The Spine Journal
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Clinical Study
Posterior fixation including the fractured vertebra for severe unstable thoracolumbar fractures Rishi M. Kanna, MS, MRCS, FNB, Ajoy Prasad Shetty, MS, DNB, S. Rajasekaran, MS, MCh, FRCS(Ed), FRCS(London), FACS, PhD* Department of Orthopaedics and Spine Surgery, Ganga Hospital, 313, Mettupalayam Rd, Coimbatore 641043, Tamil Nadu, India Received 11 March 2014; revised 16 July 2014; accepted 12 September 2014
Abstract
BACKGROUND CONTEXT: Traditional short-segment fixation of unstable thoracolumbar injuries can be associated with progressive kyphosis and implant failure. Load sharing classification (LSC) recommends supplemental anterior reconstruction for fractures of score 7 or greater. Posterior fixation including the fractured vertebra (PFFV) has biomechanical advantages over conventional short-segment fixation. However, its efficacy in severe thoracolumbar injuries (LSC$7) has not been studied. PURPOSE: To study the clinical, functional, and radiologic results of PFFV for severe, unstable thoracolumbar injuries (LSC$7) at a minimum of 2 years. STUDY DESIGN: A retrospective review of case records. PATIENT SAMPLE: Thirty-two patients with an unstable burst fracture of LSC$7 treated with PFFV were included. OUTCOME MEASURES: They included clinical outcomes: American Spinal Injury Association grade, visual analog scale (VAS), Oswestry Disability Index (ODI); and radiologic measures: segmental kyphosis angle, vertebral wedge angle, and percentage loss of anterior and posterior vertebral height. METHODS: Thirty-two patients with LSC$7 who had undergone PFFV, with a minimum followup of 2 years were studied for demographic, injury, and surgical details. Clinical and radiologic outcomes were measured before surgery and at 6, 12, and 24 months postoperatively. The presence of screw breakage, screw pullout, peri-implant loosening, and rod breakage were considered as criteria for implant failure. RESULTS: None of the patients had postoperative implant failure at the final follow-up. The mean preoperative kyphosis angle was 22.9 67.6 . This improved significantly to 9.2 66.6 after surgery (p5.000). There was a loss of mean 2.4 (mean kyphosis angle of 11.6 66.3 ) at the final follow-up. The mean preoperative wedge angle was 23.0 68.1 . This was corrected to 9.7 66.2 (p5.000). There was a loss of kyphosis (mean 1.2 ) in the follow-up period. The mean anterior and posterior vertebral height also showed significant improvements postoperatively, which were maintained at the final follow-up. The mean ODI and VAS scores at the end of 2 years were 17.5% and 1.6, respectively. CONCLUSIONS: Reduction of unstable thoracolumbar injuries even with LSC$7 can be achieved and maintained with the use of short-segment pedicle screw fixation including the fractured vertebra, avoiding the need for anterior reconstruction. In the current era of evolving concepts of fracture fixation, the relevance of LSC in the management of unstable burst fractures is questionable. Ó 2014 Elsevier Inc. All rights reserved.
Keywords:
Thoracolumbar; Trauma; Load sharing classification; Intermediate screw; Kyphosis; Short segment; Posterior
FDA device/drug status: Not applicable. Author disclosures: RMK: Nothing to disclose. APS: Nothing to disclose. SR: Grants: Ganga Orthopaedic Research and Education Foundation (A, Paid direcly to institution). The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. The study is funded by Ganga Orthopaedic Research and Education Foundation. http://dx.doi.org/10.1016/j.spinee.2014.09.004 1529-9430/Ó 2014 Elsevier Inc. All rights reserved.
This study was approved by internal review board of Ganga Hospital, Coimbatore, India. * Corresponding author. Department of Orthopaedics and Spine Surgery, Ganga Hospital, 313, Mettupalayam Rd, Coimbatore 641043, Tamil Nadu, India. Tel.: (91) 422-2485000/4250000; fax: (91) 4222451444. E-mail address: [email protected] (S. Rajasekaran)
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Introduction Management of unstable thoracolumbar burst fractures traditionally involves posterior pedicle screw fixation, with pedicle screws at the levels immediately adjacent to the fractured vertebral body. However in some fractures, this method of stabilization can be associated with progressive loss of fracture reduction and screw breakage [1,2]. The biomechanical failures after short-segment posterior fixation have been attributed to the deficient anterior column [3]. To prevent implant failure, various efforts to reconstruct the anterior column either by direct anterior reconstruction [4–7] or through a posterior approach such as transpedicular bone grafting, vertebroplasty [8], and augmentation with calcium hydroxyapatite [9] have been described. McCormack et al. [10] proposed the load sharing classification (LSC) in 1994 to predict unstable thoracolumbar injuries that would require supplemental anterior reconstruction. They proposed that fractures with LSC$7 require anterior reconstruction because posterior short-segment fixation alone would result in implant failures. However, direct anterior vertebral corpectomy and reconstruction in the setting of trauma can be associated with significant morbidity. A balance between avoiding anterior surgeries and preventing failure in posterior surgeries can be achieved by increasing the number of fixation points along the posterior construct [11], using intracorporeal filling techniques [8,9,12–14] and ‘‘intermediate’’ screws at the level of the fracture [15–18]. The use of intermediate screw is a novel technique to increase the fixation strength of a posterior short-segment construct [16]. Biomechanical studies have shown that addition of a screw at the level of the fracture, in a short-segment fixation ( posterior fixation including fractured vertebra [PFFV]), increases the stiffness of the construct and protects the anterior column during loading [3,16,17,19]. Previous studies in the literature have shown that the use of intermediate screws have better outcomes than patients with short-segment posterior fixation alone [17,18,20]. But there are no studies that have specifically studied the effectiveness of short-segment posterior fixation with intermediate screws in fractures with LSC$7. The present study describes the midterm clinical and radiologic results of 32 patients who underwent PFFV for unstable thoracolumbar injuries with LSC$7. Materials and methods The study was performed in a tertiary spinal care center and was approved by the institutional review board of the hospital. It was a retrospective review of case records of all patients with unstable thoracolumbar fractures with LSC$7, who had completed a minimum follow-up of 2 years. In the authors’ institute, PFFV is the standard surgical technique for all unstable thoracolumbar fractures. A total of 277 patients with thoracolumbar fracture had been
