Is Insufficient Use of Polymethylmethacrylate a Cause for Vertebroplasty Failure Necessitating Repeat Vertebroplasty?

I wish to compliment Gaughen et al on their continued valuable contributions to the literature as they critically evaluate their vertebroplasty patients. Sharing their experience with others is important to continue to make vertebroplasty an excellent treatment in selected patients.

In this article (1), the authors stress the point that they can perform a second vertebroplasty on previously treated vertebral levels as their major emphasis. They also mention that one possible cause for re-treatment resulted from inadequate cement deposition. Although they mention the fact of potential inadequate cement deposition, this feature in the article is not prominently mentioned or emphasized. In their article, there are several cases where polymethylmethacrylate (PMMA) is instilled with very small volumes (1–3.5 mL). These are extremely small amounts of PMMA, unless one is dealing with a severe vetrabra plana. Because many of these patients have osteoporosis, if PMMA is placed in only a small part of the vertebral body, why should the remainder of the vertebral body not have a good chance to fracture later?

When I first learned how to perform vertebroplasty, maximal filling of a vertebral body to prevent later collapse of the vertebra was stressed. Subsequently, published literature has stated that only a small amount of PMMA needs to be instilled into a vertebral body to gain effective treatment (2). I have attended a meeting where there have been comments stressing the point that only a minimal amount of PMMA needs to be injected to get satisfactory results. Anecdotally, people attending other meetings have told me that speakers stressed this same point, that only a small amount of PMMA needs to be injected. Subsequently, I realize that there are potentially two schools of thought with respect to vertebroplasty, one being that of the “minimalist” school, where only a small amount of PMMA is injected. The other is that of the “maximalist” school, where as much PMMA as is safe is injected into the vertebral body. I have been a supporter of this latter school since learning vertebroplasty because of my belief that if a vertebral body is fully or nearly filled with PMMA, it cannot collapse further. The criteria for adequate filling I have tried to achieve is filling of a vertebral body from superior to inferior endplate from one side of the vertebral body to at least the medial border of the opposite pedicle. One person with extensive percutaneous vertebroplasty experience (Dr. Gregory J. Lawler, Nashville, TN, personal communication, Sundance Vertebroplasty Conference, Sundance, UT, August 5–8, 1999) subscribed to the “minimalist” school. He had had several cases where PMMA filled most of one side of a vertebral body and later the opposite side of the vertebral body without PMMA collapse. He then re-treated the area in that vertebral body without PMMA with relief of symptoms.

Since starting vertebroplasty, I have been involved with more than 900 vertebroplasties and have had two cases where there has been a need to inject the same vertebral body twice. One was a case where there was patchy distribution of PMMA throughout the vertebral body in a patient with multiple myeloma. He did well for 1 year. At the end of that year, he had two additional fractures, and an MR examination at that time showed a fracture cleft within the previously treated vertebral body. All three vertebral bodies were treated at that second treatment time, with elimination of the patient’s presenting symptoms. That case was early in my experience. Today I recognize that patchy distribution of PMMA through the vertebral body may be faced with additional collapse in the vertebral body if there is not a solid column of PMMA extending from the superior to the inferior endplate. Another case that needed a second vertebroplasty at the same level was one where PMMA passed in the central part of the vertebral body and immediately started to flow through the superior and inferior endplates into the adjacent disks. I stopped the vertebroplasty at that point. The patient still had some residual pain afterward while making beds in a tourist lodge. She returned for a second vertebroplasty, and PMMA was placed both into the right and left sides of the same vertebral body to fill the vertebral body more fully, with subsequent relief of symptoms.

Injection of larger amounts of PMMA requires careful observation of well-opacified PMMA during vertebral body filling. In many cases, it may be necessary to stop PMMA injection temporarily to let PMMA thicken or harden, after which injection can resume. Needle adjustment by advancing or withdrawing the needle slightly may be valuable in selected cases. In other cases, bipedicular injection or placing a new needle into the same needle tract may be helpful (3). Potential leakage of PMMA during injection is a concern of everyone performing vertebroplasty; however, small amounts of leakage recognized early that do not pass into the spinal canal or impinge on exiting nerves are well tolerated (4). Using conscious sedation, keeping the patient awake enough to respond to pain rather than general anesthesia, also allows the patient to respond as soon as any symptom arises during injection. Midline pain of presenting type has been acceptable during injection, except when injecting metastases. With metastases, it is important to check PMMA placement carefully when any pain develops during injection before instilling more PMMA. With osteoporotic or metastatic diseased vertebrae, pain other then midline requires circumferential check of PMMA placement to be certain leakage out of the vertebral body is not taking place. Finally, as has been recently published (5), “blush venography” may be very helpful to plan injection strategy.

In summary, I compliment the authors on their honesty in bringing forth the possibility that vertebral bodies can be re-treated; however, I strongly recommend that persons performing vertebroplasty reconsider accepting installation of only a minimal amount of PMMA, because such vertebra can be associated with further fracture in the remaining portion of the vertebral body without PMMA. As the authors have demonstrated in their article, such untreated vertebrae can be the source of continued or recurrent pain.