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Surgical outcomes of temporary short-segment instrumentation without augmentation for thoracolumbar burst fractures
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Surgical outcomes of temporary short-segment instrumentation without augmentation for thoracolumbar burst fractures Hiroyuki Aono a,*, Hidekazu Tobimatsu a, Kenta Ariga b, Masayuki Kuroda c, Yukitaka Nagamoto a, Shota Takenaka a, Masayuki Furuya d, Motoki Iwasaki e a
Department of Orthopedic Surgery, Osaka National Hospital, Osaka, Japan Department of Orthopedic Surgery, Osaka Police Hospital, Osaka, Japan Department of Orthopedic Surgery, Yao Municipal Hospital, Osaka, Japan d Department of Orthopedic Surgery, Osaka University Graduate School of Medicine e Department of Orthopedic Surgery, Osaka Rosai Hospital, Osaka, Japan b c
A R T I C L E I N F O
A B S T R A C T
Article history: Accepted 4 March 2016
Background: Short-segment posterior spinal instrumentation for thoracolumbar burst fracture provides superior correction of kyphosis by an indirect reduction technique, but it has a high failure rate. We investigated the clinical and radiological results of temporary short-segment pedicle screw fixation without augmentation performed for thoracolumbar burst fractures with the goal of avoiding treatment failure by waiting to see if anterior reconstruction was necessary. Methods: We studied 27 consecutive patients with thoracolumbar burst fracture who underwent shortsegment posterior instrumentation using ligamentotaxis with Schanz screws and without augmentation. Implants were removed approximately 1 year after surgery. Neurological function, kyphotic deformity, canal compromise, fracture severity, and back pain were evaluated prospectively. Results: After surgery, all patients with neurological deficit had improvement equivalent to at least 1 grade on the American Spinal Injury Association impairment scale and had fracture union. Kyphotic deformity was reduced significantly, and maintenance of the reduced vertebra was successful even without vertebroplasty, regardless of load-sharing classification. Therefore, no patients required additional anterior reconstruction. Postoperative correction loss occurred because of disc degeneration, especially after implant removal. Ten patients had increasing back pain, and there are some correlations between the progression of kyphosis and back pain aggravation. Conclusion: Temporary short-segment fixation without augmentation yielded satisfactory results in reduction and maintenance of fractured vertebrae, and maintenance was independent of load-sharing classification. Kyphotic change was caused by loss of disc height mostly after implant removal. Such change might have been inevitable because adjacent endplates can be injured during the original spinal trauma. Kyphotic change after implant removal may thus be a limitation of this surgical procedure. ß 2016 Elsevier Ltd. All rights reserved.
Keyword: Thoracolumbar burst fracture Short-segment instrumentation No augmentation Back pain
Introduction Thoracolumbar burst fractures are the most common spine fracture of those that are treated surgically. These fractures are classified as anterior and midcolumn injuries according to the three-column classification proposed by Denis [1]. Proper management of these fractures remains controversial and includes
* Corresponding author at: Department of Orthopedic Surgery, Osaka National Hospital, 2-1-14 Hoenzaka, Chuo-ku, Osaka 540-0006, Japan. Tel.: +81 6 6942 1331; fax: +81 6 6943 3555. E-mail address: [email protected] (H. Aono).
nonoperative treatment, anterior surgery, posterior surgery, and a combination of anterior and posterior surgery. Short-segment posterior spinal instrumentation (pedicle screw instrumentation one level cephalad and caudad to the fractured vertebra) without fusion has merit because it preserves segment motion, provides superior correction of kyphosis using an indirect reduction technique, and is less invasive than other procedures. However, there have been frequent reports that this procedure has failed, with or without instrumentation failure [2–4]. Recent reports suggest that additional vertebroplasty provides supplemental load-sharing through anterior reconstruction and support and that it reduces loss of kyphosis correction [5,6].
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Please cite this article in press as: Aono H, et al. Surgical outcomes of temporary short-segment instrumentation without augmentation for thoracolumbar burst fractures. Injury (2016), http://dx.doi.org/10.1016/j.injury.2016.03.003
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McCormack et al. [3] proposed the load-sharing classification system in 1994 in which the parameters of comminution, fragment apposition, and reproducibility of sagittal deformation are each given 1 point (low score) to 3 points (high score), and the total of those points serves as the load-sharing score, which can range from 3 to 9. They recommend anterior reconstruction for patients with a score of 7, because patients with scores of 6 had no screw fractures; all fractures that showed evidence of screw fracture had scores of 7. In our institution, we perform posterior reduction and fixation first to establish spinal stability and reduce surgical stress. Then if anterior reconstruction is considered to be necessary, we plan anterior reconstruction as a second procedure. Thus, we conducted a study to investigate the surgical results of temporary shortsegment pedicle screw fixation without augmentation for the surgical treatment of thoracolumbar burst fractures.
Patients and methods Our study group consisted of 27 consecutive patients in whom a single thoracolumbar burst fracture, with or without neurological impairment, was diagnosed between September 2006 and July 2012 at Osaka National Hospital. This study has been approved by institutional review board of our hospital and informed consent was obtained from all patients. There were 19 men and 8 women, with an average age of 43 years (range, 20–66 years). The injuries were caused by traffic accidents (6 patients), falls from a significant height (20 patients), and being hit by falling object (1 patients). Thus, all patients suffered high-energy injuries. Twenty-two patients had associated injuries: extremity fracture in 14 patients, stable pelvic fractures in 7, lung injury in 4, abdominal injury in 2, cerebral contusion in 2. The level of spinal involvement was T11 in 1 patient, T12 in 5 patients, L1 in 8, L2 in 10, and L3 in 3. The neurological status of the patients was assessed using the American Spinal Injury Association (ASIA) impairment scale. We also evaluated (low) back pain before injury and at the final followup examination using the Denis pain scale [7] (Table 1). Radiographic assessment was performed using supine anteroposterior and lateral roentgenograms, computed tomography (CT) scans (GE Discovery CT750 HD; slice thickness 0.625 mm), and magnetic resonance imaging ([MRI] Philips 1.5T NT- Intera) before surgery. All patients were monitored radiographically after surgery using standing anteroposterior and lateral roentgenograms and CT scans just after surgery, 6 months later, 1 year later (around the time of implant removal), and 2 years later (approximately 1 year after removal). MRI was performed 1 year after surgery and 1 year after implant removal. Three independent observers evaluated all radiographs and CT scans. The sagittal plane contour was assessed by measuring (1) the vertebral body angle (VBA), which was measured between the superior and inferior endplates of the injured vertebra, and (2) the superoinferior endplate angle (SIEA), which was measured between the superior endplate of the intact vertebra cephalad to the fracture and the inferior endplate of the vertebra caudad to the fracture with using the Cobb method (Fig. 1).
Table 1 Denis pain scale. Pain
P1: no pain P2: occasional minimal pain; no need for medication P3: moderate pain, occasionally medications; no interruption of work or activities of daily living P4: moderate to severe pain, occasionally absent from work; significant changes in activities of daily living P5: constant, severe pain; chronic pain medications
Fig. 1. Radiographic measurement of the sagittal plane contour. The vertebral body angle is the angle between B and C. The superoinferior endplate angle in the angle between A and D.
