Radiographs are the first radiologic study undertaken when stress fracture is suspected. When positive, radiographs demonstrate focal periosteal reaction and occasionally endosteal cortical thickening and/or a lucent fracture line in the cortex. However, only about 10 % of radiographs are positive initially, as findings take from 2 to 12 weeks to manifest (Coady and Micheli 1997). MRI has become the imaging method of choice to confirm or exclude stress fractures when radiographs are negative (Heyworth and Green 2008). MRI is more precise than bone scintigraphy and allows discrimination of stress fractures from other bone insults, such as osteoid osteoma, osteomyelitis, neoplasm, and ligamentous injury with secondary osseous reaction (Coady and Micheli 1997). Fredericson and colleagues developed an MRI grading system for tibial stress fractures that has been clinically validated (Fredericson et al. 1995). Grade 1 stress injuries exhibit high T2 signal along the periosteum of the tibia with no signal abnormality present within the bone marrow (Fig. 27.12). Grade 2 injuries add abnormal high T2 marrow signal to the findings, but have no abnormal T1 signal in the marrow (Fig. 27.13). In grade 3 injuries, abnormal low T1 signal is also seen within the marrow (Fig. 27.14). Finally, grade 4 injuries include all these findings but add abnormal signal within the cortex, typically a fracture line but sometimes a broader, less linear area of abnormal signal (Fig. 27.15). In common parlance, injuries of grades 1–3 are referred to as “stress responses” or “stress reactions” and grade 4 injuries are considered “stress fractures.” Increasing grade of stress injury in the tibia reflects increasing severity of injury and often directs the level of restriction of activity recommended to the athlete. Kijowski and colleagues (2007) evaluated the radiographs of 86 patients with MRI scans demonstrating tibial stress injuries. The radiographs with periosteal reaction that corresponded to the patient’s maximal point of pain correlated with high-grade stress injuries, usually grade 4 (stress fracture). This finding may obviate MRI when radiographs of the tibia are positive, as the patient can be treated for stress fracture with confidence, unlike a low-grade stress response.

Stress fractures are rare in the upper extremity of pediatric athletes. Stress fractures occasionally occur in the proximal humerus as overuse injuries in throwing athletes, including baseball pitchers and javelin throwers, and those involved in rugby, swimming, and racquetball (Caviglia et al. 2005). These injuries can be imaged with MRI, bone scan, or CT and usually heal with conservative treatment (Caviglia et al. 2005). Similarly, stress osteolysis of the distal clavicle is rare in adolescents but can occur in adolescent weight lifters. When present, this entity decreases mineralization of the distal clavicle and causes resorption of its distal tip (Fig. 27.16) (Gomez 2002).

Wrist impaction stress injuries are common in female pediatric gymnasts. “Gymnast wrist” is thought to be caused by chronic compressive impact forces and can reflect several different specific injuries, including overuse injuries of the distal radial physis, tears of the triangular fibrocartilage or rarely the scapholunate or lunotriquetral ligaments, cartilage damage along the articular surfaces of the distal radius and carpal bones, and dorsal ganglion cysts of the wrist (Mandelbaum et al. 1989). Most commonly, gymnast wrist refers to injury of the growth plate of the distal physis (Auringer and Anthony 1999). These injuries often have chronic sequelae into adulthood. The physis of the distal radius suffers marked compressive loading during gymnastics routines, especially with the wrist dorsiflexed, applying compression and shearing forces across the physis. As with the injuries of the proximal humeral and medial epicondyle physes, this injury is understood as a chronic stress injury of the physis, basically a nondisplaced Salter-Harris I stress fracture (Carter et al. 1988). This injury also occurs in weight lifters and roller skaters (Carter et al. 1988). Radiographic changes may include asymmetric widening, haziness, and irregularity of the physis, with variable sclerosis and cystic changes on the metaphyseal side (Fig. 27.17) (Carter et al. 1988; Roy et al. 1985). In some patients with the classic clinical findings of gymnast wrist (namely, wrist pain in the setting of gymnastics), radiographs appear normal. In one study, patients with normal radiographic results were able to return to gymnastics and were pain-free after resting for only a few weeks, whereas those with radiographic findings required an average of 3 months of inactivity to heal (Roy et al. 1985).

