Risk Factors for Vertebral Fractures After Vertebroplasty
Patients with osteoporosis are prone to compression fractures in the vertebrae (spinal bones). The front of a vertebra cracks under pressure, causing it to collapse in height. More than 700,000 such fractures occur every year in the United States. These fractures can be asymptomatic (no symptoms). But more often, they cause debilitating pain, poor back posture, and difficulty completing routine activities.
There is a surgical procedure to help with this problem called vertebroplasty. The surgeon uses a special type of X-ray called fluoroscopy to insert a long, thin needle through the skin and soft tissues directly into the fractured vertebra.
A special bone cement, called polymethylmethacrylate (PMMA), is then injected through the needle into the fractured vertebra. A chemical reaction in the cement causes it to harden in about 15 minutes. This fixes the bone so it can heal.
Vertebroplasty restores the strength of the fractured bone, thereby reducing pain quickly. More than 80 percent of patients get immediate relief of pain with this procedure. It is a simple procedure that can be done under a local anesthesia. But there can be problems such as damaging nerves nearby, infection, and blood clot formation.
One other complication is the subject of this study: vertebral fracture after vertebroplasty. Studies show there is a range of frequency for this problem that extends from 12 to 52 per cent. Fifty-two per cent is significantly high. There must be some reason for this happening.
To help look for risk factors for vertebral fractures after vertebroplasty, surgeons from the Republic of China took a look back at 166 of their patients who had the vertebroplasty procedure. They analyzed the medical records to look for any common cause(s) that might explain this complication.
They found one major risk factor and that was the amount of cement injected into the bone. Too much cement (excess volume) was linked with problems later on down the road. In fact, in 38 per cent of their patients, fracture of another vertebra occurred within three months of the vertebroplasty procedure. Two-thirds of these fractures affected the next level vertebra (called the adjacent vertebra). The remaining one-third were remote fractures (farther away from the vertebra corrected with vertebroplasty).
This new understanding of the cause of future vertebral fractures after vertebroplasty comes with some challenges of its own. The higher volume of cement is often needed to correct the fractured and collapsed vertebra. In fact, the more cement is used the better deformity correction is possible. So, it’s not just a matter of using less cement.
Patients in this study did receive follow-up care after the vertebroplasty procedure. A protective brace was worn for three months. Medical treatment with calcium supplementation and medications to reduce bone loss was started to help address the underlying problem of weak, brittle bones.
Physical Therapy was recommended to get patients performing specific exercises known to improve osteoporosis and to increase general levels of activity. The therapists also addressed posture and body alignment, two key areas of focus in the treatment of osteoporosis and vertebral bone fractures.
The authors suggest variations in the refracture rate could be linked with different ways patients handled the postoperative period. Although it looks as though cement volume is the only significant risk factor for refracture after vertebroplasty, further study is needed.
It’s possible that just getting older or having the osteoporosis could be enough to put someone at risk for another fracture. But since one-third of the group did not have any further fractures, further analysis and study of this fracture-free group is needed. And a second feature that deserves further investigation is the fact that two-thirds of the fractures were adjacent, while one-third were remote. It remains unknown whether there is some significance to this finding.
Various theories have been suggested. For example, maybe some patients are more active than others. This could put more pressure and load through the vertebrae, thereby increasing the risk of a fracture. It’s possible that some patients did not wear the protective brace as prescribed. Brace wearing time and pattern of use could be a significant factor and should be studied further.
Since volume of cement seems to be the most significant risk factor, additional studies are also needed to determine the optimal volume of cement to use. Research may be able to uncover the minimum amount of cement needed to restore vertebral height as well as the maximum amount that can be safely used. Coming from a different approach, the authors also suggest measuring the angle of vertebral correction to see if there is an optimal kyphotic angle for vertebroplasties to be maximally successful with minimal complications.
Reference: Yi-An, MD, et al. Subsequent Vertebral Fracture After Vertebroplasty. In Spine. February 1, 2012. Vol. 37. No. 3. Pp. 179-183.