Efficiency of Ligamentotaxis Using PLL for Thoracic and Lumbar Burst Fractures in the Load-sharing Classification

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1 Efficiency of Ligamentotaxis Using PLL for Thoracic and Lumbar Burst Fractures in the Load-sharing Classification Won-Ju Jeong, MD; Joon-Woo Kim, MD; Dong-Kyo Seo, MD; Hyun-Joo Lee, MD; Jun-Young Kim, MD; Jong-Pil Yoon, MD; Woo-Kie Min, MD, PhD abstract Full article available online at Healio.com/Orthopedics. Search: The use of pedicle screws for short-segment implants has been known to be dangerous in patients who score a 7 or higher on McCormack s classification. The efficiency of ligamentotaxis of the posterior longitudinal ligament (PLL) and short-segment implants and fusion in relation to McCormack s classification has not been proven. The purpose of this study was to compare the clinical and radiological results of indirect decompression using PLL ligamentotaxis between patients with a high- (score of 7 or higher) or low-grade (score of 6 or less) fracture. Eighteen patients (19 levels) in the low-grade fracture group were compared with 23 patients (27 levels) in the high-grade fracture group. Clinical outcomes were measured using the Oswestry Disability Index (ODI) and visual analog scale (VAS) scores; radiologic measures were determined using the spinal canal area and mean sagittal diameter; and the complications were evaluated and compared. A significant improvement in each groups was found in the mean pre- and postoperative spinal canal area, mean sagittal diameter, Cobb s angle, and anterior vertebral height compression rate. A significant difference was found between the 2 groups in the mean pre- and postoperative spinal canal area, mean sagittal diameter, and anterior vertebral height compression rate. Moreover, the VAS and ODI scores continued to significantly improve at the last follow-up in each group. No difference was found in the prevalence of complications. A Figure: Preoperative lateral radiograph of a 34-year-old man with a high-grade L3 burst fracture (A). Two-year postoperative lateral radiograph showing no significant loss in Cobb s angle and an anterior vertebral height compression rate without complications (B). B Despite a high score, no significant difference was found in the clinical and radiological results and the complications. Therefore, indirect decompression using PLL ligamentotaxis was found to be a useful technique for patients who recieve a high McCormack s classification score. The authors are from the Department of Orthopedic Surgery, Kyungpook National University Hospital, Daegu, Korea. The authors have no relevant financial relationships to disclose. Correspondence should be addressed to: Woo-Kie Min, MD, PhD, Department of Orthopedic Surgery, Kyungpook National University Hospital, 200 Dongduk-ro, Jung-gu, Daegu, South Korea, (wkmin@knu.ac.kr). doi: / MAY 2013 Volume 36 Number 5 e567

2 Finding the optimal method of treatment for burst fractures of the thoracic and lumbar spine has been difficult. One of the key factors for fracture treatment is the reduction or resolution of the posterior portion of the vertebral body that is retropulsed in the spinal canal to minimize neurological deficits. 1,2 Two applicable techniques have been used: (1) an anterior approach through a corpectomy followed by substituting anterior vertebral body for graft or cage and (2) a posterior approach to the spine and ligamentotaxis using the tension of the posterior longitudinal ligament (PLL). 3,4 Ligamentotaxis is a method of indirect reduction of a fracture using a strong distraction force, which is transmitted through intact ligaments and capsules and helps restore skeletal structures. In spinal fractures with retropulsed fragments, lordosation and distraction with the internal fixator lead to the restoration of height, kyphosis correction, and, in many cases, canal widening using ligamentotaxis of the PLL. The choice of the anterior or posterior approach for short-segment implants was based on McCormack s classification, 5 which categorizes fractions by scoring them according to the amount of bony comminution, the apposition of fragments, and kyphotic deformity correction needed in the most injured vertebral body. A score of 6 points or lower (considered a low-grade fracture) indicates that only posterior pedicle