Patients who have substantial cumulative injury to the distal radial physis may undergo premature closure of the physis and exhibit a relatively short radius (Fig. 27.18). These patients will have positive ulnar variance and may sustain the various components of ulnar impaction syndrome in their late teenage years and adulthood. This syndrome includes fraying or tearing of the triangular fibrocartilage; damage of the articular cartilage of the lunate, distal radius, and/or triquetrum; and ultimately, tears of the lunotriquetral ligament and degenerative arthrosis of the involved bones in the end stages (Zetaruk 2000). However, full-blown ulnar impaction syndrome with all the components is rare in adolescents. The main component of this syndrome seen in adolescents, other than the positive ulnar variance, is injury to the triangular fibrocartilage (Fig. 27.19) (Zetaruk 2000), which has also been reported in adolescent basketball players with positive ulnar variance (Gaca 2009).

In 1966, Adams reported five cases of Little Leaguer’s shoulder, all in adolescent male baseball pitchers (Adams 1966). Adams referred to this malady as osteochondrosis, but it is now thought of as a stress injury to the proximal humeral physis. This overuse injury is probably best considered a chronic stress form of a nondisplaced Salter-Harris I fracture and occurs in throwers aged 11–16 years, especially baseball pitchers (Lord and Winell 2004; Gomez 2002). This fracture is thought to result from rotational forces placed on the proximal humeral physis by repetitive pitching (specifically too many pitches per week over many weeks), especially curveballs, and other high-volume throwing activities. Patients describe pain particularly in the follow-through stage of the pitching motion (Saperstein and Nicholas 1996). Recent weight gain and out-of season throwing are also risk factors for this injury (Lord and Winell 2004; Latz 2006; Emery 2009). This fracture is an excellent example of the advantages of cross-training (switching sports in different seasons) to pediatric athletes. Switching to a sport that does not place similar stresses on the throwing arm would allow the physis to recover normally and reduce the risk of chronic injury.

Radiographs of patients with Little Leaguer’s shoulder may be normal. When positive for the injury, radiographs demonstrate the physis to be widened (Fig. 27.20), often with accompanying demineralization, fragmentation, cystic change, or sclerosis (Lord and Winell 2004; Emery 2009; Adams 1966). Because the changes may be subtle, the radiographs should be compared with those of the patient’s asymptomatic non-throwing shoulder if there is any uncertainty (Latz 2006). MRI is not typically performed for this injury, but when performed, it shows widening of the physis, in addition to the increased T2 signal intensity within the physis and occasionally edema in the subchondral bone adjacent to the physis. If the patient is treated appropriately with rest to the throwing arm, Little Leaguer’s shoulder is self-limited and resolves rapidly (Adams 1966); appropriate treatment is important, because the proximal humeral physis is responsible for much of the length of the growing humerus (Gomez 2002).

Most tibial stress fractures are focal injuries that occur in the proximal third of the bone, typically along the posterior medial side. The injury clinically referred to as “shin splints” is a longer segment injury, purportedly an enthesopathy that encompasses up to half the length of the bone (Carty 1998). Shin splints only exhibit periosteal signal abnormality on MRI and no abnormal signal within the marrow space (Fig. 27.21). As such, this is a form of Fredericson grade 1 stress response (Fredericson et al. 1995). Although less frequently used due to the rise of MRI, 3 phase bone scan was used previously because it was more sensitive than radiography. Shin splints present as linear increased uptake along the posterior medial tibia (Fig. 27.22).

