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AOSpine Subaxial Cervical Spine Injury Classification System: The Relationship Between Injury Morphology, Admission Injury Severity, and Long-Term Neurologic Outcome
Original Article
AOSpine Subaxial Cervical Spine Injury Classification System: The Relationship Between Injury Morphology, Admission Injury Severity, and Long-Term Neurologic Outcome Harry Mushlin1, Matthew J. Kole1, Timothy Chryssikos1, Gregory Cannarsa1, Gary Schwartzbauer1,2, Bizhan Aarabi1,2
OBJECTIVE: The AOSpine Subaxial Cervical Spine Injury Classification System was introduced to improve communication, clinical management, and research. Here, the system was studied in relation to injury severity along with admission and long term neurologic follow-up.
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METHODS: A retrospective study was performed in subaxial cervical spine injury patients. Morphology was classified using the AOSpine Subaxial Cervical Spine Injury Classification System. Six major morphology subtypes were selected for analysis. The American Spinal Injury Association (ASIA) motor and Abbreviated Injury Severity (AIS) scores were recorded at admission and at follow-up >6 months. Admission intramedullary lesion length (IMLL) on MRI was recorded.
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RESULTS: In all, 82 patients met criteria for analysis. The mean follow-up time was 11 months (range, 6e33 months). The were 36 patients with morphology subtypes A0, 4 with A1/A2, 9 with A3/A4, 8 with B2, 11 with B3, and 14 with C. The A1/2 subtype had the least severe injuries on admission. The C and A3/A4 subtypes had the most severe injuries. The subtype C had the lowest ASIA Motor Score (AMS) and second highest percentage of complete injuries. A3/A4 patients had the highest percentage of complete injuries on admission. At follow-up, A3/A4 patients had the lowest AMS, and 33% of patients continued to have complete injuries. C subtype injuries all converted to AIS incomplete injuries on follow-up (P [ 0.04). IMLL was found to be significantly different compared across
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Key words Angioplasty - Aortic arch reconstruction - Stroke -
Abbreviations and Acronyms AIS: Abbreviated Injury Severity AMS: ASIA Motor Score ASIA: American Spinal Injury Association CT: Computed tomography IMML: Intramedullary lesion length MRI: Magnetic resonance imaging
multiple morphologic subtypes. Surgical management for each morphology subtype was reported. CONCLUSION: The AOSpine Subaxial Cervical Spine Injury Classification System successfully associated injury morphology with IMLL along with admission and long-term neurologic function and recovery.
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INTRODUCTION
O
ver the past 70 years, several subaxial cervical injury classification systems have been proposed to improve communication among clinicians, patients, and researchers.1 Early classification systems from Holdsworth2 and Nicoll3 stressed the importance of discoligamentous complex integrity and the mechanism of injury; however, the system was neither well validated nor shown to be a reliable predictor of admission or follow-up neurologic function. In the 1980s, Allen et al.4 and Harris et al.5 contributed to our understanding of traumatic spine injury (TSI) by proposing 2 mechanistic classification schemes that became more widely adopted in the surgical community. Allen et al.4 proposed 6 mechanisms of injury to explain the varied fractures and dislocations seen in TSI by assessing radiographic evidence from 165 patients. Each mechanism was classified from mild to severe and associated neurologic function. Associating neurologic function with the type of injury mechanism was an improvement on previous systems; however, long-term follow-up data were never presented, and therefore the scheme was not helpful in predicting
SLIC: Subaxial Cervical Injury Classification TSI: Traumatic spine injury From the 1Department of Neurosurgery and 2Trauma Critical Care, R. Adams Cowley Shock Trauma Center, University of Maryland Medical Center, Baltimore, Maryland, USA To whom correspondence should be addressed: Harry Mushlin, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2019). https://doi.org/10.1016/j.wneu.2019.06.092 Journal homepage: www.journals.elsevier.com/world-neurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2019 Elsevier Inc. All rights reserved.
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ORIGINAL ARTICLE HARRY MUSHLIN ET AL.
SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
prognosis. In 1986, Harris et al.5 proposed yet another mechanistic system with 5 major vector forces to account for various injury morphologies, which initiated the transition toward understanding morphology along with mechanism. Although this system improved on the mechanism-based classification systems, it was not shown to predict initial neurologic injury and long-term outcomes. To improve on previous classification schemes, the Spine Trauma Study Group proposed the Subaxial Cervical Injury Classification (SLIC) system. This scheme is based on 3 major categories, including an assessment of morphology, discoligamentous complex integrity, and the neurologic status of the patient. These 3 variables provide a score to help guide management, similar to the Thoracolumbar Injury Classification and Severity score.6 Although many considered the SLIC scoring system a step forward in cervical trauma management, disagreement about its morphologic classification hindered its more widespread adoption. In addition, as with the other scoring systems mentioned above, the SLIC has not proved to be useful in providing long-term prognosis. More recently, Vaccaro et al.7 proposed the AOSpine Subaxial Cervical Spine Injury Classification System in 2016 to provide clarification of morphologic classification with the goal of improving our understanding of subaxial cervical spine injury in the clinical and research settings. Although this newer classification scheme has shown promise in reliably describing the morphologic nature of cervical spine injuries, it remains to be established that it also provides prognostic value, with only 1 study from Aarabi et al.8 in the literature. In this study, we hypothesize not only that the AOSpine morphology-based classification system can be easily implemented but also that it can help establish the association between injury morphology, injury
Figure 1. AOSpine morphologic subtypes: 6 major morphologic subtypes derived from the AOSpine subaxial cervical spine injury classification system. A0 ¼ none or only minor bony injuries; A1/A2 ¼ vertebral body fracture with no posterior wall involvement; A3/A4 ¼ vertebral body fracture with
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severity, and neurologic function. Here, we evaluated the relationship between injury morphology as determined by the AOSpine Subaxial Cervical Spine Injury Classification System and admission American Spinal Injury Association (ASIA) Motor Score (AMS), Abbreviated Injury Severity (AIS) score, intramedullary lesion length (IMLL), and long-term follow-up. MATERIALS AND METHODS A retrospective review was made of patients with cervical spine trauma who were admitted to a level 1 trauma center between 2013 and 2016. Patients were included if they had 1) blunt subaxial cervical trauma, 2) AIS grades A through D, 3) admission cervical computed tomography (CT) and magnetic resonance imaging MRI), and 4) follow-up of at least 6 months. Patients were excluded if they had 1) penetrating cervical trauma, 2) evidence of atlantoaxial trauma, 3) incomplete imaging, 4) or <6 months of follow-up. In all, 82 patients met the inclusion criteria. Admission and follow-up clinic notes were used to determine ASIA Motor Score (AMS) and AIS Score. Patients were recorded as having complete injuries (AIS A) and incomplete injuries (AIS BeD). Morphology Description Using the AOSpine Subaxial Cervical Spine Injury Classification System, all patients were classified by 4 neurosurgery residents and 1 full-time faculty trauma neurosurgeon. The 6 major morphology groupings shown in Figure 1 were derived from the AOSpine scheme for the purposes of analysis. Type A0 represents none or only minor bony injuries (i.e., transverse process, spinous process fracture); type A1/A2 represents a vertebral body fracture with no posterior wall involvement; type A3/A4 represents a vertebral body fracture with posterior wall
posterior wall involvement; B1¼ posterior column with bony involvement only, B2¼ posterior column disruption with bony and capsuloligamentous disruption; B3 ¼ anterior column disruption; C ¼ translational injuries.
