Using lamina screws as a salvage technique at C-7: computed tomography and biomechanical analysis using cadaveric vertebrae

Laboratory investigation

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Object

Transpedicular instrumentation at C-7 has been well accepted, but salvage techniques are limited. Lamina screws have been shown to be a biomechanically sound salvage technique in the proximal thoracic spine, but have not been evaluated in the lower cervical spine. The following study evaluates the anatomical feasibility of lamina screws at C-7 as well as their bone-screw interface strength as a salvage technique.

Methods

Nine fresh-frozen C-7 cadaveric specimens were scanned for bone mineral density using dual energy x-ray absorptiometry. Prior to testing, all specimens were imaged using CT to obtain 1-mm axial sections. Caliper measurements of both pedicle width and laminar thickness were obtained. On the right side, pedicle screws were first inserted and then pulled out. Salvage intralaminar screws were inserted into the left lamina from the right spinous process/lamina junction and then pulled out. All screws were placed by experienced cervical spine surgeons under direct fluoroscopic visualization. Pedicle and lamina screws were 4.35- and 3.5-mm in diameter, respectively. Screws sizes were chosen based on direct and radiographic measurements of the respective anatomical regions. Insertional torque (IT) was measured in pounds per inch. Tensile loading to failure was performed in-line with the screw axis at a rate of 0.25 mm/sec using a MiniBionix II system with data recorded in Newtons.

Results

Using lamina screws as a salvage technique generated mean pullout forces (778.9 ± 161.4 N) similar to that of the index pedicle screws (805.3 ± 261.7 N; p = 0.796). However, mean lamina screw peak IT (5.2 ± 2.0 lbs/in) was significantly lower than mean index pedicle screw peak IT (9.1 ± 3.6 lbs/in; p = 0.012). Bone mineral density was strongly correlated with pedicle screw pullout strength (r = 0.95) but less with lamina screw pullout strength (r = 0.04). The mean lamina width measured using calipers (5.7 ± 1.0 mm) was significantly different from the CTmeasured mean lamina width (5.1 ± 0.8 mm; p = 0.003). Similarly, the mean pedicle width recorded with calipers (6.6 ± 1.1 mm) was significantly different from the CT-measured mean pedicle width (6.2 ± 1.3 mm; p = 0.014). The mean laminar width measured on CT at the thinnest point ranged from 3.8 to 6.8 mm, allowing a 3.5-mm screw to be placed without difficulty.

Conclusions

These results suggest that using lamina screws as a salvage technique at C-7 provides similar fixation strength as the index pedicle screw. The C-7 lamina appears to have an ideal anatomical width for the insertion of 3.5-mm screws commonly used for cervical fusions. Therefore, if the transpedicular screw fails, using intralaminar screws appear to be a biomechanically sound salvage technique.

Abbreviations used in this paper:BMD = bone mineral density; IT = insertional torque.

Article Information

Address correspondence to: Mario J. Cardoso, M.D., D.C., Department of Neurosurgery, Walter Reed Army Medical Center, 6900 Georgia Avenue NW, Washington, DC 20307. email: mtcardoso@comcast.net.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Computed tomography scan (left) and caliper measurements (right) of lamina thickness and pedicle width.

  • View in gallery

    Radiograph and cadaveric specimen demonstrating pedicle and lamina screws.

  • View in gallery

    Line graph comparing IT per revolution between the index pedicle screw (PS) and lamina screw (LA) techniques.

  • View in gallery

    Bar graph demonstrating that pedicle peak IT was significantly greater than lamina peak IT (p = 0.012).

  • View in gallery

    Bar graph showing that pedicle and lamina pullout strength are not significantly different (p = 0.80).

References

1

Abumi KItoh HTaneichi HKaneda K: Transpedicular screw fixation for traumatic lesions of the middle and lower cervical spine: description of the techniques and preliminary report. J Spinal Disord 7:19281994

2

An HSGordin RRenner K: Anatomic considerations for plate-screw fixation of the cervical spine. Spine 16:S548S5511991

3

Berlemann UCripton PARincon LNolte LPSchlapfer F: Pull-out strength of pedicle hooks with fixation screws: influence of screw length and angulation. Eur Spine J 5:71731996

4

Bruneau MCornelius JFMarneffe VTriffaux MGeorge B: Anatomical variations of the V2 segment of the vertebral artery. Neurosurgery 59:ONS20ONS242006

5

Choueka JSpivak JMKummer FJSteger T: Flexion failure of posterior cervical lateral mass screws. Influence of insertion technique and position. Spine 21:4624681996

6

Coe JDWarden KEHerzig MAMcAfee PC: Influence of bone mineral density on the fixation of thoracolumbar implants. A comparative study of transpedicular screws, laminar hooks, and spinous process wires. Spine 15:9029071990

