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Neck and Neck
Comparing Cervical Fusion and Artifical Disc Replacement Surgery
Monday June 8, 2009

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W hen patients present with pain, weakness, tingling, or numbness in an upper extremity, cervical spinal stenosis or a herniated cervical disc is often the culprit. Fortunately, with physical therapy intervention, many cases can resolve without the need for invasive surgery. But for those that fail conservative treatment, cervical fusion has long been the standard solution — until recently.

Artificial cervical discs are so new that to date, just two of the devices have been approved by the FDA, says John Regan, MD, medical director of the California Spine Group in Los Angeles. “The Prestige disc was the first, and more recently, the ProDisc-C,” he explains. “Blue Cross in the states of Oregon and Washington has just agreed to cover them.”

The good news is that outcomes for both fusions and artificial disc surgeries are generally positive, with success rates greater than 90%, Regan says. The incidence of complications is low, although cervical fusions present certain challenges unique to the procedure.

Refusal to Fuse

With cervical fusion surgery, a bone graft from the patient’s iliac crest or from a donor cadaver is inserted into the target disc space, with a metal plate or pins usually applied to immobilize the joint until bony fusion is achieved. With autograft bone donation, healing is generally rapid and successful in as many as 95% of cases, but the need for a second incision at the hip to harvest the bone graft can be a disadvantage. With an allograft bone donation, the donor graft acts as a placeholder over which the patient’s own bone grows over time. Consequently, the healing time can be longer with allograft bone, and there is a generally higher rate of failure, especially with multilevel fusions.

In cases where the bone refuses to knit, another operation is necessary. There also is a chance the patient will develop adjacent intervertebral disc disease or instability caused by the movement stress on the levels above and below the fusion.

“People try to resume their normal range of motion, which increases the mobility of adjacent levels,” Regan notes. “In biomechanical studies where stress transducers were placed on the spine, it was shown that pressure on adjacent discs was increased after fusion. The more levels involved, the higher the risk.”

Perhaps the least desirable aspect of cervical fusion is the long recovery period.

“In both cases, many of our patients who have either [fusion or artificial disc] surgery go home the same day or the following morning,” Regan says. “The difference in terms of follow-up is that we try to protect the cervical fusion cases and don’t encourage them to do a lot of neck motion within the first three or four weeks.”

Faking It

In comparison, patients who receive an artificial disc need no grafts, pins, or plates, eliminating the pain and possible complications caused by the grafting procedure. There is no concern about fusion failure, and more important, the patient retains full range of neck motion.

“So the potential advantages are maintenance of normal motion, the absence of need to immobilize and restrict the patient as you would with fusion, and not having to worry about whether the bone will fuse or not,” Regan summarizes. “In addition, artificial replacement discs do not result in increased stresses on adjacent discs.”

Better yet, the rehabilitation process can begin almost immediately.

“We don’t put any specific restrictions on activities [for patients following artificial disc surgeries],” says Rick Sasso, MD, FACS, an orthopedic surgeon at the Indiana Spine Group in Indianapolis. “We let them get going again right away. We don’t put them in a collar — we have them begin moving their necks as soon as possible so they can get back to doing their normal activities.”

Sasso, who performed the first artificial disc replacement in the U.S., co-authored a study of 115 patients with cervical radiculopathy and single-level disc disease to determine the efficacy of artificial discs. “Our study showed that function outcome scores of patients after disc surgery were functionally better after two years — and actually at every point up to two years after the operation — than cervical fusion,” he says.

Cervical Concerns

That’s not to say that artificial disc replacement surgery is complication-free, however. “Exposure of the cervical spine during the procedure carries a small but real risk of injury to the recurrent laryngeal nerve, which causes hoarseness,” Regan says. “That can occur in up to 1% of cases. There have also been some reports of mild issues associated with swallowing after neck surgery.”

Another possible complication is heterotopic bone formation, in which bone grows around and over the disc replacement. That happens in 1% to 2% of cases, Regan says, but giving the patient prophylactic anti-inflammatory medication seems to reduce the chances of abnormal bone growth.

But not all patients are candidates for the operation.

“We don’t want to use it on patients who don’t have very much motion, who have a lot of arthritis across that segment, or on patients who have several levels that need to be addressed,” Sasso explains. “Those with significant osteoporosis or degenerative changes don’t make good candidates either, or patients with a lot of narrowing of the disc or vertebrae that are already fused.”

Postop PT

The difference between caring for a patient after cervical fusion surgery and those who’ve had artificial disc surgery is mostly a matter of speed and intensity, says Shannon Dunn, MPT, director of rehabilitation services at the Drake Center in Cincinnati. “Postoperative rehab programs for both would include reducing pain, inflammation, and muscle spasm; restoring normal, or as close to normal as possible, range of motion; increasing strength in the muscles of the neck and upper back that support and stabilize the cervical spine in addition to the arm musculature; increasing endurance; and promoting proper posture and body mechanics during ADLs and job-related tasks to protect the cervical spine,” Dunn says.

Because there are far fewer limitations on movement and activity after artificial disc surgery, physical therapy can begin much sooner than after fusion, Dunn says, noting that with either procedure, educating the patient about proper posture and body mechanics is crucial.

Dunn advises therapists who notice patients with motor weakness, decreased sensation along nerve root or peripheral nerve distributions, or radicular pain that doesn’t improve or becomes worse after therapy to immediately refer them to a physician for further evaluation.

Resources
* Goldberg G, Albert TJ, Vaccaro AR, Hilibrand AS, Anderson DG, Wharton N. Short-term comparison of cervical fusion with static and dynamic plating using computerized motion analysis.
Spine. 2007 Jun 1;32(13):E371-5.
* Sasso RC, Smucker JD, Hacker RJ, Heller JG. Artificial disc versus fusion: a prospective, randomized study with 2-year follow-up on 99 patients.
Spine. 2007 Dec 15;32(26):293.



Mark Cantrell is a medical writer for the Gannett Healthcare Group. To comment, e-mail pteditor@gannetthg.com.