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treated in the institute during the study period. Of these, 44 patients with LSC$7 had undergone a PFFV, among which 32 patients had a minimum follow-up of 2 years. The patients’ demographic, clinical, and injury details (age, sex, mode of injury, time to surgery from injury occurrence, associated injuries, pre- and postoperative neurologic status, and perioperative complications) were studied (Table). All patients had preoperative radiographs and computed tomography scan of the thoracolumbar spine. Load sharing score was calculated based on the scoring system described by McCormack et al. [10] (Fig. 1). Fracture morphology was also classified based on the AO Spine thoracolumbar injury classification system. In the radiographs, the following parameters were studied: segmental kyphosis angle, wedge angle, anterior vertebral height loss, and the posterior vertebral height loss (Fig. 2). The presence of screw breakage, screw pullout, peri-implant loosening, and rod breakage were considered as criteria for implant failure. The significance of the changes in the radiographic parameters between pre- and postoperative radiographs was statistically studied using Student t test. The patient’s functional outcome was assessed by visual analog scale (VAS) score for pain and Oswestry Disability Index (ODI) scores. Surgical procedure A standard posterior midline approach was performed and pedicle screws were inserted into the vertebra cephalad and caudal to the fracture. Screws were inserted into the pedicles of the fractured vertebrae (intermediate screws) using freehand technique. The intermediate screw heads were left slightly proud to act as a push point and also achieve reduction of kyphosis. Intermediate screws were inserted in both the pedicles of the fractured vertebra; however, if the pedicle walls were found to be broken, no screw is inserted into that pedicle. No extra effort was taken at achieving complete reduction of kyphosis or restoring vertebral height by rod over contouring, compression, or distraction. In fractures with neurologic deficit or if the spinal canal compromise is greater than 50%, a midline decompression was performed at the level of the pedicles. The degree of kyphosis correction and the position of the screws were assessed by the postoperative radiographs. In patients with coexistent fractures at adjacent levels, additional vertebrae were fixed. All patients were periodically followed-up with clinical and radiologic evaluation. Radiographs were performed at 3, 6, 12, and 24 months.
Results Patient demographics and injury information Thirty-two patients with a mean follow-up of 26.5 months (range: 24–34 months) were analyzed. The preoperative clinical data are presented in Table. The mean age of
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Table Patient demographic and injury details S No.
Age (y)
Sex
Time interval between injury and admission (d)
Time interval between injury and surgery (d)
Injured level
ASIA
Load sharing score
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
60 19 55 64 57 19 32 52 22 43 20 46 34 45 55 56 33 40 26 30 20 48 20 38 66 26 15 58 32 57 55 32
M M M M M F M M M M F M M M M M M M M M F M F M M M F M M M M M
0 0 1 1 1 2 0 4 2 1 1 2 1 2 1 0 0 1 0 9 1 2 1 2 1 4 1 2 2 1 1 0
1 0 1 1 1 2 1 4 2 2 1 2 6 2 15 0 3 2 6 10 2 2 1 3 1 4 2 2 3 1 1 1
L1 L1 L3 T12 L2 L1 L1 L1 L2 T12 L2 L4 L3 L1 L3 L2 T8 T12 L1 L2 L4 T12 L2 T11 L3 L2 L2 L1 T12 L1 L1 T12
A A E B E C C E E B E C E A C C E D E C D C C E D E B E E C E C
8 8 8 7 7 7 7 9 7 7 8 7 7 7 7 8 7 7 7 7 8 7 7 7 8 7 7 7 7 7 8 7
M, male; F, female; ASIA, american spinal injury association.
the patients was 39.8 years (range: 16–52 years). The malefemale ratio was 25:7. The mean time to operate from the time of injury was 2.65 days. About 71.8% of patients were operated within 48 hours after the injury and all the patients were operated within a week.
Injury details Among the vertebral fractures, L1 was the most commonly affected vertebra (n512), followed by L2 (n58), T12 (n56), L3 (n55), and T11 (n51). Thirteen patients had normal neurology (American Spinal Injury Association (ASIA) E), 16 had incomplete deficits (ASIA B, C, D), and three had complete deficit (ASIA A). All the fractures had a load sharing score of 7 or more. Twenty-three patients had a score of 7; eight patients had a score of 8; and one patient had a score of 9. According to AO Spine TL spine injury classification system, 19 were Type A4, 5 were A3 type, 5 were B2 with A4 type body injury, and 3 were B2 with A3 type body injury. Fall from height was the most common injury mechanism (n523) and rest of the injuries occurred in a road traffic accident.
Surgery details Posterior instrumented stabilization was performed in 13 patients (all ASIA E) and midline decompression with stabilization was performed in 19 patients with neurologic deficit. In 28 patients, only a three-level fixation has been used (one screw each at one level above, below, and at the fracture level). In four patients, four levels were fixed because of coexistent fractures at adjacent levels. In 30 patients, screws were inserted at both pedicles at the fractured vertebra, whereas two patients had screws inserted unilaterally due to broken pedicles on the opposite side. The mean operating time was 112636 minutes, the mean blood loss was 264695 mL, and the mean duration of hospitalization was 5.162.6 days. Patients with complete neurologic deficit (n53) did not show any neurologic recovery. All three ASIA B patients improved to ASIA C. Five ASIA C patients improved to ASIA E. The remaining five ASIA C patients improved to ASIA D. All three ASIA D patients improved to ASIA E. None of the patients had any postoperative implant failure at the final follow-up. All patients received only posterior surgery and anterior decompression surgery was not performed in any of the patients.