An important, albeit rare, type of tibial stress fracture occurs in the anterior cortex of the middle third of the bone. This anterior tibial stress fracture occurs in teenagers and young adults involved in sports involving frequent leaping, especially basketball (Beals and Cook 1991; Rettig et al. 1988). On radiographs these injuries are all visible, exhibiting a definite transverse lucent line through the anterior cortex and considerable cortical hypertrophy around the line (Fig. 27.23) (Beals and Cook 1991). The importance of recognizing this type of stress fracture lies in its clinical course. Unlike other stress reactions, these anterior mid-tibial stress fractures are unlikely to heal with short-term immobilization. Longer periods of inactivity are usually required and they often require surgical excision and bone grafting to heal (Beals and Cook 1991; Green et al. 1985). Before the importance of these injuries was understood, it was common for them to progress to complete fractures on resuming practice following a period of immobilization or rest (Beals and Cook 1991; Green et al. 1985). These stress fractures are considered delayed union stress fractures (Rettig et al. 1988) and the resistance to healing despite conservative treatment is thought to relate to the fact that the anterior cortex of the tibia is under tension, whereas the posterior proximal or distal cortex, which is where most tibial stress fractures occur, is under compression (Rettig et al. 1988; Green et al. 1985).

Fibular stress fractures are also relatively common in pediatric athletes (Fig. 27.24). Stress injury in the fibula most commonly occurs in the distal third of the bone (Woods et al. 2008). Cortical signal abnormality is present in most cases, either linear or more commonly globular (Woods et al. 2008). Foot and ankle stress fractures usually occur in dancers and distance runners, especially within the metatarsals, and sesamoid stress fractures have been reported in runners, ballet dancers, and soccer and field hockey players (Fig. 27.25) (Coady and Micheli 1997). Freiberg infraction typically occurs in the second or third metatarsal head of 12–15-year-old athletic girls and is related to repetitive stress. Freiberg infraction is considered to be either a stress fracture or stress-induced osteonecrosis and results in flattening and sclerosis of the metatarsal head and occasional fragmentation (Fig. 27.26) (Pommering et al. 2005; Vanhoenacker et al. 2002). Stress fractures of the tarsal navicular are rare in this age group but are ominous as they are prone to nonunion (Fig. 27.27) (Bernhardt and Landry 1995).

Femoral neck stress fractures, relatively common in adults, are rare in most reports on pediatric stress fractures. However, they do occur (Meaney and Carty 1992) and in one report comprised 5 of 53 stress fractures occurring in pediatric athletes (Fig. 27.28) (Micheli 1983). As described earlier, the Fredericson grading system for stress injuries has been clinically validated for the tibia, for which it was developed. It is frequently used when describing stress changes elsewhere in the skeletal system, but has not been similarly validated in these other settings. One should be cautious when applying this system to other bones, since the pathophysiology in other bones will not necessarily be analogous to the tibia. Because of differences in mechanics and load bearing, the clinical relevance of specific findings in the tibia may not directly translate to treatment regimens for other bones. For this reason, when observing any signs of stress injury to bones other than the tibia, it is recommended that one specifies them as “stress fractures” and delineates the specific findings, allowing the sports medicine physician to tailor the appropriate treatment. One must be especially cautious about labeling a stress injury of the femoral neck anything but a stress fracture, because a femoral neck stress fracture that is not appropriately treated and progresses on to complete fracture is a catastrophe.

The discussion of elbow injuries in pediatric athletes, especially those who are skeletally immature, centers on a set of maladies grouped under the rubric Little Leaguer’s elbow. About 20 % of pitchers aged 10–14 years have experienced elbow pain (DaSilva et al. 1998). Little Leaguer’s elbow is an overuse phenomenon resulting from chronic repetitive valgus stresses placed on the elbow by the throwing motion, typically seen in pitchers and quarterbacks who throw more than 200 times per week (Do and Herrera-Soto 2003). This valgus stress occurs during the cocking and acceleration phase of the throwing motion and places tension on the medial side of the elbow and compression on its lateral side (Gomez 2002; Ryu and Fan 1998). These forces, when repeated often enough, may result in several specific pathologic entities, including traction apophysitis of the medial epicondyle, osteochondritis dissecans of the capitellum, loose intra-articular fragments, traction apophysitis of the olecranon, premature closure of the radial physis, and/or overgrowth of the radial head (Lord and Winell 2004; Micheli 1983). Traction apophysitis describes a condition of irritation and breakdown of the apophyseal physis (Saperstein and Nicholas 1996). Apophyseal physes are most vulnerable in the growing elbow because they are weaker than the bone and the muscle-tendon unit. Certainly, apophyses that are subjected to abrupt extreme forces may displace from the underlying bone, termed an avulsion fracture; however, if the tendon repeatedly subjects the apophysis to chronic submaximal forces, the physis may develop chronic traction apophysitis.

