Purpose: At present there is no reported, valid and reproducible model of degenerative spondylolisthesis for biomechanical testing of spinal implants. The purpose of this study was to create a single functional spinal unit (FSU) model that could demonstrate anterolisthesis consistent with low grade degenerative spondylolisthesis under physiologic shear loads.

Method: Eight fresh-frozen human cadaveric, lumbar FSU’s were potted and secured in a custom jig for pure shear testing. The cranial segment was loaded from – 50N (posterior) to 250N (anterior) over three cycles for each of five test conditions with a 300N preload. Test conditions addressed known restraints to shear translation and were performed in the same order for all specimens, and included: intact, facet capsulectomy and bilateral two mm facet gap, bilateral four mm facet gap, nucleotomy, and annular release. Three-dimensional motion was recorded using an optoelectronic camera system.

Results: Mean anterior translation at 250N for the five test conditions was 0.7 mm (95% confidence interval 0.4 to 0.9), 1.2 mm (0.9 to 1.6), 1.5 mm (1.1 to 2.0), 1.9 mm (1.4 to 2.4) and 3.1 mm (2.2 to 4.0). The mean maximum anterior translation was significantly different for each test condition with two exceptions. The four mm facet gap did not result in a significantly different maximum anterior translation compared to the two mm facet gap or the nucleotomy. There were no differences in off-axis motion (lateral or superior-inferior translation, flexion-extension, axial rotation, lateral bending) between the five test conditions.

Conclusion: Anterior translation consistent with low grade degenerative spondylolisthesis was repeatedly demonstrated under physiologic shear loads using this model. All sequential destabilizations preserved anatomy critical for the application of pedicle screw constructs, interbody devices and interspinous spacers. As such, this model is appropriate for biomechanical testing of implants currently used in the treatment of low grade degenerative spondylolisthesis.

Purpose: A single level spine fracture can be dangerous, however a second spine fracture at a different level can add complexity to patient management, and if missed, can result in a significant adverse outcome. Higher rates of multiple noncontiguous spinal injury (MNCSI) have been reported in patients who die from injuries, and with more unstable spinal injuries. The reported incidence in adults is 1.6–34%, but to our knowledge there are no studies examining multiple spine injuries in a pediatric population.

Method: A retrospective review of charts at an academic pediatric level 1 trauma center over a 15 year period identified a population with MNCSI.

Results: Twenty five (11.8%) out of 211 patients were identified with MNCSI and complete charts and radiographs. The mean age was 10.7 years old. MVC (motor vehicle collision) was the most common mechanism of injury for ages 0–9, while a fall was most common for ages 10–17 years. The mean number of vertebral levels injured was 3.2 and the most common region was the thoracic spine. Patients had a mean of 5.4 (range 1 to 22) intact vertebral levels between injuries. Twenty-four percent of patients with MNCSI had a neurologic deficit compared to 9.7% in patients with single level or contiguous injuries. This was statistically significant; risk ratio was 2.48 [1.09, 5.65]. Seven (78%) of 9 patients aged 0–9 suffered an associated injury; most commonly a visceral injury. The mortality rate was 8.0% in patients with MNCSI compared to 2.7% in patients with a single level injury.

Conclusion: We report a 12 % incidence of MNCSI in a pediatric trauma population. Children with NCSI were more likely to suffer neurologic injury than with a single level injury. Younger patients with MNCSI’s had a high rate of associated injuries. A higher mortality rate was seen in patients with MNCSI (not statistically significant). MNCSI’s can occur in conjunction with SCIWORA’s in the flexible pediatric spine. Clinicians must be aware of the incidence of NCSI’s in children, as well as their associations.