The investigation were carried out on the medieval horses thoracic and lumbar spine excavated between 2009-2011 by the Institute of Archaeology, University of Wroclaw at New Market Square in Wroclaw (Wratislavia, Breslau), capital city of the Polish province of Lower Silesia. The pathological changes, like: ankylosis of the zygapophyses, fusion of the vertebral bodies and arches and the interspinal space calcification were observed. The X-ray examination was done. During medieval artefact interpretation the biomechanical aspect of horse's locomotor system was taken into consideration. The archaeozoological material was compared with modern horse's spine (with similar pathological changes and known history of disease). The analysis proved, that the observed osseous reaction was a result of the long-lasting inflammation. Such a disease appearance accompanies chronic inflammatory state of errector muscles of the spine. It is typical for those horses utilised for the saddle. Copyright (c) 2012 John Wiley & Sons, Ltd.