Radiographic findings regarding the toe crena

s / Journal of Equine Veterinary Science 33 (2013) 838–859 856 021 Radiographic findings regarding the toe crena Bjorn Berg , and Lisa S. Lancaster 2 1 Ale Animal Hospital, Equine Department, Sweden, Michigan State University Equine Foot Lab, Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI Take-home message: The bony crena is present in the majority of feet, but it may be clinically significant only if it reaches a certain size. Introduction: Radiographically, the crena is a notch in the solar margin of the distal phalanx at the mid-toe. A similarshaped region may also be visible grossly in the white line at the same location. A few studies have reported radiographic and histologic features of the crena. Materials and Methods: Radiographs were taken of one or more feet from 103 horses and evaluated for the presence and size of a bony crena. Hoof health characteristics, including the external appearance of the hoof wall, white line, and presence of a keratoma, were also recorded. Results: In most of the feet examined, the crena was not visible externally but was present radiographically. The crena varied in size; it was more often present in front than in hind feet, and when present it was larger in the front feet than in the hind. If a sagittal crack was present in the dorsal wall, it correlated with the presence of a crena. The presence of a white line crena (but not a bony crena) was seen more frequently in long-toed feet. Discussion: The crena is a common feature of equine feet, yet its prevalence and clinical significance remain largely unknown. A bony crena combined with laminar damage may be a risk factor for the development of a keratoma. Conclusion and Clinical Relevance: The bony crena is present in the majority of feet, but it may be clinically significant only if it reaches a certain size. 022 Cornification of the hoof capsule David M. Hood DVM, PhD Hoof Diagnostic and Rehabilitation Clinic, Bryan, TX Introduction: The term cornification defines the highlyregulated process by which the soft and relatively fragile keratinocytes attached to the hoof’s basement membrane are progressively transformed into the hard and resilient cells present on its outermost surface. Due to the high degree of integration that characterizes hoof function, cornification makes important contributions to the physiology of the normal foot as well as to pathologies that involve the capsule. Cornification is a sequential, multi-step process that occurs within the hierarchy of differentiating keratinocytes. A bricks-and-mortar model, in which the bricks are the keratinocytes and the mortar the extracellular matrix, is apt. The major cornification steps include: (1) formation of the keratin cytoskeleton, (2) synthesis and deposition of the keratin-associated proteins, (3) synthesis and secretion of the membrane-coating material and formation of the extracellular matrix, (4) synthesis and the formation of the cell envelope, and (5) terminal cornification. Step 1: Formation of the keratin cytoskeleton: The keratin cytoskeleton is a flexible, interconnected network of protein filaments that attaches to multiple sites on the inner surface of the cell membrane and to the fibrous membrane that surrounds the cell nucleus. Both direct and circumstantial data support that formation of the keratin cytoskeleton is initiated in the basal keratinocyte layer of the hoof wall and that it is formed by a specific family of proteins identified as keratin intermediate filaments. The keratin cytoskeleton provides the basal and spinous cells with sufficient tensile strength to resist tearing while at the same time allowing them the flexibility they need to act as a structural interface between the hoof’s basement membrane and the hoof capsule. Step 2: Synthesis and deposition of the keratinassociated proteins: The keratin-associated proteins are a large and diverse group of small proteins that perform several important roles during cornification. One subgroup of keratin-associated proteins acts to increase the tensile strength of the keratin cytoskeleton by bundling its keratin intermediate filaments together into larger macrofibers (tonofibrils). Another subgroup of keratin-associated proteins form a polymerized matrix that surrounds and incorporates the cytoskeleton’s filaments into a semisolid composite. Depending on the amino acid composition of the specific keratin-associated proteins involved in cytoplasmic matrix formation, the rigidity and transverse modulus of the keratinocyte may be significantly increased. Other keratin-associated proteins bind to the ends of keratin filament proteins and act as structural links to either cytoplasmic proteins or to proteins embedded in the cell membrane. Thus, they act to unite the structural components of the cell. The synthesis of keratin-associated proteins appears to be initiated in spinous cells and is a principle cornification event occurring in transitional keratinocytes. The filament bundling, matrix formation, and linking roles played by the keratin-associated proteins are initiated early in transitional cells but are not complete until late in the cornification process. Step 3: Synthesis and secretion of the membranecoating material and formation of the extracellular matrix: The membrane-coating material is synthesized in spinous cells, stored in membrane-coating granules, and extruded into the extracellular space by transitional cells. The secreted membrane-coating material is a complex mixture of lipids, proteins, glycolipids, glycoproteins, and calcium ions. Following secretion, some of the membranecoating material components are structurally transformed and contribute to the formation of the cell envelope and the extracellular matrix, which facilitate cell-to-cell adhesion and hoof wall growth, and are a major component of the permeability barrier that limits water movement through the hoof capsule. Step 4: Synthesis and deposition of the cell envelope: The cell envelope is a complex structure