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Background
Older horses presenting with a sudden onset of abnormal pelvic limb gait with the hindquarters consistently shifted to one side of the body have been described by Johnson and Divers 1 as 'sidewinders' or 'crabwalkers'. These horses walk on three tracks and severely affected horses spin or circle in one place with their hindquarters listing to one side and their thoracic limbs moving in a compensatory way. Different hypotheses concerning the aetiology have been described, including equine protozoal myeloencephalitis (EPM), tuber coxae injury and lymphocytic neuritis (associated with Lyme disease). None of these hypotheses has been confirmed and the exact aetiology remains unknown.
The purpose of this report is to describe the irreversible clinical signs in a horse with sidewinder syndrome associated with partial rupture and desmitis of the left ligamentum capitis ossis femoris and degenerative coxofemoral joint disease.
Case presentation
A 25-year-old Welsh Cob breeding stallion was presented to the Department of Large Animal Internal Medicine of Ghent University with sudden onset of abnormal hind limb gait. Until the day before presentation, the stallion had been fit and active with no signs of lameness. He had been used for breeding and carriage work and he was kept at pasture.
On admission, the horse was alert and in good body condition. He was unable to stand 'squarely' and was continuously leaning with the hindquarters to the right (online supplementary video 1 ). The right hind limb was positioned on the body midline, whereas the left hind limb was held caudolaterally to the right hind limb ( Fig 1 ). The left hind limb was only partially weightbearing, with the stifle and the toe rotated outwards and the hock rotated inwards. In stance, the left hind limb was stretched caudally and dragged slowly towards the plantar side of the right hind limb. Hence, the horse swayed to the right (online supplementary video 2 ), almost fell and then hopped to reposition the hind legs: weight was briefly put on the left hind limb and then the right hind limb was repositioned. At walk and trot the right hind limb was placed wide with the left hind limb in line with the right forelimb resulting in a three tracks gait (online supplementary video 3-4 ). The...