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Fig. 1. Load-sharing classification. Three factors are analyzed. (A) Comminution of vertebral body as seen in sagittal computed tomography (CT): Grade 15less than 30%; Grade 2530% to 60%; Grade 35greater than 60%. (B) Apposition of fragments as seen in axial CT: Grade 15minimal displacement; Grade 252 mm or more displacement of less than 50% cross-section of the body; Grade 352 mm or more displacement of greater than 50% crosssection of the body. (C) Amount of kyphosis correction: Grade 15correction on lateral radiograph of upto 3 ; Grade 25correction of 4 to 9 ; Grade 35 correction of 10 or more. In the case illustrated above, the score is calculated as follows: comminution of 30% to 60% (Score 2); separation of fragments greater than 50% (Score 3); and more than 9 kyphosis correction from 34 to 13 (Score 3), constituting a total load sharing classification score of 8.
Radiographic evaluation The mean preoperative kyphosis angle was 22.9 67.6 . This improved significantly to 9.2 66.6 in the immediate postoperative period (p5.000). There was a loss of mean 2.4 (mean angle of 11.6 66.3 ) at the final follow-up (Fig. 3). The mean preoperative wedge angle was 23.0 68.1 . This was corrected to 9.7 66.2 (significant, p5.000) in the immediate postoperative period. There was a loss of kyphosis (mean 1.2 ) in the follow-up period, resulting in a mean wedge angle of 10.9 65.6 . The mean
anterior vertebral height was 13.864.2 mm as compared with 27.463.3 mm in the immediate adjacent normal vertebra. This improved to 21.664.9 mm in the immediate postoperative period (p5.000). At the final follow-up, the mean anterior vertebral height was 21.164.6 mm, indicating no significant height loss during the follow-up period. The mean posterior vertebral height was 25.764.4 mm as compared with 29.563.2 mm of normal adjacent vertebra. After surgery, the mean height improved to 28.162.9 mm. This was significant (p5.001). This height restoration was
Fig. 2. In the lateral radiographs, the segmental kyphosis angle was measured between the proximal end plate of proximal vertebra and the distal end plate of distal vertebra (yellow line: Left). The wedge angle was calculated between the proximal and distal end plates of the fractured vertebra (red line: Left). The anterior vertebral height loss is defined as the anterior height of the fractured vertebral body in comparison with the anterior height of the intact adjacent vertebra (red line: Right). The posterior vertebral height loss is defined as the posterior height of the fractured vertebral body in comparison with the posterior height of the intact adjacent vertebra (yellow line: Right).
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Fig. 3. (Left) Mean kyphosis and (Right) wedge angles before and after surgery (6, 12, 24 months).
maintained till the final follow-up (28.162.6 mm) (p5.729) (Fig. 4). At final follow-up, the average VAS score for back pain was 1.660.9 (range, 1–4). The mean ODI score at final follow-up was 17.5% (range from 11% to 22.8%).
Discussion Short-segment posterior stabilization of the injured vertebral motion segments is one of the standard methods of stabilization for unstable thoracolumbar injuries. The advantages include the familiarity and simplicity of the approach and lesser complications as compared with anterior surgeries [1,2,21,22]. But this technique has been criticized because of the risks of implant failure and progression of symptomatic kyphosis [1,2]. This was attributed mainly to the defective anterior weight bearing column of the spine. The LSC was developed by McCormack et al. [10] to identify fractures that will need supplemental anterior reconstruction. They retrospectively analysed 28 patients who had been operated for thoracolumbar injuries with Steffee plates. After a mean follow-up of 3 years, they observed implant failures in 10 patients. They identified three important factors in predicting posterior fixation failure and each factor was scored on a point system from 1 to 3. They observed that anterior vertebral reconstruction is essential in patients with an LSC score of 7 or more to prevent implant failure. The classification has been validated through biomechanical studies and has been reported to have a fair interobserver reliability [23]. Wang et al. [24] created a bovine L1 burst fracture model by axial compressive impact with different energy and showed significant positive correlation between load
sharing score and spinal instability. Dai et al. [23] and Elzinga et al. [25] through independent studies have shown high levels of agreement when the LSC was used to assess thoracolumbar burst fractures. Parker et al. [26] studied 46 thoracolumbar burst fractures and concluded that the LSC was the most successful way to predict successful shortsegment thoracolumbar spinal fracture repair. Aligizakis et al. [27] concluded that LSC could predict the functional outcome in conservatively treated patients and the authors suggested patients with a score of 6 or less might be suited for conservative therapy. However, some authors have disagreed with the LSC [28]. Scholl et al. [28] reviewed 16 patients treated with short-segment posterior instrumentation and fusion, and 7 patients among them developed implant failure. The authors concluded that the LSC was not predictive of posterior instrumentation failure. Disadvantages of LSC It has been almost 20 years since the classification was first published in 1994, and since then, it has been cited in 522 articles. The article has limitations including that it is a retrospective study of only 28 patients, injuries of all severity including fracture dislocations have been included, and older generation Steffe plates and screws were the implants used to stabilize the fractures. With significant improvements in spinal stabilization systems, there have been various modifications in the surgical concepts and approach regarding spinal trauma care. Anterior approach and vertebral body reconstruction can be potentially morbid surgeries in a patient with spinal fracture, and hence, various modifications to posterior stabilization have been made to improve stiffness of the construct and reconstruct the anterior column. This includes transpedicular morselized intracorporeal bone grafting, vertebroplasty,
Fig. 4. (Left) The mean anterior and (Right) posterior vertebral height loss as compared with normal vertebra. The height restoration in the immediate and final follow-up is noted.
