACL injury. However, there is a lack of consensus regarding the relationship between the menstrual cycle phase and ACL injuries.

Modifiable risk factors include neuromuscular control, strength and proper landing mechanics. Specifically there are gender differences found in motion patterns and the forces generated from the hip and trunk to the knee. It is postulated that females have weaker hip extensors, which necessitates their use of the hip flexor muscles for trunk control over the hips during jump landing. This posture results in a more upright hip position and an altered knee angle on landing (Hewett TE, Myer GD, Ford KR, et al: Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: A prospective study. Am J Sports Med 2005;33(4):492-501.) To combat this difference, strengthening programs that emphasize hip control—gluteal and hamstring activation in a closed-chain fashion—have been shown to be beneficial in ACL injury prevention programs (Hewett TE, Lindenfeld TN, Riccobene JV, Noyes FR: The effect of neuromuscular training on the incidence of knee injury in female athletes: A prospective study. Am J Sports Med 1999;27:699-706).

ACL Prevention Programming

The medical community has demonstrated evidence that well designed and supervised injury prevention programs reduce the risk of ACL rupture. ACL injury prevention programs are becoming a mainstay of preparation for sports and recreation with today’s active adolescents and adults. ACL injuries can result in the development of osteoarthritis and injury to knee cartilage, however, timely referral and treatment may diminish the occurrence of post-traumatic osteoarthritis. A second ACL injury to the same knee or the contralateral knee can also occur, resulting in further risk of cartilage injury. Given the potentially long-term, significant impact of ACL injury, a proper program is vital.

Those who are already at risk for injury (females or those in pivoting/cutting, high risk sports) are particularly likely to see marked reduction in their risk when engaged in such programs. Since some of the risk factors are non-modifiable (for example, gender), effort focuses on modifiable risk factors, such as neuromuscular control. Maximizing strength, neuromuscular control and technique are the goals of a fruitful ACL injury prevention program, with visual and verbal feedback as a key component of the client’s success. A safe and effective ACL injury prevention program includes appropriate instruction and supervision.   Ideally, in order to prevent bad habits early-on, ACL prevention programs are initiate at or prior to the onset of puberty. Prevention programs should begin at least 6 weeks prior to the athletic season, with a maintenance program incorporated in-season.

Programming begins with a dynamic warm-up, followed by strength training, plyometrics, agility drills and technique training. Strength training focuses on improving the strength of the core, hip, and gluteal and thigh musculature. Strengthening programs in isolation do not reduce the number of ACL injuries, yet when combined with plyometric training there is a significant reduction in ACL injuries, specifically female athletes. Plyometric training focus on improving landing biomechanics while incorporating balance training attempts to eliminate or minimize limb asymmetries, which is a potential risk for ACL injury. Cutting and jumping drills comprise the technique training portion. Each of the aspects of training should include frequent feedback cueing, if possible, via video analysis. (Sanders, James O.; Brown, Gregory Alexander; Murray, Jayson. Anterior Cruciate Ligament Injury Prevention Programs. Journal of the American Academy of Orthopaedic Surgeons. 25(4):e79-e82, April 2017.)

Prevention Programming Overview

A sample ACL prevention programming is outlined (below). The program begins with a dynamic warm-up instead of static stretching to prepare the client’s muscles and joints for the day’s exercises. Strengthening of the quadriceps, hamstrings, hip abductors and core is essential to any ACL injury prevention program. When designing the strength training portion of the program, fitness professionals should think creatively about their client’s preferred sport or recreational activity and how those muscle will be utilized. For example, programming may emphasize eccentric loading reps when working with clients who need to do quick decelerations or stops. Alternatively, an athlete may need to come out more explosively from a static position, such as with a running back, therefore, the chosen exercises should reflect that need.

Plyometric and balance exercises may include single or double-legged hops, box jumps or box drops. These drills may be performed at timed intervals (for example, 30 seconds) or repetition-based (10 repetitions of single-leg hops). Verbal and visual cueing will enable the client to improve their functional and jump landing mechanics. Progression of plyometric and balance drills should remove supports the client uses to perform the exercises. For example, once a simple single leg balance exercise has been mastered, the client can close their eyes to remove the assistance they receive through their visual sense. Another technique would be to have them do a ball toss while remaining in single leg stance to draw their visual sense to the ball instead of a focused point in the distance.

Agility and sport-specific drills are the most difficult exercises for a client to maintain proper joint mechanics and neuromuscular control. During drills such as running backward, stop and start shuttle runs or crisscross lateral running, the fitness professional must be highly focused on providing verbal cueing as these drills most closely represent the real-world demands when returning to sport. Video analysis, even via a cellular phone camera, is a great tool to implement, as it may be difficult for some clients to incorporate verbal feedback with visual feedback. The choice of agility drills is dependent on the clients preferred sport or activity, and should attempt to simulate those activities. Proper mechanics emphasize symmetric lower extremity takeoff and landing for bilateral limb exercises, suitable trunk control and proper knee alignment during takeoff and landing for bilateral and unilateral drills. Proper knee alignment includes knees aligned over toes and toes pointed in a forward direction.

