The thoracolumbar junction is susceptible to injury as it is the fulcrum for increased motion between rigid thoracic spine and mobile lumbar spine. Typically, the classical surgical indications are based on kyphosis, vertebral body height, canal compromises on radiograph and integrity of the posterior ligamentous complex[2]. Moreover, the treatment for TLF varies significantly among various institutions and surgeons. Contemporary concepts propose an evolution of surgical treatment moving from long segment instrumentation toward shorter constructs, aiming at the preservation of the dynamic and protective function of the spine[4]. Nevertheless, the treatment of burst fractures is still controversial, i.e. the management of fractures, whether fusion or non-fusion procedures is debatable[4, 10, 13-15].
Wang et.al. first studied the idea of non-fusion treatment for TLF[16], which compared the short-segment reduction and stabilization with and without fusion for patients with thoracolumbar burst fractures. All fractures met generally accepted operative indications, i.e. greater than 50% loss of height, greater than 20 degrees of kyphosis, or canal compromise greater than 50%. Recent research quantified the benefits of a non-fusion approach for surgical treatment of TLF. These studies proposed that bone grafting prolonged the operation time, and increaseed the amount of bleeding, and could not improve clinical outcomes[6, 13]. In contrast, the patients who received short-segment fixation with fewer fusion segments recovered quickly and had a better clinical outcome with equal correction in the postoperative period[4]. Most surgeons concluded that bone grating was not necessary for short-segment open instrumentation for Surgically Treated Burst Fractures of the Thoracolumbar and Lumbar Spine[17, 18]. Randomized trials indicated that surgically treated TLF burst fractures with reduction, and posterior fixation were sufficient; and hence, the use of bone grafting for definitive fusion was not necessary[16]. Furthermore, the restitution of intervertebral mobility of such an unfused segment after fracture healing could unload adjacent parts of the spine and reduce the risk of degeneration of these segments[8, 9].
However, surgeons still recommend grafting for TLF, particularly for distraction injuries, fractures with extensive vertebral body comminution, and abnormal intervertebral disc signal [15]. Qian et al. compared the two cohorts of patients with thoracolumbar burst fractures treated posteriorly with and without fusion and found out that the later groups had significant loss of correction, recurrence of kyphosis, and worse functional outcome[10]. They reported that stabilization without fusion was not an optimal procedure for TLF with injured endplates and abnormal intervertebral disc signal morphology[11].
In the present study, the enrolled patients had unstable TLF with kyphotic angle above 20 degrees and vertebral body height loss of more than 40%. In our study, the non-fusion procedures were not an optimal option for their treatment. Also, the literature suggested fused schemes only after an abnormal signal of intervertebral disc was prominent [7, 11]. Hence, we proposed the selective fusion or limited fusion schemes for the TLF with short-segment instrumentation, i.e., the vertebrae above and below the fractured vertebrae that preserved not only the motion of the spine postoperatively but also, stabilized the fracture, and restored the spinal alignment. The selection of the fused segment relied on the abnormal signal in the intervertebral disc and the injured endplate. Mostly, the upper endplate was susceptible to injury in TLF. Thereofore, we chose the fusion of upper endplate as the content of this study. According to clinical practice, it was found that the group with selective fusion had low surgical complications, blood loss, and surgical time. Significance progression of regional kyphosis could be observed along with the immediate postoperative kyphotic angle in both groups, however, these were not significantly different between the two groups. Based on previous reports, progressive kyphosis might be inevitable despite fusion. For our study, the residual deformity did not correlate with the symptoms of the patients at their time of follow-up[1, 19]. The result showed that the selective fusion procedures achieved comparable clinical and radiographic outcomes with bi-segment fusion groups, which not only validated the selectively fused schemes but also is appropriate for TLF treatment.
Recently, the researchers were curious to understand if unfused segments regained motion after instrumentation removal [9, 11, 20]. Some reports stated that the potential return to the mobile, non-fused and stabilized vertebrae is highly controversial. Yurac et al.. studied 21 consecutive patients at 46 months follow-up who were treated with a limited fusion of the injured motion segment, with stabilization that included non-injured, unfused segments. The motion of unfused segments was evaluated after the removal of hardware. Overall, 75% of the segments retained motion[11]. Po-Hsin Chou et al. performed a randomized trial on 46 patients treated with posterior transpedicular screw fixation to the levels above and below the injury, with or without fusion. They reported that the non-fusion group had 4.2 degrees of segmental motion compared to 0.9 degrees for the fusion group[13].
In the present study, we compared the intervertebral mobility not only in the proximal adjacent fractured segment but also in the distal adjacent segments following temporary posterior fixation between the two cohorts of patients with single articular process fusion or bi-segments articular process fusion. The intervertebral mobility of superior distal and proximal adjacent segments had no significant difference between the two groups. By selective fusion of superior intervertebral articular process, the inferior distal and proximal adjacent segments in the selective fusion group regained more motion after instrumentation removal. The selectively fused scheme restored the spine and alleviated the adjacent vertebral degeneration[21].
Limitation
This study had several limitations. Firstly, patients with complicated injuries, such as progressive neurologic deficits, and anterior surgery, were excluded. Secondly, an increase of retained motion was observed in patients after hardware removal. However, a long-term comparative study is necessary to assess the functional and radiographic outcomes of such patients.