Cervical pedicle screws: comparative accuracy of two insertion techniques.
METHODS
Independently assessed radiographic and anatomic comparison of device implantation methods.


OBJECTIVE
To compare the relative accuracy of two techniques of inserting cervical pedicle screws.


BACKGROUND
In an attempt to define the anatomic risks of cervical pedicle screw insertion, image-guided stereotactic technology was shown to be superior to some other methods in vitro.- Meanwhile, in vivo experience with Abumi's technique of screw insertion has had few clinically relevant instances of screw malposition. There has been no direct comparison between current image-guided technology and Abumi's fluoroscopically assisted technique.


METHODS
The pedicles (C3-C7) of human cadaveric cervical spines were instrumented with 3.5-mm screws with either of two techniques. Cortical integrity and potential neurovascular injury were independently assessed by computed tomographic (CT) scans and anatomic dissection. A cortical breach was considered "critical" if the screw encroached on any vital structure. If any part of the screw violated the cortex of the pedicle but no vital structure was at risk for injury, the breach was classified as "noncritical."


RESULTS
In Group I (StealthStation; Sofamor-Danek, Memphis, TN), 82% of screws were placed in the pedicle, and 18% had a critical breach. In Group II (Abumi technique), 88% of screws were placed in the pedicle, and 12% had a critical breach. No statistically significant differences were demonstrated between each group (P = 0.59). Regarding pedicle dimensions and safety of insertion, a critical pedicle diameter of 4.5 mm was determined to be the size below which a critical breach was likely, but above which there was a significantly greater likelihood for safe screw placement. The most common structure injured in each group was the vertebral artery.


CONCLUSIONS
The use of a computer-assisted image guidance system did not enhance safety or accuracy in placing pedicle screws compared with Abumi's technique. Both techniques have a noteworthy risk of injuring a critical structure if inserted into the pedicles with a diameter of less than 4.5 mm. Under laboratory conditions, pedicles with a diameter of more than 4.5 mm have a significantly greater likelihood of being safely instrumented by either technique. These data indicate that cervical pedicle screw placement is feasible, but it should be reserved for selected circumstances with clear indications and in the presence of suitable pedicle morphology.
Ludwig
S C
SC
Department of Orthopaedic Surgery and Rehabilitation, Penn State College of Medicine, Milton S. Hershey Medical Center, Hershey, Pennsylvania, USA.
Kowalski
J M
JM
Edwards
C C
CC
Heller
J G
JG
D001863:Bone Screws / Q000009:adverse effects / Q000592:standards / Q000706:statistics & numerical data*; D002102:Cadaver; D002574:Cervical Vertebrae / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D016268:Internal Fixators / Q000009:adverse effects / Q000592:standards / Q000706:statistics & numerical data*; D007431:Intraoperative Complications / Q000145:classification / Q000209:etiology; D008297:Male; D011859:Radiography; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods; D016896:Treatment Outcome