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Fig. 5. A 32-year-old man with load sharing score of 8. (A–C) The lateral radiograph and sagittal, axial computed tomography images show burst fracture of T12 vertebra with significant retropulsion of fracture fragments. (D) The fracture has been treated by posterior fixation including the fractured vertebra technique. (E) The kyphosis angle of 28 has been corrected to 2 that is maintained as 6 in the final follow-up.
and kyphoplasty with hydroxyapatite or calcium phosphate [8,9,11–14]. Other biomechanical measures to improve the strength of the construct include the addition of crosslinks, the use of a supplemental hook fixation at the levels of the screws, and the addition of an ‘‘intermediate’’ screw [15,17,18,20]. The concept of an ‘‘intermediate’’ screw to increase the stiffness of a short-segment construct was first proposed by Dick et al [16]. In an animal cadaveric burst fracture model, Anekstein et al. [15] concluded that addition of intermediate screws significantly increased the strength of a short-segment pedicular fixation. In a human cadaveric study, Mahar et al. [18] showed that axial torsion stability improved by twofold with intermediate screws, especially in flexion-extension and lateral bending. Biomechanically, the ‘‘intermediate’’ screws can function as a push point with an anterior vector, creating
a ‘‘lordorizing’’ force that additionally corrects the kyphosis. The three-point fixation afforded decreases the cantilever effects that cause kyphosis. There have been prior clinical studies using the PFFV technique for stabilization of thoracolumbar burst fractures. In a prospective randomized study by Farrokhi et al. [20], 80 patients with thoracolumbar fractures treated with posterior pedicular fixation were randomized into two groups receiving either the short-segment fixation only (bridging group) or including the fracture level (including group). There was a high rate of instrumentation failure in the ‘‘bridging’’ group. They concluded that intermediate screws offer a better kyphosis correction, fewer instrument failures, and a comparable clinical outcome. In a study conducted by Guven et al. [17], the authors observed that fracture level fixation had lowered the rates of correction
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Fig. 6. (A and B) An unstable burst fracture treated by posterior fixation including the fractured vertebra and (C and D) postoperative computed tomography images showing good containment of the screws in the sagittal and axial images.
failure and are useful to achieve and maintain kyphosis correction. Although the biomechanical advantages provided by intermediate screws have been proved in clinical studies, its role in the management of burst fractures with LSC$7 has not been studied previously. The present study indicates that even in fractures with severe vertebral comminution and kyphosis, the use of intermediate screws provides good clinical and radiologic outcomes (Fig. 5). The technique obviates the need for vertebral body augmentation techniques and anterior vertebral reconstruction. Being a posterior short-segment fixation, the surgical time and cost incurred in this technique will be much less than a longsegment technique or a combined anterior and posterior fixation. In the present study, the mean preoperative kyphotic angle was 22.9 . This improved to mean 9.2 in the immediate postoperative period (59.8% correction of kyphosis). The average of 11.6 of kyphosis correction achieved after fracture healing assumes importance considering that all these fractures had a high preoperative load sharing score ($7). The mean preoperative wedge angle was 23.1 . This improved to 9.7 in the immediate postoperative period.
There was a loss of kyphosis in the follow-up period, resulting in a mean wedge angle of 10.9 . The parallel changes in mean kyphotic angle and the wedge angle indicate that majority of kyphosis correction occurs at the fractured vertebral body itself. Proponents of anterior surgery in thoracolumbar fractures cite the ability for complete kyphosis correction and direct spinal cord decompression as important advantages. It has been well documented in many studies that there is no direct correlation between the amount of kyphosis and clinical symptoms and the functional outcome [2,3,29,30]. The patients in the present study had a good functional outcome, indicated by a mean VAS score of 1.6 and a final mean ODI score of 17.4%. Burst fractures are usually associated with varying degrees of canal compromise because of the retropulsed fracture fragments. There are studies to prove that the geometry of the canal is not a good guide to the extent of neurologic dysfunction [31–33]. Shen et al. [34] had demonstrated that the retropulsed fragments gradually reabsorb approximately 50% within 12 months with remodeling of the canal. In the present study, no vigorous attempt was made to achieve
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complete fracture reduction or restore normal vertebral height over contouring rods, distraction, or compression of screws. The reduction achieved during prone positioning of the patient and fixation of the rod to the screws was accepted. There are theoretical concerns regarding the use of pedicle screws into the fractured vertebra as to whether it is safe to insert a screw through a broken bone without risking breach into the spinal canal. In most patients with burst fractures, the walls of the pedicle are usually intact. So inserting a screw is similar to pedicle screw insertion in other vertebrae. Our follow-up computed tomography images have also demonstrated good containment of screws (Fig. 6). Another concern is the hold (pullout strength) of the screw in the fractured body. It is well accepted that the pedicle contributes approximately 80% of the stiffness and 60% of the pullout strength at the screw-bone interface [2,35–37]. As long as the integrity of the pedicles is maintained, the screws inserted into the fractured level will have good stiffness and pullout strength.
[9]
[10] [11]
[12]
[13]
[14]
[15]
[16]
Conclusions Reduction of unstable thoracolumbar injuries even with LSC$7 can be achieved and maintained with the use of short-segment pedicle screw fixation including the fractured vertebra. This technique allows good correction of segmental kyphosis, vertebral wedging, and vertebral height loss. The radiologic correction achieved is maintained even at the end of 2 years and reflected in good functional outcomes.
[17]
[18]
[19]
[20]
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[33] Wessberg P, Wang Y, Irstam L, Nordwall A. The effect of surgery and remodelling on spinal canal measurements after thoracolumbar burst fractures. Eur Spine J 2001;10:55–63. [34] Shen WJ, Liu TJ, Shen YS. Nonoperative treatment versus posterior fixation for thoracolumbar junction burst fractures without neurologic deficit. Spine 2001;26:1038–45. [35] Tsai KJ, Murakami H, Horton WC, Fei Q, Hutton WC. Pedicle screw fixation strength: a biomechanical comparison between 4.5-mm and 5.5-mm diameter screws in osteoporotic upper thoracic vertebrae. J Surg Orthop Adv 2009;18:23–7. [36] Inceoglu S, Ferrara L, McLain RF. Pedicle screw fixation strength: pullout versus insertional torque. Spine J 2004;4:513–8. [37] Zdeblick TA, Kunz DN, Cooke ME, McCabe R. Pedicle screw pullout strength. Correlation with insertional torque. Spine 1993;18:1673–6.
