Single-Level Fixation of Flexion Distraction Injuries

Transcription

1 Journal of Spinal Disorders & Techniques Vol. 16, No. 3, pp Lippincott Williams & Wilkins, Inc., Philadelphia Single-Level Fixation of Flexion Distraction Injuries * Joel A. Finkelstein, Eugene K. Wai, Steven Shlomo Jackson, Henry Ahn, and Michael Brighton-Knight Divisions of *Orthopaedic Surgery and Orthopaedics, Sunnybrook and Women s College Health Sciences Center; Department of Orthopaedic Surgery, University of Toronto, Toronto, Ontario, Canada; and Austin & Repatriation Medical Center, Heidelberg, Australia Summary: Flexion distraction injuries of the thoracic and lumbar spine can be stabilized with a short construct spanning one motion segment. This surgical technique has not been well accepted because of the paucity of published outcomes of patients treated in this manner. The current study is a cohort of patients who underwent a standardized posterior open reduction and single-level fixation for this injury pattern. Independent observation prospectively followed the cohort for a minimum of 20 months with functional and radiologic outcomes determined. A significant (p < ) correction of deformity was achieved, from a mean preoperative kyphosis of 10.1 to a mean postoperative lordosis of 0.9. No loss of correction occurred. The mean Oswestry score was 11.5, with 88% of patients having minimal disability. This prospective study demonstrates the efficacy of posterior open reduction and single-level fixation of flexion distraction injuries. Key Words: Flexion distraction injury Spine fracture Spinal instrumentation Functional outcome. INTRODUCTION Flexion distraction injuries (FDIs) of the spine result from high-energy forces to the trunk (1). They are frequently associated with intraabdominal pathology and may be associated with neurologic injury. Classification has used various systems to define the injury (2 6). This fracture is functionally defined by the loss of integrity of the tension band of the spine, posterior column, which has failed in tension. The posterior vertebral body will also have failed in tension. The anterior column fails in compression because of a flexion force through the anterior column. Closely related to this injury is the Chance fracture whereby the anterior column fails in tension and there is no compression of the anterior vertebral body (7 9). Because these injuries behave in a biomechanically similar fashion, they are often treated similarly (1) (Fig. 1). Received December 31, 2002; accepted February 21, Address correspondence and reprint requests to Dr. Joel A. Finkelstein, Sunnybrook and Women s Health Sciences Center, 2075 Bayview Ave, Rm MG 361, Toronto, Ontario M4N 3N5, Canada. joel.finkelstein@utoronto.ca Treatment of a solely bony injury with minimal deformity (Chance type) is usually nonoperative in an extension brace. Associated intraabdominal pathology and ligamentous spinal instability are relative indications to treat these injuries surgically. Deformity of >17 of kyphosis has been shown to have a poor prognosis clinically (10) and represents true instability in vivo (11). In the absence of severe loss of anterior column height, surgical treatment has been mainly through a posterior approach with instrumentation. Controversy exists, however, about which construct to use and the number of motion segments to include in the construct. Many authors have demonstrated multilevel instrumentation techniques both in distraction and compression (12). Others have proposed shorter constructs to maintain motion segments, particularly in the lumbar spine (13,14). No large prospective study has been conducted to examine the results of short segmental fixation. The current prospective study was designed for the purpose of addressing the efficacy of single motion segment fixation for FDI by evaluating the radiographic and functional results of this treatment technique. 236

