Overview

Anterior cervical spinal fusion surgery

Understanding cervical spinal fusion
Anterior cervical spinal fusion surgeries are 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. Decreasing the motion at a painful motion segment should decrease the pain at that segment. Achieving the fusion also serves to maintain adequate space for the decompressed spinal cord and/or nerve roots. The fusion may also 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

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

1. Autograft bone for spinal fusion
Autograft bone (patient’s own bone) is harvested from the iliac crest (hip). This technique has been the gold standard since the 1950’s. Autograft bone usually achieves a fusion in 90%-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 (which happens 10% to 25% of the time)

• Infection

• Bleeding

• Damage to the lateral femoral cutaneous nerve (a sensory nerve that supplies sensation to the front of the thigh)

• Pelvis 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.

2. Allograft bone for spinal fusion
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 compared to autograft.

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

• In one-level spinal fusions, it yields nearly equivalent fusion rates as autograft bone.

• 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.

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.

Controversies about spine fusion surgery
While physicians agree on many things about spine fusion surgery, there are some areas that lack consensus. Two such areas are the type of bone used (autograft vs. allograft) and how many levels should be fused.

Type of bone used with fusion surgery
Whether an autograft or allograft is used is based mostly on a combination of the surgeon’s and patient’s preference. Some surgeons still feel most comfortable with autograft as it yields the best fusion rates. Other surgeons have had good results with allograft bone and wish to avoid the postoperative pain and possible complications associated with harvesting a bone graft.

In some instances, it may be more compelling to use a patient’s own bone. There are some situations where it is more difficult to get a solid fusion and using a better bone graft is reasonable. Factors that may make obtaining a solid fusion difficult include:

• Revision surgery (previously failed grafts)

• Smokers/smokeless tobacco product users

• Multiple level fusions

• Disease states which inhibit bone healing or which require medications that do so

Levels of fusion
Another controversy includes how many levels should be fused at the time of surgery. This is especially true in patients who are having an anterior cervical discectomy and fusion in the presence of multiple abnormal discs. Some surgeons prefer fusing all disc levels that look bad, whereas in most cases only one level will have herniated and be symptomatic. The thought is that if another level is bad it will probably need to be fused in the future. The dilemma with fusing increasing numbers of levels is that it places more pressure and strain on the unfused segments. On the other hand, trying to ‘cherry pick’ the one or two bad levels risks inadequately treating the patient’s problem. Other surgeons feel that fusing only the clearly pathological level(s) (e.g. the one with the herniation that is causing the arm pain) is desirable as it maintains more of the normal motion and biomechanics of the neck.

There is no definitive answer as to which philosophy is better, and each individual patient is a little different. As a patient, the best way to consider this factor is to realize that the number of levels fused is a balancing act. Saving motion segments is desirable but comes at the cost of either under-treating the original problem or possibly needing another level fused in the near future.

The chance that another level will need to be fused in the future is difficult to quantify. Some studies have suggested that the rate of adjacent disc breakdown requiring further surgery is between 10-25% over ten years. More data are required before we will be able to definitely answer this controversy.

By: Peter F. Ullrich, Jr., MD
October 7, 2005 (article originally published September 8, 1999)