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Clinical Study
Posterior fixation including the fractured vertebra for severe unstable thoracolumbar fractures Rishi M. Kanna, MS, MRCS, FNB, Ajoy Prasad Shetty, MS, DNB, S. Rajasekaran, MS, MCh, FRCS(Ed), FRCS(London), FACS, PhD* Department of Orthopaedics and Spine Surgery, Ganga Hospital, 313, Mettupalayam Rd, Coimbatore 641043, Tamil Nadu, India Received 11 March 2014; revised 16 July 2014; accepted 12 September 2014
Abstract
BACKGROUND CONTEXT: Traditional short-segment fixation of unstable thoracolumbar injuries can be associated with progressive kyphosis and implant failure. Load sharing classification (LSC) recommends supplemental anterior reconstruction for fractures of score 7 or greater. Posterior fixation including the fractured vertebra (PFFV) has biomechanical advantages over conventional short-segment fixation. However, its efficacy in severe thoracolumbar injuries (LSC$7) has not been studied. PURPOSE: To study the clinical, functional, and radiologic results of PFFV for severe, unstable thoracolumbar injuries (LSC$7) at a minimum of 2 years. STUDY DESIGN: A retrospective review of case records. PATIENT SAMPLE: Thirty-two patients with an unstable burst fracture of LSC$7 treated with PFFV were included. OUTCOME MEASURES: They included clinical outcomes: American Spinal Injury Association grade, visual analog scale (VAS), Oswestry Disability Index (ODI); and radiologic measures: segmental kyphosis angle, vertebral wedge angle, and percentage loss of anterior and posterior vertebral height. METHODS: Thirty-two patients with LSC$7 who had undergone PFFV, with a minimum followup of 2 years were studied for demographic, injury, and surgical details. Clinical and radiologic outcomes were measured before surgery and at 6, 12, and 24 months postoperatively. The presence of screw breakage, screw pullout, peri-implant loosening, and rod breakage were considered as criteria for implant failure. RESULTS: None of the patients had postoperative implant failure at the final follow-up. The mean preoperative kyphosis angle was 22.9 67.6 . This improved significantly to 9.2 66.6 after surgery (p5.000). There was a loss of mean 2.4 (mean kyphosis angle of 11.6 66.3 ) at the final follow-up. The mean preoperative wedge angle was 23.0 68.1 . This was corrected to 9.7 66.2 (p5.000). There was a loss of kyphosis (mean 1.2 ) in the follow-up period. The mean anterior and posterior vertebral height also showed significant improvements postoperatively, which were maintained at the final follow-up. The mean ODI and VAS scores at the end of 2 years were 17.5% and 1.6, respectively. CONCLUSIONS: Reduction of unstable thoracolumbar injuries even with LSC$7 can be achieved and maintained with the use of short-segment pedicle screw fixation including the fractured vertebra, avoiding the need for anterior reconstruction. In the current era of evolving concepts of fracture fixation, the relevance of LSC in the management of unstable burst fractures is questionable. Ó 2014 Elsevier Inc. All rights reserved.
Keywords:
Thoracolumbar; Trauma; Load sharing classification; Intermediate screw; Kyphosis; Short segment; Posterior
FDA device/drug status: Not applicable. Author disclosures: RMK: Nothing to disclose. APS: Nothing to disclose. SR: Grants: Ganga Orthopaedic Research and Education Foundation (A, Paid direcly to institution). The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. The study is funded by Ganga Orthopaedic Research and Education Foundation. http://dx.doi.org/10.1016/j.spinee.2014.09.004 1529-9430/Ó 2014 Elsevier Inc. All rights reserved.
This study was approved by internal review board of Ganga Hospital, Coimbatore, India. * Corresponding author. Department of Orthopaedics and Spine Surgery, Ganga Hospital, 313, Mettupalayam Rd, Coimbatore 641043, Tamil Nadu, India. Tel.: (91) 422-2485000/4250000; fax: (91) 4222451444. E-mail address: [email protected] (S. Rajasekaran)
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Introduction Management of unstable thoracolumbar burst fractures traditionally involves posterior pedicle screw fixation, with pedicle screws at the levels immediately adjacent to the fractured vertebral body. However in some fractures, this method of stabilization can be associated with progressive loss of fracture reduction and screw breakage [1,2]. The biomechanical failures after short-segment posterior fixation have been attributed to the deficient anterior column [3]. To prevent implant failure, various efforts to reconstruct the anterior column either by direct anterior reconstruction [4–7] or through a posterior approach such as transpedicular bone grafting, vertebroplasty [8], and augmentation with calcium hydroxyapatite [9] have been described. McCormack et al. [10] proposed the load sharing classification (LSC) in 1994 to predict unstable thoracolumbar injuries that would require supplemental anterior reconstruction. They proposed that fractures with LSC$7 require anterior reconstruction because posterior short-segment fixation alone would result in implant failures. However, direct anterior vertebral corpectomy and reconstruction in the setting of trauma can be associated with significant morbidity. A balance between avoiding anterior surgeries and preventing failure in posterior surgeries can be achieved by increasing the number of fixation points along the posterior construct [11], using intracorporeal filling techniques [8,9,12–14] and ‘‘intermediate’’ screws at the level of the fracture [15–18]. The use of intermediate screw is a novel technique to increase the fixation strength of a posterior short-segment construct [16]. Biomechanical studies have shown that addition of a screw at the level of the fracture, in a short-segment fixation ( posterior fixation including fractured vertebra [PFFV]), increases the stiffness of the construct and protects the anterior column during loading [3,16,17,19]. Previous studies in the literature have shown that the use of intermediate screws have better outcomes than patients with short-segment posterior fixation alone [17,18,20]. But there are no studies that have specifically studied the effectiveness of short-segment posterior fixation with intermediate screws in fractures with LSC$7. The present study describes the midterm clinical and radiologic results of 32 patients who underwent PFFV for unstable thoracolumbar injuries with LSC$7. Materials and methods The study was performed in a tertiary spinal care center and was approved by the institutional review board of the hospital. It was a retrospective review of case records of all patients with unstable thoracolumbar fractures with LSC$7, who had completed a minimum follow-up of 2 years. In the authors’ institute, PFFV is the standard surgical technique for all unstable thoracolumbar fractures. A total of 277 patients with thoracolumbar fracture had been
