Worrisome and Incidental Signs on Knee Radiographs SA–CME REVIEW for fatty marrow leakage into the joint space and lipohemarthrosis is pathognomonic for acute fracture. 6,14 Acute pain and swelling are classic symptoms/signs. Radiologists should consider cross-table lateral radiographs for all traumatic knee series, as standard frontal and lateral views are less likely to identify lipohemarthro- sis. 6,15 On cross-table lateral views, the key finding is a sharp linear interface between hydrophobic floating fat and hydrophilic hemar- throsis, most commonly seen at the suprapatellar pouch (Figure 3). Occasionally, lipohemarthrosis will present with three distinct layers when the hemarthrosis further sep- arates into distinct serum and red blood cell layers. 6,16 In the setting of lipohemarthrosis without a definite radiographically visible fracture, the radiologist should inform the exam requestor that additional cross-sec- tional imaging is indicated to detect and characterize the occult frac- ture. 17 Treatment is typically driven by orthopedic management of the underlying fracture, with self-resolu- tion of the lipohemarthrosis. Traumatic Malalignment Anterior tibial translation Anterior tibial translation (ATT) is an important radiographic sign of knee instability. 18 The ACL primarily Figure 1. Segond fracture. (A) AP radiograph shows a mildly displaced acute fracture fragment (arrow) from the lateral aspect of the lateral tibial plateau in a patient presenting with acute knee trauma. (B) Sagittal T2 fat-saturated MRI shows an absence of the anterior cruciate ligament at the intracondylar notch (arrows) compatible with complete tear. A B Figure 2. Tibia spine fracture. (A) AP radiograph shows a mildly displaced transverse acute fracture at the tibial spine region (arrow) of the proximal tibial epiphysis in a skeletally immature patient. There is also a nonossifying fibroma incidentally noted at the distal femoral metadiaphysis. (B) Sagittal T1 and (C) sagittal T2 fat-saturated MR images show the anterior cruciate ligament (short arrow) attached to the avulsed tibial spine fracture (long arrow) with associated bone marrow edema. A B C Applied Radiology 9 January / February 2023