MRI illustration of traumatic lipohemarthrosis of the wrist joint due to a scaphoid fracture.

Traumatic lipohemarthrosis of the wrist joint in association with a scaphoid fracture is an unreported entity. We present the first case report of MRI appearance of a double fluid-fluid level of lipohemarthrosis caused by a scaphoid fracture. The presence of a double fluid-fluid level within the injured joint definitely establishes a lipohemarthrosis. A traumatic lipohemarthrosis is considered synonymous with an intra-articular fracture and has important implications for patient management. A limited MRI scan for diagnosis or exclusion of scaphoid fracture may be more cost-effective than expectant management and subsequent followup visits.

Introduction

Lipohemarthrosis is a joint effusion that contains fat and blood mixed with the synovial fluid. Due to gravity, the lighter fat floats above the synovial fluid. The floating fat above the synovial fluid has a lower X-ray attenuation, which is seen as fluid-fluid level on imaging studies. Lipohemarthrosis was first described by horizontal beam technology several decades ago (1). Traumatic lipohemarthrosis is considered synonymous with an intra-articular fracture and occurs as a result of extrusion of fat and blood from bone marrow into the joint space after an intraarticular fracture (2). Lipohemarthrosis can also be visualized on cross-sectional imaging (such as CT) due to differences in X-ray attenuation of fat, blood products, and synovial fluid. Due to the differences in T1 and T2 relaxation times of fat, blood products and synovial fluid, lipohemarthrosis is also demonstrated on MRI scans. Traumatic lipohemarthrosis of the knee (4, 5) and to a lesser extent in the elbow joint (6) has been extensively described in the literature. In the wrist, it has been reported in association with a distal radial fracture (7). A traumatic lipohemarthrosis of the wrist joint in association with a scaphoid fracture, however, has been unreported up to now.

Case report

A healthy 14-year-old male sustained a fall on his outstretched right hand while playing basketball. On physical exam, tenderness, decreased range of motion, and mild swelling of the right wrist joint was noted. Point tenderness over the anatomical snuffbox was also present. There was a very high clinical suspicion of scaphoid fracture due to the mechanism of injury and physical exam findings.

MRI obtained two hours after the injury demonstrated lipohemarthrosis. Fat within the joint fluid was definitely identified using the fat-saturation technique (Fig. 1). Double fluid-fluid levels were seen on both T1 as well as T2 sequences (Figure 1, Figure 2). A fracture of distal scaphoid bone was identified on anatomical (T1-weighted, Fig. 3), fluid-sensitive (fat-saturated T2-weighted, Fig. 4) and volume-rendered images (Fig. 5). The patient was treated with immobilization using a long thumb spica (fiberglass cast) for six weeks. After the removal of cast and physical therapy, the patient fully recovered and returned to normal baseline activity.

Figure 1

14-year-old male with traumatic lipohemarthrosis of the wrist joint. MRI appearance of lipohemarthrosis. Axial, fat-saturated, T2-weighted image at the level of the proximal carpal row demonstrates lipohemarthrosis. Note the three different signal intensities of fat, serum, and the dependent red cells. Anterior or top layer (white asterisk) is of low signal intensity and represents fat. The first fluid-fluid level (arrow) shows the fat floating above the near-water density of serum (curved arrow). The second fluid-fluid level (arrowhead) separates the serum layer (curved arrow) and the dependent red cell layer with high hemoglobin and iron content (black asterisk).

Figure 2

14-year-old male with traumatic lipohemarthrosis of the wrist joint. MRI appearance of lipohemarthrosis. Sagittal, T1-weighted image at the level of the capitate bone redemonstrates the lipohemarthrosis. The fat, serum, and dependent red cells are seen as three different signal intensities. The top layer (white asterisk) is of higher signal intensity on this image when compared to the fat-saturated image (Fig. 1). This is consistent with fat density. The first fluid-fluid level (arrow) shows the fat layer floating above the near-water density of serum layer (curved arrow), as in Fig. 1. Again, as seen in the first figure, the second fluid-fluid level (arrowhead) separates the serum layer (curved arrow) and the dependent red-cell layer with high hemoglobin and iron content (black asterisk).

Figure 3

14-year-old male with traumatic lipohemarthrosis of the wrist joint. Coronal, T1-weighted image shows the distal scaphoid fracture (arrow).

Figure 4

14-year-old male with traumatic lipohemarthrosis of the wrist joint. Coronal, fat-saturated, T2-weighted image shows the distal scaphoid fracture (arrow). Note the high signal intensity showing the bone-marrow edema due to acute fracture.

Figure 5

14-year-old male with traumatic lipohemarthrosis of the wrist joint. Volume-rendered image (coronal) obtained from the original dataset redemonstrates the fracture line (arrow).

Discussion

In an original research article, Lugo-Olivieri et al suggested that a single fluid-fluid level could also be seen with an intra-articular hemorrhage, without the presence of fat in the joint cavity (3). They suggested instead that a double fluid-fluid level may be a more specific finding for lipohemarthrosis. Blood in the synovial fluid separates into highly concentrated, dependent red cells with high hemoglobin and iron content and near-water density of floating serum, creating the first fluid-fluid level. Due to gravity, fat (which is lighter than serum) rises above, resulting in another fluid-fluid level. The end result is two fluid-fluid levels with a lipohemarthrosis. The first fluid-fluid level is located between the fat layer (lightest) and the serum layer (intermediate). The second fluid-fluid level is located between the serum layer (intermediate) and the highly concentrated, dependent red-cell layer (heaviest).

The scaphoid is the most common carpal bone to fracture (8). In spite of this, there are many reasons why a traumatic lipohemarthrosis associated with a scaphoid fracture has not been described. First, due to the small size of the joint cavity, it is difficult to appreciate a fluid-fluid level on plain radiographs. Furthurmore, MRI for a suspected scaphoid fracture is almost never performed in the acute phase. We believe that after the several days of immobilization, fat and blood products are resorbed by the synovial membrane. This hypothesis remains to be tested in a clinical/experimental study. An experimental cadaver study demonstrated the presence of three different levels representing fat, serum, and blood cells on the T2-weighted images three days after injection of a mixture of fat and blood (5). We believe that the short time interval between injury and MRI scan in our case led to the visualization of the lipohemarthrosis.

Immobilization of the wrist is usually undertaken if there is clinical suspicion for a scaphoid fracture, also called "clinical scaphoid fracture." There has been an impetus to perform modified MRI scans optimized for detection of scaphoid fractures (9, 10). Generally, these quick scans involve two sequences. A coronal T1-weighted sequence is used to demonstrate anatomy. A fluid-sensitive sequence such as a coronal, fat-saturated, T2-weighted image is used to detect bone-marrow edema. Few studies have evaluated the economics of modified MRI in clinical scaphoid fracture. A cost-analysis study performed in Austria suggested that the cost of the MRI roughly equaled the saving in clinic attendance (10). Another similar study done in the United States also estimated that the cost of a modified MRI equaled a single clinic visit (9). In the future, modified, quick MRI scans may provide a definitive, routine, cost-effective imaging alternative for clinically suspected scaphoid fracture in carefully selected patients.