Inter-Observer Accuracy of “Fat Pad Sign” in Determining Radiological Elbow Joint Effusion with Different Levels of Experience

Abstract Background: Joint Effusion is considered as an important indicator of many joint morbid conditions. In the sitting of trauma, fat pad displacement in lateral elbow radiograph may be the only clue of occult fractures as it is referred to elbow effusion. Likewise, it's a sign of early internal joint morbidity in many articular diseases. The classic lateral radiograph is considered as the primary choice for determining elbow joint effusion because of being simple, available and reasonable tool. Aim of Study: The current study aimed to evaluate the inter-observer accuracy of fat pad signs of elbow lateral radiograph in detecting elbow joint effusion with the impact of observer experience on it. MRI was used as the gold standard. Patient and Methods: The current study is a descriptive validation study in which 52 patients were included prospec-tively in it. Inclusion criteria were positive elbow effusion by MRI with available lateral elbow radiograph within 3 days of the MRI study. Radiographs were read by 2 groups: Group I (2 senior radiology residents of 3 years' experience: Reader A & B), and group II (2 radiologists with MD degree, reader C & D). Each observer provided his readings by either proved effusion, denied effusion or asked for further evaluation. Readers were independently and blinded to the patients' clinical data. Results: The diagnostic accuracy percentages of elbow effusion detection for each reader compared to MRI were calculated as follows: Proper detection were from 59.6% to 61% in low experience, and 76.9% to 82.7% in high experience. Missed cases were (19%) in low experience and (3.8%) to (7.7%) in high experience group. While cases needed further evaluation were 19.2% to 21.2% in low experience and in high experience were ranging from 13.5% to 15.4%. Then agreement between each reader were estimated. The same level of experience showed perfect agreement, (Kappa of 0.922 and 0.965). While lower agreement was detected in different experience group with Kappa of 0.51 to 0.641, which is moderate and substantial agreement. Conclusion: The current study emphasizes that validity of radiographs in detection of elbow effusions widely varied with levels of experience. MRI is important beside lateral radiograph for detection of elbow effusion especially in low experience to avoid missed occult fractures and early morbid joint affection.