Anterior Cruciate Ligament Injury Prevention Programs

Jessica Graziano

Aisling M. Toolan

INTRODUCTION

Anterior cruciate ligament (ACL) injury in young athletes continues to be one of the most debilitating injuries despite extensive research on injury prevention. Sports participation is on the rise, and we live in an era of specialization where children are training year-round and at earlier ages. ACL injuries in children were once rare; however, they are now being seen with increased incidence paralleling the trend in specialization at younger ages.²,³,⁴,⁵ ACL injury has a significant physical and psychosocial impact resulting in time lost from play, interaction with teammates, loss of college scholarships, and decreased performance in the academic arena.¹,²

The literature has extensively reported on the high incidence of ACL injury in high school female athletes.³,⁴,⁵ With the rise in intrasubstance tears of the ACL in the prepubescent athlete, much attention is being paid to the injuries’ effects on general health.⁵,⁶,⁷,⁸,⁹ Sports injuries in children may threaten general health maintenance efforts, lead to arthritis, as well as contribute to obesity.¹⁰ In addition, the reinjury rate is highest amongt young athletes and has been reported to be 15 times more likely within the first year and 6 times more likely within the first 24 months after return to sports activity.¹¹

Given the serious impact this injury may have on young individuals, considerable effort has been directed toward prevention programs and is a rising area of interest to physicians, trainers, coaches, physical therapists, and caregivers. Approximately 70% of ACL tears occur from noncontact mechanisms such as during a jump landing or sharp deceleration.¹²,¹³ Because risk factors such as poor movement patterns and alignment with jump landings and changes in direction have been demonstrated to be modifiable, these mechanisms of injury are theoretically preventable.¹²,¹³ This chapter reviews the prevention programs centered on modifiable noncontact ACL mechanisms of injury. In order to have a better understanding of these programs, evidence-based mechanisms of injury and risk factors will be reviewed.

MECHANISM OF INJURY

Athletes may injure their knee via a contact or noncontact mechanism. A contact injury occurs when physical contact is made with another athlete. A noncontact injury is one that occurs without physical contact with another athlete.¹³ A non-contact ACL injury may occur as a result of combined motions at the knee joint, for example knee valgus and femoral internal rotation.¹⁴ Typically, these forces occur in sports during a sudden deceleration, jump landing (Fig. 14.1), and/or cutting maneuver (Fig. 14.2).

Female athletes have demonstrated the highest risk of ACL injury compared to their male counterparts, with incidence being two to eight times higher than males in soccer, basketball, and volleyball.²,¹⁵,¹⁸ Increased attention is being paid to prepubescent young athletes secondary to at-risk movement patterns being seen in children as young as 10 years of age as well as increased incidence of injury.¹¹,¹⁶,¹⁷,¹⁸ Stanitski et al.¹⁹ found that ACL injury was associated in 47% of children 7 to 12 years of age who had acute knee effusions.¹⁹ Movement patterns play a critical role in ACL injury by creating the potential for anterior tibial shear force, which directly strains the ACL.¹¹,²⁰,²¹

Both modifiable and nonmodifiable risk factors have been described in the literature. Modifiable risk factors are the premise for ACL prevention programs secondary to the potential to induce change on specific variables. Therefore, this chapter focuses on modifiable risk factors and their role in injury prevention programs.

RISK FACTORS SPECIFIC TO YOUNG ATHLETES

Early Specialization

Preadolescent and adolescent athletes are a special population secondary to the growth and development that occurs as they are trying to meet the demands of sports. Early specialization, maturation, undeveloped physical skills, high-risk movement patterns, and an inadequate strength base are all contributing factors to increased injury rates.¹¹,²² However, children do not master complex motor skills until late childhood (age 10 to 12 years) and demonstrate increased risk of injury when age-appropriate skill set does not meet the demands imposed on them by coaches and sport.¹¹,²³ If emphasis is placed on strengthening and the development of fundamental motor skills, as opposed to sports-specific training, then injuries sustained may be reduced.¹¹

Figure 14.1. An adolescent female athlete landing from a jump, demonstrating valgus (inward collapse) moments to bilateral knees, predisposing the athlete to risk of noncontact injury.

Growth Spurts and Maturation

Growth-related factors such as growth spurts, maturity-associated variation, and immature or underdeveloped coordination predispose young athletes to injury.²⁴,²⁵,²⁶ These factors may exert their influence with more frequent and intensive training and competition seen today.¹¹,²¹ There have been no differences in incidence in ACL tears reported between pre-adolescent males and females; however, differences become marked following maturation, with adolescent females demonstrating the most risk.¹¹,²⁸,²⁹ Puberty has been associated with deficits and delays in core stability and neuromuscular regression, and many sex-related differences emerge that have been associated with ACL injury.¹⁸,¹⁹,²⁰,²¹,²⁷,²⁸,²⁹,³⁰

Adolescent female athletes demonstrate measurable neuromuscular imbalances following the onset of maturation. Hewett et al.³¹ reported that female athletes landed with significantly more medial knee motion and greater maximum lower extremity valgus than male athletes following the onset of maturation. Males appear to have a neuromuscular spurt in strength, power, and coordination during puberty, which allows them to adapt to increased bony lever arms and a greater mass where females show little change (Fig. 14.3A,B).³¹,³²,³³ Core stability declines during growth spurts and may predispose athletes to at-risk movements secondary to mechanical breakdown throughout the kinetic chain.¹¹,²² During growth spurts, there is an increase in bony lever arms and the body’s center of mass changes which impacts postural alignment and neuromuscular control.²² Therefore, core strength, neuromuscular ability, coordination, and proprioception become imbalanced and contribute to risk of injury.²¹,²²,³⁰

Figure 14.2. Female athlete performing a cutting maneuver and demonstrating risk of injury secondary to a trunk lean with knee valgus and rotation.

