The Burden of Revision Spine Surgery

Introduction:

Instrumented spinal fusion is a common procedure for patients with spinal deformity or degenerative wear-and-tear disorders. Today, most patients do well following spine surgery even 8 years after surgery but some will ultimately require a revision or a “re-do” of their primary surgery(1) . As the field of spine surgery evolves, allowing older and sicker patients to undergo surgery safely, revision spine surgery is still as high as 9 to 45% depending on the complexity of the patient population(2, 3). For a “routine” spinal fusion for degenerative spondylolisthesis (a slipped vertebra), the 8-year revision rate is a little over 20%(1) . It is well known that revision surgery is technically more challenging for the surgical team, is more expensive to undertake and carries significantly more risk compared to primary surgery. Moreover, imagine being the patient faced the uncertain prospect of a re-do surgery in terms of return to work or social activities after what, statistically, should have been a first-time success. The purpose of this paper is to explore the most common reasons for revision spine surgery, discuss the impact it has on patients and the health care system, and finally how future technologies and additive manufacturing can be applied to avoid some of the most dreaded complications that lead to revision spine surgery.

Etiologies of Revision Spine Surgery:

There are multiple possible causes for revision spine surgery. In a series of over 600 patients, one study found that that 9% of patients required at least one revision procedure while an additional 1.5% required a more than one revision(3). The surgeons found that the most common cause for revision spine surgery was pseudarthrosis (failure for the bones to fuse/heal). Less common reasons included infection, additional wear-and-tear to the spine (curve progression, adjacent segment disease), and implant failure. In another study of patients specifically examining revision spine surgery, the authors concluded that the most common cause of revision was infection followed by pseudarthrosis, adjacent segment disease, and implant failure(4). While revision surgery from additional wear-and-tear to the spine is beyond the scope of this paper, the two most common causes of revision surgery, pseudarthrosis and infection may be preventable and enhanced through advances in manufacturing technology and implant design.

Impact of Revision Spine Surgery:

Revision spine surgery is technically more challenging and carriers significantly more risk as compared to a similar primary surgery. The first problem is scar tissue. While most patients just think about the skin on the surface of the skin, the muscles, nerves, and other connective tissue can be encapsulated in deep scar, resulting in distorted anatomy as well as weakened supportive structures such as the dura that surrounds the spinal cord/neural elements and holds in the spinal fluid. Surgeons will typically estimate a 2-3x increase in surgical time when working around scar tissue. Often, the revision requires the old implants to be removed, discarded, and replaced with new implants. Additionally, the revision surgery may involve extending the fusion to a larger portion of the spine (i.e. the adjacent segment). Given the complexity of revision surgery, it is understandable that patients have significantly more complications as compared to primary surgery. As much as 34.4% of patients undergoing revision surgery will suffer a major complication such as infection, implant failure, pseudarthrosis, neurological injury, or even death – there can be more bleeding around scar tissue and the prolonged anesthesia adds additional stress the lungs and heart. Many of the complications suffered from a revision surgery will ultimately require yet another revision procedure to address (2, 5). It been estimated that as much as 21% of patients undergoing revision spine surgery will require another revision spine surgery in the future (6).

It is well documented that patients who undergo revision spine surgery do worse than patient undergoing a similar primary procedure. Following revision surgery, patients have worse functional outcomes and quality of life scores as measured by the ODI and SF-36, two validated measures(7).

In addition to the impact on the patient, revision spine surgery carries significant economic burden. Numerous studies have demonstrated that the cost of revision spine surgery can be averages between $68,294 to $137,990 per episode of care depending on complexity (8, 9). These costs are simply the financial cost to the hospital, and do not account for the patient’s lost wages, prolonged or permanent disability, let alone human costs of dealing with the frustration and fear of uncertainty, the countless trips to the hospital not just for the surgery but follow-up care and rehabilitation. Each spine surgery can take 3 to 4 months of recovery before it is even known if the surgery is successful.

Preventing Revision Spine Surgery:

The most common causes of revision spine surgery, namely infection and pseudarthrosis, are where advances in technology will help reduce and possibly prevent occurrences. Surgeons already utilize oral, IV, or intraoperative medications to minimize infection and enhance bony healing such as antibiotics and bone-graft substitutes such as BMP-2 to prevent these complications. One of the most exciting innovations is enhancing and improving spinal implants to address and prevent these complications. Additive manufacturing and nanotechnology can provide us with implants designed to specifically address each of these dreaded outcomes.

To prevent pseudarthrosis, an implant must promote bone growth as well as osseointegration (bone through-growth and in-growth). Traditional spinal interbody implants are effectively hollow-rings to provide some structural support between two vertebrae and an open channel to allow bone to grow through the implant. With additive manufacturing and other nanotechnologies, novel implant designs can be manufactured with roughened surfaces and other porous lattice structures that promote bony ingrowth and on-growth (10-12). New studies have even shown effects at the cellular level (13, 14). More information on this topic can be found in our previous published white paper, “Lattice Structures in Orthopaedic Implants.”

While preventing infection may be a more challenging task, PrinterPrezz’s advanced research & development program is investing in combining additive manufacturing with nanotechnology to alter the implant characteristics when it comes to bacteria without affecting the desired bone in-growth and through-growth characteristics.