Canal compromise was determined using CT scanning by directly measuring the anteroposterior canal dimension at the maximum area of the retropulsed osseous fragment or fragments and was recorded in millimetres. This value was then compared with the average of similar dimensions measured at the levels above and below the injury. The result of this comparison was recorded as the percentage of anteroposterior canal compromise at the injured vertebra. The extent of intervertebral disc degeneration was evaluated on midsagittal T2-weighted MRI according to the criteria of Borenstein et al. [8] as follows: normal (score = 0); mild, with slight dehydration of the disc on T2-weighted images (score = 1); moderate, with disc dehydration and mild loss of disc height (score = 2); and severe, with total disc dehydration and nearly complete loss of disc height (score = 3). Discs above and below the fractured vertebra were graded. Fracture severity was calculated using the load-sharing classification [3], the AO classification [9], and the Denis classification [1]. Patients were allowed to sit up as soon after surgery as a custom-moulded thoracolumbosacral brace was fabricated. Nine patients had delay to sitting up because of an associated injury. However, they could sit up by 1 week, and no patient was required to remain lying in bed for a long period. The brace was used for at least 3 months after surgery. During this period, physical activity was restricted, and if kyphotic deformity due to vertebral collapse was observed, we planned to perform anterior reconstruction. Sports activities and strenuous labour were prohibited for 6 months after surgery. Removal of implants was performed approximately 1 year after initial surgery after confirming union of the fracture by CT scan and MRI, because of the preservation of segment motion and the possibility of implant failure, which was explained before initial surgery. Therefore, the pedicle screw implants were only temporary. All patients were monitored
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clinically and radiographically for a minimum of 2 years, with the median follow-up duration being 50 months (range, 24–84 months). Surgical techniques All surgical procedures were performed under controlled general anaesthesia. Patients were placed in a prone position; initial postural reduction was then obtained. Using a standard posterior midline approach, we exposed the levels above and below the injured segment. Schanz pedicle screws (AO Universal Spine System, DePuy Synthes, West Chester, PA) with a diameter of 6.2 or 7.0 mm and a thread length of 35–40 mm were placed down the pedicles of the bilateral vertebrae above and below the fracture. Pedicle screws with the largest possible diameter were used. In patients with narrow pedicles, we attempted to place at least a 6.2-mm pedicle screw, even if this required expansion of the pedicles. The exception was one of the earlier cases, in which 5.0-mm pedicle screws were used. Posterior wall decompression by way of indirect reduction via ligamentotaxis was performed using the following technique, which is based on a technique described by Aebi et al. [10]. The lordosing manoeuvre was performed first, followed by segmental distraction. Before reduction with Schanz screws, 2 half-rings were placed on each of the 6-mm rods, at a distance of approximately 5 mm from the clamp of the Schanz screw, to protect the posterior wall of the vertebral body from compression. We then corrected the kyphosis by manually approximating the dorsal ends of the Schanz screws. Furthermore, we applied distraction using spreader forceps. Cross-links were not routinely used. For all 27 patients, procedures were checked by lateral-view radiographs. We did not perform open reduction, decompression, laminectomies, or laminotomies, with one exception: One patient required laminectomy to treat eruption of the cauda equina caused by injury to the posterior column. In addition, we did not perform autologous iliac bone fusion, posterior fusion, posterolateral fusion, or vertebroplasty.
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Table 2 Neurologic function (ASIA Impairment Scale). Postoperative neurologic status (no. of patients) A Preoperative A B C D E
B
C
D
E
3
1 8 13
2
pain. At the final follow-up examination, 10 patients reported increased back pain; however, no patients had interruptions in their activities of daily life or work because of pain (Table 3). Complications No patients had iatrogenic neurological deficits or developed infections. At implant removal, there were no instances of instrumentation failure, including breakage, bending, or loosening of the pedicle screws; the only exception was the breakage of one 5-mm cephalad pedicle screw 8 months after the initial operation. There have been no additional procedures. Radiological results Kyphotic deformity was evaluated and mean values were calculated. All patients had union of the injured vertebrae, which was confirmed by MRI and CT scans. Vertebral body angle
Statistical analyses were performed using the Wilcoxon test. The level of significance was set at p < 0.05.
The VBA was corrected from 17.38 (range, 31–88) before surgery to 6.18 (range, 11–18) after surgery. Loss of correction was 0.58 before removal, which deteriorated by another 0.38 after removal. Total loss of correction was 0.88 from the initial surgery. Thus, fractured vertebrae were corrected and maintained after surgery. Therefore, none of our patients needed anterior reconstruction. Statistical analysis revealed that the VBA was significantly reduced (p < 0.001) and there was no significant loss of correction in the series (Table 4; Figs. 2 and 3).
Results
Superoinferior endplate angle
Clinical results
The SIEA was corrected from 138 (range, 298 to 168) before surgery to 18 (range, 248 to 248) after surgery. Correction loss was 2.38 before removal, which deteriorated by another 7.58 after removal, making the total correction loss 9.88 from the initial surgery. A mean kyphotic deformity of 10.68 (range, 288 to 188) remained by the time of the final follow-up examination. Six patients (24%) had kyphotic deformity that was >208 (range, 21– 288). The SIEA was also significantly reduced (p < 0.001), and there was a statistically significant loss of correction after removal of instrumentation (p = 0.012; Table 4 and Figs. 2 and 4). Taken together, these results indicate that postoperative kyphotic change was related to disc level, not to the fractured vertebrae; maintenance of reduced vertebral body height was successful regardless of load-sharing classification. CT scans revealed a mean spinal canal narrowing of 50.2% (range, 14–88%) before surgery, 26.3% (range, 7–48%) after surgery, and 14.8% (range, 5.1–34%) by the time of final follow-up examination, showing further improvement (Fig. 5, Table 4). The mean fracture severity according to load-sharing classification was 7.1 points. Three patients had a score of 9 points, 8 had a score of 8, 8 had a score of 7, 6 had a score of 6, and 2 had a score of
Statistical analysis
Nine patients were taken to the operating room for surgical stabilisation within 24 hours of injury, another 10 patients underwent surgery within 3 days, and the remaining 8 patients had surgery within 4 to 9 days. The cause of surgery delay in the latter group was abdominal injury in 3, head injury in 2, delay of admission to our hospital in 2, and myocardiac infarction in 1. Thus, the mean time elapsed between injury and surgery was 3.5 days. The mean duration of all surgical procedures was 101 minutes (range, 70–158 minutes), and the mean estimated blood loss was 142 mL (range, 10–420 mL). Fifty-two percent (14 of 27) of patients had a neurological deficit: 2 patients had an ASIA grade of B, 4 had a grade of C, and 8 had a grade of D. All patients had improved neurologically by at least 1 ASIA grade by the final follow-up examination (Table 2). No patients needed additional anterior reconstruction due to kyphotic deformity because of vertebral collapse. As defined by the Denis scale, 3 patients had moderate back pain, 13 had occasionally minimum back pain, and 11 had no back
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4 Table 3 Back pain (Denis pain scale).
