Review of mechanisms of expandable spine surgery devices

ABSTRACT

Introduction

Expandable devices such as interbody cages, vertebral body reconstruction cages, and intravertebral body expansion devices are frequently utilized in spine surgery. Since the introduction of expandable implants in the early 2000s, the variety of mechanisms that drive expansion and implant materials have steadily increased. By examining expandable devices that have achieved commercial success and exploring emerging innovations, we aim to offer an in-depth evaluation of the different types of expandable cages used in spine surgery and the underlying mechanisms that drive their functionality.

Areas Covered

We performed a review of expandable spinal implants and devices by querying the National Library of Medicine MEDLINE database and Google Patents database from 1933 to 2024. Five major types of mechanical jacks that drive expansion were identified: scissor, pneumatic, screw, ratchet, and insertion-expansion.

Expert Opinion

We identified a trend of screw jack mechanism being the predominant machinery in vertebral body reconstruction cages and scissor jack mechanism predominating in interbody cages. Pneumatic jacks were most commonly found in kyphoplasty devices. Critically reviewing the mechanisms of expansion and identifying trends among effective and successful cages allows both surgeons and medical device companies to properly identify future areas of development.

KEYWORDS:

• Expandable cage
• mechanical jack
• scissor jack
• screw jack
• spinal implant

Article highlights

• Five major types of mechanical jacks that drive expansion of spinal implants were identified: scissor, pneumatic, screw, ratchet, and insertion-expansion.

• Screw jack mechanism was the predominant machinery in vertebral body reconstruction cages.

• Scissor jack mechanism was the predominant machinery in interbody cages.

• Pneumatic jacks were most commonly found in kyphoplasty devices.

• Critically reviewing the mechanisms of expansion and identifying trends among effective and successful cages allows both surgeons and medical device companies to properly identify future areas of development.

Declaration of interest

Michael P. Steinmetz receives royalties from Zimmer Biomet and Globus Medical as well as speaker fees from Cerapedics. Thomas E. Mroz receives royalties from Stryker Medical. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewers disclosure

Peer reviewers on this manuscript have no relevant financial relationships or otherwise to disclose.

Additional information

Funding

This paper was not funded.