Biomechanical Tolerance of Whole Lumbar Spines in Straightened Posture Subjected to Axial Acceleration

Quantification of biomechanical tolerance is necessary for injury prediction and protection of vehicular occupants. This study experimentally quantified lumbar spine axial tolerance during accelerative environments simulating a variety of military and civilian scenarios. Intact human lumbar spines (T12‐L5) were dynamically loaded using a custom‐built drop tower. Twenty‐three specimens were tested at sub‐failure and failure levels consisting of peak axial forces between 2.6 and 7.9 kN and corresponding peak accelerations between 7 and 57 g. Military aircraft ejection and helicopter crashes fall within these high axial acceleration ranges. Testing was stopped following injury detection. Both peak force and acceleration were significant (p \u3c 0.0001) injury predictors. Injury probability curves using parametric survival analysis were created for peak acceleration and peak force. Fifty‐percent probability of injury (95%CI) for force and acceleration were 4.5 (3.9–5.2 kN), and 16 (13–19 g). A majority of injuries affected the L1 spinal level. Peak axial forces and accelerations were greater for specimens that sustained multiple injuries or injuries at L2–L5 spinal levels. In general, force‐based tolerance was consistent with previous shorter‐segment lumbar spine testing (3–5 vertebrae), although studies incorporating isolated vertebral bodies reported higher tolerance attributable to a different injury mechanism involving structural failure of the cortical shell. This study identified novel outcomes with regard to injury patterns, wherein more violent exposures produced more injuries in the caudal lumbar spine. This caudal migration was likely attributable to increased injury tolerance at lower lumbar spinal levels and a faster inertial mass recruitment process for high rate load application. Published 2017. This article is a U.S. Government work and is in the public domain in the USA

BIOMECHANICS OF SPINAL INJURIES PRODUCED BY VERTICAL COMPRESSION

Fifty-six cadavers were studied to analyze failure mechanics of the spine using vertical compression loading. In addition, six other spines were studied with three- or four-point loading. The cervical spine was loaded to failure in 13 cadavers. Ten were studied as isolated columns; the other three were intact. Forces were directed axially, or spines were loaded in preflexion or extension. Loads required to produce injury ranged from 645 to 7439 N. Flexion injuries were produced at an average value of 1989 Newtons and extension at 2196 N; failures with axial loading averaged 5969 N. The column alterations produced, particularly the ligament avulsions seen, correlated only partially with the force direction. Observed alterations were clinically consistent, however. The thoracolumbar spine was studied in 29 cadavers. Eighteen columns and five intact cadavers were subjected to flexion compression loading and six columns to three- or four-point bending. The most common levels of fracture were T11 and T12. Isolated columns failed at 2360 N (556-5275 N), and the intact cadavers at 1737 N (range 1110-2750 N). Mean bending moments were 168 Nm for the isolated columns, and 187 Nm for the intact cadavers. Differences in loads and moments between isolated columns and intact cadavers were not statistically significant. The three spines subjected to three-point bending failed at an average of 1761 N; mean failure was 2716 N for four-point bending. Mean bending moments were 115 and 136 Nm, respectively, and were significantly different than those reported for column loading. The injuries provided by (vertical) compression were reproducible and similar to those routinely seen. In nine isolated thoracolumbar column and five intact cadavers, the flexion/compression technique was applied to compare the failure characteristics of spines instrumented sequentially with modified Weiss springs, Harrington distraction rods, and Luque rods. Mean initial spine failure was 1833 N; spines instrumented with the springs failed (with production of spinal angles equal to those seen after initial fracture) at 1128 N (54% of control) by allowing bending of the spine. Harrington rodded-spines failed at 859 N (42%), by hook extrusion and lamina fractures. Luque rods failed at 83% of control at acute angles and provided the most rigid stabilization, followed by the modified springs. The consistent nature of the trauma and clinical pertinence make compression loading of the spine a valuable technique in spine analysis

Marsupialization and distal obliteration of a lumbosacral dural ectasia in a nonsyndromic, adult patient

Dural ectasia is frequently associated with connective tissue disorders or inflammatory conditions. Presentation in a patient without known risk factors is rare. Moreover, the literature regarding the treatment options for symptomatic dural ectasia is controversial, variable, and limited. A 62-year-old female presents with intractable, postural headaches for years. A lumbar puncture revealed opening pressure 3 cm of water. A computed tomography myelogram of the spine demonstrated erosion of her sacrum due to a large lumbosacral dural ectasia. An initial surgery was attempted to reduce the size of the expansile dura, and reconstruct the dorsal sacrum with a titanium plate (Depuy Synthes, Westchester, PA, USA) to prevent recurrence of thecal sac dilatation. Her symptoms initially improved, but shortly thereafter recurred. A second surgery was then undertaken to obliterate the thecal sac distal to the S2 nerve roots. This could not be accomplished through simple ligation of the thecal sac circumferentially as the ventral dura was noted to be incompetent and attempts to develop an extradural tissue plane were unsuccessful. Consequently, an abundance of fibrin glue was injected into the thecal sac distal to S2, and the dural ectasia was marsupialized rostrally, effectively obliterating the distal thecal sac while further reducing the size of the expansile dura. This approach significantly improved her symptoms at 5 months follow-up. Treatment of dural ectasia is not well-defined and has been variable based on the underlying manifestations. We report a rare patient without risk factors who presented with significant lumbosacral dural ectasia. Moreover, we present a novel method to treat postural headaches secondary to dural ectasia, where the thecal sac is obliterated distal to the S2 nerve roots using an abundance of fibrin glue followed by marsupialization of the thecal sac rostally. This method may offer an effective therapy option as it serves to limit the expansile dura, reducing the cerebrospinal fluid sump and the potential for intracranial hypotension