Revision of cannulated and perforated cement-augmented pedicle screws: a biomechanical study in human cadavers.
METHODS
Biomechanical investigation of primary and revised cement-augmented pedicle screws in comparison with unaugmented screws.


OBJECTIVE
To evaluate revision of cannulated pedicle screws and investigate cement-augmented and nonaugmented screws biomechanically, testing the torque of primary screws and axial pullout force of revised screws in cadaver vertebrae.


BACKGROUND
Cement augmentation increases the pullout force and stability of pedicle screws in vertebrae with low bone mineral density, but surgeons are concerned about complications during revision.


METHODS
Bone mineral density was measured using quantitative computed tomography (CT) in 23 osteoporotic thoracolumbar junction vertebrae from human cadavers. Cannulated pedicle screws, augmented with bone cement (on right) or unaugmented (left), were inserted into each vertebra. After CT control, extraction torque was measured and the pedicles were reinstrumented with larger-diameter screws. The right screws were augmented again, with another CT control, before pullout testing.


RESULTS
Mean vertebral bone density was 52.6 mg/cm. No major screw malpositioning was observed on primary CTs. Cement leakage was observed anterolaterally and into the spinal canal. Mean maximal torque in augmented screws (1.2 Nm, SD: 0.6) differed significantly from nonaugmented screws (0.8 Nm, SD: 0.6). Screw removal did not lead to vertebral destruction. No relevant changes due to positioning or leakage were observed on CT after revision procedures compared with primary findings. Maximal pullout force in revised augmented screws (713.2 N, SD: 254.6) differed significantly compared with nonaugmented screws (554.0 N, SD: 296.5). Bone damage was observed in several vertebrae during pullout force testing in augmented screws.


CONCLUSIONS
Revision of cement-augmented pedicle screws was feasible without bone destruction, and larger-diameter screws can be used in revision procedures. The pullout force after revision was significantly better in cement-augmented screws. During pullout testing, the cement-bone interface broke before the screw-cement interface in several vertebrae, fracturing the pedicles.
Department of Orthopedics and Tumor Orthopedics, Muenster University Hospital, Muenster, Germany. bullmanv@uni-muenster.de
Viola
V
Bullmann
Werner
W
Schmoelz
Marcus
M
Richter
Corinna
C
Grathwohl
Tobias L
TL
Schulte
D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001843:Bone Cements / Q000494:pharmacology*; D015519:Bone Density; D001863:Bone Screws; D002102:Cadaver; D020878:Device Removal / Q000009:adverse effects; D005240:Feasibility Studies; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D010024:Osteoporosis / Q000000981:diagnostic imaging / Q000601:surgery*; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013314:Stress, Mechanical; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D014057:Tomography, X-Ray Computed; D019415:Torque
D001843:Bone Cements