Traction apophysitis of the medial epicondyle is one of the most frequent components of Little Leaguer’s elbow (Saperstein and Nicholas 1996). The medial epicondyle is the origin of the flexor pronator tendon group, which places tension on the medial epicondyle when strong valgus forces are in effect. This condition afflicts not only preadolescent and adolescent pitchers who engage in heavy throwing regimens but also tennis players and javelin throwers (Gomez 2002; Stanitski 1997). Radiographs demonstrate variable irregularity of ossification, fragmentation, and sclerosis of the apophysis as well as widening and indistinctness of the physis (Fig. 27.29) (Saperstein and Nicholas 1996; Auringer and Anthony 1999; Bernhardt and Landry 1995). MRI demonstrates widening of the physis and increased T2 signal intensity within and possibly adjacent to the physis. The apophysis may be segmented and partially resorbed (Sugimoto and Ohsawa 1994).

Traction apophysitis in the elbow is not limited to the medial epicondyle ossification center. This overuse injury can also affect the olecranon apophysis, though less commonly. Occasionally mentioned as a component of Little Leaguer’s elbow, traction apophysitis of the olecranon more commonly afflicts high-level gymnasts (Maffulli et al. 1992). Football players, competitive divers, and hockey players have also been diagnosed with olecranon apophysitis (Do and Herrera-Soto 2003; Maffulli and Baxter-Jones 1995). Radiographic findings are analogous to those at the medial epicondyle, with variable degrees of physeal widening and apophyseal indistinctness and fragmentation (Maffulli et al. 1992). Caution must be applied in interpreting the lateral radiograph in children because in young children the normal physis may measure up to 5 mm; by the age of 12 years, though, the physis should be narrow, with serpiginous but congruent apposing borders (Chan et al. 1991). Stress fractures are known to occur in the olecranon after physeal closure (Maffulli et al. 1992) but may even occur within the olecranon ossification center before skeletal maturity in baseball pitchers, wrestlers, and gymnasts. When this fracture occurs, radiographs reveal fragmentation and sclerosis of the apophysis and widening of the physis (Maffulli and Baxter-Jones 1995; Chan et al. 1991; DaSilva et al. 1998); undoubtedly, there must be a clinical and radiographic overlap between stress fractures of the apophysis and stress injuries of the physis itself.

One of the causes of a chronically painful hip in pediatric athletes is traction apophysitis. Pelvic apophysitis results in dull, activity-related pain near the hip. Apophysitis in the hip and pelvis is described in runners, dancers, and in hockey, lacrosse, and football players (Frank et al. 2007). Any of the pelvic apophyses may be involved by traction apophysitis. Acute avulsions are commonly seen in the anterior inferior iliac spine and anterior superior iliac spine but traction apophysitis can also occur at both locations (Fig. 27.30). Traction apophysitis also occurs at the iliac crest, often in runners (Fig. 27.31), and the ischial tuberosity (Fig. 27.32) (Auringer and Anthony 1999; Hotchkiss et al. 2007). On radiographs, the physis may have a normal appearance or appear mildly widened, but not displaced (Frank et al. 2007). At the ischial tuberosity, the apophysis may not be ossified yet, in which case traction apophysitis will cause the margins of the bone to appear irregular and sclerotic, with lucent defects (Kozlowski et al. 1989). MRI of traction apophysitis in the pelvis reveals abnormally increased T2 signal in the bone and sometimes the attached tendon. Ultrasound demonstrates soft tissue thickening about the enthesis and thickening and increased echogenicity of the tendon at the attachment site (Carty 1998).

