Stabilization of subaxial cervical spinal injuries

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Stabilization of Subaxial Cervical Spinal Injuries VanBuren Ross Lemons, M .D., and Franklin C . Wagner, Jr., M.D. Department of Neurological Surgery, University of California, Davis, California

Lemons VR, Wagner FC Jr. Stabilization of subaxial cervical spinal injuries . Surg Neurol 1993 ;39 :511-18 . With subaxial cervical spine fractures, it has not been established which injuries can be adequately stabilized by external orthoses and which will require surgical stabilization . After review of 64 consecutive patients with C 3 -C, spinal injuries, fracture characteristics on admission roentgenograms were identified that accurately predict the success or failure of nonoperative management . These include evidence of severe ligamentous injury (SLI) and severe vertebral body injury (SVBI) . The presence of SLI, SVBI, or both SLI and SVBI correlated strongly with nonoperative stabilization failure (p < 0 .001, p = 0.002, and p = 0 .004, respectively) . Injuries without SLI or S VBI were all successfully stabilized by cervical orthoses . Additionally, characterizing injuries by evidence of SLI and SVBI directs the approach for surgical stabilization . Cervical fractures ; Spinal instability ; Spinal stabilization ; Halo-vest KEYWORDS :

Following cervical spinal injury, stabilization of the injured motion segment remains a primary management goal . As the diagnosis of spinal instability has become clearer, its management remains controversial . Failure to adequately stabilize the injured cervical spine can result in loss of fracture reduction and spinal deformity, which, in turn, may produce neurologic deterioration and chronic pain syndromes [24,26) . Over the last 20 years, the halo-vest has been used extensively to stabilize cervical spinal fractures . The reported success rate of halo stabilization is misleading because atlantoaxial injuries are typically combined with subaxial injuries . When C I and C, fractures are factored out, halo stabilization failure varies between 23 and 41% for C 3C, fractures [5,9,16,29,33) . Previous descriptions of spinal instability do not adequately predict the success or failure of nonoperative stabilization [11,19,28,31,331 . Although Denis' modifi-

cation of Holdsworth's approach to spinal instability has been applied to cervical fractures, it remains uncertain how to translate this three column concept into indications for surgical or nonsurgical stabilization [10,11,19,371 . Sears and Fazi [33) reported no correlation between the number of columns injured and the outcome of halo-vest stabilization . Similarly, the work of White and Panjabi [401 has served to define clinical instability, but it has not been established which unstable injuries can be adequately stabilized by cervical orthoses and which will require surgical stabilization . We propose that the severity of injury to the major stabilizing structures of the cervical spine will determine the instability of the injury, predict the outcome of nonoperative stabilization, and guide the approach for optimal stabilization . In its basic design, the vertebral column consists of ligamentous structures holding osseous structures in place . Consequently, with significant injury to the ligamentous structures, there will be inadequate tension between osseous structures to maintain cervical alignment under physiologic loads [30) . Of the osseous structures, only the vertebral body plays a significant role in spinal stability by resisting axial loads [32) . The facets in the cervical spine bear only a minor portion of axial loads, and, because of their relatively horizontal orientation, contribute only modestly to resisting rotational forces . The remaining osseous structures assist in stability only by serving as an insertion for ligamentous structures . Therefore, we suggest that the severity of injury to the ligamentous structures and vertebral bodies will determine the stabilization requirements . In the present study, the clinical course and diagnostic imaging studies of 64 consecutive patients with cervical subaxial spine injuries were reviewed . We have sought to identify characteristics of the injuries that would predict the success or failure of nonoperative stabilization and that would direct the optimal approach for surgical stabilization .

