Comparison of the Immature Sheep Spine and the Growing Human Spine

Abstract

A comparative study on growth of the sheep and human spine. To validate the immature sheep spine as model for the growing human spine and to yield a database for planning and interpretation of future animal experiments. With the current change of paradigm to nonfusion strategies for pediatric spine deformities, experimental surgery on spines of growing goats, sheep, and pigs has gained importance as preclinical proof-of-concept test. However, despite the proceeding use of animals, there is a lack of knowledge regarding the growth of the sheep spine and the relation to the human spine. Thoracic and lumbar cadaver spines were harvested from 50 Swiss alpine sheep. Specimens were obtained from newborn, 1, 3, 6, 9 and 12, 15 and 18 months old female sheep. Direct spondylometry yielded vertebral body heights, widths, and depths and spinal canal size, which were compared to pooled data on human spine growth retrieved from the literature. Sheep spine growth ceases at age 15 to 18 months, which corresponds to a time-lapse model of human growth. Main growth occurs within the first 3 to 6 months of life, as opposed to human spines with maximal growth during the first 4 years and puberty. The relation between sheep and human vertebral shape is continuously changing with growth: at birth, sheep vertebrae are twice as tall, but equally wide and deep. At skeletal maturity, height is 15% to 25% bigger in sheep, but width 15% to 30% and depth 30% to 50% are smaller. The immature sheep spine offers fast effects if growth-modulating interventions are performed within the first 3 to 6 months of age. The differences in vertebral shapes and further distinctions between human and sheep spines such as biomechanics, facet anatomy, and rib cage morphology have to be considered when interpreting results after experimental surgery.