Spinal Motion and Muscle Activity during Active Trunk Movements - Comparing Sheep and Humans Adopting Upright and Quadrupedal Postures.

Stephanie Valentin,Theresia F Licka

doi:10.1371/journal.pone.0146362

Stephanie Valentin, Theresia F Licka

Open Access

https://doi.org/10.1371/journal.pone.0146362

Copy DOI

Abstract

Sheep are used as models for the human spine, yet comparative in vivo data necessary for validation is limited. The purpose of this study was therefore to compare spinal motion and trunk muscle activity during active trunk movements in sheep and humans. Three-dimensional kinematic data as well as surface electromyography (sEMG) of spinal flexion and extension was compared in twenty-four humans in upright (UR) and 4-point kneeling (KN) postures and in 17 Austrian mountain sheep. Kinematic markers were attached over the sacrum, posterior iliac spines, and spinous and transverse processes of T5, T8, T11, L2 and L5 in humans and over the sacrum, tuber sacrale, T5, T8, T12, L3 and L7 in sheep. The activity of erector spinae (ES), rectus abdominis (RA), obliquus externus (OE), and obliquus internus (OI) were collected. Maximum sEMG (MOE) was identified for each muscle and trial, and reported as a percentage (MOE%) of the overall maximally observed sEMG from all trials. Spinal range of motion was significantly smaller in sheep compared to humans (UR / KN) during flexion (sheep: 6–11°; humans 12–34°) and extension (sheep: 4°; humans: 11–17°). During extension, MOE% of ES was greater in sheep (median: 77.37%) than UR humans (24.89%), and MOE% of OE and OI was greater in sheep (OE 76.20%; OI 67.31%) than KN humans (OE 21.45%; OI 19.34%), while MOE% of RA was lower in sheep (21.71%) than UR humans (82.69%). During flexion, MOE% of RA was greater in sheep (83.09%) than humans (KN 47.42%; UR 41.38%), and MOE% of ES in sheep (45.73%) was greater than KN humans (14.45%), but smaller than UR humans (72.36%). The differences in human and sheep spinal motion and muscle activity suggest that caution is warranted when ovine data are used to infer human spine biomechanics.

Highlights

Sheep are a commonly used animal model for the human spine, as anatomical similarities in the human and sheep thoracolumbar spine have been described [1]
As all trials of humans led to a loss of marker visibility during UR extension, no data are available for this movement and posture
There were no significant differences in spinal range of motion between the young and the mature humans, and there were no significant correlations between sheep spinal range of motion and age

Summary

Introduction

Sheep are a commonly used animal model for the human spine, as anatomical similarities in the human and sheep thoracolumbar spine have been described [1]. The craniocaudal variation in range of motion of single-joint spinal segments under loaded conditions is similar between these species [2] and as a result, sheep are deemed suitable for in vitro spinal range of motion testing [3]. Such in vitro studies are generally performed on functional spinal units devoid of soft tissue. In vitro investigations allow the possibility of measuring parameters which would be difficult or impossible to measure in vivo, the removal of soft tissue structures in vitro will alter the biomechanical behaviour of the spine. The behaviour of a biological system in its entirety (i.e. in vitro and in vivo) should be considered to allow a more comprehensive biomechanical evaluation of the suitability of an animal model for the human spine

Objectives

Methods

Results

Conclusion