Methods and Materials Address reprint requests to : VanBuren

R . Lemons, M .D ., Department of Neurological Surgery, 2516 Srockton Blvd ., Room 254, Sacramento, CA 95817 . Received December 28, 1992 ; accepted January 7, 1993 . 3 ; 1993 by Elsevier Science Publishing Co ., Inc

The study population consisted of all patients who presented to the University of California, Davis, Medical Center with nonpenetrating cervical subaxial spinal cord 0090-30191931$6 .00



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and spine injuries (C3-C,) during a four and a half year period from January 1986 through June 1990 . The neurological status of each patient was graded at admission and follow-up . A 10 point grading system was utilized which establishes the level of spinal cord injury and quantifies motor and sensory function below that level [7] . The percent of lost neurological function recovered was determined at follow-up by dividing the actual recovery (follow-up score minus admission score) by the potential recovery (10 minus admission score) . In addition, the presence of neck pain was recorded and graded at follow-up . The diagnostic imaging studies obtained at the time of admission and follow-up in each case were extensively reviewed . Multiple fracture characteristics were evaluated, including the type and extent of bony and ligamentous injury and the degree to which spinal deformation was corrected . Fractures were classified according to the mechanism of injury [1,26] . Vertebral body injuries were assessed by comparing the height of injured and uninjured, adjacent vertebral bodies and recorded as a percentage of lost vertebral body height . Ligamentous injuries were evaluated by determining the percent displacement of one vertebral body on another, the degrees of angular deformity in the sagittal plane, and the amount of distraction with the application of axial traction . Magnetic .resonance imaging findings of disruption of the anterior or posterior longitudinal ligaments, hemorrhage or interruption of the intraspinous ligament, and damage to the interverrebral disc were considered further evidence of ligamentous injury [14,38] . Fracture reduction was considered successful if there was no significant translational deformity ( :
Results Sixty-four patients with middle to lower cervical spinal cord and spine injuries (C 3-C7) were admitted to the University of California, Davis, Medical Center from January 1986 through June 1990 . Their ages ranged

Lemons and Wagner

from 14 to 93, with a mean of 32 . Most injuries resulted from traffic accidents (n = 39) and diving accidents (n = 16). Follow-up examinations were performed at a minimum of six months after injury, with a mean follow-up of 16 months. Except for two patients who died within five weeks of injury, no other patients were lost to follow-up . On admission, 32 patients presented with a complete transverse myelopathy and 32 patients with an incomplete myelopathy. All patients underwent a complete series of roentgenograms and computerized tomography (CT) of their injury at the time of admission . There were 14 compression injuries, 12 flexion-compression/distraction injuries, 12 unilateral facet fracture/dislocations, 16 bilateral facet fracture/dislocations, and 10 hyperextension injuries. Follow-up radiographs were obtained at a minimum of three months postinjury, and the mean radiographic follow-up period was five months . Additionally, 27 patients underwent MR studies at the time of admission . In 91 % of cases, the fractures were successfully reduced by nonoperative means . Once satisfactorily reduced, the injuries were initially stabilized by external orthosis in 38 patients and by surgery in 26 patients . Of the patients initially stabilized by a halo-vest orthosis, fracture reduction could not be maintained in 16 cases (42%) . Nine of these patients developed recurrent translational deformity, typically occurring within the first week (mean of 7 .6 days) following placement of the halo-vest orthosis . Three other patients developed a combination of recurrent translational deformity and worsening kyphotic deformity within 10 days of treatment with a halo-vest . These 12 patients went on to surgical stabilization . The final four patients demonstrated a more gradual progression of their kyphotic deformity in which their sagittal angulation increased by over 15° by three months postinjury . In these patients, no attempt was made to correct their kyphotic deformities . The fracture patterns of 16 patients who were not successfully stabilized by the halo-vest orthosis included : three compression injuries, five flexion-compression/ distraction injuries, four unilateral and four bilateral facet fracture/dislocations . There was no correlation between the mechanistic fracture classification and stabilization failure with the halo-vest orthosis . The characteristics on admission radiographs that correlated best to these halo-vest stabilization failures included: translational deformity at or exceeding 20% of the corresponding vertebral body width, sagittal angulation of 15° or greater, a positive "stretch test" [40] and decreased vertebral body height by 40% or greater compared to an adjacent level . The translational and sagittal angulation deformities of this magnitude as well as the positive "stretch test" cannot occur without extensive



