Orthopedic Reviews 2017; volume 9:7030 Radiographic evaluation ative to the capitellum, and Baumann’s of common pediatric elbow angle.3 More subtle radiographic features, Correspondence: Steven F. DeFroda, such as the posterior fat pad sign, may be Department of Orthopaedics, Alpert Medical injuries indicative of an underlying fracture even School of Brown University, 593 Eddy Street, when a fracture is not radiographically Providence, RI 02903, USA. 6 Tel: +1.4014444030 - Fax: +1.4014446182. Steven F. DeFroda,1 Heather Hansen,2 apparent. The purpose of this review is to E-mail: [email protected] Joseph A. Gil,1 Ashraf H. Hawari,3 describe the radiographic characteristics Aristides I. Cruz Jr.2 associated with common pediatric elbow Conflict of interest: the authors declare no injuries and to highlight common pitfalls 1Department of Orthopaedics, Alpert potential conflict of interest. associated with pediatric elbow diagnostic Medical School of Brown University, Key words: Elbow; Pediatrics; Fracture; 2 imaging. Providence, RI; Division of Pediatric Radiographs; Development. Orthopaedic Surgery, Department of Orthopaedics, Alpert Medical School Received for publication: 6 January 2017. Accepted for publication: 2 February 2017. of Brown University, Providence, RI; Normal anatomy and development 3 Focus Medical Imaging-Garfield This work is licensed under a Creative Medical Center, Monterey Park, CA, Radiographic evaluation of the skeletal- Commons Attribution NonCommercial 4.0 USA ly immature elbow requires knowledge of License (CC BY-NC 4.0). the normal sequence and appearance of the secondary ossification centers of the elbow ©Copyright S.F. DeFroda et al., 2017 in order to correctly distinguish pathology Licensee PAGEPress, Italy Abstract from normal anatomy (Figure 1). At birth Orthopedic Reviews 2017;9:7030 the elbow joint is completely cartilaginous doi:10.4081/or.2017.7030 Normal variations in anatomy in the and cannot be reliably evaluated via plain skeletally immature patient may be mistak- radiography.7 The appearance of secondary en for fracture or injury due to the presence ossification centers of the elbow are pre- around age 3-4 years. As it ossifies, the of secondary centers of ossification. dictable, however may vary from patient to metaphysis of the radial neck may appear Variations in imaging exist from patient to patient based on sex, maturity, and may angulated with a notch at the lateral cortex, patient based on sex, age, and may even even vary from one extremity to the other, which fills in with time, however, this may vary from one extremity to the other on the making imaging of the contralateral elbow be mistaken for a fracture.7 The medial epi- same patient. Despite differences in the useful in identifying subtle abnormalities.7 condyle ossifies between 3-6 years of age. It appearance of the bony anatomy of the The mnemonic device CRITOL can be used is variable in its ossification pattern and is elbow there are certain landmarks and rela- to remember the chronologic order of ossi- often the last center to fuse at approximate- tionships, which can help, distinguish nor- fication (capitellum, radial head, medial ly 17 years of age.7 The trochlea exhibits mal from abnormal. We review common epicondyle, trochlea, olecranon, lateral epi- radiographic parameters and pitfalls associ- condyle). This can also be remembered as multiple ossification centers beginning ated in the evaluation of pediatric elbow CRITOE (capitellum, radial head, internal around age 7-8 years. Its fragmented imaging. We also review common clinical ossification center, trochlea, olecranon, appearance should not be confused with a diagnoses in this population. pathological condition, such as fracture or external ossification center. Ossification 7 begins at 1 year old and each ossification avascular necrosis. The olecranon begins to center sequentially appears at about every 2 ossify around age 9 years via two or more years thereafter (Table 1).7 ossification centers. Its ossification begins Introduction distally before migrating proximally to form a concentric articulation with the dis- Pediatric elbow fractures represent up tal humerus.7,8 As the physis closes, it has to 10% of all fractures that occur in chil- sclerotic margins that appear different than 1,2 Secondary ossification centers dren. The most common fractures are a fracture, with final closure occurring by supracondylar humerus fractures, radial The capitellum appears between 1 and 2 age 14-15 years.9 Lastly, the lateral epi- neck fractures, lateral condyle fractures, years of age, however it may appear as early condyle begins ossifying around age 11 1 and medial epicondyle fractures. as 3 months.7 Normally, the capitellum is years. It begins as a thin flake, which may Interpretation of pediatric elbow radi- anteverted approximately 40 degrees, form- be mistaken as an avulsion fracture, before ographs is complicated by the cartilaginous ing