Impinging and Overriding Spinous Processes in Horses: A Narrative Review

The term overriding spinous processes (ORSPs), commonly known as "kissing spine syndrome," refers to a skeletal abnormality in horses that is characterized by the narrowing (<4 mm) of the interspinous space and touching or overlapping of the spinous processes (SPs). This condition primarily affects the mid- and caudal thoracic vertebrae; however, ORSP can also affect the lumbar SPs. In the veterinary community, kissing spine is widely recognized as a common condition in sport horses, as it is often associated with chronic back pain and contributes to poor performance. Despite its significant clinical implications, the true incidence of pain arising from ORSPs in the equine population remains speculative and the demonstrated lack of correlation between diagnostic imaging findings and clinical signs complicates the clinical scenario. Over the years, several treatment approaches, both conservative and surgical, have been suggested to manage ORSP in horses. Although the development of these therapeutic strategies reflects ongoing efforts to address the complex nature of ORSP, the pathogenesis of the condition remains poorly understood. The aim of this review is to examine the literature to evaluate the current approaches to ORSPs and to highlight gaps in knowledge and directions for future research to improve the understanding, diagnosis, and treatment of this condition.