Monosegmental anterior column reconstruction using an expandable vertebral body replacement device in combined posterior-anterior stabilization of thoracolumbar burst fractures

Abstract

Introduction: In combined posterior-anterior stabilization of thoracolumbar burst fractures, the expandable vertebral body replacement device (VBRD) is typically placed bisegmentally for anterior column reconstruction (ACR). The aim of this study, however, was to assess feasibility, outcome and potential pitfalls of monosegmental ACR using a VBRD. In addition, clinical and radiological outcome of monosegmental ACR was related to that of bisegmental ACR using the same thoracoscopic technique.

Methods: Thirty-seven consecutive neurologically intact patients with burst fractures of the thoracolumbar junction (T11-L2) treated by combined posterior-anterior stabilization were included. Monosegmental ACR was performed in 18 and bisegmental ACR in 19 patients. Fracture type and extent of vertebral body comminution were determined on preoperative CT scans. Monosegmental and bisegmental kyphosis angles were analyzed preoperatively, postoperatively and at final radiological follow-up. Clinical outcome was assessed after a minimum of 2 years (74 ± 45 months; range 24-154; follow-up rate 89.2%) using VAS Spine Score, RMDQ, ODI and WHOQOL-BREF.

Results: Monosegmental ACR resulted in a mean monosegmental and bisegmental surgical correction of - 15.6 ± 7.7° and - 14.7 ± 8.1°, respectively. Postoperative monosegmental and bisegmental loss of correction averaged 2.7 ± 2.7° and 5.2 ± 3.7°, respectively. Two surgical pitfalls of monosegmental ACR were identified: VBRD positioning (1) onto the weak cancellous bone (too far cranially to the inferior endplate of the fractured vertebra) and (2) onto a significantly compromised inferior endplate with at least two (even subtle) fracture lines. Ignoring these pitfalls resulted in VBRD subsidence in five cases. When relating the clinical and radiological outcome of monosegmental ACR to that of bisegmental ACR, no significant differences were found, except for frequency of VBRD subsidence (5 vs. 0, P = 0.02) and bisegmental loss of correction (5.2 ± 3.7° vs. 2.6 ± 2.5°, P = 0.022). After exclusion of cases with VBRD subsidence, the latter did not reach significance anymore (4.9 ± 4.0° vs. 2.6 ± 2.5°, P = 0.084).

Conclusions: This study indicates that monosegmental ACR using a VBRD is feasible in thoracolumbar burst fractures if the inferior endplate is intact (incomplete burst fractures) or features only a single simple split fracture line (burst-split fractures). If the two identified pitfalls are avoided, monosegmental ACR may be a viable alternative to bisegmental ACR in selected thoracolumbar burst fractures to spare a motion segment and to reduce the distance for bony fusion.

Keywords: 360° fusion; Anterior column reconstruction; Burst fracture; Combined posterior–anterior stabilization; Monosegmental; Spinal injury; Thoracolumbar fracture; Vertebral body replacement.

Fig. 1

Anterior column reconstruction (ACR) using a vertebral body replacement device (VBRD). In bisegmental ACR (a), the VBRD is placed bisegmentally between the superior endplate of the caudad intact vertebra and the inferior endplate of the cephalad intact vertebra. In monosegmental ACR (b), the VBDR is placed monosegmentally between the inferior endplate of the fractured vertebra and the inferior endplate of the cephalad intact vertebra

Fig. 2

First illustrative case of VBDR subsidence through the inferior endplate after monosegmental ACR. Axial (a), sagittal (b) and coronal (c) CT reconstructions showing a complete burst fracture of L1. The axial CT reconstruction at the level of the inferior endplate of the fractured vertebra (a) reveals multiple fracture lines at the inferior end plate. Intraoperative lateral radiograph (d) showing monosegmental VBRD placement. Postoperative lateral radiographs at 3 days (e), 1 month (f), 4 months (g) and 34 months (h after implant removal) demonstrating VBDR subsidence through the severely compromised inferior endplate and into the adjacent intervertebral disc

Fig. 3

Second illustrative case of VBDR subsidence through the inferior endplate after monosegmental ACR. Multiplanar CT reconstructions in the axial (a), median sagittal (b), paramedian sagittal (e) and coronal (c, f) plane showing a complete burst fracture of T12. The fracture may be misinterpreted as a burst-split fracture when analyzing the standard median sagittal and coronal reconstructions only. However, the axial CT reconstruction at the level of the inferior endplate (a) as well as the paramedian sagittal reconstruction (e) clearly depict multiple additional subtle fracture lines at the inferior endplate (indicated by white arrows). Intraoperative lateral radiograph (d) already showing minimal VBRD subsidence after positioning onto the “free floating” central inferior endplate fragment created by the presence of multiple fracture lines. Postoperative lateral radiographs and CT images at 1 week (g–i) and 14 months (j) demonstrating VBDR subsidence through the inferior endplate and into the adjacent intervertebral disc. The central inferior endplate fragment below the VBDR is indicated by white arrows (h, i)

Fig. 4

Illustrative case of VBRD subsidence into the cancellous bone after monosegmental ACR. Axial (a), sagittal (b) and coronal (c) CT reconstructions showing a burst-split fracture of L2 and one single split fracture line at the inferior endplate of the fractured vertebra (a). Intraoperative lateral radiograph (d) demonstrating that the VBRD was placed too far cranially to the inferior endplate of the fractured vertebra and anchored into the weak cancellous bone. Postoperative lateral radiographs at 1 month (e), 3 months (f), 6 months (g) and 13 months (h after implant removal): VBDR subsidence occurred between 1 and 3 months after surgery and is clearly evident at 3-month follow-up (f)