An experimental study on initial fixation strength in transpedicular screwing augmented with calcium phosphate cement.
METHODS
An experimental study.


OBJECTIVE
To clarify the optimal insertion timing of transpedicular screws when the initial fixation strength reaches in maximum as calcium phosphate cement (CPC) hardens, in cases augmented by CPC to the vertebrae.


BACKGROUND
CPC goes easily into the bone trabeculae and excels in the bone compatibility. However, it is still unknown as for differences of fixation effects by CPC hardening time at actual insertion of the pedicle screw.


METHODS
Fifty-seven vertebrae obtained from 11 human cadavers. The CPC and titanium pedicle screws were used. Experimental groups were decided as follows. (1) Control group (without CPC). (2) CPC group (augmented with CPC); the mixed CPC infused into the screw hole, afterwards the pedicle screw inserted at a set time (passage time from the initiation of powder and liquid agent mixing). The CPC group was further divided into 3 subgroups, with respect to insertion time of the pedicle screws: 2, 5, and 10 minute subgroups. Maximum pull-out strength was compared, and cross sectioned specimens of the 5 and 10 minute groups were prepared and observed.


RESULTS
CPC group showed a pull-out strength of about 177% that of the control group. For inserting timing of the pedicle screw and pull-out strength, no apparent statistically significant difference was found between each subgroups, although the 10-minute group showed the lowest. Cross sectional observations revealed that the CPC diffused deeper into the bone trabeculae in the 5-minute group than in the 10 minutes.


CONCLUSIONS
CPC augmentation enabled an average 77% increase of the maximum pull-out strength compared to the control group. The study of screw insertion timing augmented with CPC was indicative of the fact that an increase in the initial fixation of the pedicle screw can be achieved when the screw is inserted before initiation of CPC hardening.
Masaki
Taiga
T
Department of Orthopaedic Surgery, St. Marianna University School of Medicine, Kawasaki, Japan. t2masaki@marianna-u.ac.jp
Sasao
Yutaka
Y
Miura
Takehiko
T
Torii
Yoshiaki
Y
Kojima
Atsushi
A
Aoki
Haruhito
H
Beppu
Moroe
M
D001843:Bone Cements; D001863:Bone Screws; D002102:Cadaver; D002130:Calcium Phosphates; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery; D008422:Materials Testing; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013904:Thoracic Vertebrae / Q000601:surgery
D001843:Bone Cements; D002130:Calcium Phosphates