A Clearly Observable Cold Fracture Line of an Early Occult Hip Fracture on Bone Scintigraphy

DISCUSSION

The whole-body bone scintigram revealed a clearly defined linear area of no uptake, or the so-called cold line, crossing the left femoral neck (Fig. 1). This cold line was felt to be suggestive of a fracture. However, given that the typical appearance around a fracture site on bone scintigraphy is an increase in tracer uptake, we were hesitant to unambiguously diagnose our observations as a true fracture. After ruling out any possibility of a secondary cause for the cold line (an external object lying on the patient within the viewing area), additional spot views of the pelvis (Fig. 2) were obtained. These again revealed the obvious cold line in the same location. Because of that finding, we increasingly suspected a fracture, despite the lack of obvious tracer uptake. The repeated anterior–posterior pelvic radiograph provided additional evidence for a fracture line across the left femoral neck. MR imaging of the left hip further confirmed a left subcapital femoral neck fracture with associated bone marrow edema (Fig. 3). We also observed increased tracer uptake at the T12 vertebra (Fig. 1) from the whole-body bone scintigram (this uptake was absent from a bone scintigram before the fall [Fig. 4]). The T12 observation was thought to be related to the fall and not a metastatic lesion. Radiographs of the spine (not shown) revealed an acute compression fracture of T12.

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FIGURE 4.

Same whole-body bone images displayed with more intensity on left than right to define different lesions better. These images taken in 2009 demonstrated no scintigraphic evidence of osseous metastasis or fracture in T12 and no cold fracture line seen in left hip. Arrows indicate injection site.

It is reported and commonly accepted that on scintigraphy, an acute hip fracture typically appears as a generalized diffuse increase in radionuclide activity around the fracture site. Although the mechanism of ^99mTc-labeled phosphate accumulation around a fracture is unclear, theories include hyperemia, inflammation, increased metabolic rate, and bone repair (1–4).

Prior bone scintigram observations of false-negative cold fracture areas (2,3) of the hip have been reported. In those reports, the areas were in the femoral head or neck region but showed no localized increased uptake to suggest a fracture. In two of the cases these observations initially were considered to represent an avascular femoral head (3) but were later proven to be hip fracture. Fortunately, in our case a clear cold line in the femoral neck was demonstrated on the bone scintigram and could easily be connected with a diagnosis of fracture even in the absence of increased activity.

The reason for the lack of increased uptake around a fracture site is not clearly understood. It has been suggested that in older osteoporotic patients, significant focal accumulation of activity may not occur until 72 h after injury (5). Our patient had severe osteoporosis.