Thoracolumbar burst fractures are common spinal injuries caused by vertical loading, and affect at least two columns of the spine predominantly in younger patients, whereas thoracolumbar burst fractures accompanied by osteoporosis increase with age⁵⁾. The goals of surgical treatment for thoracolumbar burst fractures are to restore stability of the vertebral column and to decompress the spinal canal, which when achieved, lead to early mobilization. Despite general agreement regarding the goals of surgical treatment, the management of thoracolumbar burst fractures accompanying osteoporosis without neurological deficit remains controversial. The traditional procedures for treating thoracolumbar burst fractures in patients with osteoporosis entail bone fusion with supplemental long-level instrumentation. However, these surgeries have distinct disadvantages. Extensive dissection of paraspinous muscles may be associated with massive blood loss and lead to persisting sequelae, such as, muscular denervation, atrophy, and pain. On the other hand, recent reports on burst fractures have demonstrated the efficacy of bone cement augmented short segment fixation in terms of preventing implant failure^1,3). Furthermore, percutaneous screw fixation has been proposed and applied to minimize the negative consequences of traditional open surgery, which include muscular denervation and atrophy^6,8). However, no prospective study has been conducted on the clinical outcomes of short segment fixation by percutaneous screw insertion without bone fusion for burst fractures in a background of osteoporosis. Accordingly, we designed this prospective study to evaluate the clinical outcomes of short segment fixation without bone fusion of thoracolumbar burst fractures in osteoporotic patients. We also examined whether implant removal aggravates kyphotic deformities and adversely affects clinical outcomes. The hypothesis of this study was that screw removal would not affect spinal stability.

The goals of the surgical treatment of thoracolumbar burst fractures are; to restore vertebral column stability, to decompress the spinal canal, and to facilitate early ambulation. Stabilization by open surgery continues to be widely used to treat thoracolumbar burst fractures, but traditional open surgery is highly invasive and requires a long skin incision. Furthermore, when performed anteriorly, it requires significant invasion of the retroperitoneal space or thoracic cavity and a wide dissection margin^2,9). Therefore, when there is no need to decompress neural elements, multi-segment fixation using a posterior approach is usually performed. However, this also requires extensive dissection of the paraspinal muscles of the back and resection of the posterior elements of the spine, which makes it difficult to preserve motion segments¹⁵⁾. Due to several problems associated with extensive long level fusion, posterior short-segment fusion is now preferred for the treatment of thoracolumbar burst fractures¹³⁾. The main advantage of short-segment fixation is that it preserves motion segments more so than long-level fixation. However, failure to restore anterior column support can lead to secondary kyphosis, which primarily depends on the residual load transfer capacity of the fractured vertebral body. To date, the results of short-segment fixation have not been good, and implant failure rates of 10 to 30% have been reported^7,10,16). Moreover, in severe osteoporotic patients, the anchoring effect that holds screws in place is diminished, and the probability of hardware failure is high, and thus, the risk of non-union is increased¹⁷⁾. In 2006, Wang et al.¹⁸⁾ reported satisfactory results for short-segment fixation without fusion in surgically-treated burst fractures of the thoracolumbar spine, and found that for surgically treated burst fractures, clinical results were similar for those treated with or without bone fusion. The advantages of instrumentation without fusion are the elimination of donor site complications, the preservation of motion segments, reduced blood loss, and a shorter operation time. More recently, some investigators have reported successful surgical outcomes for percutaneous non-fusion short-segment fixation^6,8). The preservation of the segmental stability obtained by posterior screw fixation is not easily achieved before the fusion of fractured vertebra, and screw loosening or vertebral collapse may occur more frequently after percutaneous screwing procedures. In addition, these problems may be more significant in patients with severe osteoporosis. To overcome these limitations, we attempted bone cement augmentation at adjacent vertebrae. In addition, the insertion of bone cement-augmented pedicle screws at fracture levels resulting in segmental constructs with improved biomechanical stability due to the protection afforded fractured vertebral bodies and indirect support of the anterior column^11,12). Furthermore, the insertion of bone cement-augmented pedicle screws can significantly reduce pedicle screw bending and increase initial stiffness in the flexion-extension plane. In a previous study, it was found that PMMA can increase pull-out strength from 96 to 262% and transverse bending stiffness by up to 153%¹⁹⁾. In addition, spontaneous remodeling of the spinal canal was shown to occur after a burst fracture, regardless of the treatment modality used. Scapinelli and Candiotto¹⁴⁾ concluded that rhythmic respiratory oscillations in cerebrospinal fluid pressure and loss of mechanical loading are important components of bone remodeling. de Klerk et al.⁴⁾ reported that the process of remodeling mainly takes place during the first year after injury, and that subsequently, little remodeling takes place, which is why, we removed implants at 1 year after screw fixation. Furthermore, after bone cement-augmented short segment fixation without bone fusion, early ambulation was possible and motion segments were preserved by screw removal, which contrasts to that observed after long level instrumentation and fusion. The advantages of short segment fixation without bone fusion also include immediate pain relief due to the elimination of donor site pain, reduced blood loss, and a short operative time. The present study demonstrates the efficacy of short segment fixation without fusion in patients with a thoracolumbar burst fracture but without neurologic deficit, but this method is by no means indicated in all patients with a thoracolumbar burst fracture, and in particular, may be contraindicated in patients with a highly unstable fracture and severe neurologic injury. In the present study, we addressed the question as to whether simultaneous fusion is necessary when treating a thoracolumbar burst fracture by percutaneous short-segment fixation rather than addressing controversial issues related to the indications for operative or nonoperative treatment. Furthermore, we acknowledge that some of the patients in the present series might also have been appropriate candidates for balloon kyphoplasty. In fact, we know that nonoperative treatment is also safe and effective for selected patients with an osteoporotic thoracolumbar burst fracture, as demonstrated by improvements in pain and work status. Randomized, comparative, clinical trials in larger populations are required in the near future.

Bone cement augmented, percutaneous short segment fixation following postural reduction without fusion might be an alternative to traditional long level fusion for the management of patients with a thoracolumbar burst fracture accompanied by severe osteoporosis but without neurologic deficit. In the present study, this technique was found to reduce the number of screw fixation levels, preserve motion segments, and correct kyphotic deformities. Furthermore, improved canal compromise and kyphotic deformity were maintained during follow-up after screw removal.