Utility of motor evoked potentials to diagnose and reduce lower extremity motor nerve root injuries during 4,386 extradural posterior lumbosacral spine procedures.

BACKGROUND CONTEXT: Motor evoked potentials (MEPs) have excellent sensitivity for monitoring the functional integrity of the lateral corticospinal tract of the spinal cord. The sensitivity for nerve root function, however, is not as well established; consequently, MEPs are often not utilized for posterior extradural spine procedures distal to the conus. Spontaneous electromyography (sEMG) and somatosensory evoked potentials (SSEPs) are often included for these procedures, but their limited sensitivity has been well documented. Given the risk of motor nerve root injuries during spine procedures, and specifically increased vulnerability of the L4 and L5 nerves, the sensitivity of MEPs was evaluated for diagnostic accuracy and therapeutic impact. PURPOSE: To determine the diagnostic sensitivity of MEPs during lumbosacral spine procedures and the potential therapeutic impact of the resolution of MEP alerts. STUDY DESIGN: A total of 4,386 posterior extradural lumbosacral spine procedures utilizing multimodality intraoperative neuromonitoring (IONM) with sEMG, SSEPs, and MEPs were abstracted from a multi-institutional database. All cases took place between October 2015 and October 2017. No external funding was provided. OUTCOME MEASURES: Sensitivity and specificity, as well as positive and negative likelihood ratios for new postoperative neurologic deficits were calculated for each modality individually as well as when combined (multimodality). PATIENT SAMPLE: Age 18 and older METHODS: Data entered in the electronic medical record were analyzed. Alerts to sEMG activity, decreases in SSEP amplitude, or decreases in MEP amplitude were documented as well as the status of the alerts at closure: resolved or unresolved. The presence of an sEMG alert or an unresolved MEP or SSEP alert at closure was considered a positive diagnostic result, and these results were assessed relative to presence of new immediate onset neurologic deficits as documented in the electronic record. RESULTS: The sensitivity and specificity of multimodality IONM for new immediate-onset lower extremity motor deficits were 100.0% (95% confidence interval: [64.6, 100.0]) and 92.2% (91.1, 93.1), respectively. Looking at the modalities in isolation, the sensitivity of MEPs was considerably better than either lower extremity sEMG or posterior tibial nerve SSEPs: 100.0% (78.5, 100.0) versus just 14.3% (4.0, 39.9) and 28.6% (8.2, 64.1), respectively. Surprisingly, the specificity of lower extremity MEPs was better than sEMG, 97.9% (97.5, 98.3) versus 95.4% (94.7, 96.0) (χ2=43.0, p<.001). The specificity of lower extremity SSEPs was 99.0% (98.5, 99.3). Only 4.4% of all procedures had a lower extremity MEP alert. There were 14 significant new nerve root injuries and all 14 had unresolved MEPs at closure. Total 85.7% of those nerve root injuries were dorsiflexion foot drop injuries and all had unresolved tibialis anterior MEP alerts. Although the overall rate of nerve root injuries was 0.32% (14/4,386), the rate for procedures with unresolved isolated tibialis anterior MEP alerts was 44.4% (12/27). The therapeutic impact is evident in the 2.0% of cases (87/4,386) with lower extremity MEP alerts that were able to be fully resolved by closure and for which the rate of injury was zero. CONCLUSIONS: The diagnostic accuracy of MEPs for anterior tibialis-related nerve root dysfunction supports the inclusion of this modality during routine posterior extradural lumbosacral procedures, especially when the L4 or L5 nerve roots are at risk. Moreover, therapeutic interventions that lead to the resolution of MEP alerts avert postoperative neurologic injuries.

The influence of fracture mechanism and morphology on the reliability and validity of two novel thoracolumbar injury classification systems.

STUDY DESIGN: The Thoracolumbar Injury Severity Score (TLISS) and the Thoracolumbar Injury Classification and Severity Score (TLICS) were prospectively evaluated. OBJECTIVES: To compare the reliability and validity of the TLISS and TLICS schemes to determine the importance of injury mechanism and morphology to the identification and treatment of thoracolumbar fractures. SUMMARY OF BACKGROUND DATA: Two novel algorithms have been developed for the categorization and management of thoracolumbar injuries: the TLISS system emphasizing injury mechanism and the TLICS scheme involving injury morphology. METHODS: The clinical and radiographic findings of 25 patients with thoracolumbar fractures were prospectively presented to 5 groups of surgeons with disparate levels of training and experience with spinal trauma. These injuries were consecutively scored, first using the TLISS and then 3 months later with the TLICS. The recommended treatments proposed by the 2 schemes were compared with the actual management of each patient. RESULTS: For both algorithms, the interrater kappa statistics of all subgroups (mechanism/morphology, status of the posterior ligaments, total score, predicted management) were within the range of moderate to substantial reproducibility (0.45-0.74), and there were no statistically significant differences noted between the respective kappa values. Interrater correlation was higher for the TLISS paradigm on mechanism/morphology, integrity of the posterior ligaments, and proposed management (P < or = 0.01). The TLISS and TLICS schemes both exhibited excellent overall validity. CONCLUSIONS: Although both schemes were noted to have substantial reproducibility and validity, our results indicate the TLISS is more reliable than the TLICS, suggesting that the mechanism of trauma may be a more valuable parameter than fracture morphology for the classification and treatment thoracolumbar injuries. Since these injury characteristics are interrelated and are critical to the maintenance of spinal stability, we think that both concepts should be considered during the assessment and management of these patients.

The adoption of a new classification system: time-dependent variation in interobserver reliability of the thoracolumbar injury severity score classification system.

STUDY DESIGN: Prospective clinical assessment of the interobserver reliability of the Thoracolumbar Injury Classification and Severity Score (TLISS) in a series of consecutive patients. OBJECTIVE: To evaluate the time-dependent changes in interobserver reliability of the TLISS system. SUMMARY OF BACKGROUND DATA: Reliability of an injury classification system is fundamental to its usefulness. A system that can be taught and implemented effectively will be highly reliable. Vaccaro et al recently introduced a novel thoracolumbar injury classification and treatment recommendation system called the "Thoracolumbar Injury Classification and Severity Score." An improvement over previous traumatic thoracolumbar systems, it has been designed to be both descriptive as well as prognostic. To define better the benefits of this system, the purpose of our study was to assess the time-dependent changes associated with implementation of the TLISS system at 1 institution. METHODS: Seventy-one consecutive patients presenting with acute thoracolumbar injury were prospectively assessed at a single training institution. Plain radiographs, computed tomography, and magnetic resonance imaging were independently reviewed, and each case was classified according to the TLISS system. Seven months later, 25 consecutive patients presenting with acute thoracolumbar injuries were prospectively assessed at the same institution. TLISS classification criteria were again applied after reviewing plain radiographs, computed tomography, and magnetic resonance imaging. The unweighted Cohen kappa coefficient and Spearman correlation values were calculated to assess interobserver reliability at each assessment time. Interobserved reliability at the time of the first assessment was then compared with interobserver reliability from the second assessment. RESULTS: Statistically significant (P < 0.05) improvements in interobserver reliability were observed. Both the unweighted Cohen kappa coefficient and Spearman correlation values increased across all comparable fields: TLISS subscores (mechanism of injury, posterior ligamentous complex), total TLISS, and TLISS management scores. CONCLUSIONS: The significant improvements observed in interobserver reliability of the TLISS system suggest that the classification system can be taught effectively and be readily incorporated into daily practice. The strong correlation values obtained at the second assessment time suggest that the TLISS system may be reproducibly used to describe thoracolumbar injuries.