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Journal of anatomy2007; 211(5); 662-672; doi: 10.1111/j.1469-7580.2007.00800.x

Morphologic changes associated with functional adaptation of the navicular bone of horses.

Abstract: Failure of functional adaptation to protect the skeleton from damage is common and is often associated with targeted remodeling of bone microdamage. Horses provide a suitable model for studying loading-related skeletal disease because horses are physically active, their exercise is usually regulated, and adaptive failure of various skeletal sites is common. We performed a histologic study of the navicular bone of three groups of horses: (1) young racing Thoroughbreds (n = 10); (2) young unshod ponies (n = 10); and (3) older horses with navicular syndrome (n = 6). Navicular syndrome is a painful condition that is a common cause of lameness and is associated with extensive remodeling of the navicular bone; a sesamoid bone located within the hoof which articulates with the second and third phalanges dorsally. The following variables were quantified: volumetric bone mineral density; cortical thickness (Ct.Th); bone volume fraction, microcrack surface density; density of osteocytes and empty lacunae; and resorption space density. Birefringence of bone collagen was also determined using circularly polarized light microscopy and disruption of the lacunocanalicular network was examined using confocal microscopy. Remodeling of the navicular bone resulted in formation of transverse secondary osteons orientated in a lateral to medial direction; bone collagen was similarly orientated. In horses with navicular syndrome, remodeling often led to the formation of intracortical cysts and development of multiple tidemarks at the articular surface. These changes were associated with high microcrack surface density, low bone volume fraction, low density of osteocytes, and poor osteocyte connectivity. Empty lacunae were increased in Thoroughbreds. Resorption space density was not increased in horses with navicular syndrome. Taken together, these data suggest that the navicular bone may experience habitual bending across the sagittal plane. Consequences of cumulative cyclic loading in horses with navicular syndrome include arthritic degeneration of adjacent joints and adaptive failure of the navicular bone, with accumulation of microdamage and associated low bone mass, poor osteocyte connectivity, and low osteocyte density, but not formation of greater numbers of resorption spaces.
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Publication Date: 2007-09-11 PubMed ID: 17850287PubMed Central: PMC2375782DOI: 10.1111/j.1469-7580.2007.00800.xGoogle Scholar: Lookup
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  • Comparative Study
  • Journal Article
  • Research Support
  • Non-U.S. Gov't

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research explores the changes in the navicular bone of horses due to intense physical activities and presents findings about the effects of such changes to the bone structure. It studies how these changes can lead to diseases and other health issues in horses.

Objective of the Research

  • The primary objective of this research was to understand the failure of functional adaptation in the skeleton which is often associated with targeted remodeling of bone microdamage. This study also seeks to understand changes observed in the navicular bone of horses, specifically the effects of high-activity pursuits such as horse racing on the bone structure.

Methodology

  • The research utilized a histologic study of navicular bones from three groups of horses: young racing Thoroughbreds, young unshod ponies, and older horses diagnosed with navicular syndrome, a common cause of lameness due to extensive remodeling of the navicular bone.
  • The researchers quantified various variables such as volumetric bone mineral density; cortical thickness; bone volume fraction, microcrack surface density; density of osteocytes and empty lacunae; and resorption space density. They also examined the disruption of the lacunocanalicular network and the birefringence of bone collagen using appropriate microscopy techniques.

Observations and Findings

  • Remodeling of the navicular bone brought about the formation of transverse secondary osteons, and bone collagen was similarly oriented. In horses with navicular syndrome, remodeling resulted in the formation of intracortical cysts and the development of multiple tidemarks at the articular surface.
  • Further, these changes brought forth significant levels of microcrack surface density, a low bone volume fraction, low osteocyte density, and deteriorating osteocyte connectivity. The study also noted an increase in empty lacunae in thoroughbred horses.
  • The study did not find an increase in resorption space density in horses diagnosed with navicular syndrome. This could mean that while the disease may affect bone density and structure, it may not necessarily lead to bone loss.

Conclusion

  • Based on their findings, the researchers suggest that the navicular bone may experience habitual bending across the sagittal plane due to the high physical activity involved in horse racing.
  • This kind of cumulative cyclic loading can lead to arthritic degeneration of nearby joints and the adaptive failure of the navicular bone. There is also a corresponding increase in microdamage, low bone mass, poor osteocyte connectivity, and a drop in osteocyte density; nonetheless, there is no creation of a higher number of resorption spaces.

Cite This Article

APA
Bentley VA, Sample SJ, Livesey MA, Scollay MC, Radtke CL, Frank JD, Kalscheur VL, Muir P. (2007). Morphologic changes associated with functional adaptation of the navicular bone of horses. J Anat, 211(5), 662-672. https://doi.org/10.1111/j.1469-7580.2007.00800.x

Publication

Journal of anatomy
ISSN: 0021-8782
NlmUniqueID: 0137162
Country: England
Language: English
Volume: 211
Issue: 5
Pages: 662-672

Researcher Affiliations

Bentley, V A
  • Comparative Orthopaedic Research Laboratory, School of Veterinary Medicine, University of Wisconsin--Madison, Madison, WI 53706, USA.
Sample, S J
    Livesey, M A
      Scollay, M C
        Radtke, C L
          Frank, J D
            Kalscheur, V L
              Muir, P

                MeSH Terms

                • Animals
                • Bone Density
                • Bone Diseases / pathology
                • Bone Diseases / physiopathology
                • Bone Remodeling
                • Breeding
                • Horse Diseases / pathology
                • Horse Diseases / physiopathology
                • Horses
                • Microscopy, Confocal
                • Microscopy, Fluorescence
                • Osteocytes / cytology
                • Osteocytes / pathology
                • Physical Conditioning, Animal
                • Tarsal Bones / anatomy & histology
                • Tarsal Bones / pathology
                • Tarsal Bones / physiopathology
                • Tarsus, Animal / anatomy & histology
                • Weight-Bearing

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                Citations

                This article has been cited 8 times.
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