General Principles
Sport-specific injury prevention training programs are utilized across the country as an aid to increase performance and decrease injury rates. Two common areas of athletic injuries include the shoulder and knee. Among the athletic population, injuries to the throwing shoulder are becoming more apparent as a result of overuse and poor conditioning. Similarly, the number of anterior cruciate ligament (ACL) knee injuries continues to rise each year among the athletic population. This chapter focuses on specific prevention protocols for reducing the likelihood of athletic knee injuries and specific to ACL pathology and injuries to the throwing shoulder of young and elite athletes.
ACL Injury Prevention
Epidemiology and Injury Statistics
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Injury to the ACL can be functionally debilitating and often requires surgical intervention.
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ACL injuries are common in sports and strenuous work activities.
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Approximately 200,000 ACL injuries occur annually in the United States.
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Over a 20-year period, ACL surgery procedures have increased by 58%, with 148,714 ACL surgeries performed in 2013 (PearlDiver Technologies. PearlDiver supercomputer database. Available at: http://www.pearl-diverinc.com/ ).
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One in 3,500 people will sustain an ACL injury.
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In total, 62%–66% of ACL injuries are sports related, often in a noncontact manner (i.e., running, cutting, or landing from a jump).
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Females are 4–6 times more likely to sustain an ACL injury than their male counterparts.
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There is a 10-times greater risk of developing osteoarthritis in an injured ACL knee.
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In total, 67% of ACL injuries occur in individuals aged 15–29 years.
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Athletes are at an increased risk of contralateral ACL injury following a first-time ACL injury.
Risk Factors for ACL Injury
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Increased knee valgus with running, cutting, and jump landing
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Decreased knee flexion angles with jump landing; this is often present in a quadriceps-dominant knee
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Decreased hamstring-to-quadriceps strength ratios: Females rely more on their quadriceps to stabilize their knee joints and tend to have lower hamstring-to-quadriceps muscle strength ratios. Hamstring-to-quadriceps ratios of <75% and a bilateral hamstring difference of >15% have been correlated to a higher incidence of ACL injuries in female athletes (Knapik et al: AJSM 1991).
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Neuromuscular control deficits can create a difficulty in generating muscular force. This limits the ability to resist displacing loads through dynamic stabilization of the knee.
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A smaller intercondylar notch has been found to be associated with the risk of ACL rupture in a skeletally immature population.
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Lateral trunk displacement with jump landing
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Poor hip strength and control
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Ligamentous laxity: Athletes with greater generalized laxity demonstrate increased midfoot loading and valgus collapse. This valgus force can be most apparent during running, cutting, or landing from a jump.
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Hormonal changes
Review of Literature
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A 6-week prevention program focusing on plyometrics, neuromuscular and strength training, flexibility, and appropriate body mechanics reported that subjects of an untrained group had a 2.4–3.6 higher ACL injury rate.
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A study of trained soccer players aged 14–18 years who performed preventative stretching, strengthening, plyometrics, and agility drills reported an 88% reduction in the rate of ACL injuries over 1 year and a 74% reduction in ACL injuries over 2 years. Those in the untrained group were at a 10 times greater risk of ACL injury.
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A study of the Norwegian team handball players analyzed over 3 years reported significantly fewer noncontact injuries in participants of the intervention group. Subjects performed proprioceptive, agility, plyometric, and balance drills 3 times a week for 5–7 weeks before the season and then once a week during the season.
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In a program of 4,700 ski instructors and patrollers that consisted of educational training on avoiding high-risk behaviors, recognizing potentially dangerous situations, and how to respond to situations, the injury rate was reduced by 62% over a span of 3 years.
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A study of 600 Italian semiprofessional and amateur soccer players participating in a proprioception and balance-training program reported reduced ACL injury rates by 87% over a duration of 3 seasons.
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An 8-week preseason program for German female handball players reported significantly lower rates of ankle and knee injuries. It emphasized the role of educational training with regard to injury mechanisms. Subjects participated in balance-board training drills that consisted of double- and single-leg stance, catch with a partner, and throws at a goal. Jump training exercises were also performed, including forward, backward, and lateral jumps, drop jumps onto a mat, and jump landing with eyes closed.
Prevention Training
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ACL prevention training should focus on the following:
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Hip control
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Aimed to prevent valgus knee collapse
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Target muscle groups should be those that control hip abduction, hip external rotation (ER), and hip extension.
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Example exercises include hip external/internal rotation (ER/IR) with resistance band (Theraband CLX; Performance Health, Akron, OH), single-leg front step downs, lateral slides with resistance bands (Theraband CLX; Performance Health, Akron, OH) ( Fig. 65.1 ) , unilateral Romanian deadlifts (RDLs), side-lying manual resistance clams, and stability ball bridging.
Figure 65.1
Lateral slides with resistance bands (Theraband CLX; Performance Health, Akron, OH) around the distal femur to strengthen gluteus medius musculature of the hip.
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Neuromuscular control and proprioception
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Athletes should be aware of where their knee is relative to their body in space.
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Dynamic joint stability is dependent on neuromuscular response time.
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Improving neuromuscular co-activation enhances knee stability.
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Manual perturbations can be implemented into drills to create a postural disturbance, thus further enhancing neuromuscular control.
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Neuromuscular training can also help improve an athlete’s confidence.
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Example exercises include balance board drills with double- or single-leg stance. The difficulty of this activity can be progressed by having the athlete play catch with a ball. This drill can be further enhanced by having the athlete maintain balance while stabilizing against manual perturbations, while also playing catch ( Fig. 65.2 ).
Figure 65.2
Manual perturbations with ball catches.
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Trunk control and core strengthening
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Important in preventing lateral displacement
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Females tend to land from jumping with greater lateral trunk motion than males.
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Example exercises include prone or side planks and single-leg medicine ball cross-patterns on a foam disc ( Fig. 65.3 ). Cross patterns are performed by having the athlete move extended arms side-to-side and then up/down.
Figure 65.3
Single-leg cross pattern on a foam disc to alter the patient’s center of gravity.
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Hamstring strengthening
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An athlete is dependent on muscular co-activation to maintain appropriate knee joint dynamic stabilization.
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The goal is to eliminate a quadriceps-dominant knee and establish an appropriate hamstring-to-quadriceps muscle strength ratio.
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Examples exercises include physioball bridging with concomitant hamstring curls ( Fig. 65.4 ), prone machine hamstring curls, and eccentric Nordic hamstring drills.
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