Spina accresco mechanicus: On the developmental biomechanics of the spine

Epidemiological data and clinical indicia reveal devastating consequences associated with pediatric neck injuries. Neither injury prevention nor clinical management strategies will be able to effectively reduce these effects on children, without an understanding of cervical spine developmental biomechanics. This investigation examines the biomechanical characteristics (functional biomechanics and tolerance) and morphological patho-mechanics of injury (tissue failure) in the maturing cervical spine. The cadaveric baboon (Papio anubis) spine, an anatomic and kinematic analog to the human cadaveric spine, served as the model to investigate these issues across the developmental spectrum. Significant relationships were discovered between both structural and material properties and developmental age. Further, significant gender, spinal level and loading rate effects were found to be associated with the mechanical development of the spine. Structural properties were strongly correlated with maturation indicating that tissue size may be a positive predictive tool. Unfortunately, size alone cannot predict pediatric spinal mechanics since its material properties also increased with development. The complex maturation process involves concomitant increases in both intrinsic material properties and structure giving rise to an age-specific mechanical response of the spine. These functional and tolerance data were employed in computational modeling efforts, which may facilitate the generation of enhanced pediatric injury prevention schema. The functional biomechanics data were used to generate maturation-specific constituent relationships and the tolerance data provide injury criteria for this computational model as well as physical (anthropomorphic test dummy) models. Another facet of this research evaluated clinically relevant injuries to identify the patho-mechanical response of the developing spine. Every injury created in the pediatric spine involved the failure of the growth plate (physis) regardless of mechanism. In compression the compromised growth plate was associated with vertebral fractures or disc herniations. Tensile mechanisms involved the growth plate zone of calcification separating from the vertebral body, yet this severe injury did not affect the developing intervertebral disc. These patterns support a physis focused assessment and management of pediatric injuries. The sum of this research fills a dearth in the developmental biomechanics literature concerning the spinal mechanical characteristics motivating injury prevention and the spinal patho-mechanical patterns aiding clinical management techniques.