January 01, 2006
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Increasing cervical and lumbar fusion with bone growth stimulators

Implanting devices during initial procedures may help avoid Medicare reimbursement issues.

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2006 Special Focus: Bone Growth StimulatorsBone growth stimulators may help surgeons achieve higher fusion rates for challenging cervical and lumbar spine cases.

In a multicenter, randomized, prospective Investigational Device Exemption study of multilevel fusion patients and smokers undergoing anterior cervical discectomy and fusion (ACDF) using allografts, Kevin T. Foley, MD, and his colleagues found that 83.6% of patients receiving postoperative pulsed electromagnetic field stimulation achieved fusion by six months after surgery. Only 68.6% of the nonpulsed electromagnetic field stimulation (PEMF) group healed after the same period.

“One would conclude that in a patient population where allograft bone and an anterior cervical plate were used for ACDF and where those patients were either smokers or were undergoing multilevel surgery, the use of PEMF appeared to accelerate the rate of fusion. At six months postoperatively, a statistically significant difference in fusion was seen in those patients treated with PEMF vs. those who did not have PEMF,” Foley, a professor at the University of Tennessee, told Orthopedics Today. At one year, the researchers found no significant differences between the PEMF and non-PEMF groups ( P=.1129).

In analyzing fused and nonfused patients, the researchers discovered significant differences regarding six-month Visual Analog Scores. The fused patients reported less pain at rest (P=.0189) and during activity (P=.0125) than those rated as not fused. “The other conclusion from this work is that there appeared to be a correlation between postoperative, patient-derived pain scores both at rest and with activity and fusion status,” Foley said.

“This was interesting because it’s really the first level 2 data to show a difference in outcome with fusion, be it in the cervical or the lumbar spine,” he said. The trial helped the PEMF device used in the study, the Cervical-Stim (Orthofix; Huntersville, N.C.) gain FDA approval for cervical fusion.

Surgeons using the Cervical-Stim should notice graft integration, but should not expect immediate healing, Foley said. “Traditionally, fusion criteria include things like bridging of bone across the gap between the graft and the vertebral surface and disappearance of any radiolucency around the graft,” he said. “Finally, you look for absence of motion at the graft-vertebral interface.”

Off-label use

Despite good short-term outcomes with the Cervical-Stim, researchers remain unsure if the results continue long term. “That study hasn’t been done essentially,” Foley said. He added that his research was designed only to determine statistical differences up to six-months postop. “Well, it may be that there is a statistically significant difference at one year, but the study wasn’t powered for that,” he said.

The Cervical-Stim is the only FDA-approved device for cervical fusion. Foley cautioned that using other technologies or modalities, such as direct current, might not produce similar results. “Often times people ask me, ‘Well can I just use a different device?’ ” Foley said. “If it were a PEMF device delivering a signal, similar to what the device in this study delivered, then one could expect similar results. If it’s a different technology, you really don’t know what you’re getting and, again, we’re just lacking data answer that question.”

PEMF vs. other modalities

Researchers will need to conduct additional studies before comparing the efficacy of PEMF to other fusion treatments. This research includes trials using autograft instead of allograft. “We know that autograft tends to heal more quickly than allograft,” Foley said. “However, many surgeons prefer the use of allograft to avoid the morbidity of hip graft harvest.”

“Another strategy would be to look at the BMPs to see if they might accelerate cervical fusion with allograft,” he said. “Personally, I believe that they may, but we don’t have definitive data along those lines. I think only a pilot trial has been done. There is not a randomized prospective study, to the best of my knowledge, addressing that topic.”

chart
Patients with fused spines reported lower VAS scores during activity than patients without fusion (P=.0125).

chart
Patients rated as fused also had less pain at rest than those rated as not fused at six-month follow-up (P=.0189).

Source: Kevin Foley

Lumbar fusion

Unlike the field of cervical spine fusion, lumbar fusion provides surgeons with greater array of approved stimulation devices. Lumbar spine surgeon Arnold Graham Smith, MD, has amassed nearly 18 years of experience using bone growth stimulators. “I use them on all primary fusions, simply because I don’t like having a small group of nonunions at the end of my job,” he told Orthopedics Today.

He outfits patients using the Spinal Pak Spine Fusion Stimulator (EBI; Parsippany, N.J.) or the Spinal-Stim (Orthofix) At roughly the size of a cell phone, patients can conceal the Spinal Pak under clothes, but must wear the stimulator for 23 hours/day. Graham Smith also found that some patients had adverse skin reactions wearing the device. “Occasionally, patients are sensitive to the gel in which the electrodes attach to the skin,” he said. “I’ve got one or two people who can’t use it for that reason. Their skin breaks out in blotches.”

The Spinal-Stim requires a shorter wear time (four hours/day), but the device proves “bulky,” Graham Smith said. However, the product includes a tracker, which details the duration of wear. “You can measure patient compliance, because it’s a recording device to show how much it’s been used,” he said. “We think it’s very helpful.”

The Spinal-Stim may prove successful in 92% cases when used adjunctively, according to product information on the manufacture’s Web site. Although he does not track his failure rate, Graham Smith said that he gets good results with the stimulator. “I can simply say that in the people that consistently use this, the Orthofix [Spinal-Stim], we see very few nonunions,” he said.

Smoking, nonunions

He cites technical reasons for nonunions. “A bone graft or a cage that worked loose, I would expect to become a nonunion and I wouldn’t blame the Orthofix [device] for it,” Graham Smith said. “So in the scenario where everything goes right, the bone grafts, the cages and everything are appropriate, then we have a very high fusion rate using the Orthofix [stimulator].”

The manufacture’s site also lists a “48% improvement in smokers vs. nonsmokers,” with adjunctive application. Yet, Graham Smith avoids performing surgery on this traditionally high-failure group. “It’s not that I don’t accept that, it’s that I don’t see why anybody who really wants to get better continues smoking anyway,” he said. “So I don’t challenge it. I don’t therefore say, ‘It doesn’t matter if you smoke because I’m going to use this toy instead.’ I won’t operate on smokers in any case because they have a higher nonunion rate and I want everything possible to be going right. Therefore, we encourage and help patients who smoke to stop before considering spine surgery.”

Implantable devices

He implants elderly patients with the SpF Spine Fusion Stimulator [EBI] during initial surgery, because Medicare coverage does not include external stimulators until failure has occurred. The practice saves his patients money while increasing their odds for union. “This means that essentially all of my primary fusions are covered using one kind of stimulation or another — either the external one in the younger population or the implanted one in the senior citizens,” Graham Smith said. “And in the same way, I’m very pleased to say that putting in an implanted stimulator means very few nonunions.”

Surgeons with high nonunion rates who do not use stimulators may discover that using the devices can help them avoid re-operation and increase patient satisfaction. “My view is that the people who come to me would like to get as near a guarantee as possible that they are going to heal,” Graham Smith said.

He views the use of bone growth stimulators as an extension of the success achieved with screws and internal fixation. These advancements increased fusion rates by 20%, but still left patients with a 20% chance for nonunion, Graham Smith said. “It’s to attack that last group that I’m using the stimulator,” he said.

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