Postoperative status (no. of patients)
Pre-injury P1 P2 P3 P4 P5
P1 (no pain)
P2 (occasionally minimal)
P3 (moderate)
11
8 5
1 1 1
P4 (moderate–severe)
P5 (severe)
Table 4 Radiological findings: mean values (SD).
Vertebral body angle (VBA) Superoinferior endplate angle (SIEA) Canal compromise a
Pre-op
After reduction
At implant removal
Final follow-up
Total correction loss
17.38 (6.0) 138 (9.6) 50.2% (19.9)
6.18 (3.5) 18 (10.2) 26.3% (13.5)
6.68 (3.4) 3.38 (10.0)
6.98 (3.5) 10.88 (12.5) 14.8% (9.5)a
0.88 (0.7) 9.88 (5.3)
Two-year follow up examination.
5. Nineteen patients (70%) had a score of 7, a score for which anterior reconstruction is traditionally recommended. However, statistical analysis revealed that there was no significant relation between load-sharing score and correction loss. Using the AO
classification, we found that 21 patients had type A3 fractures, 3 patients had type B1, and another 3 patients had type B2, whereas under the Denis classification, 7 patients had type A fractures, 19 patients had type B fractures, and 1 patient had a type C fracture.
Fig. 2. Lateral radiographs of a 56-year-old man with an L1 burst fracture, showing changes over time in the superoinferior endplate angle (SIEA) and vertebral body angle (VBA). a: Before surgery, the VBA was 318 and the SIEA was 248. b: After surgery, the VBA and SIEA were corrected to 88 and 78, respectively. c: By 1 year after surgery, there had been no change in either angle. d: By 2 years after surgery, the VBA remained unchanged but the SIEA had changed to 148 (correction loss of 78).
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Fig. 3. Statistical analysis shows that the vertebral body angle was significantly corrected after surgery and maintained after implant removal.
Fig. 4. Statistical analysis shows that the superoinferior endplate angle was significantly corrected after surgery but that there was significant correction loss after implant removal.
At the 2-year follow-up examinations, MRI revealed that disc degeneration had accelerated at least 1 grade in all 27 patients, at the level above the injury in 23 patients, and at the level below the injury in 6 patients (Fig. 6).
The mean correction loss in patients with and without back pain aggravation was 14.68 and 7.58, respectively. Because this difference was statistically significant (Fig. 7), back pain aggravation may have some correlation with correction loss. The mean
Fig. 5. Computed tomography (CT) scans of the same 56-year-old man as in Fig. 2 show changes in spinal canal stenosis. a: Preoperative retropulsion of 64%. b: Postoperative CT showed spinal canal stenosis of 32%. c: Two years after the initial operation, spinal stenosis had decreased to 15%. d: The patient’s load-sharing classification score was 9 (apposition: (apposition: 3 points; comminution: 3 points; kyphotic correction: 3 points; 238).
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Fig. 6. Midsagittal T2-weighted magnetic resonance images of the same 56-year-old man as in Fig. 2 show progressive disc degeneration. a: Before surgery. b: One year after surgery, there did not appear to be progression of degeneration in either adjacent disc. c: Two years after surgery (1 year after implant removal), progression of degeneration was apparent in the disc below the fractured vertebra.
range of motion in flexion-extension radiographs of the SIEA was 88 at the 2-year follow-up examination.
Discussion Several studies have shown that short-segment pedicle screw instrumentation without support of the anterior column for the treatment of unstable thoracolumbar burst fractures is associated with a high rate of early instrumentation failure and progression of kyphotic deformity [2–4]. In their study, kyphotic deformity was indicated by the collapse of corrected vertebra, which led to instrumentation failure. In contrast, in our study the reduced fractured vertebral body was maintained after surgery and kyphotic deformity occurred because of a loss of disc height that developed mainly after implant removal. Furthermore, we observed no early instrumentation failure, even in patients whose load-sharing classification score was 7, the point at which anterior reconstruction is traditionally recommended. Multiple factors contributed to the success of this surgical procedure. One factor is the material used in instrumentation. Ebelke et al. [2] reported that high failure rates may result if anterior bone augmentation is not performed. McLain et al. [4] also noted that 10 of 19 patients (53%) whose surgical repair involved short-segment pedicle instrumentation alone had instrumentation failure.
McCormack et al. [3] reported that 10 of 28 patients (36%) who underwent surgery using short-segment pedicle instrumentation without restoration of the anterior column had subsequent screw breakage. These previous reports of failure (Ebelke et al., McLaine et al., and McCormack et al.) were published in the early 1990s, and the research described in them was carried out between 1986 and 1991. At that time, the material used for surgical implants was stainless steel. The implant material currently used is titanium; in our study, the implants were made of titanium plus 10% vanadium. Because titanium has almost two times the strength and elasticity of stainless steel [11,12] (Table 5), the screws have the strength to sustain the implant through fusion of the fracture. Once fracture fusion has occurred, stress on the pedicle screws decreases, even without anterior augmentation. Implant failure would thus be reduced. A second factor is the diameter of the pedicle screws. If the diameter of the patient’s pedicles was large enough, we used 7-mm pedicle screws. This is the largest diameter of screw available for this system. In patients with narrow pedicles, we attempted to place at least a 6.2-mm screw, even if this required pedicle expansion (Fig. 8). Misenheimer et al. [13] reported that if the screw diameter exceeds the endosteal diameter of the pedicle, the pedicle will adapt in one of three ways: pedicle expansion, pedicle cutout by screw threads, or pedicle fracture. Misenheimer et al. noted pedicle changes when the screw size exceeded 80% of the outer cortical diameter. Sjo¨stro¨m et al. [14] also noted that when the screw diameter exceeded 65% of the outer cortical pedicle diameter, 85% of the pedicles expanded. The larger the diameter of the pedicle screw, the more durable the instrumentation will be. Taking these reports into consideration, we believe that placing large pedicle screws into smaller-diameter pedicles is acceptable and could prevent instrumentation failure. Another factor contributing to the success of this technique is the preservation of the posterior column. We did not perform laminectomy or laminotomy, even in patients with neurological deficits. There is only a minor relationship between decompression and neurological recovery [4,15,16]. Toyone et al. [6] reported good neurological improvement in 15 patients with thoracolumbar Table 5 Strength and elasticity of two materials.
Fig. 7. Statistical analysis showed that patients with back pain aggravation had statistically significant correction loss.
