Unipedicular versus bipedicular percutaneous vertebroplasty for osteoporotic vertebral compression fractures: a prospective randomized study

PVP is the optimal treatment for OVCF and provides rapid pain relief and stabilization
of the fractured vertebral bodies 8], 20], 21]. Although cement leakage is reported as high as 73 % for both PVP types, most leakages
remain clinically asymptomatic, and even small quantities of leakage may have a significant
clinical impact 12]. The three factors that may influence the cement flow into and out of the vertebral
body include: bone and fracture-related parameters, cement properties, and injection
methods. Although fracture morphology is impossible to control, the cement properties
and method of injection may be manipulated to ultimately decrease the complication
rate.

Viscosity of bone cement used in PVP is hypothesized to influence the outcome of the
procedure in various ways. Increased viscosity leads to increased circularity of the
cement cloud and decreased spreading distance 22], 23]. PVP with high-viscosity cement offers all the advantages, especially minimizing
the risk of cement leakage and significantly increasing the clinical safety 22], 24]. In the PVP procedure, unipedicular approach is being increasingly used to treat
OVCF, to reduce medical costs and X-ray exposure, as well as for better clinical efficacy
25], 26]. In our prospective, randomized study, both unipedicular and bipedicular PVP group
achieved satisfactory results and patients’clinical outcome parameters were significantly
improved and consistent compared to pre-surgical levels. The improvement in the clinical
outcome and recovery of vertebral heights were not significantly different between
the two groups under the strict inclusion criteria.

In theory, bipedicular PVP shows increased incidence of complications such as tissue
trauma, nerve injury and pedicle fractures. However, in our study, no pedicle fractures
or nerve damage occurred in either group. The complications resulting largely from
poor operative technique can be minimized at the operator level.

Some clinical studies have positively correlated the bone cement injection volume
with the leakage of bone cement 27]. In theory, the risk of bone cement leakage is also twice that of unipedicular approach.
However the difference in cement leakage rates between unipedicular and bipedicular
PVP with conventional viscosity cement was not statistically significant 28]–31]. The cement leakages in PVP with high-viscosity cement are still unknown. A larger
volume of injected cement through the bipedicular approach is also more likely to
result in extravasations. The most common cement leakage was venous leakage (6.1 %)
and intradiscal leakage (8.2 %) in PVP with high-viscosity Confidence bone cement
reported by Anselmetti et al. 22]. However, the leakage rate was almost as high as 47 % reported by Georgy et al. 18]. The cement leakage rates in the above two studies were far different. By comparison,
we found that the biggest difference may be the methods adopted (unipedicular approach
by Anselmetti vs. bipedicular approach by Georgy) and cement leakages detected (CT
by Anselmetti vs. plain film by Georgy). CT is now regarded as the gold standard to
assess cement leakage 12]. Whether the lower cement leakage rate reported by Anselmetti was due to the different
PVP is unclear. In this study, the cement leakage rates of both groups were lower
but not statistically significant compared with PVP using standard low-viscosity cement.
The results suggested that increased bone cement injection did not result in increased
bone cement leakage rate, which may be attributed to the nature of high-viscosity
bone cement itself.

The X-ray exposure and operation time of unipedicular approach were significantly
reduced. Unipedicular PVP lessens the radiation dose, thereby reducing health risks
to the medical staff performing the PVP. If 5 % of all vertebral compression fractures
in the United States were treated by unipedicular kyphoplasty, instead of bipedicular
kyphoplasty, the savings would be??$32 million per year 32]. Thus, our results support the concept that the unipedicular technique is a faster,
cost-effective alternative that still provides a comparable correction of spinal deformity
to the bipedicular technique. The unipedicular technique is specifically indicated
for the elderly, or patients who have more than one affected vertebra.

The limitations of our study are related to the relatively small sample size and the
follow-up of only three days and two years. We also failed to perform a direct comparison
of vertebroplasty with kyphoplasty using high-viscosity cement. Further study using
a larger sample size and longer or more frequent follow-ups are needed to confirm
our results.