Stabilization of Subaxial Cervical Spinal Injuries

ligamentous rupture or laxity (Figure 1) . Therefore, these characteristics were considered indicative of severe ligamentous injury (SLI) . Vertebral body injuries of sufficient magnitude to result in loss of vertebral body height by 40% or greater represented severe vertebral body injury (SVBI) . SLI occurred in 37 cases, and SVBI was found in 16 cases . SLI and SVBI occurred in combination in 12 cases . SLI was diagnosed by translational deformity in 11 cases, kyphotic deformity in 3 cases, positive "stretch test" in I case, and a combination of the above in 22 cases . Evidence of SLI, SVBI or both SLI and SVBI correlated strongly to nonoperative stabilization failure (p < 0 .001, p = 0 .004, and p = 0 .002, respectively) . Injuries without evidence of SLI or SVBI (23 cases) were all adequately stabilized by cervical orthosis alone . As Figure 2 demonstrates, this criterion provided no false positive or false negative predictions of halo stabilization failure . Although MRI was more sensitive in detecting ligamentous injuries (Figure 3), these findings did not correlate to nonoperative stabilization failure . Further, no other fracture characteristics on roentgenograms, CT scans or MR studies could be identified which would adequately predict halo stabilization failure . Thirty-eight patients ultimately underwent surgical stabilization . Twenty-six patients were stabilized by posterior fixation and fusion, which included spinous process and facet wiring techniques, as well as lateral mass

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Figure 1 . Roentgenograms demonstrating evidence of SLI : translation greater than 20% of the corresponding vertebral body width indicative of severe injury or disruption of the anterior and posterior longitudinal ligaments, the intervertebral disc, and usually the facet joints and posterior ligamentous structures (A) ; sagittal angulation greater than 15 degrees suggesting rupture or laxity of the interspinous ligament, ligamentum flarum, facet joints, and posterior longitudinal ligament (8) ; and positive 'stretch test" demonstrating incompetence of all ligamentous structures (C) .

plating . Cervical corpectomies with iliac crest or fibular strut graft fusions were performed in four patients . Both anterior and posterior operations were carried out in eight patients . Of the patients stabilized surgically, fracture reduction could not be maintained in five cases . All of these injuries which failed surgical stabilization had evidence of both SLI and SVBI . In two of these cases initially managed by posterior fixation and fusion along with a halo-vest orthosis, one patient redeveloped kyphotic angulation by 10 days postoperatively and went on to corpectomy, and the other patient developed a more gradual kyphotic angulation by 2 months postoperatively which was not corrected . Of the other three patients who were initially managed by corpectomy, strut graft, and halo-vest orthosis, two developed recurrent translational deformity by two weeks postoperatively and underwent posterior fixation and fusion, and the other patient redeveloped kyphotic angulation by three months postoperatively which was not corrected . All injuries characterized by both SLI and SVBI were



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100 -

Underwent Surgical Stabilization

90 d t.. 7 •

LL C O

∎ Allowed to Heal In Deformity

80 70 60 -

•

N

50 -

•M

40

O

4+

U)

30 -

°

20 10 0%

su

SVBI

Figure 2 . Percent halo-vest stabilization failure for injuries with SLI . SVBI, both SLI and SVBI, and neither SLI nor SVBI . (N = 38)

successfully stabilized by corpectomy and strut graft fusion along with posterior fixation and fusion . The combination SLI and SVBI correlated strongly to failure of surgical stabilization when not managed by both anterior and posterior stabilization (p = 0.002) . All patients with only SLI were successfully stabilized by posterior. fixation and fusion . Patients with SVBI alone were stabilized effectively by corpectomy and strut graft fusion (Figure 4). Our initial stabilization (surgical and nonsurgical) was unsatisfactory in 21 cases . Comparing these patients to those adequately stabilized, no significant difference was detected in terms of the presence or severity of chronic pain syndromes. Further, there was no significant difference in the percentage neurologic recovery between these two groups . Patients with complete myelopathy were considered separately from those with incomplete myelopathy .

