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Morphologic changes associated with functional adaptation of the navicular bone of horses.
J Anat. 2007 Nov; 211(5):662-72.JA

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.

Authors+Show Affiliations

Comparative Orthopaedic Research Laboratory, School of Veterinary Medicine, University of Wisconsin--Madison, Madison, WI 53706, USA.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Comparative Study
Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

17850287

Citation

Bentley, V A., et al. "Morphologic Changes Associated With Functional Adaptation of the Navicular Bone of Horses." Journal of Anatomy, vol. 211, no. 5, 2007, pp. 662-72.
Bentley VA, Sample SJ, Livesey MA, et al. Morphologic changes associated with functional adaptation of the navicular bone of horses. J Anat. 2007;211(5):662-72.
Bentley, V. A., Sample, S. J., Livesey, M. A., Scollay, M. C., Radtke, C. L., Frank, J. D., Kalscheur, V. L., & Muir, P. (2007). Morphologic changes associated with functional adaptation of the navicular bone of horses. Journal of Anatomy, 211(5), 662-72.
Bentley VA, et al. Morphologic Changes Associated With Functional Adaptation of the Navicular Bone of Horses. J Anat. 2007;211(5):662-72. PubMed PMID: 17850287.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Morphologic changes associated with functional adaptation of the navicular bone of horses. AU - Bentley,V A, AU - Sample,S J, AU - Livesey,M A, AU - Scollay,M C, AU - Radtke,C L, AU - Frank,J D, AU - Kalscheur,V L, AU - Muir,P, Y1 - 2007/09/11/ PY - 2007/9/14/pubmed PY - 2008/1/17/medline PY - 2007/9/14/entrez SP - 662 EP - 72 JF - Journal of anatomy JO - J. Anat. VL - 211 IS - 5 N2 - 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. SN - 0021-8782 UR - https://www.unboundmedicine.com/medline/citation/17850287/Morphologic_changes_associated_with_functional_adaptation_of_the_navicular_bone_of_horses_ L2 - https://doi.org/10.1111/j.1469-7580.2007.00800.x DB - PRIME DP - Unbound Medicine ER -