Cervical spine pedicle screws: a biomechanical comparison of two insertion techniques.
METHODS
Biomechanical testing of the pullout strengths of pedicle screws placed by two different techniques in adult human cadaveric cervical spines.


OBJECTIVE
To determine whether there is a significant difference in screw purchase of two commonly proposed methods of cervical pedicle screw insertion.


BACKGROUND
Wiring techniques remain the gold standard for posterior cervical fixation. However, absent or deficient posterior elements may dictate the use of alternative fixation techniques. Cervical pedicle screws have been shown to have significantly higher pullout strength than lateral mass screws.


METHODS
Fifty fresh disarticulated human vertebrae (C3-C7) were evaluated with computed tomography for anatomic disease and pedicle morphometry. The right and left pedicles were randomly assigned to either a standard method or the Abumi insertion method. In the latter technique the cortex and cancellous bone of lateral mass are removed with a high-speed burr, which provides a direct view of the pedicle introitus. The pedicle is then probed and tapped and a 3.5-mm cortical screw inserted. Each screw was subjected to a uniaxial load to failure.


RESULTS
There was no significant difference in the mean pullout resistance between the Abumi (696 N) and standard (636.5 N) insertion techniques (P = 0.41). There was no difference in pullout resistance between vertebral levels or within vertebral levels. Two (4%) minor pedicle wall violations were observed.


CONCLUSIONS
In selected circumstances pedicle screw instrumentation of the cervical spine may be used to manage complex deformities and patterns of instability. Surgeons need not be concerned about reduced screw purchase when deciding between the Abumi method and its alternatives.
Kowalski
J M
JM
Department of Orthopaedic Surgery, State University of New York at Buffalo, 14215, USA. JOSEPH.KOWALSKI@GTE.NET
Ludwig
S C
SC
Hutton
W C
WC
Heller
J G
JG
D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000601:surgery*; D006801:Humans; D008875:Middle Aged; D011475:Prosthesis Failure; D013718:Tensile Strength; D016474:Weight-Bearing