Material
Ultimate tensile strength (Mpa)
Young’s (tensile) modulus of elasticity (GPa)
Stainless steel Titanium 10% vanadium
580 900
193 105–120
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Fig. 8. CT scan of a 19-year-old woman with pedicle expansion. a: Before surgery, pedicles of L2 vertebra was thin (diameter 4.0 mm). b: After surgery, we placed 6.2 mm pedicle screws to expand her pedicles. c: After removal, the pedicles was expanded.
fracture and incomplete neurological deficits whom they treated using short-segment pedicle screw fixation without laminectomy or laminotomy. Limb et al. [17] reported that neurological damage occurs at the time of trauma rather than as a result of pressure from fragments in the spinal canal. Boerger et al. [18] concluded that the geometrical parameters of canal compromise do not relate to initial neurological deficits, and that there is no evidence that operative clearance helps the neurological situation. Therefore, according to these reports, posterior decompression is not necessary, even in patients with neurological deficit. Because preservation of the posterior column leads to the reduction of stress in the injured anterior and middle columns, it may prevent early instrumentation failure. In one of our earlier cases involving pedicle screw breakage, 5-mm screws had been used. Eruption of the cauda equina because of injury to the posterior column was observed, and laminectomy had to be performed. This result supports our hypothesis. In our study, kyphotic deformity was corrected satisfactorily during surgery. Maintenance of the reduced fractured vertebral body height was successful regardless of the load-sharing classification, even without augmentation. Postoperative kyphotic changes occurred because of loss of disc height, not as a result of the fracture of the vertebral body itself. However, kyphotic deformity occurred because of vertebral collapse, not because of disc degeneration during the early phase before implant removal in previous failure reports. Our results are different from those of previous studies. Concerning the loss of adjacent disc height and disc degeneration after surgery, Wang et al. [19] reported that disc degeneration
usually occurs at the level adjacent to the fractured endplate of thoracolumbar burst fractures after implant removal in shortsegment pedicle screw fixation without augmentation. They also concluded that endplate fracture is strongly associated with disc degeneration. Because all patients in our study had endplate fracture, disc degeneration after implant removal might have been unavoidable in our patients. Furthermore, thoracolumbar burst fractures involve not only injury to the vertebral body but also complex tissue injuries. Such damage inevitably includes injury to endplates and adjacent discs. Consequently, it is impossible to prevent disc degeneration. Disc injury at onset might have been connected with loss of correction in our series. Thus, correction loss at adjacent discs could be unavoidable, and this might be a limitation to this surgical procedure. Six (22%) of our patients had kyphotic deformity of >208. Fortunately, none of our patients had back pain severe enough to interrupt their daily activities or work. We could have performed short-segment fusion with augmentation, such as posterolateral fusion without implant removal, for these 6 patients, because kyphotic change had occurred mostly after implant removal. However, this would not have allowed preservation of segment motion. Moreover, it is impossible to predict this major kyphotic deformity preoperatively, because correction of kyphosis by vertebral collapse was achieved during the initial operation in these 6 patients, and progression of kyphosis occurred mostly after implant removal, just as for other patients without major kyphotic deformity. Additional surgery such as osteotomy might be needed later in patients who have severe back pain due to major kyphotic deformity.
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Conclusion Temporary short-segment fixation without augmentation yielded satisfactory results in the reduction and maintenance of fractured vertebrae, independent of load-sharing classification. Kyphotic change occurred because of loss of disc height mostly after implant removal. Such change might be inevitable because adjacent discs and endplates can be injured at the onset. Kyphotic change may thus be a limitation of this surgical procedure. There is some correlation between back pain aggravation and progression of kyphosis after implant removal. However, we did not determine the factor responsible for progression of kyphosis. Conflict of interest statement All authors report no support and no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. Acknowledgments Medical editor Katharine O’Moore-Klopf, ELS (East Setauket, NY, USA) provided professional English-language editing of this article. References [1] Denis F. The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 1983;8:817–31. [2] Ebelke DK, Asher MA, Neff JR, Kraker DP. Survivorship analysis of VSP spine instrumentation in the treatment of thoracolumbar and lumbar burst fracture. Spine 1991;16:S428–32. [3] McCormack T, Karaikovic E, Gaines RW. The load sharing classification of spine fractures. Spine 1994;19:1741–4. [4] McLain RF, Sparling E, Benson DR. Early failure of short-segment pedicle instrumentation for thoracolumbar fractures. J Bone Joint Surg Am 1993;75: 162–167.
[5] Marco RA, Meyer BC, Kushwaha VP. Thoracolumbar burst fractures treated with posterior decompression and pedicle screw instrumentation supplemented with balloon-assisted vertebroplasty and calcium phosphate reconstruction. Surgical technique. J Bone Joint Surg Am 2010;92(Suppl. 1 (Pt 1)):67–76. [6] Toyone T, Tanaka T, Kato D, Kanetama R, Otsuka M. The treatment of acute thoracolumbar burst fractures with transpedicular intracorporeal hydroxyapatite grafting following indirect reduction and pedicle screw fixation: a prospective study. Spine 2006;31:E208–14. [7] Denis F. Spinal stability as defined by three-column spine concept in acute spinal trauma. Clin Orthop 1984;189:65–76. [8] Borenstein DG, O’Mara Jr JW, Boden SD, Laueman WC, Jacobson A, Platenberg C, et al. The value of magnetic resonance imaging of the lumbar spine to predict low-back pain in asymptomatic subjects. J Bone Joint Surg Am 2001;83:1306–11. [9] Magerl F, Aebi M, Gertzbein SD, Harms J, Nazarian S. A comprehensive classification of thoracic and lumbar injuries. Eur Spine J 1994;3:184–201. [10] Aebi M, Thalgott JS, Webb JK. Stabilization techniques: thoracolumbar spine. In: AO ASIF principles in spine surgery. Berlin: Springer; 1998. p. 107–22. [11] Brunette DM, Tengvall P, Textor M, Thomsen P. Titanium in medicine. Berlin: Springer; 2001. p. 25–53. [12] Richards RG, Perren SM. Implants and materials in fracture fixation. In: Ruedi TP, Buckley RE, Moran CG, editors. AO principles of fracture management. 2nd ed., New York: Thieme; 2007. p. 33–45. [13] Misenhimer GR, Peek RD, Wiltse LL, Rothman SL, Widell Jr EH. Anatomic analysis of pedicle cortical and cancellous diameter as related to screw size. Spine 1989;14:367–72. [14] Sjo¨stro¨m L, Jacobsson O, Karlstro¨m G, Pech P, Rauschning W. CT analysis of pedicles and screw tracts after implant removal in thoracolumbar fractures. J Spinal Disord 1993;6:225–31. [15] Esses SI, Botsford DJ, Kostuik JP. Evaluation of surgical treatment for burst fractures. Spine 1990;15:667–73. [16] Shuman WP, Rogers JV, Sickler ME. Thoracolumbar burst fractures: CT dimensions of the spinal canal relative to postsurgical improvement. Am J Roentgenol 1985;145:337–41. [17] Limb D, Shaw DL, Dickson RA. Neurological injury in thoracolumbar burst fractures. J Bone Joint Surg Br 1995;75:774–7. [18] Boerger TO, Limb D, Dickson RA. Does ‘canal clearance’ affect neurological outcome after thoracolumbar burst fractures? J Bone Joint Surg Br 2000;82: 629–635. [19] Wang J, Zhou Y, Zhang ZF, Li CQ, Zheng WJ, Liu J. Radiological study on disc degeneration on thoracolumbar burst fractures treated by percutaneous pedicle screw fixation. Eur Spine J 2013;22:489–94.