2 FIXATION OF FLEXION DISTRACTION INJURIES 237 FIG. 1. Common variants of posterior column distraction injuries. A and B: Failure in tension of all columns. A: Bony injury (Chance type). B: Soft tissue disruption. Combination of bone and ligamentous injuries may also occur. C: Failure in tension of the posterior column, with failure of the anterior column in compression. METHODS All patients with a diagnosis of FDI were prospectively identified over a 48-month period from January 1996 to December Flexion distraction injury is defined by a distractive injury to the posterior column and an intact anterior longitudinal ligament (5). Compression of the anterior column is common. However, if the fulcrum of injury lies anterior to the anterior longitudinal ligament, the anterior column will fail in tension and create the Chance fracture subset of injuries. As has been noted above, both injury patterns share the same biomechanical properties and are often treated in a similar fashion. For purposes of this study, we have combined these injuries under the single designation, FDI. Nonoperatively treated fractures were excluded. Patients with other spine fractures, i.e., AO-ASIF type A or type C, were excluded (5). The indication for surgery was unsuitability for extension bracing, failure of bracing, and predominance of a ligamentous injury. Patients with noncontiguous spine fractures that included an FDI were included. Demographic information, comorbid conditions, other injuries, neurologic status, operative details, and complications were recorded. Plain radiographs and CT scans were available on all patients preoperatively. Preoperative radiographic review included an assessment of the specific injury to the posterior columns distinguishing a predominantly ligamentous or bony injury. Injury from T1 to T10 was defined as thoracic, T11 to L2 as thoracolumbar, and L3 to L5 as lumbar. Focal kyphosis was determined by measuring the Cobb angle (15) of the superior endplate of the first intact vertebrae above and below the injured level. Postoperative radiologic evaluation included a radiograph within 1 week of surgery and the most recent upright radiographs. These were evaluated for focal kyphosis and instrumentation failure. Radiographic progression was defined as a >5 increase in kyphosis between the initial postoperative radiographs and the most recent radiograph (16). Radiographic reviewers were blinded to the functional outcome of the patient and the time of follow-up. The Oswestry Functional Assessment Questionnaire (17) was administered by mail at follow-up. This provided the most recent evaluation of a patient s back-related postoperative disability. Statistical Analysis Preoperative and postoperative radiographs were compared using paired t tests. Student t test or Pearson s correlation was used to determine any relationship between Oswestry score and other variables. Ad hoc power analysis demonstrated that with a power of 0.8, alpha of 0.05, and standard deviation of 8, there would be sufficient power to detect a 5.1 difference in kyphosis. Surgical Technique All patients were positioned prone on bolsters. Their hips were extended to facilitate reduction of the fracture. Neural monitoring was used routinely. A midline posterior approach was performed. The extent of the injury was defined. This commonly demonstrated significant disruptions of posterior soft tissue structures, including facet capsule, interspinous ligament, ligamentum flavum, and epidural veins. On occasion, tears in the dural sac were noted. Posterior decompression was performed to ensure that the disrupted soft tissues did not compress neural elements during final reduction. Decompression also included undercutting the disrupted lamina and evacuation of any epidural hematoma from the enlarged epidural space. Interspinous wiring of the adjacent levels reduced the fracture. The facets and other bony structures were used to judge an anatomic reduction. Overcompression was avoided. Only the injured motion segment was stabilized. If the pedicles were intact, screws were inserted at the two adjacent levels. Laminar hooks were used when pedicles were not available because of fracture or insufficient pedicle diameter. The screws or hooks were connected with rods as a neutralization construct (Fig. 2). Iliac crest autograph was placed between the transverse pro-

3 238 J. A. FINKELSTEIN ET AL. FIG. 2. A and B: Posterior distraction and anterior compression. C and D: Eighteen-month postoperative films. Maintenance of reduction with posterior fixation of a single motion segment.

