Percutaneous Vertebroplasty Causing an Increase in Retropulsion of Bone Fragments

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Herein, I report on a patient with acute exacerbation of pain immediately after an L1 vertebroplasty, apparently because cement infusion caused further retropulsion of a preexisting, retropulsed fragment of bone. The presence of bone fragments causing canal compromise is considered by some, including the authors of the American College of Radiology (ACR) standards for vertebroplasty (1), to be a relative contraindication to performing the procedure. The rationale for avoiding vertebroplasty in cases of bone retropulsion is not specifically delineated in the ACR standards. Previous investigators have reported good outcomes after vertebroplasty in patients with preexisting retropulsed bone fragments (2).

The patient was a 79-year-old woman treated with long-term steroid therapy for polymyalgia rheumatica who presented with a 9-day history of severe middle and low back pain refractory to intravenous narcotic medication. Institutional review board approval was not required in our institution for a single case report. Magnetic resonance (MR) imaging showed severe compression of the first lumbar vertebral body (L1) with retropulsion of bone fragments (Figure, part a). A fluid-filled cavity was present along the inferior endplate, consistent with vertebral osteonecrosis (3). Computed tomography (CT) showed approximately 30% compromise of the spinal canal (Figure, part b). The patient underwent L1 vertebroplasty, with needle placement into the preexisting, fluid-filled cavity. Exact delineation of the posterior cortex of the bone fragments was not possible with the images obtained during vertebroplasty. Four milliliters of barium-opacified polymethylmethacrylate (PMMA) (Ava-Tex; Cardinal Health Care, McGaw, Ill) was infused (Figure, part c). After 2 hours of supine positioning, the patient was slowly mobilized. Her back pain had resolved but she noted new onset of severe, bilateral hip pain. This hip pain was unrelenting. A follow-up CT scan showed marked worsening of retropulsed fragments, which apparently were impinging on descending nerve roots (Figure, part d). The patient was discharged home with ongoing pain, which was managed medically.

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  (a) Sagittal T2-weighted MR image shows fracture at L1 with approximately 30% compromise of the spinal canal resulting from a retropulsed bone fragment. A fluid-filled cavity is present along the inferior endplate. (b) Axial CT scan through the L1 fracture shows bone retropulsion of fragments, with fracture lines along the lateral aspect of the posterior vertebral body. (c) Lateral radiograph obtained after vertebroplasty shows barium-opacified PMMA in a pattern typical for the filling of a preexisting cavity associated with vertebral osteonecrosis. (d) Axial CT scan obtained after vertebroplasty at a similar level as b shows a substantial interval increase in degree of bone retropulsion.

This case represents a putative example where infusion of PMMA caused increased retropulsion of bone fragments, with resultant severe hip pain likely on the basis of compression of descending nerve roots. Although the exact cause of the retropulsion cannot be proved in this case, the clinical and imaging findings suggest that the retropulsion was temporally related to the infusion of cement. Awareness of this case may be of value to practitioners of vertebroplasty when considering treatment of patients harboring retropulsed bone fragments.

It is likely that some practitioners would have avoided vertebroplasty in this case, not only because of the bone retropulsion but also because of the acute nature of the fracture. It may be that bone fragments in acute fractures are more likely than those in chronic fractures to undergo displacement. Furthermore, obvious fracture lines were present across the posterior cortex, which may have augmented the chance of bone displacement.

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References 

1. Barr JD, Mathis JM, Barr MS, et al. Standard for the performance of percutaneous vertebroplasty. In: American College of Radiology standards. Reston, Va: American College of Radiology; 2000;p. 441–448
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2. Appel NB, Gilula LA. Percutaneous vertebroplasty in patients with spinal canal compromise. AJR Am J Roentgenol. 2004;182:947–951
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3. Naul LG, Peet GJ, Maupin WB. Avascular necrosis of the vertebral body: MR imaging. Radiology. 1989;172:219–222
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