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Surgical outcomes of temporary short-segment instrumentation without augmentation for thoracolumbar burst fractures Hiroyuki Aono a,*, Hidekazu Tobimatsu a, Kenta Ariga b, Masayuki Kuroda c, Yukitaka Nagamoto a, Shota Takenaka a, Masayuki Furuya d, Motoki Iwasaki e a
Department of Orthopedic Surgery, Osaka National Hospital, Osaka, Japan Department of Orthopedic Surgery, Osaka Police Hospital, Osaka, Japan Department of Orthopedic Surgery, Yao Municipal Hospital, Osaka, Japan d Department of Orthopedic Surgery, Osaka University Graduate School of Medicine e Department of Orthopedic Surgery, Osaka Rosai Hospital, Osaka, Japan b c
A R T I C L E I N F O
A B S T R A C T
Article history: Accepted 4 March 2016
Background: Short-segment posterior spinal instrumentation for thoracolumbar burst fracture provides superior correction of kyphosis by an indirect reduction technique, but it has a high failure rate. We investigated the clinical and radiological results of temporary short-segment pedicle screw fixation without augmentation performed for thoracolumbar burst fractures with the goal of avoiding treatment failure by waiting to see if anterior reconstruction was necessary. Methods: We studied 27 consecutive patients with thoracolumbar burst fracture who underwent shortsegment posterior instrumentation using ligamentotaxis with Schanz screws and without augmentation. Implants were removed approximately 1 year after surgery. Neurological function, kyphotic deformity, canal compromise, fracture severity, and back pain were evaluated prospectively. Results: After surgery, all patients with neurological deficit had improvement equivalent to at least 1 grade on the American Spinal Injury Association impairment scale and had fracture union. Kyphotic deformity was reduced significantly, and maintenance of the reduced vertebra was successful even without vertebroplasty, regardless of load-sharing classification. Therefore, no patients required additional anterior reconstruction. Postoperative correction loss occurred because of disc degeneration, especially after implant removal. Ten patients had increasing back pain, and there are some correlations between the progression of kyphosis and back pain aggravation. Conclusion: Temporary short-segment fixation without augmentation yielded satisfactory results in reduction and maintenance of fractured vertebrae, and maintenance was independent of load-sharing classification. Kyphotic change was caused by loss of disc height mostly after implant removal. Such change might have been inevitable because adjacent endplates can be injured during the original spinal trauma. Kyphotic change after implant removal may thus be a limitation of this surgical procedure. ß 2016 Elsevier Ltd. All rights reserved.
Keyword: Thoracolumbar burst fracture Short-segment instrumentation No augmentation Back pain
Introduction Thoracolumbar burst fractures are the most common spine fracture of those that are treated surgically. These fractures are classified as anterior and midcolumn injuries according to the three-column classification proposed by Denis [1]. Proper management of these fractures remains controversial and includes
* Corresponding author at: Department of Orthopedic Surgery, Osaka National Hospital, 2-1-14 Hoenzaka, Chuo-ku, Osaka 540-0006, Japan. Tel.: +81 6 6942 1331; fax: +81 6 6943 3555. E-mail address: [email protected] (H. Aono).
nonoperative treatment, anterior surgery, posterior surgery, and a combination of anterior and posterior surgery. Short-segment posterior spinal instrumentation (pedicle screw instrumentation one level cephalad and caudad to the fractured vertebra) without fusion has merit because it preserves segment motion, provides superior correction of kyphosis using an indirect reduction technique, and is less invasive than other procedures. However, there have been frequent reports that this procedure has failed, with or without instrumentation failure [2–4]. Recent reports suggest that additional vertebroplasty provides supplemental load-sharing through anterior reconstruction and support and that it reduces loss of kyphosis correction [5,6].
http://dx.doi.org/10.1016/j.injury.2016.03.003 0020–1383/ß 2016 Elsevier Ltd. All rights reserved.
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McCormack et al. [3] proposed the load-sharing classification system in 1994 in which the parameters of comminution, fragment apposition, and reproducibility of sagittal deformation are each given 1 point (low score) to 3 points (high score), and the total of those points serves as the load-sharing score, which can range from 3 to 9. They recommend anterior reconstruction for patients with a score of 7, because patients with scores of 6 had no screw fractures; all fractures that showed evidence of screw fracture had scores of 7. In our institution, we perform posterior reduction and fixation first to establish spinal stability and reduce surgical stress. Then if anterior reconstruction is considered to be necessary, we plan anterior reconstruction as a second procedure. Thus, we conducted a study to investigate the surgical results of temporary shortsegment pedicle screw fixation without augmentation for the surgical treatment of thoracolumbar burst fractures.
Patients and methods Our study group consisted of 27 consecutive patients in whom a single thoracolumbar burst fracture, with or without neurological impairment, was diagnosed between September 2006 and July 2012 at Osaka National Hospital. This study has been approved by institutional review board of our hospital and informed consent was obtained from all patients. There were 19 men and 8 women, with an average age of 43 years (range, 20–66 years). The injuries were caused by traffic accidents (6 patients), falls from a significant height (20 patients), and being hit by falling object (1 patients). Thus, all patients suffered high-energy injuries. Twenty-two patients had associated injuries: extremity fracture in 14 patients, stable pelvic fractures in 7, lung injury in 4, abdominal injury in 2, cerebral contusion in 2. The level of spinal involvement was T11 in 1 patient, T12 in 5 patients, L1 in 8, L2 in 10, and L3 in 3. The neurological status of the patients was assessed using the American Spinal Injury Association (ASIA) impairment scale. We also evaluated (low) back pain before injury and at the final followup examination using the Denis pain scale [7] (Table 1). Radiographic assessment was performed using supine anteroposterior and lateral roentgenograms, computed tomography (CT) scans (GE Discovery CT750 HD; slice thickness 0.625 mm), and magnetic resonance imaging ([MRI] Philips 1.5T NT- Intera) before surgery. All patients were monitored radiographically after surgery using standing anteroposterior and lateral roentgenograms and CT scans just after surgery, 6 months later, 1 year later (around the time of implant removal), and 2 years later (approximately 1 year after removal). MRI was performed 1 year after surgery and 1 year after implant removal. Three independent observers evaluated all radiographs and CT scans. The sagittal plane contour was assessed by measuring (1) the vertebral body angle (VBA), which was measured between the superior and inferior endplates of the injured vertebra, and (2) the superoinferior endplate angle (SIEA), which was measured between the superior endplate of the intact vertebra cephalad to the fracture and the inferior endplate of the vertebra caudad to the fracture with using the Cobb method (Fig. 1).
Table 1 Denis pain scale. Pain
P1: no pain P2: occasional minimal pain; no need for medication P3: moderate pain, occasionally medications; no interruption of work or activities of daily living P4: moderate to severe pain, occasionally absent from work; significant changes in activities of daily living P5: constant, severe pain; chronic pain medications
Fig. 1. Radiographic measurement of the sagittal plane contour. The vertebral body angle is the angle between B and C. The superoinferior endplate angle in the angle between A and D.