Increased demand for peak performance is expected at younger ages during a time of major physiologic change.¹⁰,²¹ Care should be taken to ensure demands such as expected sports-specific movement patterns or training loads placed on the athlete’s body does not exceed their physiologic capabilities. In addition, a child may master a skill prior to their growth spurt but may need to revisit that skill later on in order to refine the movement patterns secondary to the changes they incur. To successfully reduce the incidence of ACL injuries in young athletes, one must demonstrate an understanding of modifiable risk factors specific to injury prevention programs.

MODIFIABLE RISK FACTORS: COMPONENTS OF ANTERIOR CRUCIATE LIGAMENT PREVENTION PROGRAMS

Many risk factors have been described in the literature. The most effective prevention programs combine a multifaceted approach to address various components. These components
include neuromuscular training, plyometric training, resistance training, flexibility, proprioception training, and technique monitoring and feedback. Neuromuscular training has received a lot of attention in the literature secondary to demonstrating the most promise in terms of altering movement patterns and decreasing ACL injuries.¹⁴,¹⁵ Athletes may display movement patterns, which put them at risk because of one or more imbalances that can be easily addressed with interventions. Hewett et al.²⁹ describe several modifiable risk factors, which have been demonstrated to reduce risk of ACL injury when addressed: ligament dominance, quadriceps dominance, leg dominance, and trunk dominance. Identification of these risk factors allows individuals potentially at risk to be identified and prevention strategies to be provided.

Figure 14.3. A. Prepubescent male performing lateral jumps with trunk shift over his right lower extremity and overall decreased control. B. Same male after puberty performing lateral jumps with good control, proper alignment, and more power.

NEUROMUSCULAR CONTROL

Ligament Dominance

Ligament dominance is defined as the tendency for valgus collapse secondary to neuromuscular imbalances and lack of muscular support about the knee affecting the ability to absorb ground reaction forces²⁹ (Fig. 14.4A,B). Therefore, the static restraints about the knee including bone, cartilage, and ligaments take the increased force.¹⁴ An athlete is at high risk when displaying substantial medial knee motion in the coronal plane combined with a low knee flexion angle.³⁴,³⁵,³⁶,³⁷ Gluteals, hamstrings, and gastrocnemius-soleus strength are critical components in prevention of ACL injury, and improper recruitment during landing tasks result in high abduction moments with increased strain on the ACL.³⁴,³⁵,³⁶,³⁷ In addition, several studies have demonstrated that high school female athletes demonstrate greater maximum knee valgus angle and greater ground reaction forces with a drop vertical jump than males and uninjured athletes, which may explain the higher prevalence of ACL injury in that population.³⁵,³⁶

Female athletes have been shown to exhibit greater hip adduction and internal rotation with decreased knee flexion during tasks such as walking, running, anticipated and unanticipated cutting, and landing.³⁸,³⁹,⁴⁰ Increased hip adduction and internal rotation predispose the athlete to valgus collapse at the knee. Gluteus maximus and medius play a role in prevention of dynamic valgus collapse by controlling hip adduction and femoral rotation. Weakness has been associated as a predictor
of injury secondary to inability of the weak musculature to keep the hip abducted during high-level single-leg activities such as landing and cutting.³⁸,³⁹,⁴⁰ Studies have demonstrated improved control of dynamic valgus collapse of the knee with gluteus maximus and medius strengthening.¹¹,¹³,³⁸ Several electromyographic studies have reported that side-lying hip abduction, side planks, and lateral band walks elicit sufficient maximal voluntary activation for strengthening of gluteus medius (Fig. 14.5A).⁴¹ Side-lying hip abduction may be performed during a side plank if appropriate control and stability can be maintained (Fig. 14.5B). Single-leg squats and single-leg deadlifts have also been demonstrated to maximally elicit gluteus maximus.⁴¹

Figure 14.4. Ligament dominance. A. Young athlete performing jumps in place and demonstrating valgus loading bilaterally. B. Same young athlete demonstrating proper alignment with jump landings 2 months after receiving intervention and feedback.

Quadriceps Dominance

Quadriceps dominance occurs during sports maneuvers such as cutting or jumping when preferential activation of knee extensors over flexors occurs.²⁹ The quadriceps acts as an antagonist, exerting maximum strain to the ACL in the last 30 degrees of knee extension.³⁹ In addition, it has been demonstrated that preferential activation of the quadriceps while landing in an erect position exerts anterior shear stress to the knee (Fig. 14.6A-C).²⁸,²⁹,³⁴,³⁷ Hamstring activation has been shown to play a role in controlling dynamic valgus by resisting anterior and lateral tibial translation and rotation.¹¹,²⁷,³⁴,³⁷,³⁹ In addition, hamstring activation with a jump landing or during a cutting maneuver results in a flexed knee posture (Fig. 14.7A-C) and is more protective to the ACL.³⁷,³⁹

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