Is a fusion considered an implant?

October 2, 2025 •

5 min read

Over 400,000 interbody spinal fusions are performed in the United States each year. Despite the high frequency of this procedure, many people wonder: Is a fusion considered an implant? The simplest answer is no; a fusion is the biological process of bones healing together, while an implant is a medical device that a surgeon uses to facilitate this process.

Quick Summary

A fusion is a surgical procedure that encourages two or more vertebrae to grow into a single bone. Implants, such as cages, rods, or plates, are medical devices inserted during the surgery to provide stability and support the fusion process.

Key Points

Fusion is a biological process: A spinal fusion is the medical term for the process where two or more vertebrae heal and join together into one solid bone.
Implants are surgical tools: Implants are the hardware, such as rods, plates, and cages, used by a surgeon to hold the spine stable and facilitate the fusion process.
Implants provide stability: While the bone graft biologically creates the fusion, implants offer immediate mechanical support, acting as an internal brace while the bones heal.
Variety of implant materials: Implants are made from biocompatible materials like titanium, PEEK, or stainless steel, each with different properties suited for various applications.
Bone grafts are necessary for fusion: The actual fusion requires bone graft material (autografts, allografts, or synthetic substitutes) to act as a scaffold for new bone growth, regardless of the implants used.
Successful fusion depends on both: The ideal outcome relies on a combination of biological healing (fusion) and mechanical support from the implants.

The crucial difference between fusion and implants

While a spinal fusion procedure often involves implants, the two terms are not interchangeable. The key distinction lies in function: one is the biological process, and the other is the mechanical device. A fusion is the actual healing process in which two or more vertebrae grow together into a single, solid bone. The goal is to eliminate motion at a painful segment of the spine to provide stability and relieve discomfort. This biological weld is the ultimate objective of the surgery.

Implants, on the other hand, are the biocompatible medical devices used by surgeons to support and stabilize the spine during the fusion process. These devices act as a temporary internal brace, holding the vertebrae in the correct position until the natural bone healing process is complete. Without these implants, the bone graft and surrounding vertebrae would not have the necessary support to fuse properly, potentially leading to a failed fusion (pseudarthrosis).

The multifaceted role of implants in spinal fusion

Implants serve several critical roles during spinal fusion surgery. They provide immediate, rigid stabilization, which is essential for successful bony fusion. This mechanical support holds the vertebral segments immobile, creating the optimal environment for new bone growth to occur. Implants can also help to restore or maintain the proper height and alignment of the spine, which helps to decompress nerves and alleviate pain.

Common types of implants used in spinal fusion

Spinal surgeons utilize a variety of implants, often in combination, to achieve a successful fusion. The choice of implant depends on the surgical approach, the specific condition being treated, and the patient's anatomy. Here are some of the most common types:

Interbody Cages: These small, hollow devices are placed into the disc space after the damaged disc has been removed. They are typically filled with bone graft material and help to restore disc height and create a supportive environment for fusion. Cages are made from materials like titanium or a special polymer called polyetheretherketone (PEEK).
Rods: Strong, flexible rods are used to support and stabilize the spine over a larger area, often correcting deformities like scoliosis or kyphosis. They are typically connected to the vertebrae with screws or hooks.
Plates: Commonly used in cervical (neck) fusions, small plates are secured to the front of the vertebrae with screws to provide stability.
Screws: Pedicle screws are inserted into the bony portion of the vertebrae and are then connected to rods. This system provides a very stable construct to hold the spine in position while it fuses.

The process and science of fusion

The biological process of a spinal fusion is achieved through the use of a bone graft. The graft material acts as a scaffold, providing a framework for new bone cells to grow across the space between the vertebrae. The bone graft is the critical biological component that enables the actual fusion, while the implants provide the necessary mechanical support.

