In recent years, the field of spine surgery has borne witness to a variety of new techniques and technologies aimed at effectively treating spinal pathology without requiring fusion. The concept of motion-preserving spine surgery has gained popularity as an avenue for minimizing the potential downsides of spinal fusion, such as loss of range of motion or progression of degeneration of other spinal segments that have not been fused. Having evolved for several decades, artificial discs for cervical and lumbar disc replacement have arguably become standard of care for certain neck and low back conditions. The design of these implants continues to progress to allow for improved mechanics and durability. Emerging alternative options for motion-sparing spinal surgery in the lumbar spine include TOPS, MOTUS, and PerQdisc. Additionally, cutting edge research in the field of disc regeneration is ongoing, which has potential treatment applications for both cervical and lumbar conditions. This article will explore these technologies.
Disc Designs
The discs are located in the anterior (front) of the spine. There are a few factors that must be considered with regards to the design of artificial discs used for cervical and lumbar disc replacement: motion, durability, and implantation. Artificial discs on the market vary in design, in effort to optimize these three elements.
Artificial discs aim to allow motion similar to the native disc’s natural motion at the treated spinal segment. Most devices consist of separate pieces including a metal baseplate and plastic polymer that allow for a constrained gliding motion.1 As we learn from the field of hip and knee replacement, the long-term wear on these materials may influence the long-term motion of the device or require revision surgery.2 Optimizing the durability of materials used is an ongoing pursuit, and forthcoming long-term studies will help in understanding the impact of this on patient outcomes.
In addition to biomaterials, artificial discs vary in the way they are surgically implanted and subsequently interact with the vertebra. Some devices employ a keel which requires a cut in the bone to allow for mechanical fit while others utilize specific finishes on the metal baseplate to encourage on-growth of bone after implantation. Future artificial discs will need to ensure rapid and reliable stability between the vertebrae of the treated level, while minimizing the impact of the surgical procedure or to surrounding structures.
Facet Joint Replacement
Facet joints are small joints in the posterior (back) of the spine that allow for motion of a spinal segment together with the disc in the anterior (front) of the spine. In patients for whom a posterior (back) surgery is indicated, such as a lumbar decompression to address neural compression, and fusion, several alternatives have been recently developed to allow for motion of the facet joints.
The TOPS System (Premia Spine, Ltd.) uses pedicle screw fixation, similar to those used in most lumbar fusions. In fusion procedures, the pedicle screws are then attached to rigid rods that stop the motion at that level. Conversely, with the TOPS procedure, the pedicle screws are attached to an articulating metal and plastic polymer component designed to mimic the function of native lumbar facet joints by maintaining motion. In 2023, the TOPS System received FDA approval for treatment of grade I lumbar spondylolisthesis from L2-L5.3
The MOTUS investigational device (3Spine, Inc.) is designed to serve as a replacement for the entire motion segment. As with TOPS, this is implanted after a thorough posterior decompression. Two devices are then fixed to both vertebrae of the treated level with components in both the disc and facet joints of the spine. This aims to preserve the height of the removed disc and to facilitate motion. Still in the early phases of testing, an IDE clinical trial for FDA approval is currently ongoing.4
Lumbar Disc Nucleus Replacement
There are two main parts of a spinal disc, the nucleus (center) and the annulus (outer ring). Artificial discs replace the entire disc (nucleus and annulus), known as a total disc replacement. For treatment of low back pain due to degenerative disc disease, a novel implantable device, called PerQdisc (Spinal Stabilization Technologies, LLC), offers a fluid-filled chamber that replaces the nucleus of a lumbar disc, but keeps the native annulus intact. This is designed to distribute forces on the spinal segment and maintain or restore motion. Implanted through an anterior or lateral approach to the spine through the flank, this technology is actively being investigated in multiple clinical trials.
Disc Regeneration
Looking further down the line, the science of influencing, maintaining, and even re-building cervical and lumbar disc material and function is an immensely exciting field. A collection of biologic and chemical therapies including exosomes, stem cells, and structural scaffolds offer promise regarding the potential to regrow injured or degenerated discs and avoid the need for future invasive surgery. Clinical scientists have recently published the results of an animal study using a repair patch for herniated discs which incorporates mechanically-activated microcapsules for delivery of biologic agents to influence the healing process; we look forward to human application research in the coming years.5
Conclusion
Spinal motion preservation is a rapidly evolving concept in spinal healthcare. Much research is being done in this field to create the best options for patients with symptomatic disc disease. This is promising to the vast number of those affected by spinal conditions. The National Spine Health Foundation is dedicated to bringing the most up-to-date information to the spinal community.
1 Patwardhan AG, Havey RM. Biomechanics of Cervical Disc Arthroplasty-A Review of Concepts and Current Technology. Int J Spine Surg. 2020 Aug;14(s2):S14-S28. doi: 10.14444/7087. PMID: 32994302; PMCID: PMC7528772.
2 Zavras AG, Dandu N, Nolte MT, Butler AJ, Federico VP, Sayari AJ, Sullivan TB, Colman MW. Segmental range of motion after cervical total disc arthroplasty at long-term follow-up: a systematic review and meta-analysis. J Neurosurg Spine. 2022 Apr 22;37(4):579-587. PMID: 35453108.
3 Pinter ZW, Freedman BA, Nassr A, Sebastian AS, Coric D, Welch WC, Steinmetz MP, Robbins SE, Ament J, Anand N, Arnold P, Baron E, Huang J, Whitmore R, Whiting D, Tahernia D, Sandhu F, Chahlavi A, Cheng J, Chi J, Pirris S, Groff M, Fabi A, Meyer S, Kushwaha V, Kent R, DeLuca S, Smorgick Y, Anekstein Y; TOPS Study Group. A Prospective Study of Lumbar Facet Arthroplasty in the Treatment of Degenerative Spondylolisthesis and Stenosis: Results from the Total Posterior Spine System (TOPS) IDE Study. Clin Spine Surg. 2023 Mar 1;36(2):E59-E69. PMID: 36191093
4 Alex Sielatycki J, Devin CJ, Pennings J, Koscielski M, Metcalf T, Archer KR, Dunn R, Craig Humphreys S, Hodges S. A novel lumbar total joint replacement may be an improvement over fusion for degenerative lumbar conditions: a comparative analysis of patient-reported outcomes at one year. Spine J. 2021 May;21(5):829-840. doi: 10.1016/j.spinee.2020.12.001. Epub 2020 Dec 17. PMID: 33346156.
5 Peredo AP, Gullbrand SE, Friday CS, Orozco BS, Dehghani B, Jenk AC, Bonnevie ED, Hilliard RL, Zlotnick HM, Dodge GR, Lee D, Engiles JB, Hast MW, Schaer TP, Smith HE, Mauck RL. Tension-activated nanofiber patches delivering an anti-inflammatory drug improve repair in a goat intervertebral disc herniation model. Sci Transl Med. 2023 Nov 15;15(722):eadf1690. doi: 10.1126/scitranslmed.adf1690. Epub 2023 Nov 15. PMID: 37967202; PMCID: PMC10812087.