Canal compromise was determined using CT scanning by directly measuring the anteroposterior canal dimension at the maximum area of the retropulsed osseous fragment or fragments and was recorded in millimetres. This value was then compared with the average of similar dimensions measured at the levels above and below the injury. The result of this comparison was recorded as the percentage of anteroposterior canal compromise at the injured vertebra. The extent of intervertebral disc degeneration was evaluated on midsagittal T2-weighted MRI according to the criteria of Borenstein et al. [8] as follows: normal (score = 0); mild, with slight dehydration of the disc on T2-weighted images (score = 1); moderate, with disc dehydration and mild loss of disc height (score = 2); and severe, with total disc dehydration and nearly complete loss of disc height (score = 3). Discs above and below the fractured vertebra were graded. Fracture severity was calculated using the load-sharing classification [3], the AO classification [9], and the Denis classification [1]. Patients were allowed to sit up as soon after surgery as a custom-moulded thoracolumbosacral brace was fabricated. Nine patients had delay to sitting up because of an associated injury. However, they could sit up by 1 week, and no patient was required to remain lying in bed for a long period. The brace was used for at least 3 months after surgery. During this period, physical activity was restricted, and if kyphotic deformity due to vertebral collapse was observed, we planned to perform anterior reconstruction. Sports activities and strenuous labour were prohibited for 6 months after surgery. Removal of implants was performed approximately 1 year after initial surgery after confirming union of the fracture by CT scan and MRI, because of the preservation of segment motion and the possibility of implant failure, which was explained before initial surgery. Therefore, the pedicle screw implants were only temporary. All patients were monitored
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clinically and radiographically for a minimum of 2 years, with the median follow-up duration being 50 months (range, 24–84 months). Surgical techniques All surgical procedures were performed under controlled general anaesthesia. Patients were placed in a prone position; initial postural reduction was then obtained. Using a standard posterior midline approach, we exposed the levels above and below the injured segment. Schanz pedicle screws (AO Universal Spine System, DePuy Synthes, West Chester, PA) with a diameter of 6.2 or 7.0 mm and a thread length of 35–40 mm were placed down the pedicles of the bilateral vertebrae above and below the fracture. Pedicle screws with the largest possible diameter were used. In patients with narrow pedicles, we attempted to place at least a 6.2-mm pedicle screw, even if this required expansion of the pedicles. The exception was one of the earlier cases, in which 5.0-mm pedicle screws were used. Posterior wall decompression by way of indirect reduction via ligamentotaxis was performed using the following technique, which is based on a technique described by Aebi et al. [10]. The lordosing manoeuvre was performed first, followed by segmental distraction. Before reduction with Schanz screws, 2 half-rings were placed on each of the 6-mm rods, at a distance of approximately 5 mm from the clamp of the Schanz screw, to protect the posterior wall of the vertebral body from compression. We then corrected the kyphosis by manually approximating the dorsal ends of the Schanz screws. Furthermore, we applied distraction using spreader forceps. Cross-links were not routinely used. For all 27 patients, procedures were checked by lateral-view radiographs. We did not perform open reduction, decompression, laminectomies, or laminotomies, with one exception: One patient required laminectomy to treat eruption of the cauda equina caused by injury to the posterior column. In addition, we did not perform autologous iliac bone fusion, posterior fusion, posterolateral fusion, or vertebroplasty.
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Table 2 Neurologic function (ASIA Impairment Scale). Postoperative neurologic status (no. of patients) A Preoperative A B C D E
B
C
D
E
3
1 8 13
2
pain. At the final follow-up examination, 10 patients reported increased back pain; however, no patients had interruptions in their activities of daily life or work because of pain (Table 3). Complications No patients had iatrogenic neurological deficits or developed infections. At implant removal, there were no instances of instrumentation failure, including breakage, bending, or loosening of the pedicle screws; the only exception was the breakage of one 5-mm cephalad pedicle screw 8 months after the initial operation. There have been no additional procedures. Radiological results Kyphotic deformity was evaluated and mean values were calculated. All patients had union of the injured vertebrae, which was confirmed by MRI and CT scans. Vertebral body angle
Statistical analyses were performed using the Wilcoxon test. The level of significance was set at p < 0.05.
The VBA was corrected from 17.38 (range, 31–88) before surgery to 6.18 (range, 11–18) after surgery. Loss of correction was 0.58 before removal, which deteriorated by another 0.38 after removal. Total loss of correction was 0.88 from the initial surgery. Thus, fractured vertebrae were corrected and maintained after surgery. Therefore, none of our patients needed anterior reconstruction. Statistical analysis revealed that the VBA was significantly reduced (p < 0.001) and there was no significant loss of correction in the series (Table 4; Figs. 2 and 3).
Results
Superoinferior endplate angle
Clinical results
The SIEA was corrected from 138 (range, 298 to 168) before surgery to 18 (range, 248 to 248) after surgery. Correction loss was 2.38 before removal, which deteriorated by another 7.58 after removal, making the total correction loss 9.88 from the initial surgery. A mean kyphotic deformity of 10.68 (range, 288 to 188) remained by the time of the final follow-up examination. Six patients (24%) had kyphotic deformity that was >208 (range, 21– 288). The SIEA was also significantly reduced (p < 0.001), and there was a statistically significant loss of correction after removal of instrumentation (p = 0.012; Table 4 and Figs. 2 and 4). Taken together, these results indicate that postoperative kyphotic change was related to disc level, not to the fractured vertebrae; maintenance of reduced vertebral body height was successful regardless of load-sharing classification. CT scans revealed a mean spinal canal narrowing of 50.2% (range, 14–88%) before surgery, 26.3% (range, 7–48%) after surgery, and 14.8% (range, 5.1–34%) by the time of final follow-up examination, showing further improvement (Fig. 5, Table 4). The mean fracture severity according to load-sharing classification was 7.1 points. Three patients had a score of 9 points, 8 had a score of 8, 8 had a score of 7, 6 had a score of 6, and 2 had a score of
Statistical analysis
Nine patients were taken to the operating room for surgical stabilisation within 24 hours of injury, another 10 patients underwent surgery within 3 days, and the remaining 8 patients had surgery within 4 to 9 days. The cause of surgery delay in the latter group was abdominal injury in 3, head injury in 2, delay of admission to our hospital in 2, and myocardiac infarction in 1. Thus, the mean time elapsed between injury and surgery was 3.5 days. The mean duration of all surgical procedures was 101 minutes (range, 70–158 minutes), and the mean estimated blood loss was 142 mL (range, 10–420 mL). Fifty-two percent (14 of 27) of patients had a neurological deficit: 2 patients had an ASIA grade of B, 4 had a grade of C, and 8 had a grade of D. All patients had improved neurologically by at least 1 ASIA grade by the final follow-up examination (Table 2). No patients needed additional anterior reconstruction due to kyphotic deformity because of vertebral collapse. As defined by the Denis scale, 3 patients had moderate back pain, 13 had occasionally minimum back pain, and 11 had no back
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4 Table 3 Back pain (Denis pain scale).
