Definitions and Epidemiology

Very little data are available on the epidemiology of sport-related musculoskeletal injuries in children and adolescents.1–6 It is estimated that approximately 30 million children and adolescents participate in organized sports each year in the United States.3 The Centers for Disease Control and Prevention High School Sports-Related Injury Surveillance Study was conducted in 2005–2006. There were 7.2 million students who participated in high school sports in 2005–2006. It is estimated that high school sports account for two million injuries, 500,000 physician visits, and 30,000 hospitalizations every year. In the CDC study, sports injuries were defined as those (1) resulting from participation in an organized high school athletic practice or competition, (2) requiring medical attention from a certified athletic trainer or a physician, and (3) restricting the athlete’s participation for 1 or more days beyond the day of injury. An athlete exposure was defined as one athlete participating in one practice or competition during which the athlete was exposed to the possibility of athletic injury.

Sports-specific injury rates are shown in Table 19-1, proportion of injuries in practice and competition by diagnosis is shown in Figure 19-1, and proportion of injuries by sport and number of days lost are shown in Figure 19-2.

Based on the CDC study, the overall injury rate in all high school sports combined was 2.44 injuries per 1000 athlete exposures. Football has the highest injury rate at 4.36 injuries per 1000 athlete exposures. In each of the nine sports for which data were collected, approximately 80% of the injuries reported were new injuries. Overall, the injury rates were higher for competition compared to practice. Approximately 50% of the injuries resulted in less than 7 days of time lost from participation. No deaths were reported in the study.

Much less is known about the epidemiological characteristics of specific injuries and these are reviewed where information is available in specific chapters in this section of the book.

Mechanisms

In order to understand the mechanism and pathoanatomy of injuries in children and adolescents it is useful to briefly consider some unique aspects related to growth and development (Table 19-2). Implications of childhood growth and development for sport participation are reviewed in Chapters 1 and 2. Certain aspects unique to the adolescent age group that have implications for sport injuries include somatic growth, presence of growth cartilage, and properties and growth characteristics of bones are considered here.7–27

Height and Weight

The adolescent growth spurt in weight and height contributes to increased momentum and force in collision between athletes, for example, in football. Also, the axial skeleton must support the increased weight, and increased load.11 This increased weight and load increases the risk and severity of injuries. It has been observed that the number of football injuries increases with age throughout adolescence as the athletes get bigger. The matching of athletes based on their chronologic age and grade levels may contribute to an increased risk of injury for the late maturing athlete competing against the larger early maturing athlete.13

Muscle Growth, and Strength

There is an increased muscle hypertrophy during adolescence as a result of increased androgens.9 The spurt in muscle strength and increased training effects during adolescence is more pronounced in boys than in girls.9,10,14 The spurt in muscle strength occurs approximately 1 year after the spurt in muscle mass.9,14,15 In girls there is very little increase in muscle strength after menarche, whereas boys continue to gain strength throughout the adolescent years.8–10 The gain in strength correlates more precisely with the sexual maturity rating (SMR) than the chronologic age.9,10,12 For both, boys and girls, the response to strength and endurance training increases during SMR 4 and 5.7,13 In boys, the peak gain in strength is noted approximately 14 months following peak height velocity (PHV) and 8 months following the peak weight velocity.7,8,10,14 In adolescent males the peak of growth spurts in height, weight, and muscle mass occur at the same time, whereas in girls, the peak growth spurts in height, weight, and muscle mass occur sequentially in that order.7

Motor Skills and Performance

Agility, motor coordination, power, and speed show improvement during adolescence.7,10,14,15 Overall, girls perform better at balance tasks compared with boys. In boys, motor performance continues to improve throughout the adolescence, whereas in girls there is very little, if any, improvement after the age of 14 years.7,10,14,15 In boys, the maximal speed peak precedes PHV, while strength and power peak follow PHV; in girls, no clear patterns can be discerned. In adolescent boys, there appears to be a positive correlation between advancing biologic maturity and muscle strength and motor performance.7,10,14,15 Thus, both boys and girls show improvement in motor skills and performance; each gender follows a different course of development.

The increased skill level of the athlete can lead to a higher level of competition requiring a higher intensity of participation. Because, the maximal speed peak leads to an increase in the momentum during a collision and necessitates a quicker muscular response, both of these factors add to the risk and severity of injury in contact/collision sports.11 Skill level of the athlete is correlated with the level of competition by intensity of participation.

Body Composition

Gender differences in body composition are described in terms of fat mass (FM), fat-free mass (FFM), and body fat distribution. During adolescence, body composition and body fat distribution change; generally in boys there is a relative loss of FM, whereas in girls there is a relative gain in FM.7,8,16 Typically, both FM and FFM increase during early to middle adolescent years in adolescent boys and girls. In boys a transient decrease in fat accumulation occurs in the extremities during peak height velocity. On the other hand, girls continue to gain fat through late adolescence predominantly in lower trunk and thighs, and by SMR 4 and 5; the FM in girls can reach twice that of boys.4,7–9 The pattern of growth of FFM is similar to that noted for growth in height and weight.