an angle of 130 degrees with the humer- eventually fusing with the capitellum and 3 nature of the immature elbow. It is critical al shaft. The posterior aspect of its cartilagi- the humerus.7 to identify subtle fractures and dislocations nous physis is wider than the anterior because missed injuries can be associated aspect, potentially leading to the misdiagno- with deformity, pain and neurologic compli- sis of a fracture at this location.7 With age, 4,5 cations. Because of the challenges pre- fusion of the capitellum occurs, frequently Radiographic relationships sented when evaluating pediatric elbow to the trochlea and lateral epicondyle first, radiographs, systematic assessments of followed by fusion to the distal humerus by Knowledge of normal radiographic numerous radiographic measurements are approximately age 14 years.7 The capitel- relationships within the pediatric elbow is useful. These include evaluating the lum serves as a critical landmark when important for diagnostic evaluation. anatomic relationships of the ossification evaluating pediatric elbow x-rays. For Assessment of the radiocapitellar joint is centers of the elbow, including the position example, the radial head should align with performed by drawing a line down the mid- of the radial head relative to the capitellum, the capitellum in all views in order to rule dle of the radial neck or shaft on standard the relationship of anterior humeral line rel- out dislocation. The radial head ossifies at anteroposterior (AP), oblique and lateral [Orthopedic Reviews 2017; 9:7030] [page 21] Review radiographs. This line should intersect the measurement is also useful both during studies have shown that the posterior fat capitellum at approximately its middle third operative fixation and during follow up pad sign suggests a fracture with a sensitiv- on all radiographic views. Understanding evaluations to assess for any residual varus ity ranging from 15-76%.6,16,17 Al-Aubaidi this relationship is critical in assessing the or valgus malalignment.15 et al performed a study in which patients joint, especially in the setting of specific The fat pad sign is indicative of intra- with a posterior fat pad sign on x-ray were fractures, such as an ulna fracture which can articular elbow pathology even when a frac- referred for an MRI to assess for the pres- be associated with a radiocapitellar joint ture is not apparent on standard elbow radi- ence of an occult fracture. In 26 patients, 6 dislocation (i.e. Monteggia fracture) (Figure ographs.6 The fat pad, or sail sign, is caused were found to have occult fractures, and 19 2). Ramirez et al. examined the reliability by an intra-articular elbow effusion or had a bone bruise.18 This led the authors to of this landmark in normal pediatric elbows hemarthrosis either anteriorly or posteriorly conclude that MRI does not change man- and found that in 8.6% of elbows the radio- on lateral radiographs of the elbow. Past agement of patients with a posterior fat pad capitellar line did not intersect the capitel- lum.10 They found that this measurement was more accurate when the line was drawn through the radial head rather than the neck, and that it was less likely to miss the Table 1. Summary of the appearance of ossification centers of the pediatric elbow (in capitellum in patients older than 5 years.10 years). The anterior humeral line (AHL) is an Ossification center Girls Boys Approximate important radiographic landmark used to C 1 1 1 assess the alignment of the distal humerus and is often used to evaluate the anterior- R 4 5 3 posterior displacement of supracondylar M 5 7 5 humerus fractures. This line is drawn on the T 8 9 7 lateral projection of the elbow along the O 8 10 9 anterior cortex of the humerus and should L 11 12 11 intersect the middle third of the capitellum C, capitellum; R, radial head; M, medial epicondyle; T, trochlea; O, olecranon; L, lateral condyle. in most normal elbows.3 To accurately assess this line, a perfect lateral of the elbow is essential since oblique projections may be susceptible to misinterpretation. In extension type supracondylar humerus frac- tures, the capitellum will be posterior to the AHL (Figure 3). Although commonly uti- lized, the AHL can vary based on patient age. Rogers et al showed that this relation- ship does not normalize until patients are older than 2.5 years old due to the small size of the capitellum in younger patients.11 Herman et al examined the normal radi- ographs of different age groups and found that the AHL passed through the middle one third of the capitellum in 62% of patients aged 4-9 years, compared to 42% in those young four years old.12 Ryan et al examined 124 true lateral radiographs in patients aged 5 months to 11.7 years.13 The authors found that the AHL went through the middle third of the capitellum in all patients ≥5 years old; however, in 25% of patients <5 years old the AHL fell outside the middle third of the capitellum.