Perspectives on vertebral augmentation:
Kyphoplasty, vertebroplasty or "no-plasty"
Vertebral augmentation has become a hot topic for orthopaedic surgeons seeing patients presenting with osteoporotic compression fractures. Traditional management with analgesics, with or without bracing, continues to be effective for a large number of patients. Unfortunately, there are also a significant proportion of patients who fail to heal their fractures and consequently live with chronic pain, limiting their mobility and impairing their quality of life. Vertebral augmentation is an attempt to provide stabilization of the fracture via a percutaneous approach, with the primary goal of pain control.
Two perspectives on vertebral augmentation are presented to provide readers with a basic understanding of the rationale behind the procedures. At present, specific clinical and radiographic features that would predict the failure of traditional management of compression fractures have yet to be defined. As such, augmentation of fractures during the first 4-6 weeks of symptoms may result in treatment of patients who would otherwise have healed their fractures.
The use of polymethylmethacrylate to treat osteoporotic compression fractures is considered an "off-label" use of bone cement by the Food and Drug Administration. Future long-term studies of these technologies should include traditional management controls to better define the indications for vertebral augmentation.
The introduction to the following perspectives on vertebral augmentation is by John S. Kirkpatrick, MD, chair of the AAOS Biomedical Engineering Committee. He is on staff in Department of Orthopaedic Surgery, University of Alabama at Birmingham.
By Joseph M. Lane, MD, and Ashley R. Poynton, MD
In osteoporotic vertebral fragility fractures, percutaneous vertebral body stabilization may be achieved with one of two currently available techniques. Vertebroplasty involves injection of cement under pressure. In kyphoplasty, a balloon is used that can be expanded within the vertebral body potentially leading to fracture reduction. This creates a void that can be subsequently filled with cement under low pressure. Correction of spinal alignment secondary to height restoration is a theoretical advantage.
The two major complications associated with vertebroplasty are pulmonary compromise and neurological sequelae. Vertebroplasty in a sheep model induced fat and bone marrow emboli resulting in a two-phase decrease in arterial blood pressure, sustained increase in pCO2 and respiratory acidosis.1 The reported pulmonary complication rate for vertebroplasty is higher than that for kyphoplasty 2 and death has been reported following vertebroplasty.3 Low pressure cement injection during kyphoplasty may reduce the rate of emboli, though this has not been studied in either humans or animals. At our institution, The Hospital for Special Surgery in New York City, O2 desaturation has been observed following vertebroplasty but has not occurred in 200 consecutive kyphoplasties.
The incidence of cement leakage is higher with vertebroplasty compared to kyphoplasty and, again, this is related to cement viscosity and filling pressure.2 Kyphoplasty enables a much more controlled fill of higher viscosity cement and therefore extravasation occurs less frequently. Philips et al 4 demonstrated less vascular fill and local leakage of contrast with kyphoplasty compared to vertebroplasty following intra-vertebral contrast injection. This may explain the lower rate of neurological complications secondary to cement leakage into the spinal canal with kyphoplasty. 2
Fracture reduction and restoration of spinal alignment is a potential major advantage of kyphoplasty.
While kyphoplasty has been shown to partially restore height in 70 percent of vertebral compression fractures, the functional consequences of this restoration have not been clearly demonstrated.5 From a series of cohort studies, the rate of pain relief achieved by these techniques is comparable.2 At present, prospective studies are underway to evaluate the efficacy of kyphoplasty in deformity correction and the effect of this on functional outcome. However, a prospective randomized trial comparing both techniques is required to demonstrate the potential superiority of kyphoplasty over vertebroplasty.
Joseph M. Lane, MD, ( a consultant to Kyphon, Inc.) and Ashley R. Poynton, MD, serve on the faculties of the Departments of Metabolic Bone Diseases and Orthopaedic Surgery, Hospital for Special Surgery, New York, NY.
By Tom Faciszewski, MD and Fergus McKiernan, MD
Prevention and treatment of osteoporosis has entered a new age of optimism on the shoulders of rigorous, randomized, double-blind placebo controlled trials. Nevertheless, painful vertebral compression fractures (VCFs) still occur and call for improved management strategies that target both acute fracture pain and the chronic biomechanical consequences of vertebral fracture.
Vertebroplasty is the percutaneous fixation of painful VCF with polymethlymethacrylate (PMMA). On the basis of substantial and compelling observational evidence, vertebroplasty is gaining acceptance as an effective intervention for relief of vertebral fracture pain. Kyphoplasty, a proprietary derivative of vertebroplasty, is the PMMA fixation of fractured vertebrae after purported vertebral end-plate elevation using a percutaneous inflatable balloon tamp. Not surprisingly, kyphoplasty appears to afford fracture pain relief similar to vertebroplasty although the peer-reviewed evidence supporting this assertion is comparatively scant. 1
Biomechanical consequences of vertebral fracture, such as sagittal malalignment and postural deficit, contribute substantially to the long-term morbidity and economic impact of osteoporosis. Therein lies a second target for osteoporosis intervention. Accordingly, Lieberman, et al 1 attempted to elevate the vertebral end-plates of 70 VCFs in 35 osteoporotic patients with kyphoplasty. In that series vertebral end-plate elevation was documented in 48percent of VCFs and ascribed to a balloon tamp. At the Marshfield Clinic in Marshfield, Wisconsin, we have documented vertebral end-plate elevation in a remarkably similar proportion of patients (44 percent) and VCFs (35 percent) with vertebroplasty alone 2 and shown this to result from an intrinsic property of osteoporotic VCFs we term "dynamic mobility." 3 Average anterior vertebral height restoration in our patients was 8.41 mm (4.1 mm in the Lieberman series) and cement leak rate was 7.7 percent (8.6 percent in the Lieberman series). 1,2
Fracture mobility, whether intrinsic or induced, is predicated on gross disruption of cortico-cancellous bone. The presence of dynamic mobility in many osteoporotic VCFs is irrefutable. 2,3 Based on our radiographic evidence, the fracture property that provides a low resistance reservoir for PMMA and permits vertebral height restoration is most likely the intravertebral cleft. 2
A rigorously controlled head-to-head comparison of vertebroplasty with kyphoplasty is unlikely to be completed in the foreseeable future. In its absence any claim of vertebral height restoration or low risk cement injection that does not carefully control for the presence of intravertebral clefts and dynamic fracture mobility is no longer tenable.
Tom Faciszewski, MD and Fergus McKiernan, MD, are on staff at the Marshfield Clinic, Dept. of Orthopaedic Spine Surgery, Marshfield, Wisc.