Athletes may take extreme measures to manipulate body weight and composition so as to enhance sports performance. In fact, this may result in poor caloric intake, dehydration, and decreased performance. Wrestlers, gymnasts, ballet dancers, and football players all have been reported to engage in unhealthy weight control and dietary behaviors.7,13 In girls, such caloric deficit, weight loss, and intense training may lead to menstrual irregularities including amenorrhea.7,14,15,20,21 Decreased caloric intake and prolonged amenorrhea associated with hypoestrogenemia can lead to irreversible bone loss and contribute to increased risk for stress fractures.13–15,20,21 Menstrual irregularities along with bone mineral loss and disordered eating are components of the female athlete triad.

Flexibility

Adolescent girls are usually more flexible compared with boys. In girls, the flexibility increases during adolescence eventually plataueing at approximately 14 to 15 years of age.10,13–15 In boys, flexibility seems to decline from approximately ages 7 to 8 through mid-adolescence, then increase in late adolescence.10,13,14 During the growth spurt, the linear growth in bones occurs first, followed by secondary growth in soft connective tissue, thus leading to a period when there is myo-osseous disproportion and a relative decrease in flexibility.10,11,17 This decreased flexibility may contribute to an increased risk for injuries, especially overuse. Decreased flexibility is particularly noticeable in hamstrings and ankle dorsiflexors, especially in young dancers and gymnasts. In general, flexibility is influenced by internal factors such as bone structure, muscle volume, and tissue elasticity; as well as external factors such as ambient temperature, warm-up time, and physical exercise.7

In the adolescent, growth cartilage is present at epiphyseal plate, joint surface (articular cartilage), and apophysis (traction epiphysis—insertion site of major tendons) (Figure 19-3).17 These areas are susceptible to acute and chronic injuries, and are unique to the adolescent age group. The growth cartilage is the “weakest link” and therefore more prone to injury, compared with the ligaments.11,17

The impact of the forces applied to the bone can either be increased or decreased by the presence of the growth plate.11 The unlocking of the growth plate has been noted during the adolescent growth spurt, making it more susceptible to injury by shear forces.11,27 The risk of growth plate injury, especially in contact/collision sports, during the rapid growth period is also increased because of the different times at which they close.11 The articular cartilage is susceptible to repetitive microtrauma, potentially contributing to osteochondritis dissecans type lesions.17–19 The relatively less resilient articular cartilage is also more susceptible to injury from an increased force transmitted through the bone.11 Various apophyseal injuries, unique to adolescents, occur at tendon insertion sites.17–19 The risk of injuries to the growth plate from weight training has been the subject of long-term controversy. However, it is increasingly recognized that as more and more adolescents (and children) are participating in weight training, properly supervised weight training programs do not seem to increase the risk of injuries to the growth plate.13 However, competitive weight lifting, maximal weight lifts and powerlifting may increase risk for injuries in adolescents and may not be advisable for the young athlete.

A certain amount of load is necessary for normal bone growth and remodeling. Most of bone mineral density is acquired during the adolescent years and bone mass may fail to accrue optimally because of dieting and weight loss.16,20,21 The strength development of bones lags behind that of ligaments and tendons.11 This lag increases the risk of tendon or bone avulsions at the apophyseal insertion compared to a ligament injury; for instance, the avulsion of tibial spine would be more likely than sprain of the anterior cruciate ligament.17,19 In the adolescent, the bone has a greater potential for remodeling, which may also increase the risk of overgrowth and angular deformation.11 The size of the athlete is a poor indicator for the maturity of the bones or the growth cartilage. Thus, the bigger-looking athlete may be skeletally weaker and, therefore, at an increased risk of injury because of higher expectations and key positions given to her or him on the team.7,11,14

The most common mechanism of musculoskeletal injuries in children and adolescents relate to overuse, that is too much stress to the normal tissues without allowing adequate time for the tissues to adapt to an increasing level of physical stress. Acute catastrophic trauma, especially of the head and neck, is fortunately rare in youth sports. Of specific importance in children and adolescents are acute and chronic stress injuries of the growth plate. These categories of injuries are reviewed in detail in the subsequent sections below.

Clinical Presentation

The key elements of history to be ascertained in the evaluation of an athlete who presents with a musculoskeletal injury or symptom are summarized in Table 19-3. The examination should focus on the area injured as well as other areas or systemic examination based on the history. Specific aspects of examination are reviewed in the discussion of various injuries in subsequent chapters.

Clinical presentations of musculoskeletal injuries will vary based on the type of injury and the predominant area involved. Clinically sport-related musculoskeletal injuries can be categorized as follows: overuse injuries, acute soft tissue injuries, acute and chronic growth plate injuries, acute bone fractures, stress fractures, and joint dislocations, the general concepts of which are reviewed below.

When an athlete presents with a history of musculoskeletal injury or symptom or sign, the differential diagnosis should include a wide range of conditions in addition to different injuries as summarized in Table 19-4.