Another overuse injury of the pelvis, osteitis pubis, does not occur in young children but is seen in late adolescent runners, fencers, and soccer, hockey, and football players (Hotchkiss et al. 2007; Waite and Krabak 2008). The concepts regarding etiology of osteitis pubis and the broader topic of athletic pubalgia continue to evolve, but osteitis pubis is clearly a chronic overuse injury and likely results from stress related to shear forces from unbalanced traction on the pubic symphysis (Waite and Krabak 2008; Paletta and Andrish 1995). Osteitis pubis results in a gradual onset of pubic pain related to activity. Radiographs reveal sclerosis and rarefaction of the subchondral bone at the pubic symphysis, as well as erosions and cystic changes (Fig. 27.33). However, it can be difficult to discriminate these abnormalities from normal irregularity and fragmentation at the symphysis in the skeletally immature patient (Hotchkiss et al. 2007; Waite and Krabak 2008). MRI demonstrates T2 signal abnormality in the subchondral bone (Fig. 27.34).

Anterior knee pain is the most common complaint in the adolescent and preadolescent athlete (Ryu and Fan 1998), and many of these complaints stem from the extensor mechanism. Osgood-Schlatter disease is one of the common causes of anterior knee pain in this age group. Most common in 12–15-year-old boys and 8–12-year-old girls, Osgood-Schlatter is a traction apophysitis related to strong forces from the quadriceps mechanism. It occurs at the insertion of the patellar tendon on the tibial tuberosity (Gholve et al. 2007). Repeated jumping, squatting, and/or kneeling leads to Osgood-Schlatter, which produces local pain, swelling, and tenderness at the tuberosity (Gholve et al. 2007). Radiographs reveal irregularity of the apophysis, occasional widening of the physis, and separate bone fragments within the distal tendon near its insertion (Fig. 27.35). Thickening of the tendon will also be present (Gholve et al. 2007; Rosenberg et al. 1992). Bone fragments within the tendon are present in 50 % of cases (Stanitski 1993). On MRI, there is abnormal high signal within and surrounding the tendon on T2-weighted images, and deep infrapatellar bursitis is often present (Auringer and Anthony 1999; Rosenberg et al. 1992). On ultrasound, the tendon will be thickened and heterogeneous and may exhibit echogenic bone fragments and increased vascularity (Fig. 27.36). This malady is considered self-limited, but even with a reduction in athletic activities, symptoms may take months or years to resolve (typically at skeletal maturity), if they ever do (Gholve et al. 2007; Davids 1996).

Sinding-Larsen-Johansson disease is a similar traction apophysitis that affects the origin of the patellar tendon at the inferior pole of the patella in a slightly younger age group (Bernhardt and Landry 1995; Lyon and Street 1998). Technically not an apophysis, the inferior pole of the patella reacts just like the tibial tubercle when subjected to chronic traction forces by the extensor mechanism, so Sinding-Larsen- Johansson is considered a traction apophysitis (Wojtys 1987). The radiographic and MRI findings of Sinding-Larsen-Johansson are identical to those of Osgood-Schlatter, except that they occur at the origin of the patellar tendon (Fig. 27.37) (Auringer and Anthony 1999). For both Osgood-Schlatter and Sinding-Larsen- Johansson, ossicles within the tendon are not enough to make the diagnosis; there must be soft tissue swelling of the tendon, as bone fragments occasionally may occur at the entheses of the tendon as a normal variant (Gaca 2009). The situation changes in skeletally mature adolescents, because similar chronic traction phenomena at the inferior pole of the patella result in jumper’s knee, which is chronic patellar tendinitis (Bernhardt and Landry 1995; Stanitski 1993). MRI findings include thickening and high T2 signal in and around the tendon (Fig. 27.38). Partial tears should be sought, as they may change treatment. On ultrasound, the normal fibrillar echo pattern of the patellar tendon becomes heterogeneous. The tendon will be swollen and may exhibit partial tears (Roberts et al. 2002).