There are several types of bone grafts used:

Autograft: Bone harvested from the patient's own body, often the pelvis. It is considered the 'gold standard' because it contains living bone cells, proteins, and the ideal scaffold for new bone growth.
Allograft: Bone tissue obtained from a deceased donor through a tissue bank. It is processed to remove cellular material and acts as a scaffold for the patient's own cells to grow.
Synthetic Bone Substitutes: Man-made materials, like ceramics, that provide a scaffold for new bone to grow. These can often be supplemented with biologics like bone morphogenetic proteins (BMPs) to stimulate bone growth.

Materials used for implants

Modern spinal implants are designed to be biocompatible, durable, and strong. The most common materials include:

Titanium and Titanium Alloys: Highly biocompatible, strong, and lightweight. Unlike stainless steel, they are compatible with MRI scans.
Polyetheretherketone (PEEK): A special type of plastic polymer that is radiolucent (meaning it doesn't show up on X-rays) and has an elasticity closer to natural bone, which some studies suggest can promote better healing.
Stainless Steel: A traditional, strong, and durable material, though it can cause issues with future MRI imaging due to its magnetic properties.

Fusion vs. implant surgery: Key comparisons

To better illustrate the differences, consider this comparison:


Feature	Fusion (Surgical Procedure)	Implants (Medical Devices)
Definition	A medical procedure to permanently join two or more vertebrae.	Man-made hardware (cages, rods, screws) used to support the spine.
Purpose	To eliminate motion and stabilize a painful segment of the spine.	To provide immediate mechanical support and promote successful fusion.
Permanence	The ultimate goal is a permanent biological bond between the bones.	The devices are typically permanent, but their primary function is temporary stabilization.
Primary Mechanism	Biological bone growth and healing using bone graft material.	Mechanical stabilization and structural support.
Materials	Bone graft (autograft, allograft, synthetic) is used for the biological process.	Titanium, PEEK, stainless steel, etc., used for the hardware.

The risks and benefits of spinal implants in fusion

The primary benefit of using implants during a fusion procedure is improved outcomes. The immediate stability they provide increases the likelihood of a successful fusion, particularly in complex cases. This stabilization can lead to a significant reduction in chronic back or neck pain and improved functionality. However, like any surgical intervention, there are risks involved. These include infection, allergic reaction to the implant material, and potential implant failure or loosening over time. Non-smokers, for example, have a significantly higher fusion success rate than smokers, as nicotine can inhibit bone healing. It's essential for patients to discuss the potential risks and benefits with their surgeon.

Conclusion

In summary, asking if a fusion is considered an implant is a matter of distinguishing between a process and a tool. A fusion is the desired outcome—a biological joining of bone. An implant is the crucial piece of hardware that assists the body in achieving that outcome by providing stability and support. The two are inextricably linked in modern spinal surgery, with implants playing a vital role in ensuring the biological fusion process is successful. By understanding this distinction, patients can better grasp the details of their surgical treatment and recovery. For further information on spine health and surgical procedures, resources from the American Academy of Orthopaedic Surgeons (AAOS) provide valuable insights.

Frequently Asked Questions

The primary purpose of a spinal implant is to provide immediate stability to the vertebrae and support the bone graft during a spinal fusion procedure, which creates an optimal environment for bone healing.

No, not all spine surgeries involving implants are fusions. Some procedures, like artificial disc replacement, use implants but are designed to preserve motion rather than eliminate it.

Bone graft is the biological material used to stimulate new bone growth, while an implant is the mechanical device used for stabilization. The implant acts as a support structure for the bone graft to fuse the vertebrae.

Yes, some historical fusion techniques or non-instrumented fusions may not have used rigid hardware, relying solely on bone graft and external bracing. However, modern spinal fusions almost always involve internal fixation (implants) to increase stability and improve the success rate.

Spinal implants are intended to be permanent, providing long-term support. While they are durable, no medical device is guaranteed to last indefinitely, and there are risks of complications or loosening over time.

Interbody cages are hollow implants placed in the disc space after a damaged disc is removed. They restore disc height, decompress nerves, and contain bone graft material to encourage fusion.

Fusion is the process of permanently joining vertebrae to eliminate motion, while artificial disc replacement is a surgery that uses an implant to replace a damaged disc and preserve motion.