SUMMARY Macroscopic, microscopic and radiological examinations of the navicular bones of 83 horses and ponies showed that the navicular bone in the adult horse has 2 principal routes of blood supply. One supply is present at birth, the other develops within the first 2 to 3 years of life, in response to increasing activity. The size of the nutrient foramina, as seen on radiographs, is related to the type, frequency and regularity of work done by the horse. These foramina are normally conical in shape, alteration to a circular, or mushroom‐shape being evidence of occlusive vascular disease in the navicular bone. These changes are visible on a standard antero‐posterior radiograph of the navicular bone. A common cause of lameness in the horse is ischaemia of the navicular bone, due to progressive arterial occlusion. Occlusion of at least 2 primary arteries, and some involvement of the compensating collateral blood supply must be present before lameness results. RÉSUMÉ Des examens macroscopiques, microscopiques et radiologiques des os naviculaires de 83 chevaux et poneys ont montré que chez l'adulte l'os naviculaire reçoit du sang par deux voies différentes. L'une de ces voies est présente à la naissance et la seconde se développe durant les deux ou trois premières années de la vie. Les dimensions des foramens perçus sur les radiographies dépendent du type, de la fréquence et de la régularité du travail effectué par le cheval. Ces foramens qui présentent normalement une forme conique se trouvent altérés jusqu'à prendre une forme circulaire ou en champignon lorsque se développe une maladie vasculaire occlusive dans l'os naviculaire. Ces modifications sont visibles sur les images antero postérieures classiques de l'os naviculaire. L'ischemie secondaire à une occlusion artérielle progressive est une cause de boiterie. Il faut cependant qu'au moins daux artères primaires soient affectées avec interférence sur la circulation collatéral de compensation pour que la boiterie se produise. ZUSAMMENFASSUNG Makroskopische, mikroskopische und radiologische Untersuchungen der Strahlbeine von 83 Pferden und Ponies wiesen nach, dass das Strahlbein beim erwachsenen Pferd über zwei Hauptwege mit Blut versorgt wird. Der eine Weg ist schon bei der Geburt vorhanden, der andere entwickelt sich innert der ersten 2–3 Lebensjahre als Antwort auf die zunehmende Beanspruchung. Die Grösse der Ernährungslöcher auf den Röntgenaufnahmen ist abhängig von der Art, der Häufigkeit und der Regelmässigkeit der zu leistenden Arbeit. Diese Foramina sind in der Regel von konischer Gestalt; eine Veränderung zu runden oder pilzförmigen Umrissen ist Ausdruck einer occlusiven Gefässerkrankung im Strahlbein. Diese Veränderungen sind sichtbar auf anterio‐posterioren Röntgenaufnahmen des Strahlbeins. Eine häufige Ursache von Lahmheiten ist in einer Ischaemie des Strahlbeins zu sehen, die ihrerseits auf einem progressiven Arterienverschluss beruht. Die Occlusion von mindestens zwei Primärarterien und eine gewisse Beteiligung der kompensatorischen, kollateralen Blu...

Carotid and cerebral angiography has been found to be a relatively simple technique to carry out in the horse. At most it involves a cutdown approach to the carotid artery, followed by catheterisation of the artery and selective catheterisation, if necessary, of one of its three branches. The technique can be carried out with standard equipment normally available within equine hospital facilities. The authors have employed angiography as a routine aid to diagnosis over the past nine years, without encountering any serious complications or adverse reactions. Carotid angiography has been especially valuable in the investigation of horses with guttural pouch mycosis. The technique has permitted the presence of aneurysms to be detected in many cases and significant vascular abnormalities in four cases. This information is valuable for the surgical treatment of horses with guttural pouch mycosis by ligation of the appropriate artery. Other indications for the use of carotid angiography include the investigation of ethmoidal haematoma, idiopathic Horner's syndrome, neoplasia of the head, venous aneurysms and arterial aneurysms in sites not associated with the guttural pouch. There are fewer occasions for the use of cerebral angiography in the horse, but it is indicated as an aid to the differential diagnosis of some abnormalities of the central nervous system.

Navicular disease and its treatment by Chrs Colles A SURVEY in 1962 showed that navicular disease was diagnosed as the cause of about one-third of all cases of chronic forelimb lameness in the horse. Descriptions of the disease are numerous and, in many cases, contradictory. Recently, the idea has been advanced that pain results, not from the classically described erosions of the flexor cartilage, but from ischaemia within the substance of the bone. This allows a complete reassessment of the condition to be made and opens the possibility of completely new lines of treatment. The ischaemic changes can be related to radiological changes which aids making a definite diagnosis.

Summary Avulsion fractures from the distal border of the navicular bone are relatively common, but normally of little clinical significance. Other fractures are uncommon and have a poor prognosis. Surgical fixation of parasagittal fractures (lag screw) is technically quite difficult, but potentially improves the prognosis for return to work to about 80%. If surgical fixation is not possible, then farriery to raise the heels of the foot may be of benefit.

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