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treated in the institute during the study period. Of these, 44 patients with LSC$7 had undergone a PFFV, among which 32 patients had a minimum follow-up of 2 years. The patients’ demographic, clinical, and injury details (age, sex, mode of injury, time to surgery from injury occurrence, associated injuries, pre- and postoperative neurologic status, and perioperative complications) were studied (Table). All patients had preoperative radiographs and computed tomography scan of the thoracolumbar spine. Load sharing score was calculated based on the scoring system described by McCormack et al. [10] (Fig. 1). Fracture morphology was also classified based on the AO Spine thoracolumbar injury classification system. In the radiographs, the following parameters were studied: segmental kyphosis angle, wedge angle, anterior vertebral height loss, and the posterior vertebral height loss (Fig. 2). The presence of screw breakage, screw pullout, peri-implant loosening, and rod breakage were considered as criteria for implant failure. The significance of the changes in the radiographic parameters between pre- and postoperative radiographs was statistically studied using Student t test. The patient’s functional outcome was assessed by visual analog scale (VAS) score for pain and Oswestry Disability Index (ODI) scores. Surgical procedure A standard posterior midline approach was performed and pedicle screws were inserted into the vertebra cephalad and caudal to the fracture. Screws were inserted into the pedicles of the fractured vertebrae (intermediate screws) using freehand technique. The intermediate screw heads were left slightly proud to act as a push point and also achieve reduction of kyphosis. Intermediate screws were inserted in both the pedicles of the fractured vertebra; however, if the pedicle walls were found to be broken, no screw is inserted into that pedicle. No extra effort was taken at achieving complete reduction of kyphosis or restoring vertebral height by rod over contouring, compression, or distraction. In fractures with neurologic deficit or if the spinal canal compromise is greater than 50%, a midline decompression was performed at the level of the pedicles. The degree of kyphosis correction and the position of the screws were assessed by the postoperative radiographs. In patients with coexistent fractures at adjacent levels, additional vertebrae were fixed. All patients were periodically followed-up with clinical and radiologic evaluation. Radiographs were performed at 3, 6, 12, and 24 months.
Results Patient demographics and injury information Thirty-two patients with a mean follow-up of 26.5 months (range: 24–34 months) were analyzed. The preoperative clinical data are presented in Table. The mean age of
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Table Patient demographic and injury details S No.
Age (y)
Sex
Time interval between injury and admission (d)
Time interval between injury and surgery (d)
Injured level
ASIA
Load sharing score
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
60 19 55 64 57 19 32 52 22 43 20 46 34 45 55 56 33 40 26 30 20 48 20 38 66 26 15 58 32 57 55 32
M M M M M F M M M M F M M M M M M M M M F M F M M M F M M M M M
0 0 1 1 1 2 0 4 2 1 1 2 1 2 1 0 0 1 0 9 1 2 1 2 1 4 1 2 2 1 1 0
1 0 1 1 1 2 1 4 2 2 1 2 6 2 15 0 3 2 6 10 2 2 1 3 1 4 2 2 3 1 1 1
L1 L1 L3 T12 L2 L1 L1 L1 L2 T12 L2 L4 L3 L1 L3 L2 T8 T12 L1 L2 L4 T12 L2 T11 L3 L2 L2 L1 T12 L1 L1 T12
A A E B E C C E E B E C E A C C E D E C D C C E D E B E E C E C
8 8 8 7 7 7 7 9 7 7 8 7 7 7 7 8 7 7 7 7 8 7 7 7 8 7 7 7 7 7 8 7
M, male; F, female; ASIA, american spinal injury association.
the patients was 39.8 years (range: 16–52 years). The malefemale ratio was 25:7. The mean time to operate from the time of injury was 2.65 days. About 71.8% of patients were operated within 48 hours after the injury and all the patients were operated within a week.
Injury details Among the vertebral fractures, L1 was the most commonly affected vertebra (n512), followed by L2 (n58), T12 (n56), L3 (n55), and T11 (n51). Thirteen patients had normal neurology (American Spinal Injury Association (ASIA) E), 16 had incomplete deficits (ASIA B, C, D), and three had complete deficit (ASIA A). All the fractures had a load sharing score of 7 or more. Twenty-three patients had a score of 7; eight patients had a score of 8; and one patient had a score of 9. According to AO Spine TL spine injury classification system, 19 were Type A4, 5 were A3 type, 5 were B2 with A4 type body injury, and 3 were B2 with A3 type body injury. Fall from height was the most common injury mechanism (n523) and rest of the injuries occurred in a road traffic accident.
Surgery details Posterior instrumented stabilization was performed in 13 patients (all ASIA E) and midline decompression with stabilization was performed in 19 patients with neurologic deficit. In 28 patients, only a three-level fixation has been used (one screw each at one level above, below, and at the fracture level). In four patients, four levels were fixed because of coexistent fractures at adjacent levels. In 30 patients, screws were inserted at both pedicles at the fractured vertebra, whereas two patients had screws inserted unilaterally due to broken pedicles on the opposite side. The mean operating time was 112636 minutes, the mean blood loss was 264695 mL, and the mean duration of hospitalization was 5.162.6 days. Patients with complete neurologic deficit (n53) did not show any neurologic recovery. All three ASIA B patients improved to ASIA C. Five ASIA C patients improved to ASIA E. The remaining five ASIA C patients improved to ASIA D. All three ASIA D patients improved to ASIA E. None of the patients had any postoperative implant failure at the final follow-up. All patients received only posterior surgery and anterior decompression surgery was not performed in any of the patients.
