2008 Faculty Researchers

John T. Anderson, MD & Daniel Hoernschemeyer, MD

The superior articular process as an external landmark for determining transverse plane angulation of thoracic pedicles.

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Department

Orthopaedic Surgery

Office:

University of Missouri Health Care
One Hospital Drive, MC213
Columbia, MO 65212

Phone #:

Office: (573) 884-2522
Fax: (573) 882-1760

E-mail:

andersonjo@health.missouri.edu

Summary

There are many devices that can be used to gain purchase of the spine during procedures that require stabilization. In the past, most surgeons relied on devices such as hooks and wires to stabilize the thoracic spine. These devices gain purchase of only the posterior elements of the vertebra. Pedicle screws, which gain purchase of the entire vertebra, were reserved for fixation of the lumbar spine as most surgeons feared the risk of spinal cord injury during insertion in the thoracic spine. The last couple of decades have produced several reports that substantiate the use of thoracic pedicle screws. In trained hands, they can be inserted predictably and safely.

Many surgeons have evolved to place pedicle screws with a free hand technique, which utilizes vertebral landmarks as guides to place the screws without the use of intraoperative fluoroscopy. Cadaveric and radiological studies have helped surgeons understand the pedicle anatomy of the thoracic spine. Particularly difficult, however, is determining the correct transverse plane trajectory when inserting screws. Obviously, if one inserts the screws too medially, the spinal canal will be entered, which can result in an iatrogenic spinal cord injury. Conversely, placing a screw too laterally can produce injury to the lung or anterior great vessels. Thus, determining the correct transverse plane trajectory is of utmost importance when placing thoracic pedicle screws. Although cadaveric studies have given surgeons some estimate of the transverse angulation of thoracic pedicles, this data is difficult to apply surgically.

A fairly consistent external landmark would obviously be helpful to spine surgeons when trying to determine the correct transverse plane angulation during thoracic pedicle screw insertion. Some authors have alluded to using the superior articular process as a useful landmark. Many feel the pedicle predictably travels at a right angle to the plane of the superior articular process; this claim, however, has never been validated in a cadaveric or radiological study.

The objective of this study is to investigate the angular relationship of the pedicle and superior articular process in the thoracic spine. This will be accomplished by reviewing computed tomography (CT) scans of the thoracic spine that have already been obtained at the University of Missouri Health Care. The CT scans will be reviewed by a medical student(s) that will be recruited to act as co-investigator(s).

This project will give the student(s) an opportunity to be involved in literature review, project development, institutional review board procedures, data collection, data presentation and publication. The student(s) will work directly with faculty of the department of orthopaedic surgery.