4 FIXATION OF FLEXION DISTRACTION INJURIES 239 cesses to facilitate posterolateral bony fusion. Patients were mobilized immediately in a hyperextension brace for 6 weeks, worn only when ambulating. Two patients over the period of the study were not stabilized with single-level fixation despite an FDI. One patient had stabilization performed with anterior instrumentation. Another patient with a T3 T4 FDI required instrumentation to be placed such that an extra level was included because of small lamina size in the upper thoracic spine. RESULTS Between 1996 and 2000, a total of 22 consecutive patients were identified (Table 1). One patient was excluded because he required transfer to another institution resulting from insufficient bed resources. The average age at surgery was 27.9 years (range, years). There were 14 females and seven males. Significant preoperative comorbidities included one patient with bipolar affective disorder and one patient with systemic lupus erythematosus (Table 1). The most common associated injuries were head and abdomen, whereas eight patients (38%) sustained an isolated injury to the spine. Two fractures (10%) involved the thoracic region, 13 (62%) involved the thoracolumbar region, and 6 (28%) involved the lumbar region (Table 1). Eleven fractures (52%) were classified as primarily bony, and 10 fractures (48%) were classified as primarily ligamentous (Table 1). The average preoperative kyphosis measured 10.1 (standard deviation 8.7 ). One patient had an incomplete neurologic injury, and one patient had a complete neurologic injury related to a thoracic fracture dislocation at a noncontiguous level above her FDI. The average operating time was 2.8 hours (range, 2 4 hours) and average estimated blood loss was 676 ml (range 200 2,400 ml). All patients had improvements in their sagittal alignment postoperatively with an average improvement of 12.8 following surgery. Of the 21 eligible patients, 17 had adequate follow-up radiographs (81%) with an average final follow-up of 17.6 months (range, 9 36 months). The average initial postoperative focal kyphosis was 0.9 (standard deviation 10.5 ), and at the latest follow-up, the final focal lordosis was 0.5 (standard deviation 11.3 ). There was a significant improvement between preoperative and postoperative values (t 5.0, p < ) and no difference between initial postoperative and final postoperative radiographs (t 0.6, p 0.54). The maximum amount of progression between initial postoperative and final postoperative values was 4. At final follow-up, the average kyphosis was 11 at the thoracic level, 3.6 at the thoracolumbar level, and there was an average of 13.4 lordosis at the lumbar TABLE 1. Summary of consecutive patients with flexion distraction injuries Patient no. Age (yr)/sex Injury Associated injuries/ comorbidity Preoperative kyphosis Operative procedure a Immediate postoperative kyphosis Latest postoperative kyphosis Oswestry Notes 1 23/F L1 Bony Abdo/UE/LE/pelvis/chest 20 T11 L1 LH 0 0 n/a Epidural hematoma 2 24/F T12 Bony 15 T11 T12 LH /F L1 Bony Abdo/UE/pelvis 10 T12 LH & L1 PS /M L2 Bony Pelvis/bipolar 15 T12 L2 Ant Broken screw 5 17/F T5 T6 Ligamentous Abdo/head/UE/LE 4 T5 T6 PS Instrumentation 6 22/F T12 Bony 21 T11 T12 LH /M L1 Bony Head 10 T12 L1 LH /M T12 Bony LE 18 T12 L1 PS 2 n/a n/a Died 2 yr postop 9 51/M L4 L5 Ligamentous 7 L4 L5 PS /F L3 Ligamentous Head/LE 0 L2 L3 PS /F T12 L1 Ligamentous UE/spine 19 T11 T12 PS Instrumentation 12 29/M L3 Bony 24 L2 L3 PS Instrumentation 13 16/F L3 L4 Ligamentous Abdo 7 L3 L4 LH 8 8 n/a 14 21/M L1 L2 Ligamentous 0 L1 L2 LH Instrumentation 15 46/F L4 L5 Ligamentous Abdo/head/SLE 5 L4 L5 PS /F L1 L2 Ligamentous Head 3 L1 L2 LH 6 8 n/a 17 20/M T11 T12 Ligamentous Abdo 7 T11 T12 LH 3 n/a 5 Postoperative pneumonia 18 33/F L1 Bony Head/UE 15 T12 L1 LH /F L2 Bony 8 L2 L3 LH 10 n/a /F L3 L4 Ligamentous 5 L2 L3 LH 8 n/a /F T4 Bony 20 T3 T5 LH Abdo, abdominal injury requiring laporatomy; Bipolar, bipolar affective disorder; Chest, chest injury; LE, lower extremity fracture; LH, laminar hook; n/a, not available; Pelvis, pelvic fracture; PS, pedicle screws; SLE, systemic; lupus erythematosus; UE, upper extremity fracture; Ant, Anterior approach, corpectomy and instrumented fusion. a All posterior procedures were also reduced and instrumented with instraspinous wiring.