7

Coe JDWarden KESutterlin CE 3rdMcAfee PC: Biomechanical evaluation of cervical spinal stabilization methods in a human cadaveric model. Spine 14:112211311989

8

Dmitriev AEKuklo TRLehman RA JrRosner MK: Stabilizing potential of anterior, posterior, and circumferential fixation for multilevel cervical arthrodesis: an in vitro human cadaveric study of the operative and adjacent segment kinematics. Spine 32:E188E1962007

9

Fehlings MGCooper PRErrico TJ: Posterior plates in the management of cervical instability: long-term results in 44 patients. J Neurosurg 81:3413491994

10

Harris BMHilibrand ASNien YHNachwalter RVaccaro AAlbert TJ: A comparison of three screw types for unicortical fixation in the lateral mass of the cervical spine. Spine 26:242724312001

11

Heller JGEstes BTZaouali MDiop A: Biomechanical study of screws in the lateral masses: variables affecting pull-out resistance. J Bone Joint Surg Am 78:131513211996

12

Heller JGSilcox DH 3rdSutterlin CE 3rd: Complications of posterior cervical plating. Spine 20:244224481995

13

Hong JTSung JHSon BCLee SWPark CK: Significance of laminar screw fixation in the subaxial cervical spine. Spine 33:173917432008

14

Johnston TLKaraikovic EELautenschlager EPMarcu D: Cervical pedicle screws vs lateral mass screws: uniplanar fatigue analysis and residual pullout strengths. Spine J 6:6676722006

15

Jones ELHeller JGSilcox DHHutton WC: Cervical pedicle screws versus lateral mass screws. Anatomic feasibility and biomechanical comparison. Spine 22:9779821997

16

Karaikovic EEDaubs MDMadsen RWGaines RW Jr: Morphologic characteristics of human cervical pedicles. Spine 22:4935001997

17

Kothe RRuther WSchneider ELinke B: Biomechanical analysis of transpedicular screw fixation in the subaxial cervical spine. Spine 29:186918752004

18

Kretzer RMSciubba DMBagley CAWolinsky JPGokaslan ZLGaronzik IM: Translaminar screw fixation in the upper thoracic spine. J Neurosurg Spine 5:5275332006

19

Kuklo TRLehman RA Jr: Effect of various tapping diameters on insertion of thoracic pedicle screws: a biomechanical analysis. Spine 28:206620712003

20

Lehman RA JrDmitriev AEHelgeson MDSasso RCKuklo TRRiew KD: Salvage of C2 pedicle and pars screws using the intralaminar technique: a biomechanical analysis. Spine 33:9609652008

21

Lehman RA JrKuklo TR: Use of the anatomic trajectory for thoracic pedicle screw salvage after failure/violation using the straight-forward technique: a biomechanical analysis. Spine 28:207220772003

22

Liljenqvist UHackenberg LLink THalm H: Pullout strength of pedicle screws versus pedicle and laminar hooks in the thoracic spine. Acta Orthop Belg 67:1571632001

23

Ludwig SCKramer DLVaccaro ARAlbert TJ: Transpedicle screw fixation of the cervical spine. Clin Orthop Relat Res 359:77881999

24

Rhee JMKraiwattanapong CHutton WC: A comparison of pedicle and lateral mass screw construct stiffnesses at the cervicothoracic junction: a biomechanical study. Spine 30:E636E6402005

25

Rogers WA: Fractures and dislocations of the cervical spine; an end-result study. J Bone Joint Surg Am 39-A:3413761957

26

Sran MMBoyd SKCooper DMKhan KMZernicke RFOxland TR: Regional trabecular morphology assessed by micro-CT is correlated with failure of aged thoracic vertebrae under a posteroanterior load and may determine the site of fracture. Bone 40:7517572007

27

Sutterlin CE 3rdMcAfee PCWarden KERey RM JrFarey ID: A biomechanical evaluation of cervical spinal stabilization methods in a bovine model. Static and cyclical loading. Spine 13:7958021988

28

Vaccaro ARRizzolo SJAllardyce TJRamsey MSalvo JBalderston RA: Placement of pedicle screws in the thoracic spine. Part I: Morphometric analysis of the thoracic vertebrae. J Bone Joint Surg Am 77:119311991995

29

Vaccaro ARRizzolo SJBalderston RAAllardyce TJGarfin SRDolinskas C: Placement of pedicle screws in the thoracic spine. Part II: An anatomical and radiographic assessment. J Bone Joint Surg Am 77:120012061995

30

Weiland DJMcAfee PC: Posterior cervical fusion with triplewire strut graft technique: one hundred consecutive patients. J Spinal Disord 4:15211991

31

Xu RBurgar AEbraheim NAYeasting RA: The quantitative anatomy of the laminas of the spine. Spine 24:1071131999

32

Zdeblick TAKunz DNCooke MEMcCabe R: Pedicle screw pullout strength. Correlation with insertional torque. Spine 18:167316761993

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