Armed Kyphoplasty: An Indirect Central Canal Decompression Technique in Burst Fractures

DISCUSSION

In this study, AKP using recently introduced vertebral body fracture internal distraction devices such as VBS and SJ was safely able to obtain VBH restoration and PWR correction in traumatic (Figs 3 and 4), osteoporotic (Figs 1 and 3), and neoplastic burst fractures (Fig 2). It was used as a stand-alone minimally invasive procedure in most cases or in combination with a posterior surgical approach (Fig 4), but without the need to perform any direct form of PWR correction. This minimally invasive approach had only 2 periprocedural complications, both with benign clinical resolution; showed durable results at follow-up; and required no re-intervention on the target level.

There is no definite consensus on the management of burst fractures with PWR. Some authors support a conservative approach in neurologically intact patients, claiming the possible spontaneous remodeling and resorption of the posterior wall osseous fragment encroaching the central canal,²⁸ while others suggest a variety of surgical approaches, including decompressive laminectomy, stabilization of the anterior column combined with a dorsal instrumentation,^13,15 and direct or indirect repositioning of retropulsed bone fragments.^9,10

The goals of treatment are to obtain early patient mobilization and a painless, balanced, stable vertebral column with maximum spine mobility and optimal neurologic function. In neurologically intact patients, the different surgical techniques are not necessarily superior to a nonoperative approach.⁶ These results might be influenced by the potentially significant morbidity and increased cost of an anterior column reconstructive surgery and by the failure rate of stand-alone posterior surgical fracture reduction and stabilization.^11,12 A safe, effective, and durable minimally invasive solution to reduce and stabilize the fracture might perform differently and better approach the ideal treatment goals.

BKP has been used to treat burst fractures, especially in a combined approach with dorsal instrumentation,^17,18 but its potential to effectively obtain VBH restoration has been questioned^20,21 and might even be relatively contraindicated.²⁹ With all that in mind, in clinical practice, BKP is likely used relatively frequently, given the extreme pain and functional limitations of patients for extended times. VBS and SJ have been reported as an alternative to BKP to reduce the deflation effect and potentially guarantee more reliable height restoration in wedge-shaped or incomplete burst compression fractures.^30⇓–32 A recent randomized controlled trial showed better kyphosis correction, maintained at 12 months for SJ versus BKP in osteoporotic compression fractures.³³ A cadaveric study³⁴ has shown the ability of SJ to reposition the retropulsed posterior wall of a burst fracture model and substantially maintain this gain after cyclic recompression, while posterior instrumentation alone did not maintain central canal clearance, but the potential of AKP to restore VBH and correct the PWR in burst fractures has not been investigated in vivo. In fact, most studies reporting the use of VBS and SJ have focused on wedge compression fractures of an osteoporotic nature,^25,30,31 and fewer have dealt with incomplete burst fractures.³² Within these studies, pain outcome was typically the primary end point, while kyphosis or VBH correction was secondary. In general, repositioning of the posterior fragments is underrepresented in most evaluations.³⁴

AKP can effect VBH restoration, avoiding height loss due to deflation effect, and is increasingly used as a stand-alone measure to reconstruct and restore axial-load capability in traumatic, osteoporotic, and malignant fractures.^26,35 As a consequence of the internal fracture distraction and kyphosis reduction, AKP appears to allow ligamentotaxis correction of the PWR without the need to perform external distraction through a posterior instrumentation or even more invasive maneuvers of fragment repositioning through direct impaction. In this study, we included 8 neoplastic fractures that had a retropulsed bone fragment (Fig 2), while we did not include cases with epidural nonosseous soft-tissue masses. An epidural soft-tissue mass might, in fact, behave differently from an osseous PWR and would have been more difficult to measure on postoperative CT. Intraoperative myelography, already described in the setting of vertebral augmentation procedures at risk for central canal encroachment,³⁶ was used in only a minority of cases in this series, but it seemed potentially useful in selected patients to have a visual control under fluoroscopy of the PWR and to directly demonstrate the effect of ligamentotaxis during fracture reduction (Fig 1).