There is some overlap of true traction apophysitis entities in the foot and ankle with cases of osteochondrosis, which is a term for disordered endochondral ossification that becomes symptomatic. Sever disease is a common overuse traction apophysitis at the calcaneal tuberosity (Pommering et al. 2005) that causes exquisite tenderness at the attachment of the Achilles to the apophysis (Stanitski 1997). This apophysitis usually occurs in 10- to 13-year-olds with tight Achilles tendons and plantar fasciae who have undergone recent growth spurts and concurrent increases in activity (Pontell et al. 2006; Saperstein and Nicholas 1996). Sever disease may lead to fragmentation and sclerosis of the apophysis and widening of the physis (Fig. 27.39), but these findings are often present to a similar degree in asymptomatic preadolescents (Pommering et al. 2005). As such, there are no reliable radiographic signs of Sever disease, and this diagnosis is a purely clinical one. Even MRI often demonstrates moderate high T2 signal in the calcaneal apophysis in asymptomatic youths, so MRI also is not diagnostic (Vallejo and Jaramillo 2001). Iselin disease is a similar traction apophysitis that occurs at the attachment of the peroneus brevis tendon onto the fifth metatarsal base apophysis in runners (Pontell et al. 2006). Radiographs are typically normal (Bernhardt and Landry 1995) but may demonstrate enlargement or fragmentation of the apophysis and widening of the physis (Canale and Williams 1992).

OCD of the capitellum is also a frequent component of Little Leaguer’s elbow, causing insidious lateral pain and sometimes locking and catching (Kobayashi et al. 2004). OCD is a condition in which a layer of subchondral bone and sometimes the overlying articular cartilage become damaged and separate from the underlying bone, whether the fragment displaces or not. Some degree of necrosis of the fragment occurs, but the injury may heal. If the injury worsens, the fragment may eventually break down and displace (Ryu and Fan 1998). OCD of the capitellum is thought to be caused by overuse/repetitive trauma, probably shear and compressive forces that accompany the valgus load experienced by overhead throwing pitchers and similar athletes, including gymnasts. This condition is most common between the ages of 12 and 16 years (Ryu and Fan 1998; DaSilva et al. 1998).

Radiography of the elbow is the first step in imaging. Radiography demonstrates a well-defined lucent lesion with sclerotic borders (DaSilva et al. 1998), flattening of the articular surface, or fragmentation of the subchondral bone. Some cases may be radiographically occult (Kijowski and De Smet 2005b). Displaced fragments are most commonly located in the olecranon fossa (Fig. 27.40) (Kijowski and De Smet 2005c). MRI positively identifies these lesions and accurately depicts their size and whether or not there is a displaced fragment (Fig. 27.41) (Bowen et al. 2001). MRI demonstrates that the lesion occurs in the anterolateral aspect of the capitellum and often helps guide surgical intervention (Emery 2009). Surgery may be performed in the setting of unstable lesions, which rarely heal, but is largely directed by clinical findings of persistent symptoms (Kobayashi et al. 2004). On MRI, OCD is well demarcated with a linear interface surrounding a crescentic focus of high T2 signal intensity along the articular surface of the subchondral bone anterolaterally. Occasional early cases may show only the focus of the edema and may not have developed the well-defined sclerotic margin yet. MRI signs of instability include a rim of high T2 signal intensity surrounding the lesion or cysts underlying the interface of the lesion with the adjacent normal bone (Emery 2009; Kijowski and De Smet 2005b). Stable lesions have low T2 signal intensity surrounding the OCD (Kijowski and De Smet 2005b). One must not mistake the pseudo-defect of the capitellum, a common normal variant demonstrating a small focus of cartilage absence in the posterolateral capitellum, with OCD, which occurs anteriorly and laterally (Tuite and Kijowski 2006). OCD of the capitellum more often leads to an inexorable worsening of clinical findings than OCD in the knee, and chronic irregularity of the articular surface and displaced intraarticular fragments are frequent in the elbow (Bowen et al. 2001). Although surgery often improves the condition, both nonsurgically and surgically treated patients may have chronic pain, premature degenerative arthritis, and loss of terminal extension (Tuite and Kijowski 2006).

