Passive load-relevant structures of the musculoskeletal system in the forelimb of the horse
Monika Egerbacher1, Gerhard Forstenpointer1, Gerald Weissengruber1, Theresia Licka2, Christian Peham3
Department of Pathobiology, Institute of Anatomy, Histology & Embryology1,Clinic for Large Animals/Orthopaedics2, Movement Science Group3, University of Veterinary Medicine Vienna, A-1210 Vienna, Austria, phone: *43-1-25077-3400, fax: *43-1-25077-3490, email:
BACKGROUND The aim of the study was to describe the structural differences of different fascia of the forelimb in the horse. We compared histological samples from the craniolateral section of the fascia brachii, the fascia antebrachii and the pars cruciformis vaginae fibrosae of the vagina fibrosa digitorum manus.
MATERIAL & METHODS Tissue samples were dissected from formalin fixed legs of horses, embedded in paraffin and cut in 2 planes. Sections were stained with H&E for general overview and Azan blue and Weigert's resorcin fuchsin for detection of fiber composition. Immunohistochemical staining was performed in order to classify the cells as fibroblasts, myofibroblasts or muscle cells. We used the following antibodies: Mcmouse anti-human smactin, Clone 1A4 (1:400), mc mouse anti-human desmin,Clone D33 (1:300), mcmouse anti-human vimentin, Clone V9 (1:200), (all: DakoCytomation, Glostrup, Denmark) andmcmouse anti-human smmyosin, ClonehSM-V (1:300, Sigma, St. Louis, MO, USA).
RESULTS The fascia brachii contained thick bundles of elastic fibers running longitudinally in proximodistal direction as well as weaker strands running perpendicularly. They areaccompanied by loose connective tissue and lined by layers of coarse collagen fibers. At the proximal end of the sample, extending muscle fibers of the deltoid muscle can be found between two thick sheets of coarse connective tissue. A surprising observation concerned the shape of the nuclei. Whereas cell nuclei were elongate in the coarse collageneous connective tissue, they appeared wavy and corksrew-like in the elastic tissue. The fascia antebrachii consists of separate layers of collagen fiber bundles of various thickness arranged in a very regular pattern. It contained only a few very thin elastic fiberspreferably running in the loose connective tissue between the layers. In the vagina fibrosa, the collagen fibers were arranged in parallel strands loosely connected by thinner fibrils containing a fair amount of thin elastic fibers. In all investigated samples, fibroblasts were positive for vimentin only. The cells did not show any signs of differentiation towards myofibroblasts shown by the negative staining with the respective markers.
CONCLUSIONS We show the varied composition of 3 different fascial structures in the forelimb of the horse. Contrary to other fascia e.g. in humans, our investigated samples did not contain myofibroblasts. The nuclear deformation may represent a functional adaptation of the respective tissue components with respect to mechanotransduction of tissue loads into cellular signals. More detailed studies are necessary in order to relate to functional aspects and age-related adaptations of these structures.