Sidewinder syndrome associated with complete rupture of the <i>ligamentum capitis ossis femoris</i> in a horse

Summary A 10‐year‐old mixed‐breed gelding was admitted to a referral hospital following the acute onset of an asymmetrical hind end gait. The abnormal gait was characterised by marked leaning of the hindquarters to the left while standing and ambulating. While stalled, the horse was also observed to intermittently lean to the left and rest the left pelvic area against the wall for support. Medical management with anti‐inflammatories and antiprotozoal medications had not improved the condition. The neurologic examination upon presentation did not find ataxia but the horse had a pronounced and consistent hind end tracking gait to the left. No definitive cause for the gait abnormality was identified from the clinical exam. Although advanced imaging of the upper portion of the pelvic limbs, the pelvis and caudal spine in addition to a spinal tap were offered, euthanasia was elected by the owner because of lack of response to the recent medical treatments and a guarded prognosis for return to the intended performance level. Post‐mortem examination revealed coxofemoral osteoarthritis with a complete rupture of the right ligamentum capitis ossis femoris (LCOF) as the cause of the sidewinder gait. Complete rupture of the LCOF contralateral to the leaning side, should be considered amongst the differential diagnoses for the acute onset of sidewinder gait in horses.