TY - JOUR
T1 - Biomechanical advantage of the index-level pedicle screw in unstable thoracolumbar junction fractures
T2 - Presented at the 2010 Joint Spine Section Meeting - Laboratory investigation
AU - Baaj, Ali A.
AU - Reyes, Phillip M.
AU - Yaqoobi, Ali S.
AU - Uribe, Juan S.
AU - Vale, Fernando L.
AU - Theodore, Nicholas
AU - Sonntag, Volker K.H.
AU - Crawford, Neil R.
PY - 2011/2
Y1 - 2011/2
N2 - Object. Unstable fractures at the thoracolumbar junction often require extended, posterior, segmental pedicular fixation. Some surgeons have reported good clinical outcomes with short-segment constructs if additional pedicle screws are inserted at the fractured level. The goal of this study was to quantify the biomechanical advantage of the index-level screw in a fracture model. Methods. Six human cadaveric T10-L4 specimens were tested. A 3-column injury at L-1 was simulated, and 4 posterior constructs were tested as follows: one-above-one-below (short construct) with/without index-level screws, and two-above-two-below (long construct) with/without index-level screws. Pure moments were applied quasistatically while 3D motion was measured optoelectronically. The range of motion (ROM) and lax zone across T12-L2 were measured during flexion, extension, left and right lateral bending, and left and right axial rotation. Results. All constructs significantly reduced the ROM and lax zone in the fractured specimens. With or without index-level screws, the long-segment constructs provided better immobilization than the short-segment constructs during all loading modes. Adding an index-level screw to the short-segment construct significantly improved stability during flexion and lateral bending; there was no significant improvement in stability when an index-level screw was added to the long-segment construct. Overall, bilateral index-level screws decreased the ROM of the 1-level construct by 25% but decreased the ROM of the 2-level construct by only 3%. Conclusions. In a fracture model, adding index-level pedicle screws to short-segment constructs improves stability, although stability remains less than that provided by long-segment constructs with or without index-level pedicle screws. Therefore, highly unstable fractures likely require extended, long-segment constructs for optimum stability.
AB - Object. Unstable fractures at the thoracolumbar junction often require extended, posterior, segmental pedicular fixation. Some surgeons have reported good clinical outcomes with short-segment constructs if additional pedicle screws are inserted at the fractured level. The goal of this study was to quantify the biomechanical advantage of the index-level screw in a fracture model. Methods. Six human cadaveric T10-L4 specimens were tested. A 3-column injury at L-1 was simulated, and 4 posterior constructs were tested as follows: one-above-one-below (short construct) with/without index-level screws, and two-above-two-below (long construct) with/without index-level screws. Pure moments were applied quasistatically while 3D motion was measured optoelectronically. The range of motion (ROM) and lax zone across T12-L2 were measured during flexion, extension, left and right lateral bending, and left and right axial rotation. Results. All constructs significantly reduced the ROM and lax zone in the fractured specimens. With or without index-level screws, the long-segment constructs provided better immobilization than the short-segment constructs during all loading modes. Adding an index-level screw to the short-segment construct significantly improved stability during flexion and lateral bending; there was no significant improvement in stability when an index-level screw was added to the long-segment construct. Overall, bilateral index-level screws decreased the ROM of the 1-level construct by 25% but decreased the ROM of the 2-level construct by only 3%. Conclusions. In a fracture model, adding index-level pedicle screws to short-segment constructs improves stability, although stability remains less than that provided by long-segment constructs with or without index-level pedicle screws. Therefore, highly unstable fractures likely require extended, long-segment constructs for optimum stability.
KW - Biomechanical study
KW - Pedicle screw
KW - Spine fracture
KW - Thoracolumbar junction
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U2 - 10.3171/2010.10.SPINE10222
DO - 10.3171/2010.10.SPINE10222
M3 - Article
C2 - 21214311
AN - SCOPUS:79551714181
SN - 1547-5654
VL - 14
SP - 192
EP - 197
JO - Journal of Neurosurgery: Spine
JF - Journal of Neurosurgery: Spine
IS - 2
ER -