Biomechanical analysis of a novel hook-screw technique for C1–2 stabilization

Technical note

Restricted access

The Food and Drug Administration has not cleared the following medical devices for the use described in this study. The following medical devices are being discussed for an off-label use: cervical lateral mass screws.

Object

As an alternative for cases in which the anatomy and spatial relationship between C-2 and a vertebral artery precludes insertion of C-2 pedicle/pars or C1–2 transarticular screws, a technique that includes opposing laminar hooks (claw) at C-2 combined with C-1 lateral mass screws may be used. The biomechanical stability of this alternate technique was compared with that of a standard screw-rod technique in vitro.

Methods

Flexibility tests were performed in 7 specimens (occiput to C-3) in the following 6 different conditions: 1) intact; 2) after creating instability and attaching a posterior cable/graft at C1–2; 3) after removing the graft and attaching a construct comprising C-1 lateral mass screws and C-2 laminar claws; 4) after reattaching the posterior cable-graft at C1–2 (posterior hardware still in place); 5) after removing the posterior cable-graft and laminar hooks and placing C-2 pedicle screws interconnected to C-1 lateral mass screws via rod; and 6) after reattaching the posterior cable-graft at C1–2 (screw-rod construct still in place).

Results

All types of stabilization significantly reduced the range of motion, lax zone, and stiff zone compared with the intact condition. There was no significant biomechanical difference in terms of range of motion or lax zone between the screw-rod construct and the screw-claw-rod construct in any direction of loading.

Conclusions

The screw-claw-rod technique restricts motion much like the standard Harms technique, making it an acceptable alternative technique when aberrant arterial anatomy precludes the placement of C-2 pars/pedicle screws or C1–2 transarticular screws.

Abbreviations used in this paper:LZ = lax zone; ROM = range of motion; SZ = stiff zone; VA = vertebral artery.

Article Information

Address correspondence to: Neil R. Crawford, Ph.D., c/o Neuroscience Publications, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, 350 West Thomas Road, Phoenix, Arizona 85013. email: neuropub@chw.edu.

Please include this information when citing this paper: published online July 6, 2012; DOI: 10.3171/2012.5.SPINE1242.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Atlantoaxial fixation instrumentation. A: Posterior photograph of the screw-rod technique interconnecting polyaxial screws at C-1 and C-2 with rods. B: Screw and hook instrumentation attached on a rod before instrumentation of specimens. C: Posterior photograph of the screw-claw-rod technique. A wired interspinous bone graft (wood used as a substitute) was also applied.

  • View in gallery

    Bar graphs showing the angular motion results. Left: All 6 conditions are studied, including intact and grafted conditions. Right: Rigidly instrumented conditions only, shown on a magnified scale. Full bars represent ROM; horizontal lines on each bar demarcate the LZ (closer to zero) and SZ. Error bars show the standard deviation of the ROM.

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