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ORIGINAL ARTICLE HARRY MUSHLIN ET AL.
SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
Table 1. Basic Demographics and Clinical Characteristics Characteristic Number of patients Overall mean age, years
Value 82 53.5
Total male
60
Total female
22
AOSpine morphologic subtype
A0
A1/A2
A3/A4
B2
B3
C
36
4
9
8
11
14
58.4
48.3
39
50.9
63.7
45.3
23
4
7
7
9
10
Number Demographics Age, years Male Female
13
0
2
1
2
4
22.8
17.8
48.1
11.2
25.5
32.9
Admission
70 (31)
97 (2.5)
42 (43.5)
75 (40.5)
41 (27.9)
38 (40.3)
Follow-up
90 (19.9)
83 (32.8)
48 (38.8)
95 (11.4)
75 (33.1)
56 (36.2)
P value (Mann-Whitney)
<0.0001
0.84
0.59
0.3
0.03
0.13
12
17
9
8
10
10
Mean intramedullary lesion length, mm ASIA (SD)
Mean months to follow-up AIS impairment (%) Admission complete Admission incomplete Follow-up complete
1 (2.8)
0 (0)
5 (55.6)
1 (12.5)
0 (0)
5 (35.7)
34 (94.4)
3 (75)
4 (44.4)
5 (62.5)
10 (90.9)
9 (64.3)
0 (0)
0 (0)
3 (33.3)
0 (0)
0 (0)
0 (0)
Follow-up incomplete
36 (100)
4 (100)
6 (66.7)
8 (100)
11 (100)
14 (100)
P value (Fisher exact)
0.49
1
0.64
0.43
1
0.04
Six major morphologic types are identified: A0, A1/A2, A3/A4, B2, B3, and C. Admission ASIA Motor Score (AMS) and follow-up scores were recorded and compared using the Mann Whitney U test. AIS severity recorded as complete (AIS A) versus incomplete (AIS BeD) and compared using Fisher exact test. Mean months to follow-up was recorded. Significant differences are in bold (P < 0.05). AIS, Abbreviated Injury Severity; ASIA, American Spinal Injury Association; SD, standard deviation.
involvement; type B1 injury morphology has posterior column disruption with bony involvement only; type B2 injury morphology has posterior column disruption with bony and capsuloligamentous disruption; type B3 has anterior column disruption, and type C injury morphology represents translational injuries. Although in some instances multiple morphology types were applied to specific patients, in each case the dominant type or most severe injury type was assigned to each case. Reviewers addressed all discrepancies and ultimately reached consensus on a final classification for each patient.
Measurement of Intramedullary Lesion Length Four senior neurosurgical residents measured the IMLL for each patient using a preoperative admission MRI. IMLL was the rostrocaudal length of high-signal intensity from the injury epicenter, measured in millimeters. IMLL was measured on T2-weighted images or short T1 inversion recovery sequence. Interclass correlation across all 4 independent reviewers was determined to be 0.79 (95% confidence limits: 0.71, 0.85).
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Statistical Analysis Statistical analysis was performed to assess the relationship between AMS and AIS score and morphology classification. The AMS was compared at admission and follow-up using a Table 2. Admission ASIA Motor Scores A0 A0 A1/A2
0.65
A3/A4
0.14
A1/A2
A3/A4
B2
B3
C
0.65
0.14
0.27
0.009
0.018
0.9
0.007
0.04
0.24
0.72
0.83
0.07
0.11
0.16 0.16
B2
0.27
0.9
0.24
B3
0.009
0.007
0.72
0.07
C
0.018
0.04
0.83
0.11
0.62 0.62
Statistical comparison of admission American Spinal Injury Association (ASIA) Motor Scores across all morphology injury subtypes. Significant differences are in bold (P < 0.05).
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SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
Table 3. Follow-Up ASIA Motor Scores A0 A0
Table 5. Follow-up AIS Scores
A1/A2
A3/A4
B2
B3
C
0.81
0.007
0.57
0.11
0.004
A0
1
0.32
0.18
A1/A2
1
0.027
0.15
0.57
A3/A4
0.006
0.5
0.09
0.018
B2
1
1
0.21
0.29
B3
1
1
0.074
1
C
1
1
0.047
1
A1/A2
0.81
A3/A4
0.007
0.18
0.18
B2
0.57
1
0.027
B3
0.11
0.32
0.15
0.09
C
0.004
0.18
0.57
0.018
0.29
Statistical comparison of follow-up (>6 months) American Spinal Injury Association (ASIA) Motor Scores across all morphology injury subtypes. Significant differences are in bold (P < 0.05).
Mann-Whitney signed ranked test. Comparison was made within and across morphology subtypes. Using a Fisher exact test, AIS grade at admission and follow-up grade were compared. P values <0.05 were defined as statistically significant. RESULTS The major injury morphology of 82 patients was established according to the AOSpine Subaxial Classification System. Table 1 shows the basic demographics and clinical characteristics of these patients identified at admission and at follow-up. We identified the following injury morphology subtypes: 36 A0, 4 A1/ A2, 9 A3/A4, 8 B2, 11 B3, and 14 C. The mean time to follow-up was 11 months (range, 633 months). There was no was statistical difference in age or sex between the 2 groups. The lowest mean AMS was 38 in the C subtype, and the highest was 97 in the A1/A2 subtype. Significant improvement in AMS was found between admission and follow-up in A0 (70 and 90, respectively, P < 0.0001) and B3 (41 and 75, respectively, P ¼ 0.03). The AIS impairment grade was recorded as complete (AIS A) and incomplete (AIS BeD) for all morphology types. Group A3/A4 had the highest percentage of patients with complete injuries (5/9, 55.6%) and at follow-up (3/9, 33.3%). Group A0 had 1 patient with complete injury at admission (1/36, 2.8%) and none at follow-up Table 4. Admission AIS Scores A0 A0
A1/A2
A3/A4
B2
B3
C
1
0.0006
0.27
1
0.005
0.2
1
1
0.51
A1/A2
1
A3/A4
0.0006
0.2
0.27
1
B2
0.29 0.29
B3
1
1
0.01
0.38
C
0.005
0.51
0.42
0.61
0.01
0.42
0.28
0.61 0.05
0.05
Statistical comparison of admission Abbreviated Injury Severity (AIS) scores across all morphology injury subtypes. Patients were classified as having either incomplete (ASIS BeE) or complete (ASIA A) injuries. Significant differences are in bold (P < 0.05).
