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Home / Equine Research Bank / J Anat / Parameters and functional analysis of the deep epaxial muscl...
Journal of anatomy2018; 233(1); 55-63; doi: 10.1111/joa.12818

Parameters and functional analysis of the deep epaxial muscles in the thoracic, lumbar and sacral regions of the equine spine.

Abstract: The epaxial muscles produce intervertebral rotation in the transverse, vertical and axial axes. These muscles also counteract the movements induced by gravitational and inertial forces and movements produced by antagonistic muscles and the intrinsic muscles of the pelvic limb. Their fascicles are innervated by the dorsal branch of the spinal nerve, which corresponds to the metamere of its cranial insertion in the spinous process. The structure allows the function of the muscles to be predicted: those with long and parallel fibres have a shortening function, whereas the muscles with short and oblique fibres have an antigravity action. In the horse, the multifidus muscle of the thoracolumbar region extends in multiple segments of two to eight vertebral motion segments (VMS). Functionally, the multifidus muscle is considered a spine stabiliser, maintaining VMS neutrality during spine rotations. However, there is evidence of the structural and functional heterogeneity of the equine thoracolumbar multifidus muscle, depending on the VMS considered, related to the complex control of the required neuromuscular activity. Osteoarticular lesions of the spine have been directly related to asymmetries of the multifidus muscle. The lateral (LDSM) and medial (MDSM) dorsal sacrocaudal muscles may be included in the multifidus complex, the function of which is also unclear in the lumbosacral region. The functional parameters of maximum force (F ), maximum velocity of contraction (V ) and joint moment (M) of the multifidus muscles inserted in the 4th, 9th, 12th and 17th thoracic and 3rd and 4th lumbar vertebrae of six horses were studied postmortem (for example: 4MT4 indicates the multifidus muscle that crosses four metameres with cranial insertion in the T4 vertebra). Furthermore, the structural and functional characteristics of LDSM and MDSM were determined. Data were analysed by analysis of variance (anova) in a randomised complete block design (P ≤ 0.05). For some muscles, the ordering of V values was almost opposite to that of F values, generally indicating antigravity or dynamic functions, depending on the muscle and VMS. The muscles 3MT12, 3ML3 and 4ML4 exhibited high F and low V values, indicating a stabilising action. The very long 7MT4 and 8MT4 multifidus had low F and high V values, suggesting a shortening action. However, some functional characteristics of interest did not fall within these general observations, also indicating a dual action. In summary, the results of the analysis of various structural and functional parameters confirm the structural and functional heterogeneity of the equine thoracolumbar multifidus complex, depending on the VMS, regardless of the number of metameres crossing each fascicle. To clarify the functions of the equine multifidus muscle complex, this study aimed to assess its functional parameters in thoracolumbar VMSs with different movement characteristics and in the MDSM and LDSM muscles, hypothesising that the functional parameters vary significantly when the VMS is considered.
© 2018 Anatomical Society.
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Publication Date: 2018-04-30 PubMed ID: 29708263PubMed Central: PMC5987835DOI: 10.1111/joa.12818Google Scholar: Lookup
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Summary

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This research investigates the structure and function of deep back muscles (epaxial muscles) in horses, specifically in the thoracic, lumbar, and sacral spine regions. Exploring the functional parameters—maximum force, maximum contraction speed, and joint moment—of these muscles in different vertebras of horses, the study discovers variations that can impact how these muscles contribute to horse movement and spinal stability.

Function and Characteristic of Epaxial Muscles

  • Epaxial muscles are located along the spine and play a crucial role in vertebral rotation across different axes. These muscles help counteract gravitational and inertial forces and movements generated by opposing muscles and the innate muscles of the horse’s leg.
  • Depending on their fibre structure, these muscles can either shorten or provide anti-gravity effects. Long, parallel fibres indicate the muscles’ shortening function, while short, oblique fibres suggest an anti-gravity action.

Structural and Functional Heterogeneity in the Multifidus Muscle

  • The multifidus muscle in a horse’s thoracolumbar region plays a vital role in spinal stabilization. It extends across multiple segments each composed of two to eight Vertebral Motion Segments (VMS). Different functional and structural aspects of this muscle vary depending on the VMSs.
  • Misalignments in the multifidus muscle are related directly to spinal injuries. Other sacrocaudal muscles – the lateral dorsal sacrocaudal muscle (LDSM) and medial dorsal sacrocaudal muscle (MDSM) – encompassed in the multifidus complex have uncertain roles in the lumbar and sacral regions.

Functional Parameters Study and Findings

  • The study examined the functional parameters (maximum force, maximum contraction speed, and joint moment) of the multifidus muscles connected to specific thoracic and lumbar vertebrae in six horses. It also determined the structural and functional features of LDSM and MDSM.
  • The findings noted variations in muscle function based on the VMS. Specifically, some muscles demonstrated stabilizing actions, while others suggested a shortening action. However, there were exceptions where muscles showed a dual action.

Conclusion

  • The research confirms the multifidus muscles’ structural and functional heterogeneity, which depends on VMS, regardless of the number of metameres (segments of a creature’s body) each fascicle (bundle of muscle fibres) passes through.
  • The study highlights the need for further research to clearly establish the differing functions of the equine multifidus muscle complex across the VMSs.

Cite This Article

APA
García Liñeiro JA, Graziotti GH, Rodríguez Menéndez JM, Ríos CM, Affricano NO, Victorica CL. (2018). Parameters and functional analysis of the deep epaxial muscles in the thoracic, lumbar and sacral regions of the equine spine. J Anat, 233(1), 55-63. https://doi.org/10.1111/joa.12818

Publication

Journal of anatomy
ISSN: 1469-7580
NlmUniqueID: 0137162
Country: England
Language: English
Volume: 233
Issue: 1
Pages: 55-63

Researcher Affiliations

García Liñeiro, J A
  • Department of Health and Equine Production, School of Veterinary Sciences, Buenos Aires University, Buenos Aires, Argentina.
Graziotti, G H
  • Department of Anatomy, School of Veterinary Sciences, Buenos Aires University, Buenos Aires, Argentina.
Rodríguez Menéndez, J M
  • Department of Anatomy, School of Veterinary Sciences, Buenos Aires University, Buenos Aires, Argentina.
Ríos, C M
  • Department of Anatomy, School of Veterinary Sciences, Buenos Aires University, Buenos Aires, Argentina.
Affricano, N O
  • Department of Anatomy, School of Veterinary Sciences, Buenos Aires University, Buenos Aires, Argentina.
Victorica, C L
  • Department of Anatomy, School of Veterinary Sciences, Buenos Aires University, Buenos Aires, Argentina.

MeSH Terms

  • Animals
  • Back Muscles / anatomy & histology
  • Back Muscles / physiology
  • Horses
  • Lumbar Vertebrae / anatomy & histology
  • Lumbar Vertebrae / physiology
  • Sacrum / anatomy & histology
  • Sacrum / physiology
  • Thoracic Vertebrae / anatomy & histology
  • Thoracic Vertebrae / physiology

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Citations

This article has been cited 2 times.
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  2. Ogden NKE, Winderickx K, Stack JD. Computed tomography of the equine caudal spine and pelvis. Pathological findings in 56 clinical cases (2018-2023). Equine Vet J 2025 Sep;57(5):1279-1289.
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