What Is Spinal Instrumentation and Spinal Fusion?

Written by Jason M. Highsmith, MD

Spinal instrumentation, also known as spinal implants, devices or hardware, uses surgical procedures to implant titanium, titanium-alloy, stainless steel, or non-metallic devices into the spine. Instrumentation provides a permanent solution to spinal instability. There are many different types, shapes and sizes of medical implants designed specifically to treat spinal disorders in people of all ages.

Examples of spinal implants include:

Spinal fusion is a process using bone graft to cause 2 opposing bony surfaces to grow together. In medical terminology, spinal fusion is called arthrodesis. Bone graft can be taken from the patient (termed autologous or allograft bone) during the primary surgical procedure or harvested from other individuals (termed allograft bone). Another option for some patients undergoing lumbar (low back) spine surgery is bone morphogenetic protein (BMP). BMP helps to stimulate new bone to grow.

Examples of Different Types of
Spinal Instrumentation

Why Instrumentation and Fusion Are Performed Together
Instrumentation is used during spinal fusion because it helps maintain spinal stability while facilitating the process of bone fusion. These procedures are used to restore stability to the spine, treat spinal deformity (such as scoliosis), and bridge space created by the removal of a spinal element (eg, intervertebral disc) during a spinal decompression procedure.

Both procedures work together to immobilize the involved spinal level(s). This does not necessarily mean the patient is unable to move (eg, bend over). Many patients report that they actually feel more mobile because their pain has been reduced or eliminated as a result of spinal fusion surgery.

Rods and screws are types of instrumentation.
With instrumentation, there is less need for rigid external spinal bracing after spinal fusion. Much like a cast stabilizes a broken bone to heal, instrumentation stabilizes the 2 bony components of a fusion while they heal. The hardware basically functions like an internal brace. In fact, most instrumented spinal fusions are so stable that bracing may only recommended for comfort.

Instrumentation placed without fusion can result in hardware failure. All metal fatigues with repetitive stress. Continual stress on an implant, unsecured by a solid bone growth (healed fusion), can lead to screw pullout or even fracture of the metal. This can result in broken screws, rods, and even complete breakdown of the construct. Consequently, a solid bony fusion is crucial to the proper healing of a spinal fusion.

Factors such as osteoporosis and smoking are known to impair bone healing and reduce the success of fusion. These patients are more likely to have a pseudofusion (false fusion), which can result in continued pain at the surgical site and implant/device failure. A bone growth stimulator may be prescribed by the surgeon to help avoid fusion problems.

An Old Concept Made New: History of Spinal Instrumentation
Spinal instrumentation and fusion are not new surgical concepts. Dr. Paul Harrington developed spinal instrumentation in the late 1950s.

During that time, many children with polio developed spinal deformities. In an attempt to treat these children, Dr. Harrington developed the first spinal instrumentation system (Harrington Instrumentation). Rods were secured to the spine at 2 ends using hooks. The position of the spine was adjusted using a tackling type of device. Through Dr. Harrington's experience, fusion was discovered to be a necessary adjunct to instrumentation. Today, fusion remains an integral part of procedures using instrumentation.

An example of spinal cages implanted after discectomy.

During the 1960s, instrumentation became more mainstream as doctors saw the benefits to patients and found almost 50 ways to modify Harrington's original system. Bone screws and threaded cabling were developed. In the 1970s, Dr. Eduardo Luque was using smooth, bendable rods and wire to stabilize the spine.

In the 1980s, instrumentation evolved into a three-dimensional approach to spinal correction. Rods, hooks, and screws were streamlined to meet individual patient needs with less demand on the surgeon to customize implants on the spot.

Today, spinal instrumentation continues to develop as technology advances the machining, biomechanics, and usability of these implants. Areas of development include smaller, low profile devices to reduce patient discomfort. Many implants can be implanted during minimally invasive spine approaches, and bioabsorbable implants can dissolve after the bony fusion has occurred.

In some cases, rigid titanium or metal implants are too strong and can erode into bone. Consequently, some implants are now made out of polymers that more closely resemble the characteristics of bone.

Advancements in 3D printing have also given us a peek into the future of spinal implants. Although its in the early stages, spine surgeons have successfully used 3D printing to custom-make spinal instrumentation for complex cases that require the utmost precision.

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