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A0
A1/A2
A3/A4
B2
B3
C
1
0.006
1
1
1
0.5
1
1
1
0.21
0.074
0.047
1
1 1
1
Statistical comparison of follow-up (>6 months) Abbreviated Injury Severity (AIS) scores across all morphology injury subtypes. Patients were classified as having either incomplete (ASIS BeD) or complete (ASIA A) injuries. Significant differences are in bold (P < 0.05).
(0%). Groups A1/A2 and B3 had no patients with complete injuries at either admission or follow-up (0/4 and 0/11, respectively). Group B2 had 1 patient with complete injury at admission (1/8, 12/ 5%) and none at follow-up (0%). Group C injuries showed statistically significant AIS grade conversion from complete to incomplete neurologic status (P ¼ 0.04); 5 patients with complete injuries at admission (35.7%) transitioned to incomplete injuries at follow-up. Analysis for differences in AMS was carried out across all subtypes. Table 2 shows that significant differences were found between admission AMS between A0 versus B3 and C (P ¼ 0.009 and P ¼ 0.018, respectively), as well as A1/A2 versus B3 and C (P ¼ 0.007 and P ¼ 0.04, respectively). Table 3 shows that significant differences in follow-up (>6 months) AMS were found between A0 versus A3/A4 and C (P ¼ 0.007 and P ¼ 0.004, respectively), A3/A4 versus B2 (P ¼ 0.027), and B2 versus C (P ¼ 0.018). The AIS impairment grades (complete vs. incomplete) were compared across all subtypes on admission and follow-up. Table 4 shows the significant differences for AIS incomplete versus AIS complete injuries at admission between A0 versus A3/A4 and C (P < 0.001 and P ¼ 0.005, respectively), A3/A4 versus B3 (P ¼ 0.01), and B3 versus C (P ¼ 0.05). Table 5 demonstrates significant differences in AIS incomplete versus AIS complete injuries found at follow-up between A0 versus A3/A4 (P ¼ 0.006) and A3/4 versus C (P ¼ 0.05). Surgical management for each morphology was described with the surgical goal of spinal cord decompression, fixation, and alignment. There were a total of 44 anterior discectomy and fusions (53.7%), 10 anterior discectomy and fusions with laminectomy (12.2%), 2 anterior cervical corpectomies (2.4%), 2 anterior cervical corpectomies with laminectomy (2.4%), 18 laminectomies (22.0%), and 7 nonoperative conditions managed with a collar (7.3%). Table 6 shows the overall surgical management grouped according to morphology subtype. The IMLL was measured to assess admission injury severity across morphology subtypes. The overall mean IMLL for each subtype is shown in Table 1. The IMLL lengths in ascending order
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ORIGINAL ARTICLE HARRY MUSHLIN ET AL.
SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
Table 6. Surgical Intervention Morphology
Table 7. Comparison of Intramedullary Lesion Length
Number of Patients
Surgical Intervention
20
ACDF
1
ACDF þ laminectomy
11
Laminectomy
4
Collar
3
ACDF
<0.001
1
ACCF
B2 versus B3
A0
A0 versus A1/2 0.42
A1/A2
A1/2 versus A3/4 <0.001 A3/4 versus B2
<0.001
A3/A4 ACDF
B3 versus C
1
ACCF
0.06
1
ACDF þ laminectomy Laminectomy
1
Collar
7
ACDF
1
ACDF þ laminectomy
5
ACDF
B2
B3
3
ACDF þ laminectomy
2
Laminectomy
1
Collar
8
ACDF
4
ACDF þ laminectomy
2
ACCF þ laminectomy
C
The following procedures/management were reported: anterior cervical discectomy and fusion (ACDF); anterior cervical corpectomy and fusion (ACCF); ACDF þ laminectomy; laminectomy; and collar.
were B2 (11.2 mm), A1/2 (17.8 mm), A0 (22.3 mm), B3 (25.5 mm), C (32.9 mm), and A3/4 (48.1 mm). Comparison of the mean IMLL across subtypes revealed multiple significant differences. The following comparisons were all found to be significantly different: A0 versus A3/4, A0 versus B2, A0 versus C, A1/2 versus A3/4, A1/2 versus C, A3/4 versus B2, A3/4 versus B3, A3/4 versus C, B3 versus B3, and B2 versus C (P < 0.001; P < 0.001; P ¼ 0.01; P < 0.001; P < 0.001; P ¼ 0.013; P < 0.001; P < 0.001). The findings are summarized in Table 7. DISCUSSION The AOSpine Subaxial Cervical Spine Injury Classification System was created to improve communication in the clinical and research settings. A primary aim of this system has been to
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A0 versus B2
A0 versus B3
A0 versus C
<0.001 A1/2 versus B2
<0.001
0.23
0.001
A1/A2 versus B3
A1/2 versus C
0.26
0.2
0.02
A3/4 versus B3
A3/4 versus C
<0.001
0.013
B2 versus C <0.001
1
5
A0 versus A3/4
Statistical comparison of intramedullary lesion length across all morphology subtypes. Significant differences are in bold (P < 0.05).
improve the morphologic descriptions of subaxial cervical injuries in response to prior criticisms of earlier classification schemes. As noted above, these earlier systems were not shown to predict neurologic injury and prognosis, were difficult to implement, and consequently were not widely adopted. Here, we successfully and easily implemented the AOSpine classification system to classify 82 patients with subaxial cervical spine injury based on injury morphology and relation to IMLL and neurologic function on admission and long-term follow-up (>6 months). In applying this morphology-based classification system to our TSI cohort, several patterns became evident. A0 subtype was the most common subaxial cervical injury within this cohort (36 patients), representing morphology with the absence of any or only minor bony injuries, These patients were found to have significant improvement in AMS on follow-up from 70 to 90 (P < 0.0001) (Table 1).9 In addition to A0 injuries, those with a B3 pattern of injury (anterior column injuries) also showed significant improvement in AMS at follow-up (from 41 to 75, P ¼ 0.03). A1/ A2 type injuries had the highest AMS (least neurologically severe injuries) on admission, with a mean score of 97. This was found to be significantly greater than the AMS for C and B3 injuries (Table 2). A1/A2 subtypes include minor fractures of the vertebral body that typically do not compromise the cervical spinal cord and therefore portend better clinical presentations and outcomes relative to the more severe injury subtypes. The worst neurologic injuries were C and A3/A4 subtypes, which incorporate translational and tear drop/burst fractures, respectively. On admission, C subtype injuries had the lowest AMS, with a mean score of 38 and the second highest percentage of patients with complete injuries (33.3%). The mean admission AMS of the C subtype was significantly less than of the A0 and A1/ A2 type injuries (P ¼ 0.018 and P ¼ 0.04, respectively). Translational injuries as seen in the C subtype often present with severe compromise of the cervical canal and put patients at greater risk for neurologic deficit.
