The Anatomy and Function of the equine thoracolumbar Longissimus dorsi muscle

The aim of this thesis was to evaluate the structure and function
of the largest muscle of the equine back, the Longissimus dorsi
muscle (LD) and investigate the usefulness of ultrasonography in
determining LD architecture in live horses. Dissection of
clinically normal horse and pony cadaver backs demonstrated the
complex architecture of this muscle with its regional variations in
diameter, muscle fibre length and pennation angle. The observed
anatomical differences corresponded to regional differences in
muscle activity pattern and the intensity of muscle activity in six
horses examined. Electrmyographic measurements showed significant
diffeneces at different anatomical locations, gait, speed and
inclines. Ultrasonography was evaluated as a tool to visualize and
quantify LD architecture in live horses. In the first
ultrasonographic study the ultrasonographic anatomy of the LD was
determined by matching ultrasonographic images to corresponding
frozen sections in a cadaver. Inter- and intra-operator
repeatability of ultrasound based muscle measurements showed that
muscle thickness measurements were found to be reapeatable,
pennation angle was not. The presented thesis contributes to
understanding the biomechanics of the equine LD by illustrating the
relationship between anatomy and function through integrating
cadaveric data with measurements in live horses. In the second part
the use of ultrasonography in determining LD architecture and
functioin in live horses as future diagnostic tool was investigated
and its usefulness and limitations established.