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Sonographic and CT Findings in Lipohemarthrosis

Hospital das Clinicas, Universidade de Sao Paulo, Sao Paulo, Brazil

 
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A 25-year-old man presented to the emergency department because of pain and swelling of the left knee after a motorcycle accident that had occurred 2 days earlier. He had no previous significant clinical or surgical history. Clinical examination suggested the presence of joint effusion in the suprapatellar pouch, with severe pain and consequent functional deficit in the affected knee. A radiograph of the knee showed no signs of fracture. Sonographic examination requested to further evaluate the joint effusion revealed a large joint effusion consisting of two fluid-fluid levels and three distinct layers (Fig. 1A). CT of the left knee confirmed the presence of these distinct layers within the effusion (Fig. 1B), with corresponding attenuation coefficients of fat, water, and blood. The underlying oblique fracture of the tibial plateau was detected on the CT examination (Fig. 1C).

View larger version (102K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A —25-year-old man with pain and swelling of left knee. Sonographic longitudinal image (A) of suprapatellar pouch and axial CT image (B) in corresponding plane show large joint effusion with two distinct fluid-fluid levels (arrowheads) and three distinct consequent layers: superior layer of hyperechogenic-hypoattenuating fat (F), intermediate almost anechogenic-isoattenuation layer of mixed serum and synovial liquid (L), and inferior hypoechogenic-hyperattenuating layer of blood cells (B).

View larger version (146K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B —25-year-old man with pain and swelling of left knee. Sonographic longitudinal image (A) of suprapatellar pouch and axial CT image (B) in corresponding plane show large joint effusion with two distinct fluid-fluid levels (arrowheads) and three distinct consequent layers: superior layer of hyperechogenic-hypoattenuating fat (F), intermediate almost anechogenic-isoattenuation layer of mixed serum and synovial liquid (L), and inferior hypoechogenic-hyperattenuating layer of blood cells (B).

View larger version (54K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C —25-year-old man with pain and swelling of left knee. Reformatted sagittal CT image of knee shows underlying tibial plateau fracture (arrows) running into articular surface.

Joint effusion is a common finding in traumatic injuries. Lipohemarthrosis results from the extrusion of fat and blood from bone marrow into the joint space after an intraarticular fracture. This was first described by Kling [1] in 1929. Lipohemarthrosis is more common in knee fractures, especially those affecting the tibial plateau, but it has also been described in shoulder, elbow, and hip fractures [2-4].

Because fat floats on the associated blood, a fat-fluid level is present and may be shown on radiographs when the image is taken with a horizontal beam [3]. Nevertheless, because dependent RBCs with high hemoglobin and iron content versus the near-water density of floating serum can generate fluid-fluid levels, the presence of fluid-fluid levels on radiographs does not necessarily reflect the presence of free fat within the joint. The double fluid-fluid level is a more specific finding for intraarticular fat and an underlying fracture [4].

Because of inherent technical aspects, both CT and MRI can provide a more specific assessment than conventional radiography of the composition of joint effusions. Although not commonly performed, sonography also plays an important role in accurately depicting lipohemarthrosis and therefore suggesting the presence of an intraarticular fracture [4, 5].

In conclusion, it is important to remember that lipohemarthrosis presents characteristic imaging findings. Because its presence is strong evidence of a potential overlooked intraarticular fracture—which is a clinically relevant finding itself—radiologists should be aware of these characteristic imaging findings.

References

Top References

 

1. Kling DH. Fat in traumatic effusions of knee joint. Am J Surg 1929; 6:71 -74[CrossRef]
2. Arger PH, Oberkircher PE, Miller WT. Lipohemarthrosis. Am J Roentgenol Radium Ther Nucl Med1974; 121:97 -100[Medline]
3. Lugo-Olivieri CH, Scott WW Jr, Zerhouni EA. Fluid-fluid levels in injured knees: do they always represent lipohemarthrosis? Radiology 1996;198 : 499-502[Abstract/Free Full Text]
4. Bianchi S, Zwass A, Abdelwahab IF, Ricci G, Rettagliata F, Olivieri M. Sonographic evaluation of lipohemarthrosis: clinical and in vitro study. J Ultrasound Med 1995;14 : 279-282[Abstract]
5. Bonnefoy O, Diris B, Moinard M, Aunoble S, Diard F, Hauger O. Acute knee trauma: role of ultrasound. Eur Radiol2006 :16:2542 -2548[CrossRef][Medline]

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This Article Figures Only Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Costa, D. N. Articles by Sernik, R. A. Search for Related Content PubMed PubMed Citation Articles by Costa, D. N. Articles by Sernik, R. A. Social Bookmarking                      What's this?