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SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
The A3/A4 patients had the highest percentage of patients with complete injuries on admission (55.6%). Importantly, at followup, A3/A4 patients had the lowest AMS (mean, 48). This was significantly worse than A0 and B2 (P ¼ 0.007 and P ¼ 0.27, respectively). In addition to having the lowest follow-up AMS, A3/ A4 was the only subtype to have patients with complete injuries at follow-up (33.3%). In comparison, C subtype injuries all converted to incomplete on follow-up (P ¼ 0.04), and although statistical significance was not achieved, these patients did have a higher mean AMS at follow-up compared with A3/A4 (56 vs. 48, respectively). We hypothesize that although C subtype injuries present with significant cord compression and neurologic injury, this injury morphology is more amenable to closed reduction, which theoretically reduces time to decompression. This favorable time to decompression translates into improved long-term outcomes, in contrast to A3/A4 injuries, which involve compromise of the posterior vertebral body and a high-impact injury to the spinal cord, and can be decompressed only with surgery. Further investigation of this hypothesis is warranted. Finally, we looked at admission IMLL as a marker for injury severity and association with each morphology subtypes. Previous clinical studies have demonstrated the important of IMLL and its relationship to AIS grade and neurologic outcome. Le et al.10 showed greater IMLL length expansion in AIS grades A and B. Aarabi et al.11 then showed that IMLL helped predict the AIS conversion. In this study, there were many significant differences between the IMLL across numerous morphology subtypes (Table 7). Importantly, we showed that the most serious injuries, A3/4 and C, had the longest IMLL. Furthermore, the IMLL of A3/4 was found to be significantly different from that of C (P ¼ 0.013). A3/4 had the highest IMLL (48.1 mm) and the worst neurologic outcome across all morphologic subtypes, adding to the literature further evidence of the importance of IMLL and neurologic outcome. In conclusion, we propose that the AOSpine spine morphologybased classification system has greater utility in assessing injury to the spinal cord than a mechanistic system. Previous classification systems, such that of Harris et al.,5 failed to predict neurologic injury and prognosis and instead focused on the optimal system to classify radiographic findings. Allen et al.4 did associate their mechanistic classification system with neurologic function, but well-established long-term follow-up was never published. These systems were devised without the availability of MRI and high-resolution CT, so practitioners were dependent on both radiographs and injury mechanism to determine classification and proper treatment. However, in today’s age of accessible high-
REFERENCES 1. Aarabi B, Walters BC, Dhall SS, et al. Subaxial cervical spine injury classification systems. Neurosurgery. 2013;72:170-186. 2. Holdsworth F. Fractures, dislocations, and fracture-dislocations of the spine. J Bone Joint Surg Am. 1970;52:1534-1551. 3. Nicoll EA. Fractures of the dorso-lumbar spine. J Bone Joint Surg Br. 1949;31-B:376-394.
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resolution MRI and CT scans, providers are easily able to assess morphologic damage. Here, by using the well-defined morphology-based AOSpine system, patients were easily classified, and each demonstrated distinct natural histories and injury severity. Previous work done by Aarabi et al.8 also implemented the use of the AOSpine classification system; however, there are important differences between the 2 studies. This current study included AIS A through D and nonoperative patients. These broader inclusion criteria led to a greater variation in our morphology analysis and allowed 6 distinct morphologies to be analyzed instead of 4. Furthermore, we eliminated the use of hybrid classifications to help simplify the application of the AOSpine system. In addition, although the 2 studies were from the same institution, this cohort was analyzed from a different consecutive group of patients with distinct morphology. Finally, the IMLL reported was from preoperative MRIs, which clinically allowed for earlier injury assessment. We believe the results presented in this study will help providers more confidently discuss prognosis with patients and families during the acute stages of management and later recovery by being able to have more granular understanding of the cervical injury. The limitations of this study are that it was a retrospective chart review of notes and radiographic data. Some patients were lost to follow-up. Owing to the varied number of subtypes, once our cohort was subdivided, some of the subtypes had a small number of patients for analysis, which could have limited statistical comparisons within and between various morphologic groupings. Overall, using the AOSpine classification system we have reported the most comprehensive subaxial cervical spine injury study reported to assess IMLL along with admission and long-term neurologic function based on injury morphology. CONCLUSION The AOSpine Subaxial Cervical Spine Injury Classification System was created to improve morphology-based classification systems with the goal of facilitating communication in clinical and research settings. We were able to successfully identify an association between certain morphology subtypes with admission IMLL and AMS and AIS score at admission and follow-up. We believe that this study and continued use of the AOSpine Subaxial Cervical Spine Injury Classification System will lead to greater understanding of injury morphology as it correlates to neurologic injury and will help improve communication among clinicians and patients to discuss initial injury and prognosis.
4. Allen BL, Ferguson RL, Lehmann TR, O’Brien RP. A mechanistic classification of closed, indirect fractures and dislocations of the lower cervical spine. Spine. 1982;7:1-27. 5. Harris JH, Edeiken-Monroe B, Kopaniky DR. A practical classification of acute cervical spine injuries. Orthop Clin North Am. 1986;17:15-30. 6. Vaccaro AR, Hulbert RJ, Patel AA, et al. The subaxial cervical spine injury classification system: a novel approach to recognize the importance of morphology, neurology, and integrity of
the disco-ligamentous complex. Spine. 2007;32: 2365-2374. 7. Vaccaro AR, Koerner JD, Radcliff KE, et al. AOSpine subaxial cervical spine injury classification system. Eur Spine J. 2016;25:2173-2184. 8. Aarabi B, Oner C, Vaccaro AR, Schroeder GD, Akhtar-Danesh N. Application of AOSpine subaxial cervical spine injury classification in simple and complex cases. J Orthop Trauma. 2017;31: S24-S32.
WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2019.06.092
ORIGINAL ARTICLE HARRY MUSHLIN ET AL.
SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
9. Stevenson CM, Dargan DP, Warnock J, et al. Traumatic central cord syndrome: neurological and functional outcome at 3 years. Spinal Cord. 2016;54:1010-1015. 10. Le E, Aarabi B, Hersh DS, et al. Predictors of intramedullary lesion expansion rate on MR images of patients with subaxial spinal cord injury. J Neurosurg Spine. 2015;22:611-621. 11. Aarabi B, Sansur CA, Ibrahimi DM, et al. Intramedullary lesion length on postoperative magnetic
resonance imaging is a strong predictor of ASIA impairment scale grade conversion following decompressive surgery in cervical spinal cord injury. Neurosurgery. 2017;80:610-620.
Citation: World Neurosurg. (2019). https://doi.org/10.1016/j.wneu.2019.06.092 Journal homepage: www.journals.elsevier.com/worldneurosurgery Available online: www.sciencedirect.com
Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
1878-8750/$ - see front matter ª 2019 Elsevier Inc. All rights reserved.
