Bone bruises: MR characteristics and histological correlation in the young pig
Introduction
Magnetic resonance (MR) imaging has been shown to be sensitive in the detection of occult bone lesions. With the increasing application of MRI in patients with acute musculoskeletal trauma, more occult traumatic lesions of bone are being identified [1]. The MR imaging findings in trauma cases do not depend on direct visualization of the trabeculae either at the time of initial injury or during repair. Rather, MR imaging depends on imaging the marrow and its evolution in response to acute injury. With a fracture of the trabeculae, one might expect hemorrhage and edema in the tissues surrounding the injury [1], [2].
Radiographically, occult injuries to the bone, otherwise referred to as occult fractures, bone bruises, bone contusions or microtrabecular trauma/fracture, may account for a patient's pain and may have important prognostic implications and sequelae if not recognized and treated appropriately [3], [4]. Blood, edema, hyperemia and perhaps microfracture of the trabeculae may all contribute to the marrow signal alteration [1], [5]. To our knowledge, bone bruises, as shown on MR imaging, have not been correlated with histologic study, and their MR signal characteristics have not been defined. We undertook this study to compare bone bruises seen on MR images with the corresponding histology and to determine the MR signal characteristics of these lesions using a young pig model.
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Experimental models
We studied 14 tibiae of 10 pigs (both tibiae in four pigs and one tibia in six pigs). All of them were 8 weeks old at the beginning of the experiment. The study was approved by our institution's animal research committees. A bone bruise was created in the proximal tibial metaphysis of 14 tibiae.
The animals were anesthetized with an intramuscular injection of 25 mg/kg of tiletamine-zolazepam hydrochloride (Zoletil; Virbac Lab., Carros, France). We established an intravenous channel in the ear's
Comparison of MR imaging and histologic findings of acute contusion (14 MR imaging studies, five gross specimens)
The histological and MR imaging findings were summarized in Table 1. On T1-weighted images, three distinct patterns could be observed on the day of surgery. MR images of 14 tibiae showed 10 with focal or diffuse low signal intensities at the contusion sites Fig. 1, Fig. 2, three with no abnormal signal intensities, and one with focal linear low signal intensity at the subcortical area.
On FSE T2-weighted images, the 10 tibiae that showed focal or diffuse low signal intensities on T1-weighted
Discussion
MRI is extremely sensitive in the detection of abnormal amounts of water in tissues, either because of edema from inflammation or the separation of serum from the cellular components of blood. This characteristic probably explains the apparent increased sensitivity of MRI over plain radiographs in the early detection of bone bruises [6]. Bone bruises have been believed to be self-limiting benign abnormalities with no sequelae. Following trauma, the alterations identified in the bone marrow
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