screw-based, shortsegment implants and fusion (ie, pedicle screw insertion 1 level above and 1 level below a fracture) are recommended to withstand load transmission through the injured vertebral body itself along with the implant. A score of 7 points or higher (considered a high-grade fracture) indicates poor withstanding of load transmission due to severe comminution, which results in the need for augmentation of the anterior instrumentation and strut grafting. The use of pedicle screws for shortsegment implants of spinal fractures is a dangerous and inappropriate method to use for high-grade fractures. However, soft tissue injuries or ruptures, such as those to the PLL, vertebral disks, and ligamentum flavum, are not taken into account in this classification. Unidentified ligamentous ruptures, spontaneously reduced thoracolumbar subluxations or dislocations, and an inability to demonstrate the maximal displacement of any given injury by available imaging techniques are limitations of McCormack s classification because it does not measure the degrees to which the soft tissue injuries influence the stability of the injured vertebral body and reflect the severity of thoracolumbar vertebra. To the authors knowledge, no articles have reported results with only short-segment implants and PLL ligamentotaxis in highgrade thoracic and lumbar burst fractures. The efficiency of ligamentotaxis of the PLL and short-segment implants and fusion in McCormack s classification has not been proven. The purpose of this study was to compare the clinical and radiologic results of high- and low-grade burst fractures according to McCormack s classification that were treated with indirect decompression using PLL ligamentotaxis. Materials and Methods The authors performed a retrospective review of 72 patients (94 levels) with unstable thoracic and lumbar burst fractures who underwent surgical treatment between May 2004 and November 2011 by a single senior surgeon (M.W.K.). Institutional review board approval was obtained for this retrospective review. 1A 1B 1C 1D 1E Figure 1: Preoperative lateral radiograph of a 34-year-old man with a high-grade L3 burst fracture (A). Preoperative sagittal computed tomography scan showing approxiamtely 50% of comminution (2 points on McCormack s classification) (B). Preoperative coronal computed tomography scan showing at least 2-mm dispacement of more than 50% of a cross section body (3 points on McCormack s classification) (C). Immediate postoperative lateral radiograph showing the kyphotic angle corrected more than 10 (3 points on McCormack s classification) (D). Two-year postoperative lateral radiograph showing no significant loss in Cobb s angle and an anterior vertebral height compression rate without complications (E). Total McCormack s classification score was 8 points. e568 ORTHOPEDICS Healio.com/Orthopedics

3 Thoracolumbar Burst Fractures Jeong et al 2A 2B 2C 2D 2E Figure 2: Preoperative lateral radiograph of a 42-year-old man with a low-grade L3 burst fracture according to McCormack s classification (A). Preoperative sagittal computed tomography scan showing less than 30% comminution (1 point on McCormack s classification) (B). Preoperative coronal computed tomography scan showing at least 2-mm dispacement of less than 50% of a cross-section of the body (2 points on McCormack s classification) (C). Immediate postoperative lateral radiograph showing the kyphotic angle corrected approximately 4 (2 points on McCormack s classification) (D). Two-year postoperative lateral radiograph showing no significant loss in Cobb s angle and an anterier vertebral height compression rate without complications(e). Total points on McCormack s classification score was 5 points. Inclusion criteria were thoracic and lumbar burst fractures; a fractured posterior vertebral surface dislocated into the spinal canal; no neurological deficit; a minimum of 1-year follow-up; indirect decompression using the ligamentotaxis technique; and short-segment implants (1 level above and 1 level below the fracture). Exclusion criteria were a complete tear of the PLL as seen on magnetic resonance imaging and any neurolgical deficit. A total of 41 patients (46 levels) with Table 1 Patient Demographics Fracture Group Variable Low-grade High-grade P Mean age (range), y 37.1 (15-72) 38.8 (16-61).812 a Sex, No. M/F 11/7 15/8.806 b Mean BMI (range), kg/m ( ) 23.7 ( ).615 a FU duration (range), y 2.3 ( ) 2.3 ( ).925 a Time between injury and operation (range), d Abbreviations: BMI, body mass index; FU, follow up. a Independent t test. b Chi-square test (0.4-7) 2.37 (0.3-7).211 a burst fractures and a fractured posterior vertebral surface dislocated into the spinal canal but without neurological deficit were included in this study. For these 41 patients, complete pre- and postoperative records were available for retrospective evaluation, and a minimum of 1-year follow-up was available. Twenty-six men (30 levels) and 15 women (16 levels) with a mean age of 38.1 years (range, years) were operated on using a posterior approach and ligamentotaxis using the tension of the PLL. Mean follow-up was 2.3 years (range, years). Surgery was performed a mean of 2.8 days after injury (range, 0.3 to 7 days). Computed tomography-aided planimetry of the spinal canal was undertaken preoperatively and within 1 week postoperatively to determine the effect of kyphosis correction and spinal canal widening due to ligamentotaxis. The amount of damage to the PLL was evaluated using preoperative magnetic resonance imaging of the thoracic and lumbar spine. Patients with complete rupture of the PLL were excluded. Patients confirming the effect of ligamentotaxis through pre- and postoperative computed tomography without preoperative magnetic resonance imaging were included in the study. Causes of the fracture included a fall down (ie, a highenergy trauma) in 38 levels (34 patients), motor vehicle accidents in 5 levels (4 patients), and a slip down (ie, low-energy trauma)in 3 levels (3 patients). In the current study, fractures with severe comminution (defined by McCormack s classification as a total score of 7 or more points) were regarded as high-grade fractures (Figure 1) and fractures with mild comminution (defined MAY 2013 Volume 36 Number 5 e569

4 by McCormack s classification as a total score of 6 or fewer points) as low-grade fractures (Figure 2). Twenty-three patients (27 levels) in the high-grade fracture group were compared with 18 patients (19 levels) in the low-grade fracture group. No statistically significant differences were found between groups regarding age, sex, body mass index, time between trauma and surgery, and mean follow-up (Table 1). While in the prone position, all patients were operated on using a posterior approach and ligamentotaxis using the tension of the PLL, regardless of McCormack s classification grade. With the hip in extension, pedicle screws were placed 1 level above and 1 level below the fracture level (Figures 3A, B) and a rod contoured for lordosis was inserted. The first distraction was achieved using a spreader between a pedicle screw on the side of the unfractured body and the rod holder in the middle of the rod (Figures 3C, D). Then, the unilateral rod was removed and a pedicle screw was fixed at the fractured vertebra (Figure 3E). 6,7 The rod was reinserted through the 3 pedicle screws. The second distraction was achieved between pedicle screws (Figure 3F) and the same operative procedures were performed on the opposite side (Figure 3G). Restoration of vertebral height and Cobb s angle were confirmed using an intraoperative C-arm. Final tightening, decortication, and posterolateral fusion were performed after both rods were placed and tightened. In cases of double-level fractures, no difference in surgical procedure existed except for posterior instrumentation with short fusion on 2 injured levels. This method was applied to both singleand double-level fractures. Each level was measured independently. Patients were analyzed clinically using the Oswestry Disability Index (ODI), visual analog scale (VAS), and complication types and analyzed radiologically by measuring the spinal canal area, midsagittal 3A 3D 3B Figure 3: Preoperative lateral radiograph showing a burst fracture of L2 (A). Intraoperative anteroposterior fluoroscopic image showing the short-segment implant (B). Intraoperative photograph showing the first distraction using a spreader between a pedicle screw and rod holder (C). Intraoperative lateral fluoroscopic image after distraction (D). Intraoperative photograph showing the fixation of a pedicle screw on L2 (E). Intraoperative photograph showing the second distraction between pedicle screws (F). Final intraoperative lateral fluoroscopic image after the second distraction and tightenting (G). 