CT in Musculoskeletal Trauma

Introduction

The advent of increasing numbers of rows of detectors has expanded the utility for CT technology. Multidetector CT (MDCT) has the ability to produce near-isotropic voxel images that allow multiplanar reformations and faster data acquisition. This technique is particularly valuable in the setting of trauma, for which conventional radiographs can be difficult to obtain because patients may be unable to comply with positioning requirements. Volume-rendered spiral CT can result in significant savings in terms of patient time spent in the radiology department. This technique also provides useful information for appropriate treatment and surgical planning by displaying three-dimensional spatial relationships in a two-dimensional image.

CT has two major roles in the evaluation of musculoskeletal trauma: (1) to define or exclude a fracture that was equivocal on conventional radiographs and (2) to determine the extent of a previously diagnosed fracture to assist in guiding therapy. In both trauma and nontrauma settings, spiral CT can provide information regarding soft-tissue abnormalities and demonstrate the osseous anatomy, particularly in anatomically complex areas such as the spine, pelvis, and scapula, for which conventional radiography may be limited.

Optimization of scanning techniques depends on the clinical question being addressed and the anatomic location to be examined. Small areas of interest combine narrow collimation (1–2 mm) and a pitch of 1 to 1.5 with small reconstructed increments (1 mm). Large areas of interest can be examined with wider collimation (3 mm) and a pitch of 1 to 2 with reconstruction every 2 to 3 mm.

There is considerable interest in CT dose reduction. In some circumstances, such as imaging of metallic prostheses, the exposure factors (peak kilovoltage and tube current) cannot be reduced without image quality being affected. The patient dose can be limited by careful positioning of the anatomic structure and limiting the area to be scanned. Low-kilovoltage techniques have been described for extremity and pelvis imaging without significant degradation of images. The polytrauma patient dose can be decreased by making a single pass of the chest, abdomen, and pelvis rather than scouting and scanning each region separately.

In the setting of trauma, MDCT is used to assess other body regions, and studies have shown that the spine can be included as part of the scan. Because of the high-quality two- and three-dimensional images, adequate images of the thoracic and lumbar spine can be obtained from chest and abdominal CT data ( Fig. 19.1 ).

Three-dimensional reconstructions are often performed for fractures of the acetabulum, scapula, and calcaneus and for complicated fractures of the pelvis to assist with surgical planning ( Fig. 19.2 ).

According to the current American College of Radiology appropriateness criteria, the use of radiography in patients suspected of having a cervical spine injury should be reserved for adult patients when MDCT is not readily available, indicating that radiography should not be considered a substitute for CT. However, radiation exposure should always be minimized. Exposure during CT evaluations can be reduced by the use of automated exposure-control options according to the patient’s body habitus. Many manufacturers of CT equipment have developed dose-reduction solutions.

Cervical Spine Trauma

MDCT can detect 97% to 100% of cervical spine fractures, compared with 60% to 70% for conventional radiography. MDCT is widely used to complement conventional radiography for examination of the cervical spine following blunt trauma. Before helical scanning became available, conventional radiographs were the only radiologic means of imaging the cervical spine to exclude or diagnose injury following blunt trauma. The limitations of conventional radiography include poor visualization of areas with overlapping structures and the presence of other disease such as osteoarthrosis or rheumatoid arthritis or superimposed artifacts such as an endotracheal tube ( Fig. 19.3 ). In addition, the lower cervical and upper thoracic spine can be difficult to image on conventional radiographs for similar reasons and is well visualized by MDCT ( Fig. 19.4 ).

Importantly, in the clinical setting of spine fusion, either with hardware or secondary to ankylosis from ankylosing spondylitis or diffuse idiopathic skeletal hyperostosis, in a patient who presents with suspected injury after blunt trauma, a search for a fracture must include CT with reformatted images ( Fig. 19.5 ).

The detection accuracy for ligamentous injury of MDCT is not clearly documented, and magnetic resonance imaging (MRI) is highly sensitive in detecting these injuries.