The aiming device for cervical distractor pin insertion: a proof-of-concept, feasibility study

Torphong Bunmaprasert,Raphi Raphitphan,K Daniel Riew,Sittichai Luangkittikong,Supachoke Nivescharoenpisan,Nantawit Sugandhavesa,Menghong Tosinthiti,Wongthawat Liawrungrueang

doi:10.1186/s12891-021-04533-w

Abstract

BackgroundRestoration of cervical lordosis after anterior discectomy and fusion is a desirable goal. Proper insertion of the vertebral distraction or Caspar pin can assist lordotic restoration by either putting the tips divergently or parallel to the index vertebral endplates. With inexperienced surgeons, the traditional free-hand technique for Caspar pin insertion may require multiple insertion attempts that may compromise the vertebral body and increase radiation exposure during pin localization. Our purpose is to perform a proof-of-concept, feasibility study to evaluate the effectiveness of a pin insertion aiming device for vertebral distraction pin insertion.MethodsA Smith-Robinson approach and anterior cervical discectomy were performed from C3 to C7 in 10 human cadaveric specimens. Caspar pins were inserted using a novel pin insertion aiming device at C3-4, C4-5, C5-6, and C6-7. The angles between the cervical endplate slope and Caspar pin alignment were measured with lateral cervical imaging.ResultsThe average Superior Endplate-to-Caspar Pin angle (SE-CP) and the average Inferior Endplate-to-Caspar Pin angle (IE-CP) were 6.2 ± 2.0° and 6.3 ± 2.2° respectively. For the proximal pins, the SE-CP and the IE-CP were 4.0 ± 1.1°and 5.2 ± 2.4° respectively. For the distal pins, the SE-CP and the IE-CP were 7.7 ± 1.4° and 6.2 ± 2.0° respectively. No cervical endplate violations occurred.ConclusionThe novel Caspar pin insertion aiming device can control the pin entry points and pin direction with the average SE-CP and average IE-CP of 6.2 ± 2.0° and 6.3 ± 2.2°, respectively. The study shows that the average different angles between the Caspar pin and cervical endplate are less than 7°.

Highlights

Restoration of cervical lordosis after anterior discectomy and fusion is a desirable goal
The purpose of this study was to perform a proof-ofconcept, feasibility study to evaluate the efficacy of a Caspar pin aiming device for ACDF that was designed to improve the precision of pin placement and minimize radiation exposure during pin insertion
No significant differences were found between the superior and inferior endplate slopes except C3 (11.7 ± 3.4° vs. 7.4 ± 5.5°, P-value = 0.048), suggesting that the endplate slopes were mostly parallel in this study

Summary

Introduction

Restoration of cervical lordosis after anterior discectomy and fusion is a desirable goal. Anterior cervical discectomy and fusion (ACDF) is a safe and effective operation for degenerative cervical diseases and various disorders. One of the important steps of ACDF is the distraction of the intervertebral space. This step helps the surgeon to expose the disc space during discectomy, The Caspar cervical distractor system (Fig. 1A) is considered a standard tool in performing cervical distraction. Caspar distraction pins (Fig. 1B) may improve disc space visualization and control cervical alignment during direct vertebral distraction (Fig. 1C). The trajectory and position of the Caspar cervical pins affect disc space visualization and working spaces during operation. Pin malposition may occur even with experienced spine surgeons using a freehand technique, which may result in adverse outcomes [3]

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