Both SLI & SVBI

Neither SLI nor SVBI

Fifty-eight patients' injuries healed with the fractures adequately reduced (good anatomic outcome), and six patients' injuries were allowed to heal with inadequately reduced alignment (poor anatomic outcome) . Comparing these two groups, there was no significant difference in the presence or severity of chronic pain syndromes . Further, there was no significant difference in the percentage neurologic recovery in those patients who presented with complete myelopathy . As Figure 5 demonstrates, in patients who presented with incomplete myelopathy, there was a notable difference between those with good and those with poor anatomic outcomes . This difference, however, did not quite reach statistical significance (p = 0 .07) . Discussion This study indicates that classifying subaxial cervical spine injuries according to the presence of SLI and SVBI not only accurately predicts the success or failure of nonoperative management, but also indicates which surgical stabilization procedure will be the most effective .



Stabilization of Subaxial Cervical Spinal Injuries

The criteria for SLI and SVBI can be easily detected on roentgenograms . Although additional information from CT and MRI studies may also influence management decisions, these studies were no more predictive than roentgenograms in identifying injuries which could not be adequately stabilized nonoperatively . The relatively high frequency of nonoperative stabilization failure in this series needs to be addressed . All of these patients had associated spinal cord injuries, suggesting that these cases represent severe cervical injuries . Further, the criteria for stabilization failure varies from one report to the next [5,9,16,29,35] . As the goal of stabilization is to maintain the alignment achieved by closed reduction, failure to accomplish this with allowances made for minor changes in alignment was considered inadequate stabilization in this study . When similar criteria are applied to other subaxial cervical spine injuries, halo-vest stabilization failure occurs in over 40% of cases [33] . The characteristics used to define SLI in this report are consistent with previous laboratory studies . Significant translational and kyphotic deformities, as well as a positive "stretch test," must be interpreted as ligamentous rupture or extreme laxity, as normally ligamentous structures strongly resist these deformations . White and Panjabi [30] demonstrated that with all ligamentous struc-

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Figure

3 . MRI eoidence of ligamentout injury: disruption of anterior longitudinal ligament (A) ; disruption of posterior longitudinal ligament and interspinous ligament (B) .

cures intact, the maximal motion segment deformity did not exceed 2 .7 millimeters of translation or 11 degrees of rotation under physiologic loads . By sequentially sectioning ligamentous structures in a cervical motion segment subjected to physiologic loads, ligamentous failure occurred suddenly and dramatically with no consistent prefailure phase, suggesting a threshold to ligamentous failure [30] . We propose that the characteristics presented for SLI represent ligamentous injury which has surpassed the threshold for ligamentous failure . Optimal management of cervical injuries with evidence of SLI must include reestablishment of the function served by the injured ligaments and compensation for poor ligamentous healing. As this study demonstrates, these objectives cannot be accomplished by a halo-vest orthosis . External cervical bracing does not reestablish a tension band between the involved vertebrae and probably does not significantly affect ligamentous healing . Potentially, fusion of the injured osseous structures could compensate for lost ligamentous function . This is unlikely, because with nonoperative management, ligamentous structures, especially disc material