We found a statistically significant difference between the mean degree of PWR and VBH pre- and postoperatively, which suggests the biomechanical effectiveness of the technique.

Besides the statistically significant postoperative changes of PWR and VBH, we found 2 cases in which VBH was reduced postoperatively, 6 cases with worsened PWR, and 6 cases with unchanged PWR. Explanations for such technical failures are not clear. Worsening PWR can certainly be an undesired effect of the internal vertebral body distraction, as generally feared, if ligamentotaxis does not occur; but fracture, VBH, and PWR might have also negatively evolved in the time lapse between preoperative imaging and the procedure. Unchanged PWR might also be related to osseous healing and/or nonefficient ligamentotaxis, which might not have allowed fragment repositioning. In addition, the group of patients we analyzed was heterogeneous, having included traumatic, osteoporotic, and malignant fractures, which theoretically may respond differently to AKP. While it is difficult to relate the technical efficacy in VBH restoration and PWR correction observed in this cohort to a definite measure of clinical benefit, PWR is still considered a relative contraindication to vertebral augmentation. Not infrequently, it represents an argument for open stabilization surgery. The results of this study might serve to mitigate the fear that AKP might worsen the status of neurologically intact patients with burst fractures. In the group of patients with available VAS assessment, there was significant and sustained pain reduction as expected compared with previously published larger series using similar treatment techniques.³⁶ In the 41 levels with available follow-up, the results ob-tained with AKP were confirmed to be stable at a mean follow-up of 8 months (range, 1–36 months) because in 38/41, the postoperative VBH was either stable or showed only minimal endplate subsidence (Fig 3); only in 3 cases did we encounter a refracture of the vertebral body treated with AKP, with VBH loss. As to a PWR correction, 14/22 patients who had cross-sectional imaging follow-up available showed stable PWR at follow-up. Some degree of PWR recurrence was noted in 8/30, associated with recurrent collapse (2/8) or subsidence. Patients with refracture of the target level and/or PWR recurrence presented with mild or no new symptoms at clinical follow-up, did not show neurologic deterioration, and did not require any further invasive treatment.

One might consider subsidence of the endplates and minimal PWR recurrence as nearly physiologic changes after AKP, namely because the surrounding fractured and weakened bone of the vertebral body on weight-bearing loading remodels and might undergo resorption phenomena against the new rigid internal scaffold, represented by VBS and SJ with polymethylmethacrylate, but usually these outcomes do not have clinical significance. The 3 new collapses reported in this series occurred in elderly patients treated for traumatic (1/3) and osteoporotic (2/3) fractures, all in the context of nontreated osteopenia. The importance of a thorough management of frequently underlying osteopenia or osteoporosis in patients at risk remains critical to reduce new fracture risk or hardware failure.³⁷

AKP was performed using VBS in 46 levels, and SJ, in the remaining 7. We tend to use SJ for AKP when bone mass is preserved, especially in young patients with traumatic mechanism of fracture and impacted morphology of the fracture, to the impacted morphology needs a powerful internal fracture distraction, while we rather use VBS in bone of poor quality with a high degree of vertebral body fragmentation, osteoporosis, and lytic lesions, in which the vertebral body rather needs an internal scaffold to restore its stability and axial-load capability.³⁸

There are several limitations to the present study, including its retrospective design, the small size and heterogeneity of the sample, and nonsystematic follow-up. There might have been a selection bias in the studied patient series, but the decision to treat with AKP versus a standard surgical approach was reached for every individual patient by a multidisciplinary spine board. The inclusion in this series of patients treated in combination with a posterior surgical approach underscores the possibility of treating even severe burst fractures with AKP, avoiding surgical stabilization of the anterior column and more invasive maneuvers to clear the central canal.

Given the small number of patients and confounding factors, including concurrent surgical interventions, fracture etiology heterogeneity, and technical differences in performing the AKP procedure, the conclusions of our analysis need to be confirmed in larger prospective studies.