3E 3C 3F 3G diameter, Cobb s angle, and anterior vertical compression ratio using serial radiographs. Comparisons were made between the 2 groups. Radiologic data, such as the spinal canal area, midsagittal diameter, Cobb s angle, and anterior vertical compression ratio, were collected immediately postoperatively. However, clinical data, such as the ODI and VAS, were obtained 2 weeks postoperatively. Clinical preoperative data were surveyed through telephone calls or postal mail. Preoperative computed tomographyaided planimetry scans were assessed using the PACS (G3; Infinitt, Seoul, Korea) system to determine the spinal canal area. Preinjury dimensions of the canal were estimated by averaging the canal dimensions of the adjacent vertebrae. Scans were taken a few days postopera- e570 ORTHOPEDICS Healio.com/Orthopedics

5 Thoracolumbar Burst Fractures Jeong et al 4A 4C Figure 4: Lateral radiographs showing the measurement of pre- (A) and postoperative (B) midsagittal diameter and axial computed tomography images showing pre- (C) and postoperative (D) spinal canal area stenosis. 4B 4D tively, and canals measurements were made by 5 coauthors (J.W.J., K.J.W., S.D.K., K.J.W., R.I.H.) who were not associated with patient selection or treatment. The mean of the 5 readings was used to obtain each value. To obtain a precise measurement of the encroachment of the spinal canal, the midsagittal diameter and spinal canal area were measured according to guidelines from Mumford et al. 8 For the current study, the mean preoperative midsagittal diameter and spinal canal area reduction differentiated independently from the fracture level by only a few percentage points. Postoperatively, the repositioning of the posterior vertebral bone had a greater effect on the measured spinal canal area (numerical difference between pre- and postoperative percentage value) because the area was measured to the power of 2. The measurement of the midsagittal diameter alone did not consider that the greatest dislocation of the vertebral fragment may not be located in the center, but in the periphery of the spinal canal. Moreover, the shape and size of the fragment were not measured (Figure 4). Thus, for a comprehensive statement of the compression of the spinal cord, the spinal canal area is the parameter of choice. To measure the degree of kyphosis improvement, the authors calculated the Cobb s angle and the anterior vertical compression ratio according to Jiang et al 9 (Figure 5). As with the midsagittal diameter or spinal canal area, the Cobb s angle and the anterior vertical compression ratio at the fracture level were measured pre- and postoperatively and at the last follow-up. A paired Student s t test was used to determine the differences between preand postoperative data in thoracic and lumbar burst fracture and the differences in continuous variables, both measured using VAS, ODI, Cobb s angle, anterior vertical compression ratio, spinal canal area, and midsagittal diameter, between the 2 groups. Differences between the rates and proportion of complications (ie, metal failure, neurologic deficit, thromboembolism, posttraumatic kyphosis, and adjacent spine disease) were assessed using the chi-square or Fisher s exact test. 10 All reported P values were 2-tailed. All statistical analyses were performed using SPSS version 18.0 software (SPSS Inc, Chicago, Illinois). A P value less than or equal to.05 was considered statistically significant. 5A 5B 5C 5D Figure 5: Lateral radiographs showing the measurement of pre- (A) and postoperative (B) anterior vertical compression ratio and pre- (C) and postoperative (D) Cobb s angle. Results For patients with a mean 2.3-year follow-up, mean stenosis of the estimated original spinal canal area decreased from 27.4% preoperatively to 21.8% immediately postoperatively (15.6%) (P5.004), and mean stenosis of the midsagittal diameter decreased from 30.8% preoperatively MAY 2013 Volume 36 Number 5 e571

