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. 2014 Sep;11(3):117-20.
doi: 10.14245/kjs.2014.11.3.117. Epub 2014 Sep 30.

A Surgical Method for Determining Proper Screw Length in ACDF

Hae-Gi Park  1 , Moo-Sung Kang  1 , Kyung-Hyun Kim  1 , Jeong-Yoon Park  1 , Keun-Su Kim  1 , Sung-Uk Kuh  1
Affiliations

A Surgical Method for Determining Proper Screw Length in ACDF

Hae-Gi Park et al. Korean J Spine. 2014 Sep.

Abstract

Objective: We describe a surgical tool that uses the distractor pin as a reference for determining proper screw length in ACDF. It is critical that screw purchase depth be as deep as possible without violating or penetrating the posterior cortical wall, which ensures strong pull out strength.

Methods: We enrolled 81 adult patients who underwent ACDF using an anterior cervical plate from 2010 to 2012. Patients were categorized into Groups A (42 patients: retractor pin used as a reference for screw length) and B (39 patients: control group). Intraoperative lateral x-rays were taken after screwing the retractor pin to confirm the approaching vertebral level. The ratio of retractor pin length to body anteroposterior (A-P) diameter was measured as a reference. Proper screw length was determined by comparison to the reference.

Results: The average distance from screw tip to posterior wall was 3.0±1.4mm in Group A and 4.1±2.3mm in Group B. The ratio of screw length to body sagittal diameter was 86.2±5.7% in Group A and 80.8±9.0% in Group B. Screw length to body sagittal diameter ratios higher than 4/5 occurred in 33 patients (90%) in Group A and 23 patients (59%) in Group B. No cases violated the posterior cortical wall.

Conclusion: We introduce a useful surgical method for determining proper screw length in ACDF using the ratio of retractor pin length to body A-P diameter as a reference. This method allows for deeper screw purchase depth without violation of the posterior cortical wall.

Keywords: Anterior cervical discectomy and fusion (ACDF); Screw length; Screw pullout strength.

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Conflict of interest statement

The authors have no actual or potetinal conflict of interest in relation to this article.

Figures

Fig. 1
Fig. 1
A: Intraoperative x-ray film was taken after placing the retractor pin. In this example, the ratio of retractor pin to vertebrae A-P diameter was over 90%, so a 14-mm screw was used. B: Post operative film showed that the ratio of screw length to body A-P diameter was over 4/5.
Fig. 2
Fig. 2
The ratio of screw length to sagittal diameter.
Fig. 3
Fig. 3
A case in which disc space was violated by the retractor pin.
See this image and copyright information in PMC

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