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100

Posterior Fixation/ Fusion

90

Vertebrectomy + Strut Graft

80

Vertebrectomy + Strut Graft and Posterior Fixation/ Fusion

70 60 50

33%

40

25%

30 20 10 0 SLI

Figure 4 . Percent surgical stabilization success for injuries with SLI, SVBI, and both SLI and SVBI . (N = 38) and facet cartilage, remain in place separating adjacent vertebral structures and interfering with arthrodesis . Further, the halo-vest orthosis does not provide complete immobilization of the cervical spine and may allow up to 30% of normal cervical motion in an uninjured cervical spine [21-23,41] . With SLI, the injured hypermobile motion segment cannot be adequately immobilized with the halo orthosis, resulting in loss of fracture reduction and further compromise of fracture healing [5,34,41) . Therefore, optimal management of cervical injuries with SLI requires surgical stabilization . Posterior fixation and fusion provides the best stabilization for cervical injuries accompanied by SLI, as it recreates a tension band between the injured vertebra . All of our injuries with SLI were caused by flexion mechanisms; consequently, the posterior ligamentous structures would be expected to suffer more severe injury than the anterior ligamentous structures [40] . Therefore, posterior stabilization provides the most direct compensation for the injured ligamentous structure [2,3,42] . All of our cases of SLI managed by posterior

SVBI

Both SLI & SVBI

fixation and fusion were successfully stabilized . In our cases of SLI, which were managed by anterior fusion and halo-vest, the majority (75%) were not adequately stabilized, consistent with previous reports [6,39] . Further, anterior fusion combined with anterior cervical plating will not adequately stabilize fractures with SLI, since biomechanical studies have demonstrated these plates to fail in flexion with less than physiologic loads [27] .

Figure

5 . Percent neurologic recovery for patients presenting with incomplete myelopathy who had a good versus poor anatomic outcome of their fracture management.

Percentaa

aNeurologiic

Recovery

Incomplete Myelopathy~= ) (mean ± standard error)

Good Anatomic Outcome

71 .5% ± 4.8%

Poor Anatomic Outcome

47 .4% ± 14 .9%



Stabilization of Subaxial Cervical Spinal Injuries

Severe vertebral body fractures occur by axial loading, typically with some degree of flexion [26,37) . This results in more severe injury to the anterior aspect of the vertebral body compared to the posterior vertebral body, leaving the cervical spine in some degree of kyphotic angulation [24]. Cervical braces cannot be expected to reestablish this lost vertebral body height and cannot adequately protect the injured segment from axial loads [3,8]. As this study shows, injuries with SVBI, which are managed by halo orthosis, can be expected to fall out of reduction and develop progressive kyphotic angulation . Optimal management of SVBIs requires surgical reconstruction of the injured vertebral body- In all of our cases of SVBI stabilized by corpectomy and strut graft fusion, this progressive sagittal angulation was prevented . In the majority of cases (67%) with SVBI that were managed by posterior fixation, the kyphotic deformity progressed . The impact of optimal fracture stabilization on clinical outcome remains controversial . Some authors have reported improved neurologic outcomes in patients with stable, well-aligned fractures, where others have found no association between posttraumatic spinal deformity and neurologic recovery [3,12,13,18,20,25,35,36,43) . Our results suggested that with incomplete spinal cord injuries, those patients with stable well-aligned fracture outcomes have better neurologic recovery than those with poor anatomic fracture outcomes, although the differences did not reach statistical significance . This lack of statistical significance is probably due to the small number of patients in this series whose fractures healed in significant deformity . Possibly, optimal fracture stabilization combined with high dose methylprednisolone and other pharmacologic agents will maximize neurologic recovery [4,15,17] . Although previous studies have suggested that severe spinal deformities result in chronic pain, our results did not confirm this [3] . In conclusion, identifying evidence of SLI or SVBI on admission roentgenograms accurately predicts the success or failure of nonoperative stabilization . Further, identifying SLI or SVBI guides the approach for surgical stabilization, as SLIs require posterior fixation and fusion and SVBIs require vertebrectomy and strut graft stabilization . Injuries with both SLI and SVBI require both anterior and posterior stabilization . Subaxial cervical fractures with neither SLI nor SVBI can be successfully stabilized nonoperatively .

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