6 Table 2 Between Group Comparison of Preop and Postop Cobb s Angle, avhcr, SCA, and MSD Stenosis Measurements Mean (Range) Radiologic Value Preop Measure Postop Measure P Difference, Mean (Range) P a, Mean (Range) Cobb s angle, deg.849 Low-grade fracture group 16.2 ( ) 3.7 ( ), ( ) High-grade fracture group 17.4 ( ) 4.9 ( ), ( ) avhcr, %.004 Low-grade fracture group 23.7 ( ) 11.1 ( ) ( ) High-grade fracture group 37.5 ( ) 14.0 ( ), ( ) SCA stenosis, %.015 Low-grade fracture group 18.0 ( ) 12.3 ( ) ( ) High-grade fracture group 39.3 ( ) 29.0 ( ), ( ) MSD stenosis, %.029 Low-grade fracture group 20.2 ( ) 16.3 ( ), ( ) High-grade fracture group 35.0 ( ) 27.2 ( ), ( ) Abbreviations: avhcr, anterior vertical compression ratio; deg, degree; MSD, midsagittal diameter; postop, postoperative; preop, preoperative; SCA, spinal canal area. a Group comparison. to 21.9% (18.9%) immediately postoperatively (P,.001). Mean VAS score increased from 7.72 (range, 6-10) preoperatively to 6.80 (range, 2-9) immediately postoperatively (P,.001), and mean ODI scores increased from 40.2 (range, 35-45) preoperatively to 35.1 (range, 10-41) immediately postoperatively (P,.001). The VAS scores and ODI continued to improve significantly by the last follow-up. For patients in the high-grade fracture group, mean stenosis of the estimated original spinal canal area decreased from 39.3% preoperatively to 29.0% immediately postoperatively (110.2%), and mean stenosis of the midsagittal diameter decreased from 35.0% preoperatively to 27.2% immediately postoperatively (17.8%) (P,.001). For patients in the low-grade fracture group, mean stenosis of spinal canal area decreased from 18.0% preoperatively to 12.3% immediately postoperatively (15.6%) (P5.001), and mean stenosis of midsagittal diameter decreased from 20.2% preoperatively to 16.3% immediately postoperatively (13.9%) (P,.001). Comparing the 2 groups, a significant difference was found in mean pre- and postoperative stenosis of the spinal canal area, midsagittal diameter, and amount of improvement (Table 2). In the high-grade fracture group, mean Cobb s angle decreased from 17.4% preoperatively to 4.9% immediately postoperatively (112.4%) (P,.001), and mean height of the anterior vertical compression ratio as an index of kyphosis decreased from 37.5% preoperatively to 14.0% immediately postoperatively (123.4%) (P,.001). In the low-grade fracture group, Cobb s angle significantly improved from 16.2% preoperatively to 3.7% immediately postoperatively (P5.001), and the anterior vertical compression ratio significantly improved from 23.7% preoperatively to 11.1% immediately postoperatively (P,.001). Comparing the 2 groups, a significant difference was found in the mean preoperative and immediately postoperative data for spinal canal area, midsagittal diameter, and the anterior vertical compression ratio (Table 2); however, at last follow-up, the measurements were significantly worse than those made immediately postoperatively (P5.001 for both). A greater loss of reduction was observed in the high-grade fracture group (Table 3). Mean VAS score significantly improved from 7.8 (range, 7-10) preoperatively to 7.4 (range, 6-9) immediately postoperatively (P5.048) in the highgrade fracture group and from 7.6 (range, 6-10) preoperatively to 6.0 (range, 2-9) immediately postoperatively (P5.001) in the low-grade fracture group. Mean ODI scores improved from 40.9 (range, 36-44) preoperatively to 36.1 (range, 21-41) immediately postoperatively (P,.001) in the high-grade fracture group and from e572 ORTHOPEDICS Healio.com/Orthopedics

7 Thoracolumbar Burst Fractures Jeong et al Table 3 Between Group Comparision of Immediate Postoperative and Last Follow-up Cobb s Angle and Anterior Vertical Compression Ratio (avhcr) Measurements Mean (Range) Radiologic Value Postop Measure Last Follow-up Measure P Cobb s angle, deg Low-grade fracture group 3.7 ( ) 6.9 ( ),.001 High-grade fracture group 4.9 ( ) 9.3 ( ),.001 avhcr, % Low-grade fracture group 11.1 ( ) 14 ( ),.001 High-grade fracture group 14.0 ( ) 20.9 ( ).001 Abbreviations: deg, degree; postop, postoperative; preop, preoperative (range, 35-45) preoperatively to 33.6 (range, 10-41) immediately postoperatively in the low-grade fracture group. (P5.002). The VAS and ODI scores continuously significantly improved at last follow-up (Table 4). These indicated a successful result of posterolateral fusion of vertebra that was confirmed with radiological evidence at the final follow-up. Complications included metal failure, neurologic deficit, thromboembolism, posttraumatic kyphosis, and adjacent spine disease. 