OCD in the elbow may also affect the trochlea (Fig. 27.42). Marshall and colleagues (2009) reported a series of osteochondral lesions of the trochlea, including three cases of medial trochlear OCDs, ten cases of lateral trochlear OCDs, and five cases of osteonecrosis. The lateral trochlear OCD cases occur in a relative vascular watershed, especially in football players, pitchers, and gymnasts. Lateral trochlear OCD is also seen in longtime skateboarders. Trochlear OCD is seen less frequently than OCD of the capitellum. As with OCD of the capitellum, surgical treatment of trochlear OCD may consist of debridement, stabilization with various hardware, microfracture and drilling, or mosaicplasty (Ansah et al. 2007).

OCD of the capitellum can be confused with Panner disease. Both lesions are best understood as osteochondral lesions of the capitellum. However, Panner disease, classified as true osteochondrosis of the capitellum (Ruch and Poehling 1991), usually occurs in children younger than 10 years and most frequently involves the entire ossification center (Bowen et al. 2001; Kobayashi et al. 2004; Maffulli and Baxter-Jones 1995). OCD develops after the age of 10 years and involves only a portion of the capitellum. Panner disease results in more dramatic findings on radiographs, resembling those of Legg-Calvé-Perthes disease of the proximal femoral epiphysis, with irregularity, fissuring, fragmentation, and collapse of the epiphysis (Fig. 27.43) (Kobayashi et al. 2004). However, Panner disease responds well when the affected extremity is rested. Clinical series report good long-term results in the vast majority of patients treated without surgery (Kobayashi et al. 2004; Bowen et al. 2001). Some think that Panner disease and OCD represent a continuum of disordered endochondral ossification, but it remains unclear if these are distinct entities or not (Kobayashi et al. 2004). Nevertheless, their radiographic findings and age at presentation differ, and the prognosis for Panner disease is much better than that for OCD.

In the knee, OCD affects the posterior lateral (mesial) portion of the medial femoral condyle in more than 70 % of cases, the central lateral femoral condyle in 15–20 % (Fig. 27.44), and the patella in 5–10 % (Kocher et al. 2006). Patellar lesions occur almost exclusively in the lower pole (Fig. 27.45), which distinguishes OCD from the upper pole location of dorsal defects of the patella (Edwards and Bentley 1977). These lesions present in children, adolescents, and young adults and are separated into two groups: juvenile OCD occurs in patients with completely open physes; adult OCD occurs in patients with closing or closed physes (De Smet et al. 1997). This distinction is important, as juvenile OCD lesions usually heal without consequence using conservative measures but adult OCD is more likely to become unstable, worsen clinically, require surgical intervention, and lead to premature degenerative arthrosis (Kocher et al. 2006; Sales de Gauzy et al. 1999). As with many other overuse injuries, the incidence of OCD of the knee is increasing in pediatric athletes, thought likely to be due to increasing participation in competitive sports (Kocher et al. 2006). There is not enough evidence to conclusively prove the cause of OCD of the knee, but most investigators believe the root cause is repetitive trauma or shear forces leading to a stress reaction that progresses to a stress fracture in the subchondral bone with components of ischemia. With cessation of impact loading, the lesion may revascularize and heal over time, but continued stresses cause further progression (Kocher et al. 2006; Micheli et al. 2006; Hefti et al. 1999). End-stage lesions delaminate on a macroscopic level and fragments displace from the bed into the joint (Micheli et al. 2006). Of the different sites in the knee, OCD occurring in the medial femoral condyle and trochlea (rare) are most likely to heal (Micheli et al. 2006). Surgical techniques for OCD include fixation with several devices such as variably threaded screws, K wires, and tacks, picking/microfracture, autologous cartilage implants, and mosaicplasty (Micheli et al. 2006).