Received 6 May 2019; accepted 12 June 2019
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AOSpine Subaxial Cervical Spine Injury Classification System: The Relationship Between Injury Morphology, Admission Injury Severity, and Long-Term Neurologic Outcome Harry Mushlin1, Matthew J. Kole1, Timothy Chryssikos1, Gregory Cannarsa1, Gary Schwartzbauer1,2, Bizhan Aarabi1,2
OBJECTIVE: The AOSpine Subaxial Cervical Spine Injury Classification System was introduced to improve communication, clinical management, and research. Here, the system was studied in relation to injury severity along with admission and long term neurologic follow-up.
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METHODS: A retrospective study was performed in subaxial cervical spine injury patients. Morphology was classified using the AOSpine Subaxial Cervical Spine Injury Classification System. Six major morphology subtypes were selected for analysis. The American Spinal Injury Association (ASIA) motor and Abbreviated Injury Severity (AIS) scores were recorded at admission and at follow-up >6 months. Admission intramedullary lesion length (IMLL) on MRI was recorded.
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RESULTS: In all, 82 patients met criteria for analysis. The mean follow-up time was 11 months (range, 6e33 months). The were 36 patients with morphology subtypes A0, 4 with A1/A2, 9 with A3/A4, 8 with B2, 11 with B3, and 14 with C. The A1/2 subtype had the least severe injuries on admission. The C and A3/A4 subtypes had the most severe injuries. The subtype C had the lowest ASIA Motor Score (AMS) and second highest percentage of complete injuries. A3/A4 patients had the highest percentage of complete injuries on admission. At follow-up, A3/A4 patients had the lowest AMS, and 33% of patients continued to have complete injuries. C subtype injuries all converted to AIS incomplete injuries on follow-up (P [ 0.04). IMLL was found to be significantly different compared across
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Key words Angioplasty - Aortic arch reconstruction - Stroke -
Abbreviations and Acronyms AIS: Abbreviated Injury Severity AMS: ASIA Motor Score ASIA: American Spinal Injury Association CT: Computed tomography IMML: Intramedullary lesion length MRI: Magnetic resonance imaging
multiple morphologic subtypes. Surgical management for each morphology subtype was reported. CONCLUSION: The AOSpine Subaxial Cervical Spine Injury Classification System successfully associated injury morphology with IMLL along with admission and long-term neurologic function and recovery.
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INTRODUCTION
O
ver the past 70 years, several subaxial cervical injury classification systems have been proposed to improve communication among clinicians, patients, and researchers.1 Early classification systems from Holdsworth2 and Nicoll3 stressed the importance of discoligamentous complex integrity and the mechanism of injury; however, the system was neither well validated nor shown to be a reliable predictor of admission or follow-up neurologic function. In the 1980s, Allen et al.4 and Harris et al.5 contributed to our understanding of traumatic spine injury (TSI) by proposing 2 mechanistic classification schemes that became more widely adopted in the surgical community. Allen et al.4 proposed 6 mechanisms of injury to explain the varied fractures and dislocations seen in TSI by assessing radiographic evidence from 165 patients. Each mechanism was classified from mild to severe and associated neurologic function. Associating neurologic function with the type of injury mechanism was an improvement on previous systems; however, long-term follow-up data were never presented, and therefore the scheme was not helpful in predicting
SLIC: Subaxial Cervical Injury Classification TSI: Traumatic spine injury From the 1Department of Neurosurgery and 2Trauma Critical Care, R. Adams Cowley Shock Trauma Center, University of Maryland Medical Center, Baltimore, Maryland, USA To whom correspondence should be addressed: Harry Mushlin, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2019). https://doi.org/10.1016/j.wneu.2019.06.092 Journal homepage: www.journals.elsevier.com/world-neurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2019 Elsevier Inc. All rights reserved.
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ORIGINAL ARTICLE HARRY MUSHLIN ET AL.
SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
prognosis. In 1986, Harris et al.5 proposed yet another mechanistic system with 5 major vector forces to account for various injury morphologies, which initiated the transition toward understanding morphology along with mechanism. Although this system improved on the mechanism-based classification systems, it was not shown to predict initial neurologic injury and long-term outcomes. To improve on previous classification schemes, the Spine Trauma Study Group proposed the Subaxial Cervical Injury Classification (SLIC) system. This scheme is based on 3 major categories, including an assessment of morphology, discoligamentous complex integrity, and the neurologic status of the patient. These 3 variables provide a score to help guide management, similar to the Thoracolumbar Injury Classification and Severity score.6 Although many considered the SLIC scoring system a step forward in cervical trauma management, disagreement about its morphologic classification hindered its more widespread adoption. In addition, as with the other scoring systems mentioned above, the SLIC has not proved to be useful in providing long-term prognosis. More recently, Vaccaro et al.7 proposed the AOSpine Subaxial Cervical Spine Injury Classification System in 2016 to provide clarification of morphologic classification with the goal of improving our understanding of subaxial cervical spine injury in the clinical and research settings. Although this newer classification scheme has shown promise in reliably describing the morphologic nature of cervical spine injuries, it remains to be established that it also provides prognostic value, with only 1 study from Aarabi et al.8 in the literature. In this study, we hypothesize not only that the AOSpine morphology-based classification system can be easily implemented but also that it can help establish the association between injury morphology, injury
Figure 1. AOSpine morphologic subtypes: 6 major morphologic subtypes derived from the AOSpine subaxial cervical spine injury classification system. A0 ¼ none or only minor bony injuries; A1/A2 ¼ vertebral body fracture with no posterior wall involvement; A3/A4 ¼ vertebral body fracture with
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severity, and neurologic function. Here, we evaluated the relationship between injury morphology as determined by the AOSpine Subaxial Cervical Spine Injury Classification System and admission American Spinal Injury Association (ASIA) Motor Score (AMS), Abbreviated Injury Severity (AIS) score, intramedullary lesion length (IMLL), and long-term follow-up. MATERIALS AND METHODS A retrospective review was made of patients with cervical spine trauma who were admitted to a level 1 trauma center between 2013 and 2016. Patients were included if they had 1) blunt subaxial cervical trauma, 2) AIS grades A through D, 3) admission cervical computed tomography (CT) and magnetic resonance imaging MRI), and 4) follow-up of at least 6 months. Patients were excluded if they had 1) penetrating cervical trauma, 2) evidence of atlantoaxial trauma, 3) incomplete imaging, 4) or <6 months of follow-up. In all, 82 patients met the inclusion criteria. Admission and follow-up clinic notes were used to determine ASIA Motor Score (AMS) and AIS Score. Patients were recorded as having complete injuries (AIS A) and incomplete injuries (AIS BeD). Morphology Description Using the AOSpine Subaxial Cervical Spine Injury Classification System, all patients were classified by 4 neurosurgery residents and 1 full-time faculty trauma neurosurgeon. The 6 major morphology groupings shown in Figure 1 were derived from the AOSpine scheme for the purposes of analysis. Type A0 represents none or only minor bony injuries (i.e., transverse process, spinous process fracture); type A1/A2 represents a vertebral body fracture with no posterior wall involvement; type A3/A4 represents a vertebral body fracture with posterior wall
posterior wall involvement; B1¼ posterior column with bony involvement only, B2¼ posterior column disruption with bony and capsuloligamentous disruption; B3 ¼ anterior column disruption; C ¼ translational injuries.
