Muscle Fibre Architecture of Thoracic and Lumbar Longissimus Dorsi Muscle in the Horse.
Abstract: As the longissimus dorsi muscle is the largest muscle in the equine back, it has great influence on the stability of the spine and facilitates proper locomotion. The longissimus muscle provides support to the saddle and rider and thereby influences performance in the horse. Muscular dysfunction has been associated with back disorders and decline of performance. In general, muscle function is determined by its specific intramuscular architecture. However, only limited three-dimensional metrical data are available for the inner organisation of the equine longissimus dorsi muscle. Therefore, we aimed at investigating the inner architecure of the equine longissimus. The thoracic and lumbar longissimus muscles of five formalin-fixed cadaveric horse backs of different ages and body types were dissected layerwise from cranial to caudal. Three-dimensional coordinates along individual muscle fibre bundles were recorded using a digitisation tool (MicroScribe), to capture their origin, insertion and general orientation. Together with skeletal data from computed tomography (CT) scans, 3D models were created using imaging software (Amira). For further analysis, the muscle was divided into functional compartments during preparation and morphometric parameters, such as the muscle fascicle length, pennation angles to the sagittal and horizontal planes, muscle volume and the physiological cross-sectional area (PCSA), were determined. Fascicle length showed the highest values in the thoracic region and decreased from cranial to caudal, with the cranial lumbar compartment showing about 75% of cranial fascicle length, while in most caudal compartments, fascicle length was less than 50% of the fascicle length in thoracic compartments. The pennation angles to the horizontal plane show that there are differences between compartments. In most cranial compartments, fascicles almost run parallel to the horizontal plane (mean angle 0°), while in the caudal compartment, the angles increase up to a mean angle of 38°. Pennation angles to the sagittal plane varied not only between compartments but also within compartments. While in the thoracic compartments, the fascicles run nearly parallel to the spine, in the caudal compartments, the mean angles range from 0-22°. The muscle volume ranged from 1350 cm to 4700 cm depending on body size. The PCSA ranged from 219 cm to 700 cm depending on the muscle volume and mean fascicle length. In addition to predictable individual differences in size parameters, there are obvious systemic differences within the muscle architecture along the longissimus muscle which may affect its contraction behaviour. The obtained muscle data lay the anatomical basis for a specific biomechanical model of the longissimus muscle, to simulate muscle function under varying conditions and in comparison to other species.
Publication Date: 2021-03-23 PubMed ID: 33806991PubMed Central: PMC8004997DOI: 10.3390/ani11030915Google Scholar: Lookup
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- Journal Article
Summary
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The research article explores the intricacies of the longissimus dorsi muscle (largest muscle in a horse’s back) and its architecture. This muscle plays a prominent role in equine locomotion and performance.
Study Objectives and Methodology
- The primary goal of the research was to investigate the inner architecture of the equine longissimus dorsi, for which not much three-dimensional metrical data was available. Knowledge about the muscle’s anatomy could help understand disorders associated with muscular dysfunction in horses.
- The research was conducted on the thoracic and lumbar longissimus muscles in five horses of varying ages and body types. The skeletal data were gauged through CT scans, while the coordinates along the individual muscle fibre bundles were recorded using a MicroScribe digitisation tool.
- Three-dimensional models of the muscle structure were created employing imaging software (Amira).
- The muscle was divided into functional compartments for easier analysis of parameters like muscle fascicle length, pennation angles to the sagittal and horizontal planes, muscle volume, and the physiological cross-sectional area (PCSA).
Observations and Results
- The study found that the fascicle length exhibited the highest values in the thoracic region and saw a reduction from cranial to caudal.
- The pennation angles to the horizontal plane showed differences between compartments, suggesting slight differences in architecture overseeing different muscle functions.
- Regarding muscle volume, a range from 1350 cm up to 4700 cm was observed, which was dependent on the body size of the horse. The PCSA displayed a range from 219 cm up to 700 cm, reliant on the muscle volume and mean fascicle length.
- The researchers noted individual differences in size parameters, as expected. However, they also identified substantial systemic differences within the muscle architecture along the longissimus muscle.
Research Implications
- The collected data provides a solid anatomical basis for creating a biomechanical model of the longissimus muscle.
- Such a model could simulate muscle function under various conditions, potentially providing further insights into back disorders tied to muscular dysfunction in horses.
- The research findings can also be compared with the longissimus muscle data from other species to understand the structural differences and similarities better.
Cite This Article
APA
Dietrich J, Handschuh S, Steidl R, Böhler A, Forstenpointner G, Egerbacher M, Peham C, Schöpper H.
(2021).
Muscle Fibre Architecture of Thoracic and Lumbar Longissimus Dorsi Muscle in the Horse.
Animals (Basel), 11(3), 915.
https://doi.org/10.3390/ani11030915 Publication
Researcher Affiliations
- Institute of Anatomy, Histology and Embryology, Department of Pathobiology, University of Veterinary Medicine, 1210 Vienna, Austria.
- Movement Science Group Vienna, Equine Clinic, Department for Companion Animals and Horses, University of Veterinary Medicine, 1210 Vienna, Austria.
- VetImaging, VetCore Facility for Research, University of Veterinary Medicine, 1210 Vienna, Austria.
- Movement Science Group Vienna, Equine Clinic, Department for Companion Animals and Horses, University of Veterinary Medicine, 1210 Vienna, Austria.
- Diagnostic Imaging, Department for Companion Animals and Horses, University of Veterinary Medicine, 1210 Vienna, Austria.
- Institute of Anatomy, Histology and Embryology, Department of Pathobiology, University of Veterinary Medicine, 1210 Vienna, Austria.
- Institute of Anatomy, Histology and Embryology, Department of Pathobiology, University of Veterinary Medicine, 1210 Vienna, Austria.
- Movement Science Group Vienna, Equine Clinic, Department for Companion Animals and Horses, University of Veterinary Medicine, 1210 Vienna, Austria.
- Institute of Anatomy, Histology and Embryology, Department of Pathobiology, University of Veterinary Medicine, 1210 Vienna, Austria.
Conflict of Interest Statement
The authors declare no conflict of interest.
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