*4.3. Implication for Clinical Practice*

Although implant removal accounts for almost one-third of all elective operations in orthopedics, there remains an ongoing debate concerning the justification for such procedures [32]. The thoracolumbar junction is a transitional zone that constitutes the relatively fixed kyphotic thoracic area and the mobile lordotic lumbar region; therefore, it is a vulnerable region for injury. In theory, when natural bone healing and consolidation of fractured vertebrae has occurred, implant removal should allow complete motion segment preservation, but it is hard to decide for the thoracolumbar junction.

## 4.3.1. Kyphosis Recurrence

Kyphosis recurrence after implant removal is not uncommon (Table 2 and Supplementary Material Table S3). Previous studies have suggested that kyphotic recurrence is inevitable during the medium- to long-term period, regardless of the pedicle screw fixation with or without fusion, and the process of kyphotic recurrence may be accelerated after removal of the pedicle screw instrument, which has been reported in case reports and case series, and some of the observational studies [50,56]. However, there remains a lack of robust clinical evidence and long-term follow-up data, and our systematic review found that currently conflicting data was more present, highlighting this clinical dilemma.

In addition, these studies also investigated the mechanism of sagittal correction loss after implant removal. Some studies [39,44] have implicated that failure to support the anterior spinal column and vertebra collapse after implant removal lead to eventual loss of correction; however, more recent studies [38,46,51–53] have found that intervertebral disc collapse and loss of disc height are the main factors contributing to postoperative kyphosis in patients with thoracolumbar burst fracture, no matter with or without vertebroplasty. Patients with incomplete and complete thoracolumbar burst fractures always suffer severely injured endplates and discs, so post-traumatic disc degeneration and height loss when loaded after implant removal are unavoidable. Thus, a mono-segmental fusion is better indicated in cases of expected disc injury to prevent secondary loss of reduction resulting from the collapse of the disc space, especially in younger patients. Removal of the implants may, therefore, not be necessary.

The relatively high incidence of kyphosis recurrence after implant removal may be caused by various factors. The surgical intervention for thoracolumbar burst fracture aims to restore stability, prevent neurological deterioration, attain canal clearance, prevent kyphosis, and provide rapid pain relief. Therefore, sufficient stability is important to avoid postoperative loss of segmental kyphosis correction, regardless of whether fusion is performed. Although the pedicle screw instrument is only to provide temporary fixation of the unstable spine and permanent restoration of spinal stability through achieving a solid fusion as the primary purpose, the pedicle screw instrument may still play an important role in maintaining the reduction, offering rigid fixation, and enhance bony union or fusion after bone healing. A previous study also suggested that the severity of the initial trauma also predicts the loss of correction after implant removal: the more severe the preoperative collapse of the fractured vertebral body is, the higher loss of correction after implant removal has to be expected [51]. In addition, other factors, such as the integrity of the posterior ligamentous complex, are also crucial, and implant removal in patients with non-healing of the posterior ligamentous complex would also induce instability and progressive kyphosis [53,56,66].
