Skeletal maturation of the elbow centers on the primary ossification centers of the humerus, ulna, and radius and on six distinct secondary centers of ossification. The chronological appearance and closure of these centers has been well documented6,7,8 (Fig. 5.1). Childhood terminates with the appearance of all secondary centers of ossification, adolescence terminates with the fusion of all secondary centers of ossification, and young adulthood terminates with the completion of all bone growth and the achievement of final muscular form. These events usually occur 6 months to 1 year earlier in girls than in boys.
Immature athletes are different anatomically, biome-chanically, and biochemically from adult athletes. These differences give rise to unique injury patterns in the young throwing athlete's elbow. The most common sites of injury in the young athlete's elbow are the epiphyseal plate, the joint surface, and the apophyseal insertion of the major tendon units. The growing athlete has unique injury risk factors due to the growth process itself. Longitudinal bone growth may cause injury to the muscle-tendon units, bone, and joints from a relative strength and flexibility imbalance, especially during growth spurts. The increase in muscle-tendon tightness about the elbow joint enhances the susceptibility to overuse injury. The presence of physeal cartilage at the plate, at joint surfaces, and at all sites of major tendinous insertions creates a special type of overuse and traumatic injuries. Growth cartilage, including the articular cartilage, is more susceptible to injury from repetitive microtrauma than is adult cartilage. The zone of hypertrophy is the structurally weakest portion of the epiphyseal plate, especially between the layers of degeneration and partial calcification. During adolescent growth spurts, this area of the physeal plate is weaker than the surrounding ligaments. As the
plate matures and becomes stronger than the surrounding ligaments, the area of potential injury changes. Therefore, adolescents tend to sustain physeal plate injuries, whereas the prepubescent child or skeletally mature athlete is more likely to sustain tendinous or ligamentous injuries.
Throwing imparts significant stresses on the developing elbow. To understand the mechanism of injury, it is important to understand the biomechanics of the overhead throwing motion, which is discussed in detail in Chapter 2 (Fig. 5.2). Certain stresses on the elbow occur during different phases of the throwing motion.9 Most injuries occur during the late cocking and acceleration phases. During these phases, the forces placed on the elbow result in valgus stress and hyperextension creating medial tension (distraction) overload on the medial restraints, lateral compression overload on the capitellar and radial head articular surfaces, posterior medial shear forces on the posterior articular surfaces and structures, and distraction anteriorly on the capsule (Fig. 5.3). All the manifestations of Little League elbow result from these forces.
Little League elbow is predominately an overuse syndrome of immature baseball pitchers but its manifestations are also seen in all positions of baseball and in other overhead activities, such as tennis, volleyball, javelin, and the quarterback position in football.10 Passing a football, serving a tennis ball, and spiking a volleyball place similar forces on the elbow as the pitching motion does. These overuse problems also occur in young gymnasts who place similar forces on the elbow by using it as a weight-bearing joint during maneuvers.11,12
The most common risk factor for developing Little League elbow is overuse. Poor throwing technique may also be a cause, and sometimes it is a combination of the two. The two can be cumulative as well, with overuse leading to fatigue, which contributes to poor technique and, conversely, poor technique leading to fatigue and overuse. Either way the end result is loss of the balanced interaction between muscle, ligament, and bone, creating an environment that places the elbow at risk of injury. There is a positive correlation between pitching frequency and repetitive trauma injuries.13 Overuse injuries result from repetitive submaximal loads that cause an accumulation of microtrauma that damages tissues quicker than the bodies ability to repair them. These injuries include stress fractures (bone and physeal), tendon breakdown, joint cartilage impaction injuries, and progressive ligament and capsular stretching. Overuse injuries can be insidious and chronic in nature or sudden, with an acute event superimposed on already weakened and damaged tissues or structures.
Often young athletes are subjected to the misguided "too much, too soon" training phenomenon.14 Many factors contribute to this phenomenon. Sport-specific summer camps have become popular during which the young athlete is required to participate suddenly in intensive training, often without preconditioning. Many young athletes now participate on multiple teams and throughout the entire year. Particularly at risk are those young athletes who demonstrate above-average skills. These outstanding young players are called on to perform too often. Coaches and parents are often guilty of trying to create an all-star athlete or to have a winning team while not understanding the potential risk of injury to a talented young player. All these factors contribute to potential overuse problems from excessive throwing and too little time for recovery.
Poor throwing techniques increase the stresses on the elbow beyond normal limits, making it it more susceptible to injury. In contrast, proper throwing techniques have been shown to reduce the incidence of injury in pitch-ers.15 Analysis of the overhand pitching mechanism and the sidearm pitching mechanism has demonstrated that the sidearm motion is three times more likely to lead to elbow problems.15 The type of pitch thrown can also increase the stresses on the elbow and focus these stresses in certain locations about the joint. At the end of the follow-through, the fastball pitch places more stress on the radiocapitellar joint because of terminal pronation, whereas the curveball creates more stress on the medial joint line because of terminal supination. Electromyo-graphic and high-speed film analysis has shown that the forearm supination required to throw a curveball pitch creates higher stresses on the elbow than a fastball pitch.13
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Since World War II, there has been a tremendous change in the makeup and direction of kid baseball, as it is called. Adults, showing an unprecedented interest in the activity, have initiated and developed programs in thousands of towns across the United States programs that providebr wholesome recreation for millions of youngsters and are often a source of pride and joy to the community in which they exist.