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Fig. 1. Load-sharing classification. Three factors are analyzed. (A) Comminution of vertebral body as seen in sagittal computed tomography (CT): Grade 15less than 30%; Grade 2530% to 60%; Grade 35greater than 60%. (B) Apposition of fragments as seen in axial CT: Grade 15minimal displacement; Grade 252 mm or more displacement of less than 50% cross-section of the body; Grade 352 mm or more displacement of greater than 50% crosssection of the body. (C) Amount of kyphosis correction: Grade 15correction on lateral radiograph of upto 3 ; Grade 25correction of 4 to 9 ; Grade 35 correction of 10 or more. In the case illustrated above, the score is calculated as follows: comminution of 30% to 60% (Score 2); separation of fragments greater than 50% (Score 3); and more than 9 kyphosis correction from 34 to 13 (Score 3), constituting a total load sharing classification score of 8.
Radiographic evaluation The mean preoperative kyphosis angle was 22.9 67.6 . This improved significantly to 9.2 66.6 in the immediate postoperative period (p5.000). There was a loss of mean 2.4 (mean angle of 11.6 66.3 ) at the final follow-up (Fig. 3). The mean preoperative wedge angle was 23.0 68.1 . This was corrected to 9.7 66.2 (significant, p5.000) in the immediate postoperative period. There was a loss of kyphosis (mean 1.2 ) in the follow-up period, resulting in a mean wedge angle of 10.9 65.6 . The mean
anterior vertebral height was 13.864.2 mm as compared with 27.463.3 mm in the immediate adjacent normal vertebra. This improved to 21.664.9 mm in the immediate postoperative period (p5.000). At the final follow-up, the mean anterior vertebral height was 21.164.6 mm, indicating no significant height loss during the follow-up period. The mean posterior vertebral height was 25.764.4 mm as compared with 29.563.2 mm of normal adjacent vertebra. After surgery, the mean height improved to 28.162.9 mm. This was significant (p5.001). This height restoration was
Fig. 2. In the lateral radiographs, the segmental kyphosis angle was measured between the proximal end plate of proximal vertebra and the distal end plate of distal vertebra (yellow line: Left). The wedge angle was calculated between the proximal and distal end plates of the fractured vertebra (red line: Left). The anterior vertebral height loss is defined as the anterior height of the fractured vertebral body in comparison with the anterior height of the intact adjacent vertebra (red line: Right). The posterior vertebral height loss is defined as the posterior height of the fractured vertebral body in comparison with the posterior height of the intact adjacent vertebra (yellow line: Right).
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Fig. 3. (Left) Mean kyphosis and (Right) wedge angles before and after surgery (6, 12, 24 months).
maintained till the final follow-up (28.162.6 mm) (p5.729) (Fig. 4). At final follow-up, the average VAS score for back pain was 1.660.9 (range, 1–4). The mean ODI score at final follow-up was 17.5% (range from 11% to 22.8%).
Discussion Short-segment posterior stabilization of the injured vertebral motion segments is one of the standard methods of stabilization for unstable thoracolumbar injuries. The advantages include the familiarity and simplicity of the approach and lesser complications as compared with anterior surgeries [1,2,21,22]. But this technique has been criticized because of the risks of implant failure and progression of symptomatic kyphosis [1,2]. This was attributed mainly to the defective anterior weight bearing column of the spine. The LSC was developed by McCormack et al. [10] to identify fractures that will need supplemental anterior reconstruction. They retrospectively analysed 28 patients who had been operated for thoracolumbar injuries with Steffee plates. After a mean follow-up of 3 years, they observed implant failures in 10 patients. They identified three important factors in predicting posterior fixation failure and each factor was scored on a point system from 1 to 3. They observed that anterior vertebral reconstruction is essential in patients with an LSC score of 7 or more to prevent implant failure. The classification has been validated through biomechanical studies and has been reported to have a fair interobserver reliability [23]. Wang et al. [24] created a bovine L1 burst fracture model by axial compressive impact with different energy and showed significant positive correlation between load
sharing score and spinal instability. Dai et al. [23] and Elzinga et al. [25] through independent studies have shown high levels of agreement when the LSC was used to assess thoracolumbar burst fractures. Parker et al. [26] studied 46 thoracolumbar burst fractures and concluded that the LSC was the most successful way to predict successful shortsegment thoracolumbar spinal fracture repair. Aligizakis et al. [27] concluded that LSC could predict the functional outcome in conservatively treated patients and the authors suggested patients with a score of 6 or less might be suited for conservative therapy. However, some authors have disagreed with the LSC [28]. Scholl et al. [28] reviewed 16 patients treated with short-segment posterior instrumentation and fusion, and 7 patients among them developed implant failure. The authors concluded that the LSC was not predictive of posterior instrumentation failure. Disadvantages of LSC It has been almost 20 years since the classification was first published in 1994, and since then, it has been cited in 522 articles. The article has limitations including that it is a retrospective study of only 28 patients, injuries of all severity including fracture dislocations have been included, and older generation Steffe plates and screws were the implants used to stabilize the fractures. With significant improvements in spinal stabilization systems, there have been various modifications in the surgical concepts and approach regarding spinal trauma care. Anterior approach and vertebral body reconstruction can be potentially morbid surgeries in a patient with spinal fracture, and hence, various modifications to posterior stabilization have been made to improve stiffness of the construct and reconstruct the anterior column. This includes transpedicular morselized intracorporeal bone grafting, vertebroplasty,
Fig. 4. (Left) The mean anterior and (Right) posterior vertebral height loss as compared with normal vertebra. The height restoration in the immediate and final follow-up is noted.
