ELBOW EFFUSION: UTILITY AND LIMITATIONS OF RADIOGRAPHY IN PEDIATRIC INJURIES SA-CME DETAILS ON PAGE 10 16 n www.appliedradiology.com May–June 2021 flat on the table during acquisition helps to improve lateral radiograph qual- ity. Adjusting the table or patient-seat height, with the patient’s thumb point- ing upward, can help achieve this po- sition. Optimal positioning can also be achieved with the “standing salute” and 90-degree abduction at the shoulder and 90-degree flexion at the elbow. 15 The posterior fat pad may be normally vis- ible by obtaining the lateral radiograph in extension, as the olecranon process displaces the fat pad outward in this po- sition (Figure 7). 9 Effusion size also matters with re- spect to diagnosing elbow effusion from radiographs. A small effusion may elevate only the posterior fat pad, with the anterior fat pad appearing nor- mal (Figure 8). 9 At the other end of the spectrum, a very large effusion may ef- face both the anterior and the posterior fat pads, rendering them invisible on ra- diographs (Figure 9). Complete lack of visibility of the anterior fat pad may be a clue to the presence of a large effusion in this situation. A traumatic rupture of the elbow joint capsule may lead to a false-neg- ative fat pad sign, as the capsular tear would allow joint fluid extravasation into the surrounding tissues. 16 It is also worth emphasizing that ra- diographic exposure in the lateral view should be sufficient to differentiate fat from soft-tissue density. An underex- posed radiograph may not demonstrate abnormal fat pads even if elbow effu- sion is present. Similarly, radiologists should be sure to adjust the window width and level while evaluating for elbow effusion, as fat and soft-tissue contrast may not be visible at the default window setting (Figure 10). Conclusion Elbow effusion on radiographs may be the only indication of occult fracture in children. Several factors can cause false-positive or false-negative diag- noses of elbow effusion, and knowing these pitfalls is essential to accurately interpret pediatric elbow radiographs. REFERENCES 1. DeFroda SF, Hansen H, Gil JA, et al. Radio- graphic evaluation of common pediatric elbow injuries. Orthop Rev (Pavia). 2017(1); 9: 7030. 2. Emery KH, Zingula SN, Anton CG, et al. Pedi- atric elbow fractures: a new angle on an old topic. Pediatr Radiol. 2016; 46(1):61-66. 3. Major NM, Crawford ST. Elbow effusions in trauma in adults and children: is there an occult fracture? AJR Am J Roentgenol . 2002;178(2): 413-418. 4. Pudas T, Hurme T, Mattila K, et al. Magnetic resonance imaging in pediatric elbow fractures. Acta Radiol. 2005; 46(6):636-644. 5. Skaggs DL, Mirzayan R. The posterior fat pad sign in association with occult fracture of the elbow in children. J Bone Joint Surg Am. 1999;81(10):1429-1433. 6. Donnelly LF, Klostermeier TT, Klosterman LA. Traumatic elbow effusions in pediatric patients: are occult fractures the rule? AJR Am J Roent- genol. 1998;171(1):243-245. 7. Al-Aubaidi Z, Torfing T. The role of fat pad sign in diagnosing occult elbow fractures in the pediatric patient: a prospective magnetic reso- nance imaging study. J Pediatr Orthop B. 2012; 21(6): 514-519. 8. Donnelly LF. Traumatic elbow effusions in children are not synonymous with occult frac- ture-even with evaluation by MR imaging. AJR Am J Roentgenol. 2002;179(2):531-532. 9. Murphy WA, Siegel MJ. Elbow fat pads with new signs and extended differential diagnosis. Radiology. 1977;124(3): 659-665. 10. Blumberg SM, Kunkov S, Crain EF, et al. The predictive value of a normal radiographic anterior fat pad sign following elbow trauma in children. Pediatr Emerg Care. 2011;27(7): 596-600. 11. Kamineni S, Bachoura A, Sasaki K, et al. Inner synovial membrane footprint of the interior elbow capsule: an arthroscopic boundary. Anat Res Int. 2015:426974. 12. Sheehan SE, Dyer GS, Sodickson AD, et al. Traumatic elbow injuries: what the ortho- pedic surgeon wants to know. Radiographics. 2013;33(3):869-888. 13. Kilborn T, Moodley H, Mears S. Elbow your way into reporting paediatric elbow fractures – A simple approach. SA Journal of Radiology. 2015; 19(2):881. doi 10.4102/sajr.v19i2.881. 14. Skibo L, Reed MH. A criterion for a true lat- eral radiograph of the elbow in children. Can Assoc Radiol J. 1994; 45(4): 287-291. 15. Eren MB, Asci M, Bilgic E, et al. A practical method for obtaining true lateral elbow X-rays in a pediatric age group: lateral elbow X-ray in the standing salute position. Ind J Ortho. 2020; doi 10.1007/s43465-020-00238-9. 16. Bledsoe RC, Izenstark JL. Displacement of fat pads in diseases and injury of the elbow: a new radiographic sign. Radiology. 1959; 73: 717-724.