When the athlete is in-season, a maintenance program begins. Maintenance programming should not be performed on game days; instead, perform the program prior to practice or conditioning two to three times per week while in-season.

ACL Injury Prevention Program Exercises

10-15 repetitions of 3 sets per exercise

  1. Walking lunges:
  2. Mountain climbers
  3. Jump rope (single or double leg)

General tips:

  • Bend from the hips and knees, especially during jump landing
  • Keep the knees over the toes when squatting, lunging or landing jumps, and keep the toes straight forward (don’t turn the knee inward)
  • Land softly and with control. Land on the balls of the feet instead of the heels.
  • Proper technique is essential. Technique begins to fail with fatigue, therefore, incorporate in rest once form suffers.

  1. Single leg balance: stand on one leg with slight bend of the knee and maintain balance for 15 to 30 seconds. Repeat on both legs, 3 repetitions per side.
    1. Progression: Single leg balance with eyes closed
  2. Heel drops: stand on a sturdy box or platform approximately 12-18 inches high. Move toward one edge of the box and stand on the “inside” leg with the “outer” leg hovering over the edge. While maintaining hands on hips, knees aligned with toes, and toes pointed straight ahead, bend from the stance leg hip and knee to lower the non-stance heel to the floor. Repeat on both legs, 10 repetitions and 3 sets per side.
    1. Progression: hold a medicine ball with both hands and concurrently raise the ball overhead while perform heel drops.
  3. Walking lunges: alternate legs while performing standard walking lunges. Focus on knee/foot alignment and an upright chest and torso. Repeat for 20 repetitions, 3 sets.
    1. Progression 1: add an upper body twist. With palms together and arms extended straight ahead, while lowering down into a lunge, twist to one side. Alternative sides.
    2. Progression 2: add a medicine ball to the upper body twist
  4. Hamstring curls on ball: begin lying supine with heels on a large thera-ball. With arms resting on the floor, bridge the torso up until a straight line from torso to heels is formed. Next, contract the hamstrings to curl the thera-ball inward while maintaining the bridge position. Lower and repeat 10 repetitions, 3 sets.
    1. Progression: single leg hamstrings curls on ball
  5. Russian Hamstrings: begin kneeling on the ground with hands on hips. A partner or trainer holds the client’s ankles firmly. With a straight torso, lean forward with the hips. The body should be in a straight line from the shoulders through the torso, hips and knees, Lower the body as long as alignment may be maintained, then return to the starting position. Avoid bending at the waist. Repeat for 10 repetitions, 3 sets.
    1. Progression 1: hold a medicine ball
    2. Progression 2: place a foam pad or other unstable soft surface under the knees to enhance core engagement

Perform for 30 seconds each

  1. Lateral hopping: place a piece of tape on the floor on one side of the client’s feet. Hop over the line with both feet, then hop back and forth over the line
    1. Progression 1: Place a small cone on the floor instead of the tape
    2. Progression 2: single leg hop
  2. Forward and backward hopping: as above with lateral hopping, but proceed in a forward and backward direction
    1. Progression 1: Place a small cone on the floor instead of the tape
    2. Progression 2: single leg hop
  3. Box jumps: begin standing on a sturdy box approximately 2-3 feet off the ground. While maintaining knees aligned with toes and toes pointed straight ahead, bend from the hips and knees and jump onto the floor. Land softly.
    1. Progression 1: alter box height or add a medicine ball for added weight
    2. Progression 2: combine an upper extremity ball toss (or catch) with jumping down
  4. Scissor jumps: lunge forward with your the leg, keeping the knee over toes. Push off with the right foot and propel the left leg forward into a lunge position. Land softly with each repetition.
    1. Progression 1: increase duration of the drill
    2. Progression 2: add a ball toss with each lunge

Increase dynamic stability of the entire lower extremity kinetic chain with shuttle runs, forward and backward running, running with quick stops, and cutting and bounding runs. The key to these drills is the supervision. Drills can be tailored to the needs of the client’s sport, however, the value of providing the athlete with feedback cueing in real-time and with video review is immeasurable. Focus should be placed on maintaining alignment of the knee over the toes and consistently bending from the hip and knee.

  1. Forward and Backward running: place cones approximately 20 to 30 feet apart. Sprint forward from cone one to cone two, then run backward to the starting cone. Repeat for 30 seconds, three to five repetitions.
    1. Progression: increase distance or duration
  2. Bounding runs: place cones 20 to 40 yards apart. Begin running with knees lifting up high toward the chest while maintaining an upright torso. Land softly on the ball of the feet with slight bend of the knee. Repeat for 30 seconds, three to five repetitions.
    1. Progression: increase distance or duration
  3. Ladder drills: place an exercise ladder on the floor (or create a ladder shape on the floor using masking tape). Sprint the length of the ladder touching down with alternating feet in between ladder rungs. Repeat the length of the ladder for 5 repetitions.
    1. Progression: increase distance or duration

Include a traditional static stretching program to include all the major lower extremity musculature, as well as the trunk and core. All stretches are held for 30 seconds and repeated twice per side. The cool-down should also incorporate planks, abdominal crunches and other core exercises.

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