Aug 11 2009
A new study by Mayo Clinic researchers has given rise to more questions than answers about the effectiveness of vertebroplasty to treat osteoporotic spinal fractures.
Vertebroplasty is a widely used procedure in which medical cement is injected into vertebrae to relieve pain and improve mobility in patients who have osteoporotic fractures. This study, funded by the National Institutes of Health, was the first of its kind, using a double-blinded research model to examine the impact of vertebroplasty. It was published last week in The New England Journal of Medicine to mixed reviews by the medical community.
"This was an extremely interesting study, but the results are far from conclusive due to several weaknesses in the method used. Additional research is definitely indicated," said Dr. Mubin I. Syed, a neuroradiologist and diagnostic, interventional and vascular radiologist.
One major issue cited by Dr. Syed was the small size of the study group. To demonstrate statistical differences between groups requires that the research team enroll enough patients for the statistics to have meaning. The original group size for the Mayo Clinic study was to be 250 patients. Due to difficulties in recruiting participants, the final group size was reduced to 131 people, nearly half of the original design.
"This is important," explained Dr. Syed, "because the trends in the data show that if the study had enough patients, the group receiving vertebroplasty could have demonstrated a clinically meaningful improvement in pain. It is therefore surprising that a study that was showing a trend toward statistical significance was terminated early with only half the number of patients recruited. A huge doubt now remains as to whether a study with the original intended group size would have yielded a different outcome."
Additionally, selection bias could have also played a large part in the study's results. "Only 131 out of 431 (30.4 percent) eligible patients elected to participate, increasing the potential for selection bias," noted Dr. Syed.
A third issue was the crossover rate for patients who received the control or "placebo" procedure. Patients in the trial were able to "cross over" and get the other treatment after one month.
"Even though they had no confirmation of which treatment they received, nearly four times as many patients or 43 percent who had the control treatment crossed over to have vertebroplasty performed, compared to 12 percent of vertebroplasty patients who switched," said Dr. Syed.
The final issue to consider is that the control procedure included injecting 0.25 percent of bupivicaine into the periosteum of the pedicles. "The problem," explained Dr. Syed, "is that this resembles a medial branch block for the treatment of facet-related pain. The duration of relief following medial branch block is variable, but may last for several weeks."
He added that many patients with compression fractures have concurrent facet-related pain due to stress on the facet joint as a result of the fracture.
"I applaud Dr. Kallmes for his work. His study is very interesting, but I don't think it's conclusive. Additional research is needed to truly assess the efficacy of vertebroplasty," said Dr. Syed.
Dr. Syed is on staff at Good Samaritan Hospital and Dayton Heart Hospital in Dayton. He is also a founding partner of Dayton Interventional Radiology. In addition, Dr. Syed has participated in clinical trials and published several papers on vertebroplasty.
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