Anterior Cervical Spinal Fusion Surgery

Fig. 1: Bone graft
(larger view)

Anterior cervical spinal fusion surgery is commonly done in conjunction with an anterior cervical discectomy. For many patients, cervical spinal fusion surgery (fusing one vertebra to another) is often done to:

• Eliminate motion at a vertebral segment, which should decrease the pain at that segment
• Maintain adequate space for the decompressed spinal cord and/or nerve roots
• Prevent the spine from falling into a collapsed deformity (kyphosis ).

Additionally, anterior cervical spinal fusions are also done to treat cervical instability due to:

• Trauma (fractures or dislocations)
• Tumor
• Infection.

Bone Grafts in Spinal Fusion Surgery

To achieve a spinal fusion, a bone graft (see Figure 1) is used to promote two bones growing together into one. The patient’s own bone will grow into and around the bone graft and incorporate the graft bone as its own. This process creates one continuous bone surface and eliminates motion at the fused joint. A small piece of bone is used to fuse a disc space, and a longer, so-called ‘strut graft’ is used to bridge across multiple disc spaces if a ‘corpectomy’ has been performed.

There are several options available to patients and surgeons for bone grafts in anterior cervical spine surgery, including:

• Autograft bone
• Allograft bone
• Bone graft substitutes.

Autograft Bone for Cervical Spinal Fusion Surgery

Autograft bone (a patient’s own bone) is harvested from the iliac crest (hip). This technique has been the gold standard since the 1950s. Autograft bone usually achieves a fusion in 90% to 95% of patients.

The principal disadvantage with using autograft bone is that another incision needs to be made over the hip to harvest the bone graft.

Possible complications associated with taking out bone graft include:

• Graft site chronic pain (with pain lasting anywhere from 12 to 24 months 25% to 30% of the time)^{1, 2}
• Infection
• Bleeding
• Damage to the lateral femoral cutaneous nerve (a sensory nerve that supplies sensation to the front of the thigh)
• Pelvic bone fracture.

The chances of a complication increase with the size of the bone graft and patient obesity. For those who opt to use an autograft, many patients find the bone graft harvest site to be more painful than the cervical surgery site itself.

Allograft Bone for Cervical Spinal Fusion Surgery

Allograft bone (a.k.a. ‘bank’ bone or donor bone from a cadaver) eliminates the need to harvest the patient’s own bone. Basically, the donor graft acts as a bone scaffolding onto which the patient’s own bone grows and eventually replaces over years. There are no living cells in the bone graft, so there is little chance of a graft rejection, like with an organ transplant.

However, bone graft healing remains an issue, as there is a somewhat greater likelihood of bone graft failure with allograft bone compared to autograft. With that said, it should be known that certain studies have shown allograft to be comparable to autograft in terms of producing successful fusions.^{3, 4, 5}

With allografts, the speed of healing may be slower than an autograft bone fusion. Additionally:

• Allograft yields nearly equivalent fusion rates as autograft bone in one-level spinal fusions
• Anterior cervical instrumentation (plates & screws) are commonly employed with allografts to increase fusion rates
• With increasing numbers of levels to be grafted/fused, the differences in fusion rates between allograft and autograft become more significant

There is a theoretical risk of transmission of an infection from a donor. The risk of contracting a disease such as HIV or hepatitis from an allograft has been estimated to be between 1 in 200,000 to 1 in 1 million. However, with modern procurement and sterilization methods for bone tissue, the risk is essentially moot.

Bone Graft Substitutes for Cervical Spinal Fusion Surgery

There are now multiple commercially available bone graft substitute options available. The advantages include no risk of disease transmission and ready availability.

Many bone graft substitutes, however, are not structural and need to be combined with a manufactured device that holds it in place while the bone graft substitute heals. Typically, spinal implants are either manufactured out of a metal product (usually titanium), plastic (also known as polyetheretherketone-PEEK), or carbon-fiber.

In 2009, the Food and Drug Administration issued a warning letter concerning the use of bone morphogenic proteins (BMP) in cervical surgery. There have been reports of it causing a large inflammatory reaction postoperatively, which can lead to a subsequent loss of the patient’s airway. This is a serious postoperative complication that can be potentially fatal.

Cervical Spinal Fusion Surgery Risks and Complications

Potential risks and complications of a spinal fusion surgery include:

• The principal risk from a spine fusion is that the graft does not heal. In general, allograft bone does not heal quite as well as autograft bone, but both yield good results when used in the anterior cervical spine.
• If a graft is used without instrumentation, there is a small chance (1% to 2%) of a graft dislodgment or extrusion. If this happens, another operation is necessary to reinsert the bone graft, and instrumentation (plates) can then be used to hold it in place.

References

Complete Listing of References

• Article written By:
• Peter F. Ullrich, Jr., MD

January 8, 2010

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