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ORIGINAL ARTICLE HARRY MUSHLIN ET AL.
SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
Table 1. Basic Demographics and Clinical Characteristics Characteristic Number of patients Overall mean age, years
Value 82 53.5
Total male
60
Total female
22
AOSpine morphologic subtype
A0
A1/A2
A3/A4
B2
B3
C
36
4
9
8
11
14
58.4
48.3
39
50.9
63.7
45.3
23
4
7
7
9
10
Number Demographics Age, years Male Female
13
0
2
1
2
4
22.8
17.8
48.1
11.2
25.5
32.9
Admission
70 (31)
97 (2.5)
42 (43.5)
75 (40.5)
41 (27.9)
38 (40.3)
Follow-up
90 (19.9)
83 (32.8)
48 (38.8)
95 (11.4)
75 (33.1)
56 (36.2)
P value (Mann-Whitney)
<0.0001
0.84
0.59
0.3
0.03
0.13
12
17
9
8
10
10
Mean intramedullary lesion length, mm ASIA (SD)
Mean months to follow-up AIS impairment (%) Admission complete Admission incomplete Follow-up complete
1 (2.8)
0 (0)
5 (55.6)
1 (12.5)
0 (0)
5 (35.7)
34 (94.4)
3 (75)
4 (44.4)
5 (62.5)
10 (90.9)
9 (64.3)
0 (0)
0 (0)
3 (33.3)
0 (0)
0 (0)
0 (0)
Follow-up incomplete
36 (100)
4 (100)
6 (66.7)
8 (100)
11 (100)
14 (100)
P value (Fisher exact)
0.49
1
0.64
0.43
1
0.04
Six major morphologic types are identified: A0, A1/A2, A3/A4, B2, B3, and C. Admission ASIA Motor Score (AMS) and follow-up scores were recorded and compared using the Mann Whitney U test. AIS severity recorded as complete (AIS A) versus incomplete (AIS BeD) and compared using Fisher exact test. Mean months to follow-up was recorded. Significant differences are in bold (P < 0.05). AIS, Abbreviated Injury Severity; ASIA, American Spinal Injury Association; SD, standard deviation.
involvement; type B1 injury morphology has posterior column disruption with bony involvement only; type B2 injury morphology has posterior column disruption with bony and capsuloligamentous disruption; type B3 has anterior column disruption, and type C injury morphology represents translational injuries. Although in some instances multiple morphology types were applied to specific patients, in each case the dominant type or most severe injury type was assigned to each case. Reviewers addressed all discrepancies and ultimately reached consensus on a final classification for each patient.
Measurement of Intramedullary Lesion Length Four senior neurosurgical residents measured the IMLL for each patient using a preoperative admission MRI. IMLL was the rostrocaudal length of high-signal intensity from the injury epicenter, measured in millimeters. IMLL was measured on T2-weighted images or short T1 inversion recovery sequence. Interclass correlation across all 4 independent reviewers was determined to be 0.79 (95% confidence limits: 0.71, 0.85).
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Statistical Analysis Statistical analysis was performed to assess the relationship between AMS and AIS score and morphology classification. The AMS was compared at admission and follow-up using a Table 2. Admission ASIA Motor Scores A0 A0 A1/A2
0.65
A3/A4
0.14
A1/A2
A3/A4
B2
B3
C
0.65
0.14
0.27
0.009
0.018
0.9
0.007
0.04
0.24
0.72
0.83
0.07
0.11
0.16 0.16
B2
0.27
0.9
0.24
B3
0.009
0.007
0.72
0.07
C
0.018
0.04
0.83
0.11
0.62 0.62
Statistical comparison of admission American Spinal Injury Association (ASIA) Motor Scores across all morphology injury subtypes. Significant differences are in bold (P < 0.05).
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SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
Table 3. Follow-Up ASIA Motor Scores A0 A0
Table 5. Follow-up AIS Scores
A1/A2
A3/A4
B2
B3
C
0.81
0.007
0.57
0.11
0.004
A0
1
0.32
0.18
A1/A2
1
0.027
0.15
0.57
A3/A4
0.006
0.5
0.09
0.018
B2
1
1
0.21
0.29
B3
1
1
0.074
1
C
1
1
0.047
1
A1/A2
0.81
A3/A4
0.007
0.18
0.18
B2
0.57
1
0.027
B3
0.11
0.32
0.15
0.09
C
0.004
0.18
0.57
0.018
0.29
Statistical comparison of follow-up (>6 months) American Spinal Injury Association (ASIA) Motor Scores across all morphology injury subtypes. Significant differences are in bold (P < 0.05).
Mann-Whitney signed ranked test. Comparison was made within and across morphology subtypes. Using a Fisher exact test, AIS grade at admission and follow-up grade were compared. P values <0.05 were defined as statistically significant. RESULTS The major injury morphology of 82 patients was established according to the AOSpine Subaxial Classification System. Table 1 shows the basic demographics and clinical characteristics of these patients identified at admission and at follow-up. We identified the following injury morphology subtypes: 36 A0, 4 A1/ A2, 9 A3/A4, 8 B2, 11 B3, and 14 C. The mean time to follow-up was 11 months (range, 633 months). There was no was statistical difference in age or sex between the 2 groups. The lowest mean AMS was 38 in the C subtype, and the highest was 97 in the A1/A2 subtype. Significant improvement in AMS was found between admission and follow-up in A0 (70 and 90, respectively, P < 0.0001) and B3 (41 and 75, respectively, P ¼ 0.03). The AIS impairment grade was recorded as complete (AIS A) and incomplete (AIS BeD) for all morphology types. Group A3/A4 had the highest percentage of patients with complete injuries (5/9, 55.6%) and at follow-up (3/9, 33.3%). Group A0 had 1 patient with complete injury at admission (1/36, 2.8%) and none at follow-up Table 4. Admission AIS Scores A0 A0
A1/A2
A3/A4
B2
B3
C
1
0.0006
0.27
1
0.005
0.2
1
1
0.51
A1/A2
1
A3/A4
0.0006
0.2
0.27
1
B2
0.29 0.29
B3
1
1
0.01
0.38
C
0.005
0.51
0.42
0.61
0.01
0.42
0.28
0.61 0.05
0.05
Statistical comparison of admission Abbreviated Injury Severity (AIS) scores across all morphology injury subtypes. Patients were classified as having either incomplete (ASIS BeE) or complete (ASIA A) injuries. Significant differences are in bold (P < 0.05).