Postoperative status (no. of patients)
Pre-injury P1 P2 P3 P4 P5
P1 (no pain)
P2 (occasionally minimal)
P3 (moderate)
11
8 5
1 1 1
P4 (moderate–severe)
P5 (severe)
Table 4 Radiological findings: mean values (SD).
Vertebral body angle (VBA) Superoinferior endplate angle (SIEA) Canal compromise a
Pre-op
After reduction
At implant removal
Final follow-up
Total correction loss
17.38 (6.0) 138 (9.6) 50.2% (19.9)
6.18 (3.5) 18 (10.2) 26.3% (13.5)
6.68 (3.4) 3.38 (10.0)
6.98 (3.5) 10.88 (12.5) 14.8% (9.5)a
0.88 (0.7) 9.88 (5.3)
Two-year follow up examination.
5. Nineteen patients (70%) had a score of 7, a score for which anterior reconstruction is traditionally recommended. However, statistical analysis revealed that there was no significant relation between load-sharing score and correction loss. Using the AO
classification, we found that 21 patients had type A3 fractures, 3 patients had type B1, and another 3 patients had type B2, whereas under the Denis classification, 7 patients had type A fractures, 19 patients had type B fractures, and 1 patient had a type C fracture.
Fig. 2. Lateral radiographs of a 56-year-old man with an L1 burst fracture, showing changes over time in the superoinferior endplate angle (SIEA) and vertebral body angle (VBA). a: Before surgery, the VBA was 318 and the SIEA was 248. b: After surgery, the VBA and SIEA were corrected to 88 and 78, respectively. c: By 1 year after surgery, there had been no change in either angle. d: By 2 years after surgery, the VBA remained unchanged but the SIEA had changed to 148 (correction loss of 78).
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Fig. 3. Statistical analysis shows that the vertebral body angle was significantly corrected after surgery and maintained after implant removal.
Fig. 4. Statistical analysis shows that the superoinferior endplate angle was significantly corrected after surgery but that there was significant correction loss after implant removal.
At the 2-year follow-up examinations, MRI revealed that disc degeneration had accelerated at least 1 grade in all 27 patients, at the level above the injury in 23 patients, and at the level below the injury in 6 patients (Fig. 6).
The mean correction loss in patients with and without back pain aggravation was 14.68 and 7.58, respectively. Because this difference was statistically significant (Fig. 7), back pain aggravation may have some correlation with correction loss. The mean
Fig. 5. Computed tomography (CT) scans of the same 56-year-old man as in Fig. 2 show changes in spinal canal stenosis. a: Preoperative retropulsion of 64%. b: Postoperative CT showed spinal canal stenosis of 32%. c: Two years after the initial operation, spinal stenosis had decreased to 15%. d: The patient’s load-sharing classification score was 9 (apposition: (apposition: 3 points; comminution: 3 points; kyphotic correction: 3 points; 238).
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Fig. 6. Midsagittal T2-weighted magnetic resonance images of the same 56-year-old man as in Fig. 2 show progressive disc degeneration. a: Before surgery. b: One year after surgery, there did not appear to be progression of degeneration in either adjacent disc. c: Two years after surgery (1 year after implant removal), progression of degeneration was apparent in the disc below the fractured vertebra.
range of motion in flexion-extension radiographs of the SIEA was 88 at the 2-year follow-up examination.
Discussion Several studies have shown that short-segment pedicle screw instrumentation without support of the anterior column for the treatment of unstable thoracolumbar burst fractures is associated with a high rate of early instrumentation failure and progression of kyphotic deformity [2–4]. In their study, kyphotic deformity was indicated by the collapse of corrected vertebra, which led to instrumentation failure. In contrast, in our study the reduced fractured vertebral body was maintained after surgery and kyphotic deformity occurred because of a loss of disc height that developed mainly after implant removal. Furthermore, we observed no early instrumentation failure, even in patients whose load-sharing classification score was 7, the point at which anterior reconstruction is traditionally recommended. Multiple factors contributed to the success of this surgical procedure. One factor is the material used in instrumentation. Ebelke et al. [2] reported that high failure rates may result if anterior bone augmentation is not performed. McLain et al. [4] also noted that 10 of 19 patients (53%) whose surgical repair involved short-segment pedicle instrumentation alone had instrumentation failure.
McCormack et al. [3] reported that 10 of 28 patients (36%) who underwent surgery using short-segment pedicle instrumentation without restoration of the anterior column had subsequent screw breakage. These previous reports of failure (Ebelke et al., McLaine et al., and McCormack et al.) were published in the early 1990s, and the research described in them was carried out between 1986 and 1991. At that time, the material used for surgical implants was stainless steel. The implant material currently used is titanium; in our study, the implants were made of titanium plus 10% vanadium. Because titanium has almost two times the strength and elasticity of stainless steel [11,12] (Table 5), the screws have the strength to sustain the implant through fusion of the fracture. Once fracture fusion has occurred, stress on the pedicle screws decreases, even without anterior augmentation. Implant failure would thus be reduced. A second factor is the diameter of the pedicle screws. If the diameter of the patient’s pedicles was large enough, we used 7-mm pedicle screws. This is the largest diameter of screw available for this system. In patients with narrow pedicles, we attempted to place at least a 6.2-mm screw, even if this required pedicle expansion (Fig. 8). Misenheimer et al. [13] reported that if the screw diameter exceeds the endosteal diameter of the pedicle, the pedicle will adapt in one of three ways: pedicle expansion, pedicle cutout by screw threads, or pedicle fracture. Misenheimer et al. noted pedicle changes when the screw size exceeded 80% of the outer cortical diameter. Sjo¨stro¨m et al. [14] also noted that when the screw diameter exceeded 65% of the outer cortical pedicle diameter, 85% of the pedicles expanded. The larger the diameter of the pedicle screw, the more durable the instrumentation will be. Taking these reports into consideration, we believe that placing large pedicle screws into smaller-diameter pedicles is acceptable and could prevent instrumentation failure. Another factor contributing to the success of this technique is the preservation of the posterior column. We did not perform laminectomy or laminotomy, even in patients with neurological deficits. There is only a minor relationship between decompression and neurological recovery [4,15,16]. Toyone et al. [6] reported good neurological improvement in 15 patients with thoracolumbar Table 5 Strength and elasticity of two materials.
Fig. 7. Statistical analysis showed that patients with back pain aggravation had statistically significant correction loss.