5 240 J. A. FINKELSTEIN ET AL. level. Four patients did not have long-term radiographic follow-up. One moved out of the province, one died, and the others failed to return. Functional review was available in 17 patients (81% follow-up) with an average follow-up of 29 months (range, 9 52 months). The average Oswestry score was 11.5 (range, 0 41). Fifteen patients (88%) reported minimal disability. One patient reported moderate disability, and one patient reported severe disability. The presence of a significant abdominal injury was associated with greater disability in Oswestry scores (t 2.2, p 0.04) and may represent the severity of the initial trauma. With the numbers available, there was no relationship between Oswestry score and kyphosis, age, gender, location of spine injury, type of FDI, or other injuries. Four patients did not have functional review. One died, and one was advised by her insurance company to decline review follow-up. Two others failed to return questionnaires. There were two complications in the immediate postoperative period. One patient who was neurologically intact immediately postoperatively developed a cauda equina syndrome from an epidural hematoma, possibly related to antithrombotic prophylaxis, on the second postoperative day. Immediate surgical decompression was performed, and the patient recovered full neurologic function. As a result of this, we no longer routinely anticoagulate for FDI. One patient developed pneumonia postoperatively. One patient died at 2 years postoperatively for reasons unrelated to the spinal surgery. Four (18.1%) patients required instrumentation removal for prominence and local irritation. One patient with the anterior implant had a broken screw. There was no radiographic evidence of instrumentation failure on any patients operated on posteriorly. DISCUSSION The mechanism of FDI has been theorized for decades (3,9,18,19). The increase in incidence associated with laponly seat belts led authors to assume that a distraction force over a fulcrum was the etiology (9,20). However, this failed to explain the frequently observed anterior body compression (21). In vivo modeling using crash-test dummies suggested considerable axial compression forces in motor vehicle accidents (22). To explain these FDI compression injuries, it was hypothesised that in motor vehicle accidents an initial distraction injury was followed by a compression injury, as the patient was first flung forward and then back into the seat (3). However, FDIs occur in situations in which no external fulcrum exists and no obvious tension force exists (23). A model proposed by Hoshikawa et al. (24) shows in vivo how compression forces alone can create these injuries. Depending on the degree of flexion of the spine that exists when compression is applied, completely different injuries occur. As flexion occurs, the fulcrum around which compression is applied moves progressively anterior, from within the vertebrum to within the abdomen. Compression without flexion causes burst fractures. With moderate flexion there is FDI with anterior body compression. With increasing flexion, FDI becomes entirely distractive (Fig. 3). Thus, in motor vehicle accidents, the seat belt is not a fulcrum but the device that either permits or prevents spinal flexion as compression is applied. This explains the observation that for frontal motor vehicle collisions with the same impact mechanism, there is an increased burst fracture incidence with lap-sash seat belts, which prevent flexion, compared with an increase in FDI seen with lap-only belts, which permit spinal flexion (25). This also explains the high incidence of hollow viscus injuries in FDI as the hollow visci are burst by compression of the abdomen, rather than distraction. This concept of a single destructive force acting around a fulcrum is useful when considering management. As the forces are concentrated at a single point, reconstruction only requires that this location be addressed. Because all FDIs are created by the same mechanism, regardless of structures injured only short segment fixation is required. Although there are many different classification systems for FDI (2 6), each with multiple subcategories, this injury pattern is homogenous because of the mechanism described above. Indeed, subcategorization complicates a relatively simple pattern and in our series did not change management. Biomechanically, FDI (inclusive of the Chance fracture pattern) involves a failure of the posterior tension