The influence of the energy of trauma, the timing of decompression, and the impact of grade of SCI on outcome

ABSTRACT

 

Study design: Retrospective cohort study.

Objectives: To find out: (1) if the energy of trauma (high and low) influence the outcome after cervical spinal cord injury; (2) if time to decompression and degree of injury (complete and incomplete) influence the outcome after high- and low-energy cervical spinal cord injury.

Methods: Twenty-one consecutive patients with low-energy cervical spinal cord injury were identified from the spinal injuries unit database (eg, ball sports, diving, surfing, and falls). Twenty-one aged-matched patients with high-energy cervical spinal cord injury (eg, motor vehicle trauma) were then randomly selected and the groups were compared. All patients had formal American Spinal Injuries Association assessment on admission and at 6 months.

Results: At the 6-month follow-up, the energy of the initial trauma was not found to influence the neurological outcome (P =  = .76). Early definitive intervention (< 8 hours) for patients with incomplete cord lesions was shown to significantly affect outcome (P = .049). As expected, patients with an incomplete spinal cord injury at presentation showed significantly greater neurological improvement at follow-up compared with those with complete injuries (P = .006).

Conclusions: We were unable to find a correlation between the energy of the initial trauma causing a spinal cord injury and the neurological outcome. Early definitive decompression improved outcomes for patients with spinal cord injury, especially those with incomplete spinal cord injury.

STUDY RATIONALE AND CONTEXT Animal studies have shown that the rate, depth, and duration of spinal cord compression influence neurological prognosis 1, 2, 3, 4. The role of surgery in improving neurological recovery remains controversial. There is emerging clinical evidence that early decompression (< 24 hours) improves neurological outcome 5, 6, 7, 8, 9. Experimental evidence advocates decompression within 8 hours 10. OBJECTIVES To find out: (1) if the energy of trauma influence the outcome after cervical spinal cord injury (SCI); (2) if timing to definite decompression influence the outcome after cervical SCI. METHODS Study design: Retrospective cohort of patients treated for acute traumatic cervical SCI. Inclusion criteria: Low energy: acute traumatic cervical SCI from rugby, diving, surfing, and low-height falls. High energy: acute traumatic cervical SCI from motor vehicle trauma. Exclusion criteria: Central cord syndrome; no evidence of fracture or dislocation; coexisting significant head injury resulting in neurological impairment of the limbs. Nontraumatic causes of SCI/compression. Patient population and selection: The Princess Alexandra Hospital has an acute spinal cord trauma service and houses the Australian State of Queensland's SCI center on one campus. Over a 5-year period, 21 consecutive patients with low-energy cervical SCI admitted to the Spinal Injuries Unit were identified using the Spinal Injuries Unit Database. Patients for the low-energy cohort were age matched to within 3 years from the 139 cases of high-energy acute cervical traumatic SCI patients admitted during the same period. In cases of more than one appropriate match the high-energy cohort patient was selected using the „names from a hat” technique. All the patients underwent intervention to reduce, stabilize, and decompress the spinal cord either surgically or through traction and halo-vest immobilization. Outcomes and prognostic (risk) factors to be evaluated: The American Spinal Injuries Association (ASIA) grade at presentation and at 6 months was measured on all patients. Complete SCI was defined as ASIA grade A (no motor or sensory function at S4/5) and incomplete as ASIA grades B to D (some motor or sensory function below the injury level). Neurological outcome was assessed by comparing the proportions that improved 1 or more ASIA grade between initial presentation and 6-month follow-up. Effect of time to definitive surgical intervention on ASIA grade: Early surgery was defined as within 8 hours of injury. Paramedic, hospital emergency department admission, and operating room patient-tracking databases were used to accurately evaluate the time to surgery. The effect of low- versus high-energy injury on ASIA grade: Energy of injury was defined by mechanism. Low-energy injury was defined as those resulting from ball sports (eg, rugby, surfing, diving into shallow water, and falls from a standing height). High-energy injury was defined as those resulting from motor vehicle trauma in which the kinetic energy was deemed to be far greater. Analysis: The proportion that improved 1 or more ASIA grade between initial presentation and 6-month follow up was compared between cohorts using a Fisher's exact test. The cohorts comprised ASIA grade on presentation (complete or incomplete), time to surgery (early or late), and energy of injury (high or low).

REFERENCES

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EDITORIAL STAFF PERSPECTIVE

The reviewers congratulated McCarthy and colleagues for introducing the element of injury energy into the scientific evaluation of SCI prognosis and care. The influence of kinetic energy on outcome is indeed an often overlooked factor. Setting the bar to canal decompression much higher than previously done by others by using a cutoff of 8 hours is a step in the right direction, and much more consistent with our understanding of largely irreversible temporal physiological changes that affect the injured cord. This study also supports the findings that injury severity is a profound determinant of eventual outcome.

While these considerations were seen very favorably, the reviewers also identified a number of concerns:

• SCI is a complex multifactorial entity. Covariables, such as preexistent stenosis, injury type (unilateral versus bilateral facet dislocation-type injuries, hyperextension injuries, burst fractures, shear injuries); injury severity scores affecting other organ systems; age of patient; restoration of normotension and quality of resuscitation; type of decompression and realignment/ stabilization techniques used, are just some of the many factors which plausibly will impact patient outcomes.

• The actual differentiation of high- and low-energy injury based on described mechanisms is somewhat arbitrary as well.

• From a statistical point of view this study is most likely underpowered and suffers from some of the typical protocol inconsistencies, which decrease the evidence level of retrospective studies. For instance, McCarthy et al identified that seven patients had traction and four had external immobilization (which is a quarter of the 42-patient cohort). It is likely that these are the injuries that they referred to as ‘biomechanically stable’—but they clearly represent a subpopulation that is widely different from patients with clearly unstable and displaced injuries, such as patients with complex fracture dislocations who required combined anterior and posterior procedures. From a methodological standpoint this subentity would preferably be assessed either separately or the main cohorts should be reassessed to make sure that they are similarly represented.

• Incomplete injuries have confounded many an SCI study as they represent a complex subentity, especially as far as central cord injuries are concerned. It has become increasingly clear that central cord syndromes are some of the injuries with better recovery potential. Yet again, this represents an injury entity which may heavily influence outcomes in observation cohorts and thus has to be accounted for separately to assure absence of observation bias.

• This study—and the factors raised in this discussion—again underscores the magnitude of difficulty individual SCI researchers face. From a statistical angle any study less than 1,000 is likely underpowered. Consistent treatment and assessment protocols applied over several years are really what are necessary to allow for larger scale conclusions on SCI care to be drawn.

In the big picture McCarthy et al deserve praise for investigating important and previously not discussed variables that influence SCI outcomes. Much hope and anticipation will be placed on the results of the STASCIS group and its unprecedented number of SCI patients treated in many reputable institutions.