There are several normal osseous variants of the elbow [3, 4]. Some individuals can have a ridge that runs transversely across the middle of the sigmoid notch dividing it into proximal and distal halves (Fig. 3). This ridge is variable in size and can be absent. The thickness of the articular cartilage on the ridge can be very thin, knowing this helps avoid confusing the ridge with a central osteophyte. At the medial and/or lateral margins of this ridge, there can be a small groove, which should not be confused with an osteochondral lesion (Fig. 4). Another osseous normal variant is when there is no osseous separation between the olecranon and coronoid fossae, called an olecranon foramen.

Because the ligaments and tendons in children are relatively strong relative to bone, pediatric throwers tend to get more osseous overuse elbow injuries compared to adult throwing athletes. The two main injuries in young throwers are therefore capitellar osteochondritis dissecans (OCD), and Little Leaguer’s Elbow. The OCD in pediatric throwers typically involves the anterolateral aspect of the capitellum [5–8]. Although it usually occurs in the dominant throwing arm of 12–17 year old boys who are baseball pitchers, it can also be seen in young gymnasts and in other overhead sports such as tennis (Fig. 5). The OCD in gymnasts is often bilateral, and is felt to be due to similar repetitive shear forces to the elbow during hand springs or walking on their hands.

Most authors stress the difference between OCD and Panner disease. Panner disease is typically found in younger boys under 10 years old, and there is rarefaction and fragmentation of the entire capitellum rather than only the anterolateral portion. The condition is treated conservatively with rest, and is usually self-limited with reconstitution of the capitellum and no long term sequelae. Although some authors report no history of trauma, others believe Panner disease is probably a similar manifestation of repetitive valgus load onto the capitellum, but in younger boys with an open capitellar physis [9].

Capitellar OCD can appear on radiographs as either a subtle area of osteopenia in the capitellum, flattening of the subchondral bone plate, or fragmentation. The subtle focal osteopenia of early OCDs can be difficult to see on radiographs, with some authors reporting that only about 1/2–2/3 are seen prospectively [7]. There are several radiographic, MR and arthroscopic grading systems for capitellar OCD that are used to separate early lesions from more advanced disease. The most important imaging determinant for the surgeon, however, is whether the OCD is stable or unstable. This is best determined with MR, and can often be done on routine T2-weighted images without intravenous or intraarticular contrast [1, 5, 8, 10]. Unstable capitellar OCD lesions will have linear increased T2 signal along most of the interface between the OCD fragment and the underlying epiphysis, or have cysts at this interface [6, 8]. If the increased signal involves only a portion of the interface in a child with an open capitellar physis, it may be stable [1, 8]. A full thickness articular cartilage fissure around the circumference of the OCD fragment is sometimes considered an additional sign of an unstable OCD.

Most capitellar OCD lesions do not heal with conservative management. Several authors have found that conservative treatment should only be pursued on patients who meet all three of the following criteria: (1) stable OCD on MR, (2) open capitellar physis, and (3) near-normal elbow motion [10, 11]. Because the majority of capitellar OCD lesions do not meet all three criteria, most either need surgery or will have a poor long term prognosis. About half of patients with a capitellar OCD will go on to have pain, reduced range of motion, or elbow degenerative change [11, 12].

Another injury in skeletally immature baseball pitchers is medial epicondyle apophysitis, also known as Little Leaguer’s elbow [13, 14]. This is felt to be a chronic stress injury to the medial epicondylar physis from repetitive traction on the apophysis by the common flexor tendons and UCL from the valgus stress during throwing. The radiographic finding is abnormal widening of the physis, usually greater than 3 mm. The size of the apophysis is also often larger than that in the contralateral non-throwing elbow, probably from chronic hyperemia. On MRI in patients with Little Leaguer’s elbow, the physis is wide and higher signal than normal, and there is typically adjacent bone marrow edema (Fig. 6).

The most common sites for fractures around the elbow after acute trauma are the radial head/neck and the olecranon process in adults, and supracondylar fractures in children [1]. MR can be helpful in imaging some patients with acute elbow trauma, particularly if a fracture is suspected clinically but the radiographs only show an effusion (Fig. 7). Radiographically, occult fractures will appear as linear low signal on T1-weighted images, with a variable signal-intensity fracture line on T2-weighted images with surrounding marrow edema.

Elbow dislocations can also result in fractures, often involving the coronoid process. Isolated coronoid process fractures can be small yet the patients can have significant ligamentous injuries [15]. Although patients with a small isolated coronoid process fracture after elbow dislocation may do well with casting and conservative management, those that demonstrate a “drop sign” on lateral radiographs often require surgery [16]. The injury of a coronoid process fracture, radial head fracture, and posterior dislocation is called the elbow “terrible triad,” and these patients are at high risk for chronic instability [15]. Another osteochondral injury that can be seen after elbow dislocation is the Osborne-Cotterill lesion, an osteochondral fracture of the posterolateral capitellum with or without an impaction defect of the radial head. These patients often do not heal their LUCL and thus have posterolateral rotary instability.

MR can also be helpful in patients with degenerative change who have pain and restricted range of motion. MR is more sensitive for detecting loose bodies within the elbow, which can be removed arthroscopically to give patients improved range of motion.