Material
Ultimate tensile strength (Mpa)
Young’s (tensile) modulus of elasticity (GPa)
Stainless steel Titanium 10% vanadium
580 900
193 105–120
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Fig. 8. CT scan of a 19-year-old woman with pedicle expansion. a: Before surgery, pedicles of L2 vertebra was thin (diameter 4.0 mm). b: After surgery, we placed 6.2 mm pedicle screws to expand her pedicles. c: After removal, the pedicles was expanded.
fracture and incomplete neurological deficits whom they treated using short-segment pedicle screw fixation without laminectomy or laminotomy. Limb et al. [17] reported that neurological damage occurs at the time of trauma rather than as a result of pressure from fragments in the spinal canal. Boerger et al. [18] concluded that the geometrical parameters of canal compromise do not relate to initial neurological deficits, and that there is no evidence that operative clearance helps the neurological situation. Therefore, according to these reports, posterior decompression is not necessary, even in patients with neurological deficit. Because preservation of the posterior column leads to the reduction of stress in the injured anterior and middle columns, it may prevent early instrumentation failure. In one of our earlier cases involving pedicle screw breakage, 5-mm screws had been used. Eruption of the cauda equina because of injury to the posterior column was observed, and laminectomy had to be performed. This result supports our hypothesis. In our study, kyphotic deformity was corrected satisfactorily during surgery. Maintenance of the reduced fractured vertebral body height was successful regardless of the load-sharing classification, even without augmentation. Postoperative kyphotic changes occurred because of loss of disc height, not as a result of the fracture of the vertebral body itself. However, kyphotic deformity occurred because of vertebral collapse, not because of disc degeneration during the early phase before implant removal in previous failure reports. Our results are different from those of previous studies. Concerning the loss of adjacent disc height and disc degeneration after surgery, Wang et al. [19] reported that disc degeneration
usually occurs at the level adjacent to the fractured endplate of thoracolumbar burst fractures after implant removal in shortsegment pedicle screw fixation without augmentation. They also concluded that endplate fracture is strongly associated with disc degeneration. Because all patients in our study had endplate fracture, disc degeneration after implant removal might have been unavoidable in our patients. Furthermore, thoracolumbar burst fractures involve not only injury to the vertebral body but also complex tissue injuries. Such damage inevitably includes injury to endplates and adjacent discs. Consequently, it is impossible to prevent disc degeneration. Disc injury at onset might have been connected with loss of correction in our series. Thus, correction loss at adjacent discs could be unavoidable, and this might be a limitation to this surgical procedure. Six (22%) of our patients had kyphotic deformity of >208. Fortunately, none of our patients had back pain severe enough to interrupt their daily activities or work. We could have performed short-segment fusion with augmentation, such as posterolateral fusion without implant removal, for these 6 patients, because kyphotic change had occurred mostly after implant removal. However, this would not have allowed preservation of segment motion. Moreover, it is impossible to predict this major kyphotic deformity preoperatively, because correction of kyphosis by vertebral collapse was achieved during the initial operation in these 6 patients, and progression of kyphosis occurred mostly after implant removal, just as for other patients without major kyphotic deformity. Additional surgery such as osteotomy might be needed later in patients who have severe back pain due to major kyphotic deformity.
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Conclusion Temporary short-segment fixation without augmentation yielded satisfactory results in the reduction and maintenance of fractured vertebrae, independent of load-sharing classification. Kyphotic change occurred because of loss of disc height mostly after implant removal. Such change might be inevitable because adjacent discs and endplates can be injured at the onset. Kyphotic change may thus be a limitation of this surgical procedure. There is some correlation between back pain aggravation and progression of kyphosis after implant removal. However, we did not determine the factor responsible for progression of kyphosis. Conflict of interest statement All authors report no support and no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. Acknowledgments Medical editor Katharine O’Moore-Klopf, ELS (East Setauket, NY, USA) provided professional English-language editing of this article. References [1] Denis F. The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 1983;8:817–31. [2] Ebelke DK, Asher MA, Neff JR, Kraker DP. Survivorship analysis of VSP spine instrumentation in the treatment of thoracolumbar and lumbar burst fracture. Spine 1991;16:S428–32. [3] McCormack T, Karaikovic E, Gaines RW. The load sharing classification of spine fractures. Spine 1994;19:1741–4. [4] McLain RF, Sparling E, Benson DR. Early failure of short-segment pedicle instrumentation for thoracolumbar fractures. J Bone Joint Surg Am 1993;75: 162–167.
[5] Marco RA, Meyer BC, Kushwaha VP. Thoracolumbar burst fractures treated with posterior decompression and pedicle screw instrumentation supplemented with balloon-assisted vertebroplasty and calcium phosphate reconstruction. Surgical technique. J Bone Joint Surg Am 2010;92(Suppl. 1 (Pt 1)):67–76. [6] Toyone T, Tanaka T, Kato D, Kanetama R, Otsuka M. The treatment of acute thoracolumbar burst fractures with transpedicular intracorporeal hydroxyapatite grafting following indirect reduction and pedicle screw fixation: a prospective study. Spine 2006;31:E208–14. [7] Denis F. Spinal stability as defined by three-column spine concept in acute spinal trauma. Clin Orthop 1984;189:65–76. [8] Borenstein DG, O’Mara Jr JW, Boden SD, Laueman WC, Jacobson A, Platenberg C, et al. The value of magnetic resonance imaging of the lumbar spine to predict low-back pain in asymptomatic subjects. J Bone Joint Surg Am 2001;83:1306–11. [9] Magerl F, Aebi M, Gertzbein SD, Harms J, Nazarian S. A comprehensive classification of thoracic and lumbar injuries. Eur Spine J 1994;3:184–201. [10] Aebi M, Thalgott JS, Webb JK. Stabilization techniques: thoracolumbar spine. In: AO ASIF principles in spine surgery. Berlin: Springer; 1998. p. 107–22. [11] Brunette DM, Tengvall P, Textor M, Thomsen P. Titanium in medicine. Berlin: Springer; 2001. p. 25–53. [12] Richards RG, Perren SM. Implants and materials in fracture fixation. In: Ruedi TP, Buckley RE, Moran CG, editors. AO principles of fracture management. 2nd ed., New York: Thieme; 2007. p. 33–45. [13] Misenhimer GR, Peek RD, Wiltse LL, Rothman SL, Widell Jr EH. Anatomic analysis of pedicle cortical and cancellous diameter as related to screw size. Spine 1989;14:367–72. [14] Sjo¨stro¨m L, Jacobsson O, Karlstro¨m G, Pech P, Rauschning W. CT analysis of pedicles and screw tracts after implant removal in thoracolumbar fractures. J Spinal Disord 1993;6:225–31. [15] Esses SI, Botsford DJ, Kostuik JP. Evaluation of surgical treatment for burst fractures. Spine 1990;15:667–73. [16] Shuman WP, Rogers JV, Sickler ME. Thoracolumbar burst fractures: CT dimensions of the spinal canal relative to postsurgical improvement. Am J Roentgenol 1985;145:337–41. [17] Limb D, Shaw DL, Dickson RA. Neurological injury in thoracolumbar burst fractures. J Bone Joint Surg Br 1995;75:774–7. [18] Boerger TO, Limb D, Dickson RA. Does ‘canal clearance’ affect neurological outcome after thoracolumbar burst fractures? J Bone Joint Surg Br 2000;82: 629–635. [19] Wang J, Zhou Y, Zhang ZF, Li CQ, Zheng WJ, Liu J. Radiological study on disc degeneration on thoracolumbar burst fractures treated by percutaneous pedicle screw fixation. Eur Spine J 2013;22:489–94.
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