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A0
A1/A2
A3/A4
B2
B3
C
1
0.006
1
1
1
0.5
1
1
1
0.21
0.074
0.047
1
1 1
1
Statistical comparison of follow-up (>6 months) Abbreviated Injury Severity (AIS) scores across all morphology injury subtypes. Patients were classified as having either incomplete (ASIS BeD) or complete (ASIA A) injuries. Significant differences are in bold (P < 0.05).
(0%). Groups A1/A2 and B3 had no patients with complete injuries at either admission or follow-up (0/4 and 0/11, respectively). Group B2 had 1 patient with complete injury at admission (1/8, 12/ 5%) and none at follow-up (0%). Group C injuries showed statistically significant AIS grade conversion from complete to incomplete neurologic status (P ¼ 0.04); 5 patients with complete injuries at admission (35.7%) transitioned to incomplete injuries at follow-up. Analysis for differences in AMS was carried out across all subtypes. Table 2 shows that significant differences were found between admission AMS between A0 versus B3 and C (P ¼ 0.009 and P ¼ 0.018, respectively), as well as A1/A2 versus B3 and C (P ¼ 0.007 and P ¼ 0.04, respectively). Table 3 shows that significant differences in follow-up (>6 months) AMS were found between A0 versus A3/A4 and C (P ¼ 0.007 and P ¼ 0.004, respectively), A3/A4 versus B2 (P ¼ 0.027), and B2 versus C (P ¼ 0.018). The AIS impairment grades (complete vs. incomplete) were compared across all subtypes on admission and follow-up. Table 4 shows the significant differences for AIS incomplete versus AIS complete injuries at admission between A0 versus A3/A4 and C (P < 0.001 and P ¼ 0.005, respectively), A3/A4 versus B3 (P ¼ 0.01), and B3 versus C (P ¼ 0.05). Table 5 demonstrates significant differences in AIS incomplete versus AIS complete injuries found at follow-up between A0 versus A3/A4 (P ¼ 0.006) and A3/4 versus C (P ¼ 0.05). Surgical management for each morphology was described with the surgical goal of spinal cord decompression, fixation, and alignment. There were a total of 44 anterior discectomy and fusions (53.7%), 10 anterior discectomy and fusions with laminectomy (12.2%), 2 anterior cervical corpectomies (2.4%), 2 anterior cervical corpectomies with laminectomy (2.4%), 18 laminectomies (22.0%), and 7 nonoperative conditions managed with a collar (7.3%). Table 6 shows the overall surgical management grouped according to morphology subtype. The IMLL was measured to assess admission injury severity across morphology subtypes. The overall mean IMLL for each subtype is shown in Table 1. The IMLL lengths in ascending order
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ORIGINAL ARTICLE HARRY MUSHLIN ET AL.
SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
Table 6. Surgical Intervention Morphology
Table 7. Comparison of Intramedullary Lesion Length
Number of Patients
Surgical Intervention
20
ACDF
1
ACDF þ laminectomy
11
Laminectomy
4
Collar
3
ACDF
<0.001
1
ACCF
B2 versus B3
A0
A0 versus A1/2 0.42
A1/A2
A1/2 versus A3/4 <0.001 A3/4 versus B2
<0.001
A3/A4 ACDF
B3 versus C
1
ACCF
0.06
1
ACDF þ laminectomy Laminectomy
1
Collar
7
ACDF
1
ACDF þ laminectomy
5
ACDF
B2
B3
3
ACDF þ laminectomy
2
Laminectomy
1
Collar
8
ACDF
4
ACDF þ laminectomy
2
ACCF þ laminectomy
C
The following procedures/management were reported: anterior cervical discectomy and fusion (ACDF); anterior cervical corpectomy and fusion (ACCF); ACDF þ laminectomy; laminectomy; and collar.
were B2 (11.2 mm), A1/2 (17.8 mm), A0 (22.3 mm), B3 (25.5 mm), C (32.9 mm), and A3/4 (48.1 mm). Comparison of the mean IMLL across subtypes revealed multiple significant differences. The following comparisons were all found to be significantly different: A0 versus A3/4, A0 versus B2, A0 versus C, A1/2 versus A3/4, A1/2 versus C, A3/4 versus B2, A3/4 versus B3, A3/4 versus C, B3 versus B3, and B2 versus C (P < 0.001; P < 0.001; P ¼ 0.01; P < 0.001; P < 0.001; P ¼ 0.013; P < 0.001; P < 0.001). The findings are summarized in Table 7. DISCUSSION The AOSpine Subaxial Cervical Spine Injury Classification System was created to improve communication in the clinical and research settings. A primary aim of this system has been to
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A0 versus B2
A0 versus B3
A0 versus C
<0.001 A1/2 versus B2
<0.001
0.23
0.001
A1/A2 versus B3
A1/2 versus C
0.26
0.2
0.02
A3/4 versus B3
A3/4 versus C
<0.001
0.013
B2 versus C <0.001
1
5
A0 versus A3/4
Statistical comparison of intramedullary lesion length across all morphology subtypes. Significant differences are in bold (P < 0.05).
improve the morphologic descriptions of subaxial cervical injuries in response to prior criticisms of earlier classification schemes. As noted above, these earlier systems were not shown to predict neurologic injury and prognosis, were difficult to implement, and consequently were not widely adopted. Here, we successfully and easily implemented the AOSpine classification system to classify 82 patients with subaxial cervical spine injury based on injury morphology and relation to IMLL and neurologic function on admission and long-term follow-up (>6 months). In applying this morphology-based classification system to our TSI cohort, several patterns became evident. A0 subtype was the most common subaxial cervical injury within this cohort (36 patients), representing morphology with the absence of any or only minor bony injuries, These patients were found to have significant improvement in AMS on follow-up from 70 to 90 (P < 0.0001) (Table 1).9 In addition to A0 injuries, those with a B3 pattern of injury (anterior column injuries) also showed significant improvement in AMS at follow-up (from 41 to 75, P ¼ 0.03). A1/ A2 type injuries had the highest AMS (least neurologically severe injuries) on admission, with a mean score of 97. This was found to be significantly greater than the AMS for C and B3 injuries (Table 2). A1/A2 subtypes include minor fractures of the vertebral body that typically do not compromise the cervical spinal cord and therefore portend better clinical presentations and outcomes relative to the more severe injury subtypes. The worst neurologic injuries were C and A3/A4 subtypes, which incorporate translational and tear drop/burst fractures, respectively. On admission, C subtype injuries had the lowest AMS, with a mean score of 38 and the second highest percentage of patients with complete injuries (33.3%). The mean admission AMS of the C subtype was significantly less than of the A0 and A1/ A2 type injuries (P ¼ 0.018 and P ¼ 0.04, respectively). Translational injuries as seen in the C subtype often present with severe compromise of the cervical canal and put patients at greater risk for neurologic deficit.
