Microstructural Alterations and Navicular Bone Degeneration

Microstructural Alterations and Navicular Bone Degeneration

Researchers saw microstructural changes in the compact and trabecular areas of these severely diseased bones that were similar to what is seen in bone modeling (laying down of new bone) and pathology in other types of diseased bone.

Photo: Stacie Aarsvold, BS

Veterinarians examine navicular disease cases using lameness exams and various imaging methods, but key to understanding this common debilitating disease and pinpointing treatment is knowing what’s going on at the microscopic level. Recently, a team of researchers evaluated microstructural changes in diseased navicular bone as compared to healthy navicular bones.

Stacie Aarsvold, BS, a fourth-year veterinary student at the University of California, Davis, School of Veterinary Medicine, presented the results of the study at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas.

"Navicular bone pathology (disease) is an important component of foot lameness in horses," Aarsvold said, adding that there are a number of common clinical radiographic findings related to the navicular bone including:

  • Enlarged synovial invaginations ("holes" in the navicular bone that fill with synovial fluid—that fluid which is found in joints);
  • Bone fragmentation;
  • Enthesophytosis (small bone spurs that occur off the edges of the navicular bone);
  • Flexor cortical lysis (decomposition of the surface of the normal outer tubular layer bone—the cortical bone— in contact with the deep digital flexor tendon); and
  • Medullary sclerosis (increased density in the bone’s medullary canal--the marrow cavity).

"However, the pathogenesis and interrelationships of these changes remain poorly understood," Aarsvold noted. "The primary objective of this study was to more fully characterize alterations in microstructure of severely diseased navicular bones."

Aarsvold et al. compared 13 diseased navicular bones in vitro (in the lab) with seven control (healthy) navicular bones using microcomputed tomography (i.e., a CT scan). The team evaluated the trabecular (the scaffolding that gives bone its strength), morphology (structure), porosity, mineral density, and cortical thickness (the dense outer tubular structure of bone) of the 20 navicular bones.

The team found that "diseased bones had more and denser compact cortical bone; fewer, thicker, and less-organized trabeculae; and thicker articular (joint) and flexor cortices than control bones." Further, midline flexor cortical lucencies (areas of translucence) were found in both diseased and control bones; however, only the diseased bones had "flexor cortical surface disruption."

So, what does all this mean? Aarsvold explained that she and her colleagues saw microstructural changes in the compact and trabecular areas of these severely diseased bones that were similar to what is seen in bone modeling (laying down of new bone) and pathology in other types of diseased bone. She noted that these changes are evidence that the biomechanical environment of the entire bone has been altered on all layers.

“This study helps to clarify radiographic abnormalities identified in horses with navicular degeneration," she concluded.

"We hope to apply this type of research to less severely affected bones in the future, which would allow us to get a better idea of the disease progression," Aarsvold explained. "As we understand the progression better we will be able to design better treatments that are actually treating the disease rather than acting as palliative care." 

About the Author

Erica Larson, News Editor

Erica Larson, News Editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in three-day eventing with her OTTB, Dorado, and enjoys photography in her spare time.

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