Cervical Pedicle Screws: Comparative Accuracy of Two Insertion Techniques
Steven C. Ludwig, MD (Hershey, PA)
Joseph M. Kowalski, DC, MD, (Buffalo, NY)
Charles C. Edwards II, MD (Atlanta, GA)
Introduction:
Frameless stereotactic technology has proved superior to some methods of cervical pedicle screw insertion in vitro. In contrast, Abumi has reported few clinically relevant instances of screw mal–position in vivo. We compared the accuracy of Abumi's method versus image–guided insertion of cervical pedicle screws.
Methods:
The pedicles (C3–7) of human cadaveric spines were instrumented with 3.5mm screws with either of two techniques. Cortical integrity and potential neurovascular injury were independently assessed by CT scans and anatomic dissection. A cortical breach was considered "critical" if the screw encroached upon any vital structure. All other cortical violations were termed "noncritical".
Results:
In Group I (StealthStation) 82% of screws were placed in the pedicle, while 18% had a critical breach. In Group II (Abumi method) 88% of screws were placed in the pedicle, while 12% had a critical breach (p=0.59). A critical pedicle diameter of 4.5mm was determined to be the size below which a critical breach was likely, but above which had a significantly greater likelihood for safe screw placement. The most common structure injured in each group was the vertebral artery.
Conclusions:
Image guidance did not enhance the safety or accuracy in placing pedicle screws compared to Abumi's method. Both techniques have a noteworthy risk of injuring a critical structure between C3 and C6. Under laboratory conditions pedicles with a diameter >4.5mm have a significantly greater likelihood of being safely instrumented by either technique.
