Biomechanics of the back

Introduction

The thoracolumbar region of the equine spine provides an important structural and functional component of the locomotor apparatus, especially as it relates to ridden exercise. In the last few decades, significant advances have been made in further understanding of the role that the thoracolumbar spine plays in athletic performance and in the transfer of biomechanical forces between the thoracic and pelvic limbs during equestrian activities.

The biomechanical concept of the back

The biomechanical concept and perceived function of the quadrupedal back has changed over time. The Roman physician Galen referred to the prevailing architecture of his day and describes the quadrupedal back as a vaulted roof sustained by 4 pillars; the limbs (cited by Slijper 1946 [1]). The next concept of the quadrupedal trunk from the middle of the 19th century was again inspired by the technical advances in engineering of that era. In the bridge concept of the equine back, the limbs are considered to form the land abutments of the bridge and the gap between these abutments is spanned by the bridge itself [2] (Krüger 1939). More recently, this model has been replaced by the ‘bow-and-string’ concept, in which the bow is represented dorsally by the relatively inflexible thoracolumbar vertebral column and the string is formed ventrally by soft tissues, consisting of the linea alba, the rectus abdominis muscle and related trunk structures [1] (Slijper 1946). Although the concept does not account for some specific anatomical aspects, most notably flexion–extension at the lumbosacral junction or pelvic rotation about the coxofemoral articulation (Fig 1a,b), it is still the most widely accepted biomechanical model to date and its validity has been confirmed by recent spinal research in the horse. […]