OBJECT A range of surgical options exists for the treatment of degenerative lumbar spondylolisthesis (DLS). The chosen technique inherently depends on the stability of the DLS. Despite a substantial body of literature dedicated to the outcome analysis of numerous DLS procedures, no consensus has been reached on defining or classifying the disorder with respect to stability or the role that instability should play in a treatment algorithm. The purpose of this study was to define grades of stability and to develop a guide for deciding on the optimal approach in surgically managing patients with DLS. METHODS The authors conducted a qualitative systematic review of clinical or biomechanical analyses evaluating the stability of and surgical outcomes for DLS for the period from 1990 to 2013. Research focused on nondegenerative forms of spondylolisthesis or spinal stenosis without associated DLS was excluded. The primary extracted results were clinical and radiographic parameters indicative of DLS instability. RESULTS The following preoperative parameters are predictors of stability in DLS: restabilization signs (disc height loss, osteophyte formation, vertebral endplate sclerosis, and ligament ossification), no disc angle change or less than 3 mm of translation on dynamic radiographs, and the absence of low-back pain. The validity and magnitude of each parameter’s contribution can only be determined through appropriately powered prospective evaluation in the future. Identifying these parameters has allowed for the creation of a preliminary DLS instability classification (DSIC) scheme based on the preoperative assessment of DLS stability. CONCLUSIONS Spinal stability is an important factor to consider in the evaluation and treatment of patients with DLS. Qualitative assessment of the best available evidence revealed clinical and radiographic parameters for the creation of the DSIC, a decision aid to help surgeons develop a method of preoperative evaluation to better stratify DLS treatment options.

Whole-body vibration has been identified as a potential stressor to spinal cord injury (SCI) patients during pre-hospital transportation. However, the effect that such vibration has on the acutely injured spinal cord is largely unknown, particularly in the frequency domain of 5 Hz in which resonance of the spine occurs. The objective of the study was to investigate the consequences of resonance vibration on the injured spinal cord. Using our previously characterized porcine model of SCI, we subjected animals to resonance vibration (5.7±0.46 Hz) or no vibration for a period of 1.5 or 3.0 h. Locomotor function was assessed weekly and cerebrospinal fluid (CSF) samples were collected to assess different inflammatory and injury severity markers. Spinal cords were evaluated histologically to quantify preserved white and gray matter. No significant differences were found between groups for CSF levels of monocyte chemotactic protein-1, interleukin 6 (IL-6) and lL-8. Glial fibrillary acidic protein levels were lower in the resonance vibration group, compared with the non-vibrated control group. Spared white matter tissue was increased within the vibrated group at 7 d post-injury but this difference was not apparent at the 12-week time-point. No significant difference was observed in locomotor recovery following resonance vibration of the spine. Here, we demonstrate that exposure to resonance vibration for 1.5 or 3 h following SCI in our porcine model is not detrimental to the functional or histological outcomes. Our observation that a 3.0-h period of vibration at resonance frequency induces modest histological improvement at one week post-injury warrants further study.

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In the military environment, injured soldiers undergoing medical evacuation via helicopter or mine-resistant ambush-protected vehicle (MRAP) are subjected to vibration and shock inherent to the transport vehicle. We conducted the present study to assess the consequences of such vibration on the acutely injured spinal cord. We used a porcine model of spinal cord injury (SCI). After a T10 contusion-compression injury, animals were subjected to 1) no vibration (n = 7-8), 2) whole body vibration at frequencies and amplitudes simulating helicopter transport (n = 8), or 3) whole body vibration simulating ground transportation in an MRAP ambulance (n = 7). Hindlimb locomotor function (using Porcine Thoracic Injury Behavior Scale [PTIBS]), Eriochrome Cyanine histochemistry and biochemical analysis of inflammatory and neural damage markers were analyzed. Cerebrospinal fluid (CSF) expression levels for monocyte chemoattractant protein-1 (MCP-1), interleukin (IL)-6, IL-8, and glial fibrillary acidic protein (GFAP) were similar between the helicopter or MRAP group and the unvibrated controls. Spared white/gray matter tended to be lower in the MRAP-vibrated animals than in the unvibrated controls, especially rostral to the epicenter. However, spared white/gray matter in the helicopter-vibrated group appeared normal. Although there was a relationship between the extent of sparing and the extent of locomotor recovery, no significant differences were found in PTIBS scores between the groups. In summary, exposures to vibration in the context of ground (MRAP) or aeromedical (helicopter) transportation did not significantly impair functional outcome in our large animal model of SCI. However, MRAP vibration was associated with increased tissue damage around the injury site, warranting caution around exposure to vehicle vibration acutely after SCI.

Falls to the side are the leading cause of hip fractures in the elderly. The load that a person experiences during a fall cannot be measured with volunteers for ethical reasons. To evaluate injurious loads, while considering relevant energy input and body posture for a sideways fall, a subject-specific cadaveric impact experiment was developed. Full cadaveric femur-pelvis constructs (N = 2) were embedded in surrogate soft tissue material and attached to metallic surrogate lower limbs. The specimens were then subjected to an inverted pendulum motion, simulating a fall to the side with an impact to the greater trochanter. The load at the ground and the deformation of the pelvis were evaluated using a 6-axis force transducer and two high-speed cameras. Post-test, a trauma surgeon (PG) evaluated specimen injuries. Peak ground contact forces were 7132 N and 5641 N for the fractured and non-fractured specimen, respectively. We observed a cervical fracture of the femur in one specimen and no injuries in a second specimen, showing that the developed protocol can be used to differentiate between specimens at high and low fracture risk.

The aim of this study was to determine the effect of the posterior ligaments and facet joints on the shear stiffness of lower cervical functional spinal units in anterior, posterior, and lateral shear. Five functional spinal units were loaded in anterior, posterior, and right lateral shear up to 100 N using a custom-designed apparatus in a materials testing machine. Specimens were tested in three conditions: intact, with the posterior ligaments severed, and with the facet joints removed. There was a significant decrease in anterior stiffness in the 20–100 N load range from 186 (range: 98–327) N/mm in the intact condition to 105 (range: 78–142) N/mm in the disc-only condition (p = 0.03). Posterior stiffness between these condition decreased significantly from 134 (range: 92–182) N/mm to 119 (range: 83–181) N/mm (p = 0.03). There was no significant effect of posterior ligament removal on shear stiffness. No significant differences were found in the lateral direction or in the 0–20 N range for any direction. Under a 100-N shear load, the facet joints played a significant role in the stiffness of the cervical spine in the anterior–posterior direction, but not in the lateral direction.

HAM location in axial rotation and flexion/extension was more anterior in young females compared to adult females. Young females had a more anterior HAM location in flexion/extension compared to young males, indicating an effect of sex. For females, the HAM locations of adults were superior to those of children in flexion/extension and lateral bending whereas in males the HAM locations of adults were inferior to those of children. Age-related differences in HAM orientation were also observed in axial rotation and lateral bending. CONCLUSION.: Cervical spine kinematics vary with age and sex. The variation in spine mechanics based on age and sex found in the present study may indicate general trends that would grow stronger in even younger children (age <4 years).

Implant shear stiffness significantly affected the load sharing between the implant and the natural spine in anterior shear ex vivo. Low-stiffness implants transferred significantly greater loads to the spine. This study supports the importance of load-sharing behavior when designing new implants.