band with an intact anterior hinge. As such, FDIs are amenable to a uniform reconstructive approach that is closing the disrupted posterior interval and restoring the tension band. Despite this, a review of the literature has failed to identify a single prospective case series supporting this principle. Instead, multiple surgical approaches, often involving violation of intact structures, have been presented in the literature. Some authors have suggested that distraction is appropriate when an FDI is associated with a compression injury of the anterior vertebral body (3,26). They thought that posterior compression alone would fail because of a lack of anterior support; and with an intact anterior column, then posterior compression instrumentation was satisfactory. Other authors, however, have not made this distinction and have recommended distraction instrumentation even with intact anterior column support to minimize the risk of a disc extrusion caused by compression instrumentation (27 29). Flexion distraction injury is a canal opening injury with operative reduction leading to canal narrowing. This di-

6 FIXATION OF FLEXION DISTRACTION INJURIES 241 FIG. 3. Motion axis of fracture. A: Axial compression force without any vertebral column flexion will result in the Burst-type fracture pattern. B: Axial compression force with restricted flexion (as with a shoulder/lap seat belt). This results in posterior column disruption in tension, with anterior column compression. C: Axial compression force with unrestricted flexion (as with a lap-only seat belt). This will result in distraction injury of all three columns of the spine. [Adapted from Hoshikawa et al.) rectly contrasts to burst fractures, which are a canal compressing injury, with reduction resulting in an expanded canal. For FDI, care must be exercised to evacuate the soft tissue, which may invaginate during reduction. Epidural veins are likewise disrupted by tension and prone to bleed more so than in the burst fracture. Recognizing the potential risk of canal compromise, we have uniformly performed a small laminotomy, removing the disrupted ligamentum flavum, and evacuated the local hematoma. We further undercut the lamina adjacent to the fracture to ensure no neural compression. Using these precautions, there is no argument to be made for distraction instrumentation. A further safeguard to neural injury is the use of SSEP and/or motor evoked potentials for lumbar level injury. Following decompression a gentle and controlled reduction technique using interspinous cables can be performed. The use of modern hook/pedicle screw and rod systems generates significant compressive forces; however, they offer less control for reduction than the use of an interspinous cable. The posterior position of the cable around the spinous process permits posterior compression with little anterior effect. Final alignment can be judged by facet apposition. Following reduction, laminar hooks, pedicle screws, and rod construct are used only as a neutralization device. In our series, there was no loss of alignment, and presence or absence of anterior column compression had no effect on outcome. Although controversy has occurred in the treatment of burst fractures, with advocates of both short (30) and long fixation (31), FDI should be considered a completely different entity. Several authors have recommended multilevel compressive fixation for stabilization of FDI (3,28, 29). The disadvantage of multilevel instrumentation is loss of adjacent level motion segments. Preservation of motion segments is desired if at all possible. Single motion segment fixation has been described by Liljenqvist and Mommsen (13) and Greenwald and Mann (14). However, they had only described this technique in case reports. We have demonstrated that, in FDI, single-level fixation is biomechanically sound. Furthermore, an injury to lamina or pedicle at the zone of injury did not preclude use of that lamina to seat stable hooks in compression. There is rarely a need to bypass the injured level and, as such, single motion segment fixation can be maintained. The absence of a control group precludes absolute conclusions as to the beneficial effects of single motion segment fixation compared with multilevel fixation. Nonetheless, with the exception of two patients, one of which had a significant pre-injury comorbidity of systemic lupus erythematosus, all patients reported minimal disability related to their back and had excellent radiologic outcomes.