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Fig. 5. A 32-year-old man with load sharing score of 8. (A–C) The lateral radiograph and sagittal, axial computed tomography images show burst fracture of T12 vertebra with significant retropulsion of fracture fragments. (D) The fracture has been treated by posterior fixation including the fractured vertebra technique. (E) The kyphosis angle of 28 has been corrected to 2 that is maintained as 6 in the final follow-up.
and kyphoplasty with hydroxyapatite or calcium phosphate [8,9,11–14]. Other biomechanical measures to improve the strength of the construct include the addition of crosslinks, the use of a supplemental hook fixation at the levels of the screws, and the addition of an ‘‘intermediate’’ screw [15,17,18,20]. The concept of an ‘‘intermediate’’ screw to increase the stiffness of a short-segment construct was first proposed by Dick et al [16]. In an animal cadaveric burst fracture model, Anekstein et al. [15] concluded that addition of intermediate screws significantly increased the strength of a short-segment pedicular fixation. In a human cadaveric study, Mahar et al. [18] showed that axial torsion stability improved by twofold with intermediate screws, especially in flexion-extension and lateral bending. Biomechanically, the ‘‘intermediate’’ screws can function as a push point with an anterior vector, creating
a ‘‘lordorizing’’ force that additionally corrects the kyphosis. The three-point fixation afforded decreases the cantilever effects that cause kyphosis. There have been prior clinical studies using the PFFV technique for stabilization of thoracolumbar burst fractures. In a prospective randomized study by Farrokhi et al. [20], 80 patients with thoracolumbar fractures treated with posterior pedicular fixation were randomized into two groups receiving either the short-segment fixation only (bridging group) or including the fracture level (including group). There was a high rate of instrumentation failure in the ‘‘bridging’’ group. They concluded that intermediate screws offer a better kyphosis correction, fewer instrument failures, and a comparable clinical outcome. In a study conducted by Guven et al. [17], the authors observed that fracture level fixation had lowered the rates of correction
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Fig. 6. (A and B) An unstable burst fracture treated by posterior fixation including the fractured vertebra and (C and D) postoperative computed tomography images showing good containment of the screws in the sagittal and axial images.
failure and are useful to achieve and maintain kyphosis correction. Although the biomechanical advantages provided by intermediate screws have been proved in clinical studies, its role in the management of burst fractures with LSC$7 has not been studied previously. The present study indicates that even in fractures with severe vertebral comminution and kyphosis, the use of intermediate screws provides good clinical and radiologic outcomes (Fig. 5). The technique obviates the need for vertebral body augmentation techniques and anterior vertebral reconstruction. Being a posterior short-segment fixation, the surgical time and cost incurred in this technique will be much less than a longsegment technique or a combined anterior and posterior fixation. In the present study, the mean preoperative kyphotic angle was 22.9 . This improved to mean 9.2 in the immediate postoperative period (59.8% correction of kyphosis). The average of 11.6 of kyphosis correction achieved after fracture healing assumes importance considering that all these fractures had a high preoperative load sharing score ($7). The mean preoperative wedge angle was 23.1 . This improved to 9.7 in the immediate postoperative period.
There was a loss of kyphosis in the follow-up period, resulting in a mean wedge angle of 10.9 . The parallel changes in mean kyphotic angle and the wedge angle indicate that majority of kyphosis correction occurs at the fractured vertebral body itself. Proponents of anterior surgery in thoracolumbar fractures cite the ability for complete kyphosis correction and direct spinal cord decompression as important advantages. It has been well documented in many studies that there is no direct correlation between the amount of kyphosis and clinical symptoms and the functional outcome [2,3,29,30]. The patients in the present study had a good functional outcome, indicated by a mean VAS score of 1.6 and a final mean ODI score of 17.4%. Burst fractures are usually associated with varying degrees of canal compromise because of the retropulsed fracture fragments. There are studies to prove that the geometry of the canal is not a good guide to the extent of neurologic dysfunction [31–33]. Shen et al. [34] had demonstrated that the retropulsed fragments gradually reabsorb approximately 50% within 12 months with remodeling of the canal. In the present study, no vigorous attempt was made to achieve
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complete fracture reduction or restore normal vertebral height over contouring rods, distraction, or compression of screws. The reduction achieved during prone positioning of the patient and fixation of the rod to the screws was accepted. There are theoretical concerns regarding the use of pedicle screws into the fractured vertebra as to whether it is safe to insert a screw through a broken bone without risking breach into the spinal canal. In most patients with burst fractures, the walls of the pedicle are usually intact. So inserting a screw is similar to pedicle screw insertion in other vertebrae. Our follow-up computed tomography images have also demonstrated good containment of screws (Fig. 6). Another concern is the hold (pullout strength) of the screw in the fractured body. It is well accepted that the pedicle contributes approximately 80% of the stiffness and 60% of the pullout strength at the screw-bone interface [2,35–37]. As long as the integrity of the pedicles is maintained, the screws inserted into the fractured level will have good stiffness and pullout strength.
[9]
[10] [11]
[12]
[13]
[14]
[15]
[16]
Conclusions Reduction of unstable thoracolumbar injuries even with LSC$7 can be achieved and maintained with the use of short-segment pedicle screw fixation including the fractured vertebra. This technique allows good correction of segmental kyphosis, vertebral wedging, and vertebral height loss. The radiologic correction achieved is maintained even at the end of 2 years and reflected in good functional outcomes.
[17]
[18]
[19]
[20]
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[33] Wessberg P, Wang Y, Irstam L, Nordwall A. The effect of surgery and remodelling on spinal canal measurements after thoracolumbar burst fractures. Eur Spine J 2001;10:55–63. [34] Shen WJ, Liu TJ, Shen YS. Nonoperative treatment versus posterior fixation for thoracolumbar junction burst fractures without neurologic deficit. Spine 2001;26:1038–45. [35] Tsai KJ, Murakami H, Horton WC, Fei Q, Hutton WC. Pedicle screw fixation strength: a biomechanical comparison between 4.5-mm and 5.5-mm diameter screws in osteoporotic upper thoracic vertebrae. J Surg Orthop Adv 2009;18:23–7. [36] Inceoglu S, Ferrara L, McLain RF. Pedicle screw fixation strength: pullout versus insertional torque. Spine J 2004;4:513–8. [37] Zdeblick TA, Kunz DN, Cooke ME, McCabe R. Pedicle screw pullout strength. Correlation with insertional torque. Spine 1993;18:1673–6.