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SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
The A3/A4 patients had the highest percentage of patients with complete injuries on admission (55.6%). Importantly, at followup, A3/A4 patients had the lowest AMS (mean, 48). This was significantly worse than A0 and B2 (P ¼ 0.007 and P ¼ 0.27, respectively). In addition to having the lowest follow-up AMS, A3/ A4 was the only subtype to have patients with complete injuries at follow-up (33.3%). In comparison, C subtype injuries all converted to incomplete on follow-up (P ¼ 0.04), and although statistical significance was not achieved, these patients did have a higher mean AMS at follow-up compared with A3/A4 (56 vs. 48, respectively). We hypothesize that although C subtype injuries present with significant cord compression and neurologic injury, this injury morphology is more amenable to closed reduction, which theoretically reduces time to decompression. This favorable time to decompression translates into improved long-term outcomes, in contrast to A3/A4 injuries, which involve compromise of the posterior vertebral body and a high-impact injury to the spinal cord, and can be decompressed only with surgery. Further investigation of this hypothesis is warranted. Finally, we looked at admission IMLL as a marker for injury severity and association with each morphology subtypes. Previous clinical studies have demonstrated the important of IMLL and its relationship to AIS grade and neurologic outcome. Le et al.10 showed greater IMLL length expansion in AIS grades A and B. Aarabi et al.11 then showed that IMLL helped predict the AIS conversion. In this study, there were many significant differences between the IMLL across numerous morphology subtypes (Table 7). Importantly, we showed that the most serious injuries, A3/4 and C, had the longest IMLL. Furthermore, the IMLL of A3/4 was found to be significantly different from that of C (P ¼ 0.013). A3/4 had the highest IMLL (48.1 mm) and the worst neurologic outcome across all morphologic subtypes, adding to the literature further evidence of the importance of IMLL and neurologic outcome. In conclusion, we propose that the AOSpine spine morphologybased classification system has greater utility in assessing injury to the spinal cord than a mechanistic system. Previous classification systems, such that of Harris et al.,5 failed to predict neurologic injury and prognosis and instead focused on the optimal system to classify radiographic findings. Allen et al.4 did associate their mechanistic classification system with neurologic function, but well-established long-term follow-up was never published. These systems were devised without the availability of MRI and high-resolution CT, so practitioners were dependent on both radiographs and injury mechanism to determine classification and proper treatment. However, in today’s age of accessible high-
REFERENCES 1. Aarabi B, Walters BC, Dhall SS, et al. Subaxial cervical spine injury classification systems. Neurosurgery. 2013;72:170-186. 2. Holdsworth F. Fractures, dislocations, and fracture-dislocations of the spine. J Bone Joint Surg Am. 1970;52:1534-1551. 3. Nicoll EA. Fractures of the dorso-lumbar spine. J Bone Joint Surg Br. 1949;31-B:376-394.
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resolution MRI and CT scans, providers are easily able to assess morphologic damage. Here, by using the well-defined morphology-based AOSpine system, patients were easily classified, and each demonstrated distinct natural histories and injury severity. Previous work done by Aarabi et al.8 also implemented the use of the AOSpine classification system; however, there are important differences between the 2 studies. This current study included AIS A through D and nonoperative patients. These broader inclusion criteria led to a greater variation in our morphology analysis and allowed 6 distinct morphologies to be analyzed instead of 4. Furthermore, we eliminated the use of hybrid classifications to help simplify the application of the AOSpine system. In addition, although the 2 studies were from the same institution, this cohort was analyzed from a different consecutive group of patients with distinct morphology. Finally, the IMLL reported was from preoperative MRIs, which clinically allowed for earlier injury assessment. We believe the results presented in this study will help providers more confidently discuss prognosis with patients and families during the acute stages of management and later recovery by being able to have more granular understanding of the cervical injury. The limitations of this study are that it was a retrospective chart review of notes and radiographic data. Some patients were lost to follow-up. Owing to the varied number of subtypes, once our cohort was subdivided, some of the subtypes had a small number of patients for analysis, which could have limited statistical comparisons within and between various morphologic groupings. Overall, using the AOSpine classification system we have reported the most comprehensive subaxial cervical spine injury study reported to assess IMLL along with admission and long-term neurologic function based on injury morphology. CONCLUSION The AOSpine Subaxial Cervical Spine Injury Classification System was created to improve morphology-based classification systems with the goal of facilitating communication in clinical and research settings. We were able to successfully identify an association between certain morphology subtypes with admission IMLL and AMS and AIS score at admission and follow-up. We believe that this study and continued use of the AOSpine Subaxial Cervical Spine Injury Classification System will lead to greater understanding of injury morphology as it correlates to neurologic injury and will help improve communication among clinicians and patients to discuss initial injury and prognosis.
4. Allen BL, Ferguson RL, Lehmann TR, O’Brien RP. A mechanistic classification of closed, indirect fractures and dislocations of the lower cervical spine. Spine. 1982;7:1-27. 5. Harris JH, Edeiken-Monroe B, Kopaniky DR. A practical classification of acute cervical spine injuries. Orthop Clin North Am. 1986;17:15-30. 6. Vaccaro AR, Hulbert RJ, Patel AA, et al. The subaxial cervical spine injury classification system: a novel approach to recognize the importance of morphology, neurology, and integrity of
the disco-ligamentous complex. Spine. 2007;32: 2365-2374. 7. Vaccaro AR, Koerner JD, Radcliff KE, et al. AOSpine subaxial cervical spine injury classification system. Eur Spine J. 2016;25:2173-2184. 8. Aarabi B, Oner C, Vaccaro AR, Schroeder GD, Akhtar-Danesh N. Application of AOSpine subaxial cervical spine injury classification in simple and complex cases. J Orthop Trauma. 2017;31: S24-S32.
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ORIGINAL ARTICLE HARRY MUSHLIN ET AL.
SUBAXIAL CERVICAL INJURY CLASSIFICATION SYSTEM
9. Stevenson CM, Dargan DP, Warnock J, et al. Traumatic central cord syndrome: neurological and functional outcome at 3 years. Spinal Cord. 2016;54:1010-1015. 10. Le E, Aarabi B, Hersh DS, et al. Predictors of intramedullary lesion expansion rate on MR images of patients with subaxial spinal cord injury. J Neurosurg Spine. 2015;22:611-621. 11. Aarabi B, Sansur CA, Ibrahimi DM, et al. Intramedullary lesion length on postoperative magnetic
resonance imaging is a strong predictor of ASIA impairment scale grade conversion following decompressive surgery in cervical spinal cord injury. Neurosurgery. 2017;80:610-620.
Citation: World Neurosurg. (2019). https://doi.org/10.1016/j.wneu.2019.06.092 Journal homepage: www.journals.elsevier.com/worldneurosurgery Available online: www.sciencedirect.com
Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
1878-8750/$ - see front matter ª 2019 Elsevier Inc. All rights reserved.
Received 6 May 2019; accepted 12 June 2019
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