Biomechanical advantage of the index-level pedicle screw in unstable thoracolumbar junction fractures

Presented at the 2010 Joint Spine Section Meeting 

Restricted access

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.

Abbreviations used in this paper: LZ = lax zone; ROM = range of motion.

Article Information

Address correspondence to: Neil R. Crawford, Ph.D., c/o Neuroscience Publications, Barrow Neurological Institute, 350 West Thomas Road, Phoenix, Arizona 85013. email: neuropub@chw.edu.

Please include this information when citing this paper: published online January 7, 2011; DOI: 10.3171/2010.10.SPINE10222.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Photographs of representative specimens in each instrumented condition studied. A: Posterior view of short-segment (T12–L2) fixation without index-level screws. B: Posterior view of short-segment (T12–L2) fixation with index-level screws. C: Posterior view of long-segment (T11–L3) fixation without index-level screws. D: Posterior view of long-segment (T11–L3) fixation with index-level screws.

  • View in gallery

    Anteroposterior (left) and lateral (right) radiographs of a sample specimen after destabilization showing entry points and trajectories of index-level screws.

  • View in gallery

    Graph showing the mean unidirectional T12–L2 angular ROM. Error bars show standard deviation.

  • View in gallery

    Graph showing the mean bidirectional T12–L2 angular LZ. Error bars show standard deviation.

References

1

Been HDBouma GJ: Comparison of two types of surgery for thoraco-lumbar burst fractures: combined anterior and posterior stabilisation vs. posterior instrumentation only. Acta Neurochir (Wien) 141:3493571999

2

Benson DRBurkus JKMontesano PXSutherland TBMcLain RF: Unstable thoracolumbar and lumbar burst fractures treated with the AO fixateur interne. J Spinal Disord 5:3353431992

3

Crawford NRBrantley AGDickman CAKoeneman EJ: An apparatus for applying pure nonconstraining moments to spine segments in vitro. Spine 20:209721001995

4

Crawford NRDickman CA: Construction of local vertebral coordinate systems using a digitizing probe. Technical note. Spine 22:5595631997

5

Crawford NRPeles JDDickman CA: The spinal lax zone and neutral zone: measurement techniques and parameter comparisons. J Spinal Disord 11:4164291998

6

Crawford NRYamaguchi GTDickman CA: A new technique for determining 3-D joint angles: the tilt/twist method. Clin Biomech (Bristol Avon) 14:1531651999. [Erratum in Clin Biomech (Bristol Avon) 15:following 468 2000]

7

Danisa OAShaffrey CIJane JAWhitehill RWang GJSzabo TA: Surgical approaches for the correction of unstable thoracolumbar burst fractures: a retrospective analysis of treatment outcomes. J Neurosurg 83:9779831995

8

Eichholz KMHitchon PWFrom ARubenbauer PNakamura SLim TH: Biomechanical testing of anterior and posterior thoracolumbar instrumentation in the cadaveric spine. J Neurosurg Spine 1:1161212004

9

Flamme CHHurschler CHeymann Cvon der Heide N: Comparative biomechanical testing of anterior and posterior stabilization procedures. Spine 30:E352E3622005

10

Gurwitz GSDawson JMMcNamara MJFederspiel CFSpengler DM: Biomechanical analysis of three surgical approaches for lumbar burst fractures using short-segment instrumentation. Spine 18:9779821993

11

Haas NBlauth MTscherne H: Anterior plating in thoracolumbar spine injuries. Indication, technique, and results. Spine 16:3 SupplS100S1111991

12

Kramer DLRodgers WBMansfield FL: Transpedicular instrumentation and short-segment fusion of thoracolumbar fractures: a prospective study using a single instrumentation system. J Orthop Trauma 9:4995061995

13

Mahar AKim CWedemeyer MMitsunaga LOdell TJohnson B: Short-segment fixation of lumbar burst fractures using pedicle fixation at the level of the fracture. Spine 32:150315072007

14

McLain RFSparling EBenson DR: Early failure of short-segment pedicle instrumentation for thoracolumbar fractures. A preliminary report. J Bone Joint Surg Am 75:1621671993

15

Panjabi MM: Biomechanical evaluation of spinal fixation devices: I. A conceptual framework. Spine 13:112911341988

16

Sasso RCBest NMReilly TMMcGuire RA Jr: Anterioronly stabilization of three-column thoracolumbar injuries. J Spinal Disord Tech 18:SupplS7S142005

17

Shono YMcAfee PCCunningham BW: Experimental study of thoracolumbar burst fractures. A radiographic and biomechanical analysis of anterior and posterior instrumentation systems. Spine 19:171117221994

18

Tasdemiroglu ETibbs PA: Long-term follow-up results of thoracolumbar fractures after posterior instrumentation. Spine 20:170417081995

19

Wood KBBohn DMehbod A: Anterior versus posterior treatment of stable thoracolumbar burst fractures without neurologic deficit: a prospective, randomized study. J Spinal Disord Tech 18:SupplS15S232005

20

Yücesoy KYüksel KZBaek SSonntag VKHCrawford NR: Biomechanics of unilateral compared with bilateral lumbar pedicle screw fixation for stabilization of unilateral vertebral disease. Laboratory investigation. J Neurosurg Spine 8:44512008

TrendMD

Metrics

Metrics

All Time Past Year Past 30 Days
Abstract Views 117 117 31
Full Text Views 72 72 4
PDF Downloads 87 87 5
EPUB Downloads 0 0 0

PubMed

Google Scholar