7 242 J. A. FINKELSTEIN ET AL. We think this demonstrates that fixation of further motion segments is unnecessary. When adhering to this surgical protocol with care taken to decompress the epidural space, this study demonstrates that posterior reduction and stabilization of a single motion segment for FDI can adequately stabilize the spine and lead to excellent functional outcomes. REFERENCES 1. Anderson PA, Henley MB, Rivara FP, et al. Flexion distraction and chance injuries to the thoracolumbar spine. J Orthop Trauma 1991; 5: Denis F. The three-column spine and its significance in the classification of the acute thoracolumbar injuries. Spine 1983;8: Gertzbein SD, Court-Brown CM. Flexion-distraction injuries of the lumbar spine: mechanisms of injury and classification. Clin Orthop 1988;227: Gumley G, Taylor TK, Ryan MD. Distraction fractures of the lumbar spine. J Bone Joint Surg Br 1982;64: Magerl F, Aebi M, Gertzbein SD, et al. A comprehensive classification of thoracic and lumbar injures. Eur Spine J 1994;3: Triantafyllou SJ, Gertzbein SD. Flexion distraction injuries of the thoracolumbar spine: a review. Orthopaedics 1992;15: Bohler L. The Treatment of Fractures, 4th ed (English). Bristol, UK: John Wright & Sons, Chance GQ. Note on a type of flexion fracture of the spine. Br J Radiol 1948;21: Howland WJ, Curry JL, Buffington CB. Fulcrum injuries of the lumbar spine. JAMA 1965;193: LeGay DA, Petrie DP, Alexander DI. Flexion-distraction injuries of the lumbar spine and associated abdominal trauma. J Trauma 1990; 30: Neumann P, Nordwall A, Osvalder AL. Traumatic instability of the lumbar spine: a dynamic in vitro study of flexion distraction injury. Spine 1995;20: Bohlman HH, Ducker TB, Levine AM, et al. Spine trauma in adults. In: Herkowitz, ed. The Spine, 4th ed. Philadelphia: Saunders, Liljenqvist U, Mommsen U. Surgical treatment of thoracolumbar spinal fractures with internal fixator and transpedicular spongiosaplasty [in German]. Unfallchirurgie 1995;21: Greenwald TA, Mann DC. Pediatric seat belt injuries: diagnosis and treatment of lumbar flexion-distraction injuries. Paraplegia 1994; 32: Cobb J. Instructional Course Lecture: outline for study of scoliosis. Am Acad Orthop Surgeons 1948;5: Carman DL, Browne RH, Birch JG. Measurement of scoliosis and kyphosis radiographs: intraobserver and interobserver variation. J Bone Joint Surg Am 1990;72: Fairbank JC, Couper J, Davies JB, et al. The Oswestry low back pain disability questionnaire. Physiotherapy 1980;66: Green DA, Green NE, Spengler DM, et al. Flexion distraction injuries to the lumbar spine associated with abdominal injuries. J Spinal Disord 1991;4: Fletcher BD, Brogdon BG. Seat-belt fractures of the spine and sternum. JAMA 1967;200: Rennie W, Mitchell N. Flexion distraction fractures of the thoracolumbar spine. J Bone Joint Surg 1973;55B: Strum PF, Glass RB, Sivit CJ, et al. Lumbar compression fractures secondary to lap-belt use in children. J Pediatr Orthop 1995;15: Begeman PC, King AI, Prasad P. Spinal loads resulting from G acceleration. In: Proceedings of the 17th Stapp Car Crash Conference. New York: New York Society of Automotive Engineers, 1973: Hall HE, Robertson WW Jr. Another chance: a non-seat belt related fracture of the lumbar spine. J Trauma 1985;25: Hoshikawa T, Tanaka Y, Kokubun S, et al. Flexion-distraction injuries in the thoracolumbar sine: an in vitro study of the relation between flexion angle and the motion axis of fracture. J Spinal Disord Tech 2002;15: Ball ST, Vaccaro AR, Albert TJ, et al. Injuries of the thoracolumbar spine associated with restraint use in head on motor vehicle accidents. J Spinal Disord 2000;13: Jeanneret B, Ho PK, Magerl F. Burst-shear flexion-distraction injuries of the lumbar spine. J Spinal Disord 1993;6: Heller JG, Garfin SR, Abitbol JJ. Disk herniations associated with compression instrumentation of the lumbar flexion-distraction injuries. Clin Orthop 1992;284: Levine AM, Bosse M, Edwards CC. Bilateral facet dislocations in the thoracolumbar spine. Spine 1988;13: McGuire RA Jr, Freeland AE. Flexion-distraction injury of the thoracolumbar spine. Orthopaedics 1992;15: Benzel EC. Short-segment compression instrumentation for selected thoracic and lumbar spine fractures: the short-rod/two-claw technique. J Neurosurg 1993;79: McLain RF, Sparling E, Benson DR. Early failure of short-segment pedicle instrumentation for thoracolumbar fractures: a preliminary report. J Bone Joint Surg Am 1993;75:162 7.