11,12 The overall prevalence of complications was 37.0% (10 of 27 levels). No significant difference was found between the 2 groups. Metal failures, such as rod breakage, pedicle screw pull out, or screw breakage, occurred in 4 patients in the high-grade fracture group and 2 patients in the low-grade fracture group. Six patients were not treated with revision because they did not feel pain and they already had a posterolateral fusion of vertebra. No patients had neurologic deficits or thromboembolisms. Posttraumatic kyphosis was observed in 5 patients in the highgrade fracture group and 3 patients in the low-grade fracture group. No neurologic deficits or thromboembolisms were observed. Adjacent spine disease was found in 6 patients in the high-grade fracture group and 3 patients in the low-grade fracture group. No significant differences were found in the number of complications between the 2 groups (Table 5). Discussion Thoracic and lumbar burst fractures are common spinal injuries caused when a vertical load, with or without flexion, affects at least the anterior and middle columns of the spine. 13,14 Characteristic findings include vertebral body comminution, kyphotic deformity, and canal occlusion caused by retropulsion of the fracture segment, which can produce a neurological deficit Restoration of the spinal canal is 1 aim of internal fixator osteosynthesis. For thoracic and lumbar burst fractures, distraction and lordosation using the internal fixator contribute to this goal through ligamentotaxis. A precondition for ligamentotaxis is an intact PLL and attachment of the retropulsed fragments to the ligament. Tension on the ligament by distraction and lordosation may lead to repositioning, especially of smaller fragments, whereas large trapezoid-shaped fragments may resist reduction. 11 To the authors knowledge, no studies have re- Table 4 Between Group Comparison of Preop, Postop, and Last Follow-up VAS and ODI Scores Mean (Range) Mean (Range) Clinical Value Preop Score Postop Score P Postop Score Last Follow-up Score P Visual analog scale Low-grade fracture group 7.6 (6-10) 6.0 (2-9) (2-9) 2.9 (1-6),.001 High-grade fracture group 7.8 (7-10) 7.4 (6-9) (6-9) 4.6 (3-6),.001 Oswestry Disability Index Low-grade fracture group 39.4 (35-45) 33.6 (10-41) (10-41) 14.1(5-28),.001 High-grade fracture group 40.9 (36-44) 36.1 (21-41), (21-41) 19.6 (6-27),.001 Abbreviations: postop, postoperative; preop, preoperative. MAY 2013 Volume 36 Number 5 e573

8 Complication ported the results of posterior instrumentation and short-segment implants using ligamentotaxis of the PLL for the treatment of high-grade thoracic and lumbar burst fractures. The current study indicates that if the PLL was intact, short-segment implants and fusion alone could have positive clinical and radiological results regardless of whether fractures were classified as highor low-grade fractures. McCormack s classification, which does not take soft tissue damage into account, negates the status of the PLL. This means that if the PLL was intact, long fusion or anterior fusion would not be necessary. If the PLL is partially injured but has no neurological deficit, ligamentotaxis is an easy and effective technique that can enlarge the spinal canal. In cases of PLL rupture, in which ligamentotaxis does not work efficiently, anterior fusion or long fusion was needed. Several limitations to this study were found. First, it was a retrospective study. Second, it had a short follow-up period and a small study group size. Third, the surgical procedures for all patients were performed by a single surgeon to eliminate the surgeon variable on the outcomes. Large-scale, multicenter studies of more fracture types with participation of more Table 5 Between Group Comparison of Complications Low-grade Fracture Group surgeons are required to validate the current findings. The high-grade fracture group showed no significant difference in clinical or radiological results and complications compared with the low-grade fracture group. Indirect decompression using ligamentotaxis is a useful technique to use for high-grade fractures. References High-grade Fracture Group Metal failure Neurologic deficit 0 0 Thromboembolism 0 0 Posttraumatic kyphosis Adjacent spine disease a Fisher s exact test. 1. Hashimoto T, Kaneda K, Abumi K. Relationship between traumatic spinal canal stenosis and neurologic deficits in thoracolumbar burst fractures. 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